Foundation pit sealing structure and construction technology for shallow sand and gravel strata

Abstract

The invention discloses a bottom sealing structure and construction process for a foundation pit in a submerged sand and gravel formation. The bottom sealing structure includes a water-stop curtain inserted into the ground, and a compartment structure formed by high-pressure rotary spraying, interlocking piles or grouting at the bottom of the water-stop curtain. The water-stop curtain and the compartment structure divide the foundation pit into several small areas. The skip compartment method is used to carry out grouting and bottom sealing construction in each area. The grouting holes are divided into two sequence holes, Ⅰ and Ⅱ. The Ⅰ sequence holes are grouted with cement water glass double liquid slurry or controllable cement slurry with admixtures to form a Ⅰ sequence anti-seepage body, and the Ⅱ sequence holes are grouted with multi-ratio cement slurry to form a Ⅱ sequence anti-seepage body. The Ⅰ sequence anti-seepage body and the Ⅱ sequence anti-seepage body jointly form an anti-seepage bottom plate. The grouting process adopts bottom-up pipe grouting, and the end standard of each grouting section is determined based on the double limit of pressure and flow. The compartment structure of the invention limits the diffusion range of the slurry and improves the effective utilization rate of the slurry. On the basis of compartments, two-sequence composite grouting is adopted to improve the anti-seepage effect and overall strength of the anti-seepage bottom plate at the bottom of the pit.

Description

Technical Field

[0001] The patent of this invention relates to the technical field of bottom sealing construction of foundation pits in submerged sand and gravel strata, specifically to the grouting bottom sealing structure and construction process of foundation pits with submerged sand and gravel and no obvious water-blocking strata. Background Art

[0002] At present, in foundation pit excavation projects in water-rich strata without obvious impermeable layers, four methods are usually used: precipitation, underwater concrete pouring, freezing, and full-section grouting of the foundation bottom to solve the construction problem of groundwater level being higher than the bottom of the foundation pit.

[0003] The first dewatering method is to first use underground continuous walls, interlocking piles or bored piles and corresponding water-stop curtains as maintenance structures. After the maintenance structure is completed, dewatering is carried out inside and outside the pit. After the groundwater level drops to the designed water level, foundation pit excavation construction is carried out. This method has the advantages of convenient construction, safety and reliability, but dewatering will also cause settlement of the surrounding environment and waste of water resources to varying degrees. For areas with scarce water resources and densely built buildings, this method is gradually prohibited.

[0004] The second underwater concrete pouring method is to use underground continuous walls, interlocking piles or bored piles and corresponding water-stop curtains as maintenance structures, use plain concrete walls as partition walls, and then pour underwater concrete bottom slabs after underwater excavation to the designed depth. This method does not require precipitation, has low construction risks and has little impact on the surrounding environment, but underwater excavation and pouring construction is difficult, costly, and not suitable for dark excavation foundation pit projects.

[0005] The third freezing method is to use artificial refrigeration technology to freeze the water in the ground, turning the natural rock and soil into frozen soil, increasing its strength and stability, so that the foundation pit can be excavated under the protection of the frozen wall. This method has the advantages of environmental protection, no pollution, short construction period, good effect, and wide application range, but the cost is extremely high.

[0006] The fourth type of full-section grouting at the bottom of the foundation means that underground continuous walls, interlocking piles or bored piles and corresponding water-stop curtains are first used as maintenance structures, and then full-range grouting is performed at the bottom of the foundation pit to isolate water. The advantages of this method are that there is no need for precipitation, low construction risk, and little impact on the surrounding environment, but the slurry diffusion is difficult to control, the effective utilization rate of the slurry is low, and the uniformity of the grouting effect cannot be guaranteed. Summary of the invention

[0007] In view of the problems existing in the prior art, the present invention proposes a simple and efficient grouting bottom sealing structure and construction process for a submerged sand and gravel stratum foundation pit, which solves the defects of the current foundation pit bottom sealing structure, such as high cost, great impact on surrounding buildings, difficult to control the diffusion of grouting bottom sealing slurry, and uneven grouting effect.

[0008] The bottom sealing structure of the foundation pit in the submerged sand and gravel stratum includes a water-stop curtain inserted into the ground, a compartment structure at the bottom of the water-stop curtain, and an anti-seepage bottom plate. The anti-seepage bottom plate is tightly bonded with the water-stop curtain and the compartment structure. The present invention first proposes to use bite piles and rotary jet piles to form a compartment structure at the bottom of the foundation pit. The compartment structure divides the foundation pit into several small areas for grouting. This can not only limit the diffusion range of the slurry, improve the effective utilization rate of the slurry and reduce the cost, but also further enhance the bite effect between the rotary jet piles through grouting; secondly, the present invention proposes a skip-compartment and sequence composite grouting method, which forms an anti-seepage bottom plate through two-sequence anti-seepage bodies, which can greatly improve the uniformity of the grouting anti-seepage effect and the strength of the anti-seepage bottom plate. The grouting bottom sealing structure and construction process of deep foundation pits in high-pressure water and thick sand and gravel strata are the closest to the present application. This scheme has a large grouting amount and many processes, and it is difficult to form a complete U-shaped compartment structure using the grouting method in actual construction. The technology applied for this time forms a continuous and complete compartment structure through interlocking piles and rotary jet piles, which can ideally achieve the purpose of dividing the bottom of the foundation pit; the use of skip-compartment and sequence composite grouting technology for grouting construction in the separated area can improve the effective utilization rate of the slurry, enhance the grouting effect, and reduce the project cost.

[0009] The construction process of the bottom sealing structure of the foundation pit in the submerged sand and gravel stratum includes the following steps:

[0010] (a) The thickness of the water-stop curtain, the spacing and height of the compartment structure, and the thickness of the anti-seepage bottom plate shall be determined according to the depth of the groundwater level, the excavation area and depth of the foundation pit, and the hydrostatic pressure at the bottom of the foundation pit.

[0011] (b) The water-stop curtain is formed by underground continuous wall, interlocking piles or rotary jet piles; the compartment structure is formed by high-pressure rotary jet technology, dividing the foundation pit into several small areas.

[0012] (c) The skip-chamber method is adopted to form an anti-seepage bottom plate in each small area through the sequential pipe composite grouting process, and it is tightly bonded with the water-stop curtain and the compartment structure to form a closed structure.

[0013] (d) Set up precipitation wells and water level observation holes in each small area to drain groundwater.

[0014] The step (c) comprises the following steps:

[0015] (c1) First, the separated areas are grouted with sequence I holes to form sequence I anti-seepage bodies. The slurry is cement-water-glass double liquid slurry, and the grouting is carried out from bottom to top. The pipe lifting speed is determined according to the stratum conditions, and the construction sequence is from the periphery to the middle.

[0016] (c2) 5-10 days after the completion of grouting of sequence I holes, grouting of sequence II holes is carried out to form a sequence II anti-seepage body to improve the anti-seepage effect; the grouting liquid adopts multi-ratio cement grouting, the water-cement ratio of cement grouting is between 3:1-5:1 at the beginning of grouting, and the water-cement ratio of cement grouting is between 0.5:1-0.8:1 at the end of grouting; the grouting of sequence II holes adopts segmented grouting from bottom to top, and the distance between each segment is 0.5-3m. The completion standard of grouting of each segment is determined by the pressure-flow double limit method, and the construction sequence is from the periphery to the middle.

[0017] (c3) Grout the remaining area and repeat steps c1 and c2.

[0018] Compared with the existing technology, the present invention has the following advantages and beneficial effects:

[0019] 1 The bottom sealing structure and construction process of the submerged sand and gravel stratum foundation pit of the present invention can divide the foundation pit into several small areas through the compartment structure formed by the super jet grouting pile. The compartment structure limits the diffusion range of the slurry in the plane, avoids the occurrence of the slurry flowing along the fixed weak channel, and improves the effective utilization rate of the slurry.

[0020] 2 The structure and construction process of the bottom sealing of the submerged sand and gravel stratum foundation pit of the present invention adopts cement water glass slurry and multi-ratio cement slurry in combination, which has good anti-seepage effect and strong economy.

[0021] 3 The structure and construction process of the bottom sealing of the submerged sand and gravel stratum foundation pit of the present invention can avoid the problem of poor anti-seepage effect caused by the deviation of the rotary spraying guide hole and the dilution and scouring of the slurry by the water flow, and has higher economy than the single use of grouting full-section bottom sealing, which can improve the effective utilization rate of the slurry, enhance the anti-seepage effect and strength of the anti-seepage bottom plate, simplify the construction process and shorten the construction period.

[0022] The structure and construction process of the bottom sealing of the submerged sand and gravel stratum foundation pit of the present invention use small and flexible machines, are suitable for open excavation and concealed excavation construction of foundation pits, and have a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings are used to further illustrate the present invention and constitute a part of the present invention, but do not constitute a limitation of the present invention. In the accompanying drawings:

[0024] Figure 1 It is a cross-sectional schematic diagram of the construction structure of the present invention;

[0025] Figure 2 It is a top view of the construction structure of the present invention;

[0026] Figure 3 It is a schematic diagram of the construction structure according to the present invention in the embodiment;

[0027] Marks and corresponding parts names in the drawings:

[0028] 1- water-stop curtain, 2- compartment structure, 3- interlayer soil between structural bottom plate and grouting anti-seepage bottom plate, 4- structural bottom plate, 5- anti-seepage bottom plate, 6- water level, 7- overlying soil, 8- sequence I holes, 9- sequence II holes, 10- sequence I anti-seepage body, 9- sequence II anti-seepage body DETAILED DESCRIPTION

[0029] The present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. Example

[0030] The background of this embodiment is a subway station in Beijing. The station is constructed by the top-down method. It is 317.6 meters long, 25.3 meters wide, 16.87 meters high, and has a top plate covered with 11.9 meters of soil. The station floor is located in a highly permeable gravel layer, and the groundwater level is 5 meters above the station floor.

[0031] like Figure 1 As shown, the structure of the bottom sealing of the submerged sand and gravel stratum foundation pit is characterized by comprising a water-stop curtain 1 inserted into the ground, a compartment structure 2 and an anti-seepage bottom plate 5; the construction structure is as shown in FIG. Figure 3 .

[0032] (a) According to the hydrogeological conditions and the size of the station, the top burial depth of the water-stop curtain 1 is 11.9m, the bottom burial depth is 42.27m, and the thickness is 0.9m; the top burial depth of the compartment structure 2 is 30.77m, the bottom burial depth is 36.77m, the height is 6m, and the width is 1.5m; the top burial depth of the anti-seepage bottom plate 5 is 30.77m, the bottom burial depth is 36.77m, and the thickness is 6m.

[0033] (b) The water-stop curtain 1 is formed by interlocking piles with a diameter of 0.9 m and an interlocking thickness of 0.3 m between the piles.

[0034] (c) The compartment structure 2 is formed by interlocking high-pressure jet grouting piles with a diameter of 1.5 m and an interlocking thickness of 0.3 m.

[0035] (c1) Use cement-water-glass double liquid grouting to carry out pipe grouting from bottom to top, with a pipe lifting speed of 5 cm / min. Figure 2 Grouting is performed in hole I 8 to form a first-order anti-seepage body 10, and the construction sequence is from the surroundings to the middle.

[0036] (c2) 5-10 days after the grouting of sequence I hole 8 is completed, grouting of sequence II hole 9 is carried out to form sequence II anti-seepage body 11. The grouting liquid adopts multi-ratio cement grouting, and the process adopts segmented grouting from bottom to top. The distance between each segment is 0.5-1.5m. The grouting completion standard is determined by the pressure-flow dual limit method, and the construction sequence is from the periphery to the middle.

[0037] (c3) For the remaining area, such as Figure 2, grout the bottom and repeat steps c1 and c2.

[0038] (d) Set up precipitation wells and water level observation holes in each area to drain away groundwater.

[0039] The above implementation modes and descriptions are only used to illustrate the technical solutions of the present invention and do not limit the protection scope of the invention. Any modification, replacement and improvement made within the principle of the present invention are included in the protection scope of the present invention.

Claims

1. The bottom sealing structure of the foundation pit in the submerged sand and gravel stratum is characterized by: It comprises a water-stop curtain (1) inserted underground, a compartment structure (2), a first-order anti-seepage body (10), a second-order anti-seepage body (11) and an anti-seepage bottom plate (5); The water-stop curtain (1) is formed by underground continuous walls, interlocking piles or jet-jet piles. The compartment structure (2) is formed at the bottom of the foundation pit using jet grouting piles or interlocking piles to divide the foundation pit into several small areas; The first-order anti-seepage body (10) is formed by pouring cement water glass slurry or controllable cement slurry with additives into the first-order holes (8). The II-sequence anti-seepage body 11 is formed by pouring a multi-grade cement slurry into the II-sequence hole (9), and the I-sequence anti-seepage body (10) and the II-sequence anti-seepage body (11) are interlocked to form an anti-seepage bottom plate (5); The water-stop curtain (1), the compartment structure (2), and the anti-seepage bottom plate (5) are tightly bonded; (a) Determine the thickness of the water-stop curtain (1), the spacing and height of the compartment structure (2), and the thickness of the anti-seepage bottom plate (5) based on the depth of the groundwater level, the excavation area and depth of the foundation pit, and the hydrostatic pressure on the bottom of the foundation pit; (b) using ground-connected walls, interlocking piles or jet grouting piles to form a water-stop curtain (1), and then using jet grouting piles or interlocking piles to form a compartment structure (2) at the bottom of the foundation pit, the compartment structure (2) divides the foundation pit into several small areas; (c) using a two-sequence composite grouting process to form an anti-seepage bottom plate (5), the anti-seepage bottom plate (5) is tightly bonded with the water-stop curtain (1) and the compartment structure (2) to form a closed structure; (d) Set up drainage wells and water level observation holes in each small area to drain the groundwater; The step (c) comprises the following steps: (c1) First, cement water glass slurry or controllable cement slurry is used to grout the separated areas in the Ⅰ sequence holes (8) to form the Ⅰ sequence impermeable body (10); the construction sequence is from the periphery to the middle; (c2) 5-10 days after the grouting of sequence I holes is completed, grouting of sequence II holes (9) is carried out to form sequence II anti-seepage bodies (11) and strengthen sequence I anti-seepage bodies (10) to improve the anti-seepage effect. The grouting is carried out in sections from bottom to top. The distance between each section is 0.5-3m. The grouting completion standard of each section is determined by the pressure and flow double limit method. The construction order is from the periphery to the middle; (c3) Grout the remaining area and repeat steps c1 and c2.

2. The bottom sealing structure of the submerged sand and gravel stratum foundation pit according to claim 1 is characterized by: There are two methods for forming the compartment structure (2) using jet grouting piles. One is to form the compartment structure (2) by interlocking circular jet grouting piles, and the other is to form the compartment structure (2) by forming a grid-like pile body through ultra-high pressure swing grouting.

3. The bottom sealing structure of the submerged sand and gravel stratum foundation pit according to claim 1 is characterized by: The water-cement ratio of multi-ratio cement slurry at the beginning of grouting is between 3:1-5:1, and the water-cement ratio at the end of grouting is between 0.5:1-0.8:

1.

4. The bottom sealing structure of the submerged sand and gravel stratum foundation pit according to claim 1 is characterized by: The water-stop curtain (1), the compartment structure (2), and the anti-seepage bottom plate (5) are formed by construction on the ground, or by construction in a dark excavated pilot tunnel.

5. The bottom sealing structure of the submerged sand and gravel stratum foundation pit according to claim 1 is characterized by: The I-sequence holes (8) and II-sequence holes (9) are arranged in a quincunx shape, and the hole spacing and row spacing are determined through theoretical calculation and experiment.

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