US3818712A - Frozen embankments - Google Patents

Abstract

Improved particulate embankment structures for use in cold environments and on frozen terrain are described together with methods of construction; generally involving the introduction of up to a prescribed amount of moisture homogeneously dispersed throughout the particulate embankment such as to maximize the ice content thereof yet without appreciably moving the particles relative to one another or risking any such moving subsequently such as frost heaves, subsidence or the like. Also described are methods and arrangements for coating terrestrial and similar substrates with urethane foam and like materials. Various aspects of the preferred methods are illustratively described such as the application of foams in a laminate form; the application of a petroleum base pre-coating or similar moisture barrier; the application of petroleum based super-coatings or similar sealant; subjection of the foam and related coatings to certain heating during application; and the ''''staggering'''' of successive foam layers.

Description

United States Patent [191 Burt et a1.

[ FROZEN EMBANKMENTS [73] Assignee: Atlantic Richfield Company, New

York, N.Y.

[22] Filed: July 10, 1972 [211 Appl. No.: 270,315

Dougan 61/36 A 1 1 June 25, 1974 Primary Examiner-Mervin Stein Assistant Examiner-Alex Grosz Attorney, Agent, or Firm-Coleman R. Reap 57 ABSTRACT Improved particulate embankment structures for use in cold environments and on frozen terrain are described together with methods of construction; generally involving the introduction of up to a prescribed amount of moisture homogeneously dispersed throughout the particulate embankment such as to maximize the ice content thereof yet without appreciably moving the particles relative to one another or risking any such moving subsequently such as frost heaves, subsidence or the like. Also described are methods and arrangements for coating terrestrial and similar substrates with urethane foam and like materials. Various aspects of the preferred methods are il1ustratively described such as the application of foams in a laminate form; the application of a petroleum base pre-coating or similar moisture barrier; the application of petroleum based super-coatings or similar sealant; subjection of the foam and related coatings to certain heating during application; and the staggering of successive foam layers.

24 Claims, 5 Drawing Figures PATENIEmmSmu FIGURE FIGURE 2 FIGURE 3 FIGURE 4 r M n/ r0 7 FIGURE 5 1 FROZEN EMBANKMENTS GENERAL OBJECTS, FEATURES One object of the subject conception is to construct an improved embankment of iced particulates in which acarefullylimited amount of ice (as water adsorbed and frozen-in situ) is incorporated to make a two-phase or three-phase (aqueous) system; but one which is nonetheless stable, non-swelled" and not susceptible to frost-heaving. in a simple primitive form this concept may be visualized as providing an improved embankment for a road or structural facility according to the steps of:

l. laying a suitable particulate material, such as a mass of gravel of relatively uniform-size and spherical shape, atop a frozen substrate (e.g., a pennafrost terrain) and piling it to a prescribed height as determined by thermal constraints, and

2. wetting it by introducing an aqueous fluid to coat the particle surfaces and fill the interstices therebetween, yet without swelling theembankment, (i.e., with-mechanically moving the particles relative to one another) and, thereafter 3. freezing the adsorbed water in situ to provide the composite ice particulate pad. A related object is to provide a cryogenic foundation pad (support for construction) on frozen substrate which is more stable and longenlivedin the face of thaw conditions and which offers more impedance to retard the passage of a thaw front down through the pad (e.g., from a warm structure situated thereon, such as a heated water reservoir, a heated building, a warm-oil pipeline or the like). The height of the pad and, accordingly, its total thermal impedance will be designed to reflect a certain frozen life (before melting of the substrate) under the ambient conditions prevailing at the selected site. Such sites may include an arctic permafrost region such as along the Alaskan North Slope or in the-McKenzie River Valley. 7

One other advantage of such a concept is that many native soil particles such as sand, gravel, certain kinds of clays and the like, typically exhibit a uniform, constant void ratio,. independent of particle size as-long as the size and shapeof the particles are relatively uni-, form. ("Void ratio of a pad mass is equivalent to the reciprocal if its volume percent density.) By contrast, the closely-packed condition of graded, or nonuniform sized, soil particulates (e.g., sand, gravel or other united size soil) will exhibit an undesirably low void ratio," For example,'a well-rounded river gravel has a suitably high void-ratio only when fines and large rocks are screened out. Such gravel is available, for example, along the Sag River in the Prudhoe Bay area of Alaska. A related object is to maximize the ice content of the "iced-particle" embankment, short of "swelling" it or inducing frost-heaving.

Another advantage is that suchiced-particulate embankment construction can be quite inexpensive, requiring only water plus suitable native soils. Some desirable soils are the fat clays commonly available in Northern Alaska, and other fine soils having l a high (free" or freezable") moisture content, yet (2) without having excessive capillarity. Moisture content will be a function of permeability, that is permeability should be low enough to admit adequate liquid; yet

very little more than this so that a maximum moisture content is retained for a maximum time and also so that low permeability can be employed to resist capillary action! Of course, water is inexpensive and commonly available, even in the frozen Arctic where it is readily drawn from pools and lakes which are more than a few feet deep or else derived from melted ice and snow. Methods for constructing iced-particulate pads are quite simple involving the mere laying-up of courses of native particulates followed by a wettingdown of each course (e.g., spraying with water with conventional equipment) and allowing it to freeze.

PRIOR ART, PROBLEMS Using conventional techniques it might seem more expedient to build an ice pad" for Arctic structures by simply forming a large, monolithic ice block, consisting entirely of frozen water; perhaps also covering the block with insulation to keep it frozen hard. However, several grave difficulties exist with such ice blocks. The low cohesion and low tensile strength of the monolithic ice means that under the force of gravity, such a block will readily split and spread apart in fragments after build-up of 'a certain ice mass usually on the order of a foot or two thick, that is, as the ice layer builds in thickness the gravitational forces of its own mass tend to develop increasing tensile stresses pulling the ice apart laterally and often succeeding in parting it when its tensile strength is exceeded. Such a condition is indicated in FIG. 1 where ice cake 1, after buildup to a certain frozen height h above a supporting substrate level SS, has'cracked, more or less across its middle (at fissure 7), forming two separate pieces 3,5. Of course, this is most likelyto occur where cake 1 is not uniformly supported across its entire base; as for instance, when it rests upon an uneven substrate such as results from a protruding structure P (phantom), which protrudes above the general support level SS. By contrast, composite ice/particulate pads of the type described herein canentirely avoid this problem of splitting entirely since they are not monolithic ice and, moreover, have no associated inherent limit in the height to which they can be built.

A similar and related problem with prior art structures like these ice blocks is that they tend to freeze from-the-outside-in, starting adjacent the source of cooling. For instance, in a typical Arctic lake L, schematically shown in FIG. 2, the ice coating represented by layers T-l, T-2 will begin to develop starting at the lake shore, represented by opposed marginal structures C, C, and the ice sheet will grow towards the lakes center, ultimately leaving a central portion CT as the last to freeze. This phenomenon of freezing toward the center is well known in the art as tending to develop ice lenses," comprising ice formations which are trapped in an intregal ice sheet as it forms. When these lenses freeze, as the culmination of the formation of a continuous integral ice mass, they, of course, expand and can thereby form wedges, cracks, etc. in

- the overall ice mass. For instance, center portion CT in lake L will be understood as the last to freeze as ice sheets T-l, T-2 grow toward one another and when the central pool at CT finally freezes, it will be understood as forming a lens. Such lensing" can produce the pressure ridges commonly seen in Arctic sea-ice. Of course, the freeze-expansion of the lens tends to thrust continuous sheets T-l, T-2 outwardly against marginal structure C, C' and, to the extent it is resisted, will develop the described cracks and ridges. The resultant stresses are quite gigantic as workers in the art well know; indeed large enough to move large buildings and crack rock formations (stresses of many thousands of pounds per square inch are quite typical). In some, such stresses will be understood as giving to expansion cracking as described as well as pressure ridges, etc.

This expansion-cracking can be further complicated by the aforementioned splitting phenomenon, whereby a monolithic ice mass is cracked and split under stress of its own weight, above a certain thickness (critical mass).

With composite ice/particulate structures according to the invention, however, the foregoing problems are avoided. Problems of expansion-cracking and related stresses are substantially eliminated by maintaining the freezable liquid in small discrete noncontinuous masses distributed between particles, the interparticle voids being incompletely filled to avoid any hydraulic-spreading of particles and so as to provide expansion room for the ice. Moreover, in the liftby-lift" construction techniques according to the invention (described below) there is little or no risk of excessive build-up of monolithic ice masses; also freezing is accomplished faster and easier. The increase in freezing-speed is especially advantageous; for instance, where a monolithic ice-block may now be built up at the rate of about 6 inches per week (or about 10 feet in an entire Prudhoe Bay winter of normal temperatures); using the novel iced/particulate construction described, rates on the order of 6 inches per day (or 50 feet per winter season) may be achieved.

It might also be noted that one of the features of the instant construction is the use of a riming (liquid retained as ice coated on individual particles or like intraembankment ice) on, and among, soil particles, acting to retard warming and impede thaw. By contrast, other workers have contemplated the use of water/ice (e.g., in cooling pockets around pipe as an insulation aid) to simply maintain constant temperature (usually to maintain a constant 32F.) without particular regard for applying the liquid to native soil structures or using it as a tool for thaw retardation.

The various embankment particulates selected must be chosen to exhibit prescribed characteristics. Of course, they must have a constant void ratio i.e., their size and shape must be relatively uniform, their shape preferably being spherical or near-spherical, with a diameter within prescribed limits (except where otherwise indicated it will be understood that particle diameters may be defined (in microns) as follows: clays: 0.l 1+; silts: l+ 10+; fine sands: 10+ l+; course sands: l00+- 1,000+, i.e., l mm+; gravel: 1 mm up). Beyond this, however, there are other constraints which must be respected, for instance, to avoid the problems of frost-heave and ice lens formation. Two such factors are the capillarity and the permeability of the embankment materials used.

Capillarity is the property whereby attraction between molecules, both like and unlike, results in the rise of a liquid in small tubes or fibers or in wetting of a solid by a liquid. Of course, any substantial capillarity of embankment gravel will act to transport fluid so that it becomes non-homogeneously distributed throughout the embankment and may also result in swelling, iceheaves, etc. (or at least enhance the risk of these). For instance, in the case of a gravel pad comprised of a high capillarity" clay, such as a lean" clay like calcium bentonite or a silt under about 200 mesh, it should be expected that the capillarity of the clay will tend to deplete the moisture at the bottom of the embankment and transport it upward to eventually, build up a pool of water (ice) there and, generally, destroy homogeneity of moisture distribution. On the other hand, if according to the subject teaching one uses a fat clay like sodium bentonite or a similar lowcapillarity particulate, this should not happen. (Note: Sodium bentonite may be understood as a sodiumsaturated type of clay, capable of very high moisture content, with water adsorbed to the extent of about three to four times the volume of silicate.)

in certain cases one may add such a fat clay" to a high-capillarity particulate to fatten" it, sufficiently so that a prescribed increased amount of moisture will be retained uniformly and homogeneously throughout. Fat" clays are particularly suitable since, even when thawed, they retain a relatively large amount of moisture (up to about 30 to 50 percent water adsorbed) as well as having only a moderate capillarity. Examples of such fat clays will be apparent to those skilled in the art, e.g., including aluminum silicates (such as Kaolinite: Al O '3SiO- '2H O; halluipete: Al O '3SiO '2- H O; Montmorillonite: (Mg,Ca)O-Al O -5SiO -nH O and lllite: K O,MgO,Cl- ,O ,SiO ,H O) of the fat" (sodium) form of Kaolin (china clay) or bentonite or Fullers earth (the lean, or calcium, forms being less desirable). Other like wettable particulates," i.e., those having low capillarity and high percentage moisture retention, may be used, such as Portland Cement, lime, cellulosic or vegetative matter (e.g., tundra, hay or straw, muskeg, compost, sawdust, shredded cellulosics, etc.) and even human waste and sewage products. However, one should be sure that the material has sufficient permeability to admit adequate moisture, yet have a low enough permeability to retain most of the moisture. Many such fat clays are particularly suitable where their saturated moisture-retention capability is as high as the order of 30-40 percent volume; their void ratio being typically above 50-70 volume percent; (and many such clays are) available for mining on the Alaskan North Slope). In any event, the moisture content of the clay used must be kept below that which will overload or over-saturate it and leave no space for ice-expansion and low enough to prevent the (fat) clay from becoming too plastic and fluid in consistency and thus unable to support normal service loadmg.

It is suspected that the fat" clays are especially satisfacotry, even with their relatively high capillarity, because their permeability is still so low that it can adequately oppose capillary-transport" and so yield a relatively high, uniform moisture retention. Lean clays, on the other hand, (such as calcium bentonite and silt) are believed undesirable because their permeability is too high to adequately oppose such capillary-transport, allowing fluid transport to take place within an embankment. Particulates having low percentage moisture retention (e.g., coarse gravels) will be recognized as having too high a permeability. Of course, highly granular soils such as sands or gravel exhibit practically no capillary action and have a high percent void (especially gravel of the pea size and larger, having at least about 40 percent void ratio); whereas gravels which are relatively fine (e.g., sand and gravels smaller than pea) are apt to exhibit excessive capillary action and so are much less desirable.

Besides the fat clays and similar high capillarity/-' low permeability (i.e., wettable) particulates (assuming uniform size and shape), one may also use relatively coarse particulates for the subject icedparticulate pad. As aforestated, the particulates must in any case be ungraded, that is, be of relatively uniform size since otherwise the embankments void ratio would be too low (e.g., for typical graded gravel the void ratio is only about a few percent). Well-graded gravels may make good road surfacesbecause of this close packing, but this makes them rather unsuitable for the iced-particulate pad since they can take up only a relatively small percentage of ice and they may also exhibit too high a capillarity. Also, if packed extremely closely, they may even have too low a permeability for adequate moisture penetration and the necessary uniform distribution of ice throughout. Of course, the finer sands (below pea gravel size, approximately) more typically exhibit too much capillarity, whether graded or not. Examples of suitable coarse gravel will be the "pea gravel found in the Prudhoe Bay areaof the Alaskan Arctic.

Since the coarser gravels will have a much lowe moisture retention capability than the aforementioned fat" clays, it is prescribed, as a further improvement feature, that one may fatten up" a coarse gravel by mixing in a portion of such fat clays (or like high percent moisture retention material). Similarly, as aforementioned, the high capillarity, high permeability particulates such as lean clays or silts may likewise be fattened" by the proper addition of a fat clay or other wettable" substance. It will be apparent to those skilled in the art that new and useful features are herewith taught, unexpectedly advantageous for such construction as providing foundation embankments in Arctic regions by piling up such "stably wetting" particulates, (i.e., particulates which take up and retain a substantial amount of liquid, kept homogeneously distributed therethrough), then saturating and freezing the particulate mass to thereby present an improved, more stable thaw retarding embankment structure, especially adapted for permafrost terrain.

Of course, the liquid material to be frozen about the particulates (and in the interstices therebetween)v may most conveniently constitute water or other suitable aqueous liquid, readily freezable under the given ambient conditions. Fresh water will usually be preferred as opposed to salt water or other adulterated aqueous systems since any additives to the pure water may be expected to reduce its latent heat of fusion and thus degrade its thaw retarding capability (along with lowering the freezing point). Salt water may, however, be used where convenient and where the ambient thermal conditions permit, giving the advantage, of course, of freezing at lower temperatures while, on the other hand, thawing more readily, of course.

METHODS IN GENERAL In typical arctic regions, such as in the Prudhoe Bay area during the winter, one may expect to build-up ice lifts on the order of 6 inches by properly spraying water onto the subject particulate course and allow freezing overnight. Preferably, the water is sprayed on in a fine mist which is projected in an arc, somewhat ballistically, so as to be substantially cooled in transit and before striking the substrate (e.g., a layer of embankment particulates; note: the frigid ambient air will typically extract about 90 volume percent of the latent heat present in a water droplet, properly directed). Such a spray will also impart sufficient momentum to the droplets to mechanically splatter" them, and spread the water out in a relatively thin film about and between the substrate particles. While the water delivery system should impart sufficient momentum for this splatter," it should also distribute the liquid somewhat evenly among the particles and not cause localized moisture depletion or, even worse, inertial erosion at the point of impact. A typical nozzle useful for the Prudhoe area will deliver particles impacting with a pressure of a few hundred psi, in a ballistic arc, giving a proper degree of cooling (in transit), with proper droplet size and fluid distribution. Of course, ambient conditions, such as a high wind or a shift in temperature, can change all of these factors radically and interfere with proper spraying; thus such must be watched for and attended to.

EXAMPLES 1. Example 1 A particulate foundation pad (embankment) is to be constructed for a heat-generating facility in the Prudhoe Bay area of Alaska. Accordingly, Sag River gravel is gathered locally, in its pristine native, relatively ungraded condition, and properly screened to extract particles of relatively uniform diameter presumably on the order of pea grade gravel. Successive courses of this gravel each several inches deep, are laid directly on the chosen pad site, on the tundra (with underlying active layer and permafrost a few feet down). This is preferably done around the seasonal freezing time" at this site (here assume September or October normally). It will be-understood that native pea-grade Sag River gravel comprises relatively spherical particles with diameters on the order of inch and adapted to be piled to exhibit a void ratio on the order of 40 percent (maximum).

' Each gravel course will be laid, wetted, and then allowed to freeze-in, after which the next course will be laid and frozen, etc., to build-up a total aggregate pad height of about 18 inches. During late October, (assuming the onset of a normal winter season), this would usually mean laying on the order of 4-6 inches of gravel for each course, compressing it as necessary to reduce void percent to a satisfactory level (see below) and spraying the surface of the gravel course with water during the warmest part of the day until saturation is perceived. This is normally indicated by a Welling-up of moisture without significant drainage down through the course. Then, spraying of the subject course ceases and the pad allowed to sit and equilibrate, under freezing (nighttime) conditions until it gets frozen relatively hard. Several days should be adequate for freeze-in of such a course, here. Over-saturation of any course will be obviated by the fact that, during the warmer portions of the day considerable moisture will vaporize,

.run off, and otherwise be released.

The resultant iced-particulate pad may now be put into service, supporting the mentioned vacility. Itwill be found to provide a very solid foundation, many of Depending, of course, on the amount of heat it is subjected to (e.g., from the facility, from unusually warm weather, etc.), the pad will provide a stable foundation without significant melting or subsidance for a number of years (see further details below). Also, it will be helpful and advantageous to monitor the thaw-front as it proceeds down through the pad, plotting its position and rate of progress, to thereby check on the actual stable service life to be derived and take appropriate action (e.g., periodically cooling and refreezing as noted in copending US. Pat. application Ser. No. 270,359, of Glenn R. Burt, Albert C. Condo, and George R. Knight, filed July 10, l972, entitled IN- SULATED EMBANKMENT DESIGN, and incorporated herein by reference. Thus, an added advantage to using iced-particulate foundation pads of the type described is that, unlike prior art moisture-containing foundations, they present little or no danger of subsidance or mechanical instability and unlike conventional foundation means for Arctic structures, can readily be monitored to ascertain its themial maturity" (degree of thaw); such as by a simple visual inspection to indicate how far down the thaw-front has proceeded, how far it has to go, and at what rate it is progressing. ln all of these examples, all relevant, applicable conventional procedures and precautions will be understood as to be observed and attended to as understood in this art. For instance, the gravel and (especially) the typically wet clay will ordinarily be mined locally, if possible, during a thaw period, and made available for the pad construction in a thawed, or at least semi-thawed, condition so as to be workable, as well as wettable." In certain instances workers in the art will find that the entire pad height (here 18 inches) can be laid-up at one time (rather than course-bycourse") and then wetted, especially if a high proportion of high, homogeneous moisture-retaining (and low-capillarity or high capillarity/low permeability) materials are used, such as Sodium Bentonite. This will ordinarily be done during a thaw and, later, after freezup, one will return to complete the pad (e.g., lay on an insulation cap and/or a supercoating of gravel for structural purposes). The erection of a structural facility atop the overall pad may normally follow.

2. Example 2 The embodiment of Example 1 is reproduced, except that the pea-grade gravel is admixed with a high moisture (and stably homogeneous, thus, retention preferably low capillary-transport also) filler material, preferably wet tundra and any other waste organic material available. Tundra is typically available after preparing the pad site by scraping (balding) it clear. More compaction and pressing will be required here to get adequate structural consolidation and a satisfactorily low percent void. in this manner the moisture retention capacity of the resultant composite (three phase: ice/pea gravel/tundra) pad will be, of course, greatly enhanced, thus improving its thaw-retarding capacity and thermal stability.

3. Example 3 The embodiment of Example 1 is followed, modified, however, so that the pea-grade gravel is admixed with a native clay, mined locally, and preferably a fat clay like Sodium Bentonite (an alkaline clay with low water solubility). This clay is mixed homogeneously with the gravel and the composite particulate mass is laid-up in courses, each being wetted to saturation and then frozen, course-by-course. As with the prior examples, each course of pea gravel (preferably about 30 volume percent at least) and a fat" clay will be compressed as necessary for consolidation. A course will be wetted" to saturation and allowed to freeze-in hard before the next course is laid, as before. A particularly convenient mode of such construction is to lay each course in two successive stages: first, approximately 4 inches of pea gravel and then covering this with about 2 inches of fat" clay. The clay is then mechanically rolled and compacted into the gravel, so that the clay is incorporated relatively homogeneously and interspersed among the gravel particles to comprise about 30 percent of the composite volume. Lastly, the course is wetted by spraying water uniformly over its surface until it appears relatively saturated, preferably about 50-70 weight percent water being introduced. When a course has frozen solid, the next course is separately overlaid and frozen to provide the desired laminate of iced-particulates. During the coldest 3 months of a normal Prudhoe winter it should take one to several days for a hard-freeze of such a 6 inch" (gravel plus clay) course. It may be found that the aforementioned splitting and/or expansion-cracking occurs; to some minor extent along a given course; however, laying the icedparticulates in the aforedescribed lift-by-lift (laminate) fashin will compensate for this and the effects thereof should be insignificant.

Two more such 6 inch composite iced-particulatewater (three phase) courses are successively laid to build-up an overall pad height of about 18 inches. The overall laminated iced-particulate pad will be superior in thermal stability. It will be found that a pad thickness of from 12 to 24 inches provides a service life on the order of 3 years for this locale (e.g., supporting a structural facility on the frozen tundra without melting or subsidence). This should be compared with using a conventional all-gravel pad of 5 feet or more, without any of the described structural or materials refinements, as this may give a comparable life though of much less reliability.

Preferably, the foregoing ice-particulate pad is also capped with a suitable insulation mantle, laid down after the overall pad is frozen hard and before the spring thaw has set in. On the order of 1 to 2 inches of Arcofoam urethane type insulation is preferably used as described in US. Ser. No. 337,664 to A. C. Condo and J. Neubauer, filed Feb. 18, 1972, entitled STABI- LlZlNG ARCTIC GROUND COVER, herewith incorporated by reference.

4. Example 4 The icedparticulate pad of Example 3 is constructed; however, dispensing with the use of pea gravel and using the fat clay alone. The clay is laid, wetted, and frozen-in in successive courses 3 to 6 inches thick to build up the same 18 inches overall pad thickness.

5. Example 5 A haul road is to be built on tundra terrain in the Prudhoe Bay area using the techniques according to the invention as aforedescribed. It will be recognized that in such areas gravel is often too expensive (e.g., too little is readily available, may require a relatively long, expensive haul) although in many locations a suitable fat" clay such as Montmorillonite or other like stably wettable material is commonly available. The Montmorillonite has a relatively high, homogeneously stable moisture content and thus will be suitable for most purposes. Such haul roads are "commonly intended to carry a relatively heavy high-loading traffic throughout the year and should have a minimum 1% to 2 feet height to counteract the effects of drifting snow in this area. Thus, about 18 inches of well-graded native road-way gravel is laid down upon about, 1 inch of Arcofoam, laid on the native tundra ground cover, generally as described above. It will be found that this embankment will, under such service and ambient conditions, give a service life on the order of about 4-5 years.

This service life can be extended to the order of 20 years relatively simply by a modified construction made as follows: A suitable quantity of a fat clay is gathered during the thaw season and laid down as a roadbed material upon the native tundra vegetation of the right-of-way to a height of about 3 feet. This clay foundation pad is constructed like the pads of the prior examples, except asotherwise noted here, being saturated with water and allowed to freeze solid typically, about 2 months of a normal Prudhoe winter should be sufficient refreeze time. 7 Since this iced-clay pad is somewhat more fmonolithic," appropriate precautions should be taken against the aforedescribed splitting and centercracking phenomena described above. Thus, it may be preferable to lay down the clay in several courses, assuming either that the clay can be placed in workable condition during the cold months and moisture applied then, or that the work can be deferred so that courses can be laid during successive thaw seasons and frozen up in the interim. When the full 3 feet of iced-clay is frozen hard, the mass is capped with k to l inch of Arcofoam (plus or minus A inch), as described in the aforementioned U.S. Pat. application Ser. No. 337,664. Thereafter, on the order of 21 inches of well-graded gravel, as normally used for such road construction,is applied atop the so-frozen pad as a structural top layer (e.g., for load distribution and resistingsurface wear).

6. Example 6 The embodiment of Example 5 is reconstructed except that only 6 inches, total, of the iced-fat clay" are built up. The resultant 6 inch iced-clay pad is then covered with about /4 inch of Arcofoam and, atop this, is laid l to 2 feet of well-graded road building gravel. The service life of this embodiment will, of course, be much less than that of Example 5. However, in certain in stances it will be feasible to replenish the moisture content of the clay and refreeze it during a winter season, without substantially interrupting usage of the road. In such cases the described foam insulation layer will be dispensed-with and an extra foot or so of road-way gravel applied to take advantage of its thermal (thaw retarding) properties, however modest (thus, it is preferably ungraded, with higher void percent). Then, periodically, (e.g., each fall) the clay pad (at least the thawed upper portions thereof)-may be conveniently remoistened and wetted to restore any lost moisture. This maybe done by spraying the overall roadway with sufficient water to percolate down to the underlying pad and re-wet it (assuming, of course, that the terrain adjacent to the clay pad is sufficiently well vdrained that such a moistening will not create problems such as ice-protrusions, or interference with the frozen stability of the clay pad).

7. Example 7 The embodiment of Examples 5 and 6 is followed except that the iced-particulate pad comprises about 3 inches of wetted" ungraded pea gravel mixed with a fat clay (about 30 percent by volume) as aforeindicated. The so-fattened gravel is properly wetted and frozen-in as before. This frozen pad is then topped with from 6 to 12 inches of roadway gravel (wellgraded, etc. as aforementioned).

In certain cases this will be preferred to the construction of Example 6, especially where roadway loads might be expected to possibly.squeeze any thawed clay (and/or the water therein) outwardly, upsetting the structural supporting integrity of the pad. A thawed, wet pad of about percent pea gravel, with the'clay and water interspersed between gravel particles, will, of course, have considerably greater stability under compression, as for the instant conditions, and thus, will be preferably for certain applications.

8. Example 8 A roadway is constructed as recited in Example 7; however, the 3 inch (gravel-clay-ice) frozen pad is coated with A to A inch of Arcofoam, together with an upper and lower moisture seal (barrier coating composition) as indicated in the aforementioned U.S. Ser. No. 337,664. As before, 6 to 12 inches of gravel is also applied over the so-sealed foaminsulation. As indicated above, this will, of course, make remoistening and re freezing of the composite pad somewhat impractical; however, the foam mantle will, naturally, supplement the thaw retarding properties of the overall system and extend the stable, unmelted service life of the pad.

9. Example 9 A roadway is constructed as indicated in Example 8 except that a second frozen gravel-clay pad is constructed over the recited Arcofoam insulation layer and then covered with the roadway gravel as recited. This second layer may be identical in composition and mode of application with the first.

Consideration of FIG. 3 will now be instructive. Here, an illustration is given of a roadway constructed according to Example 9, with the construction according to prior examples also being readily inferrable. The roadway pad is FIG. 3 comprises a first icedparticulate layer A, (as described for Example 7) comprising pea gravel with fat clay and ice interspersed, layer A being laid directly upon the tundra grade level g-g (under which is situated a typical 1 to 2 foot active layer A-Z; under A-Z, in turn, is a permafrost substratum P-f). Atop layer A is a suitable insulation layer U, preferably comprising up to about 1 inch of urethane foam as described above, to radically retard thawing down through the pad. Atop the insulation U, a second iced-particulate layer B is placed, being similar in construction to the underlying layer A. A supercoating layer C of conventional roadway gravel (as described above, for supporting and distributing the traffic loads, these loads being indicated functionally by arrows T) is added atop layer B to crown the overall embankment. Of course, as indicated in phantom at U, the insulation layer U may be extended laterally outward and down (at least most of) the sides of the underlying frozen pad A for more effective thermal isolation thereof and better thaw retardation. Further to this end (and independently of whether the second icedparticulate layer B is used), the top supercoating C may similarly be spread out laterally to cover both the foam and underlying iced-layer A in cases where such mechanical and thermal protection is deemed advisable.

For the subject Example 9, the construction'of Example 8 is generally followed except as otherwise noted. This is, an iced-particulate layer A is constructed of pea gravel and clay to be about 3 inches thick, as frozen, and this is covered by a suitable layer of insulation U covering the top and side surfaces of pad A, preferably with on the order of about A to as inches of Arcofoam as aforecited.

However, as a modification of the previous embodiment, a high-water-content, relatively monolithic icedclay layer B (preferably on the order of 50 volume percent or more of ice) is laid atop this foam mantle, covering its upper surface (and also preferably its side surfaces) to a thickness of from 8 to l2 inches. A fat clay, saturated to 50 volume percent or more with water, is the preferred material here, being laid in one course, or several, as before noted. The roadway gravel layer C may then be applied atop this iced-clay monolith for the usual purposes.

It will be apparent upon consideration that the subject resultant monolithic iced-clay cap can serve several advantageous purposes: It can obviously act as a supplementary thaw barrier; and it can function as a mechanical containment cap, helping to distribute the applied roadway loads much in the manner of a superposed concrete slab (as long as B is kept frozen). As a result, the thickness of the gravel supercoat ing C may be somewhat reduced, if desired, to the order of 6 to 8 inches; where on the order of several feet might otherwise be necessary. Here (and elsewhere herein) workers in the art will recognize the important economic, convenience and ecological advantages to saving gravel.

10. Example 10 The construction of Example 9 is repeated, except as otherwise noted hereinbelow, modifying it so that the foam insulation and superposed iced-clay" layers extend down the roadway shoulders to meet grade. This modification is illustrated in FIG. 4, which shall be understood as duplicating the embodiment of FIG. 3, except as otherwise noted hereinbelow. Here, bottom iced-clay layer A rests upon grade g-g and is covered with a urethane foam layer U" in turn, covered by upper iced-clay" layer M (generally analogous to layer B in FIG. 3). Roadway gravel C is placed atop layer M as before. Here, it will be noted that foam layer U and superposed iced-clay layer M are extended outward and down to grade, thus covering and better insulating embankment shoulders. This will be understood as offering better protection against lateral intrusion of heat and moisture (e.g., a self-draining feature) and can improve resultant stability.

To further optimize stability and minimize thaw tendencies, inexpensive native materials such as native tundra vegetation (e.g., which may have been scrapedup during leveling of the right of way) is distributed along the embankment shoulders as indicated by optional vegetation layers V (in phantom). Layers V may also be covered with at least a thin layer of available native particulates, such as optional gravel coatings C-v (in phantom) to secure the vegetation in place (e.g., against wind-blowing). It will further be apparent that in the event of any upper thaw of iced-clay layer M and resultant moisture-loss, a certain amount of moisture may be sprayed onto the surface of the roadway gravel C to percolate down to, and rewet," layer M, replacing lost moisture to be later frozen-in during colder weather. It will be noted that no insulative barrier is placed above layer M as this would interfere with its cooling and refreezing in the winter season.

11. Example ll As indicated in FIG. 5, a composite improved foundation pad is constructed along the lines of the foregoing teachings as a foundation for a heated structure SR to be placed on permafrost terrain (tundra) in the Prudhoe Bay locale. Accordingly, a suitable, relatively rectangular, base site is defined on the tundra and excavated below grade (gg) so as to remove all organic (tundra vegetation) material and collect it in one pile and, further, to excavate some of the subjacent active layer soil, gathering this in a separate pile for later use. Preferably from two to four times as much soil material will be gathered as vegetation; for example, on the order of 2 inches of tundra vegetation may be scraped away and piled up; while about 3 to 6 inches of subsoil thereunder (gravel mostly, depending upon the specific site) gathered up separately. This subsoil gravel will be understood as constituting at least a fair approximation of a relatively ungraded" soil material, typically exhibiting a relatively high void ratio with particles of relatively uniform size. A preferred mode of excavation is to employ a snow-blower" type excavator which will act to both excavate and homogeneously inter mix the vegetation and soil materials as it removes then, while also projecting them (e.g, with a blower) away, into a given storage pile for later use. Of course, soil anomalies such as rocks, logs and the like should be removed separately or avoided. Such apparatus can also serve to grind up the vegetative matter while mixing it in intimately into the sub-soil.

Next, the excavation so-formed is filled with water, preferably during the winter season, to build-up a foundation block of ice I which fills the excavated cavity and, preferably, is built up slightly above-grade. This may be accomplished by known water spray/freeze techniques as indicated above, preferably building-up the block lift-by-lift," so that it ultimately intrudes about 4 to 7 inches below-grade and protrudes about the same or slightly less above-grade. The above-grade protion may be eliminated but will be seen as desirable to assure run-off of moisture in the pad so formed.

Next, an insulation cap V" of Arcofoam urethane or the like (as described above) is laid down upon ice block I, covering its top and sides to thermally insulate against its thaw and melting. Techniques for constructing ice block I and the superposed urethane cap V" may be seen in more detail in the aforecited application, U.S. Ser. No. 337,664.

Next, a composite, frozen iced-particulate layer 1-? is constructed atop the so-insulated block l. Layer L-P is constructed of wetted-frozen particulate material as aforedescribed and is preferably, laid-down along the sides, as well as covering the top, of insulated block I, much in the manner indicated for the iced-clay layer M in FIG. 4. Where a heated service facility SR is contemplated to be supported, as here, layer H is preferably comprised of volume percent pea gravel, the balance a. fat" (e.g., Montmorillonite) clay saturated with water, and will be on the order of 4 inches thick on the top of block I, being tapered-out in any convenient manner along the shoulders, as is known inthe art.

11. Example 11 As a preferable alternative to Example 10, layer I-P (FIG. is modified (over the foregoing) to be comprised of the aforementioned site excavation materials, i.e., a mixture of the active layer sub-soil and the tundra vegetation (typically about 30 volume percent vegetation). Thus, the tundra vegetation and active layer soil materials are homogeneously inter-mixed and distributed and compacted over the top of the insulated ice block I, to be, there, suitably wetted and frozen-in, as in prior embodiments, this being accomplished in one course or several, as preferred. Although any suitable thickness of the layer l-P so formed may be selected (corresponding to a prescribed service life for the pad at this locale and under the contemplated service), a thickness on the order of 4 to 8 inches (on the top, being tapered out on all sides for lateral support, as is conventional in the art) will provide a stable pad for several normal Prudhoe seasons. With excavator apparatus of the type aforedescribed, the material so.

excavated and piled thereby may be ultimately and ho- Also, it may be used during an appropriate cold season to flush cold air through layer l-P for quicker cooling andrefreezing thereof (e.g., after rewetting"). As indicated in the recited application, ducts DC may be closed off and stagnated during warm weather to minimize any tendence to warm layer l-P.

In any event, after placement of ice-particulate layer H, a top gravel layer G is laid down, sufficient to distribute the structural loads on the over-all pad as well as (especially along the sides of the embankment) to provide a certain amount of mechanical and thermal protection, as known in the art. Layer G will, here, preferably comprise on the order of 1 to 3 feet of ungraded, native gravel on top, being tapered out along the pad sides to the same depth or slightly less, as known in the art.

In embankment construction of the type described 1 above, it will be appreciated that it will often be desirmogeneously ground-up and inter-mixed all at once, to

be then-distributed by the same apparatus, at the same time; even being wetted thereby if desired. Besides convenience, this method will have the added advantage of allowing one to work in an unusually coldambient temperature; that is, where such tundra and subsoil excavation materials may be semi-frozen and somewhat unworkable in the usual circumstances, when they are so ground-up and mixed in an excavator apparatus, their cryogenic workability" will be greatly enhanced. Of course, working in such cold ambient temperatures facilitates a quicker freeze, once a given course of wetted" particulates is laid down. If necessary, the water so applied may be heated to a degree for mixing within the excavator apparatus. Of course, here and in Example 10, a supercoating of gravel G may also be superposed (FIG. 5) for structural and, if desired, thermal purposes (thermally insulation optimized if percent void maximized; hence ungraded gravel preferred).

As a further preferred optimizing feature, a row of spaced parallel cooling ducts DC may be imbedded in the iced-particulate layer l-P prior to compaction and. freezing-in; Such a ductwork may be analogous in construction and operation to that described in copending U.S. application Ser. No. 207,379, now U.S. Pat. No. 3,791,443, filed Dec. 13, 1971 by G. Burt and R. Odsather entitled FOUNDATION CONSTRUCTION FOR PERMAFROST REGIONS, herewith incorporated by reference to the extent applicable. Ducts DC may comprise any inexpensive perforated tubing, such as polyethylene tubes about to at inch diameter, laid parallel and spaced several inches apart along the upper level of layer I-P. As in the aforementioned copending U.S. application Ser. No. 207,379, now U.S.

Pat. No. 3,791,443, the indicated ducts are preferably in pneumatic communication with a matched set of similar, opposingly directed ducts (not shown in FIG. 5) to, together, circulate cooling air through layer H (where possible; e.g., after thawed) in the manner of the referenced application. It will be apparent to those skilled in the art that such a ductwork DC can provide several additional advantages insuch an embodiment. It maybe used to reintroduce moisture for .rewetting thawed portions of layer l-P, prior to refreezing LP.

able to be cognizant of the best methods and apparatus for coating such terrestrial (and similar) substrates with urethane foam or like insulation materials. Such methods may. usefully involve laying jdown a muIti-layered (laminate) foam coating; typically preceded and/or followed by a barrier coating (e.g., to seal against moisture), details for which may be better appreciated upon consideration of copending U.S. Pat. application Ser. No. 205,381, now abandoned, entitled STRUCTURE FOR PROTECTING AND INSULATING FROZEN SUBSTRATES AND METHOD FOR PRODUCING SUCH STRUCTURES, by A. C. Condo, G. R. Knight, 0'. R. Burt, and A. E. Borchert, filed Dec. 6, 1971, herewith incorporated by reference. Such laminate foam coatings and companion barrier coatings will be especially advantageous where insulation is to be laid upon a substrate which is problematically cold and/or damp and/or irregular in contour (e.g., having protruding surface anomalies like rocks.

Another advantage to such laminate foam coatings is that they may conveniently be applied very quickly and under very precise control, using high speed, automatic equipment. Such equipment may be better appreciated from consideration of copending U.S. Pat. application Ser. No. 197,219, now U.S. Pat. No. 3,786,965, entitled FLUID DISPENSER MANIPULATION, by James R. James and Kay E. Eliason, filed Nov. 10, 1971, and of U.S. Pat. application Ser. No. 181,440, now U.S. Pat. No. 3,741,482, entitled DISTRIBUTION DE- VICE, by James R. James and Kay E. Eliason, filed Sept. 17, 1971; both incorporated herein by reference.

Advantages to such laminate foam structures are associated with embankments of the type described will be apparent to workers; however, a few more will be summarized as follows. Besides the convenience and efficiency of machine application, as mentioned, a related advantage is that, quite unexpectedly, a laminate foam system may be employed with a dispensing machine of the type described to so overlap and fill-in successive foam layers as to compensate for dispenser-tosubstrate height (spray-distance) variations such as may derive from sloping terrain or from rocks or depressions there. Such systems can also compensate for variations, however irregular, in the manner and rate of foam delivery. Such a system can also compensate for the typical crowned" pattern of sprayed foam to render a relatively smooth, even foam coating, with a relatively uniform cross-sectional thickness and on which is unusually level at least on top. ln this regard, a particular formula may be prescribed for relating the number of laminations and the stepping distance" between successive spraying sweeps (nozzle passes) and the length of the off-set (or stagger) distance prescribed between successive sprayed strips.

Another advantage deriving from so deliverying such foam coatings with such equipment is that a new freedom and control in variation of resultant overall foam density may be achieved; for instance, overall coating (cross-sectional) density may be varied and controlled without substantially upsetting the regular" mode of application or machine operation, simply by varying the number and/or thickness of the laminates (skins) wherever density is to be modified (e.g., with no change in materials formulation, or skin-size, etc., by simply reducing lamination thicknesses). Even greater subtlety may be achieved within a given foam coating cross-section by allowing workers to modulate foam density top-to-bottom" something neven before achieved in a production' context. This may be done simply by modifying the spray mode to give, for example, a high-density on the lower half of a given foam coating and a lower density in the upper half e.g., simply by increasing the number of laminations in the lower half, keeping the overall coating thickness constant). A related advantage is that variations in nozzlesubstrate distance may now be compensated for, and effectively ignored; something which has never been possible heretofore as a practical matter. That is, it has been observed that despite variations in "spraydistance," the insulation thickness will remain relatively constant, with the machine simply increasing, or decreasing, the number of laminates (from the normal number).

Certain mechanical advantages are also seen to result. Laminated foam structures are observed to exhibit an enhanced resistance to incorporation of loose substrate-debris," such as small stones, over-sized soil particles and the like; especially as combined with a barrier pre-coat (as described above). This obviously helps to maintain the integrity and characteristics of the foam coating throughout more of its thickness, where, before, the bottom portion of the foam would have been wasted. Also, the overall mechanical strength of such coatings, especially flexing and bending strength, appears to be enhanced, i.e., such laminated foam structures exhibit superior tensile and compressive strength as compared with the non-laminated forms. Another important advantage of such laminated coatings is their resistance to fluid intrusion an occurrence that can virtually destroy the effectiveness of a urethane foam coating, as workers in the art well know. Laminated foam structures of the type to be described have exhibited a surprising versatility and stability when applied to wet ground substrates in the proper manner. For instance, it has been found that using about four laminations per inch with a skin thickness on the order of 5 to 7 mills and overall coating about 1 inch thick, fluid penetration is markedly reduced and/or retarded for systems of the type described, whereas a lamination density substantially lower is significantly less effective and efficient. This has been optimized using a water barrier pre-coat of petroleum residuals about 25 mils. thick (as described above), on which are laid 16 onequarter inch urethane foam (laminated) layers.

A further advantage relates to the thermal characteristics of the overall foam coating during application. It has been found that use of such a laminated foam coating system yields superior thermal characteristics during application as compared with non-laminated systems. This is apparently because, as each successive layer is applied and typically reacts to produce exothermic heat, the heat is conserved within the subject layer and heat-losses to the (heat-sink) substrate are reduced, progressively more and more, by underlying laminated layers through which it must pass. Accordingly, and when used in conjunction with a moisture barrier pre-coat, it has been found that laminated systems of the type described may even be laid upon permafrost or other icy substrates without substantially melting them, doing this in a manner that allows any minor amount of top-melt to quickly refreeze and precludes any significant moisture-contamination of the urethane. This also accomplishes a saving in blowing agent material and in the efficiency of foam cell formation, since it helps keep the foam temperatures from rising so much and so fast as to boil off the foaming agent, wasting it and rupturing cell'structures.

Another advantageous aspect of the subject method for applying foam coatings is that when the described pre-coating is applied as a moisture barrier, the foam coating may later be applied atop this so as to be inhibited (and, in most cases, prevented) from interacting with any substantial amount of water; thus being saved from significant aqueous degradation. According to one specific form this pre-coating comprises a petroleum base (preferably the residuals from a diesel topping plant) to which various thickeners and other agents may be added which is applied as a thin precoating on a bare ground surface. Such pre-coatings have been so effective as to allow urethane foaming on soil substrates which are saturated with water and entirely impracticable for conventional foam application; unexpectedly this has not prevented the formation of a reasonably satisfactory foam coating. Thus, according to this teaching, it will be found that wet gravel or wet clay substrates are quite acceptable in certain instances; where heretofore they were not. It has been observed that a pre-coating as prescribed, can also prevent air bubbles and voids from forming between the substrate and the urethane. lndeed, in certain instances it will be impractical to apply urethane coatings without using such a pre-coat. Foam coatings on moist substrates where no such pre-coat was applied have been effectively destroyed (or at least badly degraded) throughout most of their cross-section, appearing friable and quite unsuitable for normal insulation purposes.

Workers will appreciate that other expedients have been considered in place of the described petroleumbase moisture barrier material; e.g., strips of plastic or like prefabricated films. However, these are difficult to apply and to maintain adherent to the soil surfaces as well as to the overlying foam coating; also, they are quite expensive to provide and apply, and they are considerably more fragile, mechanically, their weak adhesion to soil, rock and other terrain surfaces, as well as to the supported foam laminates is a serious drawback. Moreover, and quite unexpectedly, it has been found that such petroleum base pre-coating materials may be pre-heate d and delivered to a substrate in a warm condition, thereby enhancing their adhesion to terrestrial surfaces and also providing a modicum of extra heat (pre-warming the substrate) for enhancing the foaming reaction of the following (initial) foam layers. Anotherrelated advantage is that, since such pre-coat materials typically constitute a good black body heat absorber, they are particularly effective for use with infrared and related heating devices used conjunctively with the foam delivery apparatus thus facilitating a quick and easy heating of the substrate and the incipient coating to further accelerate the foaming reaction, especially in a frigid environment.

According to another feature related to the foregoing pre-coating feature, a super-coating, similar to the pre-coat in composition and purpose, may be applied to the top surface of the laminated urethane foam. The material composition, thickness and manner of application of this may be substantially the same as that for the pre-coat and serve a similar purpose of barring (or at least inhibiting) the entry of moisture near the upper layers of foam, thus extending the useful life of the foam as well as providing a good mechanical adhesion as a seal between the foam and any overlying layers, such as gravel.

According to another feature, related to the foregoing, the described foam application methods include one or more periods of spray heating," preferably of the infrared or radiant type, during certain phases of, the composite coating procedure. It has been found particularly advantageous toarrange infrared heaters to quickly warm the precoat material as it is being spray-applied, as well as after it hits the ground, causing it to quickly set-up and gel, before dispersing too much. Such spray-heating also facilitates application of the initial laminate foam layer on the precoat, as quickly as possible after applying the precoat, and provides a foam-substrate which is (unconventionally) wann, thereby reducing foaming time (rise time, cream time). For similar reasons, it has also been found advantageous to heat the initial (and possibly successive) layers of foam, as well as the supercoating. The speed and efficiency of such spray-heating will be appreciated as enhancing any methods andapparatus like those described. The application of a prescribed avount, and preferably a prescribed radiant type. of heat during the spraying operations is advantageous in most cases; indeed critical in many.

In conjunction with sprayheating it is also often useful to stagnate the substrate area, blocking off the air-space thereby covering the top and all four sides of this area with tenting of the like. This tenting will be understood as adapted to function both as a wind screen during coating operations, as well as providing atmospheric containment for maintaining a prescribed controlled spraying atmosphere (e.g., prescribed temperatures, humidity. pressurized air-flow, etc. during spray operations within this work area). Where this area is artificially over-pressurized it can also help to contain a positive pressure," and exerta downward airflow over the substrate, helping to minimize overspray and other gaseous components there, keeping them close to the point of application and avoiding contaminations of the upper machinery parts with resulting waste of material as well as interference with operator vision, etc.

portant, it appears more critical to provide a prescribed amount of radiant heatingwhere possible. For instance with the apparatus of U.S. Ser. No. 197,219 above, now US. Pat. No. 3,741,482, ceramic type infrared units have been found quite useful, these being mounted on the spray machine, as forward and after units moving with the main frame to project heat ahead and behind, respectively, the spray-swath; preferably together with an auxiliary radiant heating unit or two surrounding the spray nozzle to follow it, focusing heat conjunctively with spraying. The latter units may, for instance, comprise a pair of 50,000 BTU radiant heaters moving with a nozzle carriage, the radiant heating therefrom being directed both upon the substrate and upon the spray material in transit thereto (after it leaves the nozzle).

Such a radiant heating system will be especially useful for heating the pre-coat (mentioned above), as well as the foam layers, radiantly heating the substrate and the transit zone (between nozzle and substrate); for instance, to maintain the temperature of the precoating and/or to heat the substrate prior to the application of the urethane. Such radiant spray-heating will be found advantageous prior to, as well as contemporaneous with, curing reactions; and also thereafter, compensating for ambient cooling influences. In most cases, such radiant heating is more critical and more effective than merely heating the sprayed materials (pre-coat or urethane) per se. It will be found that this radiant heating tends to heat the substrate much more than the intervening air, and can do so very rapidly most especially, when used in conjunction with a good black body pre-coat. Of course, provision of the shroud structure can also help conserve heat in the ambient air over the work area. Since the radiant heating should warm the sprayed urethane materials enough for the urethane curing reaction to be completed and enough to allow Freon-blowing" to proceed to completion some, or all, of the heating should be arranged to take place in transit. Material temperature, before and after spraying, should, however, not be so high as to drive off Freon and thereby make the coating density too high (as will an overcomplete atomization by the spray nozzle). As a rough guide for monitoring density rises, one may visually observe the fog normally associated with nominal-density" spraying, and when this fog becomes substantially thicker and more opaque, the coating-density will normally be rising too. It is preferred in most cases to heat the material enough so that, atthe time of reaction, it is somewhat above the specified reaction temperature, yet without getting it so hot as to blow-out Freon.

lntest coating situations, for instance, it has been found that with the polyol at F. and the isocyanate at F.. use of radiant heaters as described will yield a coated density of around 3.05 pounds/ft. indicating a K factor of about 0.128 and compression strength (at yield) of about 32 psi. By comparison, dispensing with such heaters and simply pre-heating both components to about 100F. before spraying, yields a density of about 4.5 pounds/ft. and a K factor of about 0.l34, with a compression strength at yield of 58-62 psi. This suggests that a material temperature of about F. is needed in such case, to drive the reaction to proper completion as well as yield adequate Freon-blow." The initial two laminates of such coatings, so heated, will exhibit a higher density and be thinner than the succeeding (laminate) layers; however, this may be avoided and yield improved by using such radiant heaters.

Summarizing the foregoing, improved means have been indicated whereby foam coatings may be applied to terrestrial and like substrates in a laminate form, especially for substrates which are moist and/or cold; doing so, preferably, in conjunction with a pre-coat or a prescribed type applied first; this being further optimized by the contemporaneous application of radiant heat to the coating area and materials as applied. In this manner, for instance, soil surfaces may be coated substantially as is" in cold environments and in a manner which is both convenient, effective and machineoriented; being especially adapted for constructing embankment foundations for man-made structures in permafrost regions; in certain cases being overlain with a prescribed thickness of gravel on thich may be situated housing or other man-made structures. Those skilled in the art will appreciate that this provides a stabilized building foundation which may thereby be insulated from melting and avoid subsidance of underlying permafrost substrata such as might result from solar heating or from the building structures therselves, etc. It will further be apparent that use of foam intermediates of the type described for gravel embankmentc facilitates the reduction and, in some cases, the elimination of much gravel something becoming critically important in areas such as the Arctic where gravel is often in short supply or restricted in availability. Workers will better appreciate related improved arrangements and methods for designing such embankments and related structures upon consideration of copending US. Pat. application Ser. No. 270,359 of G. R. Burt, A. C. Condo, and G. R. Knight, entitled INSULATED EM- BANKMENT DESIGN, filed July l0, i972; incorporated by reference herein.

Using some or all of the foregoing features, such embankment structures may be improved and thermally stabilized over a specific definitized service life; and a life which is much longer, for instrance. Then with embankments of gravel simply piled up by rote to a fixed invariant height where too small a gravel height will permit premature thawing and subsidance; whereas too large a height is not only costly but presents an uncomfortably high profile to the elements and is readily eroded, washed away and dissipated.

ROAD CONSTRUCTION Workers in the art will appreciate that the methods and apparatus suggested above and particularized hereafter have application not only for pad embankments like those afore-described and illustrated in FIG. 1 but also for elongated embankment" structures, such as air strips and, especially, roadways. It will be apparent that construction of said elongated structures. even in a hostile Arctic environment, involves problems similar to those of constructing the described embankments; however, amplified and complicated by the extent and variety of the terrain to be covered. For instance, a long airstrip or roadway must typically be laid over terrain which may vary from dry, bare rock to tundra vegetation, to moist hollows and even, in some cases, to ponds. Moreover, because of logistical problems of distance, material transport, etc. such elongated embankments present serious problems in terms of available time, manpower and other resources especially where the harsh cold, the wind and the darkness of arctic regions are encountered. Accordingly, methods such as those described, which lend themselves to machine application of foam foundation materials for airstrips, roadways and the like, will be unusually attractive to those working in this art.

For a more specific explanation of how the foregoing methods and equipment may be applied to maximize efficiency in laying relatively stable roadways in arctic regions, consider the following illustrative task. A reasonably stable road from point A to point B, and over intervening tundra in a permafrost locale, is to be constructed, relatively quickly and inexpensively. Thus, a roadway R is planned to comprise an initial section R-l, extending between point A and a point No. 1 about 50 miles from A enroute to B. An airstrip 8-1 is also planned to be located at point No. 1. Point A will be assumed to include its own airstrip S-A of the type suitable for accommodating the Hercules type aircraft and commonly employed now for logistical supply on the Alaskan North Slope. Roadway R is planned to be about ten feet wide whereas airstrips S-A and 8-1 may be understood to be about 30 feet wide and about k mile long. Heretofore in the Arctic such roadways have comprised simply a gravel berm, piled up on the natural terrain to a height of about 5 to 8 feet, using relatively dry native gravel as available, with sloped shoulders, as is customary elsewhere. Such roadways are obviously expensive to construct, can be quite miserable to maintain (e.g., losing gravel to melt-subsidence and down the shoulders) and can present a serious problem in availability and cost of the necessary gravel, especially in certain arctic locations remote from any gravel pits, river beds or other gravel sources. Conventionally the airstrips would have a similar gravel berm construction though perhaps a bit higher.

It is contemplated that Roadway R be constructed by substituting a laminate insulating foam thickness for a bottom portion of the gravel thickness. Thus, for instance, suitable automatic foam delivery equipment (preferably of the type described above) is programmed to lay such a foam pad under the gravel road, starting at Point A to lay the foam along R-l, with supplies being brought along (e.g., such things as fuel, urethane foam, constituents, pre-coating composition, etc., as indicated above). This first section R-l of the route would typically be leveled to a modest degree; e.g., merely removing large objects such as boulders, logs, etc., and cutting into the tundra (cut and fill) only where absolutely necessary for grade requirements, The automatic foam delivery equipment would thus proceed from Point A along the right of way to implement the described application methods by laying down a laminated foam coating as aforedescribed to support the roadway gravel berm. This would typically comprise, first, applying a pre-coat of petroleum bottoms onto the natural soil surface in a swath substantially the width of the gravel embankment and so continuously coat the ground with a sticky, adherent precoating at least about 15 to 25 mils thick. This precoat would preferably be warmed (as aforedescribed) at least to a gelling condition once it is applied, and then, within a few seconds, be followed by the first laminate layer of urethane foam, the foam being spray-applied and so heated and supplied with sufficient catalyst, etc. as to render the proper foaming actions, density, etc. Succeeding foam layers will next be similary laid down to build up laminar foam layers, separated by highdensity'skin layers (a few mils thick), having the prescribed parameters of cell content, density, K factor, etc. Such a laminate foam coat will preferably comprise about eight layers of urethane foam about A inch thick (a minor fraction of whichis skin). A supercoating, similar to the petroleum base pre-coating, will next be applied'atop the foam, in instances where the foam is subject to possible moisture from above. The'foam delivery machine will progress from point A towards point B, being continuously supplied from time to time with fuel, urethane constituents and the like from airstrip S-A, e.g., by truck shuttle based from S-A. Laying of the foam strip will be followed, as soon as appropriate, by gravel delivery; this comprising delivering grave] of prescribed characteristics (e.g., moisture, etc. as above-noted), derived locally if possible, to be piled atop the so-applied foam layers to the prescribed (reduced) height. Using the subject (approximately 2 inches) urethane foam thickness, only about 1% to 2% feet of Sag River gravel will be needed thereon to more than substitute for a conventional 5-foot, gravel-only mad; while also providing improved stability, reliability, low-maintenance, etc., as afore-indicated.

When the foam deliyery machine has progresseda suitable distance R-] from point A and airstrip S-A (the shuttle from S-A now understood as becoming somewhat cumbersome), a remote, auxiliary airstrip 8-1 is to be provided at point No. l, to replace S-A as the origin of the supply shuttle and to receive supplies, these, via the Hercules (primary supply) aircraft. This will be a more direct and effective supply line than the truck shuttle from S-A.

According to a further aspect of the subject conception, strip 8-] may be constructed in the same manner as roadway R by simply widening R-] to airstrip width," for a distance approximating airstrip length. The foam delivery machine may be used here to similarly lay a 2inch urethane foam padfor the airstrips gravel embankment (e.g., 5 to 10 feethigh, for added structural stability). The auxiliary runway length so constructed is thus made an integral part of the roadway adjacent thereto. Beyond the airstrip length, the preceding foam gravel roadway construction is resumed as before proceeding toward point B, along the next roadway section R-2 at point No. 2. in like manner, upon reaching Point No. 2, a second, auxiliary airstrip S-2 like 5-1 is to be constructed as before and for the same purpose. The mode of construction will continue in this manner, interjecting auxiliary airstrips, until point B is reached and roadway R completed.

The foregoing features of invention will be understood as described only in exemplary embodiments and obviously applicable with other equivalent means and for analogous purposes, the scope of protection pertaining hereto being limited only by the appended claims. This is, it is obvious that various modifications of the structures and/or techniques taught herein may be made without departing from the spirit of the invention as defined in the appended claims. For example, equivalent elements and steps may be substituted for those described, parts may be reversed and various features may be used independently of other features, all without departing from the spirit of the invention.

What is claimed is:

1. An improved method for constructing a composite iced particulate foundation pad adapted to support structures on frozen terrain, said pad being made of a plurality of contiguous layers of frozen particulate material, the construction of each layer comprising A. Forming a layer of particulate material the major portion of which has a relatively uniform particle size,

B. Wetting the particulate material with an aqueous liquid, and

C. Freezing the wetted particulate material, each layer being formed and frozen prior to the formation of the next sucessive layer and steps A, B and C being repeated until the desired number of layers are formed.

2. The method of claim 1 wherein said particulate material is comprised of native soil having a relatively high moisture retention and low capillarity.

3. The method as recited in claim 2 wherein said soil contains little or no lean clay material.

4. The method as recited in claim 2 wherein said particulate material is selected to exhibit a void to solid ratio on the order of at least about l:2.

5. The method as recited in claim 4 wherein said material is selected to retain on the order of at least about one-third water based on the total weight of solids and liquids.

6. The method as recited in claim 5 wherein said particulate material includes uniform diameter native gravels of pea grade of larger.

7. The method as recited in claim 5 wherein said particulate material comprises native soil particulates selected from the group consisting of aluminum silicates and the sodium forms of kaolin, bentonite or fullers earth.

8. The method as recited in claim 7 wherein said particulates include a significant portion of sodium bentonite.

9. The method as recited in claim 7 wherein said particulates include a significant portion of Montmorillonite clay material.

10. The method as recited in claim 5 wherein said particulate material comprises a significant protion of high-moisture-retention/low-effective-capillarity materials selected from the group consisting of fat clays, material containing a significant portion of calcium oxide or calcium carbonate, and finely divided organic matter.

11. The method as recited in claim 1 wherein the particulates are laid up lift-by-lift and wherein each lift is formed by laying a thickness of particulates on the order of several inches deep, wetting this layer to saturation by spraying a fine aqueous mist thereon to supercool the moisture and distribute it on the layer relatively uniformly without significantly moving the particles relative to one another; allowing this wetted layer to freeze-hard and then beginning construction of the succeeding layer in like manner to so build up the overall pad height.

12. An improved method for constructing a composite iced particulate foundation pad adapted to support structures on frozen terrain comprising A. Forming a layer of gravel the major portion of which has a relatively uniform particle size,

B. Forming a layer of high moisture retention material,

C. lntermixing the high moisture retention material with the gravel to distribute the high moisture retention material relatively homogeneously amoung the gravel particles,

D. Wetting the composite gravel-high moisture retention material layer with an aqueous liquid, and

E. Freezing the wetted composite gravel-high moisture retention material layer.

13. The method as recited in claim 12 wherein a major portion of said high moisture retention material is fat clay.

14. The method as recited in claim 12 wherein a major portion of said high moisture retention material is finely divided organic matter.

15. The method as recited in claim 13 wherein said high moisture retention material comprises sodium bentonite particulates having a void to solids ratio of about 1:4 to 1:3 and a moisture retention of at least 50 percent, based on the total weight of moisture and high moisture retention material.

16. The method as recited in claim 12 wherein said gravel-high moisture retention material layers are builtup to comprise an overall iced particulate pad on the order of l-2 feet high.

17. The method as recited in claim 12 including the steps of initially excavating the frozen terrain at the selected pad site to form a cavity; building an iced particulate pad in this cavity to a prescribed height; and covering this pad with prescribed structural materials.

18. The method as recited in claim 17 wherein said pad is covered with a thermal insulating cap of foam materials; wherein a second iced particulate pad, similar to the said pad, is constructed atop said foam cap; and wherein ungraded construction gravel is piled atop this second pad.

19. The method as recited in claim 12 wherein a prescribed ductwork is provided within said pad, the ductwork being imbedded in the pad particulates prior to freezing thereof and adapted for the selective cooling and/or selective remoistening of at least the particu- B. Forming, on said layer of thermal insulation foam a layer of particulate material the major portion of which has a relatively uniform particle size,

C. Wetting the particulate material with an aqueous liquid, and

D. Freezing the wetted particulate material.

21. The method as recited in claim 20 wherein said iced particulate pad is capped with a layer of thermal insulating foam; wherein a second iced particulate pad is constructed atop this foam cap layer; and wherein a layer of ungraded construction gravel is piled atop this second pad.

22. An improved method for constructing a composite iced particulate foundation pad adapted to support structures on forzen terrain comprising A. Forming a layer of particulate material, the major portion of which has relatively uniform particle size,

B. Wetting the particulate material with an aqueous liquid,

C. Freezing the wetted particulate material,

D. Forming a layer of thermal insulating foam over the frozen wetted particulate material, and

E. Covering said foam layer with a layer of construction gravel.

23. The method as recited in claim 22 wherein said foam comprises a layer of poly-urethane l-2 inches thick; wherein said iced particulate pad is at least about several inches thick and wherein said construction gravel coating is comprised of at least about 1 foot of ungraded gravel.

24. An improved method for constructing a composite iced particulate foundation on frozen terrain comprising A. Forming a layer of native soil particulates, the major portion of which has a relatively uniform size,

B. Wetting the native soil particulates with an aqueous liquid,

C. Freezing the wetted native soil particulates, and

D. Forming a layer of ungraded roadway gravel at least 1 foot thick on the frozen wetted native soil particulates.

Claims (24)

1. An improved method for constructing a composite iced particulate foundation pad adapted to support structures on frozen terrain, said pad being made of a plurality of contiguous layers of frozen particulate material, the construction of each layer comprising A. Forming a layer of particulate material the major portion of which has a relatively uniform particle size, B. Wetting the particulate material with an aqueous liquid, and C. Freezing the wetted particulate material, each layer being formed and frozen prior to the formation of the next sucessive layer and steps A, B and C being repeated until the desired number of layers are formed.

2. The method of claim 1 wherein said particulate material is comprised of native soil having a relatively high moisture retention and low capillarity.

3. The method as recited in claim 2 wherein said soil contains little or no lean clay material.

4. The method as recited in claim 2 wherein said particulate material is selected to exhibit a void to solid ratio on the order of at least about 1:2.

5. The method as recited in claim 4 wherein said material is selected to retain on the order of at least about one-third water based on the total weight of solids and liquids.

6. The method as recited in claim 5 wherein said particulate material includes uniform diameter native gravels of pea grade of larger.

7. The method as recited in claim 5 wherein said particulate material comprises native soil particulates selected from the group consisting of aluminum silicates and the sodium forms of kaolin, bentonite or ''''fullers earth.''''

8. The method as recited in claim 7 wherein said particulates include a significant portion of sodium bentonite.

9. The method as recited in claim 7 wherein said particulates include a significant portion of Montmorillonite clay material.

10. The method as recited in claim 5 wherein said particulate material comprises a significant protion of high-moisture-retention/low-effective-capillarity materials selected from the group consisting of fat clays, material containing a significant portion of calcium oxide or calcium carbonate, and finely divided organic matter.

11. The method as recited in claim 1 wherein the particulates are laid up ''''lift-by-lift'''' and wherein each lift is formed by laying a thickness of particulates on the order of several inches deep, wetting this layer to saturation by spraying a fine aqueous mist thereon to supercool the moisture and distribute it on the layer relatively uniformly without significantly moving the particles relative to one another; allowing this ''''wetted'''' layer to freeze-hard and then beginning construction of the succeeding layer in like manner to so build up the overall pad height.

12. An improved method for constructing a composite iced particulate foundation pad adapted to support structures on frozen terrain comprising A. Forming a layer of gravel the major portion of which has a relatively uniform particle size, B. Forming a layer of high moisture retention material, C. Intermixing the high moisture retention material with the gravel to distribute the high moisture retention material relatively homogeneously amoung the gravel particles, D. Wetting the composite gravel-high moisture retention material layer with an aqueous liquid, and E. Freezing the wetted composite gravel-high moisture retention material layer.

13. The method as recited in claim 12 wherein a major portion of said high moisture retention material is fat clay.

14. The method as recited in claim 12 wherein a major portion of said high moisture retention material is finely divided organic matter.

15. The method as recited in claim 13 wherein said high moisture retention material comprises sodium bentonite particulates having a void to solids ratio of about 1:4 to 1:3 and a moisture retention of at least 50 percent, based on the total weight of moisture and high moisture retention material.

16. The method as recited in claim 12 wherein said gravel-high moisture retention material layers are built-up to comprise an overall iced particulate pad on the order of 1-2 feet high.

17. The method as recited in claim 12 including the steps of initially excavating the frozen terrain at the selected pad site to form a cavity; building an iced particulate pad in this cavity to a prescribed height; and covering this pad with prescribed structural materials.

18. The method as recited in claim 17 wherein said pad is covered with a thermal insulating cap of foam materials; wherein a second iced particulate pad, similar to the said pad, is constructed atop said foam cap; and wherein ungraded construction gravel is piled atop this second pad.

19. The method as recited in claim 12 wherein a prescribed ductwork is provided within said pad, the ductwork being imbedded in the pad particulates prior to freezing thereof and adapted for the selective cooling and/or selective remoistening of at least the particulates surrounding the ductwork.

20. An improved method for constructing a composite iced particulate foundation pad adapted to support structures on frozen terrain comprising A. Forming a layer of thermal insulating foam upon said frozen terrain, B. Forming, on said layer of thermal insulation foam a layer of particulate material the major portion of which has a relatively uniform particle size, C. Wetting the particulate material with an aqueous liquid, and D. Freezing the wetted particulate material.

21. The method as recited in claim 20 wherein said iced particulate pad is capped with a layer of thermal insulating foam; wherein a second iced particulate pad is constructed atop this foam cap layer; and wherein a layer of ungraded construction gravel is piled atop this second pad.

22. An improved method for constructing a composite iced particulate foundation pad adapted to support structures on forzen terrain comprising A. Forming a layer of particulate material, the major portion of which has relatively uniform particle size, B. Wetting the particulate material with An aqueous liquid, C. Freezing the wetted particulate material, D. Forming a layer of thermal insulating foam over the frozen wetted particulate material, and E. Covering said foam layer with a layer of construction gravel.

23. The method as recited in claim 22 wherein said foam comprises a layer of poly-urethane 1-2 inches thick; wherein said iced particulate pad is at least about several inches thick and wherein said construction gravel coating is comprised of at least about 1 foot of ungraded gravel.

24. An improved method for constructing a composite iced particulate foundation on frozen terrain comprising A. Forming a layer of native soil particulates, the major portion of which has a relatively uniform size, B. Wetting the native soil particulates with an aqueous liquid, C. Freezing the wetted native soil particulates, and D. Forming a layer of ungraded roadway gravel at least 1 foot thick on the frozen wetted native soil particulates.

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