Polluted Soil Treatment System and Treatment Method above Subway Tunnels

Abstract

A treatment system for contaminated soil above a subway tunnel, which can divide the area where the contaminated soil is located into several independent sub-areas. A treatment method for contaminated soil above a subway tunnel, which divides the area where the contaminated soil above the subway tunnel is located into several independent sub-areas; and separately performs backfilling operations on the contaminated soil in each sub-area. The treatment system and construction method for contaminated soil above the subway tunnel provided by the present invention have a mature construction process and a simple construction method. Especially the layout structure design of the steel sheet piles can divide a large-area backfilling area into several independent backfilling areas, and perform skip excavation in stages and at different times during the backfilling operation, which can reduce the disturbance to the unexcavated strata and the deformation of the tunnel structure, so as to achieve the purpose of overall control. The construction method of the present invention is simple in construction, with a small single unloading and backfilling volume, which can reduce the rebound deformation of the segments, and the operation is safe and controllable.

Description

Technical Field

[0001] The present invention relates to the technical field of rail transit construction, and more specifically, to a contaminated soil treatment system above a subway tunnel and a method for treating contaminated soil above a subway tunnel. Background Art

[0002] With the development of China's social economy, in order to meet the requirements of urban planning and development, rail transit lines are gradually laid out towards the suburbs of the city. Generally, if a city has large-scale polluting enterprises such as oil refineries, steel mills, and chemical factories, these enterprises are mostly built around the city (suburbs), which will result in the situation that rail transit lines need to pass under many industrial factory areas (such as oil refineries, steel mills, and chemical factories). Since the above-mentioned enterprises are mostly polluting enterprises, after the plant buildings are demolished, the surface soil in the original plant site area has large areas of excessive heavy metals, fluorides, and TPH / PAHs and other pollutants, and the in-situ treatment effect of many organic pollutants is not good. In order to meet the environmental protection requirements of residential and public land, it is necessary to excavate and replace the contaminated soil.

[0003] If the excavation and replacement area is exactly above the subway tunnel, then when carrying out large-area contaminated soil replacement operations above the subway tunnel, if the construction is improper, it will cause the floating of the tunnel segments. The floating of the tunnel segments will lead to uneven stress on them. The uneven stress on the tunnel segments will cause large deformations, which will in turn cause cracks in the subway shield tunnel, affecting the structural safety performance of the subway tunnel. Especially when the subway tunnel has been opened and operated, the potential risks are greater. Summary of the Invention

[0004] Therefore, how to provide a contaminated soil excavation and replacement construction system and construction method that can not only meet the requirements of contaminated soil excavation and replacement but also reduce the impact of excavation operations above the subway tunnel on the tunnel structure has become an urgent problem to be solved by those skilled in the art.

[0005] In order to solve the problems of the prior art, the present invention provides the following technical solutions:

[0006] The present invention provides a contaminated soil treatment system above a subway tunnel. The contaminated soil is located above the subway tunnel, and the contaminated soil needs to be excavated and backfilled with a filler. The subway tunnel has a tunnel axis, and the tunnel axis is the center line in the extending direction of the subway tunnel. Specifically, the contaminated soil treatment system above the subway tunnel includes: dividing the area where the contaminated soil is located into several independent partitions.

[0007] Preferably, in the contaminated soil treatment system above the subway tunnel provided by the present invention, the area where the contaminated soil is located is divided into the partitions by steel sheet piles, and the steel sheet piles surround the outer periphery of each partition.

[0008] Preferably, in the contaminated soil treatment system above the subway tunnel provided by the present invention, the insertion ratio of the steel sheet piles ranges between 0.8 and 1.2. Vertically, the horizontal plane where the bottom of the steel sheet pile is located is more than 2 m higher than the horizontal plane where the top of the subway tunnel is located.

[0009] Preferably, in the contaminated soil treatment system above the subway tunnel provided by the present invention, the clear distance between the contaminated soil and the subway tunnel is not greater than 10 m.

[0010] Preferably, in the contaminated soil treatment system above the subway tunnel provided by the present invention, along the direction of the tunnel axis, every 3 m - 5 m is divided into several said partitions; each said partition is divided into several independent blocks by steel sheet piles, and every 3 m - 5 m is divided into several said blocks along the direction perpendicular to the tunnel axis.

[0011] Preferably, several said blocks form a matrix in the area where the contaminated soil is located.

[0012] Preferably, in the contaminated soil treatment system above the subway tunnel provided by the present invention, on both sides of the area where the contaminated soil is located, a backfill soil storage area for storing the filler and a contaminated soil storage area for storing the contaminated soil are respectively arranged.

[0013] Preferably, in the contaminated soil treatment system above the subway tunnel provided by the present invention, the clear distance between the contaminated soil storage area and the subway tunnel is not less than 50 m; the clear distance between the backfill soil storage area and the subway tunnel is not less than 20 m.

[0014] Preferably, in the contaminated soil treatment system above the subway tunnel provided by the present invention, the steel sheet pile is a U-shaped Larssen steel sheet pile, and the wall thickness range of the steel sheet pile is 10 mm - 14 mm.

[0015] The present invention also provides a method for treating contaminated soil above a subway tunnel. In this method for treating contaminated soil above a subway tunnel, the present invention divides the area where the contaminated soil above the subway tunnel is located into several independent partitions; and separately performs replacement filling operations on the contaminated soil in each partition.

[0016] Preferably, in the method for treating contaminated soil above a subway tunnel provided by the present invention, when separately performing replacement filling operations on the contaminated soil in each partition, in the direction perpendicular to the tunnel axis, the partition is divided into blocks, and then the replacement filling operation is carried out by means of skip excavation.

[0017] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a structure and construction method for treating contaminated soil above a subway tunnel, aiming to safely and effectively remove and replace the contaminated soil above the subway tunnel.

[0018] To achieve the above object, the present invention provides a contaminated soil treatment system above a subway tunnel. The contaminated soil is located above the subway tunnel, and the contaminated soil needs to be excavated and backfilled with filling materials. Specifically, the contaminated soil treatment system above the subway tunnel includes: dividing the area where the contaminated soil is located into several independent sub-areas. In addition, the present invention also provides a method for treating contaminated soil above a subway tunnel, and the method is as follows: dividing the area where the contaminated soil above the subway tunnel is located into several independent sub-areas; separately performing replacement filling operations on the contaminated soil in each sub-area.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The contaminated soil treatment system and the treatment construction method above the subway tunnel provided by the present invention have mature construction techniques and simple construction methods. Especially the layout structure design of the steel sheet piles can divide a large-area replacement filling area into several independent replacement filling areas, and during the replacement filling operation, skip excavation is carried out in stages and at different times, which can reduce the disturbance to the unexcavated formation and the deformation of the tunnel structure, so as to achieve the purpose of overall control. The construction method of the present invention is simple in construction, with a small single unloading and replacement filling volume, which can reduce the rebound deformation of the segment, and the operation is safe and controllable. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The specification drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. Among them:

[0022] Figure 1 is a top view schematic diagram of the contaminated soil treatment system above the subway tunnel in the present invention;

[0023] Figure 2 is a vertical cross-sectional structure schematic diagram of the subway tunnel and the contaminated soil treatment system above it in the present invention.

[0024] Description of the reference numerals:

[0025] Steel sheet pile 1, backfill soil storage area 2, contaminated soil storage area 3, subway tunnel 4. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The present invention will be described in detail below with reference to the drawings and in conjunction with the embodiments. Each example is provided by way of explanation of the present invention rather than limitation of the present invention. In fact, those skilled in the art will clearly understand that modifications and variations can be made to the present invention without departing from the scope or spirit of the present invention. For example, the features shown or described as part of one embodiment can be used in another embodiment to produce yet another embodiment. Therefore, it is desirable that the present invention includes such modifications and variations that fall within the scope of the appended claims and their equivalents.

[0027] In the description of the present invention, the orientation or positional relationship indicated by the terms "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and does not require the present invention to be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention. The terms "connected" and "coupled" used in the present invention should be understood in a broad sense. For example, it may be a fixed connection or a detachable connection; it may be directly connected or indirectly connected through an intermediate component. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0028] Please refer to Figure 1 and Figure 2 , wherein, Figure 1 is a top-view schematic diagram of the contaminated soil treatment system above the subway tunnel in the present invention; Figure 2 is a vertical cross-sectional structural schematic diagram of the subway tunnel and the contaminated soil treatment system above it in the present invention.

[0029] The present invention provides a contaminated soil treatment system above a subway tunnel. Among them, the contaminated soil is located above the subway tunnel 4. When performing replacement filling operations on the contaminated soil above the subway tunnel 4, it is necessary to excavate the contaminated soil and backfill it with filler. This system is used to reduce the impact of soil disturbance during replacement filling of the contaminated soil on the structure of the subway tunnel 4.

[0030] The subway tunnel has a tunnel axis, and the tunnel axis is the center line in the extending direction of the subway tunnel.

[0031] In the present invention, the contaminated soil treatment system above the subway tunnel is mainly used to divide the area where the contaminated soil is located into several independent partitions. After partitioning the contaminated soil, the replacement filling operation is as follows: after excavating the contaminated soil in one partition and backfilling it with filler, then continue to excavate the contaminated soil in the next partition and backfill it with filler until all the contaminated soil in all partitions has been excavated and backfilled with filler.

[0032] This system adopts a replacement filling method in stages and at different times, which can safely and effectively excavate and replace the contaminated soil above the subway tunnel 4, and it can reduce the impact of soil disturbance on the structure of the subway tunnel 4 during the excavation and replacement filling operation.

[0033] Specifically, the present invention uses steel sheet piles 1 to divide the area where the contaminated soil is located, and can divide the area where the contaminated soil is located into several independent partitions. The steel sheet piles 1 surround the outer periphery of each partition and are used to reduce the disturbance of the replacement filling operation inside each partition during the replacement filling operation.

[0034] When partitioning the entire area where the contaminated soil is located by setting the steel sheet piles 1, the partitioning method is as follows: Along the direction of the tunnel axis, it is divided into several partitions at intervals of 3m - 5m. Specifically, along the direction of the tunnel axis (i.e., along the extension direction of the subway tunnel 4), by inserting the steel sheet piles 1, the partition is divided into areas with a width of 3m - 5m (which can be 3m, 3.5m, 4.0m, 4.5m or 5.0m), preferably 4.0m. Compared with the original entire area, the replacement excavation area of each partition is reduced, and it is immediately backfilled after excavation, which can reduce the impact of soil disturbance during the excavation and replacement of contaminated soil on the subway tunnel 4.

[0035] In the present invention, the width of the partition is set to be 3m - 5m. If the width of the partition or the area of the partition is too small, there will be many construction steps and the construction is inconvenient. If the width of the partition or the area of the partition is too large, it will result in a large amount of soil unloading at one time, thus causing a large deformation of the tunnel.

[0036] Each partition is divided into several independent blocks by the steel sheet piles, and along the direction perpendicular to the tunnel axis, it is divided into several blocks at intervals of 3m - 5m (which can be 3m, 3.5m, 4.0m, 4.5m or 5.0m). In the present invention, the size of each block within each partition is set to be 3m - 5m. If the width of the block or the area of the block is too small, there will be many construction steps and the construction is inconvenient. If the width of the block or the area of the block is too large, it will result in a large amount of soil unloading at one time, thus causing a large deformation of the tunnel.

[0037] Compared with the entire partition, the replacement excavation area of each block is further reduced, and it is immediately backfilled after excavation, which can reduce the impact of soil disturbance during the excavation and replacement of contaminated soil on the subway tunnel 4. Further, several blocks form a matrix in the area where the contaminated soil is located. For example, a matrix of several 4m x 4m blocks (square blocks) is formed, which is convenient for excavating the contaminated soil and backfilling the filler.

[0038] The excavation area is a three-dimensional area, and the insertion depth of the steel sheet piles 1 is affected by the depth of this three-dimensional area. In order to ensure the stability of the steel sheet piles 1 inserted into the soil, in the present invention, the insertion ratio range of the steel sheet piles 1 is limited to be between 0.8 - 1.2 (specifically, it can be 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.2), preferably 1.0. The larger the value of the insertion ratio (the greater the relative insertion depth of the steel sheet piles 1), the higher the stability of the foundation pit. The insertion ratio is determined according to the soil layer properties and the depth of the foundation pit. Considering economy and foundation pit stability comprehensively, 0.8 - 1.2 is taken, preferably 1.0. In areas with poor soil layer properties, such as silt soil areas, the insertion ratio can be appropriately increased.

[0039] The insertion ratio of the above-mentioned steel sheet pile 1 specifically refers to: when the steel sheet pile 1 is inserted into the excavation area, the ratio of the dimension of the part of the steel sheet pile 1 below the bottom layer of the excavation area to the dimension of the part above the bottom layer of the excavation area. The dimension of the part below the bottom layer of the excavation area refers to the height of the steel sheet pile 1 below the bottom layer of the excavation area, and the dimension of the part above the bottom layer of the excavation area refers to the height of the steel sheet pile 1 above the bottom layer of the excavation area. Vertically, the horizontal plane where the bottom of the steel sheet pile 1 is located is more than 2 m higher than the horizontal plane where the top of the subway tunnel 4 is located, that is, there is a net distance of 2 m between the bottom of the steel sheet pile and the top of the subway tunnel 4, which can prevent the construction of the steel sheet pile 1 from deforming the subway tunnel 4.

[0040] The net distance between the contaminated soil and the subway tunnel is not greater than 10 m, specifically referring to: the net distance between the steel sheet pile 1 set on both sides of the contaminated soil area and the side line of the subway tunnel 4 on the same side is not greater than 10 m.

[0041] Generally, the replacement area of the contaminated soil is rectangular, and the side parallel to the tunnel axis of the replacement area is the long side. The steel sheet piles 1 set on both sides of the contaminated soil area mentioned above are the steel sheet piles 1 located on the long side of the replacement area.

[0042] The present invention also limits the storage of the filler (backfill soil) and the contaminated soil: along the direction of the tunnel axis, on both sides of the contaminated soil area, there are respectively arranged a backfill soil storage area 2 for storing the filler and a contaminated soil storage area 3 for storing the contaminated soil. The backfill soil storage area 3 and the contaminated soil storage area 4 are respectively located on both sides of the tunnel axis. On the vertical projection plane, the net distance between the contaminated soil storage area 3 and the outer skin of the subway tunnel 4 is ≥ 50 m, and the net distance between the backfill soil storage area 2 and the outer skin of the subway tunnel 4 is ≥ 20 m. The filler is well-graded sandy soil or gravel soil, and the compaction coefficient is ≥ 0.97. In order to ensure the backfill quality and avoid secondary settlement of the ground after backfilling, the compaction coefficient should be ≥ 0.97.

[0043] The backfill soil storage area 2 and the contaminated soil storage area 3 can be virtual areas, and in the virtual areas, the filler (backfill soil) and the contaminated soil are stored in a natural stacking manner. Of course, the backfill soil storage area 2 and the contaminated soil storage area 3 can also be areas assembled by fences and partitions.

[0044] Specifically, the steel sheet pile 1 is a U-shaped Larssen steel sheet pile. Considering economy and structural safety comprehensively, the wall thickness range of the steel sheet pile 1 is 10 mm - 14 mm (specifically, it can be: 10 mm, 11 mm, 12 mm, 13 mm, 14 mm), and preferably 12 mm.

[0045] The present invention also provides a method for treating contaminated soil above a subway tunnel. In this method for treating contaminated soil above the subway tunnel, the present invention divides the area where the contaminated soil is located above the subway tunnel 4 into zones; and separately performs backfilling operations on the contaminated soil in each zone. Further, when performing the backfilling operation on the contaminated soil in each zone, in the direction perpendicular to the tunnel axis, the zone is divided into blocks, and then the skip-digging method is used for the backfilling operation.

[0046] In the present invention, the subway tunnel 4 is assembled by precast arc-shaped reinforced concrete segments with a thickness of 350 mm and an inner diameter of 5500 mm. The above-mentioned 5500 mm refers to the inner side diameter of the reinforced concrete segment.

[0047] The backfilling area, that is, the area where the contaminated soil is located, is above the subway tunnel 4. The scope of the backfilling area (the scope of contaminated soil treatment) is: within 10 m on both sides of the side lines of the subway tunnel 4.

[0048] Steel sheet piles 1 are further arranged in the closed area along the subway tunnel axis. The backfilled soil layer in the closed area is divided into zones every 4 m, and each zone is further divided into blocks every 4 m in the transverse direction of the subway tunnel 4 (the direction perpendicular to the axis of the subway tunnel 4). In this way, the closed area is divided into several 4 m x 4 m squares, which is convenient for construction and can avoid causing tunnel deformation.

[0049] In the present invention, the steel sheet piles 1 are U-shaped Larssen steel sheet piles, and the wall thickness of the steel sheet piles 1 is 12 mm. Excavation is carried out along the boundary of the backfilling area, and then the steel sheet piles 1 are set up to form a closed retaining structure. Steel sheet piles 1 are further arranged in the closed area within this retaining structure for zoning. When the soil quality is good, the insertion ratio of the steel sheet piles 1 is controlled at about 1.0, and the distance from the bottom of the steel sheet piles 1 to the top of the subway tunnel 4 is ≥ 2 m. The above-mentioned good soil quality is determined according to mechanical parameters. Generally, the clay soil quality is better, and the silt soil quality is worse.

[0050] The present invention provides a contaminated soil storage area 3 on one side of the subway tunnel 4. The contaminated soil storage area 3 is arranged on the side far from the subway tunnel 4, and the minimum clear distance from the nearest outer skin of the subway tunnel (the outermost side of the subway tunnel) is ≥ 50 m. The present invention provides a backfill soil storage area 2 on the other side of the subway tunnel 4. The backfill soil storage area 2 is arranged on the opposite side of the contaminated soil storage area 3, and the minimum clear distance from the nearest outer skin of the subway tunnel is ≥ 20 m.

[0051] The specific implementation process of the present invention is as follows:

[0052] Step 1: Determine the scope and zoning of contaminated soil treatment.

[0053] The range of the subway tunnel protection area is 10m on each side of the 4 side lines of the subway tunnel. This method is used for the treatment of contaminated soil within the protection area. For areas outside the protection area, the impact of contaminated soil treatment on the tunnel is reduced, and other construction methods can be adopted. Within the subway tunnel protection area, a partition with a width of 4m is set along the tunnel axis direction, such as Figure 1 the A-B-C-D-E areas in

[0054] Step 2: Support with sheet piles 1.

[0055] After determining the treatment range, set sheet piles 1 at the boundary of the determined replacement area for support. Along the tunnel axis direction, set sheet piles 1 again within the enclosure structure formed by the sheet piles 1 for partitioning, with a partition width of 4m, that is, the A, B, C, D, and E areas are separated by sheet piles 1.

[0056] When the soil quality is good, the insertion ratio of the sheet piles 1 is controlled at about 1.0, and the distance between the bottom of the sheet piles 1 and the top of the subway tunnel 4 is ≥2m.

[0057] Step 3: Construct in blocks and by skip-joint method.

[0058] Carry out replacement operations on each area separately in sequence. For example: For area A, divide it into blocks every 4m along the transverse direction of the tunnel (perpendicular to the tunnel axis), forming a number of 4m x 4m square matrices within area A. In the direction perpendicular to the tunnel axis in the plane, preferentially excavate the soil within the blocks on the side of area A (starting from one side of area A and switching to the other side after completion), and finally excavate the soil directly above the subway tunnel 4. During excavation, the principle of symmetry and uniformity should be maintained.

[0059] When the distribution of the contaminated soil coverage area above the subway tunnel is uneven, for example, there are two subway tunnels 4 passing through below the pollutant, with a large contaminated soil coverage area above one of them and a small contaminated soil coverage area above the other. When implementing this step, take the subway tunnel with a large contaminated soil coverage area as the main one, and preferentially carry out skip-joint construction on the contaminated soil above it (the subway tunnel with a large contaminated soil coverage area), starting from both ends and finally excavating the soil directly above the subway tunnel 4 (the subway tunnel with a large contaminated soil coverage area). In this way, the excavation impact is relatively small.

[0060] Specifically, the construction sequence of Area A is as follows: successively excavate Ax block → backfill Ax block → excavate Ay block → backfill Ay block → excavate Aw block → backfill Aw block → excavate Az block → backfill Az block → excavate Ah block → backfill Ah block → excavate Am block → backfill Am block → excavate An block → backfill An block, and the excavation and filling of Area A are completed. When excavating each sub-block, continuous layered excavation is required, and the thickness of each layer is controlled at 1 m. During the excavation process, if the excavation thickness of each layer is too large, the amount of soil unloading is large, and the tunnel rebound deformation is large. If the excavation thickness is too small, there are many construction steps and the construction is not convenient. Therefore, considering the construction factors and tunnel deformation comprehensively, the thickness of each layer is controlled at 1 m.

[0061] Immediately after the completion of the sub-block excavation, backfill with fillers in layers. The fillers are well-graded sandy soil or gravel soil. In order to ensure the backfill quality and avoid secondary settlement of the ground after backfilling, the compaction coefficient should be ≥ 0.97.

[0062] After that, construct Area B, Area C, Area D, and Area E successively along the tunnel axis direction according to the construction method of Area A until the treatment of the contaminated soil above the tunnel is completed.

[0063] The above is only the preferred embodiment of the present invention and is not used to limit the present invention. For those skilled in the art, various changes and modifications can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A contaminated soil treatment system above a subway tunnel. The contaminated soil is located above the subway tunnel, and the contaminated soil needs to be excavated and backfilled with filler. The subway tunnel has a tunnel axis, and the tunnel axis is the center line of the extension direction of the subway tunnel. It is characterized in that, Including: Dividing the area where the contaminated soil is located into several independent sub - areas; Along the direction of the tunnel axis, dividing it into several such sub - areas every 3m - 5m; Each of the sub - areas is divided into several independent blocks by steel sheet piles, and along the direction perpendicular to the tunnel axis, dividing it into several such blocks every 3m - 5m, Several of the blocks form a matrix in the area where the contaminated soil is located; Using steel sheet piles to divide the area where the contaminated soil is located into the sub - areas, and the steel sheet piles surround the outer periphery of each sub - area; The insertion ratio of the steel sheet piles ranges between 0.8 and 1.

2. Vertically, the horizontal plane where the bottom of the steel sheet piles is located is more than 2m higher than the horizontal plane where the top of the subway tunnel is located; Taking one subway tunnel with a large coverage area of contaminated soil as the main one, carrying out skip - jack construction on the contaminated soil above the subway tunnel covered by the contaminated soil, starting from both ends and finally excavating the soil directly above the subway tunnel.

2. The treatment system for contaminated soil above a subway tunnel according to claim 1, wherein, The net distance between the contaminated soil and the subway tunnel is not greater than 10m.

3. The treatment system for contaminated soil above a subway tunnel according to claim 1, wherein, On both sides of the area where the contaminated soil is located, there are respectively arranged a backfill soil storage area (3) for storing the filler and a contaminated soil storage area (4) for storing the contaminated soil.

4. The treatment system for contaminated soil above a subway tunnel according to claim 3, wherein, The net distance between the contaminated soil storage area and the subway tunnel is not less than 50m; The net distance between the backfill soil storage area and the subway tunnel is not less than 20m.

5. The treatment system for contaminated soil above a subway tunnel according to claim 1, wherein, The steel sheet piles are U - shaped Larssen steel sheet piles, and the wall thickness range of the steel sheet piles is 10mm - 14mm.

6. A method for treating contaminated soil above a subway tunnel, wherein, Dividing the area where the contaminated soil above the subway tunnel is located into several independent sub - areas; Carrying out replacement filling operations on the contaminated soil in each sub - area separately; The subway tunnel has a tunnel axis, and along the direction of the tunnel axis, dividing it into several such sub - areas every 3m - 5m; Each of the sub - areas is divided into several independent blocks by steel sheet piles, and along the direction perpendicular to the tunnel axis, dividing it into several such blocks every 3m - 5m, Several of the blocks form a matrix in the area where the contaminated soil is located; Using steel sheet piles to divide the area where the contaminated soil is located into the sub - areas, and the steel sheet piles surround the outer periphery of each sub - area; The insertion ratio of the steel sheet piles ranges between 0.8 and 1.

2. Vertically, the horizontal plane where the bottom of the steel sheet piles is located is more than 2m higher than the horizontal plane where the top of the subway tunnel is located; Taking one subway tunnel with a large coverage area of contaminated soil as the main one, carrying out skip - jack construction on the contaminated soil above the subway tunnel covered by the contaminated soil, starting from both ends and finally excavating the soil directly above the subway tunnel.

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