Foundation pit three-dimensional blocking system for contaminated soil site and construction method

Abstract

The invention relates to a foundation pit three-dimensional blocking system for a polluted soil site and a construction method, and the foundation pit three-dimensional blocking system comprises a foundation pit support and vertical blocking structure which is an underground diaphragm wall arranged around a foundation pit; the bottom horizontal blocking structure is a basement structure bottom plate which is rigidly connected with the bottom of the underground diaphragm wall; the peripheral auxiliary blocking structure is an L-shaped concrete retaining wall arranged on the outer side of the underground diaphragm wall; by means of the three-dimensional closed system jointly formed by the underground diaphragm wall, the basement structure bottom plate and the peripheral L-shaped concrete retaining wall, effective physical blocking on polluted soil is formed in the foundation pit construction stage, and therefore in the internal area of the foundation pit, construction of a subsequent main body structure can be conducted, and the construction efficiency of the polluted soil is improved. The polluted soil blocked inside is synchronously or alternately repaired, so that the traditional limitation that repairing is conducted firstly and then construction is conducted is broken through, and the overall construction period is remarkably shortened.

Description

Technical Field

[0001] This invention relates to the fields of geotechnical engineering and environmental protection technology, and specifically to a three-dimensional barrier system for foundation pits and its construction method for contaminated soil sites. Background Technology

[0002] When constructing foundation pits on sites containing contaminated soil, the traditional practice usually requires the contaminated soil to be completely remediated first, and the foundation pit excavation and support construction can only proceed after the remediation meets the standards.

[0003] This "repair first, then construct" approach has severely extended the overall construction period, especially for projects with strict time constraints, where this contradiction is particularly prominent. Summary of the Invention

[0004] The purpose of this invention is to provide a three-dimensional barrier system and construction method for foundation pits in contaminated soil sites, overcoming the defects of the "remediation first, construction later" model in the prior art that leads to serious delays in the construction period.

[0005] To achieve the above objectives, the present invention provides a three-dimensional barrier system for foundation pits in contaminated soil sites, comprising: The foundation pit retaining and vertical barrier structure is a continuous underground wall surrounding the foundation pit. The bottom horizontal barrier structure is a basement structural slab that is rigidly connected to the bottom of the underground continuous wall; The external auxiliary barrier structure is an L-shaped concrete retaining wall set outside the underground continuous wall; The underground continuous wall, the basement structural slab, and the L-shaped concrete retaining wall together form a three-dimensional closed system for isolating contaminated soil inside and outside the foundation pit.

[0006] By adopting this technical solution, the underground continuous wall, the basement structural slab, and the L-shaped concrete retaining wall together form a three-dimensional closed system, integrating the foundation pit support function with the pollutant barrier function. A physical isolation barrier is constructed during the foundation pit construction stage, fundamentally providing a structural basis for construction and repair within the isolated area, thereby solving the problem of construction delays caused by the traditional repair-then-construction mode.

[0007] Furthermore, the diaphragm wall penetrates the contaminated soil layer and extends into the underlying stable strata.

[0008] By adopting this technical solution, the depth of the diaphragm wall is limited to penetrate the contaminated soil layer and enter the stable stratum, ensuring the integrity and reliability of the vertical barrier. This effectively prevents pollutants from migrating or bypassing through the unblocked soil below the bottom of the diaphragm wall, and enhances the vertical sealing of the entire three-dimensional barrier system.

[0009] Furthermore, the basement structural slab is provided with a seepage-proof layer, and the steel reinforcement of the basement structural slab is rigidly connected to the underground continuous wall through pre-embedded steel reinforcement or connectors.

[0010] By adopting this technical solution, on the one hand, the seepage prevention performance of the basement as a horizontal barrier is enhanced by setting a seepage-proof layer inside the basement structural basement slab; on the other hand, by limiting the rigid connection between the basement reinforcement and the underground continuous wall to be achieved by pre-embedded reinforcement or connectors, the connection strength and integrity between the horizontal barrier and the vertical barrier are ensured, avoiding the risk of pollutants leaking from the connection due to gaps caused by weak connections.

[0011] Furthermore, the L-shaped concrete retaining wall includes connected vertical wall segments and horizontal wall segments; A gap is formed between the vertical wall segment and the underground continuous wall, and the gap is filled with drainage material; The horizontal wall section extends below the clean backfill soil area outside the foundation pit.

[0012] By adopting this technical solution, the drainage gap between the vertical wall section and the underground continuous wall can effectively collect and divert any potential seepage, reducing the adverse effects of water pressure on the barrier system; the horizontal wall section extends below the clean backfill area, which can more effectively block the horizontal migration of contaminated soil from the outside and provide a clean foundation for the backfill.

[0013] Furthermore, the L-shaped concrete retaining wall is provided with diagonal reinforcing bars at the corners, and its surface facing the contaminated soil is coated with a waterproof coating.

[0014] By adopting this technical solution, the structural strength of this key load-bearing part is enhanced by setting diagonal reinforcing bars at the corner of the L-shaped concrete retaining wall, ensuring its long-term durability and stability. At the same time, the waterproof coating applied to the soil-facing side directly improves the seepage prevention performance of the retaining wall itself and enhances its reliability as an external auxiliary barrier.

[0015] The present invention also provides a construction method for a three-dimensional barrier system for foundation pits in contaminated soil sites, comprising the following steps: S1. Construction pit retaining and vertical barrier structure: Construct underground continuous walls around the pit to simultaneously form the pit support structure and the vertical pollution barrier structure; S2. Construction of the bottom horizontal barrier structure: After excavating the foundation pit to the design elevation, construct the basement structure bottom slab and rigidly connect it to the bottom of the underground continuous wall to form a horizontal pollution barrier surface; S3. Construction of external auxiliary barrier structure: On the outside of the underground continuous wall, an L-shaped concrete retaining wall is constructed to form a barrier to prevent the intrusion of external contaminated soil.

[0016] By adopting this technical solution, following the logical sequence of first vertical barrier, then horizontal enclosure, and finally external reinforcement, the steps are clear and highly operable, ensuring that the three-dimensional barrier system can be constructed correctly and efficiently.

[0017] Furthermore, in step S1, the construction of the underground continuous wall includes trenching, hoisting and placing the steel cage, pouring concrete, and setting a water-stop structure at the joint of the trench section.

[0018] By adopting this technical solution, the key control points in the construction of diaphragm walls were identified, namely trenching, hoisting and placing the steel cage, pouring concrete, and setting up water-stop structures. In particular, it was emphasized that water-stop structures should be set up at the joints of the trench sections. This is a key technical measure to ensure that the diaphragm wall is a continuous and leak-free vertical barrier, and to prevent pollutants from seeping through the joints of the wall sections.

[0019] Furthermore, in step S2, before constructing the basement structure floor slab, a cushion layer and a composite impermeable membrane are first laid at the bottom of the foundation pit; After the steel reinforcement of the basement structural slab is reliably connected to the steel reinforcement pre-embedded in the underground continuous wall, concrete is poured.

[0020] By adopting this technical solution, the construction details of the basement structural slab are refined; the pre-laying of the subbase and composite waterproof membrane adds an extra and reliable waterproof barrier to the slab; and the emphasis on the reliable connection between the slab reinforcement and the pre-embedded reinforcement of the continuous wall before pouring concrete ensures construction quality and is a technological guarantee for achieving a rigid connection between the two and forming an effective horizontal closed surface.

[0021] Furthermore, in step S3, before constructing the L-shaped concrete retaining wall, a gravel drainage layer is laid at its foundation location. The reinforcing bars of the L-shaped concrete retaining wall are connected to the underground continuous wall by rebar anchoring.

[0022] By adopting this technical solution, a gravel drainage layer is first laid, which is beneficial for foundation drainage and maintains structural stability. The retaining wall steel bars are connected to the underground continuous wall by rebar anchoring, which enhances the integrity between the outer barrier structure and the main barrier structure, making the three-dimensional closed system more stable.

[0023] Furthermore, steps S1, S2, and S3 are coordinated with the foundation pit excavation process to form a segmented construction flow. Within the foundation pit section where the three-dimensional barrier system has been completed, remediation of contaminated soil can be carried out simultaneously.

[0024] By adopting this technical solution, the construction steps can be coordinated with earthwork excavation to form a segmented process, and it is clearly pointed out that soil remediation can be carried out simultaneously in the foundation pit section where the three-dimensional barrier system has been completed. This directly reflects the core innovative concept of this invention: barrier, construction, and remediation at the same time.

[0025] Compared with the prior art, the present invention has the following advantages: The three-dimensional closed system, consisting of a diaphragm wall, a basement structural slab, and an outer L-shaped concrete retaining wall, effectively isolates the contaminated soil during the foundation pit construction phase. This allows for simultaneous or alternating remediation of the contaminated soil within the foundation pit area while the subsequent main structure construction is underway. This breaks through the traditional limitation of remediation before construction, significantly shortens the overall construction period, and achieves efficient parallel operation of pollution control and project construction. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the construction method for the three-dimensional barrier system for foundation pits used in contaminated soil sites according to the present invention. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Example

[0028] The present invention provides a three-dimensional barrier system for foundation pits in contaminated soil sites. Its core is to utilize the permanent or temporary structure of the foundation pit project itself to construct a three-dimensional, closed barrier system. The system mainly includes three structural parts: foundation pit enclosure and vertical barrier structure, bottom horizontal barrier structure, and outer auxiliary barrier structure.

[0029] First, the foundation pit retaining and vertical barrier structure is a diaphragm wall surrounding the foundation pit. This diaphragm wall has a dual function: first, it serves as a retaining structure during the foundation pit excavation stage, bearing earth pressure and water pressure to ensure the stability of the foundation pit sidewalls; second, it acts as a vertical and continuous barrier to prevent contaminated soil from the outside of the foundation pit from spreading into the foundation pit, and also to isolate the contaminated soil inside the foundation pit from the construction area after the foundation pit is excavated.

[0030] To ensure effective containment, the diaphragm wall needs to penetrate the contaminated soil layer and reach at least 1 meter below into a stable stratum (such as clay or rock) to cut off the path of pollutants flowing around the bottom of the wall. The construction of the diaphragm wall can adopt conventional processes, including site leveling, building guide walls, trenching with grab buckets or hydraulic milling machines, trench cleaning, hoisting and placing pre-fabricated steel cages, pouring impermeable concrete (such as C35P8) with guide pipes, and pulling out the joint pipes or steel sections after the concrete has initially set, and then proceeding to the construction of the next trench section until closure. Secondly, the bottom horizontal barrier structure is the basement structure slab that is rigidly connected to the bottom of the underground continuous wall. After the foundation pit is excavated to the design elevation, the construction of the basement structure slab begins. This slab is not only part of the building structure, but more importantly, it is firmly connected to the surrounding underground continuous walls to form a closed "box" slab, which constitutes a horizontal pollutant barrier surface.

[0031] To enhance the barrier effect, a composite geomembrane can be pre-laid on the concrete cushion layer of the basement structural slab as an additional anti-seepage layer; the reinforcing bars of the basement structural slab must be reliably connected (such as by welding or mechanical connection) to the reinforcing bars or connectors pre-embedded in the underground continuous wall to ensure that the two form a rigid whole and avoid leakage of pollutants due to gaps caused by deformation differences.

[0032] The construction steps for the basement structural slab may include: earthwork compaction and leveling, anti-buoyancy anchor construction, foundation layer pouring, brickwork for the slab edge and column piers, rebar tying (including connection with the pre-embedded rebar of the underground continuous wall), and concrete pouring and curing. Finally, the external auxiliary barrier structure is an L-shaped concrete retaining wall set outside the underground continuous wall, which includes connected vertical wall segments and horizontal wall segments.

[0033] The vertical wall sections are set roughly parallel to the underground continuous wall, with a certain gap between them. This gap is filled with permeable drainage materials such as sand and gravel to form a drainage channel to divert any possible seepage. The horizontal wall sections extend from the bottom of the vertical wall sections to the clean backfill area outside the foundation pit.

[0034] The L-shaped concrete retaining wall serves as a second line of defense, further preventing contaminated soil (or pollutants carried by surface runoff) from migrating towards the foundation pit from the outside and protecting the clean backfill soil from contamination. To enhance structural reliability, diagonal reinforcing bars are installed at the corners of the L-shaped concrete retaining wall, and a waterproof coating such as polyurethane is applied to the side facing the contaminated soil.

[0035] The construction steps for an L-shaped concrete retaining wall may include: leveling and setting out lines, excavating the foundation trench, laying a gravel drainage layer at the bottom of the trench, setting up formwork, tying reinforcing bars (some of which can be anchored into the underground continuous wall by rebar installation to enhance the integrity), pouring concrete, curing, and finally backfilling and compacting clean soil on the outside of the wall. By combining the above-mentioned underground continuous wall, basement structural slab and L-shaped concrete retaining wall, the system of the present invention forms a complete three-dimensional closed system around and at the bottom of the foundation pit, effectively confining the contaminated soil to a specific area or isolating it outside the construction area. Accordingly, please refer to the appendix. Figure 1The construction method of the above system, in particular, emphasizes its coordination with the progress of conventional foundation pit engineering, so as to achieve the goal of "isolation, construction and repair at the same time"; the method mainly includes three stages and steps, which can be closely integrated with the layered and zoned excavation of foundation pits.

[0036] Phase 1 (S1): Construction of the foundation pit retaining structure and vertical barrier structure.

[0037] Before or in the early stages of excavation, the construction of the diaphragm wall is completed along the perimeter of the excavation pit.

[0038] This step solved both the support and vertical isolation issues at once, creating safe and relatively enclosed conditions for subsequent operations.

[0039] Phase 2 (S2): Construct the bottom horizontal barrier structure.

[0040] As the excavation of the foundation pit is carried out in layers to the design elevation of a certain area, the construction of the basement structure floor slab in that area should be carried out immediately, and its rigid connection with the underground continuous wall should be ensured.

[0041] In this way, whenever the basement structural slab of a region is completed, the horizontal barrier surface at the bottom of that region is formed.

[0042] Phase 3 (S3): Construction of external auxiliary barrier structures.

[0043] This work can be carried out after the construction of the diaphragm wall is completed or simultaneously with the excavation of the foundation pit, depending on the overall construction plan; the foundation trench of the L-shaped concrete retaining wall is excavated on the outside of the foundation pit, and then its structural construction is completed. The core advantage lies in the ability to implement segmented, continuous operations. Specifically, the entire foundation pit can be divided into several construction sections. In a certain section, after the construction of the diaphragm wall (S1) is completed and the excavation reaches the design elevation, the basement structure slab (S2) of that section is immediately constructed, thereby forming a partially enclosed space in that section consisting of the diaphragm wall and the slab. Once this partially enclosed space is formed, the remediation of contaminated soil can be carried out immediately in this space. At the same time, other sections can carry out earthwork excavation, slab construction, or construction of the outer L-shaped retaining wall (S3) in parallel.

[0044] This process organization method allows contaminated soil remediation and foundation pit structure construction to proceed in parallel in both time and space, thereby significantly shortening the overall construction period. The present invention has been described in detail above with reference to the accompanying drawings and embodiments. Those skilled in the art can make various modifications to the present invention based on the above description. Therefore, certain details in the embodiments should not be construed as limiting the present invention, and the scope of protection of the present invention shall be defined by the appended claims.

Claims

1. A three-dimensional barrier system for foundation pits in contaminated soil sites, characterized in that, include: The foundation pit retaining and vertical barrier structure is a continuous underground wall surrounding the foundation pit. The bottom horizontal barrier structure is a basement structural slab that is rigidly connected to the bottom of the underground continuous wall; The external auxiliary barrier structure is an L-shaped concrete retaining wall set outside the underground continuous wall; The underground continuous wall, the basement structural slab, and the L-shaped concrete retaining wall together form a three-dimensional closed system for isolating contaminated soil inside and outside the foundation pit.

2. The three-dimensional barrier system for foundation pits in contaminated soil sites according to claim 1, characterized in that: The diaphragm wall penetrates the contaminated soil layer and enters the underlying stable stratum.

3. The three-dimensional barrier system for foundation pits in contaminated soil sites according to claim 1, characterized in that: The basement structure floor slab is equipped with a seepage-proof layer, and the steel reinforcement of the basement structure floor slab is rigidly connected to the underground continuous wall through pre-embedded steel reinforcement or connectors.

4. The three-dimensional barrier system for foundation pits in contaminated soil sites according to claim 1, characterized in that: The L-shaped concrete retaining wall includes connected vertical wall sections and horizontal wall sections; A gap is formed between the vertical wall segment and the underground continuous wall, and the gap is filled with drainage material; The horizontal wall section extends below the clean backfill soil area outside the foundation pit.

5. The three-dimensional barrier system for foundation pits in contaminated soil sites according to claim 4, characterized in that: The L-shaped concrete retaining wall is reinforced with diagonal reinforcing bars at the corners, and its surface facing the contaminated soil is coated with a waterproof coating.

6. A construction method for a three-dimensional barrier system for foundation pits used in contaminated soil sites as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Construction pit retaining and vertical barrier structure: Construct underground continuous walls around the pit to simultaneously form the pit support structure and the vertical pollution barrier structure; S2. Construction of the bottom horizontal barrier structure: After excavating the foundation pit to the design elevation, construct the basement structure bottom slab and rigidly connect it to the bottom of the underground continuous wall to form a horizontal pollution barrier surface; S3. Construction of external auxiliary barrier structure: On the outside of the underground continuous wall, an L-shaped concrete retaining wall is constructed to form a barrier to prevent the intrusion of external contaminated soil.

7. The construction method of the three-dimensional barrier system for foundation pits in contaminated soil sites according to claim 6, characterized in that: In step S1, the construction of the underground continuous wall includes trenching, hoisting and placing the steel cage, pouring concrete, and setting a water-stop structure at the joint of the trench section.

8. The construction method of the three-dimensional barrier system for foundation pits in contaminated soil sites according to claim 6, characterized in that: In step S2, before constructing the basement structure slab, a cushion layer and a composite impermeable membrane are laid at the bottom of the foundation pit; After the steel reinforcement of the basement structural slab is reliably connected to the steel reinforcement pre-embedded in the underground continuous wall, concrete is poured.

9. The construction method of the three-dimensional barrier system for foundation pits in contaminated soil sites according to claim 6, characterized in that: In step S3, before constructing the L-shaped concrete retaining wall, a gravel drainage layer is laid at its foundation location. The reinforcing bars of the L-shaped concrete retaining wall are connected to the underground continuous wall by rebar anchoring.

10. The construction method of the three-dimensional barrier system for foundation pits in contaminated soil sites according to claim 6, characterized in that: Steps S1, S2, and S3 are coordinated with the foundation pit excavation process to form a segmented construction flow. Within the foundation pit section where the three-dimensional barrier system has been completed, remediation of contaminated soil can be carried out simultaneously.

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