A bottom sealing structure and construction method of foundation pit in submerged sand and gravel stratum

Abstract

The invention discloses a bottom sealing structure for a foundation pit in a submerged sand and pebble stratum and a construction method. The bottom sealing structure comprises a water-stop curtain inserted underground, a partition wall, a cylindrical anti-seepage body, a first-order grouting mesh anti-seepage body, a second-order grouting anti-seepage body, and an anti-seepage bottom plate. The cylindrical anti-seepage body, the first-order grouting mesh anti-seepage body, and the second-order grouting anti-seepage body are mutually bonded to form an anti-seepage bottom plate. The construction method comprises the following steps: step one forms a water-stop curtain and a partition wall inserted underground, step two performs rotary spraying construction and forms a cylindrical anti-seepage body, step three performs I-order grouting hole drilling construction, step four performs I-order grouting hole grouting construction and forms an I-order grouting mesh anti-seepage body, step five performs II-order grouting hole drilling construction, and step six performs II-order grouting hole grouting construction and forms a II-order grouting anti-seepage body.

Description

Technical Field

[0001] The patent of this invention relates to a bottom sealing structure and construction method of a foundation pit in a submerged sand and gravel stratum, and belongs to the technical field of water stopping in construction engineering. Background Art

[0002] With the accelerated pace of urbanization in my country, the development and utilization of underground space has developed rapidly, and foundation pit projects have become more and more common. At present, in the foundation pit excavation projects in water-rich strata and 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 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 conditions.

[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 submerged sand and gravel stratum foundation pit bottom sealing structure and construction method to solve the current problems of high cost of foundation pit bottom sealing, great impact on surrounding buildings and uncontrollable diffusion of grouting bottom sealing slurry.

[0008] A bottom sealing structure for a foundation pit in a submerged sand and gravel formation includes a water-stop curtain inserted underground, a partition wall below the water-stop curtain, a cylindrical anti-seepage body, a first-order grouting hole, a first-order grouting mesh anti-seepage body, a second-order grouting hole, a second-order grouting anti-seepage body, and an anti-seepage bottom plate. The water-stop curtain inserted underground is formed by a ground-connected wall, a cast-in-place pile, a mixing pile, a rotary jet pile, or a grouting body; the partition wall is formed by a rotary jet pile, a mixing pile, or a grouting body; the cylindrical anti-seepage body is a rotary jet pile formed by a rotary jet process, and different cylindrical anti-seepage bodies are separated from each other; the first-order grouting holes are located at the midpoint of a line connecting the centers of adjacent cylindrical anti-seepage bodies, and the second-order grouting holes are located at the midpoint of a line connecting the centers of mutually oblique cylindrical anti-seepage bodies. The cylindrical anti-seepage body, the I-sequence grouting mesh anti-seepage body, and the II-sequence grouting anti-seepage body are bonded together to form an anti-seepage bottom plate. The cylindrical anti-seepage body limits the diffusion direction and range of the slurry during the grouting process of the I-sequence grouting holes; the cylindrical anti-seepage body and the I-sequence grouting mesh anti-seepage body jointly divide the anti-seepage bottom plate space into mutually separated, approximately circular narrow areas, limiting the diffusion space of the slurry during the grouting process of the II-sequence grouting holes.

[0009] A method for bottom sealing of a foundation pit in a submerged sand and gravel stratum comprises the following steps:

[0010] Step 1: Determine the thickness of the water-stop curtain 1, the spacing and height of the partition wall 2, and the thickness of the anti-seepage bottom plate 5 according to 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; use ground-connected walls, interlocking piles or jet-jet piles to form the water-stop curtain 1, and use jet-jet piles or grouting bodies to form the partition wall 2 at the bottom of the foundation pit, and the partition wall 2 divides the foundation pit into several areas;

[0011] Step 2: Select a partition area of ​​the foundation pit and perform jet grouting to form a cylindrical anti-seepage body 3;

[0012] Step 3: 5-10 days after the construction of the cylindrical anti-seepage body 3 is completed, the drilling construction of the first-order grouting hole 4 is carried out;

[0013] Step 4: Perform grouting construction of the first-order grouting holes 4 to form a first-order grouting mesh anti-seepage body 5;

[0014] Step 5: 5-10 days after the grouting of the first sequence grouting holes is completed, the drilling of the second sequence grouting holes 6 is carried out;

[0015] Step 6: Perform grouting construction of the II-sequence grouting hole 6 to form a II-sequence grouting anti-seepage body 7;

[0016] Step 7: Carry out construction in the remaining areas by repeating steps 2, 3, 4, 5 and 6.

[0017] Compared with the existing technology, the present invention has the following advantages and beneficial effects:

[0018] 1. The present invention provides a bottom sealing structure and construction method for a submerged sand and gravel stratum foundation pit. Separated cylindrical anti-seepage bodies are formed by jet grouting piles. The I-sequence grouting holes are located at the midpoint of a line connecting the centers of adjacent cylindrical anti-seepage bodies. In this way, the cylindrical anti-seepage bodies effectively limit the diffusion direction and range of slurry during the grouting process of the I-sequence grouting holes.

[0019] 2. The present invention provides a bottom sealing structure and construction method for a foundation pit in a submerged sand and gravel stratum. A first-order grouting mesh anti-seepage body is formed by grouting through first-order grouting holes. The cylindrical anti-seepage body and the first-order grouting mesh anti-seepage body jointly divide the anti-seepage bottom plate space into mutually separated, approximately circular narrow areas. The second-order grouting holes are located at the center of each narrow space area. In this way, the cylindrical anti-seepage body and the first-order grouting mesh anti-seepage body can jointly limit the diffusion space of the slurry during the grouting of the second-order grouting holes, thereby improving the diffusion uniformity of the slurry.

[0020] 3. The present invention provides a bottom sealing structure and construction method for a foundation pit in a submerged sand and gravel stratum. Compared with the single use of the rotary jet process for foundation pit bottom sealing, it can avoid the problem of poor anti-seepage effect caused by the deviation of the rotary jet guide hole and the dilution and scouring of the slurry by the water flow, and has higher economy. Compared with the single use of grouting full-section bottom sealing, it can improve the effective utilization rate of the slurry and enhance the anti-seepage effect and strength of the anti-seepage bottom plate.

[0021] 4. The present invention provides a bottom sealing structure and construction method for a submerged sand and gravel stratum foundation pit, and the machines used are small and flexible, and are suitable for open excavation, underground excavation and other working conditions.

[0022] The present invention discloses a bottom sealing structure and construction method for a foundation pit in a submerged sand and gravel stratum, which integrates the respective advantages of rotary jetting and grouting technologies. On the basis of the present invention, the rotary jetting piles are engaged, the pile spacing is increased, and the pile spacing is reduced by changing the rotary jetting hole spacing. The shape of the anti-seepage body is changed by changing the positional relationship between the rotary jetting hole spacing and the grouting hole spacing, all of which are within the protection scope of the present invention. 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 construction step diagram of the back cover structure of the present invention;

[0025] Figure 2 It is a schematic longitudinal section diagram of the back cover structure of the present invention;

[0026] Figure 3 It is a cross-sectional schematic diagram of the back cover structure of the present invention;

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

[0028] 1-water-stop curtain, 2-partition wall, 3-cylindrical anti-seepage body, 4-I-sequence grouting holes, 5-I-sequence grouting mesh anti-seepage body, 6-II-sequence grouting holes, 7-II-sequence grouting anti-seepage body, 8-anti-seepage bottom plate, 9-water level, 10-overlying soil. 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, a submerged sand and gravel stratum foundation pit bottom sealing structure includes a water-stop curtain 1 inserted into the ground, a partition wall 2, a cylindrical anti-seepage body 3, a first-order grouting mesh anti-seepage body 5, a second-order grouting anti-seepage body 7, and an anti-seepage bottom plate 8; the construction steps are as follows: Figure 2 .

[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. The cylindrical anti-seepage body is designed as a 1.5m diameter jet grouting pile with a spacing of 2.4m. The I-sequence grouting holes are located at the midpoint of the line connecting the centers of adjacent cylindrical anti-seepage bodies; the II-sequence grouting holes are located at the midpoint of the line connecting the centers of the cylindrical anti-seepage bodies obliquely opposite to each other.

[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] (d) The cylindrical anti-seepage body 3 is formed by interlocking high-pressure jet grouting piles with a diameter of 1.5 m, and the spacing between the jet grouting piles is 2.4 m.

[0036] (e) 5-10 days after the construction of the cylindrical anti-seepage body 3 is completed, the drilling construction of the first-order grouting hole 4 is carried out. After the drilling is completed, the grouting construction of the first-order grouting hole 4 is carried out. The grouting slurry is selected as cement water glass slurry, and the grouting is performed to form a first-order grouting mesh anti-seepage body 5.

[0037] (f) 5-10 days after the grouting of the first-order grouting hole 4 is completed, the drilling construction of the second-order grouting hole 6 is carried out. After the drilling is completed, the grouting construction of the second-order grouting hole 6 is carried out. The grouting slurry is selected as ultra-fine cement slurry or multi-ratio slurry, and the grouting is performed to form the second-order grouting anti-seepage body 7.

[0038] (g): Carry out construction in the remaining areas and repeat steps (e) and (f).

[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. A bottom sealing structure for a foundation pit in a submerged sand and gravel stratum, characterized in that: It includes a water-stop curtain (1) inserted into the ground, a partition wall (2), a cylindrical anti-seepage body (3), a first-order grouting hole (4), a first-order grouting mesh anti-seepage body (5), a second-order grouting hole (6), a second-order grouting anti-seepage body (7), and an anti-seepage bottom plate (8); The cylindrical anti-seepage body (3) and the first-order grouting mesh anti-seepage body (5) together divide the anti-seepage bottom plate space into mutually separated approximately circular narrow areas; the cylindrical anti-seepage body (3), the first-order grouting mesh anti-seepage body (5), and the second-order grouting anti-seepage body (7) are mutually bonded to form an anti-seepage bottom plate (8); The cylindrical anti-seepage bodies (3) are separated from each other, the first-order grouting holes (4) are located at the midpoint of the line connecting the centers of adjacent cylindrical anti-seepage bodies (3), and the second-order grouting holes (6) are located at the midpoint of the line connecting the centers of the cylindrical anti-seepage bodies (3) that are obliquely opposite to each other; Step 1: Determine the thickness of the water-stop curtain (1), the spacing and height of the partition wall (2), and the thickness of the anti-seepage bottom plate (8) according to 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; use ground-connected walls, interlocking piles or jet-jet piles to form the water-stop curtain (1), and use jet-jet piles or grouting bodies to form a partition wall (2) at the bottom of the foundation pit, and the partition wall (2) divides the foundation pit into several areas; Step 2: Select a certain partition area of ​​the foundation pit and perform jet grouting to form a cylindrical anti-seepage body (3); Step 3: 5-10 days after the construction of the cylindrical anti-seepage body (3) is completed, the drilling construction of the first sequence grouting hole (4) is carried out; Step 4: Perform grouting construction on the first-order grouting holes (4) to form a first-order grouting mesh anti-seepage body (5); Step 5: 5-10 days after the grouting of the first-order grouting holes (4) is completed, the drilling of the second-order grouting holes (6) is carried out; Step 6: Perform grouting construction on the second-order grouting holes (6) to form a second-order grouting anti-seepage body (7); Step 7: Carry out construction in the remaining areas by repeating steps 2, 3, 4, 5 and 6.

2. The bottom sealing structure of the submerged sand and gravel stratum foundation pit according to claim 1 is characterized by: The grouting pressure of the II-sequence grouting hole (6) is greater than the grouting pressure of the I-sequence grouting hole (4).

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