WO2022213766A1 - 一种微生物诱导碳酸钙沉淀砂石复合桩加固结构及施工方法 - Google Patents

一种微生物诱导碳酸钙沉淀砂石复合桩加固结构及施工方法 Download PDF

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WO2022213766A1
WO2022213766A1 PCT/CN2022/080055 CN2022080055W WO2022213766A1 WO 2022213766 A1 WO2022213766 A1 WO 2022213766A1 CN 2022080055 W CN2022080055 W CN 2022080055W WO 2022213766 A1 WO2022213766 A1 WO 2022213766A1
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calcium carbonate
aggregate
carbonate precipitation
sand
induced calcium
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PCT/CN2022/080055
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English (en)
French (fr)
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梁程
董彦同
杨鹏博
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中国长江三峡集团有限公司
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Priority claimed from CN202120713670.3U external-priority patent/CN215758963U/zh
Priority claimed from CN202110377857.5A external-priority patent/CN113174933B/zh
Application filed by 中国长江三峡集团有限公司 filed Critical 中国长江三峡集团有限公司
Publication of WO2022213766A1 publication Critical patent/WO2022213766A1/zh

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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K17/00—Soil-conditioning materials or soil-stabilising materials
    • C09K17/40—Soil-conditioning materials or soil-stabilising materials containing mixtures of inorganic and organic compounds
    • 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
    • E02D3/08—Improving by compacting by inserting stones or lost bodies, e.g. compaction piles
    • 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
    • E02D5/00—Bulkheads, piles, or other structural elements specially adapted to foundation engineering
    • E02D5/22—Piles
    • E02D5/34—Concrete or concrete-like piles cast in position ; Apparatus for making same
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D5/00—Bulkheads, piles, or other structural elements specially adapted to foundation engineering
    • E02D5/22—Piles
    • E02D5/34—Concrete or concrete-like piles cast in position ; Apparatus for making same
    • E02D5/46—Concrete or concrete-like piles cast in position ; Apparatus for making same making in situ by forcing bonding agents into gravel fillings or the soil

Definitions

  • the invention relates to a microbial-induced calcium carbonate precipitation sand-stone composite pile reinforcement structure and a construction method, belonging to the technical field of geotechnical engineering.
  • the water-rich fine-grained engineering muck landfill on the weakly permeable base is difficult to drain and consolidate, and rapid filling can easily lead to abnormal excess pore pressure in the deep part of the muck, increasing the risk of deformation and damage of the muck mound;
  • Landfills are often selected to be landfilled in a site with a certain slope, and the contact zone between the landfill and the underlying substrate is usually a weak zone that easily leads to landslide deformation. Induce landslide failure of slag mass.
  • Chinese patent CN103669340A discloses a polyurethane gravel pile, the device forms holes in the foundation, fills the sand and gravel aggregate, pours the polyurethane reaction raw material slurry, and after the polyurethane foam reaction raw material slurry is injected into the sand and gravel aggregate, the reaction occurs instantly, Fill the pores of the sand and gravel aggregate and solidify it into polyurethane foam.
  • the sand and gravel aggregate and the polyurethane foam are bonded to the pile. Strong, simple and fast construction, short construction period, no reduction in diameter, pile quality accidents, etc.
  • the polyurethane foam used in the device is an explosive and highly toxic material, which is not conducive to environmental protection and construction safety; and the construction method of the device makes it difficult to effectively and uniformly bury the in-situ gravel piles with large diameters at the project site. Inject the reaction raw material slurry.
  • Chinese patent CN108677912A discloses a CFG core sandstone composite pile, its composite foundation and construction method.
  • the CFG core sandstone composite pile in this patent includes a CFG core and a sandstone shell surrounding the CFG core, wherein the sandstone shell is made of Sand and gravel are composed of 1 to 2:1 by volume.
  • the CFG core sandstone composite pile composite foundation is characterized in that it includes a soft soil foundation, a CFG core sandstone composite pile driven into the soft soil foundation, and a cushion layer filled above the CFG core sandstone composite pile and the soft soil foundation , the mattress layer is provided with a geogrid.
  • the invention has the characteristics of simple construction, fast pile formation, rapid dissipation of superstatic pore water stress in soil between piles during construction, rapid recovery of soil strength, shortened construction period, small post-construction settlement, and reduced construction cost by utilizing industrial waste.
  • the shear resistance of the pile is mainly borne by its CFG core, and its peripheral aggregate still only has the functions of promoting the drainage and consolidation of the foundation and improving the vertical bearing capacity of the foundation of the traditional sand-stone pile.
  • the present invention It is proposed to combine the traditional sand and gravel pile technology with the microbial induced calcium carbonate precipitation technology, fully consider the engineering practice of water-rich fine-grained engineering slag slopes on weakly permeable bases, reuse engineering waste, and make in-situ production at the engineering site Microorganisms induce calcium carbonate precipitation to strengthen sand and gravel piles to promote the drainage and consolidation of water-rich fine-grained engineering slag slopes, improve the overall foundation bearing capacity and shear deformation resistance of the slopes, and achieve long-term prevention of macroscopic deformation and damage. Purpose.
  • the polyurethane foam used in the polyurethane gravel pile is an explosive and highly toxic material, which is not conducive to environmental protection and construction safety; and the construction method of the device makes it difficult to be effective for the gravel piles with deep in-situ and larger diameters at the project site. uniformly inject the reaction raw material slurry;
  • the shear resistance of the CFG core sandstone composite pile is mainly borne by its CFG core, and its peripheral aggregate still only has the function of promoting the drainage and consolidation of the foundation and improving the vertical bearing capacity of the foundation of the traditional sandstone pile.
  • the purpose of the present invention is to provide a kind of microbe-induced calcium carbonate precipitation sand-stone composite pile reinforcement structure and construction method, the present invention can reduce the weakly permeable base under the premise of not obviously reducing the initial environmental quality of the rock, soil and water body of the project site Deformation failure of upper water-rich fine-grained engineering slag slope, especially the risk of shear deformation failure.
  • the purpose of the present invention is to achieve: a microbial-induced calcium carbonate precipitation sand-stone composite pile reinforcement structure, which includes a weakly permeable base, and the top of the weakly permeable base is stacked with water-rich fine particles.
  • Granular engineering slag the interior of the water-rich fine-grained engineering slag is provided with a microbial-induced calcium carbonate precipitation strengthening sandstone pile, and the bottom end of the microorganism-induced calcium carbonate precipitation strengthening sandstone pile passes through the interface between the slag soil and the substrate , and inserted into the weakly permeable substrate for a length.
  • the microbe-induced calcium carbonate precipitation-strengthened sand-stone pile includes a central pipe located at the axis of the pile body, and the periphery of the central pipe is sequentially surrounded by a drainage aggregate section and a drainage cemented bone along its height direction from top to bottom.
  • a material segment and a cemented aggregate segment, the drained aggregate segment, the drained cemented aggregate segment and the cemented aggregate segment are cemented by microbial-induced calcium carbonate precipitation.
  • the sand and gravel aggregates of the drainage aggregate section, the drainage cemented aggregate section and the cemented aggregate section are recycled and reused engineering slag materials that are qualified in the particle gradation section.
  • the drainage aggregate section, the drainage cemented aggregate section The maximum particle size of the sand and gravel aggregate particles in the cemented aggregate section is not more than 30mm, and the components of the sand and gravel aggregate must meet the industry standards for environmental quality.
  • the engineering slag material includes waste concrete material or waste brick material.
  • the thickness of the drainage aggregate section is at least 1m, and the gradation of the sand and gravel aggregate is in the range of coarse sand to gravel;
  • the drainage cemented aggregate section is filled from the bottom of the drainage aggregate section to the interface between the slag soil and the substrate, and the sand and gravel aggregate is selected from medium sand;
  • the cemented aggregate section extends from the bottom layer of the water-rich fine-grained engineering slag to the interior of the weakly permeable base, and is buried down to a length of not less than 2m.
  • the diameter of the microbe-induced calcium carbonate precipitation strengthening sand-stone pile is controlled to be 300mm-500mm.
  • the central pipe is made of rigid PVC pipe with only the top opening, and the inner diameter of the pipe is in the range of 15mm to 30mm. It is possible to choose a PVC pipe with a smaller thickness;
  • the central pipe is divided into the upper central pipe drainage section from top to bottom, and no pipe holes are arranged on the central pipe drainage section;
  • the fine-diameter filter pipe section of the central pipe in the middle corresponds to the drainage cemented aggregate section, and the fine-diameter filter pipe section of the central pipe is evenly crossed along the axis direction to set thin pipe holes, so as to facilitate the entry of external soil seepage and the microbial-induced calcium carbonate precipitation engineering slurry to pass through this section.
  • the thin tube hole is injected into the aggregate outside the tube;
  • the coarse-diameter filter tube section of the lower central tube corresponds to the cemented aggregate section, and thick tube holes are evenly crossed along the axis direction on the tube wall of the cemented aggregate section.
  • the outer wall of the central tube is wound into a spiral shape by metal wires to separate the externally wound filter mesh.
  • the filter mesh is provided with two layers.
  • the inner filter mesh is made of 80 mesh nylon mesh or metal mesh
  • the outer filter mesh is made of 3 mesh to 10 mesh nylon mesh or metal mesh, and a layer of thick metal wire is wound around the filter mesh;
  • the plane layout of the microbial-induced calcium carbonate precipitation strengthening sand-stone pile engineering site adopts an equilateral triangle shape, and the sand-stone pile spacing is set to 2.5 to 4.5 times its diameter.
  • Microbial-induced calcium carbonate precipitation cement aggregates were generated in the aggregate particle gaps of microbial-induced calcium carbonate precipitation strengthening sand-stone piles by microbial-induced calcium carbonate precipitation technology.
  • a construction method for a microbial-induced calcium carbonate precipitation sand-stone composite pile reinforcement structure :
  • the injection device is connected with the top port of the central pipe through a soft rubber tube, and the microbial-induced calcium carbonate precipitation engineering slurry is installed in the injection device, and injected into the pores between the aggregate particles of the microbial-induced calcium carbonate precipitation strengthening sandstone pile with the help of the central pipe;
  • the microbial induced calcium carbonate precipitation engineering slurry includes urea slurry, calcium source slurry and microbial slurry;
  • the calcium source slurry is a divalent calcium ion solution, and its pH needs to be adjusted to the range of 6.5 to 7.0 by weak acid or weak base; the divalent calcium ion concentration of the calcium source slurry should be adjusted to 0.25mol/L to 0.3mol/L; urea solution The molar concentration of urea in the medium should be kept consistent with the concentration of divalent calcium ions in the calcium source slurry; the microorganisms in the microbial slurry use environmentally friendly facultative anaerobic Pasteurella, and the pH value of the microbial slurry is adjusted to 9.4-9.6.
  • the liquid concentration is higher than 1 ⁇ 105CFU/mL;
  • the injection of microbial-induced calcium carbonate precipitation engineering slurry is carried out according to the site conditions and engineering needs. First, inject a sufficient amount of microbial slurry into the pores between the aggregate particles through the central pipe, and let it stand for several hours until the bacterial solution can fully enter the aggregate particles. Then inject the required calcium source slurry through the central tube at a low speed to fully enter the pores between the aggregate particles; finally inject the required urea slurry through the central tube at a low speed to fully enter the pores between the aggregate particles; Rest for maintenance.
  • the invention can reduce the deformation damage, especially the risk of shear deformation damage, of the water-rich fine-grained engineering slag slope on the weakly permeable base without obviously reducing the initial environmental quality of the geotechnical soil and water body of the engineering site.
  • the present invention proposes to combine traditional sand and gravel pile technology with microbial induced calcium carbonate precipitation technology, fully considers the engineering practice of water-rich fine-grained engineering slag slope on weakly permeable base, and reuses engineering wastes at the engineering site.
  • the present invention can be beneficial to the drainage and consolidation of the water-rich fine-grained engineering slag layer on the weakly permeable base; It is beneficial to significantly reduce the macroscopic failure and deformation of water-rich fine-grained engineering slag slopes on weakly permeable bases, especially the risk of shear failure and deformation.
  • the increase in mechanical strength can be carried out gradually according to the actual situation on site, and the grouting treatment of the microbial induced calcium carbonate precipitation project can be gradually carried out, and it does not need to be completed at one time.
  • the materials and components produced by the present invention do not contain inflammable, explosive or highly toxic substances, and are all environmentally friendly materials, which can be used for resource utilization of medium and coarse-grained engineering slag that meets the requirements.
  • microorganism-induced calcium carbonate precipitation technology requires a time process. However, according to the difference between the engineering site and the construction of the microbial induced calcium carbonate precipitation technology, the process generally lasts for more than one day, which is conducive to the microbial induced calcium carbonate precipitation engineering slurry to fully diffuse in the target soil, so that the soil in the target area is more evenly distributed.
  • the body is cemented.
  • the present invention can also monitor the groundwater level of the engineering site for a long time through the central pipe.
  • FIG. 1 is a schematic diagram of the layout structure of the engineering site section of the present invention.
  • Fig. 2 is a schematic cross-sectional structure diagram of the present invention ((a) a schematic cross-sectional view of a single pile on-site layout structure; (b) a schematic view of the central pipe structure).
  • Fig. 3 is a schematic diagram of the arrangement structure of the central pipe hole of the present invention.
  • Figure 4 is a schematic diagram of the structure of the filler of the present invention ((a) a schematic diagram of the filler structure without the treatment of the microorganism-induced calcium carbonate precipitation technology; (b) a schematic diagram of the filler structure after the microorganism-induced calcium carbonate precipitation technology).
  • FIG. 5 is a schematic diagram of the plane layout structure of the engineering site of the present invention.
  • FIG. 6 is a schematic diagram of the operation of the microorganism-induced calcium carbonate precipitation treatment according to the present invention ((a) a schematic diagram of the operation of draining water in the central tube; (b) a schematic diagram of the operation of injecting engineering slurry).
  • a microbial-induced calcium carbonate precipitation sand-stone composite pile reinforcement structure which includes a weakly permeable base 1, the top of the weakly permeable base 1 is stacked with water-rich fine-grained engineering slag 2, and the The interior of the water-rich fine-grained engineering slag 2 is provided with a microbe-induced calcium carbonate precipitation strengthening sandstone pile 3, and the bottom end of the microbe-induced calcium carbonate precipitation strengthening sandstone pile 3 passes through the interface 4 between the slag and the base, and inserts to a length of weakly permeable substrate 1.
  • This reinforcement structure is used to prevent macroscopic deformation and damage of water-rich fine-grained engineering slag slopes on weakly permeable bases in a long-term and environmentally friendly manner.
  • the microbe-induced calcium carbonate precipitation-strengthened sandstone pile 3 includes a central pipe 5 at the axis of the pile body, and the periphery of the central pipe 5 is surrounded by drainage bones from top to bottom along its height direction.
  • the material section 6, the drainage cemented aggregate section 7 and the cemented aggregate section 8 are cemented by the microorganism-induced calcium carbonate precipitation method.
  • the sand and gravel aggregates of the drainage aggregate section 6, the drainage cemented aggregate section 7 and the cemented aggregate section 8 are recycled engineering slag materials that are qualified in the particle gradation interval. 6.
  • the maximum particle size of the sand and gravel aggregate particles in the drainage cemented aggregate section 7 and the cemented aggregate section 8 is not greater than 30mm, and the components of the sand and gravel aggregate must comply with the industry standards for environmental quality.
  • the engineering slag material includes waste concrete material or waste brick material.
  • the thickness of the drainage aggregate section 6 is at least 1 m, and the sand and gravel aggregates are selected and graded in the interval between coarse sand and gravel; the drainage cemented aggregate section 7 has been filled from the bottom of the drainage aggregate section 6.
  • the sand and gravel aggregates are selected from medium sand; the cemented aggregate section 8 extends from the bottom layer of the water-rich fine-grained engineering slag 2 to the interior of the weakly permeable base 1, and is buried downward for a length of not more than 1. Shorter than 2m, the sand and gravel aggregates are selected from fine sand to medium sand particle gradation.
  • the setting of the drainage aggregate section 6 is to consider that after the water-rich fine-grained soil is fully drained on the surface, it is easy to form a hard shell layer with a thickness of about 1 m, so the depth of the buried interval does not need to be drained laterally through sandstone piles, and the soil at this depth is It is difficult for the body to constitute the macroscopic shear deformation failure problem alone, and its shear strength does not need to be specially improved.
  • the drainage cemented aggregate section 7 is conducive to promoting the drainage of the slag body, and on the other hand, the medium-sand aggregate is more conducive to ensuring that the microbe-induced calcium carbonate precipitation technology can fully improve the shear strength of the pile body.
  • the cemented aggregate section 8 is beneficial to the microbial induced calcium carbonate precipitation technology to fully improve the shear resistance of the pile body.
  • the diameter of the microbe-induced calcium carbonate precipitation strengthening sand-stone pile 3 is controlled to be 300mm ⁇ 500mm.
  • the central pipe 5 is selected as a rigid PVC pipe with only the top opening, and the inner diameter of the pipe is in the range of 15mm to 30mm.
  • the thickness of the pipe wall should be selected as a PVC pipe with a smaller thickness; the central pipe 5 is divided into upper parts from top to bottom.
  • a thin tube hole 12 is provided to facilitate the entry of external soil seepage and the microbe-induced calcium carbonate precipitation engineering slurry to be injected into the aggregate outside the tube through the thin tube hole 12; the lower central tube coarse-diameter filter tube section 11 corresponds to the cemented aggregate section 8, Thick pipe holes 13 are uniformly intersected along the axial direction on the pipe wall of the cemented aggregate section 8 .
  • the diameter of the thin tube hole 12 is 2.5mm, so as to facilitate the entry of external soil seepage and the microbe-induced calcium carbonate precipitation engineering slurry is injected into the aggregate outside the tube through the tube hole;
  • the diameter of the thick tube hole 13 is 4mm, so as to facilitate the external Soil seepage and microbe-induced calcium carbonate precipitation engineering slurry is injected into the aggregate outside the pipe through the pipe hole.
  • the filter screen 15 is provided with two layers, and the inner layer filter screen adopts 80 mesh nylon mesh or metal mesh.
  • the layer filter is made of 3-mesh to 10-mesh nylon mesh or metal mesh, and a layer of thick metal wire 16 is wound around the filter mesh; microorganism-induced calcium carbonate precipitation strengthens the sand and gravel piles.
  • the pile spacing is set to 2.5 to 4.5 times its diameter.
  • microbe-induced calcium carbonate precipitation cement mass 18 is generated in the gaps of the aggregate particles 17 of the microbe-induced calcium carbonate precipitation strengthening sandstone pile 3 by the microbe-induced calcium carbonate precipitation technology.
  • the mechanism of the present invention is:
  • Equation 1 The theoretical mechanism of the microorganism-induced calcium carbonate precipitation technology can be characterized by Equation 1 and Equation 2:
  • the microbial induced calcium carbonate precipitation engineering slurry is composed of urea slurry, calcium source slurry and microbial slurry.
  • the calcium source slurry is a divalent calcium ion solution, such as an aqueous solution of divalent calcium ion compounds that are easily soluble in water, such as calcium chloride or calcium acetate.
  • interval, the measured value at 25 °C, the divalent calcium ion concentration of the calcium source slurry should be adjusted to 0.25mol/L to 0.3mol/L.
  • the molar concentration of urea in the urea solution should be kept consistent with the concentration of divalent calcium ions in the calcium source slurry.
  • the microorganisms in the microbial slurry can adopt environmentally friendly facultative anaerobic Pasteurella, and the pH value of the microbial slurry should be adjusted to about 9.5, 25 °C measured value, the bacterial concentration should be higher than 1 ⁇ 105CFU/mL.
  • the structure is intended to be applied to a water-rich fine-grained engineering slag slope on a weakly permeable base, and the thickness of the treated fine-grained engineering slag layer should not be less than 4 m.
  • the combined distribution of the drainage aggregate section, the drainage cemented aggregate section and the cemented aggregate section in the microbial-induced calcium carbonate precipitation strengthening sand-stone pile should be based on the fine-grained engineering slag slope and its underlying structure. The actual setting of the weakly permeable substrate.
  • the density of the pipe holes can be densified as required.
  • the engineering performance of the microbial bacteria solution is the best in the range of 20°C to 40°C, so when the technology is applied on-site, the temperature in the treatment process of the microbe-induced calcium carbonate precipitation technology should be guaranteed to be in the range of 20°C to 40°C.
  • microorganism-induced calcium carbonate precipitation engineering slurry is communicated with the top port of the central pipe through a soft rubber tube through an injection device, and the slurry is injected into the pores of the pile aggregate through the central pipe.
  • the engineering slurry it is necessary to insert a thin hard rubber tube from the top port of the central pipe to the bottom, and drain the accumulated water to the central pipe in a short time, and then start to inject the engineering slurry.
  • the injection of engineering slurry should be operated according to the site conditions and engineering needs.
  • the effect of improving the strength of the sandstone piles treated by the microorganism-induced calcium carbonate precipitation technology can be judged by comparing the water accumulation rate and the stable water head in the central pipe before and after the treatment.
  • the microorganism-induced calcium carbonate precipitation treatment the smaller the water accumulation rate in the central pipe and the greater the buried depth of the stable water level, the higher the strength of the gravel pile is.
  • the concentration of microorganisms, divalent calcium ions and urea in the extracted water from the central pipe can be tested and analyzed, combined with the judgment on the degree of increase in the strength of the pile body, which can be used for further microbe-induced calcium carbonate. Decide whether to precipitation grouting or not.
  • a construction method for a microbial-induced calcium carbonate precipitation sand-stone composite pile reinforcement structure :
  • the injection device 22 is connected to the top port of the central pipe 5 through the soft rubber tube 21, and the microorganism-induced calcium carbonate precipitation engineering slurry 23 is installed in the injection device 22, and is injected into the bone of the sandstone pile 3 by means of the central pipe 5. in the pores between the material particles 17;
  • the microorganism-induced calcium carbonate precipitation engineering slurry 23 comprises urea slurry, calcium source slurry and microorganism slurry;
  • the calcium source slurry is a divalent calcium ion solution, and its pH needs to be adjusted to the range of 6.5 to 7.0 by weak acid or weak base; the divalent calcium ion concentration of the calcium source slurry should be adjusted to 0.25mol/L to 0.3mol/L; urea solution The molar concentration of urea in the medium should be kept consistent with the concentration of divalent calcium ions in the calcium source slurry; the microorganisms in the microbial slurry use environmentally friendly facultative anaerobic Pasteurella, and the pH value of the microbial slurry is adjusted to 9.4-9.6.
  • the liquid concentration is higher than 1 ⁇ 105CFU/mL;
  • the injection of the microbe-induced calcium carbonate precipitation engineering slurry 23 is carried out according to the site conditions and engineering needs. First, inject a sufficient amount of microbial slurry into the pores between the aggregate particles 17 through the central pipe 5, and let it stand for several hours until the bacterial liquid can fully enter the bone. Then inject the required calcium source slurry through the central pipe 5 at a low speed to fully enter the pores between the aggregate particles 17; finally inject the required urea slurry through the central pipe 5 at a low speed to fully enter The pores between the aggregate particles 17; and then stand for curing.

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Abstract

本发明提供了预埋滴灌的一种微生物诱导碳酸钙沉淀砂石复合桩加固结构及施工方法，用于长期预防弱透水性基底上富水细粒工程渣土边坡宏观变形破坏。该技术融合了传统砂石桩技术和微生物诱导碳酸钙沉淀技术，主体包含处于桩体轴心的中心管和外围的填充骨料。填充骨料自地表向下可分为排水骨料段、排水胶结骨料段和胶结骨料段，骨料可资源化再利用颗粒级配符合条件的工程渣土料。微生物诱导碳酸钙沉淀工程浆液包含cop尿素浆液、钙源浆液和微生物浆液。

Description

一种微生物诱导碳酸钙沉淀砂石复合桩加固结构及施工方法 技术领域
本发明涉及一种微生物诱导碳酸钙沉淀砂石复合桩加固结构及施工方法，属于岩土工程技术领域领域。
背景技术
我国社会基础设施建设迅猛发展，过程中导致源源不断大量的工程渣土的产生与堆积。我国许多基建工程量庞大的城镇，如天津、上海、宁波、广州、深圳等，由于地下空间的开发(基坑工程、隧道工程等)，挖出了大量粉质与黏质等富水的细粒工程渣土。这些渣土多数还是通过集中堆填的方式予以处理，形成了许多工程渣土边坡，不合理的、简易的工程渣土堆填易诱发渣土边坡变形破坏灾害，2015年12月20日我国深圳光明新区工程渣土填埋场垮塌重大安全事故即为典型案例。弱透水基底上的富水细粒工程渣土堆填体一方面难以排水固结，快速堆填也容易导致渣土深部产生异常超孔压，增加渣土堆体变形破坏的风险；另一方面填埋场常选在具有一定坡度的场地内堆填，堆填土与下伏基底之间的接触带通常表现为易导致滑坡变形的软弱带，这种场地内的不合理堆填渣土易诱发渣土体的滑坡破坏。
中国专利CN103669340A公开了一种聚氨酯砂石桩，该装置在地基中成孔，填筑砂石骨料，浇注聚氨酯反应原料浆，聚氨酯泡沫反应原料浆注射进砂石骨料后，瞬间发生反应，填充砂石骨料孔隙并固化成聚氨酯泡沫，在地基中砂石骨料与聚氨酯泡沫粘结所述的桩，该桩呈腰鼓状，具有单桩承载力高，工后沉降小，抗弯能力强，施工简单快捷，工期短，不会出现缩径、断桩质量事故等优点。但是该装置采用的聚氨酯泡沫为易爆剧毒材料，不利于环保和施工安全；且该装置的施工方法导致在工程现场时，很难对原位深埋且直径较大的砂石桩有效均匀地注射反应原料浆液。
中国专利CN108677912A公开了一种CFG芯砂石组合桩、其构成的复合地基及施工方法，该专利中的CFG芯砂石组合桩包括CFG芯以及包裹CFG芯的砂石外壳，其中砂石外壳由砂和碎石按体积比1～2：1组成。CFG芯砂石组合桩复合地基，其特征在于，包括软土地基、打入软土地基的CFG芯砂石组合桩、以及填筑在CFG芯砂石组合桩和软土地基上方的褥垫层，所述的褥垫层中设有土工格栅。该发明具有施工简便、成桩速度快、施工期间桩间土中超静孔隙水应力消散迅速，土体强度恢复快，缩短工期，工后沉降小，利用工业废料降低工程造价等特点。但是该桩体的抗剪切能力主要由其CFG芯承担，其外围骨料仍只具有传统砂石桩的促地基排水固结、提高地基竖向承载力的功能。
为了在不明显降低工程场地的岩土及水体的初始环境质量的前提下，降低弱透水性基底上富水细粒工程渣土边坡的变形破坏，特别是剪切变形破坏的风险，本发明提出将传统砂石桩技术与微生物诱导碳酸钙沉淀技术相结合，充分考虑弱透水性基底上富水细粒工程渣土边坡的工程实际，对工程废料进行再利用，在工程现场原位制作微生物诱导碳酸钙沉淀强化砂石桩，以促进富水细粒工程渣土边坡排水固结，提高边坡的整体地基承载力及其抗剪切变形能力，达到长期预防其发生宏观变形破坏的目的。
聚氨酯砂石桩采用的聚氨酯泡沫为易爆剧毒材料，不利于环保和施工安全；且该 装置的施工方法导致在工程现场时，很难对原位深埋且直径较大的砂石桩有效均匀地注射反应原料浆液；
CFG芯砂石组合桩的抗剪切能力主要由其CFG芯承担，其外围骨料仍只具有传统砂石桩的促地基排水固结、提高地基竖向承载力的功能。
发明内容
本发明的目的是提供一种微生物诱导碳酸钙沉淀砂石复合桩加固结构及施工方法，本发明在不明显降低工程场地的岩土及水体的初始环境质量的前提下，可以降低弱透水性基底上富水细粒工程渣土边坡的变形破坏，特别是剪切变形破坏的风险。
为了实现上述的技术特征，本发明的目的是这样实现的：一种微生物诱导碳酸钙沉淀砂石复合桩加固结构，它包括弱渗透性基底，所述弱渗透性基底的顶部堆放有富水细粒工程渣土，所述富水细粒工程渣土的内部贯穿设置有微生物诱导碳酸钙沉淀强化砂石桩，所述微生物诱导碳酸钙沉淀强化砂石桩的底端穿过渣土与基底界面，并插入到弱渗透性基底一段长度。
所述微生物诱导碳酸钙沉淀强化砂石桩包括处于桩体轴心的中心管，所述中心管的外围，并沿着其高度方向由上至下依次包围设置有排水骨料段、排水胶结骨料段和胶结骨料段，所述排水骨料段、排水胶结骨料段和胶结骨料段通过微生物诱导碳酸钙沉淀方式予以胶结。
所述排水骨料段、排水胶结骨料段和胶结骨料段的砂石骨料采用资源化再利用颗粒级配区间合格的工程渣土料，所述排水骨料段、排水胶结骨料段和胶结骨料段的砂石骨料颗粒最大粒径不大于30mm，砂石骨料的组分均需符合环境质量行业规范。
所述工程渣土料包括废混凝土料或废砖块料。
所述排水骨料段的厚度至少为1m，砂石骨料选用级配处于粗砂至碎石区间砂石；
所述排水胶结骨料段自排水骨料段底部一直填充至渣土与基底界面，砂石骨料选用中砂；
所述胶结骨料段自富水细粒工程渣土的底层延伸至弱渗透性基底的内部，向下埋入长度不短于2m，砂石骨料选取细砂至中砂颗粒级配的砂石料。
所述微生物诱导碳酸钙沉淀强化砂石桩的直径控制在300mm～500mm。
所述中心管选用仅顶端开口的硬质PVC管，管内径处于15mm～30mm区间，管壁厚度在保证管体不会受工程现场中心管周边骨料段挤压发生明显变形的前提下，尽可能选厚度较小的PVC管；
所述中心管由上至下划分为上部的中心管排水段，中心管排水段上不布设管孔；
中间的中心管细孔径滤管段对应排水胶结骨料段，在中心管细孔径滤管段上沿轴线方向均匀交叉设置细管孔，以便于外部土体渗流进入和微生物诱导碳酸钙沉淀工程浆液通过该细管孔注射至管外骨料中；
下部的中心管粗孔径滤管段对应胶结骨料段，在胶结骨料段的管壁上沿轴线方向均匀交叉设置粗管孔。
所述中心管的外壁通过金属丝绕成螺旋形，以区隔外部缠绕的滤网，滤网设置两层，内层滤网采用80目尼龙网或金属网，外层滤网采用3目至10目尼龙网或金属网，滤网外 再绕一层粗金属丝；
微生物诱导碳酸钙沉淀强化砂石桩工程现场的平面布设采用等边三角形状，砂石桩间距设置为其直径的2.5～4.5倍。
通过微生物诱导碳酸钙沉淀技术在微生物诱导碳酸钙沉淀强化砂石桩的骨料颗粒间隙内生成微生物诱导碳酸钙沉淀胶结物团块。
一种微生物诱导碳酸钙沉淀砂石复合桩加固结构的施工方法：
进行微生物诱导碳酸钙沉淀处理前，需通过将一细硬胶抽水管从中心管顶口插入至其底部，外连抽水装置，将其中积水抽干至中心管内短时间内不会迅速产生明显积水状态，再开始微生物诱导碳酸钙沉淀技术处理；
通过软胶管将注射装置与中心管顶端口相连，将微生物诱导碳酸钙沉淀工程浆液装在注射装置中，借助中心管注射到微生物诱导碳酸钙沉淀强化砂石桩的骨料颗粒间的孔隙中；
微生物诱导碳酸钙沉淀工程浆液包含尿素浆液、钙源浆液和微生物浆液；
钙源浆液为二价钙离子溶液，需通过弱酸或弱碱将其pH调节到6.5至7.0区间；钙源浆液的二价钙离子浓度宜调节于0.25mol/L至0.3mol/L；尿素溶液中尿素的摩尔浓度应保持与钙源浆液中二价钙离子浓度一致；微生物浆液中的微生物采用环境友好型的兼性厌氧型巴氏芽孢杆菌，微生物浆液pH值调节于9.4～9.6，菌液浓度高于1×105CFU/mL；
微生物诱导碳酸钙沉淀工程浆液的注射根据场地现场状况和工程需求实施，先通过中心管向骨料颗粒间的孔隙中注射足量微生物浆液，静置若干小时待菌液能充分进入骨料颗粒间的孔隙；再通过中心管低速注入所需的钙源浆液，使其充分进入骨料颗粒间的孔隙；最后通过中心管低速注入所需的尿素浆液，使其充分进入骨料颗粒间的孔隙；再静置养护。
本发明的有益效果：
本发明在不明显降低工程场地的岩土及水体的初始环境质量的前提下，可以降低弱透水性基底上富水细粒工程渣土边坡的变形破坏，特别是剪切变形破坏的风险。本发明提出将传统砂石桩技术与微生物诱导碳酸钙沉淀技术相结合，充分考虑了弱透水性基底上富水细粒工程渣土边坡的工程实际，对工程废料进行再利用，在工程现场原位制作微生物诱导碳酸钙沉淀强化砂石桩，以促进富水细粒工程渣土边坡排水固结，提高边坡的整体地基承载力及其抗剪切变形能力，达到长期预防其发生宏观变形破坏的目的。
本发明的主要改进点：
1、本发明一方面可利于弱透水性基底上富水细粒工程渣土层排水固结，另一方面可有效均匀地提高砂石桩桩体的力学强度，特别是抗剪切强度，以利于明显降低弱透水性基底上富水细粒工程渣土边坡的宏观破坏变形，尤其是剪切破坏变形的风险。并且，这种力学强度增高可按照现场实际，逐步递进微生物诱导碳酸钙沉淀工程注浆处理，不需要一次性完成。
2、本发明所采用的材料及产生的组分不含易燃易爆或剧毒物质，均为环境友好型材料，可对符合要求的中粗粒工程渣土进行资源化利用。
3、不同于一般化学胶结物进入土体孔隙后会快速胶结土粒，封闭渗流通道，降低土体总体渗透性能，微生物诱导碳酸钙沉淀技术的微生物诱导碳酸钙沉淀需要时间过程， 在工程现场条件下，根据工程场地及微生物诱导碳酸钙沉淀技术施工的差异，该过程一般可持续一天以上，这有利于微生物诱导碳酸钙沉淀工程浆液充分在目标土体中扩散，从而较均匀地对目标区土体进行胶结。
4、本发明除了有利于预防弱透水性基底上富水细粒工程渣土边坡变形破坏的功能，还能通过中心管对工程场地的地下水水位进行长期监测。
附图说明
下面结合附图和实施例对本发明作进一步说明。
图1为本发明工程现场剖面布设结构示意图。
图2本发明剖面结构示意图((a)单桩现场布设结构剖面示意图；(b)中心管结构示意图)。
图3为本发明中心管管孔布设结构示意图。
图4为本发明填料结构示意图((a)未经微生物诱导碳酸钙沉淀技术处理的填料结构示意图；(b)经微生物诱导碳酸钙沉淀技术处理后的填料结构示意图)。
图5为本发明工程现场平面布设结构示意图。
图6为本发明微生物诱导碳酸钙沉淀处理操作示意图((a)疏干中心管积水操作示意图；(b)注射工程浆液操作示意图)。
图中：1-弱渗透性基底；2-富水细粒工程渣土；3-微生物诱导碳酸钙沉淀强化砂石桩；4-渣土与基底界面；5-中心管；6-排水骨料段；7-排水胶结骨料段；8-胶结骨料段；9-中心管排水段；10-中心管细孔径滤管段；11-中心管粗孔径滤管段；12-细管孔；13-粗管孔；14-内层金属丝；15-滤网；16-外层金属丝；17-骨料颗粒；18-微生物诱导碳酸钙沉淀胶结物团块；19-抽水管；20-抽水装置；21-软胶管；22-注射装置；23-微生物诱导碳酸钙沉淀工程浆液。
具体实施方式
下面结合附图对本发明的实施方式做进一步的说明。
实施例1：
参见图1-6，一种微生物诱导碳酸钙沉淀砂石复合桩加固结构，它包括弱渗透性基底1，所述弱渗透性基底1的顶部堆放有富水细粒工程渣土2，所述富水细粒工程渣土2的内部贯穿设置有微生物诱导碳酸钙沉淀强化砂石桩3，所述微生物诱导碳酸钙沉淀强化砂石桩3的底端穿过渣土与基底界面4，并插入到弱渗透性基底1一段长度。此加固结构用于长期环保地预防弱透水性基底上富水细粒工程渣土边坡宏观变形破坏，融合了传统砂石桩技术和微生物诱导碳酸钙沉淀技术。
进一步的，所述微生物诱导碳酸钙沉淀强化砂石桩3包括处于桩体轴心的中心管5，所述中心管5的外围，并沿着其高度方向由上至下依次包围设置有排水骨料段6、排水胶结骨料段7和胶结骨料段8，所述排水骨料段6、排水胶结骨料段7和胶结骨料段8通过微生物诱导碳酸钙沉淀方式予以胶结。
进一步的，所述排水骨料段6、排水胶结骨料段7和胶结骨料段8的砂石骨料采用资源化再利用颗粒级配区间合格的工程渣土料，所述排水骨料段6、排水胶结骨料段7和胶结 骨料段8的砂石骨料颗粒最大粒径不大于30mm，砂石骨料的组分均需符合环境质量行业规范。
进一步的，所述工程渣土料包括废混凝土料或废砖块料。
进一步的，所述排水骨料段6的厚度至少为1m，砂石骨料选用级配处于粗砂至碎石区间砂石；所述排水胶结骨料段7自排水骨料段6底部一直填充至渣土与基底界面4，砂石骨料选用中砂；所述胶结骨料段8自富水细粒工程渣土2的底层延伸至弱渗透性基底1的内部，向下埋入长度不短于2m，砂石骨料选取细砂至中砂颗粒级配的砂石料。
排水骨料段6设置是考虑到富水细粒土在经地表充分排水后，易形成1m厚左右的硬壳层，故该埋深区间无需特别通过砂石桩横向排水，且该深度的土体难单独构成宏观剪切变形破坏问题，其抗剪切强度无需特别得到提高。
排水胶结骨料段7一方面有利于促进渣土体的排水，另一方面中砂骨料较有利于保证微生物诱导碳酸钙沉淀技术处理后充分提高桩体抗剪强度。
胶结骨料段8这样利于微生物诱导碳酸钙沉淀技术处理后充分提高桩体的抗剪切能力。
进一步的，所述微生物诱导碳酸钙沉淀强化砂石桩3的直径控制在300mm～500mm。
进一步的，为充分促进渣土堆的排水固结和桩体整体强度的提升，且不能明显增加工程成本，所述中心管5选用仅顶端开口的硬质PVC管，管内径处于15mm～30mm区间，管壁厚度在保证管体不会受工程现场中心管周边骨料段挤压发生明显变形的前提下，尽可能选厚度较小的PVC管；所述中心管5由上至下划分为上部的中心管排水段9，中心管排水段9上不布设管孔；中间的中心管细孔径滤管段10对应排水胶结骨料段7，在中心管细孔径滤管段10上沿轴线方向均匀交叉设置细管孔12，以便于外部土体渗流进入和微生物诱导碳酸钙沉淀工程浆液通过该细管孔12注射至管外骨料中；下部的中心管粗孔径滤管段11对应胶结骨料段8，在胶结骨料段8的管壁上沿轴线方向均匀交叉设置粗管孔13。
进一步的，细管孔12孔径为2.5mm，以便于外部土体渗流进入和微生物诱导碳酸钙沉淀工程浆液通过该管孔注射至管外骨料中；粗管孔13孔径为4mm，以便于外部土体渗流进入和微生物诱导碳酸钙沉淀工程浆液通过该管孔注射至管外骨料中。
进一步的，所述中心管5的外壁通过金属丝14绕成螺旋形，以区隔外部缠绕的滤网15，滤网15设置两层，内层滤网采用80目尼龙网或金属网，外层滤网采用3目至10目尼龙网或金属网，滤网外再绕一层粗金属丝16；微生物诱导碳酸钙沉淀强化砂石桩3工程现场的平面布设采用等边三角形状，砂石桩间距设置为其直径的2.5～4.5倍。
进一步的，通过微生物诱导碳酸钙沉淀技术在微生物诱导碳酸钙沉淀强化砂石桩3的骨料颗粒17间隙内生成微生物诱导碳酸钙沉淀胶结物团块18。
本发明的机理为：
微生物诱导碳酸钙沉淀技术的理论机理可通过公式1和公式2表征：
Figure PCTCN2022080055-appb-000001
Figure PCTCN2022080055-appb-000002
微生物诱导碳酸钙沉淀工程浆液由尿素浆液、钙源浆液和微生物浆液组成。钙源 浆液为二价钙离子溶液，如氯化钙或乙酸钙等易溶于水的二价钙离子化合物的水溶液，该溶液现场应用前需要通过弱酸或弱碱将其pH调节到6.5至7.0区间，25℃测值，钙源浆液的二价钙离子浓度宜调节于0.25mol/L至0.3mol/L。尿素溶液中尿素的摩尔浓度应保持与钙源浆液中二价钙离子浓度一致。考虑到本发明的应用环境为地下深处，可能面临缺氧条件，微生物浆液中的微生物可采用环境友好型的兼性厌氧型巴氏芽孢杆菌，微生物浆液pH值宜调节于9.5左右，25℃测值，菌液浓度宜高于1×105CFU/mL。
进一步的，所述结构旨在应用于弱透水性基底上富水细粒工程渣土边坡，所处理的细粒工程渣土层厚度不宜小于4m。
进一步的，所述排水骨料段、排水胶结骨料段和胶结骨料段在微生物诱导碳酸钙沉淀强化砂石桩中组合分布，应根据所处理的细粒工程渣土边坡及其下伏弱透水性基底的实际予以设定。
进一步的，所述中心管针对场地探明的渣土体与下伏基底之间的接触带以及其他软弱区段，管孔布设密度可按需加密。
进一步的，所述微生物菌液在20℃至40℃区间时工程效能最佳，故本技术现场应用时，应保证微生物诱导碳酸钙沉淀技术处理环节的气温处于20℃至40℃区间。
进一步的，所述微生物诱导碳酸钙沉淀工程浆液是通过注射装置通过软胶管联通中心管顶端口，将浆液借助中心管注射到桩体骨料孔隙中。注射工程浆液前，需通过将一细硬胶管从中心管顶口插入至其底部，将其中积水抽干至中心管内短时间内不会迅速产生明显积水状态，再开始注射工程浆液。工程浆液的注射宜根据场地现场状况和工程需求操作，先通过中心管向桩体骨料孔隙中注射足量微生物浆液，静置若干小时使菌液能充分进入骨料；再通过中心管低速注入所需的钙源浆液，使其充分进入骨料间隙；最后通过中心管低速注入所需的尿素浆液，使其充分进入骨料间隙；再静置。用于注射三种工程浆液的注射器不能混用。
进一步的，所述微生物诱导碳酸钙沉淀技术处理后的砂石桩的强度的提升效果，可通过对比处理前后，中心管内的积水速率和稳定水头予以判断。微生物诱导碳酸钙沉淀处理后中心管内积水速率越小，稳定水位埋深越大，代表砂石桩的强度提升程度越高。微生物诱导碳酸钙沉淀技术注浆后，可通过测试分析中心管中抽出水体中的微生物浓度、二价钙离子浓度及尿素浓度，结合关于桩体强度提升程度的判断，可对进一步微生物诱导碳酸钙沉淀注浆与否进行决策。
实施例2：
一种微生物诱导碳酸钙沉淀砂石复合桩加固结构的施工方法：
进行微生物诱导碳酸钙沉淀处理前，需通过将一细硬胶抽水管19从中心管5顶口插入至其底部，外连抽水装置20，将其中积水抽干至中心管5内短时间内不会迅速产生明显积水状态，再开始微生物诱导碳酸钙沉淀技术处理；
通过软胶管21将注射装置22与中心管5顶端口相连，将微生物诱导碳酸钙沉淀工程浆液23装在注射装置22中，借助中心管5注射到微生物诱导碳酸钙沉淀强化砂石桩3的骨料颗粒17间的孔隙中；
微生物诱导碳酸钙沉淀工程浆液23包含尿素浆液、钙源浆液和微生物浆液；
钙源浆液为二价钙离子溶液，需通过弱酸或弱碱将其pH调节到6.5至7.0区间；钙 源浆液的二价钙离子浓度宜调节于0.25mol/L至0.3mol/L；尿素溶液中尿素的摩尔浓度应保持与钙源浆液中二价钙离子浓度一致；微生物浆液中的微生物采用环境友好型的兼性厌氧型巴氏芽孢杆菌，微生物浆液pH值调节于9.4～9.6，菌液浓度高于1×105CFU/mL；
微生物诱导碳酸钙沉淀工程浆液23的注射根据场地现场状况和工程需求实施，先通过中心管5向骨料颗粒17间的孔隙中注射足量微生物浆液，静置若干小时待菌液能充分进入骨料颗粒17间的孔隙；再通过中心管5低速注入所需的钙源浆液，使其充分进入骨料颗粒17间的孔隙；最后通过中心管5低速注入所需的尿素浆液，使其充分进入骨料颗粒17间的孔隙；再静置养护。

Claims (10)

  1. 一种微生物诱导碳酸钙沉淀砂石复合桩加固结构，其特征在于：它包括弱渗透性基底(1)，所述弱渗透性基底(1)的顶部堆放有富水细粒工程渣土(2)，所述富水细粒工程渣土(2)的内部贯穿设置有微生物诱导碳酸钙沉淀强化砂石桩(3)，所述微生物诱导碳酸钙沉淀强化砂石桩(3)的底端穿过渣土与基底界面(4)，并插入到弱渗透性基底(1)一段长度。
  2. 根据权利要求1所述一种微生物诱导碳酸钙沉淀砂石复合桩加固结构，其特征在于：所述微生物诱导碳酸钙沉淀强化砂石桩(3)包括处于桩体轴心的中心管(5)，所述中心管(5)的外围，并沿着其高度方向由上至下依次包围设置有排水骨料段(6)、排水胶结骨料段(7)和胶结骨料段(8)，所述排水骨料段(6)、排水胶结骨料段(7)和胶结骨料段(8)通过微生物诱导碳酸钙沉淀方式予以胶结。
  3. 根据权利要求1或2所述一种微生物诱导碳酸钙沉淀砂石复合桩加固结构，其特征在于：所述排水骨料段(6)、排水胶结骨料段(7)和胶结骨料段(8)的砂石骨料采用资源化再利用颗粒级配区间合格的工程渣土料，所述排水骨料段(6)、排水胶结骨料段(7)和胶结骨料段(8)的砂石骨料颗粒最大粒径不大于30mm，砂石骨料的组分均需符合环境质量行业规范。
  4. 根据权利要求3所述一种微生物诱导碳酸钙沉淀砂石复合桩加固结构，其特征在于：所述工程渣土料包括废混凝土料或废砖块料。
  5. 根据权利要求1或2所述一种微生物诱导碳酸钙沉淀砂石复合桩加固结构，其特征在于：所述排水骨料段(6)的厚度至少为1m，砂石骨料选用级配处于粗砂至碎石区间砂石；
    所述排水胶结骨料段(7)自排水骨料段(6)底部一直填充至渣土与基底界面(4)，砂石骨料选用中砂；
    所述胶结骨料段(8)自富水细粒工程渣土(2)的底层延伸至弱渗透性基底(1)的内部，向下埋入长度不短于2m，砂石骨料选取细砂至中砂颗粒级配的砂石料。
  6. 根据权利要求1所述一种微生物诱导碳酸钙沉淀砂石复合桩加固结构，其特征在于：所述微生物诱导碳酸钙沉淀强化砂石桩(3)的直径控制在300mm～500mm。
  7. 根据权利要求2所述一种微生物诱导碳酸钙沉淀砂石复合桩加固结构，其特征在于：所述中心管(5)选用仅顶端开口的硬质PVC管，管内径处于15mm～30mm区间，管壁厚度在保证管体不会受工程现场中心管周边骨料段挤压发生明显变形的前提下，尽可能选厚度较小的PVC管；
    所述中心管(5)由上至下划分为上部的中心管排水段(9)，中心管排水段(9)上不布设管孔；
    中间的中心管细孔径滤管段(10)对应排水胶结骨料段(7)，在中心管细孔径滤管段(10)上沿轴线方向均匀交叉设置细管孔(12)，以便于外部土体渗流进入和微生物诱导碳酸钙沉淀工程浆液通过该细管孔(12)注射至管外骨料中；
    下部的中心管粗孔径滤管段(11)对应胶结骨料段(8)，在胶结骨料段(8)的管壁上沿轴线方向均匀交叉设置粗管孔(13)。
  8. 根据权利要求1所述一种微生物诱导碳酸钙沉淀砂石复合桩加固结构，其特征在于：所述中心管(5)的外壁通过金属丝(14)绕成螺旋形，以区隔外部缠绕的滤网(15)，滤网(15)设置两层，内层滤网采用80目尼龙网或金属网，外层滤网采用3目至10目尼龙网或金属网，滤网外再绕一层粗金属丝(16)；
    微生物诱导碳酸钙沉淀强化砂石桩(3)工程现场的平面布设采用等边三角形状，砂石 桩间距设置为其直径的2.5～4.5倍。
  9. 根据权利要求1所述一种微生物诱导碳酸钙沉淀砂石复合桩加固结构，其特征在于：通过微生物诱导碳酸钙沉淀技术在微生物诱导碳酸钙沉淀强化砂石桩(3)的骨料颗粒(17)间隙内生成微生物诱导碳酸钙沉淀胶结物团块(18)。
  10. 权利要求1-9任意一项所述一种微生物诱导碳酸钙沉淀砂石复合桩加固结构的施工方法，其特征在于：
    进行微生物诱导碳酸钙沉淀处理前，需通过将一细硬胶抽水管(19)从中心管(5)顶口插入至其底部，外连抽水装置(20)，将其中积水抽干至中心管(5)内短时间内不会迅速产生明显积水状态，再开始微生物诱导碳酸钙沉淀技术处理；
    通过软胶管(21)将注射装置(22)与中心管(5)顶端口相连，将微生物诱导碳酸钙沉淀工程浆液(23)装在注射装置(22)中，借助中心管(5)注射到微生物诱导碳酸钙沉淀强化砂石桩(3)的骨料颗粒(17)间的孔隙中；
    微生物诱导碳酸钙沉淀工程浆液(23)包含尿素浆液、钙源浆液和微生物浆液；
    钙源浆液为二价钙离子溶液，需通过弱酸或弱碱将其pH调节到6.5至7.0区间；钙源浆液的二价钙离子浓度宜调节于0.25mol/L至0.3mol/L；尿素溶液中尿素的摩尔浓度应保持与钙源浆液中二价钙离子浓度一致；微生物浆液中的微生物采用环境友好型的兼性厌氧型巴氏芽孢杆菌，微生物浆液pH值调节于9.4～9.6，菌液浓度高于1×105CFU/mL；
    微生物诱导碳酸钙沉淀工程浆液(23)的注射根据场地现场状况和工程需求实施，先通过中心管(5)向骨料颗粒(17)间的孔隙中注射足量微生物浆液，静置若干小时待菌液能充分进入骨料颗粒(17)间的孔隙；再通过中心管(5)低速注入所需的钙源浆液，使其充分进入骨料颗粒(17)间的孔隙；最后通过中心管(5)低速注入所需的尿素浆液，使其充分进入骨料颗粒(17)间的孔隙；再静置养护。
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