CN113931209A

CN113931209A - Large-area deep foundation pit weakly permeable stratum underground water level control method

Info

Publication number: CN113931209A
Application number: CN202111159079.9A
Authority: CN
Inventors: 王怡庭; 许海钦; 黄学文; 罗光造
Original assignee: Shanghai Baoye Group Corp Ltd
Current assignee: Shanghai Baoye Group Corp Ltd
Priority date: 2021-09-30
Filing date: 2021-09-30
Publication date: 2022-01-14

Abstract

The invention relates to a method for controlling the underground water level of a weakly permeable stratum of a large-area deep foundation pit, which comprises the following steps: before earth excavation, open drain dredging construction: step two: before the bottom plate is constructed, the open trench is transformed into a blind trench, and the third step is: before backfilling the outer wall, transforming an annular ditch and a water collecting well, and the fourth step: during the basement structure construction, along with the outer wall backfill progress, upwards continue to connect the PVC tube well, when the groundwater was walked around the water stop curtain and is permeated in the foundation ditch outside the foundation ditch, can be by the blind ditch network direction hole that absorbs water, recycle auto-induction's ball valve immersible pump, immediately automatic pump drainage after the water level rose, continuous control ground water level. The invention does not pursue the precipitation speed, cuts the earth surface through the dense shallow trench, increases the hydraulic infiltration area, fully utilizes the self-infiltration capacity of the underground water, and can stably maintain the water level.

Description

Large-area deep foundation pit weakly permeable stratum underground water level control method

Technical Field

The invention relates to the field of building construction, in particular to a method for controlling underground water level of a permeable-weakly layer of a large-area deep foundation pit.

Background

The traditional deep foundation pit engineering dewatering generally adopts open trench and water collecting well drainage or well point dewatering, and the well point dewatering is divided into five types of light well point dewatering, jet well point dewatering, electroosmosis well point dewatering, tube well point dewatering and deep well point dewatering. The drainage of the open trench water collecting well is only suitable for dredging and draining surface water, well point precipitation has various defects of high cost, high energy consumption, high construction risk of deep wells, small use scale and the like according to different types, the effect on soil layers with weak permeability is weak, the density of the well points needs to be increased to play a role, and the construction cost and the risk are further increased.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, provides a method for controlling the underground water level of the weakly permeable stratum of the large-area deep foundation pit, solves the problems of drainage and water level control of the weakly permeable soil in the large-area deep foundation pit engineering, and effectively controls and continuously monitors the underground water level under the geological conditions of the large-area deep foundation pit engineering that the water is weakly permeable.

In order to solve the technical problem, the invention is realized as follows:

a method for controlling the underground water level of a permeable-weakly layer of a large-area deep foundation pit is characterized by comprising the following steps:

the method comprises the following steps: before earth excavation, open drain dredging construction:

the annular groove is arranged on the periphery of the bottom of the foundation pit, the root of the support pile is attached, the width is 600mm, the depth is 300mm, and the top of the annular groove is equal to the bottom elevation of the bottom plate cushion layer of the structure; a DN1200 double-wall corrugated pipe with the length of 1m or a finished concrete pipe is inserted into the annular ditch to be used as a water collecting well, no cushion layer is formed on the annular ditch and the water pumping well, the bottom is paved in a mode of geotextile and double-layer plastic film, the upper return height of the geotextile is 200mm, and the plastic film is required to be pressed into the cushion layer of the bottom plate for 200 mm;

arranging a longitudinal and transverse open trench at the bottom of the whole foundation pit, wherein the open trench is arranged below the elevation of the bottom plate, avoiding the position of a bearing platform and properly utilizing the position of a structural post-cast strip; the elevation of the bottom of the circular ditch is required to be properly lower than that of a longitudinal and transverse open ditch in a field, and then a water pump is used for continuously pumping and draining water in a water collecting well to reduce the underground water level of the bottom of the pit;

step two: before the bottom plate is constructed, the open trench is reformed into a blind trench, gravels are backfilled in the open trench, a PVC pipe is wrapped in a gravel layer, double-layer dense meshes are fully paved above and below the gravel layer to isolate soil and a cushion layer, holes are formed in the side wall of the PVC pipe, the hole positions are small and dense, and water flow of the blind trench is collected and guided to the annular trench;

step three: before backfilling the outer wall, reforming an annular ditch and a water collecting well, removing a plastic film in the annular ditch and the water collecting well, backfilling by graded broken stones to form a blind ditch and a water absorption pit, combining the blind ditch and a drainage network under post-cast to form an underground drainage network, vertically embedding a PVC pipe at the position of the water absorption pit, perforating the part of the tail end of the pipeline extending into the well, and keeping the upper end of the pipeline 2 meters higher than the construction surface of the structure; the submersible pump sinks into the water absorption pit through the PVC pipe, and continuously pumps and discharges to maintain the underground water level and release the water pressure;

step four: during the basement structure construction, along with the outer wall backfill progress, upwards continue to connect the PVC tube well, when the groundwater was walked around the water stop curtain and is permeated in the foundation ditch outside the foundation ditch, can be by the blind ditch network direction hole that absorbs water, recycle auto-induction's ball valve immersible pump, immediately automatic pump drainage after the water level rose, continuous control ground water level.

The invention has the beneficial effects that: compared with the traditional well point dewatering, the method is simple and convenient to operate, large-scale machinery is not needed for well excavation operation, and operation risks are greatly reduced; in the execution process of the method, the underground water is collected to the earth surface and mainly permeates by self, the energy consumption only comes from the water pump to pump and drain water outside the foundation pit, and the maintenance cost is low; the size of the area of the foundation pit does not influence the execution effect of the method, and the method is suitable for foundation pits of various sizes.

Drawings

The invention is described in further detail below with reference to the following figures and embodiments:

FIG. 1 is a schematic cross-sectional view of a ring groove.

FIG. 2 is a schematic view of the annular trench and the sump.

Fig. 3 is a schematic view of fig. 2, 1-1.

Fig. 4 is a schematic view of a base plate.

FIG. 5 is a schematic diagram of the exterior wall before backfilling.

FIG. 6 is a schematic diagram of the backfilled exterior wall.

Detailed Description

as shown in fig. 1-3: the annular groove is arranged on the periphery of the bottom of the foundation pit, the root of the support pile is attached, the width is 600mm, the depth is 300mm, and the top of the annular groove is equal to the bottom elevation of the bottom plate cushion layer of the structure; inserting a DN1200 double-wall corrugated pipe with the length of 1m or finished concrete into the annular ditch to serve as a water collecting well, wherein no cushion layer is formed on the annular ditch and the water pumping well, the annular ditch and the water pumping well are paved in a mode of geotextile and double-layer plastic film 1, the upper return height of the geotextile is 200mm, and the plastic film is required to be pressed into the position 200mm below the cushion layer of the bottom plate;

arranging a longitudinal and transverse open trench at the bottom of the whole foundation pit, wherein the open trench is arranged below the elevation of the bottom plate, avoiding the position of a bearing platform and properly utilizing the position of a structural post-cast strip; the elevation of the bottom of the circular ditch is properly lower than that of a longitudinal and transverse open ditch in the field, and then water is continuously pumped and drained in the water collecting well 2 by a water pump to reduce the underground water level of the bottom of the well;

step two: as shown in fig. 4: before the bottom plate 3 is constructed, the open trench is reformed into a blind trench, gravels are backfilled in the open trench, a PVC pipe is wrapped in the gravel layer, double-layer dense meshes are fully paved above and below the gravel layer 4 to isolate soil and a cushion layer, holes 5 are formed in the side wall of the PVC pipe, hole positions are preferably small and dense, and water flow of the blind trench is collected and guided to the annular trench;

step three: as shown in fig. 5: before backfilling the outer wall, reforming an annular ditch and a water collecting well, removing a plastic film in the annular ditch and the water collecting well, backfilling by graded broken stones to form a blind ditch and a water absorption pit 7, combining the blind ditch and a drainage network under post-cast to form an underground drainage network, vertically embedding a PVC pipe 6 at the position of the water absorption pit, perforating the part of the tail end of the pipeline extending into the well, and keeping the upper end of the pipeline 2 meters higher than the construction surface of the structure; the submersible pump sinks into the water absorption pit through the PVC pipe, and continuously pumps and discharges to maintain the underground water level and release the water pressure;

step four: as shown in fig. 6: during the basement structure construction, along with the outer wall backfill progress, upwards continue to connect the PVC tube well, when the groundwater was walked around the stagnant water curtain and is permeated in the foundation ditch outside the foundation ditch, can be by the blind ditch network direction pit that absorbs water, recycle auto-induction's ball valve immersible pump, automatic hose 8 pump drainage at once after the water level rose, continuous control ground water level.

The process principle is as follows:

in the stage of excavation of the bearing platform base plate, annular ditches are dug at the periphery of the bottom of the pit, water collecting wells are arranged on the annular ditches at equal intervals, longitudinal and transverse open ditches (sand-depositing wells are properly arranged in the middle of the foundation pit) are dug at the bottom of the foundation pit, the open ditches are communicated with the annular ditches, and a water pump is placed in the water collecting wells to pump and drain outwards, so that the underground water level is continuously reduced, and the construction requirements of the base plate are met.

Before the bottom plate construction, the open trench and the sand sediment well are backfilled by using broken stones to form a blind trench, PVC drain pipes with holes on the side walls are placed in the broken stone layers of the blind trench and are connected in a longitudinal and transverse mode to form an underground dredging and draining network which is directly communicated with a circular trench, and the backfilled broken stone layers are isolated from soil and a concrete cushion layer by using dense mesh nets.

Before backfilling the outer wall, an annular ditch and a water collecting well on the periphery of the bottom of the foundation pit are reformed in the same way, meanwhile, a vertical PVC pipe well is reserved at the water collecting well, a ball valve deep well submersible pump is arranged in the pipe well, and a PVC pipe is continuously connected upwards along with backfilling of the outer side of the basement until reaching the ground.

During the whole structure construction period, groundwater outside the foundation pit permeates into the foundation pit and must bypass the bored concrete pile waterproof curtain of the circumference, the annular ditch and the water collecting well water level tightly attached to the waterproof curtain change firstly, the ball valve floats upwards, the submersible pump starts along with the annular ditch, groundwater is pumped outwards, and the effect of continuous control of the groundwater level is achieved.

Claims

1. A method for controlling the underground water level of a permeable-weakly layer of a large-area deep foundation pit is characterized by comprising the following steps:

the annular groove is arranged on the periphery of the bottom of the foundation pit, the root of the support pile is attached, the width is 600mm, the depth is 300mm, and the top of the annular groove is equal to the bottom elevation of the bottom plate cushion layer of the structure; inserting a DN1200 double-wall corrugated pipe with the length of 1m or finished concrete into the annular ditch to serve as a water collecting well, wherein no cushion layer is formed on the annular ditch and the water pumping well, the annular ditch and the water pumping well are paved in a mode of geotextile and double-layer plastic film, the upper return height of the geotextile is 200mm, and the plastic film is required to be pressed into the position 200mm below the cushion layer of the bottom plate;

step two: before the bottom plate construction, the open ditch in the yard is reformed into a blind ditch: backfilling broken stones in the open trench, wrapping PVC pipes in the broken stone layer, fully paving double-layer dense mesh nets above and below the broken stone layer to isolate soil and a cushion layer, forming holes on the side walls of the PVC pipes, and leading hole positions to be small and dense to collect blind trench water flow and guide to the annular trench;