CN110512589B - Vacuum drainage-reducing and magnesium oxide carbonization combined shallow ultra-soft foundation curing method - Google Patents
Vacuum drainage-reducing and magnesium oxide carbonization combined shallow ultra-soft foundation curing method Download PDFInfo
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- 239000000395 magnesium oxide Substances 0.000 title claims abstract description 25
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 title claims abstract description 19
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D3/00—Improving or preserving soil or rock, e.g. preserving permafrost soil
- E02D3/02—Improving by compacting
- E02D3/10—Improving by compacting by watering, draining, de-aerating or blasting, e.g. by installing sand or wick drains
-
- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D3/00—Improving or preserving soil or rock, e.g. preserving permafrost soil
- E02D3/11—Improving or preserving soil or rock, e.g. preserving permafrost soil by thermal, electrical or electro-chemical means
-
- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D3/00—Improving or preserving soil or rock, e.g. preserving permafrost soil
- E02D3/12—Consolidating by placing solidifying or pore-filling substances in the soil
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- Structural Engineering (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Soil Sciences (AREA)
- Environmental & Geological Engineering (AREA)
- Agronomy & Crop Science (AREA)
- Mining & Mineral Resources (AREA)
- Paleontology (AREA)
- Civil Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Treatment Of Sludge (AREA)
- Investigation Of Foundation Soil And Reinforcement Of Foundation Soil By Compacting Or Drainage (AREA)
Abstract
The invention discloses a shallow layer ultra-soft foundation curing method combining vacuum dewatering and water discharging with magnesium oxide carbonization, and belongs to the technical field of silt soft soil reinforcement treatment in environmental geotechnical engineering. The method comprises vacuum dewatering and water discharging treatment and magnesia carbonization and solidification treatment, and specifically comprises the steps of primary exploration and pretreatment, vacuum dewatering and water discharging system arrangement, secondary exploration and treatment, uniform mixing of cushion sand, uniform mixing of curing agents, connection and carbonization of a ventilation system and the like. The invention firstly reduces the water content of the silt soil by a physical treatment mode, then determines the mixing amount and the mixing ratio of the curing agent according to physical indexes, and rapidly improves the strength of the silt soil by a chemical curing method of magnesium oxide carbonization. The method has the characteristics of economy, environmental protection, short treatment period, good treatment effect and the like, and realizes the resource utilization of industrial slag, building waste residue and carbon dioxide in the soft foundation treatment.
Description
Technical Field
The invention belongs to the technical field of sludge soft soil reinforcement treatment in environmental geotechnical engineering, and particularly relates to a shallow ultra-soft foundation curing method combining vacuum dewatering and water discharging with magnesium oxide carbonization.
Background
With the high-speed development of civil engineering construction in China, a large amount of silt, mucky soil or dredger fill is frequently encountered in the construction of airports, docks, railways and civil buildings, and particularly in coastal and river-side areas, silt soft soil has high water content, high permeability, large liquid plastic limit and low shear strength and cannot meet the direct requirements of engineering. Drainage and solidification treatment of these soft soil foundations are often required to reduce the groundwater level and uneven settlement, and to improve the foundation strength. The traditional sludge soft soil treatment method comprises physical treatment and chemical curing treatment, and specifically comprises vacuum preloading treatment, heat treatment, pumping, precipitating, airing or mud throwing treatment, chemical curing agent treatment and the like. The vacuum drainage preloading method is a common physical treatment method, and the cement solidification method is the most common chemical method in soft foundation reinforcement engineering. The heat treatment method is a method for converting sludge into building materials by a heating or sintering method, and has small treatment capacity, high cost and difficult large-scale utilization; the sediment is dried or the mud is thrown and is disposed and will occupy a large amount of places of piling, and low water permeability silt makes the land that occupies hardly reuse in the short time, has increased engineering cost, and easily causes the secondary pollution of air, water and soil etc. at pump drainage or ectopic landfill in-process.
The vacuum preloading method needs to naturally air-cure or sand cushion layer paving or bamboo raft paving on the blow-filled soft soil at the upper part to enable the soft soil at the upper part to bear the load required by the mechanical approach construction of the inserting plate, and the method is a more common method for improving the bearing capacity of the sludge on site at present. But natural sunning and lay the bed course need consume longer time and a large amount of grit material, through vacuum apparatus to pumping out in the water absorption pipeline of burying underground in the sand cushion course, form the negative pressure in the soil body to the hole water in the soil body space is sucked and is taken out through the water absorption pipeline in the sand cushion course through the vertical drainage channel in the plastics drain bar, with reduce hole water pressure, increase effective stress, make the soil body produce the consolidation, reduce the later stage and subside, realize the purpose that the ground bearing capacity improves. The treatment efficiency of the vacuum pumping drainage is reduced along with the prolonging of the treatment period, soil columns and silting are easily generated around the drainage plate in the post-treatment process, the engineering requirements can be met only by long-time vacuum preloading, generally more than 6 months, and the bearing capacity of the treated foundation is low (less than 60 kPa). When the soft foundation treatment is carried out by adopting the vacuum combined preloading method, the preloading pressure on the upper part of the sand cushion layer is realized by jointly loading soil, the more the loaded earthwork is, the larger the preloading pressure is, a large amount of piled soil is difficult to obtain near a construction site, the large transportation cost is consumed for taking the soil from a remote place, and the earthwork needs to be cleaned up after the engineering is finished, so that the construction cost is increased, and the local ecological environment is damaged. Therefore, the traditional vacuum preloading and vacuum combined surcharge preloading have the defects of high operation difficulty, long period, high construction cost, ecological environment damage, low treatment strength and the like. The document (CN 106013048B) discloses a vacuum preloading seepage consolidation combined precipitation preloading consolidation method for an ultra-soft foundation, which mainly comprises the arrangement of a vacuum system, vacuum preloading and vacuum precipitation preloading. But the method has the following defects: pumping underground water and completely recharging the pumped underground water into a cofferdam dike of the area to be reinforced, and prepressing a soft foundation by the weight of the overlying water; the cofferdam is excavated for drainage after a period of prepressing, the whole treatment process involves multiple times of pumping and drainage, the operation is complex, the prepressing time is relatively long, the prepressing strength may be uneven, and the strength increase is limited. The invention patent (201811211504.2) discloses a novel vacuum preloading soft foundation combined preloading system and a construction method, and the novel vacuum preloading soft foundation combined preloading system has the advantages that sealed water is filled as load for preloading on a soft soil foundation, compared with the traditional preloading method, water injection and drainage are relatively easy, but the period is relatively long, water is used as preloading pressure, the foundation bearing capacity of a dredger fill layer after reinforcement treatment is increased, and the treatment depth is limited (less than or equal to 80kPa), so that the popularization and application of the method are restricted to a certain extent; and if the mud bag is used as the stacking pressure, the mud bag needs to be removed after treatment, and the application is inconvenient. The document (CN 104120710B) discloses a soft foundation treatment method combining vacuum preloading and blowing-filling of slurry, which is mainly characterized in that the slurry is blown-filled on a pretreated soft foundation to form a sealing film and a loading layer. However, the method has the defects that the vertical drainage plates need to be inserted on the pretreated soft foundation and the hydraulic filling slurry layer respectively, and the vertical drainage plates are difficult to insert on the hydraulic filling slurry layer.
In order to accelerate the treatment progress of soft soil fields and improve the bearing capacity of soft foundation treatment, an in-situ chemical curing method is a commonly used treatment method at present, namely, curing agents such as cement, fly ash and the like are fully mixed with silt soft soil through grouting or powder spraying stirring equipment, so that the curing agents are subjected to hydration and chemical reaction, the water content of the silt soft soil is reduced to a certain extent, and the generated hydrate and the soft soil are gelated and hardened, so that the aim of reinforcing the soft soil is fulfilled. However, for soft soil with water content far higher than the liquid limit, more curing agents are required to be added to achieve the expected strength, the disposal cost is obviously increased, and the solidified silt soil has more pores and enhanced brittleness, is easy to generate instantaneous damage and is not suitable to be directly used as an engineering foundation. Document (201310488540.4) discloses a system and a method for in-situ solidification and stabilization treatment of contaminated soil, which uses a special feeding device of a stirrer for in-situ solidification and stabilization of contaminated soil, and adopts a strong stirring method to realize the sufficient mixing of sludge and a curing agent, so that the sludge is rapidly dehydrated and wrapped and hardened with the curing agent, and the safe treatment requirement of solidification and stabilization is met. But the method is difficult to be applied to large-area high-water-content sludge fields, and the construction machinery is difficult to enter the field. The document (201910160700.X) discloses a high-efficiency curing method for a soft soil field with high water content, which combines chemical curing of a curing agent with prepressing drainage, and adopts the curing agent to stir and then perform prepressing drainage. But the disadvantages are: for silt soft soil with too high water content, the curing agent is easy to run off and the activity is reduced in the water discharging process, so that the cementation rate of the curing agent is reduced; the curing agent is mainly cement with great pollution in the production process. The patent (201310204944.6) discloses an environment-friendly sludge solidification method, which is to use the iron tailings slag of industrial waste as aggregate, a mixture of Portland cement and carbide slag as a curing agent, and the aggregate and the curing agent are mixed for sludge solidification treatment. The obvious defects of cement are as follows: the production process has high energy consumption (the calcining temperature is up to 1450 ℃), large carbon dioxide emission and serious environmental pollution; pollutants such as dust, carbon dioxide and the like discharged in the production are increasing day by day and are bottlenecks which restrict the stable development of economic environment and socialization. In order to protect the environment and reduce the use of traditional cement, the applicant subject group discloses some treatment methods based on activated magnesium oxide carbonization and solidification, such as ' a treatment system and method for thermally reinforcing soft soil foundation by using industrial waste gas ' (201310122135.0) ' a treatment system and carbonization and pile-forming method for foundation reinforcement ' (201410203978.8) ' a filling-up layer replacement carbonization and reinforcement method for soft soil foundation ' (201410272957.1) ' a shallow soft foundation in-situ carbonization and solidification treatment method ' (201510348797.9) ' an ex-situ activated magnesium oxide carbonization and solidification sludge soil method ' (201711194797.3) ', and the like. The similar characteristics of the invention patents are that active oxide is used as soil curing agent, carbon dioxide gas is introduced into the mixed soil to realize carbonization and reinforcement treatment of weak foundation soil, and the invention patents have the characteristics of high reinforcement speed, high strength, good environmental benefit and the like, and accord with the development trend of green construction of civil engineering. However, the carbon dioxide gas has the problems of short migration distance, difficult migration and non-uniformity in the high-water-content silt soft soil.
By combining the characteristics of high sludge water content and small pores and the defects of the existing soft soil treatment technology, the method for treating sludge with low carbon, high efficiency, economy and reasonability is an important subject to be solved in the industry based on the current situation and the requirement of rapid development of engineering construction in China. Therefore, the method for treating the magnesia carbonized and cured shallow soft foundation of the vacuum dewatering water has very important engineering significance for treating sludge soft soil in geotechnical engineering.
Disclosure of Invention
In view of the defects in the prior art, the invention aims to provide a shallow layer ultra-soft foundation curing method combining vacuum dewatering and water discharging with magnesium oxide carbonization, and solves the technical problems of long treatment period, low bearing strength, high economic cost, poor environmental benefit and poor stability of high-water content silt soft soil in the prior art. The method combines the traditional vacuum preloading and the novel magnesium oxide carbonization technology, fully exerts the water seepage, drainage and ventilation effects of the drainage plate, reduces the water content of the sludge soft soil, rapidly increases the strength, has the characteristics of good treatment effect, economy, environmental protection, short treatment period and the like, and simultaneously realizes the resource utilization of industrial waste residues, building garbage and carbon dioxide in the soft foundation treatment.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a vacuum drainage-reducing water combined magnesia-carbonization shallow-layer ultra-soft foundation solidification method is characterized by comprising vacuum drainage-reducing water treatment and magnesia-carbonization solidification treatment, and specifically comprises the following steps:
a. primary exploration and treatment: measuring basic physicochemical indexes of the ultra-soft foundation soil, including field area, mud depth, water content, liquid-plastic limit, organic matter content and pH value, performing partition and drainage ditch excavation on the ultra-soft foundation field, cleaning and leveling the periphery of the field,
the ultra-soft foundation field partitioning method is determined according to the physical and chemical indexes of the excavator arm length, the stirring arm length, the sludge depth and the sludge of the uniform mixing equipment;
b. arranging a vacuum dewatering and drainage system: laying a sand cushion layer on an ultra-soft foundation with the mud depth not more than 4m, inserting vertical drainage plates into a pretreatment area, wherein the inserting depth of the vertical drainage plates is not less than the mud depth, the distance between every two adjacent vertical drainage plates is 1-2 m, connecting the upper ends of the vertical drainage plates to a vacuum pump through a hard horizontal water suction pipe with holes, laying non-woven geotextile and a sealing membrane in sequence, starting the vacuum pump to vacuumize and drain water,
the cushion sand is broken fine particles of river sand, sea sand or building garbage, and the maximum particle size is not more than 5 cm;
the thickness of the sand cushion layer is determined according to the mud depth of the ultra-soft foundation, and when the mud depth is within 1m, the thickness of the sand cushion layer is 15-20 cm; when the depth of the mud is 1-2 m, the thickness of the sand cushion layer is 20-30 cm; when the depth of the mud is 2-3 m, the thickness of the sand cushion layer is 30-40 cm; when the depth of the mud is 3-4 m, the thickness of the sand cushion layer is 40-50 cm;
c. secondary exploration and treatment: measuring the water content and depth of silt soil after dewatering and draining, lifting the sealing film and geotextile, removing the horizontal water suction pipe,
d. uniformly mixing cushion layer sand: opening the uniform mixing equipment to uniformly stir the upper cushion sand and the silt,
e. uniformly mixing a curing agent: determining the mixing amount of the curing agent, the stirring time and the stirring speed of the soft soil in unit volume according to the physical indexes of secondary measurement, starting a curing agent controller, uniformly stirring the powdery curing agent and the silt soil, leveling the field after stirring to form a pretreated foundation,
the curing agent consists of 50 to 60 percent of active magnesium oxide, 30 to 60 percent of slag powder, 10 to 20 percent of steel slag powder, 5 to 10 percent of quicklime powder and 5 to 10 percent of anhydrous magnesium chloride powder;
the curing agents are uniformly mixed along the annular and outside-in directions of the pretreated foundation;
f. connecting and carbonizing an aeration system: the vertical drainage plate is hermetically connected with the main ventilation pipe through the branch ventilation pipe, the main ventilation pipe is connected with a carbon dioxide high-pressure gas tank, the non-woven geotextile and the sealing membrane are laid, the gas pressure regulating valve is regulated, ventilation and carbonization are carried out,
the aeration carbonization is carried out along the annular and outside-in directions of the pretreated foundation;
the carbon dioxide is industrial waste gas of a cement plant or an iron and steel plant, the concentration of the carbon dioxide is not lower than 40%, the ventilation pressure is not lower than 200kPa, the ventilation mode is continuous ventilation or intermittent ventilation, the carbonization time is determined according to the ventilation pressure, the distance between the vertical drainage plates and the water content of the mixed soil, and the accumulated carbonization time is 12-24 hours.
As an improvement of the invention, the vertical drainage plate is a hollow hard plastic drainage plate or a concrete permeable tubular pile, the cross section of the vertical drainage plate is rectangular, square or circular, the length or the diameter of the cross section is 10-30 cm,
the horizontal water suction pipe is embedded in the sand cushion layer, the water suction pipe outside the sand cushion layer is provided with a filter and a control valve, the filter is positioned above the drainage ditch, the control valve is positioned between the filter and the vacuum pump,
the number of the vacuum pumps is determined according to the site area of the ultra-soft foundation, and the processing area of a single vacuum pump is not more than 1600m2The negative pressure of the vacuum pump is not lower than 90kPa, the working time of the vacuum pump is determined according to the water content of the silt after dewatering and draining, and the water content after dewatering and draining is not higher than 90% of the liquid limit of the silt.
As another improvement of the invention, the uniform mixing device comprises a digger arm, a stirring arm, a curing agent controller, a curing agent storage tank, a main powder conveying pipe and a powder spraying pipe, wherein the curing agent controller is fixed on the uniform mixing device, a rotary joint is arranged between the digger arm and the stirring arm, the main powder conveying pipe is positioned between the curing agent storage tank and the curing agent controller, the powder spraying pipe is arranged between the curing agent controller and the rotary joint and is additionally arranged on the digger arm, the ventilation branch pipe is connected to the upper end of the vertical drainage plate through a sealing connection sleeve, the ventilation branch pipe is connected with the ventilation main pipe through a quick-connection joint, the ventilation main pipe is positioned between the ventilation main pipe and the high-pressure gas tank, and a heater and a supercharger are arranged on.
Compared with the prior art, the invention has the technical advantages and beneficial effects that:
(1) simple operation and short processing period
The method has the advantages of both the vacuum preloading drainage consolidation method and the magnesia carbonization solidification method, and is simple to operate; the water content of the vacuum dewatering and drainage water is only reduced to be near the liquid limit, and compared with the traditional vacuum preloading drainage consolidation, the consolidation time is shortened; the magnesium oxide can reach higher strength only by 24 hours of aeration and carbonization during carbonization and solidification, and the solidification period is shortened compared with the traditional cement solidification.
(2) Fully exert the functions of the vertical drainage plate and the sand cushion layer
The vertical drainage plate and the sand cushion layer have water seepage and drainage functions in the physical treatment process, have the function of improving the air permeability in the ventilation and carbonization process, and have the functions of reinforcing and skeleton of a cured structure body after curing treatment.
(3) The carbon dioxide utilization rate and the carbonization efficiency are high: the main ventilation pipe is provided with the heater and the supercharger, so that stable infiltration of carbon dioxide gas is ensured, condensation and frosting of the air pipe and insufficient ventilation pressure are avoided, and compared with the existing carbonization treatment method, the ventilation efficiency is greatly improved.
(4) The treatment effect is good: the silt soil particles are effectively cemented by using hydration products and carbonization products of the curing agent, the skeleton effects of sand grains, construction waste particles and the like are exerted, and the vertical drainage plates are used as a reinforcement material of the foundation structure body, so that the strength and the stability of the silt soil foundation are enhanced.
(5) Low carbon and environmental protection: the curing agents used in the chemical curing process mainly comprise active magnesium oxide, quicklime, slag powder, steel slag powder and anhydrous magnesium chloride powder, the mixed curing agent treatment comprises a plurality of curing mechanisms, and compared with the traditional portland cement, the cement mortar has the characteristics of low carbon and environmental protection, the used sand cushion material can be building waste crushed particles, industrial waste carbon dioxide is utilized in carbonization, and the used materials are all low carbon and environmental protection materials.
(6) Reasonable treatment process and high continuous operation rate: the chemical curing treatment process is that the uniform mixing equipment is carried out along the periphery of the pretreatment field, the air pipe and the coating film can be communicated after uniform mixing, carbonization can be carried out, after one circle is finished, the uniform mixing machine can walk on the carbonized foundation to carry out construction of a new circle inwards, uniform mixing stirring and carbonization are carried out simultaneously, and the operation efficiency is greatly improved.
Drawings
FIG. 1 is a schematic view of solidification of a shallow ultra-soft foundation by combining vacuum dewatering and magnesia carbonization;
in the figure: 1. super soft foundation, 2, vertical drain bar, 3, geotechnological cloth, 4, the pipe that absorbs water, 5, the sand bed course, 6, the seal membrane, 7, the escape canal, 8, the filter, 9, the control valve, 10, the vacuum pump, 11, dig the arm, 12, rotary joint, 13, the rabbling arm, 14, the equipment that mixes evenly, 15, curing agent controller, 16, curing agent storage tank, 17, main defeated powder pipe, 18, the pipe that dusts, 19, preliminary treatment foundation, 20, sealed adapter sleeve, 21, the branch pipe of ventilating, 22, the main pipe of ventilating, 23, high-pressure gas pitcher, 24, the air-vent valve, 25, the heater, 26, the booster.
Detailed Description
The embodiment of the invention solves the technical problems of long treatment period, low bearing strength, high economic cost, poor environmental benefit and poor stability of the ultra-soft foundation in the prior art through a vacuum dewatering and water discharging combined magnesium oxide carbonization shallow ultra-soft foundation curing method; through jointly using traditional vacuum preloading and novel magnesium oxide carbonization technique, the infiltration drainage and the ventilation action of full play drain bar and sand bed course make silt weak soil moisture content reduce, intensity increase fast, have characteristics such as the treatment effect is good, economic environmental protection, processing cycle are short, realize industrial waste residue, building rubbish and carbon dioxide resource utilization in soft base treatment.
For better understanding of the technical solutions, technical objectives and effects, the technical solutions will be further described with reference to the drawings and the detailed description, i.e., the embodiments and specific features of the embodiments of the present invention are described in detail and are not intended to limit the technical solutions of the present application. In addition, in the description of the present invention, the directional relationships indicated by "upper", "lower", "top", "bottom", "inner", "outer", and the like are based on the directional relationships shown in the drawings, and are only for convenience of describing the present invention, and do not indicate or imply the specific directions referred to. That is, the technical features in the embodiments and examples of the present application may be combined with each other without conflict.
Referring to fig. 1, a method for solidifying a shallow ultra-soft foundation by combining vacuum drainage and magnesia carbonization is characterized by comprising vacuum drainage treatment and magnesia carbonization solidification treatment, and specifically comprises the following steps:
a. primary exploration and pretreatment: measuring basic physicochemical indexes of the ultra-soft foundation 1 soil, including field area, mud depth, water content, liquid-plastic limit, organic matter content and pH value, excavating the ultra-soft foundation 1 field by partitioning and a drainage ditch 7, cleaning and leveling the periphery of the field,
the method for partitioning the ultra-soft foundation 1 field is determined according to physical and chemical indexes of the length of a digging arm 11, the length of a stirring arm 13, the depth of sludge and the sludge of uniform mixing equipment 14;
b. arranging a vacuum dewatering and drainage system: laying a sand cushion layer 5 on an ultra-soft foundation 1 with the mud depth not more than 4m, inserting vertical drainage plates 2 into a pretreatment area, wherein the inserting depth of the vertical drainage plates 2 is not less than the mud depth, the distance between every two adjacent vertical drainage plates 2 is 1-2 m, the upper ends of the vertical drainage plates 2 are connected to a vacuum pump 10 through hard horizontal water suction pipes 4 with holes, laying non-woven geotextile 3 and a sealing membrane 6 in sequence, starting the vacuum pump 10 to vacuumize and drain,
the sand of the sand cushion layer 5 is broken fine particles of river sand, sea sand or construction waste, and the maximum particle size is not more than 5 cm;
the thickness of the sand cushion 5 is determined according to the mud depth of the ultra-soft foundation 1, and when the mud depth is within 1m, the thickness of the sand cushion 5 is 15-20 cm; when the mud depth is 1-2 m, the thickness of the sand cushion layer 5 is 20-30 cm; when the mud depth is 2-3 m, the thickness of the sand cushion layer 5 is 30-40 cm; when the mud depth is 3-4 m, the thickness of the sand cushion layer 5 is 40-50 cm;
c. secondary exploration and treatment: measuring the water content and the mud depth of the silt soil after drainage, lifting the sealing film 6 and the geotextile 3, removing the horizontal water suction pipe 4,
d. uniformly mixing cushion layer sand: the mixing device 14 is started to uniformly stir the sand and the sludge of the upper mat layer,
e. uniformly mixing a curing agent: determining the mixing amount of the curing agent, the stirring time and the stirring speed of the soft soil in unit volume according to the physical indexes of secondary measurement, starting the curing agent controller 15, stirring the powdery curing agent and the silt soil, leveling the field after stirring to form a pretreated foundation 19,
the curing agent consists of 50 to 60 percent of active magnesium oxide, 30 to 60 percent of slag powder, 10 to 20 percent of steel slag powder, 5 to 10 percent of quicklime powder and 5 to 10 percent of anhydrous magnesium chloride powder;
the curing agent is uniformly mixed, aerated and carbonized along the annular and outside-in direction of the pretreated foundation 19;
f. connecting and carbonizing an aeration system: the vertical drainage plate 2 is hermetically connected with a main ventilation pipe 22 through a branch ventilation pipe 21, the main ventilation pipe 22 is connected with a high-pressure carbon dioxide gas tank 23, the non-woven geotextile 3 and the sealing membrane 6 are laid, the pressure regulating valve 24 is regulated for ventilation carbonization treatment,
the aeration carbonization is performed along the annular and outside-in direction of the pretreated foundation 19;
the carbon dioxide is industrial waste gas of a cement plant or an iron and steel plant, the concentration of the carbon dioxide is not lower than 40%, the ventilation pressure is not lower than 200kPa, the ventilation mode is continuous ventilation or intermittent ventilation, the carbonization time is determined according to the ventilation pressure, the distance between the vertical drainage plates 2 and the water content of the mixed soil, and the accumulated carbonization time is 12-24 hours.
As will be described in detail below.
The vertical drainage plate 2 is a hollow rigid plastic drainage plate or a concrete permeable tubular pile, the cross section of the vertical drainage plate is rectangular, square or circular, and the length or the diameter of the cross section is 10-30 cm;
the horizontal water suction pipe 4 is embedded in the sand cushion layer 5, a filter 8 and a control valve 8 are arranged on the horizontal water suction pipe 4 outside the sand cushion layer 5, the filter 8 is positioned above the drainage ditch 7, and the control valve 9 is positioned between the filter 8 and the vacuum pump 10;
the number of the vacuum pumps 10 is determined according to the site area of the ultra-soft foundation 1, and the processing area of a single vacuum pump 10 is not more than 1600m2The negative pressure of the vacuum pump 10 is not lower than 90kPa, the working time of the vacuum pump 10 is determined according to the water content of the silt after dewatering and draining, and the water content after dewatering and draining is not higher than 90% of the liquid limit of the silt.
Preferably, the uniform mixing device 14 comprises a digging arm 11, a stirring arm 13, a curing agent controller 15, a curing agent storage tank 16, a main powder conveying pipe 17 and a powder spraying pipe 18, the curing agent controller 15 is fixed on the uniform mixing device 14, the digging arm 11 and the stirring arm 13 are connected through a rotary joint 12 to realize large-angle rotation, the main powder conveying pipe 17 is located between the curing agent storage tank 16 and the curing agent controller 15, the powder spraying pipe 18 is located between the curing agent controller 15 and the rotary joint 12, the powder spraying pipe 18 is attached to the digging arm 11 of the uniform mixing device 14, the ventilation branch pipe 21 is connected with the upper end of the vertical drainage plate 2 through a sealing connection sleeve 20, the ventilation branch pipe 21 is connected with the ventilation main pipe 22 through a quick connection joint, the ventilation main pipe 22 is located between the ventilation branch pipe 21 and the high-pressure gas tank 23, and the ventilation main pipe 22 is provided with a heater 25 and a supercharger 26.
Preferably, the first and second electrodes are formed of a metal,
this will be described in connection with figure 1 and an embodiment.
Examples
a. Initial exploration and pretreatment
Measuring basic physicochemical index of ultra-soft foundation 1 soil, wherein the field area is 2500m2Average mud depth of 2.5m (depth of core area of 20m field diameter of 3m, depth of the rest part of 2m), water content of 130%, specific gravity of 2.63, liquid limit of 60%, plastic limit of 30%, organic matter content of 7.0%, pH value of 7.2, length of digging arm 11 of curing agent uniform mixing equipment 14 is 7m, length of stirring arm 13 is 4.5m, physical and chemical indexes are combined, annular area is divided into the ultra-soft foundation 1 according to the length of digging arm 11 and stirring arm 13, radius of the annular area is set to be 5m, drainage ditch 7 is dug at the outermost side of ultra-soft foundation 1, andand cleaning and leveling the periphery of the field.
b. Vacuum dewatering and drainage system arrangement
River sand is taken near pretreatment, a sand cushion layer 5 is laid on an ultra-soft foundation 1, the thickness of the sand cushion layer 5 is 35cm, plastic vertical drainage plates 2 are selected, the plastic drainage plates are inserted into the bottom of the ultra-soft foundation 1 by means of an auxiliary insertion plate machine, the vertical drainage plates 2 are distributed according to a regular triangle, the distance between every two adjacent vertical drainage plates 2 is 1.0m, the upper ends of the vertical drainage plates 2 are connected to a vacuum pump 10 through horizontal water suction pipes 4, the horizontal water suction pipes 4 are embedded in the sand cushion layer 5, then non-woven geotextile 3 and a sealing film 6 are laid on the sand cushion layer 5 in sequence, two vacuum pumps 10 are prepared in the whole site, finally, the vacuum pump 10 and a control valve 9 are started to vacuumize and drain water, and the pumped water flows into a drainage ditch 7 after being filtered through a filter 8. And after the ultra-soft soil foundation is vacuumized for 45 days, closing the vacuum pump 10 when the average water content is reduced to about 54 percent.
c. Secondary exploration and treatment
And measuring the water content of the silt soil after dewatering and draining to be 54% and the mud depth to be 2.4m, then sequentially lifting the sealing film 6 and the geotextile 3, and dismantling the horizontal water suction pipe 4.
d. Bedding sand is mixed evenly
And (3) starting the uniform mixing equipment 14 to uniformly stir the sand and the sludge of the upper cushion layer, so as to increase the porosity ratio of the sludge soft soil.
e. The curing agent is mixed evenly
Determining the mixing amount of the curing agent to be 15% according to the physical index (the water content is 54%) of secondary measurement, wherein the curing agent consists of 50% of active magnesium oxide, 30% of slag powder, 10% of steel slag powder, 5% of quicklime powder and 5% of anhydrous magnesium chloride powder, determining the using amount of the curing agent in the unit volume of the silt soft soil according to the mixing amount of the curing agent, and determining the powder spraying time of the homogenizing device 14 in the unit volume of the silt soil according to the powder spraying efficiency of the curing agent. According to the stirring speed of the uniform mixing equipment 14, the stirring time is adjusted so that the powdery curing agent and the silt soil are uniformly stirred, the vertical drainage plates 2 are prevented from being distorted and damaged in the stirring process, and the ground is leveled and compacted again after stirring to form a pretreated foundation.
f. Aeration system connection and carbonization
Fixing a sealing connecting sleeve 20 at the upper end of the vertical drainage plate 2, connecting the sealing connecting sleeve 20 in parallel through a ventilation branch pipe 21, connecting the ventilation branch pipe 21 to a ventilation main pipe 22 through a quick-connection joint, and connecting the other end of the ventilation main pipe 22 to a carbon dioxide high-pressure gas tank 23; laying a non-woven geotextile 3 and a sealing film 6 on a pretreatment field in sequence to ensure the surface sealing of the field; the main ventilation pipe 22 is provided with a heater 25 and a supercharger 26, the heater 25 and the supercharger 26 are opened, and the pressure regulating valve 24 is regulated to stabilize the gas pressure to 400 kPa; the carbonization adopts an intermittent aeration mode, the aeration is stopped for 0.5 hour every 1.0 hour, the cumulative aeration time is 24 hours, and the aeration is stopped. After the aeration carbonization is finished, carrying out dynamic penetration test and dynamic resilience modulus test on a treatment site, converting the test into the condition that the average bearing capacity of the foundation is 650kPa, and the dynamic elasticity modulus is 16MPa, and meeting the bearing capacity standard requirement of the subgrade foundation; after carbonization and curing for 7 days, the test is carried out, the average bearing capacity is 832kPa, and the dynamic elastic modulus is 21 MPa.
The implementation basis and the disclosed principle of the embodiment are as follows:
(1) the inserting distance of the vertical drainage plates 2 is determined according to the water content and the liquid limit, and the larger the two index values are, the larger the distance between the two index values is; the material type of the vertical drainage plate 2 is selected according to the bearing requirement of the soft foundation to be treated; when the bearing capacity requirement is not high, a rigid plastic drainage plate can be selected, and when the bearing capacity requirement is high, a cement concrete pipe pile can be selected.
(2) The thickness of the sand cushion 5 laid on the soft foundation is determined according to the thickness and the liquid limit value of the sludge of the ultra-soft foundation 1, and the larger the thickness and the liquid limit value of the sludge are, the larger the thickness of the sand cushion 5 is. The selection of the cushion layer sand is mainly based on the fact that materials are easy to obtain, besides river sand and sea sand, crushed particles of the construction waste can be selected, and besides a large pore ratio, most of the construction waste such as broken particles of clay bricks also has large water absorption, and has a certain promotion effect on the drainage of the ultra-soft foundation 1.
(3) The quantity of the vacuum pumps 10 is determined according to the area and the water content of the treatment site, the distance between the vertical drainage plates 2 and the expected dewatering time, and the larger the area and the water content of the treatment site are, the smaller the distance between the vertical drainage plates 2 and the expected dewatering time are, and the larger the quantity of the vacuum pumps 10 is.
(4) The selection of the mixing amount of the curing agent is determined according to the water content after dewatering and drainage and the expected bearing capacity requirement, and the higher the water content and the expected bearing capacity requirement is, the mixing amount of the curing agent can be properly increased. The mixing ratio of the curing agent is determined according to the water content, the liquid limit, the pH value and the organic matter content, if the water content is higher, the proportion of the active magnesium oxide to the anhydrous magnesium chloride can be properly increased so as to increase the water absorption of the curing agent, and meanwhile, the magnesium oxide and the anhydrous magnesium chloride can perform a hard condensation reaction under the condition of water so as to increase the strength. If the organic matter content is high and the pH value is low, the proportion of the slag powder can be properly increased, and after aeration and carbonization, the curing and maintaining time is properly prolonged, so that the strength advantage generated by later alkali-activated slag is exerted.
(5) Compare in single vacuum preloading drainage and traditional solidification treatment, this technique has realized the rapid processing of super soft foundation, makes the super soft foundation after the preliminary treatment can accomplish the carbonization of ventilating in 24 hours, realizes that intensity and bearing capacity increase fast, has also satisfied construction machinery's walking needs simultaneously.
The foregoing detailed description has been given for the purpose of illustration and explanation, rather than limitation, and it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention; the scope of the claims should be determined only by the following claims and their equivalents without departing from the spirit and scope of the present invention.
Claims (3)
1. A vacuum drainage-reducing water combined magnesia-carbonization shallow-layer ultra-soft foundation solidification method is characterized by comprising vacuum drainage-reducing water treatment and magnesia-carbonization solidification treatment, and specifically comprises the following steps:
a. primary exploration and treatment: measuring basic physicochemical indexes of the ultra-soft foundation soil, including field area, mud depth, water content, liquid-plastic limit, organic matter content and pH value, performing partition and drainage ditch excavation on the ultra-soft foundation field, cleaning and leveling the periphery of the field,
the ultra-soft foundation field partitioning method is determined according to the physical and chemical indexes of the excavator arm length, the stirring arm length, the sludge depth and the sludge of the uniform mixing equipment;
b. arranging a vacuum dewatering and drainage system: laying a sand cushion layer on an ultra-soft foundation with the mud depth not more than 4m, inserting vertical drainage plates into a pretreatment area, wherein the inserting depth of the vertical drainage plates is not less than the mud depth, the distance between every two adjacent vertical drainage plates is 1-2 m, connecting the upper ends of the vertical drainage plates to a vacuum pump through a hard horizontal water suction pipe with holes, laying non-woven geotextile and a sealing membrane in sequence, starting the vacuum pump to vacuumize and drain water,
the cushion sand is broken fine particles of river sand, sea sand or building garbage, and the maximum particle size is not more than 5 cm;
the thickness of the sand cushion layer is determined according to the mud depth of the ultra-soft foundation, and when the mud depth is within 1m, the thickness of the sand cushion layer is 15-20 cm; when the depth of the mud is 1-2 m, the thickness of the sand cushion layer is 20-30 cm; when the depth of the mud is 2-3 m, the thickness of the sand cushion layer is 30-40 cm; when the depth of the mud is 3-4 m, the thickness of the sand cushion layer is 40-50 cm;
c. secondary exploration and treatment: measuring the water content and depth of silt soil after dewatering and draining, lifting the sealing film and geotextile, removing the horizontal water suction pipe,
d. uniformly mixing cushion layer sand: starting uniform mixing equipment to uniformly stir the upper cushion sand and the silt;
e. uniformly mixing a curing agent: determining the mixing amount of the curing agent, the stirring time and the stirring speed of the soft soil in unit volume according to the physical indexes of secondary measurement, starting a curing agent controller, uniformly stirring the powdery curing agent and the silt soil, leveling the field after stirring to form a pretreated foundation,
the curing agent consists of 50 to 60 percent of active magnesium oxide, 30 to 60 percent of slag powder, 10 to 20 percent of steel slag powder, 5 to 10 percent of quicklime powder and 5 to 10 percent of anhydrous magnesium chloride powder;
the curing agents are uniformly mixed along the annular and outside-in directions of the pretreated foundation;
f. connecting and carbonizing an aeration system: the vertical drainage plate is hermetically connected with the main ventilation pipe through the branch ventilation pipe, the main ventilation pipe is connected with a carbon dioxide high-pressure gas tank, the non-woven geotextile and the sealing membrane are laid, the gas pressure regulating valve is regulated, ventilation and carbonization are carried out,
the aeration carbonization is carried out along the annular and outside-in directions of the pretreated foundation;
the carbon dioxide is industrial waste gas of a cement plant or an iron and steel plant, the concentration of the carbon dioxide is not lower than 40%, the ventilation pressure is not lower than 200kPa, the ventilation mode is continuous ventilation or intermittent ventilation, the carbonization time is determined according to the ventilation pressure, the distance between the vertical drainage plates and the water content of the mixed soil, and the accumulated carbonization time is 12-24 hours.
2. The method for solidifying the shallow ultra-soft foundation by combining vacuum drainage and magnesia carbonization according to claim 1, characterized in that: the vertical drainage plate is a hollow hard plastic drainage plate or a concrete permeable tubular pile, the cross section of the vertical drainage plate is rectangular, square or circular, the length or the diameter of the cross section is 10-30 cm,
the horizontal water suction pipe is embedded in the sand cushion layer, the water suction pipe outside the sand cushion layer is provided with a filter and a control valve, the filter is positioned above the drainage ditch, the control valve is positioned between the filter and the vacuum pump,
the number of the vacuum pumps is determined according to the site area of the ultra-soft foundation, and the processing area of a single vacuum pump is not more than 1600m2The negative pressure of the vacuum pump is not lower than 90kPa, the working time of the vacuum pump is determined according to the water content of the silt after dewatering and draining, and the water content after dewatering and draining is not higher than 90% of the liquid limit of the silt.
3. The method for solidifying the shallow ultra-soft foundation by combining vacuum drainage and magnesia carbonization according to claim 1, characterized in that: the uniform mixing equipment comprises a digging arm, a stirring arm, a curing agent controller, a curing agent storage tank, a main powder conveying pipe and a powder spraying pipe, wherein the curing agent controller is fixed on the uniform mixing equipment, a rotary joint is arranged between the digging arm and the stirring arm, the main powder conveying pipe is arranged between the curing agent storage tank and the curing agent controller, the powder spraying pipe is arranged between the curing agent controller and the rotary joint, the powder spraying pipe is attached to the digging arm, the ventilation branch pipe is connected to the upper end of the vertical drainage plate through a sealing connection sleeve, the ventilation branch pipe is connected with the ventilation main pipe through a quick-connection joint, the ventilation main pipe is arranged between the ventilation branch pipe and the high-pressure gas tank, and a heater and a supercharger are arranged on.
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| CN111395309B (en) * | 2020-04-30 | 2024-04-30 | 华中科技大学 | Equipment and method for treating dredging sludge by combining vacuum preloading, permeation increasing and solidification |
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| CN112251235B (en) * | 2020-10-23 | 2021-11-26 | 安徽理工大学环境友好材料与职业健康研究院(芜湖) | Preparation method of steel slag-based curing agent and treatment system and method of Cd-polluted soil |
| CN114570754A (en) * | 2021-11-05 | 2022-06-03 | 南京林业大学 | Method for treating low-boiling-point volatile organic polluted soil by using carbon dioxide |
| CN114086539A (en) * | 2021-11-24 | 2022-02-25 | 安徽理工大学环境友好材料与职业健康研究院(芜湖) | Equipment and method for in-situ curing of building waste slurry |
| CN114457856B (en) * | 2022-02-26 | 2022-10-04 | 北京城建华夏基础建设工程有限公司 | Water stop construction equipment for locally deepening foundation pit and water stop construction method thereof |
| CN114960609A (en) * | 2022-04-25 | 2022-08-30 | 三明学院 | Composite foundation for reinforcing saturated soft soil by single-component geopolymer and construction method thereof |
| CN115879772B (en) * | 2023-02-21 | 2023-05-09 | 达濠市政建设有限公司 | Method for treating coastal deep soft soil foundation by combining industrial slag with cement |
| CN116289868A (en) * | 2023-05-12 | 2023-06-23 | 中交第四航务工程勘察设计院有限公司 | Vacuum preloading method based on machine-made gravel material |
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