CN113250220A

CN113250220A - Novel dewatering method for deep foundation pit close to existing building

Info

Publication number: CN113250220A
Application number: CN202110520367.6A
Authority: CN
Inventors: 黄玉林; 王聪; 鲜兵
Original assignee: China Railway No 5 Engineering Group Co Ltd; Chengdu Engineering Co Ltd of China Railway No 5 Engineering Group Co Ltd
Current assignee: China Railway No 5 Engineering Group Co Ltd; Chengdu Engineering Co Ltd of China Railway No 5 Engineering Group Co Ltd
Priority date: 2021-05-13
Filing date: 2021-05-13
Publication date: 2021-08-13

Abstract

The invention discloses a novel dewatering method for a deep foundation pit close to an existing building, which specifically comprises the following steps: construction preparation, namely flattening a field, lofting a well position by using a total station, and constructing a sewage system; step two: logging off well positions and digging a exploration well; measuring the well placement position according to actual requirements, wherein the distance from the central position of the dewatering well to the center of the fender post is 1.4m and the distance from the central position of the dewatering well to the edge of the foundation pit is 2.0m according to the placement position of the dewatering well; if the enclosing range and other conditions limit and the requirements cannot be met, arranging the dewatering well between the enclosing piles or in the foundation pit; step three: embedding a mouth guard pipe, accurately and stably embedding a pile casing according to the pile position determined by measurement, and arranging 2 grout overflow ports at the top of the pile casing, wherein the grout overflow ports are 20cm higher than the ground; the method can effectively solve the problems of low construction efficiency and poor precipitation settling effect in subway construction due to complicated environment near a station site and staggered environment of an underground water system and nearby buildings.

Description

Novel dewatering method for deep foundation pit close to existing building

Technical Field

The invention belongs to the technical field of subway construction, and particularly relates to a novel dewatering method for a deep foundation pit close to an existing building.

Background

In the subway construction process, a dewatering well is often arranged to protect the foundation structure of the subway, and due to the complex environment near the subway and the staggering of an underground water system and a nearby building, the effect of the existing dewatering well construction method cannot be completely applied or the efficiency is insufficient.

Buildings near the subway construction comprise various commercial buildings, original various subway loops, original vegetation and the like; underground water systems near subways are more complex and mainly comprise a filling layer, a sticky silt layer, a pebble layer, a sand-pebble layer and the like, and all the performances of different levels are the same;

the pebble layer has the characteristics of good water permeability, good water-rich property and large water inflow amount, the stability of the pebble layer in a natural state is poor, and the self-stability of pebbles is reduced after the underground water level is reduced; during the precipitation process of the foundation pit, a large amount of fine particulate matters in the stratum are easily lost, sand is formed and is corroded, ground settlement, pit wall collapse and ground deformation are caused, and the safety of surrounding structures, buildings and underground pipelines is endangered.

The existing construction method of the subway dewatering well and the existing dewatering well cannot cope with the complicated environment.

Disclosure of Invention

The invention provides a novel method for lowering water near a deep foundation pit of an existing building, and aims to solve the existing problems.

The invention is realized by the following steps,

the method comprises the following steps: construction preparation, namely flattening a field, lofting a well position by using a total station, and constructing a sewage system;

step two: logging off well positions and digging a exploration well; measuring the well placement position according to actual requirements, wherein the distance from the central position of the dewatering well to the center of the fender post is 1.4m and the distance from the central position of the dewatering well to the edge of the foundation pit is 2.0m according to the placement position of the dewatering well; if the enclosing range and other conditions limit and the requirements cannot be met, arranging the dewatering well between the enclosing piles or in the foundation pit;

step three: embedding a mouth guard pipe, accurately and stably embedding a pile casing according to the pile position determined by measurement, and arranging 2 grout overflow ports at the top of the pile casing, wherein the grout overflow ports are 20cm higher than the ground;

step four: installing a drilling machine, wherein a rotary drilling hole forming process is adopted in dewatering well construction, the base level of the drilling machine is adjusted to be vertical to a drilling tower when the drilling machine is in place, the drilling machine is cushioned by a machine table wood, the drilling machine is stably arranged after the drilling machine is aligned to a hole position, a drilling rod is vertical, and the alignment deviation is not more than 50 mm;

step five: drilling to form a hole, wherein the hole diameter of the open pore of the dewatering well is phi 600 mm; in the drilling process, slurry in the hole is ensured to keep a certain water head height, and the collapse of the hole wall is prevented; under the condition that the formation condition allows, the formation self-made mud is used as much as possible for forming the hole;

step six: cleaning holes and changing slurry, after drilling to a designed elevation, lifting the drill rod to be 0.50m away from the bottom of the hole before lifting the drill, punching to remove impurities in the hole, simultaneously gradually adjusting the density of the slurry in the hole to 1.05, and enabling the returned slurry not to contain mud blocks;

step seven: hoisting a well casing, hoisting by adopting a crane, slowly lowering, connecting the well casing when the difference between a pipe orifice and a well mouth is 200mm, and connecting by adopting steel rings at two welded ends; in order to prevent the dislocation of the upper and lower sections, the well pipe is erected in the well direction before the pipe is put down;

step eight: filling filter materials, wherein the filter materials are uniformly filled along the periphery of the well hole and continuously extruded out of the well hole; when the filter material is filled, the filling height of the filter material is measured along with filling, and when the filling amount is inconsistent with the theoretical calculation amount, the reason is searched in time; a loader is not needed to be used for direct filling, and a shovel is used for blanking so as to prevent uneven or impact on a well wall;

step nine: washing a well by adopting an air compressor, wherein the well washing of the air compressor is not less than 2 machine shifts; the well washing is carried out within 8 hours of the completion of the well, so that the phenomenon that the wall protection mud skin is aged gradually and is difficult to damage and the water seepage effect is influenced due to overlong time is avoided;

step ten: a pump is arranged for trying to pump, and after well completion construction is finished, a submersible pump is timely put into the well to drain drainage pipelines, cables and the like;

step eleven: the drainage pipe of the dewatering well adopts an in-pipeline drainage system and is provided with a sedimentation tank; the setting of the sedimentation tanks is arranged according to the distribution condition of a municipal pipe network on site and the construction general plane layout of the station, and water extracted from two sedimentation tanks is discharged into a city rainwater pipe after five-stage sedimentation;

step twelve: pumping water by adopting each pump pipe of each well to drain, collecting the ground pipes into a sedimentation tank, precipitating the pumped water by the sedimentation tank and filtering by a filter screen, separating sand mud and impurities, and then intensively discharging the water into a municipal pipeline, wherein the sedimentation tank is provided with a sewer close to an access port of a city pipe network;

thirteen step; in order to ensure the safety of the foundation pit supporting structure, the sedimentation tank and the drainage pipeline are strictly impermeable and leak-proof.

Based on the novel method for lowering the water level near the deep foundation pit of the existing building, in the second step, the pipeline on the known site is marked obviously, and the pipeline is prevented from being broken in the drilling process; before drilling, a measurer determines a central line of exploratory trench excavation according to pile center coordinates of a pile foundation plane layout drawing, the exploratory trench adopts slope excavation, the slope of the slope is 1:0.25, the width of an upper opening is 4.5m, the width of a base is 3m, and the excavation depth below the earth surface is not less than 3 m; for pipelines possibly with unknown pipelines under the exploratory ditches, firstly exploring by using a geophysical prospecting device, then exploring by using a Luoyang shovel for 2m, if suspicious pipelines are discovered, manually and carefully excavating to the pipelines, arranging a specially-assigned person to track the responsible guidance excavation, exploring the pipeline condition, and timely contacting with property units for migration and modification or protection; when the well point is affected by ground obstacle or construction condition, the site can be adjusted properly.

Based on the novel method for lowering the water level near the deep foundation pit of the existing building, in the third step, the pile casing is rolled by a steel plate with t being 6mm, the length is 3m, the inner diameter of the construction pile casing is larger than the diameter of a drill bit by 10cm, the pile casing is embedded by adopting an embedding method, a pile position locator is used for ensuring that the center of the pile casing is consistent with the center of the pile position, and the deviation is not more than 50 mm; the water level of the slurry surface in the protective cylinder is higher than the underground water level by more than 1.5 m.

Based on the novel dewatering method for the deep foundation pit close to the existing building, in the fifth step, if the drilled hole passes through a sand flowing layer of a hole easy to collapse or a stratum with serious slurry loss, the slurry is manually mixed to protect the wall for drilling, and the specific gravity of the slurry is controlled within the range of 1.10-1.30.

Based on the novel method for lowering the water level of the deep foundation pit close to the existing building, in the seventh step, the hoisting well pipe is kept vertical and kept in the center of the well hole, in order to prevent rainwater, mud and sand or foreign materials from flowing into the well, the well pipe is higher than the ground by not less than 200mm, and a temporary protection cover is added.

Based on the novel dewatering method close to the existing building deep foundation pit, the method further comprises the steps of intercepting and draining water outside the foundation pit and draining water in the foundation pit.

Based on the novel dewatering method close to the existing building deep foundation pit, the drainage steps outside the foundation pit specifically comprise: c30 reinforced concrete retaining sills which are 30cm higher than the ground and 30cm thick are arranged at the top of the top beam of the foundation pit to seal the foundation pit and prevent surface water from flowing back into the foundation pit, C30 concrete is adopted for hardening treatment on the ground outside the retaining wall, 450 mm-400 mm reinforced concrete drainage ditches are arranged along the periphery of the foundation pit at the outside according to actual site, and the concrete is C30; a rain grate with the thickness of 450 x 750mm is arranged at the top of the ditch and is used for collecting surface water outside the foundation pit formed by rainfall; set up the sedimentation tank according to the actual conditions in place, the interior ponding of escape canal is through the sedimentation tank after deposiing, discharges into municipal administration rain and sewage pipe network.

Based on the novel dewatering method close to the existing building deep foundation pit, the step of open drainage in the foundation pit specifically comprises the following steps: measuring and positioning a drainage ditch and a water collecting well → digging the drainage ditch, the water collecting well and a sedimentation tank → checking the gradient and the direction of flowing water → finishing and leveling → installing pumping equipment → draining construction.

Based on the novel method for dewatering the deep foundation pit close to the existing building, the structure of the dewatering well is respectively set to be a general stratum dewatering structure and a special stratum water filter pipe structure in different environments: the general stratum precipitation structure is specifically as follows;

the well pipe is made of reinforced concrete pipe with the inner diameter of phi 300, and 1 layer of 50-mesh nylon net is coated outside the reinforced concrete pipe; the water filter pipe adopts a reinforced concrete pipe with strip-shaped holes, each length is 2.5m, the total length of the water filter pipe is 5m, the filter material adopts clean pebbles, the specification is 3-8 grades, the non-uniform coefficient is less than 2, and the impurity content is not more than 3%.

Based on the novel method for dewatering the deep foundation pit close to the existing building, the structure of the special stratum water filter pipe specifically comprises the following steps: when the filter pipes of the precipitation well with the main structure are all positioned in the compact pebble soil layer and are far away from the lens sand layer, all the filter pipes of the precipitation well do not penetrate through the sand-containing layer, so that precipitation cannot cause a large amount of fine sand loss, and the filter pipes are constructed by wrapping a layer of nylon net outside

Compared with the prior art, the invention has the beneficial effects that:

1. the method can effectively solve the problems of low construction efficiency and poor precipitation settling effect in subway construction due to complicated environment near a station site and staggered environment of an underground water system and nearby buildings.

Drawings

FIG. 1 is a process flow diagram of the construction process of the foundation pit dewatering well;

FIG. 2 is an enlarged view of the construction details of the dewatering well in embodiment 3 of the present invention;

FIG. 3 is a schematic view of the overall structure of a dewatering well in embodiment 3 of the present invention

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

In the description of the present invention, it is to be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on the orientations or positional relationships illustrated in the drawings, and are used merely for convenience in describing the present invention and for simplicity in description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, are not to be construed as limiting the present invention. Further, in the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

Example 1

The method is specifically implemented in a station of No. 13 line of a subway in a certain city, the station is arranged along the road in the east-west direction, underground pipelines are distributed in a field range and mainly comprise rainwater, sewage, water supply, gas, electric power, communication and the like, the minimum distance between a main foundation pit and a surrounding house is about 2m,

two rows of vertical sleeve valve pipes are arranged along the periphery of a house foundation for grouting, the interval between the vertical sleeve valve pipes and the house foundation is 1.0m, the vertical sleeve valve pipes and the house foundation are arranged in a quincunx manner, inclined holes are arranged to the lower side of the house projection as far as possible, and the area which cannot be reinforced is reduced as far as possible. The drilling arrangement can properly adjust the drilling position and spacing according to the actual situation on site. And after the whole grouting is finished, adopting cement mortar to plug the drilled hole. The grouting depth is 2m below the substrate;

a fourth artificial filling layer (Q4ml) is covered in the field range; the fourth system is totally new flood surging layer (Q4al + pl) of silty clay, clay silty soil, fine sand, medium sand and pebble. And dividing rock-soil layers according to layering basis and combining the geological section of the engineering. Each geotechnical layer is described as follows:

(1) fourth system complete new union artificial filling (Q4ml)

<1-1> miscellaneous fill, which is miscellaneous color, loose, slightly wet. Mainly takes backfilled broken stones, bricks, construction wastes which are newly removed and left, original building foundations and terrace vestiges as main materials. The layers are distributed in the field range generally, and the thickness of each layer is 1.0-4.0 m.

(2) The fourth is the new system Honghua layer (Q4al + pl)

<2-2> powdery clay: the coating is yellow brown, gray yellow and brown gray, is plastic, is locally hard and plastic, has slight lustrous reaction, no shaking reaction, medium dry strength and medium toughness, mainly comprises sticky particles, contains a small amount of powder particles, is slightly sandy by hand twisting, is generally distributed in a field range, and is 0.7-3.6 m thick.

<2-3> clay silt: earthy yellow and gray yellow, dense-dense, wet, clotted, fragile by hand kneading, pure, no-gloss reaction, moderate shaking reaction, low dry strength, low toughness, mica-containing, mainly distributed in a pebble layer, the layer developing like a lens, only M13CZ-SBWG-005 is disclosed in the exploration, and the layer thickness is 1.3M-1.8M.

<2-4-1> Fine Sand: grayish and grayish yellow, wet-saturated and loose, and its main components are feldspar and quartz, and mica is used for the second time, and a small quantity of pebbles are partially sandwiched between them. The layer is distributed on the upper part of the pebble in a lens shape in the field. The layer thickness is 0.8-1.6 m.

<2-4-2> medium sand: grayish brown, grayish green, slightly dense, pure in quality, wet to saturated, with feldspar and quartz as main components, mica as secondary components, and individual pebbles partially sandwiched. The layer is distributed in the pebble layer in a lens shape in the field, and is only exposed at a part of the drilled hole. The layer thickness is 0.4-1.2 m.

<2-5> pebble: brown gray, light gray, wet-saturated, slightly dense-dense as main, loose part. The pebble component mainly comprises magma rocks and metamorphic rocks. The abrasive disc has good roundness, mainly sub-circular shape, small amount of circular shape, poor sorting property and moderate to slight weathering. The pebble layer is distributed with medium sand lens with uneven thickness and random distribution.

<2-5-1> loose pebbles: brown gray, light gray, wet-saturated, pebble composition is mainly magma rock and metamorphic rock. The abrasive wheel has good roundness, mainly sub-circular shape, small amount of circular shape, poor sorting property, and moderate weathering and slight weathering. The pebble content is about 50-55%, the particle size is generally 20-100mm, and the particle size is respectively more than 200 mm. The pebbles are filled with the round pebbles, the medium and fine sands, the roundness of the pebble mill is better, and the sorting property is poorer. The thickness of the layer is 1.1-7.6 m.

<2-5-2> slightly pebble: brown gray, light gray, moist to saturated, slightly dense, pebbles accounting for about 55-60 percent, generally 50-150 mm in particle size, filled with round pebbles, medium and fine sands, mainly comprising sandstone, quartz sandstone, limestone, granite and the like, better in roundness grinding and poorer in sorting property. The thickness is 0.7 to 7.3 m.

<2-5-3> medium dense pebbles: brown gray, light gray and saturated, and the pebble components mainly comprise magma rocks and metamorphic rocks. The abrasive wheel has good roundness, mainly sub-circular shape, small amount of circular shape, poor sorting property, and moderate weathering and slight weathering. The pebbles have a content of about 60-70%, a particle size of generally 50-200mm, a particle size of more than 480mm, and a layer thickness of 0.6-16.4 m.

<2-5-4> dense pebbles: brown gray, light gray and saturated, and the pebble components mainly comprise magma rocks and metamorphic rocks. The roundness is good, the roundness is mainly sub-circular, and the weathering is moderate-slightly. The content of cobbles is more than 70 percent, the particle size is generally 50-200mm, and the particle size is respectively more than 400 mm. Good roundness grinding, poor sorting, filling with round gravel and medium sand. Drilling to expose a layer thickness of 1-39.0 m;

the geology of the station in this embodiment is from top to bottom in proper order: 1-1 part of miscellaneous filling soil, 2-2 parts of powdery clay, 2-5-1 parts of loose pebbles, 2-5-2 parts of slightly dense pebbles, 2-5-3 parts of medium dense pebbles, 2-5-4 parts of dense pebbles and 2-4-1 parts of fine sand, wherein a station structure is mainly positioned in a pebble layer;

the ground water of the station mainly belongs to the fourth series of pores for diving, and the main aquifer is a sandy gravel layer and a single-layer aquifer, belonging to the medium complex field of precipitation engineering. During exploration (water-rich period), the underground water level buried depth is 3.70-5.50 m and the elevation is 498.6-500.71 m. The main excavation strata are filled with soil, clay silt and pebble beds. The excavated stratum has poor self-stability, and meanwhile, the pebble layer has the characteristics of good water permeability, good water-rich property and large water inflow amount, the stability of the pebble layer in a natural state is poor, and the self-stability of the pebbles is reduced after the underground water level is reduced; during the precipitation process of the foundation pit, a large amount of fine particulate matters in the stratum are easily lost, sand is formed and is corroded, ground settlement, pit wall collapse and ground deformation are caused, and the safety of surrounding structures, buildings and underground pipelines is endangered. According to the engineering characteristics and hydrogeological conditions of a site, combining the experience of dewatering in the construction of subway foundation pits in the urban area, adopting a pipe well dewatering scheme to reduce underground water in the excavation of the engineering foundation pit, wherein the dewatering depth is reduced to below 1.0m of an excavation surface;

the invention provides a technical scheme, as shown in figure 1: a novel dewatering method for a deep foundation pit close to an existing building specifically comprises the following steps:

(1) leveling field

Before formal approach construction, after pipeline investigation, manually excavating a trench if necessary, clearing obstacles within 2 meters below the ground of a construction site, making protective measures which cannot be cleared, and then leveling and tamping; meanwhile, the positions of construction machinery, a conveying pipeline and a power line are reasonably arranged, and the tee joint of a construction site is guaranteed to be flat.

(2) Well position lofting

Before construction, the control point of dewatering well construction is measured with total station, buried stone is marked, after the test line is passed, the pile position is laid on site with steel ruler and measuring line, and the pile is nailed tightly with bamboo stick, and the error is not more than 2 cm. A fixed pile is arranged at the turning position of the axis of the dewatering well, and a control pile is arranged on the construction axis.

(3) Building sewage discharge system

The construction process of dewatering well will produce waste slurry, the waste slurry is led into a sedimentation tank, the sedimentation tank is processed into 2 x 1.5 x 3m steel plate on site, and the clear water after sedimentation can be discharged without pollution according to site conditions. The settled soil is aired and then transported out of the field.

2) Logging and releasing well positions and digging and exploring wells:

and measuring the well placement position according to the dewatering well point plane layout drawing, wherein the distance from the central position of the dewatering well to the center of the fender post is 1.4m and the distance from the central position of the dewatering well to the edge of the foundation pit is 2.0m according to the laying position of the dewatering well. If the restriction of the enclosing range and other conditions cannot meet the requirement, the dewatering well can be arranged between the enclosing piles or in the foundation pit. If special conditions (such as underground obstacles, ground or air obstacles) occur, the well position needs to be adjusted, and technicians are informed of the on-site adjustment in time.

Combining the issued pipeline data to obviously mark the pipeline on the known site, and preventing the pipeline from being broken in the drilling process; before drilling, a measurer determines a central line of exploratory trench excavation according to pile center coordinates of a pile foundation plane layout drawing, the exploratory trench adopts slope excavation, the slope of the slope is 1:0.25, the width of an upper opening is 4.5m, the width of a base is 3m, and the excavation depth below the earth surface is not less than 3 m; and (3) exploring pipelines possibly with unknown pipelines under the exploratory ditch by adopting a geophysical prospecting device, then exploring for 2m by using a Luoyang shovel, if suspicious pipelines are discovered, manually and carefully excavating the pipelines, arranging a specially-assigned person to track the responsible guidance excavation, exploring the pipeline condition, and contacting property units to carry out migration or protection in time. When the well point is affected by ground obstacle or construction condition, the site can be adjusted properly.

3) Burying a mouth protecting pipe: and (4) accurately and stably burying the pile casing according to the pile position determined by measurement. The protective cylinder is made of a steel plate with the length of 3m and the t being 6mm, the inner diameter of the protective cylinder during construction is 10cm larger than the diameter of the drill, and the top of the protective cylinder is provided with 2 grout overflow ports which are 20cm higher than the ground. The pile casing is buried by digging and burying method, and the pile position locator is used to ensure the center of the pile casing to be consistent with the center of the pile position, and the deviation is not more than 50 mm. The water level of the slurry surface in the pile casing is higher than the underground water level by more than 1.5m, so that the hole wall is not collapsed, and the outer side of the pile casing is densely backfilled with clay.

4) Installing a drilling machine: the construction of the dewatering well adopts a rotary drilling hole forming process, the base of the drilling machine is adjusted to be horizontal and vertical to the drilling tower when the drilling machine is in place, the drilling machine is cushioned by machine wood, the drilling machine is stably arranged after the drilling machine is aligned with a hole position, a drilling rod is vertical, and the alignment deviation is not more than 50 mm.

5) Drilling to form a hole: the aperture of the dewatering well is phi 600 mm. And the slurry in the hole is ensured to keep a certain water head height in the drilling process, so that the hole wall is prevented from collapsing. Under the condition that stratum conditions allow, stratum self-made slurry is used as much as possible for pore forming, if a drilled hole passes through a shifting sand layer of a hole easy to collapse or a stratum with serious slurry loss, manual stirring slurry is used for wall protection drilling, and the specific gravity of the slurry is controlled within the range of 1.10-1.30.

6) Cleaning holes and replacing slurry: and after drilling to a designed elevation, lifting the drill rod to 0.50m away from the bottom of the hole before lifting the drill, punching to remove impurities in the hole, and simultaneously gradually adjusting the density of slurry in the hole to 1.05 until the returned slurry does not contain mud blocks.

7) Hoisting a well pipe: the well casing adopts reinforced concrete pipe, and the strainer adopts the reinforced concrete pipe of taking the bar hole, and 50 mesh nylon wire nets of one deck outsourcing adopt the crane hoist and mount, slowly transfer, when the mouth of pipe differed 200mm with the well head, connect the well casing of festival, adopt the steel ring at welding both ends to connect. In order to prevent the upper and lower sections from being dislocated, the well pipe is erected in the well direction before the lower pipe is placed. The well pipe is vertically hung and kept in the center of the well hole, in order to prevent rainwater, mud and sand or foreign materials from flowing into the well, the well pipe is not less than 200mm higher than the ground, and is covered with a temporary protection.

8) Filling a filter material: the filter material is graded in a specification of 3-8 mm, the non-uniformity coefficient is less than 2, and the impurity content is not more than 3%. Sampling detection is carried out after the filter material enters a field, and blanking can be carried out after the filter material meets the requirements. And filling a filter material immediately after the well pipe is put into the well pipe. The filter material is uniformly filled along the periphery of the well bore, and the slurry is extruded out of the well bore while the filter material is continuously maintained. When the filter material is filled, the filling height of the filter material is measured along with filling, and when the filling amount is inconsistent with the theoretical calculation amount, the reason is timely searched. The direct filling of a loader and the blanking of a shovel are avoided, so that the uneven or impact on the well wall is prevented. And (4) after well washing, if the filter material sedimentation is too large, filling.

9) Well flushing: and (3) washing the well by adopting an air compressor, wherein the air compressor is not less than 2 machine shifts for washing the well, so that the well washing quality is ensured. The well washing is carried out within 8 hours of the completion of the well, so that the phenomenon that the wall protection mud skin is aged gradually and is difficult to damage to influence the water seepage effect due to overlong time is avoided. And observing the change conditions of the water level and the water yield in the well washing process.

10) Installing a pump for trying pumping: after the well completion construction is finished, a submersible pump is timely put into the well to arrange drainage pipelines, cables and the like, and the cables and the pipeline systems are arranged by paying attention to avoid being rolled and damaged by an excavator, a crane and the like in the water pumping process, so that the equipment needs to be marked on site. After the water pumping and draining system is installed, the water pumping can be tried.

11) The drainage pipe of the dewatering well adopts an in-pipeline drainage system and is provided with a sedimentation tank. The setting of sedimentation tank is arranged according to the distribution condition of municipal pipe network on site and the general construction plane layout of this station, and two sedimentation tanks (cover plate construction stage and main structure construction stage) are set up altogether, and the water that extracts is discharged into city downspout after five grades of deposits.

13) Pumping water adopts each pump calandria precipitation of each well, ground calandria concentrates to the sedimentation tank, and the water of taking out is through sedimentation of sedimentation tank and filter screen filtration, separates behind sand mud and debris, concentrates again and discharges into municipal administration pipeline, and the sedimentation tank preparation position is close to the sewer of city pipe network access mouth (the specific position is confirmed on the spot).

14) In order to ensure the safety of the foundation pit supporting structure, the sedimentation tank and the drainage pipeline are strictly impermeable and leak-proof.

Example 2

Based on the above embodiment, the scheme is also provided with a step of intercepting and draining water outside the foundation pit and a step of draining water in the foundation pit:

the concrete steps of the outer intercepting drainage of the foundation pit are as follows:

the top of the top beam of the foundation pit is provided with a C30 reinforced concrete retaining ridge which is 30cm higher than the ground and 30cm thick to seal the foundation pit and prevent surface water from flowing back into the foundation pit, the ground outside the retaining wall is hardened by C30 concrete, a reinforced concrete drainage ditch of 450mm x 400mm is arranged outside along the periphery of the foundation pit according to actual conditions, and the concrete is C30. And a rain grate with the thickness of 450 × 750mm is arranged at the top of the ditch and is used for collecting surface water outside the foundation pit formed by rainfall. Considering that the whole small mileage is high and the whole large mileage is low, a 2.5m 7.5m five-stage sedimentation tank is arranged at the large mileage end according to the actual situation on site, and accumulated water in the drainage ditch is discharged into a municipal rainwater and sewage pipe network after being precipitated by the sedimentation tank.

Wherein the step of open drainage in the foundation pit comprises the following steps:

the base plate of the foundation pit of the station is positioned in the pebble bed, and drainage must be performed by combining an open drainage method in order to ensure the dry operation construction in the foundation pit. The open drain method mainly adopts a precipitation scheme combining open drain and sump well drainage, and the sand production rate of drainage is strictly controlled during precipitation and is not more than 1/100000.

(1) Process flow

Measuring and positioning drainage ditch and water collecting well → digging drainage ditch, water collecting well and sedimentation tank → checking gradient and direction of flowing water → finishing and leveling → installing pumping equipment → draining construction

(2) Operation process

Firstly, the distance between the edge layer of the drainage ditch and the slope foot is not less than 0.3m, the width of the ditch bottom is 0.3m, and the gradient is 0.2-0.5%.

Secondly, a certain height difference is kept between the drainage ditch and the water collecting well, the bottom of the water collecting well is 1.0M lower than the bottom of the drainage ditch, and the bottom of the drainage ditch is 0.3-0.5M lower than the soil digging surface.

Thirdly, the diameter of the water collecting well is generally 0.7-1.0 m, the depth is 1.0m, the well wall can be temporarily supported by a soil retaining plate, a cement pipe or bricks, and gravel and a dense mesh net with the thickness of 0.3m are paved at the bottom of the well so as to prevent the water pump from being blocked by the silt.

And fourthly, the water pump water pumping faucet is wrapped by a filter screen to prevent mud and sand from entering the water pump.

Pumping water continuously until the foundation construction is finished and stopping after backfilling.

Example 3

Based on the above embodiment, as shown in fig. 2 to 3, the structure of the precipitation well is respectively set as a general formation precipitation structure and a special formation strainer structure in different environments:

1) general stratum dewatering structure

2) Structure of water filtering pipe for special stratum (sand-containing layer)

When the filter pipes of the dewatering well with the main structure are all positioned in the compact pebble soil layer and are far away from the lens sand layer, all the filter pipes of the dewatering well do not penetrate through the sand-containing layer, so that dewatering does not cause a large amount of fine sand loss, and the filter pipes are constructed by wrapping a layer of nylon net outside.

The present invention is not limited to the above preferred embodiments, and any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A novel dewatering method for a deep foundation pit close to an existing building is characterized in that: the method specifically comprises the following steps of,

step five: drilling to form a hole, wherein the hole diameter of the open pore of the dewatering well is phi 600 mm; in the drilling process, slurry in the hole is ensured to keep a certain water head height, and the collapse of the hole wall is prevented; using the formation self-made mud to form a hole when the formation conditions allow;

step ten: a pump is arranged for trying to pump, and after well completion construction is finished, a submersible pump is timely put into the well to drain a drainage pipeline and a cable;

2. The novel method for lowering water in a deep foundation pit near an existing building, according to claim 1, is characterized in that: in the second step, the pipeline on the known site is marked obviously, so that the pipeline is prevented from being broken in the drilling process; before drilling, a measurer determines a central line of exploratory trench excavation according to pile center coordinates of a pile foundation plane layout drawing, the exploratory trench adopts slope excavation, the slope of the slope is 1:0.25, the width of an upper opening is 4.5m, the width of a base is 3m, and the excavation depth below the earth surface is not less than 3 m; for pipelines possibly with unknown pipelines under the exploratory ditches, firstly exploring by using a geophysical prospecting device, then exploring by using a Luoyang shovel for 2m, if suspicious pipelines are discovered, manually and carefully excavating to the pipelines, arranging a specially-assigned person to track the responsible guidance excavation, exploring the pipeline condition, and timely contacting with property units for migration and modification or protection; when the well point is affected by ground obstacle or construction condition, the site can be adjusted properly.

3. The novel method for lowering water in a deep foundation pit near an existing building, according to claim 1, is characterized in that: in the third step, the pile casing is rolled by a steel plate with t being 6mm, the length is 3m, the inner diameter of the construction pile casing is larger than the diameter of a drill bit by 10cm, the pile casing is embedded by adopting an excavating and burying method, a pile position locator is used for ensuring that the center of the pile casing is consistent with the center of a pile position, and the deviation is not larger than 50 mm; the water level of the slurry surface in the protective cylinder is higher than the underground water level by more than 1.5 m.

4. The novel method for lowering water in a deep foundation pit near an existing building, according to claim 1, is characterized in that: in the fifth step, if the drilled hole passes through a flowing sand layer of a hole easy to collapse or a stratum with serious slurry loss, manual mixing slurry is used for protecting the wall and drilling, and the specific gravity of the slurry is controlled within the range of 1.10-1.30.

5. The novel method for lowering water in a deep foundation pit near an existing building, according to claim 1, is characterized in that: and seventhly, the hoisting and releasing well pipe is kept vertical and at the center of the well hole, in order to prevent rainwater, sand and foreign materials from flowing into the well, the well pipe is not less than 200mm higher than the ground, and the well pipe is covered with a temporary protection.

6. The novel method for lowering water level near a deep foundation pit of an existing building according to any one of claims 1-5, wherein: the method also comprises a step of intercepting and draining water outside the foundation pit and a step of draining water in the foundation pit.

7. The novel method for lowering water in a deep foundation pit near an existing building, according to claim 6, is characterized in that: the step of intercepting and draining water outside the foundation pit specifically comprises the following steps: c30 reinforced concrete retaining sills which are 30cm higher than the ground and 30cm thick are arranged at the top of the top beam of the foundation pit to seal the foundation pit and prevent surface water from flowing back into the foundation pit, C30 concrete is adopted for hardening treatment on the ground outside the retaining wall, 450 mm-400 mm reinforced concrete drainage ditches are arranged along the periphery of the foundation pit at the outside according to actual site, and the concrete is C30; a rain grate with the thickness of 450 x 750mm is arranged at the top of the ditch and is used for collecting surface water outside the foundation pit formed by rainfall; set up the sedimentation tank according to the actual conditions in place, the interior ponding of escape canal is through the sedimentation tank after deposiing, discharges into municipal administration rain and sewage pipe network.

8. The novel method for lowering water in a deep foundation pit near an existing building, according to claim 6, is characterized in that: the step of open drainage in the foundation pit specifically comprises the following steps: measuring and positioning a drainage ditch and a water collecting well → digging the drainage ditch, the water collecting well and a sedimentation tank → checking the gradient and the direction of flowing water → finishing and leveling → installing pumping equipment → draining construction.

9. The novel method for lowering water level near a deep foundation pit of an existing building according to any one of claims 1-5, wherein: the structure of the precipitation well is respectively set as a general stratum precipitation structure and a special stratum water filter pipe structure in different environments: the general stratum precipitation structure is specifically as follows;

10. A novel method of lowering water in a deep foundation pit adjacent to an existing building as claimed in claim 9, wherein: the structure of the special stratum water filter pipe is as follows: when the filter pipes of the dewatering well with the main structure are all positioned in the compact pebble soil layer and are far away from the lens sand layer, all the filter pipes of the dewatering well do not penetrate through the sand-containing layer, so that dewatering does not cause a large amount of fine sand loss, and the filter pipes are constructed by wrapping a layer of nylon net outside.