NO841280L - ELEVATIVE BOYYLE DRAINAGE MATS - Google Patents

Description

The present invention relates to drainage mats

when extending in several directions and which are useful and effective, for example for roadside drainage for dewatering of road surface systems.

The problem of: water in well covers has been a concern of technicians for a considerable time. As early as 1823, McAdam communicated to the London Board of Agriculture the importance of keeping the road surface dry in order to carry heavy loads without danger. He discussed the importance of maintaining an impervious surface over the base layer to keep water out of the base layer.

Nature of road surface hazards caused by water

is quite versatile. These are discussed in a publication entitled "Highway Pavement Distress Identification Manual" of 1979 prepared for The Federal Highway Administration in the U.S.A. Department of Transportation.

Moisture in road surface systems can arise from several sources. Moisture can penetrate through the sides, especially when there are coarse-grained layers or when the drainage possibilities of the surface in the area are insufficient. The ground water can rise and this can be expected in the winter" and in the spring. Surface water can penetrate into joints and cracks in the road surface, penetrate through the edges of the surface and penetrate up through this and the road shoulders. Water can move vertically in capillaries or continuous water membranes. Moisture can move in vapor form according to suitable temperature gradients and air-containing spaces.Furthermore, the problem of water in road surface systems is often more serious in areas where there is the effect of frost or periods of thawing of frost as well as in areas with the ground and in shale layers.

The types of hazards for road surfaces caused by water are quite numerous and vary depending on the nature of the road surface system. For flexible road surface systems, some of the hazards associated with water, either alone or in combination with temperature, will include: potholes, loss of aggregate, wear during driving, weathering, "crocodile cracks", reflective cracks, creep cracks, accumulations and elevations (in frost or swelling substrate). For rigid pavement systems, some of the hazards include buckling, joint failure, pumping, corner cracks, diagonal cracks, transverse cracks, longitudinal cracks, creep cracks, swelling or the formation of bulges, curls, D-cracks, surface spalling and steel corrosion, and uplift (due to of frost or expansion of the substrate).

Similar types of hazards occur on airport runways.

Many of the above-mentioned hazards or injuries

is linked to water pumping and erosion in the road surface base materials used in rigid road surface constructions. Water pumping and erosion of the road surface's base materials have been observed as the cause of harmful effects also on road shoulders. Likewise, many of the hazards that have been observed for asphalt concrete road surfaces are produced or accelerated by water.

For example, joint failure is a common result

of damage to non-reinforced concrete pavement without load transfer. Failure can occur under the following conditions: 1. The road concrete surface must have a slight curl down the individual plate edges slightly lifted from the underlying stabilized layer (thermal gradients and abnormal dryness inside the plate produce this condition).

2. Free water must be available.

3. Heavy loads must cross the transverse joints and first depress the approach side of the joint and then allow a sudden return, while at the same time impinging on the exit side of the joint and causing a strong pumping action of free water. 4. Pumpable finely divided material must be present (untreated base material), the surface of the stabilized base or support layer, and foreign material that enters the joints can be classified as pumpable finely divided material).

Failure of 0.6 cm or more will adversely affect the ride quality of the road surface system.

Methods for predicting and managing the water content of pavement systems are well documented in another publication entitled "Climatic Effects on Airport Pavement Systems-

State of the Art" of 1976, published by the United States Department of Defense and the United States Department of Transportation. Methods of controlling the moisture in pavement systems can generally be classified in terms of protection by the use of waterproofing membranes and anticapillary runs, the use of materials such as are insensitive to humidity variations and emptying of water using gutters.

The investigation in the field suggests that emptying using a gutter system is often a preferred method for managing water in road surface systems. In this connection, the correct selection, construction and execution of the gutter system is important for the long-term function of the road surface. A culvert drainage system for a country road must, among other functions, be able to interrupt or stop the intrusion across an impervious boundary, draw down or lower the groundwater and/or collect the flow from other drainage systems.

Existing road drainages include a large number of structures. Among the simplest are those that comprise a perforated pipe mounted at the bottom of an excavated trench backfilled with sand and coarse aggregates. For example, a standard drainage prescribed by the state of Illinois requires a perforated pipe with a diameter of 10.16 cm placed in the bottom of a trench with a width of 20.3 cm and a depth of 76 cm. The trench is then filled with coarse sand equivalent to an Illinois standard FA1 or FA2. Such drains are expensive to manufacture in terms of labor and materials. For example, the material excavated from the trench must be transported to an emptying site and backfill sand must be obtained and transported to the site for drainage construction.

Other types of drains have attempted to avoid the use of the perforated pipeline by using a synthetic textile fabric as a lining for the trench. The textile-lined trench is filled with a coarse additive that provides a substrate for the textile fabric. The empty space inside the combined additive serves as a conductor for collected water that penetrates the textile fabric. Such drainages are expensive to install, for example when it comes to the work of inserting and breaking the textile fabric as well as when it comes to transporting excavated and backfilling material. In addition, a significant amount of the textile material is sealed by contact with the added surface. This leads to an increased hydraulic resistance through the textile areas that are in contact with the additive surface.

Other modifications of drainage material include perforated piping covered with textile fabric, such as corrugated piping as shown and described in US Patent 3,830,373 or raised surface piping described and

shown in US-Patent 4,182,581. A disadvantage is that the planar surface area available for collecting the ground water is limited to about the diameter of the pipeline unless the textile-coated perforated pipeline is installed at the bottom of a collection trench which is filled, for example, with coarse sand. Another "disadvantage" is that much of the textile fabric's surface, for example around 50%, is in contact with the pipeline and thereby reduces the effective collection area.

The problem of limited planar surface areas for capturing groundwater is the subject of US Patent Nos. 3,563,038 and 3,654,765. These patents generally describe a planar extended surface core covered with a filter material that serves as a water collector. One edge of the core ends in a tube-like channel for transporting the collected water. Among the configurations of the planar extended core are a square corrugated sheet and an expanded metal sheet. A significant disadvantage of the constructions proposed in the latter patents is that the drains are rigid and not flexible; this presupposes the excavation of sufficiently long trenches so that an entire length of drainage pipe can be laid. The pipe-like channel requires a wider trench than would otherwise be required. In addition, the core of expanded metal sheet does not provide sufficient support for the textile material which can easily collapse against the surface of the opposite textile material and thereby greatly reduce the flow capacity inside the core. Likewise, the square corrugated plate core is limited in that at least 50% of the arc of the textile surface is closed by the core, thereby reducing the water collection area.

A related expanded surface drainage material is a two-layer composition of polyester nonwoven filter material heat-bonded to an expanded nylon nonwoven mat, such as the "ENKADRAIN" foundation drainage material marketed. The rollable drainage material has filter material on one side of the nylon non-woven mat. The drainage material serves only as a collector and requires the installation of a channel at the lower edge. This necessitates expensive excavation of wide trenches in addition to the canal's costs.

Another related extended surface drainage material comprises a core coated with a filter material and of pointed or burred polymeric plate, such as "STRIPDRAIN" which is marketed. This impermeable polymeric sheet divides the core into two insulated opposing sections that keep water collected on one side on this side. Moreover, for the drainage material to be flexible, the core must be contained in an enclosure of loose material which, as it is not supported on the core, can collapse due to stress from the soil into the core and thereby block flow channels. The polymeric plate with points or burrs is only flexible along two mutually perpendicular axes in the plane of the plate. This makes the installation somewhat difficult, e.g. entire lengths must be laid simultaneously in an excavated trench.

A further similar polymeric drainage product comprises a perforated plate attached to planar surfaces of truncated cones extending from an impermeable plate, such as a plate-shaped drainage material designated "CULDRAIN" marketed. The perforated plate has holes in the range of 0.5 - 2.0 mm in diameter and allows fine and small particles to be washed out from the subsoil.

The available drainage materials have one or more significant disadvantages, including economic disadvantages in that they require extensive work for installation and functional disadvantages such as that they require separate channels for removing collected water. A further functional disadvantage is that the drainage materials use mesh material which, depending on the adjacent soil, may become clogged with soil particles or may allow too much material to pass through, leading to a loss of subsoil support.

The present invention remedies most, if not all, of the significant disadvantages of such drainage materials. As an example, the drainage mat according to the present invention serves both as a collecting device and as a channel for removing collected ground water. The drainage mat according to the invention is flexible along any axis in a plane of its main longitudinal surface, as this greatly facilitates the assembly of large lengths of drainage mat in running lengths as trenches are dug out and filled within a short length. This provides a significant economic advantage in construction costs when automatic installation equipment is used. An embodiment of the drainage mat according to the invention can, depending on the hydraulic gradient, allow collected water to flow through any surface of the mat to a common channel.

In the description of the present invention, the following definitions are used.

The term "elongate drainage mat" as used in the present application refers to a drainage mat with a length substantially greater than its width or depth.

The term "axis of extension" used in this application refers to the axis that passes through the center of an elongated drainage mat along its length.

The term "rectangular cross-section" used in this application refers to a cross-section of an elongated drainage mat in a plane perpendicular to the longitudinal axis of the drainage mat.

The term "pointing" used in this application means a direction in which the axis of the extension of an elongated drainage mat extends or points.

An elongated drainage mat is said to be "vertically oriented" when the axis of extension of the drainage mat is substantially vertical to the soil surface.

An elongated drainage mat is said to be "horizontally oriented" when the axis of extension of the drainage mat is substantially horizontal with respect to the surface of the earth.

The term "orientation" as used in the present application refers to the position of an elongated drainage mat which has a rectangular cross-section determined by the ratio between the axes of the rectangular cross-section.

An elongated horizontally oriented drainage mat having a rectangular cross-section is said to be "vertically oriented" when the axis of the rectangular cross-section having the largest dimension is in a vertical position and the axis of the rectangular cross-section having the smaller dimension is in a horizontal position. The same drainage mat, when rotated 90° about its longitudinal axis, is said to be "horizontally oriented".

Among the useful parameters for characterizing textile material applicable in drainage mats according to the invention is the permeability coefficient which indicates the amount of water flow through a textile material at a differential pressure between the two surfaces of the material expressed in speed, e.g. centimeters per second. Such coefficients of permeability can be determined in accordance with (ASTM) Standard D-737. Due to difficulties in determining the thickness of a textile material for use in determining a permeability coefficient, it is often more appropriate and important to characterize the textile material in terms of "permittivity", which is a ratio between the permeability coefficient and material the thickness expressed as speed per thickness, which reduces to inverse time, e.g. seconds -1. Permittivity may be determined in accordance with a process defined in "Appendix A of Transportation Research Report 8 0-2 published by The United States Department of Transportation, Federal Highway Administration.

Plant textile materials used in drainage mats can be quite effective in protecting soil from erosion while allowing water to pass through the textile material to the channel portion of the drainage mat. However, the textile material must not become clogged or in any other way significantly reduce the flow rate. At the same time, the textile material must not allow too much material to pass through, otherwise clogging of the drainage mat could occur. However, loss of base layer soil can also occur.

When considering the interaction between the soil filter and the textile material, a rather complex bridging or arching occurs in the soil closest to the textile material which allows particles much smaller than the openings in the textile material to be retained. Failure of the soil mass-textile material system can be the result either of too strong removal of soil particles through the textile material or of a significant reduction in permeability through the textile material and the adjacent soil mass.

The application of construction textile materials

in drainage mats for road surfaces requires a further factor to be taken into account. A roadway is exposed to repeated dynamic loads from traffic. Such loading can lead to significant pore pressure pulses in a saturated road surface system. During and after heavy rain, a soil filter textile material at the edge of the road surface can be exposed not only to a static hydraulic gradient, but also to a dynamic gradient caused by the traffic load on the motorway.

In this regard, another useful parameter for characterizing the textile material applicable to the drainage mat according to the invention consists in "dynamic permeability" which indicates the rate of water flow through a column of specially graded soil mass over a layer of textile material under a combined static and dynamic hydraulic gradient. Dynamic permeability characterizes the behavior of textile material in resisting caking or clogging under conditions that duplicate the effects of repeated traffic loading. The procedure for determining dynamic permeability is shown in example III of this description.

The present invention provides a flexible drainage mat with a rectangular cross-section. The drainage mat comprises a polymer core with a number of fingers extending from one side of a layer and an enclosing water permeable textile material. For convenience during installation, the mat is often elongated.

So that the textile material does not collapse

prematurely in a flow-obstructing manner in the channel area of the mat, it is usually desirable that the textile material be attached to a sufficient number of the ends of the fingers. In most

constructions, the mat is flexible only in such a way that the surface closest to the layer becomes convex.

This invention provides a drainage mat comprising a three-dimensional perforated product covered on at least one major surface with a water-permeable material having a permittivity of from 0.2 seconds 1 to

-1

2.0 seconds and which exhibits a dynamic permeability after 10 loads of at least 10 cm/s.

The invention will be better understood from the following description with reference to the drawings, where fig. 1 shows an embodiment of a drainage mat in accordance with the invention, fig. 2 shows an embodiment of a perforated layer with rod-like protrusions usable as the three-dimensional core in a drainage mat according to the invention, fig. 3 shows a cross-section of a drainage mat, fig. 4 schematically shows a cross-section of a road surface system with a drainage mat according to the invention mounted near a road shoulder, fig. 5 schematically shows the position of bending axes with reference to the extension axis superimposed on the surface of the drainage mat which is close to the ends of the fingers, fig. 6 schematically shows the properties of a drainage mat to change the horizontal/vertical direction by turning about a bending axis placed at an angle of 45° from the extension axis, fig. 7 schematically shows a partial section of a device for continuous injection molding for the production of a polymer core for use in the drainage mat, fig. 8 is a plan view of a usable core material opposite the side from which the fingers extend, fig. 9 is a schematic view of an artificial lawn using a drainage mat according to the invention, fig. 10 is a schematic diagram of a railway system using the drainage mat according to the invention, fig. 11 is a section of a triaxial cell device which can be used for determining dynamic permeability, fig. 12 is a schematic representation of a triaxial cell device and dependent equipment used for the determination of dynamic permeability, fig. 13 is a diagram of particle size analysis for a soil mixture used to determine dynamic permeability and FIG. 14, 15 and 16 are diagrams of dynamic permeability for accumulated loads for various construction textiles.

The elongated flexible polymeric drainage mat having a rectangular cross section comprises a polymeric core with a number of substantially rigid fingers extending from one side of a layer and an enclosing water permeable textile material. In a preferred embodiment of the invention, the textile material has a permittivity of 0.2 seconds<-1>

— 1 6

to 2.0 seconds and a dynamic permeability after 10 be--4

loads of at least 10 cm/s. It is usually desirable for the textile material to be attached to the core to avoid unwanted movement of the textile material in relation to the core. E.g. the textile material may be attached to the layer. In these cases, when the layer is perforated or otherwise permeable, the textile material should completely enclose the core including the perforated layer so that the perforations in the layer are covered by the textile material. To avoid clogging of flow channels inside the core, the textile material should also be attached to a sufficient number of ends of said fingers so that the textile material does not prematurely collapse into the space around the fingers. In some cases, it may be sufficient that the textile material is attached to relatively few of the number of fingers, e.g. less than 50%, e.g. even less than 30% or even 10% of the fingers to avoid movement of the textile material in relation to the ends of the fingers so that the textile material will unnecessarily collapse into the space around the fingers and thereby stop the cross-sectional area that is otherwise available for fluid flow. In other cases, it may be desirable that the textile material is attached to essentially all the fingers to ensure that the structure of the drainage mat is maintained with maximum cross-sectional area even after hard treatment, e.g. during installation.

The drainage mats according to the invention have unique properties that are characterized by a large surface area available for drainage, flexibility for easy installation and a large open cross-sectional area that serves as a channel to allow large multidirectional flow volumes to empty quickly of collected water.

A preferred embodiment of the drainage mat according to the invention is shown in fig. 1, 2 and 3. In general, fig. 1 schematically an embodiment of a section of the drainage mat according to the invention, where water-permeable textile material 1 surrounds a core 2 with a number of mainly rigid fingers 4 that extend from one side of a layer 3. The axis of the mat's longitudinal direction is indicated by 5. Fig. 2 schematically shows an embodiment of a section of a polymer core used in the drainage mat, where the core has a. number of fingers 24 extending from the layer 23. Fig. 3 schematically shows a cross-section of a drainage mat, where the textile material 31 encloses a core with a number of substantially rigid fingers 34 extending from one side of a layer 33.

With reference to fig. 3, the drainage mat according to the invention is easily bendable to the surface 35 near the ends 37 of the fingers 34. That is. that the drainage mat can easily be bent only so that the surface 35 near the ends 37 of the fingers 34 becomes concave and the surface 36 near the layer 33 becomes convex.

In this regard, the drainage mat cannot be folded against itself to the surface 36 near the layer 33 without an undue force likely to tear the textile material or deform the core or cause it to collapse. This is especially the case when the textile material is bonded to the core. However, the mat can be bent without further force with a little force so that the surface 35 near the ends 37 of the fingers 34 readily and easily bends towards itself even up to 180° about a bending axis with a radius of less than about 2.54 cm, f .ex. down to 0.63 cm. This bending to the surface near the ends of the fingers can be achieved about any bending axis parallel to the surface 35. In this regard, fig. 5 different bending axes applied to a drainage mat surface 56 near the ends of the fingers. These bending axes are parallel to the surface 56 and are defined by their rotational position from the longitudinal axis 50 of the drainage mat. A bending axis can be rotatably arranged at any angle from 0 to 180° from the longitudinal axis 50. E.g. is the bending axis 51 perpendicular to the longitudinal axis 50 (i.e. that the bending axis 51 is rotatably arranged at an angle of 90° in relation to the longitudinal axis 50). The drainage mat can be folded against itself around the bending axis 51, leading to a shorter length, or this mat can be rolled into a short cylindrical spiral roll. The bending axis 52 is parallel to the longitudinal axis 50 (ie the bending axis 52 is rotatably arranged at an angle of 0° from the longitudinal axis 50). The drainage mat can be folded around the bending axis 52 against itself in the longitudinal direction or rolled into a long spiral-shaped roll.

When the drainage mat is folded towards itself up to 180° about a bending axis 53 which is rotatably arranged at an angle of 45° in relation to the longitudinal axis 50, the longitudinal axis 50 of the drainage mat will cause a 90° bend as shown in fig. 6. This property of the drainage mat is particularly useful for such installations where the drainage mat 61 is to be installed below the plan in a vertical orientation. In this regard, the drainage mat may be arranged in a vertical orientation above the plan and led to a roller 62 at an angle of 45°. The drainage mat directed around such a roller 62 will be perpendicular to a horizontal plane and can be led to a secondary roller 63 at an angle of 45° at a height below the plane. This secondary roller 63 will direct the drainage mat to a vertical orientation below the plan in a position for its use.

Of course, rollers at other angles can be used to effect such changes in height. In addition, changes in horizontal position can also be effected by rollers arranged in horizontal parallel planes.

The drainage mat according to the invention produces a large open cross-sectional area which offers little resistance to flow in any direction. A large open cross-sectional area is produced by selecting an optimal number of mainly rigid fingers which form the mutually separated textile material surfaces.

The core used in the drainage mat according to the invention is three-dimensional and has a number of mainly rigid fingers extending from one side of a layer. The layer can be impermeable or perforated depending on the intended application. When it is desired that the drainage mat should be able to collect water from both main surfaces, the layer should be perforated. A core with a perforated layer is shown in fig. 2, where the layer 23 has a number of perforations 25. These perforations must have a sufficiently large area to allow water containing suspended solids to pass freely through the layer without clogging it by trapped or bridging

forming solids.

The fingers may comprise a very large group of shaped protrusions. As shown in fig. 2, a preferred finger is a rod-like projection which is cylindrical and projects in a direction perpendicular to the plane of the layer. Fingers with other shapes can be used, for example fingers with a square, hexagonal, star-shaped or oblong cross-section or with fins etc. Such shapes can be affected by the construction of the mold used during the core forming process. Although solid fingers can be used, it is often desirable that the fingers are hollow both to facilitate manufacture and to reduce to a minimum the mass of the core to facilitate installation.

Regardless of the shape, the fingers can be characterized as

if they have a nominal diameter which is an average transverse dimension through the cross section of a finger. When finger-n has a cylindrical shape perpendicular to the plane of the substrate, the nominal diameter is the diameter of the circular cross-section. If the finger has some deviant geometric shape, the nominal diameter is an average transverse dimension, e.g.

when the finger is square in shape, the mean transverse diameter is slightly larger than one side of the square or square but slightly smaller than the diagonal of the square. The nominal diameter dimension can be approximately calculated by the mean value of the maximum and the minimum distance from the center of the mold to a surface.

In most cases it is preferred that the fingers have a central axis which is perpendicular to the plane of the perforated layer. In other cases, it may be desirable for the fingers to protrude at some deviant angle from the perforated layer. The core can be characterized as having fingers of a nominal diameter such that the ratio of the length of the fingers measured from the perforated layer to the end of the finger and the nominal diameter of the finger is in the range of from about 1:1 to about 8:1.

In order to provide a core with a maximum value of the cross-sectional area for fluid flow with minimal resistance produced by fingers, it is desirable to provide a maximum distance between the fingers. However, the fingers must not be so far apart that the textile material will collapse into the space between the fingers due to a lack of support. In this respect, it is usually desirable that the core be equipped with an optimal distance between the fingers, which can be characterized as a mean center distance, i.e. the distance between centers for fingers that cut the substrate. Average center distance can be between about 0.76 cm and 7.6 cm or more.

In many cases, it is desirable that the average center distance is between 2.3 cm and 3.2 cm.

Cores used in the drainage mat according to the invention can have fingers with a length of from 0.3 cm to 7.6 cm and a nominal diameter of between 0.25 cm and 2.54 cm or more. However, it is often desirable that the fingers have a length between 1.3 cm and 3.8 cm and a nominal diameter between 0.4 cm and 1.3 cm.

The depth of the drainage mat will be approximately determined by the length of the fingers and the length can be very long, e.g. up to 122 m. The width of the drainage mat, i.e. the largest dimension of the rectangular cross-section can be between 15.2 cm and more than 122 cm, e.g. even up to 365 cm or more. The width will depend on the dimensions of the device used to produce the core. Larger dimensions can be produced by attaching two or more widths of core to each other.

Drainage mats can be made from a very large number of different polymeric materials. Among the preferred materials for the core are thermoplastic materials, such as polyethylene and polypropylene. For some applications, the preferred materials include low density polyethylene or linear low density polyethylene.

A polymeric core applicable to the drainage mat according to the invention can be produced using thermo-plastic molding apparatus and methods well known to those skilled in the art. A preferred method for producing polymeric cores with hollow cylindrical fingers involves the use of a continuous casting apparatus described in US patent 3,507,010.

Fig. 7 shows a cross-section of such a continuous casting apparatus comprising a rotating cylindrical drum 70 with a number of regularly distributed injection cavities 71. The cylindrical drum 70 rotates in conjunction with a stationary injection head 74. The distance between the injection cavities, 71 will correspond to the mean center distance for the fingers extending from one side of the core. The cross-sectional shape of the injection cavities can be varied to produce fingers with a desired cross-section, e.g. circular, rectangular, star-shaped, etc. These fingers can also be conical depending on the construction of the cavity. Hollow fingers can also be produced by arranging an annular injection cavity as shown in fig. 7, where each cavity 71 is equipped with an inserted pin 72 with an extension 73 of reduced diameter. The length of the reduced diameter extension can be varied depending on the desired depth of the hollow bore in the finger. .The stationary injection head 74 has two rows of elongated nozzles - high-pressure nozzles 76 and low-pressure nozzles 75. The high-pressure nozzles 76 deliver molten thermoplastic material P from a pressure vessel 77 to the injection cavities 71 as they rotate in accordance with the end of the high-pressure nozzle 76. A high-pressure nozzle 76 is aligned with each row of injection cavities 71 which are aligned around the circumference of the cylindrical drum 70. The low pressure nozzles 75 are supplied with molten thermoplastic material P from the pressure vessel 77. Constrictions 78 in each low pressure nozzle reduce the pressure of the thermoplastic material emerging at the end of each low-pressure nozzle and produces longitudinal carriers between rows of fingers.

The core geometry can be varied as desired by arranging such a continuous injection molding apparatus with suitable dimensions.

The enclosing water permeable textile material may comprise a large number of different materials. Among the preferred textile materials are those comprising polymeric materials such as polyethylene, polypropylene, polyamides, polyesters and polyacrylic. In most cases, it is preferred that the textile material comprises a hydrophobic material such as polypropylene or polyester. Such textile materials must be sufficiently water permeable that they exhibit a -1 permittivity for water within the range from 0.2 seconds to 2.0 seconds -1. More preferred materials are those having a permittivity in the range of from 0.5 seconds -1 to about 1.0 seconds -1 . The textile material can either be a woven or a non-woven product; however, woven materials are generally not preferred.

This permittivity indicates that the textile material allows sufficient water flow through the textile material to the channel part of the drainage mat. This water flow is not so great that it allows so much suspended material to pass through the textile material that this would lead to either a loss of support for the support layer or clogging of the drainage mat.

The textile material must also show significant resistance to covering and clogging, as it e.g. can be caused by bridging or arching of soil particles closest to the material. As the textile material in many facilities, e.g. in the case of edge drainages on motorways, are exposed to both static and dynamic hydraulic gradients due to repeated traffic loads, dynamic permeability is an essential feature of the drainage mat according to the invention. In general, the textile material must exhibit a dynamic permeability after 10^ loads as described in the method in example III below, of at least 10 -4 cm per second. A more preferred textile material will exhibit a dynamic permeability after

6 -3 10 loads of at least 10 cm per second, e.g. in the range -2 -3 10 to 10 cm per second. In some cases, a textile material exhibiting a dynamic permeability as small as 10~<5>cm per second be acceptable.

Dynamic permeability values may vary during repeated loads, e.g. above 10 ^ loads. It is usually desirable that the variations in dynamic permeability should be within an acceptable range based on the highest value for dynamic permeability. E.g. shall be the ratio of the highest value of dynamic permeability to the lowest value of dynamic permeability over 10^ loads (a ratio of dynamic permeability at

1,000,000 loads) does not exceed 100. It is more preferred that the permeability ratio at 1,000,000 loads

is about 50 or less.

It is often desirable for the water-permeable textile material to enclose the entire core. When the layer is not perforated, the textile material only needs to overlap the edges of the layer. When, on the other hand, the layer is perforated, the textile material must completely surround the core. The textile material can be arranged as a sock to be passed over the core. Alternatively, the textile material may be wrapped around the core in such a way that there is an overlapping longitudinal joint to form the enveloping textile material.

The textile material must of course be attached to the core, particularly at the ends of the fingers to avoid the textile material collapsing into the channel space in the core. Very different methods can be used for attaching textile material to the core. E.g. the textile material may be attached to the core using a bonding agent, such as a hot melt adhesive. The textile material can also be attached to the core by using mechanical fasteners or by ultrasonic welding. Alternatively, the textile material may be attached to the ends of the fingers by causing the material at the ends of the fingers to flow into the textile material.

The drainage mat according to the invention is usable

in any number of applications where it is desired to remove water from an area. E.g. the mat can be used in aquariums as a substrate for gravel. The permeability of the textile material can be varied depending on whether filtration is desirable.

The drainage mat can also be advantageously used as a base for both natural and artificial grass mats. It is sometimes desirable to grow a grass mat over a paved surface, e.g. a courtyard or a roof. The drainage mat according to the invention can be laid in a horizontal orientation, preferably within a defined area and then covered with a layer of soil, such as loam, to support a natural turf.

In many cases it is desirable to install artificial grass, such as synthetic grass-like playgrounds, on a flat surface. This has some disadvantages with outdoor facilities that are exposed to rain. Rain often causes accumulations on level facilities with artificial grass to the detriment of sports activities. The drainage mat according to the invention can be advantageously mounted under the artificial grass, which is usually permeable to water, in order to collect and carry away rainwater. Even when installed on a level paved surface, the depth of the drainage mat will provide sufficient height to allow sufficient water flow over several hundred meters to drain connections. The drainage mat according to the invention has sufficient strength to support activities including vehicle traffic

the supported artificial turf.

In fig. 9 shows a cross-section of an artificial grass mat for play and games supported by a drainage mat in accordance with the invention. Artificial grass mat 91 is laid over an elastic mat 92 with a number of perforations 93. The elastic mat 92 is mounted over a drainage mat 94 in accordance with the invention. A drainage mat can be installed with the layer against a supporting level surface 95. As an alterna-. tive and if the layer is perforated, the drainage mat can be mounted with the layer against the elastic mat 92. In some cases, the drainage mat can be used without any surrounding water-permeable textile material, e.g. when the drainage mat is installed over a concrete floor, etc. However, when the drainage mat is installed above soil, it is desirable to use an enveloping textile material to prevent water-saturated soil from entering the mat.

It is particularly useful for installations below the surface, where it is desirable to remove water. A large area available for drainage is provided by means of it

rectangular cross-section of the drainage mat. The drainage mat according to the invention is advantageously applicable for traffic-carrying surfaces to carry traffic with motor vehicles, aircraft, rail vehicles and even pedestrians. Such use of this drainage mat is particularly advantageous in facilities where the drainage mat is installed so that the greater part of its cross-sectional dimensions are perpendicular to an area to be drained. E.g. is the mat applicable in a vertical orientation as an edge drainage for a traffic-bearing surface, such as an edge drainage on a motorway or as a joint drainage for example where two road surface segments meet. In the vertical orientation, the drainage mat is also useful for

prevent ground water from flowing towards constructions, such as the motorway's bearing base, railway bearing layers, retaining walls, building foundations and underground walls etc. Such an advantageous installation is in a motorway system, where the drainage mat is installed parallel to the road, e.g. in a vertical orientation under a freeway shoulder joint. In this connection, fig. 4 a motorway system comprising a concrete cover 41 with associated shoulder 4 2 which can be covered. The concrete deck 41 lies on top of a bearing layer 43. The shoulder lies on top of the support 44. In such a facility, infiltration of water in a vertical direction through the highway shoulder joint 4 6 can be intercepted by the narrow cross-sectional area at the top of the drainage mat 4 5, water present under the highway can be intercepted by the large cross-sectional area that is perpendicular to the motorway's bearing layer and the opposing large cross-sectional areas can intercept groundwater approaching the motorway from the outside. All this collected water can be carried away as soon as it is collected by the drainage mat.

In other facilities where it is desirable to maintain a moisture level in a base layer for a highway, a drainage mat with an impermeable layer in contact with the vertical edge of the base layer can prevent the flow of ground water either into or out of the base layer. The drainage mat can collect and carry away groundwater that would otherwise enter the base layer.

The drainage mat is also advantageously applicable in railway systems when mounted in a horizontal orientation, e.g. under or inside a substrate. Fig. 10 schematically shows such a facility, where a pair of rails 9 6 lie on sleepers 97 which are supported by a substrate 98. The drainage mat 99 according to the invention can lie under or inside the substrate to stabilize the railway system by capturing and carrying away rainwater that would allow the substrate and soil to mix with each other and undermine the support.

The drainage mat according to the present invention is easily assembled with simple connecting and transition pieces. E.g. rectangular molded connectors that fit over the ends of the drain mat can easily join two lengths of drain mat. Transition pieces designed to intercept the bottom edge of the drainage mat are used to connect the drainage mat to standard circulation channels or pipelines to carry collected water away from the drainage mat to a sewer or drainage system.

The present invention shall be further illustrated, but not limited to the following examples.

Example I

An apparatus for producing continuous lengths of three-dimensional molded products composed of a matrix of protrusions extending from a surface as described in US Patent 3,507,010 was constructed to provide an artificial grass-like material. The apparatus comprises a cylindrical drum provided with a plurality of evenly spaced rows of cavities, e.g. with 1.2 mm center distance. Knurled insert pins were fitted with a press fit in the cavities to selectively limit the penetration of injected molten polymer into the drum and thus control the height of the protrusions formed by the polymer.

In a quarter of the cavities, the inserted pins were replaced with insert pins with an extension of reduced diameter which formed an annular molding space in the injection cavity. The annular mold chamber had an outside diameter of about 0.64 cm, an inside diameter of about 0.48 cm and a length of about 2.54 cm. The remaining three-quarters of the cavities were plugged again with filler pins. The modifications to the pin resulted in a cylindrical drum with annular injection cavities spaced 2.54 cm on center.

Pellets of linear low density polyethylene were melted and fed under hydraulic pressure from a screw extruder into the distribution nozzle of the apparatus with two rows of holes which directed the polymer into the cavities and grooves of the cylindrical drum. The first row of holes in contact with the rotating cylindrical drum delivered polymer to the annular casting cavities as well as the blanked cavities. The second row of holes delivered polymer to connecting grooves in the drum. Stationary fingers located in the grooves of the cylindrical drum insulate each cavity while casting takes place and thus form a zone of high pressure which allows penetration to full depth in the annular casting cavities as well as a short post piece in the blinded cavities. Polymer was deposited in connecting grooves at a pressure slightly above atmospheric pressure to control the amount of polymer fed to each groove. By adjusting the narrowing rings, it was possible to achieve an equalization of the casting pressures to completely fill the annular casting cavities and produce carrier strips flush with the surface of the cylindrical drum.

The shape of the molded product is shown schematically in fig. 2 showing a perforated layer with a number of hollow cylinders extending from one surface of the layer. The cylinders have a length of 2.54 cm and an outside diameter of about 0.64 cm and an inside diameter of about 0.48 cm. The cylinders were spaced approximately 2.54 cm on center with two rows of carrier strips extending between the rows of cylinders longitudinally. Circular plugs produced connections between the carrier strips with a center distance of about 1.27 cm as shown in fig. 2. This produced a continuous layer of butterfly-shaped perforations as shown in fig. 8 which is a bottom view of the molded core. The molded core was produced with a width of about 15.24 cm with continuous length. The core can be cut to any desired length, e.g. down to 1.5 m or less or up to 122 m or more.

Example II

Three varieties of construction textiles were provided. These three textile materials and their equivalent mesh size (corresponding to U.S. sieve no. determined by test method CW-02215) are listed in Table 1. The three textile materials were subjected to permittivity analysis. The results of this analysis based on ten random samples for each textile material and ten test runs for each sample are shown in Table 2.

Example III

This example describes the method of testing things for determining "dynamic permeability" for a textile material. The three types of building textiles determined in Example II were subjected to dynamic permeability analysis using an apparatus with a triaxial cell schematically shown in fig. 11. This apparatus comprises a metal bottom plate 101 with a central raised flange 104 with a diameter of 20 cm and an annular groove for receiving a cylinder 102. The metal bottom plate has a fluid opening from the center of the raised flange 104 to the circumference. A flexible outer boundary membrane 103 of thickness 0.8 mm of neoprene rubber is attached to the circumference of the central raised flange 104. Silicone grease is applied to the contact surface between the outer boundary membrane and the central raised flange to provide a watertight seal.

A porous carborundum stone 105 with a diameter of 20 cm is placed on the central raised flange 104. Four perforated rigid plastic discs 106 with a diameter of 20 cm are placed on the carborundum stone 105. A piezometric pressure outlet tube 107 is mounted in a hole in the outer bounding membrane 103 equally below the top of the plastic discs 106. A single layer of glass balls 108 with a diameter of 1.5 cm is placed on the top plastic disc.

A flexible inner membrane 109 with a diameter of 20 cm and with a disc 110 of construction textile material attached to the bottom edge of the flexible inner membrane 109 is inserted into the flexible outer membrane 103 so that the disc 110 rests on the layer of glass beads 108. A coating of silicone grease on the transition between the flexible inner membrane 9 and the membrane 103 provides a watertight seal between the two membranes.

Water is allowed to flow into the bounding membrane 103 from the opening in the bottom plate to a level above the textile disc to remove any trapped air. The water is then drained down to the level of the textile disc 110.

A dry soil mixture of 90% concrete sand by weight

"Class X" (none minus No. 200 screening material) and 10% by weight of sludge "Roxana" are prepared. The dry soil has a gradation analysis as shown in fig. 13. 13.6 kg of dry soil is thoroughly mixed with 2 L of water to give a mixture with close to 100% water saturation. The mixture M is filled into the flexible inner membrane 109 to a height of about 24 cm above the textile disc 110. As the mixture M is filled into the membrane, excess water is allowed to drain from the mixture M by maintaining the open end of the pipe 107 at a height of about 1 cm above the textile disc 110.

After all excess water has been drained from the mixture Mr, a porous carborundum stone 111 with a diameter of 20 cm is placed on the mixture M. A metal cap 112 with a diameter of 20 cm is placed over the stone 111. Silicone grease is applied to the transition surface between the cap 112 and the flexible inner membrane 109. Tape (not shown) is used to attach the membranes to the cap 112. The cap 112 has two openings and a raised central flange. A transparent cylinder 102 is placed over the equipment with the bottom edge of the cylinder 102 fitted into the annular groove in the bottom 101. A metal cell top 113 is placed over the cylinder 102 with the upper edge of the cylinder fitted into an annular groove in the cell top 113. The cell top 113 and the bottom plate 101 is held against the cylinder 102 by means of bolts (not shown).

The cell top 113 has four openings, one opening connected to the pipe 114 which supplies the cell with pressurized water, another opening is connected to the pipe 115 which extends through the cell top 113 to an opening in the cap 112 which can be used to provide flushing water for the confined mixture M Another opening is connected to the tube 116 which extends through the cell top 113 to an opening in the cap 112 which provides a flow of water for analysis. The fourth opening is connected to a pipe 107 which is used to control the pressure under the textile disc 110. The cell top 113 has a bore through the

height flange 117. The bore allows the load rod 118 to be passed through the cell top 113 to the top of the metal cap 112. The bottom surface of the load rod 118 and the top surface of the metal cap 112 have spherical recesses for receiving a metal ball 119 which enables the transmission of a point load-

nothing. O-rings (not shown) provide a seal between the load rod 118 and the bore through the cell top 113.

The device with the triaxial cell is ready for

operation by filling the annular space between the cylinder 102 and the membranes with water to the level of the cap 112. The pipes 115 and 116 are connected from the openings in the cap 112 to openings on the cell top 113. Water is allowed to enter the membrane containing the mixture M, upwards from bottom to saturate the mixture. M. The valve 120 on the tube 115 can be operated to release air. Water is allowed to fill the pipe 116 connected to a pair of pressurized deaerated water containers. The pressure inside the membranes (the internal pressure) can be adjusted through the tube 116 connected to the container which is filled with air pressure.

The pressure in the space surrounding the membranes (the ambient pressure)

can be adjusted through the tube 114.

Reference should now be made to fig. 12 which is a simplified . schematic representation of the device shown in fig. 11 together with one of the deaerated water containers 122 which can be pressurized, mercury manometers 123 and water manometers 124.

clean 122 is located above the triaxial cell 125, e.g. an appropriate distance between the mean height of water i

the container and the level of water 126 in the triaxial cell 125 of 100 cm.

It is desirable to work with an air pressure in the container 122 of around 220 kN/m 2 while maintaining a "net limiting pressure" of 12.1 kN/m 2 . The limiting pressure P can be calculated from the following equation: P = 1.33 (H-Hw/13.6),

where P is the net confining pressure expressed in values of kN/m 2,

H is the pressure difference measured with the mercury manometer 23 for excess air pressure at pipe 14 over the air pressure at pipe 27, and

HW is the average distance between the water level in the container 22 and the water level 2 6 in the triaxial cell 25.

If e.g. HW is about 100 cm, it is desirable to slowly increase the limiting pressure measured at pipe 114 to at least 15 cm Hg greater than the pressure at pipe 127. Then both pressures are slowly increased until the air pressure on container 122 is about 220 kN/m 2. The limiting pressure must be adjusted so that the mercury manometer 123 indicates that the air pressure at pipe 114 is 16.5 cm Hg greater than the air pressure at pipe 127. This should give a net limiting pressure of around 12.1 kN/m 2.

Flow is initiated by opening the air valve 128. The flow rate is adjusted to produce a pressure drop measured at the water manometer 124 in the range of 24 - 26 cm of water. Readings of the flow rate, time and water manometer differential are noted until the permeability is stabilized, e.g. usually 10 - 15 minutes. Axial loading through the load rod or filler rod 118 is then initiated.

An air-driven diaphragm air cylinder (not shown) is connected to the load rod 118. A load pulse of 17.5 kN/m 2 is applied to the cap 112 and transferred to the mixture M with a frequency of one per two seconds (0.5 hertz). This load simulates stresses inside the mixture M, similar to the stresses of the bearing layer in the case of truck loads on the roadway system.

Readings are taken after 1, 10, 100 and 500 loads and then usually at six hour intervals.

The dynamic permeability for building textiles is calculated from the following equation:

K = QL/HAT

where K is dynamic permeability expressed in values

of cm/sec;

Q is water flow volume expressed in values of

of cm^, collected over time T;

L is the height of the soil mixture M expressed in

values of cm;

H is the hydraulic gradient across the mixture measured with the water manometer 24 expressed in values of cm;

A is the cross-sectional area of the textile disc 10

expressed in values of cm 2 and

T is the time of collection of a volume Q expressed

in values of seconds.

The dynamic permeability for building textiles given in Example I is shown in figures 14, 15 and 16 which are diagrams of dynamic permeability over loads.

Fig. 14 is a diagram of dynamic permeability recorded for fabric No. 1, which decreases to less than

-4

10 cm/sec. after around 450,000 loads.

Fig. 15 is a diagram of dynamic permeability recorded for fabric No. 2, which gradually decreases but remains above 10 -4 cm/sec even after one million loads. Fig. 16 is a diagram of dynamic permeability remaining between 10 -3 and 10 -2 cm/sec over the application of one million loads.

Considering the results of dynamic permeability analysis, textile No. 1 would be unacceptable for use in the drainage mat according to the invention, while textile No. 2 and textile No. 3 would be acceptable for use in the drainage mat according to the invention. Textile No. 3 is an example of a more preferred textile material.

Example IV

A 0.61 m x 1.2 m section of core material

was produced from cast core material as produced in Example I. A drainage mat was produced by enveloping the section of core with a water-permeable textile material

which was attached to the back of the perforated plate and to the ends of the hollow cylinders with a hot-melt adhesive. The water permeable textile material was a non-woven polypropylene textile material marketed under the designation PROPAX 4545. Such material is stated to have the following properties: tensile strength of 40.9 kg determined by ASTM standard test method D-1682, elongation of 60% measured by ASTM-D-1682, breaking strength of 1589.9 Kilopascal determined by "Mullen Burst Test" accelerated breakdown strength maintained at 70% determined by test method CCC-T-191 No. 5804 (500 hour test), equivalent mesh size of 70 (minimum equivalent US sieve no.), determined by CW-02215, and a permeability coefficient of

0.2 cm/sec, determined by the drop height method from 75 mm to 25 mm.

The textile material was also determined to have a permittivity per textile layer of 0.75 cm/sec determined by the test method defined in Appendix A in Transportation Research Report 80-2.

The textile material was also determined to have a dynamic permeability after 10 6 loads of at least 10 -4 cm/sec. In reality, the dynamic permeability was greater than 10^ cm/sec.

Example V

The drainage mat prepared in Example IV was installed in a "lysimeter" for outflow studies to estimate its drainage performance. The lysimeter consisted of a large waterproof box 24 4 cm long, 122 cm deep and 122 cm wide. The top of the box was open. The box was filled to a depth of 91.4 cm with compacted base layer soil with characteristics according to the AASHTO classification system A-7-6. 20.3 cm wide slits were then excavated in the base layer material to a depth of 61 cm.

A drain line was installed through the side wall of the watertight box to collect the excavated slot at the bottom. The drainage mat was mounted in a vertical orientation with the surface of the mat near the perforated bottom lying against the side wall of the slot. The lower 30.5 cm of the slot was filled with compacted base layer soil as defined above. The remainder of the slot as well as the 15.2 cm above the depth of compacted base soil was filled with coarse sand material.

F or carrying out the outflow studies, a drop height for the water was maintained in the lysimeter at a level 12.7 cm above the surface of the coarse sand material. Water flowing from the outflow line was measured periodically to determine an outflow rate. Instantaneous outflow rates measured in values of gallons per day was recorded after different elapsed time, measured in units of days. These outflow rates are listed in Table III.

Example VI

This example illustrates the deflection resistance of the drainage mat prepared according to Example IV. A section of drainage mat prepared according to Example IV was laid in a horizontal orientation with the surface closest to the perforated layer in contact with a foundation. A rectangular box with open bottom and open top and with internal dimensions 10.2 cm and 14.0. cm was placed on the surface of the drainage mat closest to the ends of the cylinders. The box was partially filled with soil (AASHTO A-7-6) which was covered with a 10.2 cm x 14.0 cm steel compression plate. Conduit was fitted through holes in the compression plate through the soil mass for contact with the surface of the drainage mat. A guide tube was installed on the textile material above one cylinder, another guide tube was installed on the textile material between the cylinders. Extension pins from scale instruments were passed through the guide tubes to the surface of the textile material. As the load on the compression plate was increased in increments of 0.445 N, the deflection of the surface of the drainage mat was measured with scale instruments. The result of this load deflection test is listed in Table 4.

While. the invention is described above in connection with certain particular embodiments, it is not limited in this way. It should be understood that variations and modifications of this can be made by professionals in the field without deviating from the basic idea and framework of the invention.

Claims (10)

1. Drainage mat, characterized by a three-dimensional perforated material covered on at least one main surface with a water-permeable textile material, with a permittivity from 0.2 sec^ to 2.0 sec^ and which exhibits a dynamic permeability after 10^ loads of at least -4 10 cm/sec. 2. Elongate flexible" drainage mat having a rectangular cross-section, characterized by a polymeric core having a number of substantially rigid fingers extending from one side of a layer and an enclosing water-permeable textile material, the textile material being attached to a sufficient number of ends of said fingers so that the textile material does not collapse unnecessarily. . 3. Mat according to claim 2. characterized in that the textile material has a permittivity from 0.2 sec ^ to — 1 6 2.0 sec and exhibits a dynamic permeability after 10 -4 loads of at least 10 cm/sec. 4. Mat according to claim 3, characterized in that it is readily bendable only so that the surface of the drainage mat nearest the ends of the fingers can be rolled concavely about any bending axis parallel to the plane of the layer and rotatably placed at any angle from 0 - 18 0° from the mat's longitudinal axis. 5. Mat according to claim 4, characterized in that the surface of the drainage mat nearest the ends of the fingers can be rolled concavely up to 180° over a bending axis with a diameter of less than 2.54 cm. 6. Mat according to one of claims 2-5, characterized in that the fingers have a length from 1.3 - 3.8 cm, a nominal diameter from 0.4 - 1.1 cm and an average center distance from 2.3 - 3 .2 cm and that the rectangular cross-section has a length dimension from 15 cm to 3.6 m, and that the polymeric core comprises a polymeric material selected from the group consisting of polyethylene and polypropylene and that the textile material comprises a polymeric material selected from the group consisting of polypropylene, polyamide, polyester and polyacrylic or a glass fiber material. 7. Motorway system comprising a road surface over a bearing layer, an adjacent shoulder and a drainage system for a subgrade shoulder, characterized in that the subgrade shoulder's drainage system comprises a layered flexible polymer drainage mat with a rectangular cross-section, said mat comprising a polymer core with a number of mainly rigid fingers extending from one side of a layer and an enclosing water-permeable textile material, wherein the textile material is attached to a sufficient number of ends of said fingers, so that the textile material does not collapse unnecessarily, and that the enclosing water-permeable textile material has a permittivity of 0.2 sec <-1> to 2.0 sec 1 and exhibits a dynamic permeability after 10 <6> loads of at least 1 <-4> cm/sec. 8. Artificial grass mat equipment for mounting on a bearing surface, characterized by a layer of artificial grass mat and a drainage mat, where the drainage mat comprises a polymer core with a number of substantially rigid fingers extending from one side of a layer. 9. Equipment according to claim 8, characterized in that the drainage mat also comprises a water-permeable textile material which encloses said core. 10. Railway system comprising at least one set of rails mounted on sleepers carried by ballast, characterized in that at least part of said ballast lies above an elongated horizontally oriented drainage mat with a rectangular cross-section, the drainage mat comprising a polymer core having a number of mainly rigid fingers which extends from one side of a layer and an enclosing water-permeable textile material, the textile material having a permittivity -1 -1 from 0.2 sec to 2.0 sec and exhibits a dynamic permeability-6 -4 tet after 10 loads of at least 10 cm/sec.