CN111851546A

CN111851546A - Construction method for sealing precipitation of drainage well in deep foundation pit construction

Info

Publication number: CN111851546A
Application number: CN202010494035.0A
Authority: CN
Inventors: 成军; 张烽; 李伟杰
Original assignee: Nantong University
Current assignee: Nantong University
Priority date: 2020-06-03
Filing date: 2020-06-03
Publication date: 2020-10-30

Abstract

The invention discloses a construction method for sealing precipitation of a drainage well in deep foundation pit construction, which comprises the following steps: (1) setting out and positioning a well point; (2) forming a hole; (3) drilling and protecting the wall; (4) cleaning holes; (5) a lower pipe; (6) filling gravel and stopping water; (7) washing the well; (8) water is tried to be pumped. The engineering project of the invention is constructed by adopting a method of layered precipitation and layered excavation by combining with the actual situation of the site. From the whole effect, the foundation pit soil body consolidation degree is good, and the observation water level outside the pit is stable, has created good condition for foundation pit earthwork excavation. The method completes the pouring from the earth excavation to the two horizontal concrete supports and then to the foundation slab cushion layer in a short time, thereby not only improving the working efficiency, but also shortening the time for exposing the deep foundation pit hazard source on the whole. The scene is still concentrated the pumping body of precipitation institute and is deposited in cistern and fire water pond, recycles when making things convenient for later stage major structure to construct, improves water resource utilization ratio.

Description

Construction method for sealing precipitation of drainage well in deep foundation pit construction

Technical Field

The invention belongs to the field of building construction, and particularly relates to a construction method for sealing precipitation of a drainage well in deep foundation pit construction.

Background

With the continuous development of urbanization and the increasing shortage of urban construction land, the safety of buildings and sites around construction projects is ensured by adding horizontal supports to the guard piles for deep foundation pit construction, and the outer waterproof curtain and the high-pressure rotary jet bottom sealing provide good conditions for sealing the deep foundation pit and lowering water.

The engineering field of the invention belongs to the coastal plain landform of the southeast front edge of the Yangtze river delta entrance. The cement floor is present in the field, the terrain slightly fluctuates, and the ground elevation is between +4.230 and + 4.530.

6-layer buildings are planned on the engineering ground, 2 layers of basements are arranged, and a piled raft foundation is adopted. The +/-0.000 engineering part is +4.950 and is divided into an underground garage area foundation pit and a car ramp area foundation pit, the area of the underground garage area foundation pit is about 6557 square meters, and the area of the two car ramp area foundation pits is 246 square meters. The general excavation depth of underground garage regional foundation ditch is about 9.45m, and the local deep excavation is dug deeply and is dug deeply 10.55m, and the regional maximum excavation depth of car ramp is about 5.1 m.

The design scheme of the total enclosure of the foundation pit is as follows: the peripheral enclosure body is formed by combining a cast-in-place pile row enclosure wall with an outer triaxial cemented soil mixing pile water-stop curtain, and two reinforced concrete supporting systems are vertically arranged in the foundation pit. Reinforcing the passive area around the foundation pit

Double-shaft cement-soil mixing pile and

high-pressure jet grouting pile. The reinforcing bodies of the double-shaft cement-soil mixing pile are distributed in a grid manner, and the width of the reinforcing bodies is about 5.2 m. The reinforcement depth ranged from the bottom of the first support to 4m below the substrate. And a space of 200 is kept between the fender pile and the passive region reinforcement of the double-shaft cement-soil mixing pile, and compaction grouting @1000 is adopted for filling reinforcement. The deep pit area of the water collecting well with the falling depth of more than 1.5m is adopted

High-pressure jet grouting pile for pit periphery reinforcement and sealingAnd (5) bottom reinforcement. Guard post and

and hollow spaces between the waterproof curtains of the triaxial cement-soil mixing pile are filled and reinforced by adopting compaction grouting and are arranged along the periphery of the foundation pit.

The cast-in-place pile row pile enclosure wall combines the high-pressure jet grouting pile back cover reinforcement that the triaxial soil cement mixing pile in the outside and the sump pit region that the depth of fall is greater than 1.5m adopted, forms good stagnant water curtain at the foundation ditch periphery, can effectively block the groundwater inflow foundation ditch of foundation ditch lateral wall and foundation ditch bottom surface, forms the prerequisite that the foundation ditch seals precipitation construction at the foundation ditch precipitation stage.

Disclosure of Invention

The purpose of the invention is as follows: in order to solve the defects of the prior art, the invention provides a construction method for sealing precipitation of a drainage well in deep foundation pit construction.

The technical scheme is as follows: a construction method for sealing precipitation of a drainage well in deep foundation pit construction comprises the following steps: (1) well point setting-out positioning; (2) forming a hole; (3) drilling and protecting the wall; (4) cleaning holes; (5) a lower pipe; (6) filling gravel and stopping water; (7) washing the well; (8) trying to pump water; wherein:

The pore-forming: the aperture of the opening is 650mm, one drill reaches the bottom, and when the drilling construction reaches the design depth, the drill is more than 0.3-0.5 m; drilling construction description records are made, designers need to be informed in time in the drilling process if actual geological conditions are inconsistent with data provided in exploration, the structure of the well is adjusted in time, and the arrangement position of the water filter pipe can be ensured to be capable of effectively feeding water; when drilling and tapping, a large hook steel wire rope is hung tightly, the steel wire rope is slightly pressed and slowly rotated, the level of a drilling machine is ensured in the drilling process so as to ensure the verticality of a drilled hole, hole-forming construction adopts in-hole natural slurry making, the density of slurry is controlled to be 1.10-1.15 in the drilling process, and when the drilling machine is lifted or stopped, the slurry in the hole is fully pressed so as to prevent the hole wall from collapsing;

the lower pipe is as follows: a. before pipe laying, measuring and recording the well pipe water filter pipes one by one on the ground, pre-preparing on the ground, plugging the bottom of the settling pipe, and ensuring that the bottom of the settling pipe is firmly plugged, wherein the thickness of a lower plugging iron plate is not less than 4 mm;

b. well pipe welding: the welded joint of the well pipe adopts a sleeve joint type, the length of a sleeve joint coupling is 10mm, the sleeve joint coupling is sleeved into each of the upper well pipe and the lower well pipe by 5mm, the sleeve joint coupling is firmly welded with the well pipe, the welding seam is uniform and has no blowholes, the height of the welding seam is not less than 6mm, and the sleeve joint coupling is firmly welded with the well pipe by adding three iron plates or 1cm steel bars;

c. In order to ensure the centering of the filter pipe, centralizers are arranged at the upper part and the lower part of the filter pipe, each group of centralizers adopts omega-shaped iron rings with the width of 5-6cm, the number of the centralizers is 4, and the centralizer iron rings at the upper part and the lower part are staggered by 1/2 and are not on the same straight line; the diameter of the circumference formed by the 4 centralizers is less than the aperture of 10 cm;

d. the process of lowering the well pipe should be continuously carried out, and the well pipe should be stopped in the middle, for example, the well pipe should be pulled out again due to collapse or excessive deposition caused by mechanical failure, and then the well pipe should be lowered again after hole sweeping and hole cleaning, and the well pipe should be prevented from being forcibly inserted into the collapsed hole bottom.

As an optimization: and (3) well point setting-out positioning: according to the measurement control points provided by surveying and mapping units, measuring and setting out to determine the position of a well point, and excavating the well point; a small soil pit with the depth of 500mm is dug on site so as to collect water during hole opening and fill sand during pipe burying, and the small pit and the water pit are connected by a ditch so as to drain redundant water.

As an optimization: the drilling protection wall comprises: the specific weight of the drilling mud at the bottom of the hole is 1.10-1.15, and the sand content is less than 8%; the sand content of the returned mud is not more than 12%.

As an optimization: the hole cleaning: and (3) repeatedly sweeping the hole from top to bottom by adopting a drilling tool with the same diameter before the pipe is lowered, gradually replacing slurry in the hole by fresh dilute slurry while sweeping the hole, repeatedly sweeping the hole at the filter part, wherein slurry returned upwards in the hole does not contain a sludge block, the sand content is less than 12%, and when the specific gravity is 1.10, the slurry replacement is stopped, and the drilling tool is lifted.

As an optimization: gravel filling and water stopping: after the pipe is lowered, a well pipe is fixed to a middle hole opening by using a clamping plate, a drill rod is lowered into the well pipe to a position 50cm away from the bottom of the well for slurry replacement, and the well pipe and an active drill rod are connected and sealed and are impermeable; the drilling rod sends the slurry into the bottom of the well, and the slurry returns to the ground through the annular gap between the well pipe and the hole wall through the filter; the mud dilution should be carried out gradually and slowly, so that the specific gravity difference between the fed mud and the returned mud is not large, when the specific gravity of the upward returned mud in the hole reaches 1.05, the mud is backfilled by a moving water gravel filling method, and the pump amount is adjusted to be small according to the water returning condition of the hole opening; tracking and measuring the upward return height of the gravel material in the gravel filling process, and after the gravel material is compacted to the designed height, throwing clay between the well pipe and the hole wall for water stop, wherein the clay is high-quality yellow clay, the sand content is less than 5%, the thickness of the water stop clay is not less than 2m, and the hole opening is compacted by filling yellow mud;

the clay is crushed and filled before the enclosing filling, the grain diameter is preferably less than 3cm, the filling speed and the filling quantity are controlled during the enclosing filling, the enclosing filling is carried out along the periphery of the well pipe according to the principle of 'less than slow down', and then the sealing work is carried out outside the wellhead pipe.

As an optimization: the well washing: firstly, removing mud skin on a well wall, pumping out mud deep into a water-bearing stratum and recovering pores of the water-bearing stratum; pumping out a part of fine particles in the aquifer, expanding the pores of the aquifer and forming an artificial filtering layer; and the well washing adopts a sewage pump to repeatedly perform recovery pumping washing until the water is cleaned and sand is removed.

As an optimization: the water trying is carried out: after the well is washed, trial pumping is carried out in time, the water pump is placed in a filter section during trial pumping, the power of the water pump is determined according to design requirements and the pumping amount of the pumping well, the trial pumping time is controlled by taking sand removal of water pumped by the pumping well as the standard, and the control time is controlled to be 2 hours.

Has the advantages that: the engineering project of the invention is constructed by adopting a method of layered precipitation and layered excavation by combining with the actual situation of the site. From the whole effect, the foundation pit soil body consolidation degree is good, and the observation water level outside the pit is stable, has created good condition for foundation pit earthwork excavation. The method completes the pouring from the earth excavation to the two horizontal concrete supports and then to the foundation slab cushion layer in a short time, thereby not only improving the working efficiency, but also shortening the time for exposing the deep foundation pit hazard source on the whole. The scene is still concentrated the pumping body of precipitation institute and is deposited in cistern and fire water pond, recycles when making things convenient for later stage major structure to construct, improves water resource utilization ratio.

Drawings

FIG. 1 is a flow chart of the construction method for sealing precipitation of the drainage well in foundation pit construction.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below so that those skilled in the art can better understand the advantages and features of the present invention, and thus the scope of the present invention will be more clearly defined. The embodiments described herein are only a few embodiments of the present invention, rather than all embodiments, and all other embodiments that can be derived by one of ordinary skill in the art without inventive faculty based on the embodiments described herein are intended to fall within the scope of the present invention.

Examples

1 landform

1.1 engineering geological conditions

The engineering substrate is positioned in a fourth layer of gray muddy clay, and a first layer, a second layer, a third layer, an interlayer and a fourth layer of soil are arranged in a soil layer within the excavation depth range, wherein the third layer and the fourth layer are saturated muddy soil layers, and the creep phenomenon is easy to generate in the excavation process of a foundation pit.

The shallow powdery soil layer of the planned site is developed (the third interlayer is a sticky powdery soil layer), and the phenomenon of sand flowing or piping can be generated due to the water head difference in the excavation process of the foundation pit. Therefore, effective water retaining and isolating measures must be taken to ensure the construction safety of the engineering foundation pit.

The soil layer of the base can be divided into 7 layers and mainly comprises saturated cohesive soil, silty soil and sandy soil. The main characteristics of each soil layer are as follows:

the first 1 layer is made of variegated and miscellaneous filling soil, is loose, the surface layer is a cement floor, the lower part is cohesive soil containing plant roots, broken stones, bricks and the like, and the soil quality is loose and uneven.

The first 2 layers of gray black creek soil contain organic matter and rotten plants and have odor.

Secondly, the brown yellow to gray yellow powdery clay is wet to very wet, and can be molded to soft plastic and contains mica, iron oxide spots and iron manganese tuberculosis; a small amount of powder soil is added, and no shaking reaction occurs; moderate toughness, moderate dry strength and slight luster.

The third layer of gray silt silty clay is saturated, fluid plastic, contains mica and is sandwiched with thin layer silty soil; no shaking reaction; moderate toughness, moderate dry strength and slight luster.

Thirdly, the interlayer gray clay silt is saturated, loose and slightly dense, contains mica, and is interlayer with thin layer sand silt, and the local part of the interlayer gray clay silt is in a mutual layer shape; the shaking reaction is moderate; low toughness, low dry strength and no luster.

Fourthly, the layer of gray silty clay is saturated, flow-plastic, contains mica and organic matters and is even sandwiched with lamellar silty soil; no shaking reaction; the soil quality is uniform; high toughness, high dry strength and lustre.

The fifth layer of gray clay is wet, soft and plastic, contains mica, organic matters and humic substances, and is sandwiched with lamellar silt; no shaking reaction; high toughness, high dry strength and lustre.

Sixthly, 1, dark green powdery clay which is slightly wet, hard and plastic and contains iron oxide specks and iron manganese nodules is sandwiched with thin layer of powdery soil; no shaking reaction; moderate toughness, moderate dry strength and slight luster.

Sixthly, the straw yellow powdery clay is wet and plastic and contains iron oxide specks and iron manganese nodules and is laminated locally; no shaking reaction; moderate toughness, moderate dry strength and slight luster.

Seventhly 1, the grass yellow sandy silt is saturated, medium dense, contains mica, quartz, feldspar and the like, is sandwiched with thin layers of cohesive soil, has rough cut surface, low toughness, low dry strength and quick shaking reaction.

And seventhly 2, the gray yellow silt is saturated, dense, contains mica, quartz, feldspar and the like, and has poor grain composition.

1.2 hydrogeological conditions

(1) Diving

The underground water in the shallow soil layer of the proposed site belongs to a diving type, the main supply source is atmospheric precipitation, and the stable water level burial depth is 0.5-0.7 m.

(2) Confined water

The exploration depth of the planned site of the project is mainly provided with pressurized water on layers of sixty (2), seventy (1) and seventy (2). According to the long-term observation data of Shanghai city, the water level of the confined aquifer changes periodically, and the change range of the water level burial depth is generally 3.0-12.0 m.

The diving is carried out in shallow soil filling, cohesive soil and silty soil layers, wherein the interlayer is silty soil and is buried shallowly. The silty soil can produce bad phenomena such as quicksand, piping and the like under hydrodynamic force conditions, and in order to maintain the stability of the foundation pit, a vacuum dewatering well can be adopted for dewatering, so that the diving water level is lowered to below 1.0 meter of the bottom surface of the foundation pit, and a water level observation well is arranged in a certain range outside the foundation pit so as to know whether the waterproof curtain leaks or not in time.

2 Foundation pit piping stability analysis

And sixthly 2 to seventeenth 2 layers of confined water are distributed on the proposed site, the maximum buried depth of the engineering foundation pit is about 10.55m, and according to geotechnical engineering survey specifications of Shanghai city engineering construction specifications, the buried depth of a confined water head of the layer must be controlled in the excavation process to prevent the foundation pit from generating a piping accident, so that the stability analysis of the piping of the foundation pit must be carried out.

And (3) the stability condition of the foundation pit bottom plate against inrush is as follows: between the foundation pit bottom plate and the confined aquifer top plate, the deadweight pressure of soil is greater than the confined water jacking force at the confined aquifer top plate, and the confined water level can be controlled according to the following formula:

in the formula: f- - -safety factor (1.05)

hs- - -Foundation pit excavation depth (m)

D- - -safe bearing head burial depth value (m)

Gammas-layer thickness weighted average of soil layer gravities between foundation pit bottom plate and bearing water-containing layer top plate (18.00 kN/m3 is selected in the project)

Gammaw- - -groundwater gravity (10.00kN/m3)

According to the long-term observation and investigation of Shanghai city, the water level burial depth changes periodically, and is generally 3.0-12.0 m. The excavation depth of the project is 9.45-10.55 m, according to the survey report, the shallowest burial depth of the top of the confined aquifer of the field is about 27.90m, and the water head burial depth is taken as the worst 3.0 m.

The critical depth is calculated as:

(27.90-h0)×18.0＝(27.9-3.0)×10×1.05

H0＝13.30m

Namely: under the condition that the initial water level of the confined water is buried to be 3.0m, when the excavation depth of the foundation pit exceeds 13.30m, the water level of the confined water needs to be reduced, which means that the foundation pits of the engineering do not need to carry out dewatering treatment on the sixth to seventh gears 2 to 2.

3. Precipitation purpose and analysis of precipitation in pit

3.1 purpose of precipitation

(1) The water content of underground water of a shallow soil body in the field is reduced, so that the underground water level in the soil layer in the field is reduced, and an excavator and workers can conveniently carry out construction operation in a pit;

(2) and soil bodies in the foundation pit and under the pit bottom are consolidated, so that the consolidation degree of the soil body in the pit is improved, and the uplift of the pit bottom and the deformation of the foundation pit are reduced.

3.2 analysis of precipitation in pit

The foundation pit dewatering is carried out before earthwork excavation, deep wells are drained in vacuum in an underground garage area, light well points are used in a lane area, and the dewatering depth is controlled to be 0.5-1.0 m below the pit bottom. And pre-dewatering before excavation of the foundation pit for not less than 2 weeks. According to the hydrogeological conditions of the field and the excavation depth of the foundation pit, 31 dredging wells are arranged in the foundation pit of the engineering, and 6 diving observation wells are arranged outside the pit (the construction is closed when the structure is out of zero, and the operation is considered for 6 months).

TABLE 1 dewatering well information statistics table

(1) Dewatering deep well for main foundation pit

In order to ensure the smooth excavation of the foundation pit, the water content of the soil body within the excavation depth range of the foundation pit needs to be reduced, and the engineering needs to dry the diving in a certain depth above the excavation surface of the foundation pit.

Based on the geological conditions and the hydrological conditions of the existing site and according to the design condition of the engineering foundation pit support structure, the vacuum dewatering well is adopted for carrying out the dewatering of the submergence above the basement and near the basement.

Due to the special structure of the dredging well, free water in the soil layer is fully absorbed, collected in the deep well and discharged by a water pump in the deep well; meanwhile, as the free water is fully discharged, the pore ratio of the soil body is reduced under the action of gravity, the strength of the soil body is improved, and the method is very favorable for engineering construction safety and environmental protection.

The total area of the underground garage area is 6557m2, the excavation depth of a foundation pit of a general area is 9.5m, and the excavation depth of a bearing platform area is 10.55 m. In order to ensure the smooth excavation of the foundation pit, the underground garage area needs to be drained, and the layers I, II, III, IV and IV are submerged in the pit.

Wherein, the number of drained deep wells is determined according to the following formula:

n-A/a well

In the formula: n-well number (port);

area (m) of foundation pit to be drained²)；

a well-single well effective drainage area (m)²)

According to the experience of precipitation in Shanghai areas, the effective dewatering area a well of a single well in a diving aquifer is 200-250 m²Comprehensively considering the effective drainage area of a single well according to 200m²Arranging, 31 drainage wells are to be arranged, the well depth is 16.0m,

In the engineering foundation pit, a submersible observation well and an emergency standby well are required to be arranged, and 6 observation wells are arranged in total. In the dewatering and dewatering process, the water level change condition of a diving layer is timely and accurately mastered, the opening time of the dewatering well and the pumping and dewatering diving amplitude are controlled, the water level control is ensured to meet the requirement of foundation pit safety, and the influence of dewatering on the surrounding environment is reduced.

The principle of arrangement of the drainage wells is as follows:

in the foundation pit engineering, the well depth of the drainage well is conventionally required to exceed the bottom of the foundation pit by not less than 5 m.

When soil is adopted in the pit for reinforcement, the dredging well needs to avoid the pit.

The construction trestle and the pile foundation are avoided.

The dribbling well is provided with a plurality of filter heads, and solid pipes with proper lengths are arranged at the positions of the cross supports and the large bottom plate.

The diameter of the formed hole needs to meet the requirement that the thickness of the filler between the well wall and the hole wall is not less than 150mm, and the well position can be properly adjusted according to the actual situation on site during construction.

The shallow layer dredging well must give sufficient pre-pumping time (not less than 20 days), and the water level is controlled to be 1.0m below the excavation surface of the foundation pit according to the earthwork excavation progress.

(2) Light well point dewatering in lane area

And (3) adopting a light well point to carry out precipitation in the pit in the automobile ramp area, wherein the precipitation is required to be started 2 weeks before excavation, and the depth of the pre-precipitation in the pit is 1.0 meter below the pit bottom.

The length of the light well point branch pipes is not less than 7.0 m, the distance between the branch pipes is 1.5 m, and the well points at the side of each small foundation pit are 1 set. In order to guarantee construction period nodes and precipitation effect, 3 sets of well points are respectively arranged in two automobile ramp areas, and 6 sets of well points are counted.

And the water level in the foundation pit is reduced to 1.0 meter below the pit bottom, the excavation can be started, and the light well point in the pit stops dewatering after the bottom plate is poured for one week.

4. Closed dewatering construction of dewatering well for deep foundation pit construction

The construction flow of the invention is shown in the flow chart of the construction method for sealing precipitation of the drainage well in foundation pit construction in figure 1. The concrete well construction method comprises the following steps:

4.1 well Point payoff positioning

And according to the measurement control points provided by the surveying and mapping unit, measuring and setting out to determine the position of the well point, and excavating the well point.

A small soil pit is dug on site, the depth of the pit is about 500mm, so that water collection is facilitated during hole opening, sand filling is facilitated during pipe burying, and the small pit is connected with the water collection pit through a ditch so as to drain excess water.

4.2 Forming the holes

The aperture of the opening is 650mm, when the hole is drilled to the bottom, the hole is drilled to the designed depth, 0.3-0.5 m more hole is needed to be drilled. Drilling construction description records are made, designers need to be informed in time in the drilling process if actual geological conditions are inconsistent with data provided in exploration, the structure of the well is adjusted in time, and the arrangement position of the water filter pipe can be ensured to be capable of effectively feeding water. When drilling and tapping, a large hook steel wire rope is hung tightly, the steel wire rope is slightly pressed and slowly rotated, the level of a drilling machine is ensured in the drilling process so as to ensure the verticality of a drilled hole, hole-forming construction adopts in-hole natural slurry making, the density of slurry is controlled to be 1.10-1.15 in the drilling process, and when the drilling machine is lifted or stopped, the hole is fully pressed with slurry so as to prevent the hole wall from collapsing.

4.3 borehole wall protection

Dewatering well: because the upper part is mainly clay, the slurry is naturally made in the whole hole, the specific gravity of the slurry is 1.10-1.20, and the sand content is less than 3%. The specific weight of the drilling mud at the bottom of the hole is 1.10-1.15, and the sand content is less than 8%; the sand content of the returned mud is not more than 12%.

4.4 cleaning of holes

And (3) repeatedly sweeping the hole from top to bottom by adopting a drilling tool with the same diameter before the pipe is lowered, gradually replacing slurry in the hole by fresh dilute slurry while sweeping the hole, repeatedly sweeping the hole at the filter part, wherein slurry returned upwards in the hole does not contain a sludge block, the sand content is less than 12%, and when the specific gravity is 1.10, the slurry replacement is stopped, and the drilling tool is lifted.

4.5 lower tube

Before pipe laying, the water filter pipes of the well pipe are measured and recorded one by one on the ground, the water filter pipes are pre-prepared on the ground, the bottom of the sedimentation pipe is plugged, and in order to ensure that the bottom of the sedimentation pipe is firmly plugged, the thickness of a lower plugging iron plate is not less than 4 mm.

Well pipe welding: the welded joint of the well pipe adopts a sleeve joint type, the length of a sleeve joint coupling is 10mm, the sleeve joint coupling is sleeved in the upper well pipe and the lower well pipe by 5mm respectively, the sleeve joint coupling and the well pipe are welded firmly, the welding seam is uniform and has no sand hole, and the height of the welding seam pile is not less than 6 mm. The coupling and the well pipe are welded firmly by adding three iron plates or 1cm steel bars.

In order to ensure the centering of the filter pipes, centralizers are arranged at the upper part and the lower part of the filter pipes, each group of centralizers adopts omega-shaped iron rings with the width of 5-6cm, the number of the centralizers is 4, and the centralizer iron rings at the upper part and the centralizer iron rings at the lower part are staggered 1/2 and are not on the same straight line. The diameter of the circumference formed by the 4 centralizers is less than 10cm of the aperture.

The process of lowering the well pipe should be continuously carried out, and the well pipe should be stopped in the middle, for example, the well pipe should be pulled out again when the hole collapses or the sediment is too thick due to mechanical failure, etc., and the well pipe should be lowered again after hole sweeping and hole cleaning, and the well pipe should be prevented from being forcibly inserted into the bottom of the collapsed hole.

4.6 gravel pack and water stop

After pipe laying, the well pipe is fixed at the middle opening by a clamp plate, a drill rod is lowered into the well pipe to the bottom of the well (50 cm away from the bottom of the well) for slurry replacement, and the connection between the well pipe and the active drill rod is sealed and is waterproof. The drilling rod sends the mud into the bottom of the well, and the mud returns to the ground through the annular gap between the well pipe and the hole wall through the filter. The mud dilution should be carried out gradually and slowly, so that the specific gravity difference between the fed mud and the returned mud is not very large, when the specific gravity of the upward returned mud in the hole reaches 1.05, the mud is backfilled by a moving water gravel filling method, and the pump amount is adjusted to be small according to the water returning condition of the hole opening. Tracking and measuring the upward return height of the gravel material in the gravel filling process, and after the gravel material is compacted to the designed height, throwing clay between the well pipe and the hole wall to stop water, wherein the clay is high-quality yellow clay, the sand content is less than 5%, the thickness of the water-stopping clay is not less than 2m, and the hole opening is compacted by filling yellow mud.

The clay is crushed (with the particle size smaller than 3cm preferably) before the enclosing and filling to prevent the bridging phenomenon from generating during the enclosing and filling. During the enclosing filling, the entering speed and the entering quantity are controlled, and the enclosing filling is carried out along the periphery of the well pipe according to the principle of 'less slow down'. And then sealing work is done outside the wellhead pipe.

4.7 well flushing

The purpose of well washing is as follows: firstly, removing mud skin on a well wall, pumping out mud deep into a water-bearing stratum and recovering pores of the water-bearing stratum; pumping out partial fine particles in the aquifer, expanding the pores of the aquifer and forming an artificial filtering layer.

And the well washing adopts a sewage pump to repeatedly perform recovery pumping washing until the water is cleaned and sand is removed.

4.8 trial Water extraction

After the well is washed, trial pumping should be carried out in time, which is beneficial to dredging the hydraulic connection between the aquifer and the pumping well in time. When trying to pump water, the water pump is placed in the filter section, and the power of the water pump is determined according to design requirements and the water pumping amount of the water pumping well. The trial pumping time is controlled by taking the sand cleaning of water pumped by a pumping well as the standard, and the general control time is about 2 hours.

5. Operation after completion of closed dewatering construction of foundation pit construction dewatering well

5.1. Preparation before operation:

and putting into test operation after the construction of each well is finished so as to conveniently pump through the dewatering well in time to check the water outlet quality and the water outlet quantity.

Before test operation, the elevation and the static water level of each well mouth and the ground are measured, and then test operation is started to check whether the pumping equipment and the pumping and draining system can meet the requirement of precipitation.

Before installation, the pump body and the control system should be subjected to comprehensive and detailed inspection once. And (3) checking the rotation direction of the motor, whether the connecting bolts of all parts are screwed down, whether lubricating oil is sufficient, whether the seal of the cable joint is loosened, whether the cable is damaged or not and the like, and then rotating the cable joint on the ground for about 1min, so that the cable joint can be put into use if no problem exists. The submersible motor, cables and joints should be reliably insulated and each pump should be provided with a control switch.

Carefully checking whether the installation of the pumping equipment of each well meets the requirements, and performing water trial pumping for 5-10min after the installation is finished to ensure the normal operation of the pumping equipment.

Carefully checking whether the instrument of the monitoring system is intact, whether the signal reception is normal and whether the signal wire layout is safe.

In order to prevent the sudden occurrence of large area power failure and the failure of field circuit systems, power supply safeguards are necessary in the whole process of well operation.

5.2, formal precipitation operation:

the dewatering well is lowered at least 2 weeks ahead, vacuum negative pressure is loaded according to requirements to drain the foundation pit excavation soil body, and continuous water pumping is kept in the excavation process.

Before the drainage well pumps water formally, a monitoring unit should construct a submersible observation hole outside the pit as early as possible. And after the construction of the diving water level observation hole is completed, the drainage well is opened in time to drain water. Normally, the drain well is kept pumping water continuously for substantially 24 hours. When precipitation is abnormal, the adjustment is carried out according to the requirement.

The method for reducing the water level by adopting the vacuum pump and the submersible pump is adopted, wherein 1 vacuum pump is arranged in each 3 wells, one submersible pump is used in each well, the water pumping capacity of the submersible pump is required to be larger than the maximum water yield of the single well, and the vacuum degree of a vacuum pipeline during pre-pumping is larger than-0.06 MPa.

The engineering precipitation is used for pumping underground water, the water content in soil in the excavation range of the foundation pit is reduced, and therefore the requirement of the engineering precipitation is met by proper drainage facilities on a construction site, the smoothness of precipitation operation drainage is ensured, and the precipitation effect is guaranteed. For drainage facilities on a construction site, the design is carried out according to the actual conditions of engineering, but the following requirements are generally met:

(1) the drainage facility needs to meet the requirement of the maximum water yield of engineering precipitation and ensure the smoothness of drainage;

(2) the distance between the dewatering well and the drainage facility is shortened as much as possible, the loss of the water head along the drainage path of the dewatering well is reduced, and the lift consumption of the pumping equipment is reduced;

(3) according to the demand of drainage predicted by the project, a drainage ditch is arranged at the side of the foundation pit and is connected into the sedimentation tank. And then the water pumping body of the precipitation in the sedimentation tank is intensively stored in the reservoir and the fire pool by a water pump for later use.

5.3 well pipe dismantling:

the higher well pipe is cut off at any time along with the reduction of the excavation surface; after the cushion layer is poured, the normal operation of water pumping is required to be kept. The time for stopping pumping water is determined by the site of a building structure design unit according to the water content condition of the soil of the foundation pit. Generally, after the cushion layer is poured, the pump is stopped to remove the steel bars of the large bottom plate before the steel bars are placed. The well pipe is dismantled by a truck crane, the well pipe mouth is sleeved and slowly pulled out, the strainer is pulled out and cleaned and then used, and holes left after pulling out are filled with gravel and tamped.

5.4 deep well sealing:

the well sealing adopts a plugging method of filling sand and pebbles in a well pipe and then pouring concrete, and the basic operation sequence and the related technical requirements are as follows:

(1) after the foundation pit is dug to the designed elevation, a water stop plate is welded outside the steel pipe, and the diameter of the outer ring of the water stop plate is phi 600 mm.

(2) The sand and pebbles are filled into the well pipe layer by layer, the height of each layer is controlled within 30cm, and the backfill height is about 1.00m below the bottom plate of the foundation pit.

(3) After the sand pebbles are backfilled, quick-setting concrete is poured on the sand pebbles until the bottom surface of the bottom plate is raised.

(4) And (3) pouring concrete in the well pipe for the second time, wherein the concrete material is the same as the bottom plate concrete, and the upper part of the well pipe is sealed by full welding of round plates with the same diameter.

(5) After the foundation pit is excavated to the bottom of the foundation pit, a certain number of dewatering wells are kept to continuously operate so as to meet the anti-floating problem of the foundation pit.

5.5 water level monitoring of the submersible observation well outside the pit:

(1) according to the concrete conditions of the project, 6 diving observation wells are arranged outside the pit, and the method is the same as that in the pit.

(2) Determining that monitoring personnel are relatively fixed according to the actual conditions of the project, and carrying out duty for 24 hours; and setting up a duty report meeting the requirements, determining responsible persons and reporting time, and executing the duty report according to the requirements of owners and supervision strictly.

(3) All observation wells are monitored once a day, and records are made, and if abnormal encryption monitoring exists, the monitoring is carried out.

(4) The water level report reports the supervision and monitoring units on time every day.

6. Dewatering well pipe protection measure

(1) Before precipitation operation, arranging drainage pipelines of the precipitation well and connecting the drainage pipelines into a drainage facility on a construction site;

(2) before the precipitation operation, a precipitation power supply system is prepared and is provided with an independent power line;

(3) all the pumping wells are correspondingly marked on a power supply electronic box socket, a pumping pump cable plug and a drainage pipe, and corresponding marking change is carried out when the pumping wells change every time, so that pumping operation management is facilitated; the power supply electronic box is required to be checked regularly and provided with check records;

(4) before formal precipitation, trial operation is required, and whether a power supply system, a pumping device, a drainage system and an emergency plan can meet precipitation requirements is further checked; recording and recording the test operation result, and correspondingly modifying the part which cannot meet the rainfall requirement according to the test operation result; the water pump is started and the circuit is switched through test operation, so that the continuous operation of precipitation is ensured.

(5) And (5) checking the welding quality of the reinforced well pipe. And strictly controlling the welding quality according to the design requirements. The welding seam is uniform and has no sand hole, and the height of the welding seam pile is not less than 6 mm. And ensuring that the later stage foundation pit excavation welding seam is watertight.

(6) Before precipitation, each precipitation well needs to measure the elevation of the well mouth and the static water level and carry out related recording;

(7) The precipitation is strictly controlled according to the working conditions, so that the safety of the foundation pit is ensured and the influence on the surrounding environment is reduced;

(8) after the foundation pit is excavated, the well depth is measured when the well pipe is drained, and a dredging measure is taken in time;

(9) during the pumping process, the flow of the pumping well and the observation data record of the observed water level are made; the pumping well is required to select a representative dewatering well to install a flow meter for flow measurement; the water level observation can be carried out by utilizing the corresponding observation well.

(10) The dredging well below the trestle plate needs to be constructed before the construction of the trestle plate, and the well mouth is cut below the trestle surface in advance when the construction of the trestle plate is carried out.

The engineering project of the invention is constructed by adopting a method of layered precipitation and layered excavation by combining with the actual situation of the site. From the whole effect, the foundation pit soil body consolidation degree is good, and the observation water level outside the pit is stable, has created good condition for foundation pit earthwork excavation. The method completes the pouring from the earth excavation to the two horizontal concrete supports and then to the foundation slab cushion layer in a short time, thereby not only improving the working efficiency, but also shortening the time for exposing the deep foundation pit hazard source on the whole. The scene is still concentrated the pumping body of precipitation institute and is deposited in cistern and fire water pond, recycles when making things convenient for later stage major structure to construct, improves water resource utilization ratio.

Claims

1. A construction method for sealing precipitation of a drainage well in deep foundation pit construction is characterized by comprising the following steps: the method comprises the following steps: (1) setting out and positioning a well point; (2) forming a hole; (3) drilling and protecting the wall; (4) cleaning holes; (5) a lower pipe; (6) filling gravel and stopping water; (7) washing the well; (8) trying to pump water; wherein:

2. The construction method for closing precipitation of the dewatering well in deep foundation pit construction according to claim 1, characterized in that: and (3) well point setting-out positioning: according to the measurement control points provided by surveying and mapping units, measuring and setting out to determine the position of a well point, and excavating the well point; a small soil pit with the depth of 500mm is dug on site so as to collect water during hole opening and fill sand during pipe burying, and the small pit and the water pit are connected by a ditch so as to drain redundant water.

3. The construction method for closing precipitation of the dewatering well in deep foundation pit construction according to claim 1, characterized in that: the drilling protection wall comprises: the specific weight of the drilling mud at the bottom of the hole is 1.10-1.15, and the sand content is less than 8%; the sand content of the returned mud is not more than 12%.

4. The construction method for closing precipitation of the dewatering well in deep foundation pit construction according to claim 1, characterized in that: the hole cleaning: and (3) repeatedly sweeping the hole from top to bottom by adopting a drilling tool with the same diameter before the pipe is lowered, gradually replacing slurry in the hole by fresh dilute slurry while sweeping the hole, repeatedly sweeping the hole at the filter part, wherein slurry returned upwards in the hole does not contain a sludge block, the sand content is less than 12%, and when the specific gravity is 1.10, the slurry replacement is stopped, and the drilling tool is lifted.

5. The construction method for closing precipitation of the dewatering well in deep foundation pit construction according to claim 1, characterized in that: gravel filling and water stopping: after the pipe is lowered, a well pipe is fixed to a middle hole opening by using a clamping plate, a drill rod is lowered into the well pipe to a position 50cm away from the bottom of the well for slurry replacement, and the well pipe and an active drill rod are connected and sealed and are impermeable; the drilling rod sends the slurry into the bottom of the well, and the slurry returns to the ground through the annular gap between the well pipe and the hole wall through the filter; the mud dilution should be carried out gradually and slowly, so that the specific gravity difference between the fed mud and the returned mud is not large, when the specific gravity of the upward returned mud in the hole reaches 1.05, the mud is backfilled by a moving water gravel filling method, and the pump amount is adjusted to be small according to the water returning condition of the hole opening; tracking and measuring the upward return height of the gravel material in the gravel filling process, and after the gravel material is compacted to the designed height, throwing clay between the well pipe and the hole wall for water stop, wherein the clay is high-quality yellow clay, the sand content is less than 5%, the thickness of the water stop clay is not less than 2m, and the hole opening is compacted by filling yellow mud;

6. The construction method for closing precipitation of the dewatering well in deep foundation pit construction according to claim 1, characterized in that: the well washing: firstly, removing mud skin on a well wall, pumping out mud deep into a water-bearing stratum and recovering pores of the water-bearing stratum; pumping out a part of fine particles in the aquifer, expanding the pores of the aquifer and forming an artificial filtering layer; and the well washing adopts a sewage pump to repeatedly perform recovery pumping washing until the water is cleaned and sand is removed.

7. The construction method for closing precipitation of the dewatering well in deep foundation pit construction according to claim 1, characterized in that: the water trying is carried out: after the well is washed, trial pumping is carried out in time, the water pump is placed in a filter section during trial pumping, the power of the water pump is determined according to design requirements and the pumping amount of the pumping well, the trial pumping time is controlled by taking sand removal of water pumped by the pumping well as the standard, and the control time is controlled to be 2 hours.