CN112081125A - Bottom sealing structure and construction technology of foundation pit in submerged sand and pebble stratum - Google Patents

Abstract

The invention discloses a bottom sealing structure and a construction process of a foundation pit of a submersible sandy gravel stratum, wherein the bottom sealing structure comprises a waterproof curtain inserted into the underground, a bin dividing structure is formed at the lower part of the waterproof curtain through high-pressure rotary spraying, secant piles or grouting, and the waterproof curtain and the bin dividing structure divide the foundation pit into a plurality of small areas; grouting and bottom sealing construction is carried out in each region by adopting a skip method, grouting holes are divided into I and II holes, the I hole is filled with cement-water-glass double-liquid slurry or controllable cement slurry added with an additive to form an I impermeable body, the II hole is filled with multi-ratio cement slurry to form a II impermeable body, and the I impermeable body and the II impermeable body form an impermeable bottom plate together. The grouting process adopts follow-up pipe grouting from bottom to top, and the end standard of each grouting section is determined based on double limits of pressure and flow. The bin dividing structure limits the diffusion range of the slurry and improves the effective utilization rate of the slurry; two-stage composite grouting is adopted on the basis of the sub-bins, so that the anti-seepage effect and the overall strength of the pit bottom anti-seepage base plate are improved.

Description

Bottom sealing structure and construction technology of foundation pit in submerged sand and pebble stratum

technical field

The patent of the present invention relates to the technical field of bottom sealing construction of foundation pits in submerged sand and pebble strata, and specifically refers to the grouting bottom sealing structure and construction technology of foundation pits with submerged sand and pebble strata without obvious water-proof stratum.

Background technique

At present, in the excavation project of foundation pit in water-rich stratum and without obvious water-proof layer, four methods are usually used: dewatering, underwater concrete pouring, freezing, and full-section grouting at the bottom of the foundation to solve the construction problem that the groundwater level is higher than the bottom of the foundation pit. .

The first type of dewatering method refers to the use of underground diaphragm walls, occlusal 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, and the foundation is carried out after the groundwater level is lowered to the design level. Pit excavation construction. This method has the advantages of convenient construction, safety and reliability, but precipitation will also cause the problems of surrounding environment subsidence and waste of water resources to varying degrees. This method is gradually banned in areas with scarce water resources and dense buildings.

The second type of underwater concrete pouring method refers to the use of underground diaphragm walls, occlusal piles or bored piles, and corresponding water-stop curtains as maintenance structures, using plain concrete walls as dividing walls, and then excavating underwater to the design depth. Underwater concrete base plate pouring. This method does not require precipitation, construction risks and has little impact on the surrounding environment, but the underwater excavation and pouring construction is difficult and expensive, and it is not suitable for underground excavation foundation pit engineering.

The third freezing method refers to the use of artificial refrigeration technology to freeze the water in the stratum, turn the natural rock and soil into frozen soil, and increase its strength and stability, so that the foundation pit excavation can be carried out under the protection of the frozen wall. . The method has the advantages of environmental protection, no pollution, short construction period, good effect, and wide application range, but the cost is extremely high.

The fourth type of full-section grouting at the bottom of the foundation means that firstly, the underground diaphragm wall, occlusal pile or bored pile and the corresponding water-stop curtain are used as maintenance structures, and then full-scale grouting is performed at the bottom of the foundation pit to prevent water. The advantages of this method are that there is no need for precipitation, the construction risk is small, and the impact on the surrounding environment is small, but the slurry diffusion is not easy 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

Aiming at the problems existing in the prior art, the present invention proposes a simple and efficient grouting bottom sealing structure and construction technology for the foundation pit of submersible sand and pebble strata, which solves the problem of the high cost of the current foundation pit bottom sealing structure, great influence on surrounding buildings and difficulty in diffusing the grouting bottom sealing slurry. Control, uneven grouting defects.

The bottom cover structure of the foundation pit in the submersible sand and pebble stratum includes a water-stop curtain inserted into the ground, a sub-silo structure under the water-stop curtain, and an anti-seepage bottom plate. The present invention first proposes to use occlusal piles and rotary jet piles to form a sub-silo structure at the bottom of the foundation pit, and the sub-silo structure divides the foundation pit into several small areas before grouting. The cost is reduced, and the occlusal effect between the rotary jetting piles can be further enhanced by grouting; secondly, the present invention proposes a method of compound grouting by skipping warehouses and sequences. The anti-seepage floor is jointly formed by two sequences of anti-seepage bodies, which can greatly improve the anti-seepage of grouting. The uniformity of the effect and the strength of the impermeable bottom plate. The closest thing to the proposal of this application is the grouting back cover structure and construction process of the deep foundation pit in the high-confined water and thick sand and pebble stratum. It is difficult to form a sub-silo structure. The technology of this application adopts the continuous and complete sub-silo structure formed by the occlusal pile and the rotary jetting pile, which can ideally achieve the purpose of separating the bottom of the foundation pit; the use of the skip-sequential composite grouting process for grouting in the separated area can improve the slurry The effective utilization rate, enhance the grouting effect, and reduce the project cost.

The construction process of the bottom cover structure of the foundation pit in the submerged sand and pebble stratum includes the following steps:

(a) 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, determine the thickness of the water-stop curtain, the spacing and height of the sub-silo structures, and the thickness of the anti-seepage floor.

(b) The water-stop curtain is formed by underground diaphragm walls, occlusal piles or rotary jetting piles; the sub-silo structure is formed by high-pressure rotary jetting process, and the foundation pit is divided into several small areas.

(c) Using the method of jumping warehouses, the anti-seepage bottom plate in each small area is formed through the composite grouting process with the pipeline in sequence, and it is tightly bonded with the water-stop curtain and the sub-silo structure to form a closed structure.

(d) Dewatering wells and water level observation holes are set up in each small area to drain groundwater.

The step (c) includes the following steps:

(c1) First-order hole grouting is carried out on the separated areas to form the first-order impermeable body. The cement-water glass double-liquid slurry is used for grouting from bottom to top. The pipe-lifting speed is determined according to the stratum. The construction sequence is as follows: Around to the middle.

(c2) 5-10 days after the completion of the grouting of the first sequence holes, the second sequence hole grouting is carried out to form the second sequence impermeable body to improve the anti-seepage effect; the slurry adopts a multi-level cement slurry, and the water-cement ratio of the grouting cement slurry is between 3: 1-5:1, the water-cement ratio of the cement slurry at the end of grouting is between 0.5:1-0.8:1; the grouting of the second sequence hole is grouting from the bottom to the top, the distance of each section is 0.5-3m, and the grouting end standard of each section adopts The method of pressure and flow double limit is determined, and the construction sequence is from the surrounding to the middle.

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

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

1. The bottom cover structure and construction technology of the submerged sand and pebble stratum foundation pit of the present invention can divide the foundation pit into several small areas through the sub-silo structure formed by the super rotary jetting pile. The sub-silo structure limits the diffusion range of the slurry in the plane, avoiding The phenomenon that the slurry flows away along the fixed weak channel improves the effective utilization rate of the slurry.

2. The structure and construction process of the bottom cover of the submersible sand and pebble stratum foundation pit of the present invention are compounded with cement water glass slurry and multi-grade cement slurry, which has good anti-seepage effect and strong economy.

3. The structure and construction process of the bottom sealing of the foundation pit in the submerged sand and pebble formation of the present invention can avoid the poor anti-seepage effect caused by the deflection of the rotary jet pilot hole and the dilution and scouring of the slurry by the water flow, compared with the single use of the rotary jetting process for the bottom sealing of the foundation pit. Compared with the single use of grouting full-section back cover, it can improve the effective utilization rate of the slurry, enhance the anti-seepage effect and strength of the anti-seepage floor, simplify the construction process, and shorten the construction period.

4. The structure and construction process of the bottom cover of the foundation pit in the submerged sand and pebble stratum of the present invention are small and flexible, and are suitable for open and underground construction of the foundation pit, and have a wide range of applications.

Description of drawings

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

1 is a schematic cross-sectional view of a construction structure of the present invention;

Fig. 2 is the top view of the construction structure of the present invention;

Fig. 3 is the schematic diagram of the construction structure according to the present invention in the embodiment;

The marks in the attached drawings and the names of the corresponding parts:

1-Waterproof curtain, 2-Separation 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-Overburden soil, 8-Sequence hole I , 9-Ⅱ sequence pores, 10-Ⅰ sequence impermeable body, 9-Ⅱ sequence impermeable body

Detailed ways

The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

Example

The background of this example is a subway station in Beijing. The station adopts the underground excavation and reverse construction method, with a length of 317.6 meters, a width of 25.3 meters, a height of 16.87 meters, and a roof covering of 11.9 meters. 5 meters above the floor of the station.

As shown in Figure 1, the structure of the bottom cover of the foundation pit in the submerged sand and pebble stratum is characterized in that it includes a water-stop curtain 1 inserted into the ground, a sub-silo structure 2 and an anti-seepage bottom plate 5; the construction structure is shown in Figure 3.

(a) According to the hydrogeological conditions and the size of the station, it is determined that the water-stop curtain 1 has a top buried depth of 11.9m, a bottom buried depth of 42.27m and a thickness of 0.9m. , 1.5m in width, 30.77m deep at the top of the anti-seepage bottom plate 5, 36.77m deep at the bottom, and 6m thick.

(b) The water-stop curtain 1 is formed by occlusal piles with a diameter of 0.9m, and the occlusion thickness between the piles is 0.3m.

(c) The sub-silo structure 2 is formed by the occlusion of high-pressure rotary jet piles with a diameter of 1.5m, and the occlusion thickness is 0.3m.

(c1) Use cement-water-glass double-liquid grouting for bottom-to-top grouting, and the pipe-lifting speed is 5 cm/min. As shown in Figure 2, the first-order anti-seepage body 10 is formed by grouting the first hole 8. The construction sequence is from the surrounding to the surrounding. in the middle.

(c2) 5-10 days after the completion of the grouting of the first sequence hole 8, the second sequence hole 9 is grouted to form the second sequence impermeable body 11. The grout adopts a multi-grade cement grout, and the process adopts the grouting from bottom to top. It is 0.5-1.5m, the grouting end standard is determined by the method of pressure and flow double limit, and the construction sequence is carried out from the surrounding to the middle.

(c3) For the remaining area, as shown in Figure 2, grouting and back sealing are performed, and steps c1 and c2 are repeated.

(d) Dewatering wells and water level observation holes are set up in each area to drain groundwater.

The above embodiments 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 or improvement made within the principles of the present invention is included in the protection scope of the present invention.

Claims (7)

1. The bottom cover structure of the foundation pit of the submerged sand and pebble stratum is characterized in that it comprises a water-stop curtain 1 inserted into the ground, a sub-silo structure 2, an I-order anti-seepage body 10, a II-order anti-seepage body 11 and an anti-seepage bottom plate 5; The water curtain 1 is formed by an underground diaphragm wall, an occlusal pile or a rotary jetting pile, and the sub-silo structure 2 is formed by a rotary jetting pile, an occlusal pile or a grouting body; The controllable cement slurry is formed by adding additives. The second-order impermeable body 11 is formed by pouring multi-grade cement slurry into the second-order hole 9. The first-order impermeable body 10 and the second-order impermeable body 11 are interlocked to form an impermeable floor. 5; The water-stop curtain 1, the sub-silo structure 2, and the anti-seepage bottom plate 5 are tightly bonded. 2. The sub-silo structure 2 according to claim 1, there are two kinds of methods for forming it by using the rotary jet piles, one is to form the sub-silo structure 2 by the occlusion of the circular rotary jet pile, and the other is to form the sub-silo structure 2 by the ultra-high pressure pendulum. A grid-like pile body is formed by spraying to form a sub-silo structure 2 . 3. The multi-ratio cement slurry according to claim 1 is characterized in that the water-cement ratio of initial grouting is between 3:1-5:1, and the water-cement ratio of end grouting is between 0.5:1-0.8:1. 4. The water-stop curtain 1, the sub-silo structure 2, and the anti-seepage bottom plate 5 according to claim 1 can be formed by construction on the ground, or can be formed by construction in an undercut pilot hole. 5. the construction technique of the bottom cover structure of the foundation pit of the submerged sand and pebble stratum, is characterized in that comprising the following steps: (a) Determine the thickness of the water-stop curtain 1, the spacing and height of the sub-silo structure 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; (b) The water-stop curtain 1 is formed by using ground connecting walls, occlusal piles or rotary jetting piles, etc., and then a sub-silo structure 2 is formed at the lower part of the foundation pit by using rotary jetting piles or occlusal piles, and the sub-silo structure 2 divides the foundation pit into several small area; (c) A two-sequence composite grouting process is used to form an anti-seepage bottom plate 5, and the anti-seepage bottom plate 5 is tightly bonded with the water-stop curtain 1 and the sub-silo structure 2 to form a closed structure; (d) Set up dewatering wells and water level observation holes in each small area to drain groundwater. 6 . The construction technique of the foundation pit bottom cover structure of the submerged sand and pebble formation according to claim 5 , wherein the step (c) comprises the following steps: (c1) First, use cement water glass slurry or controllable cement slurry, and grouting the first-order holes 8 in the mutually separated areas to form the first-order impermeable body 10; the construction sequence is from the periphery to the middle; (c2) 5-10 days after the completion of the grouting of the first-order holes, grouting the second-order holes 9 to form the second-order anti-seepage body 11 and strengthen the I-order anti-seepage body 10 to improve the anti-seepage effect. For the upper section grouting, the distance between each section is 0.5-3m, and the grouting end standard of each section is determined by the method of double limit of pressure and flow; the construction sequence is from the surrounding to the middle; (c3) Grout and seal the remaining area, and repeat steps c1 and c2. 7. The first-order holes 8 and II-order holes 9 according to claim 5 are arranged in a plum blossom shape, and the hole spacing and row spacing are determined by theoretical calculation and experiments.

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