A construction method for foundation pit retaining structure for replacing contaminated soil

Abstract

The present invention relates to a construction method for a foundation pit retaining structure for replacing contaminated soil, comprising the following steps: 1. detailed investigation and 3D modeling of the contaminated site, and production of a 3D electronic map; 2. dynamic planning of pollution removal: zoning soil layers and groundwater with different contamination depths through the 3D electronic map, setting up drainage wells according to the contamination depths of different zones, and adopting a casing rotary drilling method to form holes, so as to prevent cross-layer contamination of upper and lower soil layers and groundwater during the drilling process; 3. precise control of earth excavation; 4. retaining structure construction: construction of interlocking piles and water barriers outside the pit; 5. hierarchical control of the dewatering system: arrangement of drainage wells and emergency dewatering wells; and 6. staged excavation: layered excavation and completion of temporary bottom plate construction.

Description

Technical Field

[0001] The present invention belongs to the field of building construction technology, and in particular relates to a method for constructing a foundation pit retaining structure for replacing contaminated soil with the functions of pollution isolation, precise removal, and digital control. Background Art

[0002] The containment structure and construction methods of contaminated sites are key and challenging. Traditional interlocking piles utilize a slurry-walled drilling process, which carries the risk of slurry leakage leading to the spread of soil contamination. Conventional contaminated soil treatment relies on manual exploration and demarcation, resulting in large errors in the treatment boundary, leading to the misexcavation of large amounts of non-contaminated soil and significantly increasing treatment costs. Existing foundation pit dewatering often utilizes a mixed well system for pumping and drainage, requiring the simultaneous reduction of both groundwater and confined water. This not only causes cross-layer contamination of the aquifer but also leads to waste of groundwater resources. Furthermore, the current process lacks digital control measures, and the effectiveness of contaminated soil removal relies on manual sampling and testing.

[0003] Therefore, how to provide a construction method for a foundation pit retaining structure that replaces contaminated soil is a technical problem that technical personnel in this field urgently need to solve. Summary of the Invention

[0004] In response to the technical difficulties of treating and polluting at the same time in traditional contaminated site remediation, the present invention proposes a construction method for a foundation pit retaining structure that replaces contaminated soil. Through multiple anti-seepage barriers and closed construction technology, physical isolation of contaminated soil and water is achieved throughout the excavation process, solving industry problems such as groundwater cross-contamination and secondary pollution during construction in existing technologies. This method has the functions of pollution isolation, precise removal, and digital management and control.

[0005] In order to solve the above technical problems, the present invention includes the following technical solutions:

[0006] A construction method for a foundation pit retaining structure for replacing contaminated soil comprises the following steps:

[0007] Step S1: Detailed survey and 3D modeling of the contaminated site: Use geological radar to horizontally scan the contaminated soil area, use GC-MS to detect the type and concentration of pollutants, mark the contaminated boundary, and import the geological radar scanning data, borehole sampling data, and pollutant information into AutoCAD Civil 3D software to generate a 3D electronic map that includes contaminated soil thickness, permeability coefficient, and groundwater flow direction;

[0008] Step S2: Dynamic planning of pollution removal is carried out in two steps:

[0009] Step 1: Contaminated soil excavation and zoning: Based on the three-dimensional electronic map generated in step S1, the contaminated soil area is divided into different contaminated soil layers and groundwater layers according to different contaminated depths, and the contaminated depth differences and lithologic interface changes within the contaminated soil area are identified. The contaminated soil area is divided into several zones, with the contamination depth difference greater than 2m or the lithologic interface change as the boundary. For each zone, the optimal excavation layer height is calculated based on the soil lithology and stability using the CivilGPT knowledge model combined with the finite element analysis model. The optimal layer height is determined by comprehensively considering the soil self-stabilization capacity and the efficiency of the excavation machinery. The contaminated soil is excavated and stratified using the lithologic interface stratification method according to the calculated optimal layer height.

[0010] Step 2: Control of contaminated water pumping: For each contaminated soil zone divided in step S2, dewatering wells are set at the outer edge of the foundation pit in that zone and at the contaminated depth of different zones based on the contaminated water layer depth information in the three-dimensional electronic map. The casing rotary drilling method is used to ensure that the casing is followed to at least 1.5 meters below the contaminated layer to prevent cross-layer contamination of the upper and lower soil layers and groundwater during the drilling process. The depth of the dewatering well is set to the bottom depth of the contaminated water layer in the zone + 1.5 meters. Before excavation, pumping from the dewatering well is started to ensure that the groundwater level in the zone drops to at least 0.5 meters below the bottom of the contaminated layer.

[0011] Step S3, construction of retaining structure: using the casing rotary drilling method to drill holes at the designed positions around the foundation pit, and constructing a circle of meat-vegetable interlocking piles; setting up drainage wells in the contaminated soil zone outside the foundation pit according to the second step of step S2; using the casing rotary drilling method to drill holes at the preset anti-floating point position at the bottom of the foundation pit, and constructing anti-floating piles;

[0012] Step S4, precise control of earthwork excavation: construct support in the foundation pit; carry out earthwork excavation, use the Trimble Earthworks system to link with the excavator GNSS positioning, obtain the excavator bucket position information in real time and compare it with the designed excavation surface in the three-dimensional electronic map; set the over-excavation alarm threshold to ±10cm, and trigger an alarm when the actual excavation depth exceeds the design value by ±10cm; stop excavation after excavation to 0.3~0.5m above the design elevation of the contaminated soil bottom plate, and construct the cushion layer; at the same time, actively construct an external water barrier outside the foundation pit, specifically: drive SP-IV type Larsen steel sheet piles along the outer edge line of the foundation pit to form a continuous vertical partition belt; then carry out grouting reinforcement on the outside of the steel sheet piles, with the grouting hole spacing of 0.8m, inject double liquid slurry, control the slurry diffusion radius to be ≥0.5m, and make the stratum permeability coefficient after grouting ≤1×10 -6 cm / s, forming a horizontal aquiclude.

[0013] Step S5, hierarchical control of the dewatering system: In the contaminated soil zone at the outer edge of the foundation pit, a dewatering well 15 as described in the second step of step S2 is arranged to undertake the main task of pumping out contaminated groundwater; in the non-major contaminated area or key risk location around the foundation pit, additional emergency dewatering wells 10 are arranged, with the spacing between emergency dewatering wells ≤25m, UPVC double-wall corrugated pipes pre-buried in the wells, and a backup power supply system is configured to ensure that the power switching response time after a power outage is ≤10s; the dewatering wells and the emergency dewatering wells together constitute a hierarchical dewatering system.

[0014] Step S6, excavate in layers and construct a temporary bottom plate: excavate in layers according to the layer height determined in the first step of step S2; after each layer of earthwork is excavated, immediately install the support corresponding to that layer and apply the designed prestressing force to 75%; after the excavation reaches the designed elevation of the base and the cushion layer construction is completed, construct a temporary bottom plate on the base; the temporary bottom plate is cast in batches according to the partitions, with each block size ≤6m×6m and the interval time between casting adjacent blocks ≥72 hours.

[0015] Furthermore, it also includes step S7, verification of the pollution removal effect: 1. Grid sampling points are arranged on the four walls and base of the foundation pit, and a heavy metal rapid detector is used for on-site screening; cores are drilled from suspected points and sent to the laboratory for toxicity leaching tests according to relevant standards, and toxicity leaching tests are carried out according to the national standard "Toxicity leaching method of solid waste - acetic buffer solution method" (HJ / T 299), thereby completing sampling and testing; 2. After the drainage well is continuously pumped for 48 hours, water samples are collected to test COD and heavy metal ion concentrations. After meeting the standards, an acceptance certificate is issued, thereby completing the groundwater acceptance.

[0016] Furthermore, it also includes step S8, the connection between site delivery and development: 1. The surface of the temporary bottom plate is roughened, shear steel bars are implanted, and it is cast into a whole with the permanent raft slab; a 500m high connector is reserved on the top of the column pile, which is welded and fixed to the steel column of the building basement to complete the structural transformation; 2. Fiber grating sensor groups are embedded in the key parts of the support structure, and the key parts include retaining piles (meat-vegetable bite piles) and horizontal support structures; the horizontal displacement of the retaining piles and the axial force of the horizontal support are monitored in real time; the monitoring early warning threshold is set: the cumulative change in the horizontal displacement of the retaining piles is ≤10mm / day and the total amount does not exceed the design allowable value, and the change in the horizontal support axial force does not exceed ±10% of the design value; when the monitoring data exceeds the early warning threshold, the platform alarm is automatically triggered; the monitoring data is uploaded to the cloud platform in real time to evaluate the safety status of the foundation pit structure, thereby completing the structural safety monitoring.

[0017] Furthermore, step S1 includes: when the geological radar performs horizontal scanning, the grid spacing is ≤2m×2m, and the detection depth is at least 2m below the contaminated layer; the drilling sampling spacing is ≤10m, and the sampling depth interval is at least 0.5m.

[0018] Furthermore, when the contaminated water is pumped out in step S2, it is necessary to ensure that the water level drops to at least 0.5 m below the bottom of the contaminated layer.

[0019] Furthermore, in step S3, the depth of the drainage well is +0.5m according to the depth of the polluted water in different areas, and grouting reinforcement is used outside the pit to seal the seams. Before earth excavation, the drainage well is used to pump out the polluted water 0.5m below the bottom of the polluted water.

[0020] Furthermore, in step S3, the retaining pile type is a meat-vegetable interlocking pile, and the casing rotary drilling method is used to form the hole. To ensure that the pressure water does not need to be lowered during the excavation process, the depth of the retaining piles in different zones is determined by the following formula:

[0021] D≥( γ w H w - γ s h s ) / (γ ' (1+λ));

[0022] Where D is the minimum depth of the retaining pile entering the aquiclude, in meters; γ w is the density of water, in units of 10 kN / m³; H_w: the height of the pressure head, in units of m; γ s is the weighted average density of the overlying soil layer, in kN / m³; h s is the thickness of the overlying soil layer, in m; γ ' is the effective density of the aquiclude soil; λ is the safety factor, which is 1.1~1.3.

[0023] Furthermore, in step S4, the over-excavation alarm threshold is set to ±10 cm; the contaminated soil is transported using a closed dump truck, the truck bed is covered with an impermeable membrane, and the transportation path is isolated from the clean area; after the layered excavation reaches the designed elevation, 1% polymer curing agent solution is immediately sprayed to seal the exposed soil layer to prevent the volatilization of pollutants.

[0024] Furthermore, in step S4, the active construction of the outer pit water barrier outside the foundation pit includes: driving SP-IV type Larsen steel sheet piles along the outer side of the foundation pit to form a partition belt; grouting uses double liquid slurry, the grouting hole spacing is 0.8m, the diffusion radius is ≥0.5m, and the stratum permeability coefficient after grouting is ≤1×10⁻ 6 cm / s.

[0025] Furthermore, the setting of the dewatering well in step S5 includes: the depth of the dewatering well = the bottom depth of the contaminated water layer + 1.5m, the water pump adopts a variable frequency submersible pump, and automatically starts and stops according to the real-time water level sensor data; the arrangement of the emergency dewatering well includes: the well spacing of the emergency dewatering well is ≤25m, UPVC double-wall corrugated pipes are pre-buried in the well, and the backup power supply switching response time is ≤10s.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0027] The present invention provides a method for constructing a foundation pit retaining structure for replacing contaminated soil. Through multiple anti-seepage barriers and closed construction processes, the physical isolation of contaminated soil and water in the entire excavation process is achieved, solving industry problems such as groundwater cross-contamination and secondary pollution during construction in the prior art. In response to the problems of fuzzy pollution boundaries and difficulty in quantifying the scope of treatment, innovative three-dimensional electronic map digital treatment technology is used to improve the pollution treatment accuracy from the traditional meter level to the centimeter level, while ensuring that the pollution is completely removed, and reducing the amount of ineffective earthwork treatment. By constructing a "survey-design-construction-verification" process and using three-dimensional electronic map technology, problems such as the non-traceability of treatment effects and delayed emergency responses in traditional processes are solved. A series of methods for foundation pit reinforcement are proposed to ensure the safety and stability of the foundation pit during vacancy. This method fundamentally solves the technical problem of "polluting while treating" in traditional contaminated site treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figures 1 to 5 Schematic diagram of steps S1 to S5 of a construction method for a foundation pit retaining structure for replacing contaminated soil according to an embodiment of the present invention;

[0029] Figure 6 The present invention is a flowchart of a method for constructing a foundation pit retaining structure for replacing contaminated soil in one embodiment of the present invention.

[0030] In the figure, 1-contaminated soil area, 2-local contaminated soil excavation area, 3-contaminated groundwater layer, 4-uncontaminated groundwater layer, 5-waterproof layer, 6-confined water layer, 7-cushion layer, 8-support, 9-temporary bottom plate, 10-emergency dewatering well, 11-column, 12-anti-floating pile, 13-column pile, 14-grouting reinforcement area, 15-drainage well, 16-meat-vegetable interlocking pile. DETAILED DESCRIPTION

[0031] The following is a detailed description of a construction method for a foundation pit retaining structure for replacing contaminated soil provided by the present invention, with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description.

[0032] Example

[0033] The following combination Figures 1 to 6, a detailed description of the foundation pit retaining structure construction method for replacing contaminated soil of the present invention is given.

[0034] Please continue to refer to Figures 1 to 6 A method for constructing a foundation pit retaining structure for replacing contaminated soil comprises the following steps:

[0035] Step S1, detailed investigation and 3D modeling of the contaminated site: A geological radar is used to horizontally scan the contaminated soil area 1, and a GC-MS instrument is used to detect the types and concentrations of pollutants. The contaminated boundary is marked, and the geological radar scanning data, borehole sampling data, and pollutant information are imported into AutoCAD Civil 3D software to generate a 3D electronic map that includes the contaminated soil thickness, permeability coefficient, and groundwater flow direction.

[0036] Step S2: Dynamic planning of pollution removal is carried out in two steps:

[0037] Step 1: Contaminated soil excavation and stratification: Based on the three-dimensional electronic map generated in step S1, identify the difference in contamination depth and the change in lithologic interface within the contaminated soil area; divide the contaminated soil area into several zones based on the difference in contamination depth greater than 2m or the change in lithologic interface; for each zone, calculate the optimal excavation layer height based on the soil lithology and stability using the CivilGPT knowledge model combined with the midas GTS NX finite element analysis model. The optimal layer height is determined by comprehensively considering the soil self-stabilization capacity and excavation machinery efficiency; excavate the contaminated soil in layers using the lithologic interface stratification method according to the calculated optimal layer height; please refer to Figure 2 The specific contaminated soil zoning includes: local contaminated soil excavation area 2, contaminated groundwater layer 3, uncontaminated groundwater layer 4, impermeable layer 5 and confined water layer 6.

[0038] The second step is to control the drainage of contaminated water: for each contaminated soil zone divided in the first step of step S2, a dewatering well is set in the outer edge area of ​​the foundation pit of the zone according to the depth information of the contaminated water layer in its three-dimensional electronic map; the dewatering well is drilled by the casing rotary drilling method, ensuring that the casing is followed to at least 1.5m below the contaminated layer to prevent cross-layer contamination of the upper and lower layers of soil and groundwater during the drilling process, and to ensure that all the contaminated soil is excavated; the depth of the dewatering well 15 is set to the bottom depth of the contaminated water layer in the zone + 1.5m; before excavation, start pumping water from the dewatering well and ensure that the groundwater level in the zone drops to at least 0.5m below the bottom of the contaminated layer.

[0039] Step S3, construction of retaining structure: at the designed position around the foundation pit, use the casing rotary drilling method to drill holes and construct a circle of meat-vegetable bite piles 16; in the contaminated soil zone outside the foundation pit, set up the drainage well 15 according to the second step of step S2; at the preset anti-floating point position at the bottom of the foundation pit, use the casing rotary drilling method to drill holes and construct anti-floating piles 12; Step S4, precise control of earthwork excavation: construct support 8 in the foundation pit; carry out earthwork excavation, use Trimble The Earthworks system is linked to the excavator's GNSS positioning to obtain the excavator bucket's position information in real time and compare it with the designed excavation surface in the three-dimensional electronic map. The over-excavation alarm threshold is set to ±10 cm, and an alarm is triggered when the actual excavation depth exceeds the design value by ±10 cm. Excavation is stopped after excavation reaches 0.3-0.5 m above the design elevation of the contaminated soil bottom plate, and a concrete cushion layer 7 is immediately constructed. At the same time, an external water barrier is actively constructed outside the foundation pit. Specifically, SP-IV Larsen steel sheet piles are driven along the outer edge of the foundation pit to form a continuous vertical partition belt. Grouting reinforcement is then carried out on the outside of the steel sheet piles. The spacing between grouting holes is 0.8 m, and double-liquid slurry is injected. The slurry diffusion radius is controlled to be ≥0.5 m, and the permeability coefficient of the grouting formation is ≤1×10 -6 cm / s, forming a horizontal aquiclude.

[0040] Step S5, hierarchical control of the dewatering system: In the contaminated soil zone at the outer edge of the foundation pit, a dewatering well 15 as described in the second step of step S2 is arranged to undertake the main task of pumping out contaminated groundwater; in the non-major contaminated area or key risk location around the foundation pit, additional emergency dewatering wells 10 are arranged, with the spacing between emergency dewatering wells ≤25m, UPVC double-wall corrugated pipes pre-buried in the wells, and a backup power supply system is configured to ensure that the power switching response time after a power outage is ≤10s; the dewatering wells and the emergency dewatering wells together constitute a hierarchical dewatering system.

[0041] Step S6, layered excavation and construction of temporary bottom plate 9: carry out layered excavation according to the layered height determined in the first step of step S2; after each layer of earthwork is excavated, immediately install the corresponding support of that layer and apply the designed prestressing to 75%; after the excavation reaches the designed elevation of the base and the cushion layer construction is completed, construct a temporary bottom plate on the base; the temporary bottom plate is cast in batches according to the partitions, with the size of each block ≤6m×6m, and the interval time between casting adjacent blocks ≥72 hours.

[0042] In this embodiment, more preferably, step S7 is further included, verification of the pollution removal effect: 1. Grid sampling points are arranged on the four walls and base of the foundation pit, and a heavy metal rapid detector is used for on-site screening; cores are drilled from suspected points and sent to the laboratory, and a toxicity leaching test is carried out according to the national standard "Toxicity Leaching Method of Solid Waste - Acetate Buffer Solution Method" (HJ / T 299), thereby completing sampling and testing; 2. After the drainage well is continuously pumped for 48 hours, water samples are collected to test the COD and heavy metal ion concentrations. After meeting the standards, an acceptance certificate is issued, thereby completing the groundwater acceptance.

[0043] In this embodiment, more preferably, step S8 is further included, and the site delivery and development connection are: 1. The surface of the temporary bottom plate 9 is roughened, shear steel bars are implanted, and it is cast into a whole with the permanent raft slab; a 500mm high connector is reserved on the top of the column pile 13, which is welded and fixed to the steel column of the building basement to complete the structural transformation; 2. The fiber optic Bragg grating sensor group is embedded in the key parts of the support structure, and the key parts include the retaining piles, such as the meat-vegetable bite piles 16 and the horizontal support structure; the horizontal displacement of the retaining piles and the axial force of the horizontal support are monitored in real time; the monitoring early warning threshold is set: the cumulative change in the horizontal displacement of the retaining piles is ≤10mm / day and the total amount does not exceed the design allowable value, and the change in the horizontal support axial force does not exceed ±10% of the design value; when the monitoring data exceeds the early warning threshold, the platform alarm is automatically triggered; the monitoring data is uploaded to the cloud platform in real time to evaluate the safety status of the foundation pit structure, thereby completing the structural safety monitoring.

[0044] In this embodiment, more preferably, step S1 includes: when the geological radar performs horizontal scanning, the grid spacing is ≤2m×2m, and the detection depth is at least 2m below the contaminated layer; the drilling sampling spacing is ≤10m, and the sampling depth interval is at least 0.5m.

[0045] In this embodiment, more preferably, when the contaminated water is pumped out in step S2, it is necessary to ensure that the water level drops to at least 0.5 m below the bottom of the contaminated layer.

[0046] In this embodiment, more preferably, the depth of the drainage well in step S3 is +0.5m according to the depth of the contaminated water in different areas, and grouting reinforcement is used outside the pit to block water and seal cracks to form a grouting reinforcement area 14; before earth excavation, the contaminated water 0.5m below the bottom of the contaminated water is pumped out using a drainage well.

[0047] In particular, the uncontaminated submerged layer 4 is provided with column piles 13 and anti-floating piles 12, and columns 11 are provided above the column piles 13. The function of the anti-floating piles 12 is to offset the buoyancy of groundwater, adapt to the dynamic changes of water level, and disperse the concentrated effect of buoyancy on the foundation pit bottom plate.

[0048] In this embodiment, more preferably, the retaining pile type in step S3 is a meat-vegetable interlocking pile 16, and the casing rotary drilling method is used to form the hole. To ensure that the excavation process does not require the release of pressure water, the depth of the retaining piles in different zones is determined by the following formula:

[0049] D≥( γ w H w - γ s h s ) / (γ ' (1+λ));

[0050] Where D is the minimum depth of the retaining pile entering the aquiclude, in meters; γ w is the density of water, in units of 10 kN / m³; H_w: the height of the pressure head, in units of m; γ s is the weighted average density of the overlying soil layer, in kN / m³; h s is the thickness of the overlying soil layer, in m; γ ' is the effective density of the aquiclude soil; λ is the safety factor, which is 1.1~1.3.

[0051] In this embodiment, more preferably, the over-excavation alarm threshold in step S4 is set to ±10 cm; the contaminated soil is transported by a closed dump truck, the truck bed is covered with an impermeable membrane, and the transportation path is isolated from the clean area; after the layered excavation reaches the designed elevation, 1% polymer curing agent solution is immediately sprayed to seal the exposed soil layer to prevent the volatilization of pollutants.

[0052] In this embodiment, more preferably, the active construction of the outer pit water barrier outside the foundation pit in step S4 includes: driving SP-IV type Larsen steel sheet piles along the outer side of the foundation pit to form a partition belt; grouting uses double liquid slurry, the grouting hole spacing is 0.8m, the diffusion radius is ≥0.5m, and the stratum permeability coefficient after grouting is ≤1×10⁻ 6 cm / s.

[0053] In this embodiment, more preferably, the setting of the dewatering well in step S5 includes: the depth of the dewatering well = the bottom depth of the contaminated water layer + 1.5m, the water pump adopts a variable frequency submersible pump, and automatically starts and stops according to the real-time water level sensor data; the arrangement of the emergency dewatering well includes: the well spacing of the emergency dewatering well is ≤25m, UPVC double-wall corrugated pipes are pre-buried in the well, and the backup power supply switching response time is ≤10s.

[0054] In this embodiment, more preferably, in step S6, the layered excavation control includes: excavating each layer according to the designed thickness; promptly installing steel supports after excavation and applying prestressing force to 75% of the designed value; monitoring the support axial force at a frequency of ≥ 1 time / 8 hours; triggering an audible and visual alarm when the limit (±10%) is exceeded. Construction of the temporary bottom slab 9 includes: determining the thickness of the temporary bottom slab for each zone based on the construction model, with the block size ≤ 6m × 6m and the interval between inter-slots ≥ 72 hours; controlling the concrete mold temperature between 5°C and 30°C; and covering the surface with a waterproof geomembrane during curing.

[0055] In particular, the bottom sealing plate is constructed, the emergency dewatering well 10 is set up, and the contaminated soil cleaning assessment is carried out in combination with the three-dimensional electronic map. During the period when the foundation pit is vacant, the foundation pit needs to be regularly assessed for safety to ensure the stability of the supporting structure, surrounding buildings and underground pipelines.

[0056] The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. The above embodiments only express one embodiment of the present invention, and their description is relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present invention, several variations and improvements can be made, which all fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent of the present invention shall be based on the attached claims.

Claims

1. A construction method for a foundation pit retaining structure for replacing contaminated soil, characterized in that: The steps include: Step S1: Detailed survey and 3D modeling of the contaminated site: Use geological radar to horizontally scan the contaminated soil area, use GC-MS to detect the type and concentration of pollutants, mark the contaminated boundary, and import the geological radar scanning data, borehole sampling data, and pollutant information into AutoCAD Civil 3D software to generate a 3D electronic map that includes contaminated soil thickness, permeability coefficient, and groundwater flow direction; Step S2: Dynamic planning of pollution removal is carried out in two steps: The first step is to excavate contaminated soil in layers and zones: Based on a 3D electronic map, identify differences in contamination depth and changes in lithologic interfaces within the contaminated soil area. The contaminated soil area is divided into several zones, with contamination depth differences exceeding 2m or lithologic interface changes as boundaries. For each zone, the optimal excavation layer height is calculated based on the soil lithology and stability using the CivilGPT knowledge model combined with a finite element analysis model. Using the lithologic interface stratification method, excavate and stratify the contaminated soil according to the optimal stratification height obtained by the above calculation; The second step is to control the drainage of contaminated water. For each contaminated soil zone, a drainage well is set up at the outer edge of the foundation pit in that zone based on the depth of the contaminated groundwater layer in the three-dimensional electronic map. The drainage well is drilled using the casing rotary drilling method, ensuring that the casing is extended to at least 1.5 meters below the contaminated layer to prevent cross-contamination of the upper and lower soil layers and groundwater during the drilling process. The depth of the drainage well is set to the bottom depth of the contaminated groundwater layer in the zone + 1.5 meters. Before excavation, pumping from the drainage well is started to ensure that the groundwater level in the zone drops to at least 0.5 meters below the bottom of the contaminated layer. Step S3, construction of retaining structure: at the designed location around the foundation pit, use the casing rotary drilling method to drill holes and construct a circle of meat-vegetable interlocking piles; in the contaminated soil zone outside the foundation pit, set up a drainage well according to the second step of step S2; at the preset anti-floating point position at the bottom of the foundation pit, use the casing rotary drilling method to drill holes and construct anti-floating piles; to ensure that the excavation process does not require the release of pressure water, the depth of the retaining piles in different zones is determined by the following formula: D≥( γ w H w - γ s h s ) / (c ' (1+λ)); Where D is the minimum depth of the retaining pile entering the aquiclude, in meters; γ w is the density of water, in 10 kN / m³; H w : pressure head height, in m; γ s is the weighted average density of the overlying soil layer, in kN / m³; h s is the thickness of the overlying soil layer, in m; γ ' is the effective density of the aquiclude soil; λ is the safety factor, which is 1.1~1.3; Step S4, precise control of earthwork excavation: construct support in the foundation pit; conduct earthwork excavation, use the Trimble Earthworks system to link with the excavator's GNSS positioning device, obtain the excavator bucket position information in real time and compare it with the designed excavation surface in the three-dimensional electronic map; set the over-excavation alarm threshold to ±10cm, and trigger an alarm when the actual excavation depth exceeds the design value by ±10cm; stop excavation when the distance from the contaminated soil bottom plate to 0.3-0.5m above the design elevation, and immediately construct a concrete cushion layer; at the same time, actively construct an external pit water barrier outside the foundation pit; after excavating in layers to the design elevation, immediately spray 1% polymer curing agent solution to seal the exposed soil layer to prevent pollutants from volatilizing; Step S5, hierarchical control of the dewatering system: the dewatering wells are responsible for the main task of pumping out contaminated groundwater; emergency dewatering wells are additionally arranged in non-major contaminated areas or critical risk locations around the foundation pit. The spacing between emergency dewatering wells is ≤25m, UPVC double-wall corrugated pipes are pre-buried in the wells, and a backup power supply system is configured to ensure that the power switching response time after a power outage is ≤10s; the dewatering wells and emergency dewatering wells together constitute a hierarchical dewatering system; Step S6, excavate in layers and construct a temporary bottom plate: excavate in layers according to the layer height determined in the first step of step S2; after each layer of earthwork is excavated, immediately install the corresponding support for that layer and apply the designed prestressing force to 75%; after excavating to the designed elevation of the base and completing the cushion layer construction, construct a temporary bottom plate on the base; the temporary bottom plate is cast in batches according to the partitions, with each partition size ≤6m × 6m, and the interval between casting adjacent partitions ≥72 hours.

2. The construction method according to claim 1, characterized in that: It also includes step S7, verification of pollution removal effect:

1. Grid sampling points are arranged on the four walls and base of the foundation pit, and heavy metal rapid detection instruments are used for on-site screening; cores are drilled from suspected points and sent to the laboratory for toxicity leaching tests, thereby completing sampling and testing; 2. After the drainage well is continuously pumped for 48 hours, water samples are collected to test COD and heavy metal ion concentrations. After meeting the standards, an acceptance certificate is issued, thereby completing the groundwater acceptance.

3. The construction method according to claim 2, characterized in that: The project also includes step S8, which links site delivery and development:

1. The temporary bottom slab is roughened, shear reinforcement is implanted, and the slab is cast integrally with the permanent raft slab; 500mm high connectors are reserved at the tops of the column piles, which are welded to the steel columns in the building basement to complete the structural transformation; 2. Fiber Bragg grating sensor groups are embedded in the designed locations of the support structure, including the retaining piles and horizontal supports, to monitor the horizontal displacement of the retaining piles and the axial force of the horizontal supports in real time; Set monitoring and early warning thresholds: the cumulative change in horizontal displacement of retaining piles is ≤10mm / day and the total amount does not exceed the design allowable value, and the change in horizontal support axial force does not exceed ±10% of the design value; when the monitoring data exceeds the early warning threshold, the platform alarm is automatically triggered; the monitoring data is uploaded to the cloud platform in real time to evaluate the safety status of the foundation pit structure, thereby completing structural safety monitoring.

4. The construction method according to claim 1, characterized in that: The step S1 includes: when the geological radar performs horizontal scanning, the grid spacing is ≤2m×2m, and the detection depth is at least 2m below the contaminated layer; the drilling sampling spacing is ≤10m, and the sampling depth interval is at least 0.5m.

5. The construction method according to claim 1, characterized in that: When the polluted water is pumped out in step S2, it is necessary to ensure that the water level drops to at least 0.5 m below the bottom of the pollution layer.

6. The construction method according to claim 1, characterized in that: In step S4, the over-excavation alarm threshold is set to ±10 cm; the contaminated soil is transported using a closed dump truck, the truck bed is covered with an impermeable membrane, and the transportation path is isolated from the clean area.

7. The construction method according to claim 1, characterized in that: In step S4, the active construction of the outer pit water barrier outside the foundation pit includes: driving SP-IV type Larsen steel sheet piles along the outer side of the foundation pit to form a partition belt; grouting using double liquid slurry, the grouting hole spacing is 0.8m, the diffusion radius is ≥0.5m, and the stratum permeability coefficient after grouting is ≤1×10⁻ 6 cm / s.

Images