阅读说明：本技术 一种临水围堰内管井降水法干挖施工方法 (Water-faced cofferdam inner tube well dewatering dry excavation construction method ) 是由 刘晓晗 彭申凯 钱申春 任杰 沈维成 崔健 徐磊 危明 于 2021-01-08 设计创作，主要内容包括：本发明公开了一种临水围堰内管井降水法干挖施工方法,包括插打钢板桩、降水井设置、开挖并安装第一层围檩内支撑、开挖并安装第二层围檩内支撑、浇筑封底、施工承台、回填砂土、拆除第二层围檩内支撑、承台施工后回填细砂、拆除第一层围檩内支撑以及拔除钢板桩等步骤。本发明为配合新型的围堰内降水施工技术,降水井采用升降渗透管和基底固定管的升降套接结构,实现逐段阶梯式降水方法,大幅降低所需降水量及降水井布置数量,降水快且具有应急排险优势,成本低的同时还提高降水施工效率；本发明解决了围堰合拢后内部土体难以开挖移除的问题,通过降水固结,土体得以近似干挖条件下进行移除并安全进行了围堰封底,杜绝了基坑底的涌沙涌水现象。(The invention discloses a dry-excavation construction method for a tube well in a near-water cofferdam by a dewatering method, which comprises the steps of inserting and driving steel sheet piles, arranging dewatering wells, excavating and installing a first layer of inner support of a surrounding purlin, excavating and installing a second layer of inner support of the surrounding purlin, pouring a back cover, constructing a bearing platform, backfilling sandy soil, dismantling the second layer of inner support of the surrounding purlin, backfilling fine sand after the construction of the bearing platform, dismantling the first layer of inner support of the surrounding purlin, removing the steel sheet piles and the like. The invention relates to a novel cofferdam internal dewatering construction technology, wherein a dewatering well adopts a lifting sleeve joint structure of a lifting permeation tube and a base fixing tube, so that a step-by-step dewatering method is realized, the required dewatering amount and the arrangement number of the dewatering wells are greatly reduced, dewatering is fast, the emergency danger elimination advantage is achieved, the cost is low, and the dewatering construction efficiency is improved; the cofferdam construction method solves the problem that the inner soil body is difficult to excavate and remove after the cofferdam is folded, removes the soil body under the condition of approximate dry excavation through precipitation consolidation, safely seals the bottom of the cofferdam, and avoids the phenomena of sand gushing and water gushing at the bottom of a foundation pit.)

1. A dry excavation construction method for a tube well in a near-water cofferdam by a water-dropping method is characterized by comprising the following steps:

1) inserting and driving steel sheet piles to be folded to form a cofferdam, arranging a precipitation well inside the cofferdam according to the area of the cofferdam, wherein the precipitation height of the bottom of the precipitation well is more than 1.5m at the bottom of a bearing platform, and the arrangement position of the precipitation well is as follows: a certain number of dewatering wells are arranged in a gap between the bearing platform and the cofferdam, and a certain number of dewatering wells are also arranged in the bearing platform; the arrangement of the dewatering wells adopts lattice arrangement, a plurality of groups of dewatering wells in the bearing platform are distributed in a rectangular shape, and a plurality of groups of dewatering wells outside the bearing platform are distributed in a surrounding shape;

2) the underground water level is high, water is drained section by section through a dewatering well, dry excavation is carried out when the dewatering of a pipe well in the cofferdam reaches a preset depth, the cofferdam is excavated to 0.5m below the first layer, and an inner support of the first layer of enclosing purlin is installed;

3) excavating the cofferdam to 0.5m below the second layer, and mounting an inner support of the second layer of enclosing purlin;

4) excavating the cofferdam to the bottom of the foundation pit, and pouring 30cm of bottom sealing concrete;

5) leveling a back cover, breaking a pile head, binding reinforcing steel bars, erecting a template and constructing a bearing platform;

6) after the construction bearing platform reaches the position of +15m, sandy soil is backfilled in the cofferdam;

7) removing the inner supports of the second layer of enclosing purlin and constructing the rest bearing platform;

8) after the construction of the bearing platform is completed, fine sand is backfilled around the bearing platform;

9) and constructing the pier body to a position above the mud surface, gradually backfilling the foundation pit, removing the rest inner supports of the enclosing purlin, and removing the steel sheet piles to complete construction.

2. The dry excavation construction method for the inner tube well of the waterside cofferdam according to the claim 1, wherein the specific structure of the dewatering well is as follows: the water-permeable cofferdam comprises a base fixing pipe (1) inserted at the bottom of a precipitation well hole and a lifting permeation pipe (2) sleeved at the top of the base fixing pipe (1), wherein the pipe walls of the base fixing pipe (1) and the lifting permeation pipe (2) are respectively provided with water permeable holes at equal intervals from top to bottom, the inner side and the outer side of each water permeable hole are respectively coated with a filter screen for filtering sand, the outer wall at the top end of the base fixing pipe (1) is fixedly connected in the bottom sealing concrete of the cofferdam, namely the top end of the base fixing pipe (1) is flush with the upper surface of the bottom sealing concrete of the cofferdam;

the lifting infiltration pipe (2) top end face rigid coupling has flange lid (3), the avris wall of flange lid (3) is equipped with flange lug (4), it has hanging insert tube (5) to peg graft flange lid (3), it is located lifting infiltration pipe (2) to hang insert tube (5) bottom, it stretches out flange lid (3) outer and is connected with water pump (6) to hang insert tube (5) top, flange lid (3) upper surface is equipped with the screw, the base of water pump (6) shell passes through the bolt rigid coupling at flange lid (3) upper surface, water pump (6) are connected with puts tub (7) outward, put tub (7) to put in an inclined way at the cofferdam top outward, and put tub (7) one end of keeping away from water pump (6) outward and be located outside the cofferdam for the water is discharged outside the cofferdam outward, it has grit filling layer (8) to fill between fixed tub (1) top of base and flange lid (3) bottom.

3. The dry excavation construction method for the inner tube well of the waterside cofferdam according to the claim 2, wherein the construction process of the dewatering well is as follows: drilling a dewatering well hole in advance, slightly placing the substrate fixing pipe (1) to the dewatering well hole by adopting a crane and a clamp, connecting a flange lifting lug (4) by adopting the crane and a lifting rope, enabling a flange cover (3) to be horizontal, sleeving the bottom end of the lifting permeation pipe (2) into the substrate fixing pipe (1), continuously lowering the lifting permeation pipe (2), slightly hammering the flange cover (3) to enable the bottom end of the substrate fixing pipe (1) to reach the bottom of the dewatering well hole all the time, and sealing the bottom end of the substrate fixing pipe (1) by adopting poured cement glue;

lifting the flange cover (3) to the position above the dewatering well hole, filling sand and stone in a gap between the lifting permeation tube (2) and the dewatering well hole, filling sand and stone, slightly compacting the sand and stone by hammering the flange cover (3) lightly to finally form a sand and stone filling layer (8), wherein the top surface of the sand and stone filling layer (8) is flush with the initial ground in the cofferdam before excavation;

then installing a water pump (6) on the upper surface of the flange cover (3) through bolts, connecting the hanging insertion pipe (5) and the external drainage pipe (7), enabling the insertion depth of the hanging insertion pipe (5) to be located 20-30cm below the next excavation depth, excavating a sandstone filling layer (8) at the same time when excavating a foundation pit in the cofferdam every time, enabling the sandstone filling layer (8) to be always flush with the ground in the cofferdam, slowly excavating the sandstone filling layer (8), enabling the flange cover (3) and the lifting permeation pipe (2) to be slowly lowered, enabling the height of the flange cover (3) to be always higher than the ground in the cofferdam and placing the flange cover (3) on the sandstone filling layer (8) flush with the ground in the cofferdam, realizing stepwise precipitation by sections, excavating a layer of water by layer, greatly reducing the drainage amount and the drainage speed, and improving the construction efficiency;

until the last layer is excavated, the outer wall at the top end of the base fixing pipe (1) needs to be leaked by about 30cm and continuously pumped to dry the bottom of the foundation pit, then 30cm bottom sealing concrete is poured, the top end of the base fixing pipe (1) is embedded into and flush with the bottom sealing concrete, after the construction of a bearing platform is completed, the lifting penetration pipe (2) is pulled out of the base fixing pipe (1), fine sand is backfilled into the base fixing pipe (1), fine sand is backfilled around the bearing platform, a steel sheet pile is pulled out after the cofferdam is backfilled, the lifting penetration pipe (2) is used as a recovery standard component for the next time, and the base fixing pipe (1) is buried under the cofferdam to be used as a permanent fixing support.

4. The dry-excavation construction method for the inner tube well of the waterside cofferdam according to the claim 1, characterized in that the steel sheet pile is a Larsen 4 type steel sheet pile with the diameter of 18 m.

5. The method for dry excavation construction of the inner tube well of the just-existing cofferdam according to claim 1, wherein the inner support of the first layer of enclosing purlins comprises a first layer of enclosing purlins and a first layer of inner support structure, the first layer of enclosing purlins are specifically of a square frame structure consisting of 2HN600 200 section steel, the first layer of inner support structure adopts phi 710 10mm steel tubes, 2HN600 200 section steel and 2HN700 300 section steel, the inner corners of the first layer of enclosing purlins are respectively provided with 2HN600 200 section steel diagonal braces and 2HN700 300 section steel diagonal braces which are parallel to each other, the 2HN700 300 section steel diagonal braces which are parallel to the horizontal direction of the bearing platform are arranged between the two short sides of the first layer of enclosing purlins, the 2HN700 300 section steel diagonal braces and the 710 mm steel tube diagonal braces which are parallel to the longitudinal direction of the bearing platform are arranged between the two long sides of the first layer of enclosing purlins, and the 710 steel tube diagonal braces are arranged at the narrow table top of the phi 10mm, the 2HN 700X 300 profile steel diagonal braces parallel to the longitudinal direction of the bearing platform are arranged on the wider table top of the bearing platform, and the end parts of the 2HN 700X 300 profile steel diagonal braces parallel to the longitudinal direction of the bearing platform are abutted against the inner wall of the first layer of surrounding purlin through two symmetrically arranged 2HN 600X 200 profile steel diagonal braces;

the second layer of enclosing purlin inner supports are located right below the first layer of enclosing purlin inner supports, and the structure of the second layer of enclosing purlin inner supports is identical to that of the first layer of enclosing purlin inner supports.

6. The dry-excavation construction method for the inner tube well of the waterside cofferdam according to the claim 1, wherein the thickness of the bottom sealing concrete is 30cm, and the concrete with the strength grade of C25 is adopted.

7. The dry excavation construction method for the inner tube well of the waterside cofferdam according to the claim 1, characterized in that the space between the first layer of purlin and the steel sheet pile is filled with square timber; and square timber is adopted to fill between the second layer of surrounding purlin and the steel sheet piles.

8. The method for dry excavation construction of the inner tube well of the waterside cofferdam according to the claim 1, characterized in that the cross of the 2HN 700X 300 steel butt brace and the phi 710X 10mm steel tube butt brace which are transversely parallel to the bearing platform is also provided with a vertical brace, the vertical brace extends to the rock layer, when in use, the 2HN 700X 300 steel butt brace, the phi 710X 10mm steel tube butt brace and the vertical brace can be fixed by binding, which strengthens the fixing function.

Technical Field

The invention relates to the technical field of construction of steel cofferdam bearing platforms in areas with higher underground water levels or near rivers, in particular to a dry excavation construction method of a tube well in a near water cofferdam by a dewatering method.

Background

In the bridge foundation construction, when the bridge abutment foundation is positioned below the ground surface water level, constructing earth weirs in various forms according to local materials; in rivers with deep water and large flow velocity, sheet-pile or steel sheet pile (single-layer or double-layer) cofferdams can be adopted, and at present, double-layer thin-wall steel cofferdams are mostly used. The cofferdam can be used for preventing water and enclosing water and can also be used for supporting the pit wall of the foundation pit.

The cofferdam is interior for steel sheet pile cofferdam construction completion back is underwater to inhale earth and excavates to design elevation then begins to extract water and provide the operation face after carrying out the cushion cap construction, and under the effect of water level pressure, the water pressure causes the osmotic deformation of sand, and the hole bottom of foundation ditch produces and gushes sand and gush water phenomenon, sets up and pours the process for the template and brings huge trouble, urgent solution.

Disclosure of Invention

The invention aims to solve the defects in the prior art and provides a dry excavation construction method for a tube well in a near-water cofferdam by a dewatering method.

In order to achieve the purpose, the invention adopts the following technical scheme:

a dry excavation construction method for a tube well in a near-water cofferdam by a water-lowering method comprises the following steps:

1) inserting and driving steel sheet piles to be folded to form a cofferdam, arranging a precipitation well inside the cofferdam according to the area size of the cofferdam, wherein the precipitation height of the bottom of the precipitation well is more than 1.5m of the bottom of a bearing platform, and the arrangement position of the precipitation well is as follows: a certain number of dewatering wells are arranged in a gap between the bearing platform and the cofferdam, and a certain number of dewatering wells are also arranged in the bearing platform; the arrangement of the dewatering wells adopts lattice arrangement, a plurality of groups of dewatering wells in the bearing platform are distributed in a rectangular shape, and a plurality of groups of dewatering wells outside the bearing platform are distributed in a surrounding shape;

2) the underground water level is high, water is drained section by section through a dewatering well, dry excavation is carried out when the dewatering of a pipe well in the cofferdam reaches a preset depth, the cofferdam is excavated to 0.5m below the first layer, and an inner support of the first layer of enclosing purlin is installed;

3) excavating the cofferdam to 0.5m below the second layer, and mounting an inner support of the second layer of enclosing purlin;

4) excavating the cofferdam to the bottom of the foundation pit, and pouring 30cm of bottom sealing concrete;

5) leveling a back cover, breaking a pile head, binding reinforcing steel bars, erecting a template and constructing a bearing platform;

6) after the construction bearing platform reaches the position of +15m, sandy soil is backfilled in the cofferdam;

7) removing the inner supports of the second layer of enclosing purlin and constructing the rest bearing platform;

8) after the construction of the bearing platform is completed, fine sand is backfilled around the bearing platform;

9) and constructing the pier body to a position above the mud surface, gradually backfilling the foundation pit, removing the rest inner supports of the enclosing purlin, and removing the steel sheet piles to complete construction.

Preferably, the dewatering well has the following specific structure: including pegging graft at the fixed pipe of basement of precipitation wellhole bottom and cup jointing the lift infiltration pipe at the fixed pipe top of basement, the equal top-down equidistance of pipe wall of the fixed pipe of basement and lift infiltration pipe is provided with the hole of permeating water, and the inside and outside both sides in the hole of permeating water all wrap the filter screen for filter the grit, the outer wall rigid coupling of the fixed pipe top department of basement is in the back cover concrete of cofferdam. Namely, the top end of the substrate fixing pipe is flush with the upper surface of the bottom sealing concrete of the cofferdam;

the rigid coupling of lift infiltration pipe top face has the blind flange, the avris wall of blind flange is equipped with the flange lug, the blind flange is pegged graft and is had the hanging insert tube, it is located the lift infiltration pipe to hang insert tube bottom, it stretches out the blind flange outside and is connected with the water pump to hang the insert tube top, the blind flange upper surface is equipped with the screw, the base of water pump shell passes through the bolt rigid coupling and covers the upper surface at the blind flange, the water pump is connected with puts the pipe outward, put the pipe and take in the cofferdam top to one side outward, and put the one end that the pipe kept away from the water pump outward and be located outside the cofferdam, be used for discharging water outside the cofferdam.

Preferably, the construction process of the dewatering well is as follows: drilling a dewatering well hole in advance, slightly placing the substrate fixing pipe to the dewatering well hole by adopting a crane and a clamp, connecting a flange lifting lug by adopting the crane and a lifting rope, enabling a flange cover to be positioned horizontally, sleeving the bottom end of the lifting permeation pipe into the substrate fixing pipe, continuously placing the lifting permeation pipe, slightly hammering the flange cover to enable the bottom end of the substrate fixing pipe to reach the bottom of the dewatering well hole, and sealing the bottom end of the substrate fixing pipe by adopting poured cement glue;

lifting the flange cover to the position above the dewatering well hole, filling sand and stone in a gap between the lifting permeation tube and the dewatering well hole, filling sand and stone, slightly compacting the sand and stone by hammering the flange cover to form a sand and stone filling layer finally, wherein the top surface of the sand and stone filling layer is flush with the initial ground in the cofferdam before excavation;

then installing a water pump on the upper surface of the flange cover through bolts, connecting the suspended insertion pipe and the external placing pipe, enabling the insertion depth of the suspended insertion pipe to be 20-30cm below the next excavation depth, excavating a sandstone filling layer at the same time when excavating a foundation pit in the cofferdam, enabling the sandstone filling layer to be always level with the ground in the cofferdam, slowly excavating the sandstone filling layer, enabling the flange cover and the lifting permeation pipe to be slowly placed downwards, enabling the height of the flange cover to be always higher than the ground in the cofferdam and placing the flange cover on the sandstone filling layer which is level with the ground in the cofferdam, realizing step-by-step precipitation, lowering a layer of water and excavating a layer of water, greatly reducing the water discharge and the water discharge speed, and improving the construction efficiency;

until the last layer is excavated, the outer wall at the top end of the base fixing pipe needs to be leaked by about 30cm and continuously pumped to dry the bottom of the foundation pit, then 30cm bottom sealing concrete is poured, the top end of the base fixing pipe is embedded into and level with the bottom sealing concrete, after the construction of a bearing platform is completed, the lifting permeation pipe is pulled out of the base fixing pipe, fine sand is backfilled into the base fixing pipe, fine sand is continuously backfilled around the bearing platform, a steel sheet pile is pulled out after the cofferdam is backfilled, the lifting permeation pipe is used as a recovery standard component to be continuously used next time, and the base fixing pipe is buried under the cofferdam to be used as a permanent support.

Preferably, the steel sheet pile is 18m Larsen 4 steel sheet pile.

Preferably, the first layer of purlin inner support comprises a first layer of purlin and a first layer of inner support structure, the first layer of purlin is a square frame structure formed by 2HN600 200 section steel, the first layer of inner support structure adopts phi 710 10mm steel pipes, 2HN600 200 section steel and 2HN700 300 section steel, the inner corners of the first layer of purlin are respectively provided with parallel 2HN600 200 section steel diagonal braces and 2HN700 300 section steel diagonal braces, 2HN700 300 section steel diagonal braces parallel to the transverse direction of the bearing platform are arranged between the two short sides of the first layer of purlin, 2HN700 300 section steel diagonal braces and 710 phi 10mm steel pipe diagonal braces parallel to the longitudinal direction of the bearing platform are arranged between the two long sides of the first layer of purlin, the 710 mm steel pipe diagonal braces are arranged at the narrower platform surface of the bearing platform surface, and the 2HN700 diagonal braces parallel to the longitudinal direction of the bearing platform are arranged at the longitudinal direction of the bearing platform, and the two wider 600H 700 diagonal braces are arranged at the end parts of the first layer of purlin 200 section steel and are symmetrical to the end surface of the first layer of the second layer of the first layer of the purlin 600 section steel On the wall;

the second layer of enclosing purlin inner supports are located right below the first layer of enclosing purlin inner supports, and the structure of the second layer of enclosing purlin inner supports is identical to that of the first layer of enclosing purlin inner supports.

Preferably, the thickness of the back cover concrete is 30cm, and the concrete with the strength grade of C25 is adopted.

Preferably, square timbers are used for filling the space between the first layer of surrounding purlin and the steel sheet piles; and square timber is adopted to fill between the second layer of surrounding purlin and the steel sheet piles.

Preferably, the vertical supports are further arranged at the intersections of the 2HN 700X 300 section steel diagonal supports and the phi 710X 10mm steel pipe diagonal supports which are transversely parallel to the bearing platform and extend to the rock layer, and when the vertical supports are used, the 2HN 700X 300 section steel diagonal supports, the phi 710X 10mm steel pipe diagonal supports and the vertical supports can be fixedly bound, so that the fixing effect is enhanced.

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

the steel cofferdam summarized by the implementation of the invention adopts the dewatering construction technology in the cofferdam for the first time, and comprises the steps that a dewatering well is arranged in the cofferdam, the dewatering well adopts a lifting sleeve structure of a lifting permeation tube and a substrate fixing tube, after a certain depth is excavated, the lifting permeation tube is also lowered along with the excavation depth, a water pump and a flange cover are lowered along with the lowering of the lifting permeation tube, and the section-by-section stepped dewatering method is realized by controlling the fixed depth from the excavation surface by hanging an inserting tube, and the dewatering well in the cofferdam can be arranged by the dewatering method;

and the dewatering well arranged in the cofferdam has the advantages that: firstly, the total area of the dewatering wells is smaller than that of the dewatering wells arranged outside the cofferdam, the number of the dewatering wells is reduced, and the required precipitation is also greatly reduced; secondly, the dewatering speed is high, particularly, a step-by-step dewatering method is adopted, construction is carried out in a layered mode, the water level is only required to be reduced to the position near the lower part of an excavation layer by the excavation depth of each time, the dewatering speed and the construction efficiency are greatly improved, and the water can be quickly and timely discharged even in the case of water seepage, so that the potential safety hazard of untimely emergency of the existing cofferdam outer dewatering technology is avoided;

the construction technology of the precipitation before the cofferdam is excavated is adopted, the construction technology comprises key technologies of pipe well structure, pipe well caliber, applicability of soil quality, pipe well range and interval arrangement and the like, the construction technology of steel sheet piles matched with the pipe well precipitation is adopted, and the problem that the soil body in the cofferdam is difficult to excavate and remove after the closure is solved; through precipitation consolidation, the soil body can be removed under the condition of dry excavation and cofferdam bottom sealing is safely carried out, and the phenomena of sand gushing and water gushing at the bottom of the foundation pit are avoided.

Drawings

FIG. 1 is a cross-bridge vertical view (horizontally placed) of a construction structure formed by the dry excavation construction method of the tube well in the near-water cofferdam of the present invention;

FIG. 2 is a vertical view of a longitudinal bridge of a construction structure formed by the dry excavation construction method of the tube well in the near-water cofferdam of the present invention;

FIG. 3 is a top view (horizontally placed) of a construction structure formed by the dry excavation construction method of the tube well in the near-water cofferdam according to the present invention;

FIG. 4 is a schematic diagram showing the arrangement orientation of dewatering wells in the dry-excavation construction method of the tube well in the waterside cofferdam of the present invention; wherein the numerical units of the distances in fig. 4 are in cm;

FIG. 5 shows the structure and process of dewatering well in the dry-excavation construction method of inner tube well of waterside cofferdam of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.

Example 1:

taking the construction of the steel cofferdam of the main pier of the five-bridge of the vortex river as an example, the preparation of the cofferdam material of the bearing platform is shown in table 1:

TABLE 1 materials list of inner supporting structure of cofferdam and its enclosing purlin

Geological conditions are as follows: the upper layer is silt, and the test performance is gamma 2=19.5kN/m high-speed, phi 2=20, c2=0 kPa; the lower layer is silty clay, and the test performance is gamma 2=19.2kN/m for high speed, phi 2=15.3 and c2=34.4 kPa.

The dry excavation construction method of the tube well in the near-water cofferdam by the water-dropping method comprises the following steps:

1) inserting and driving steel sheet piles to be folded to form a cofferdam, arranging no tube well precipitation outside the cofferdam, only arranging tube well precipitation inside the cofferdam, and considering the difference of the number of tube wells arranged in different cofferdam areas. The precipitation height at the bottom of the pipe well is more than 1.5m at the bottom of the bearing platform. The specific flow is that the inside and the outside of the cofferdam are soil, because the underground water level is high, dry excavation is carried out after the dewatering of a pipe well in the cofferdam reaches a preset depth, the construction of an inner support and an enclosing purlin in the cofferdam is carried out while the soil in the cofferdam is dry excavated, and the construction of a bottom sealing and a bearing platform is carried out in a dry excavation state till the bottom of the bearing platform is dry excavated;

2) referring to fig. 4, dewatering well arrangement: the bearing platform is provided with 11 openings of dewatering wells, 4 openings are arranged in the gap between the cofferdam and the bearing platform, the elevation of a well head is 20m, the diameter is 50cm, and the well depth is 25 m; 3 wells are arranged on the south side of the bearing platform, the height of a well mouth is 23m, the diameter is 50cm, and the well depth is 25 m; 4 wells are arranged on the north side and the east side of the bearing platform, the elevation of the well mouth is 20m, the diameter is 50cm, and the well depth is 25 m.

Referring to fig. 5, the dewatering well has the following specific structure: including pegging graft at the fixed pipe 1 of basement of precipitation wellhole bottom and cup jointing the lift infiltration pipe 2 at the fixed pipe 1 top of basement, the equal top-down equidistance of pipe wall of the fixed pipe 1 of basement and lift infiltration pipe 2 is provided with the hole of permeating water, and the inside and outside both sides in the hole of permeating water all wrap the filter screen for filter the grit, the outer wall rigid coupling of the fixed pipe 1 top department of basement is in the back cover concrete of cofferdam. Namely, the top end of the substrate fixing pipe 1 is flush with the upper surface of the bottom sealing concrete of the cofferdam;

2 top end face rigid couplings of lift infiltration pipe have a flange lid 3, the avris wall of flange lid 3 is equipped with flange lug 4, 3 pegs graft of flange lid have hang insert tube 5, hang 5 bottoms of insert tube and be located lift infiltration pipe 2, hang 5 tops of insert tube and stretch out 3 outer and be connected with water pump 6 of flange lid, 3 upper surfaces of flange lid are equipped with the screw, the base of 6 shells of water pump passes through the bolt rigid coupling at 3 upper surfaces of flange lid, water pump 6 is connected with puts pipe 7 outward, put pipe 7 and take in the cofferdam top to one side outward, and put the pipe 7 one end of keeping away from water pump 6 outward in the cofferdam outward, be used for discharging outside the cofferdam with water, it has grit filling layer 8 to fill between 1 top of basement fixed tube and the 3 bottom.

Preferably, the construction process of the dewatering well is as follows: drilling a dewatering well hole in advance, slightly placing the substrate fixing pipe 1 to the dewatering well hole by adopting a crane and a clamp, connecting a flange lifting lug 4 by adopting the crane and a lifting rope, enabling a flange cover 3 to be positioned horizontally, sleeving the bottom end of the lifting permeation pipe 2 into the substrate fixing pipe 1, continuously lowering the lifting permeation pipe 2, slightly hammering the flange cover 3 to enable the bottom end of the substrate fixing pipe 1 to reach the bottom of the dewatering well hole all the time, and sealing the bottom end of the substrate fixing pipe 1 by adopting poured cement glue;

lifting the flange cover 3 to the position above the dewatering well hole, filling sand and stone in a gap between the lifting permeation tube 2 and the dewatering well hole, filling the sand and stone, slightly hammering the flange cover 3 to slightly compact the sand and stone while filling, and finally forming a sand and stone filling layer 8, wherein the top surface of the sand and stone filling layer 8 is flush with the initial ground in the cofferdam before excavation;

then a water pump 6 is arranged on the upper surface of the flange cover 3 through bolts, the hanging insertion pipe 5 and the external placing pipe 7 are communicated, the insertion depth of the hanging insertion pipe 5 is positioned 20-30cm below the next excavation depth, when a foundation pit in the cofferdam is excavated each time, a sandstone filling layer 8 needs to be excavated at the same time, the sandstone filling layer 8 is always flush with the ground in the cofferdam, the excavation of the sandstone filling layer 8 needs to be slow, the flange cover 3 and the lifting permeation pipe 2 are slowly placed down, the height of the flange cover 3 is always higher than the ground in the cofferdam and is placed on the sandstone filling layer 8 flush with the ground in the cofferdam, the step-by-step precipitation is realized, one layer of water is excavated after one layer of water is excavated, the water discharge and the water discharge speed are greatly reduced;

until the last layer is excavated, the outer wall at the top end of the base fixing pipe 1 needs to be leaked by about 30cm and continuously pumped to dry the bottom of the foundation pit, then 30cm bottom sealing concrete is poured, the top end of the base fixing pipe 1 is embedded into and leveled with the bottom sealing concrete, after the construction of a bearing platform is completed, the lifting permeation pipe 2 is pulled out of the base fixing pipe 1, fine sand is backfilled into the base fixing pipe 1, fine sand is continuously backfilled around the bearing platform, a steel sheet pile is pulled out after the cofferdam is backfilled, the lifting permeation pipe 2 is continuously used as a recovery standard component next time, and the base fixing pipe 1 is buried under the cofferdam to be used as a permanent support.

3) Controlling the bottom end of the suspension inserting pipe 5 to be located 0.7-0.8m below the first layer, continuously reducing water to dry the interior of the cofferdam, excavating the interior of the cofferdam to be 0.5m below the first layer, namely excavating from an excavation surface I (namely the original ground in the cofferdam) to an excavation surface II (namely 0.5m below the first layer), and installing a first layer of inner support of the enclosing purlin;

4) excavating the cofferdam to 0.5m below the second layer, namely excavating from an excavation surface II (namely 0.5m below the first layer) to an excavation surface III (namely 0.5m below the second layer), and installing a second layer of surrounding purlin inner supports;

5) excavating to the bottom of a foundation pit in the cofferdam, namely excavating to an excavation surface IV (namely the bottom of a foundation pit) from an excavation surface III (namely 0.5m below the second layer), pouring 30cm of bottom sealing concrete, embedding the top end of the substrate fixing pipe 1 into the bottom sealing concrete, and burying the substrate fixing pipe 1 under the cofferdam to be used as a permanent support;

6) leveling a back cover, breaking a pile head, binding reinforcing steel bars, erecting a template and constructing a bearing platform;

7) pulling the lifting permeation tube 2 out of the substrate fixing tube 1, backfilling the substrate fixing tube 1 with fine sand until the construction bearing platform reaches a position of +15m, and backfilling sandy soil in the cofferdam;

8) removing the inner supports of the second layer of enclosing purlin and constructing the rest bearing platform;

9) after the construction of the bearing platform is completed, fine sand is backfilled around the bearing platform;

10) and constructing the pier body to a position above the mud surface, gradually backfilling the foundation pit, removing the rest inner supports of the enclosing purlin, and removing the steel sheet piles to complete construction.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.