Pebble bed deep foundation pit double-well tube-and-tube well structure
By adopting a double well pipe structure in the deep foundation pit of the pebble layer, filter material is set between the outer steel well pipe and the PVC inner well pipe, wall protection mud is eliminated, and holes are used to form a double filter layer, which solves the problem of collapse holes and high sand content of the pebble layer well well well well, and achieves an efficient and environmentally friendly water pumping effect.
Patent Information
- Application Number
- CN202422021950.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-20
- Publication Date
- 2025-07-25
- Estimated Expiration
- 2034-08-20
AI Technical Summary
The existing pebble layer pipe wells are prone to collapse when they become holes and need to be washed. The effluent content of the water after being drilled into a well is high, which affects the environment and pumping capacity.
A double well pipe structure is adopted, filter material is set between the outer steel well pipe and the PVC inner well pipe, and the outer steel well pipe is used as a guard wall to remove the wall mud. The submerged hammer drilling rig is used to directly form holes and a PVC inner well pipe is set in the steel well pipe to form a double filter layer.
The problem of pebble layer pipe well collapsed, reduces the sand content of the effluent, protects the environment, improves construction efficiency, and ensures water pumping capacity.
Smart Images
Figure CN223151219U_ABST
Abstract
Description
Technical Field
[0001] The utility model belongs to the technical field of foundation pit dewatering construction, and particularly relates to a double-well pipe well structure for deep foundation pits in pebble layers. Background Technique
[0002] A pipe well is a structure of a pumping well, which refers to a pumping well structure that sets a well pipe in a well hole, fills filter materials around the well pipe, and places a submersible pump in the well. Pipe wells are applicable to strata with relatively large permeability coefficients such as silty soil, sandy soil, and pebbles, and are widely applicable to various foundation pit dewatering. Pipe well dewatering is a common foundation pit dewatering technique. When forming a well, mechanical hole formation is usually first adopted, then a filter pipe is lowered into the well hole, and then filter materials are filled between the filter pipe and the hole wall. After the filter materials are filled, well washing is carried out. After well washing is completed, a submersible pump is placed in the filter pipe for pumping water. Pipe well filter pipes usually adopt non-sand concrete pipes, and steel pipes, steel reinforcement cages, etc. can also be used. The construction techniques for pipe well hole formation include reverse circulation hole formation technique, positive circulation hole formation technique, rotary drilling hole formation technique, percussion hole formation technique, etc. Different construction techniques correspond to different strata. Among them, due to the relatively large particle size of pebbles in the pebble stratum, it is impossible to effectively discharge large particle size pebbles out of the hole when using the reverse circulation or positive circulation pipe well hole formation technique, resulting in the inability to form a hole. Therefore, the pipe well hole formation in the pebble layer usually adopts the rotary drilling mud retaining wall hole formation technique. When using the rotary drilling hole formation technique, the retaining wall mud is added synchronously during the drilling and hole formation process, and at the same time, through the rotation and up and down lifting of the rotary drilling bit, a retaining wall mud skin is formed on the hole wall. After the rotary drilling machine forms a hole to the designed pipe well depth, the drill pipe and the drill bit are lifted out, and then the well pipe is hoisted in. Then, the filter materials are evenly filled into the gap between the well pipe and the hole wall from all around. After the filter materials are filled, well washing is carried out again. After well washing is completed, finally, a submersible pump is lowered for pumping water. The main disadvantages of the existing publicly disclosed rotary drilling and well formation construction technique for pipe wells in pebble layers are as follows: (1) When the rotary drilling rig forms a hole, mud must be added synchronously, and mud retaining wall is required during hole formation. The waste mud generated during construction is easy to pollute the environment and is not conducive to on-site environmental protection. (2) The pebble stratum has large pores and strong groundwater fluidity. When rotary drilling forms a hole, the retaining wall mud is prone to slurry leakage and dilution, resulting in hole wall collapse. Especially when the sand content in the pebble layer is relatively high, the retaining wall effect of the sand layer is poor and it is easy to collapse. (3) After rotary drilling and well formation, well washing is required. If well washing is not carried out in time, the retaining wall mud has a certain impact on the filtering effect of the well pipe, affecting the pumping capacity of the pipe well. Content of the Utility Model
[0003] In order to solve the above problems, the utility model provides a double-well pipe well structure for deep foundation pits in pebble layers to solve the problems of easy hole collapse, the need for well washing in the traditional rotary drilling and well formation process for pipe wells in pebble layers, and the high sand content in the water discharged from the outside when directly using a steel well pipe as the pumping well pipe, or the small water inflow due to sand particle blockage of the hole.
[0004] To achieve the above object, the utility model provides a double-well pipe well structure for deep foundation pits in pebble layers, including:
[0005] An outer steel well pipe and a PVC inner well pipe. The outer steel well pipe is embedded in the pebble layer in the deep foundation pit site area. The PVC inner well pipe is sleeved inside the outer steel well pipe. The gap between the outer steel well pipe and the PVC inner well pipe is filled with filter material. Pipe boots are provided at the bottoms of the outer steel well pipe and the PVC inner well pipe. The pipe boots are welded and fixed to the outer steel well pipe. Four second centering pads are provided between the outer steel well pipe and the PVC inner well pipe and above the pipe boots. The four second centering pads are evenly distributed along the outer wall of the PVC inner well pipe and are tied and fixed to the PVC inner well pipe. Four first centering pads are provided between the outer steel well pipe and the PVC inner well pipe and above the filter material. The four first centering pads are evenly distributed along the outer wall of the PVC inner well pipe and are tied and fixed to the PVC inner well pipe.
[0006] According to a specific embodiment of the present invention, multiple rows of water filtering slits are provided around the wall of the outer steel well pipe. The length of the water filtering slits is 100 mm, the slit width is 5 - 8 mm, the circumferential slit center distance of the water filtering slits is 150 mm, and the axial slit center distance of the water filtering slits is 300 mm.
[0007] According to a specific embodiment of the present invention, the outer diameter of the outer steel well pipe is 325 mm and the wall thickness is 5 mm.
[0008] According to a specific embodiment of the present invention, the outer diameter of the pipe boot is 325 mm, the wall thickness is 15 mm, and the height is 30 mm.
[0009] According to a specific embodiment of the present invention, the height of the outer steel well pipe is 500 mm higher than the wellhead elevation.
[0010] According to a specific embodiment of the present invention, the outer diameter of the PVC inner well pipe is 225 mm and the wall thickness is 5 mm.
[0011] According to a specific embodiment of the present invention, multiple rows of water filtering holes are provided around the wall of the PVC inner well pipe. Each cross-section of the PVC inner well pipe is provided with 8 water filtering holes. The spacing between the water filtering holes in adjacent cross-sections is 80 mm. The water filtering holes in adjacent cross-sections are staggered and arranged in a plum blossom pattern.
[0012] According to a specific embodiment of the present invention, the water filtering holes are circular water filtering holes with a diameter of 20 mm.
[0013] According to a specific embodiment of the present invention, both the first centering pads and the second centering pads are mortar cubes with dimensions of 40×40×40 mm.
[0014] According to a specific embodiment of the present invention, the filter material is round gravel or crushed stone, the minimum particle size is greater than or equal to 20 mm, and the maximum particle size is less than or equal to 30 mm.
[0015] Compared with the prior art, a double-well pipe structure for deep foundation pits in pebble layers provided by the present utility model adopts a double-well pipe structure. A filter layer is arranged between the outer steel well pipe and the inner well pipe for double filtration, so as to reduce the sand content in the effluent as much as possible, which is beneficial to protecting the surrounding environment. This application cancels the slurry for retaining wall, combines the steel pipe for retaining wall and the well pipe into one, improves the construction efficiency, and uses a down-the-hole hammer drill to synchronously follow the steel well pipe. During the hole-forming process, the pebble is directly broken by the impact bit, and then the pebble debris is blown out of the hole through the pores between the drill pipe and the steel well pipe by high-pressure air. After the drill forms the hole to the designed depth, the steel well pipe is correspondingly lowered to the designed depth, then a PVC inner well pipe is arranged inside the steel well pipe, filter material is backfilled between the PVC inner well pipe and the outer steel well pipe, and finally a submersible pump is placed inside the PVC inner well pipe. This application is applicable to the well completion of pipe wells in pebble strata without the need for slurry retaining wall, solves the problem of easy hole collapse in the rotary drilling hole-forming process of pipe wells in pebble strata, and at the same time adopts a double-well pipe, which can better filter groundwater, effectively control the sand content in the effluent, and avoid the impact on the surrounding environment of the foundation pit caused by soil erosion of the surrounding strata due to excessive sand content in the effluent. BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Figure 1 FIG. is a schematic diagram of a double-well pipe structure for deep foundation pits in pebble layers provided by an embodiment of the present utility model.
[0017] Figure 2 FIG. is a top view of the outer steel well pipe provided by an embodiment of the present utility model.
[0018] Figure 3 FIG. is a side view of the outer steel well pipe provided by an embodiment of the present utility model.
[0019] Figure 4 FIG. is a top view of the pipe shoe provided by an embodiment of the present utility model.
[0020] Figure 5 FIG. is a side view of the pipe shoe provided by an embodiment of the present utility model.
[0021] Figure 6 FIG. is a top view of the PVC inner well pipe provided by an embodiment of the present utility model.
[0022] Figure 7 FIG. is a side view of the PVC inner well pipe provided by an embodiment of the present utility model.
[0023] Figure 8 FIG. is a schematic diagram of the structure of the second central cushion block provided by an embodiment of the present utility model.
[0024] Figure 9 FIG. is a construction schematic diagram of a double-well pipe structure for deep foundation pits in pebble layers provided by an embodiment of the present utility model.
[0025] Drawing Reference Numerals:
[0026] 1 - First central cushion block; 2 - PVC inner well pipe; 3 - Filter material; 4 - Outer steel well pipe; 5 - Second central cushion block; 6 - Pipe shoe; 7 - Water extraction pipe; 8 - Submersible pump;
[0027] 21 - Water filtering holes;
[0028] 41 - Water filtering slits;
[0029] 51 - Iron wire for burning. Detailed Embodiments
[0030] In order to enable those skilled in the art to more clearly understand the concepts and ideas of the present utility model, the present utility model will be described in detail below in conjunction with specific embodiments. It should be understood that the embodiments given herein are only a part of all possible embodiments of the present utility model. After reading the specification of this application, those skilled in the art are capable of making improvements, modifications, or substitutions to some or all of the following embodiments, and these improvements, modifications, or substitutions are also included within the scope of protection required by the present utility model.
[0031] In this text, the terms "first", "second" and other similar words do not intend to imply any order, quantity, or importance, but are only used to distinguish different elements. In this text, the terms "a", "an" and other similar words do not intend to indicate that there is only one thing, but rather indicate that the relevant description is only directed to one of the things, and the thing may have one or more. In this text, the terms "comprising", "including" and other similar words are intended to express a logical relationship and should not be regarded as expressing a spatial structural relationship. For example, "A includes B" is intended to indicate that logically B belongs to A, rather than indicating that B is located inside A in terms of space. Additionally, the meanings of the terms "comprising", "including" and other similar words should be regarded as open-ended rather than closed. For example, "A includes B" is intended to indicate that B belongs to A, but B does not necessarily constitute all of A, and A may also include other elements such as C, D, E, etc.
[0032] In this text, the terms "embodiment", "the present embodiment", "one embodiment", "a single embodiment" do not mean that the relevant description only applies to a specific embodiment, but rather indicate that these descriptions may also apply to one or more other embodiments. Those skilled in the art should understand that in this text, any description made for a particular embodiment can be substituted, combined, or otherwise combined with the relevant descriptions in one or more other embodiments, and the new embodiments generated by substitution, combination, or other means are easily conceivable by those skilled in the art and fall within the scope of protection of the present utility model.
[0033] Embodiment 1
[0034] Additional aspects and advantages of embodiments of the present utility model will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of embodiments of the present utility model. In combination with Figures 1-8 , an embodiment of the present utility model provides a double-well pipe well structure for a deep foundation pit in a pebble layer, including:
[0035] An outer steel well pipe 4 and a PVC inner well pipe 2, the outer steel well pipe 4 is embedded in the pebble layer in the deep foundation pit site, the PVC inner well pipe 2 is sleeved inside the outer steel well pipe 4, a filter material 3 is filled in the gap between the outer steel well pipe 4 and the PVC inner well pipe 2, a pipe shoe 6 is arranged at the bottom of the outer steel well pipe 4 and the PVC inner well pipe 2, the pipe shoe 6 is fixedly welded to the outer steel well pipe 4, and four second centering pads 5 are arranged between the outer steel well pipe 4 and the PVC inner well pipe 2 and above the pipe shoe 6. The four second centering pads 5 are evenly distributed along the outer side wall of the PVC inner well pipe 2 and are fixedly tied to the PVC inner well pipe 2. Four first centering pads 1 are arranged between the outer steel well pipe 4 and the PVC inner well pipe 2 and above the filter material 3. The four first centering pads 1 are evenly distributed along the outer side wall of the PVC inner well pipe 2 and are fixedly tied to the PVC inner well pipe 2. The first centering pads 1 and the second centering pads 5 are both mortar blocks with a size of 40×40×40 mm. The filter material 3 is round gravel or crushed stone, the minimum particle size is greater than or equal to 20 mm, and the maximum particle size is less than or equal to 30 mm.
[0036] A new pipe well completion structure for a pebble layer formed by this application cancels the slurry for retaining wall, combines the retaining wall steel pipe and the well pipe into one body, improves the construction efficiency. This application adopts a double-well pipe structure, with a PVC inner well pipe arranged inside the outer steel well pipe. A filter material 3 is filled between the outer steel well pipe 4 and the PVC inner well pipe 2. The filter layer between the outer steel well pipe 4 and the PVC inner well pipe 2 plays a dual filtering role, minimizing the sand content in the discharged water as much as possible, which is beneficial to protecting the surrounding environment. The outer steel well pipe 4 does not need to use a bridge-type filter water steel pipe and can be processed with a welded steel pipe, saving costs.
[0037] In a specific embodiment of the present utility model, the outer steel well pipe 4 has an outer diameter of 325 mm and a wall thickness of 5 mm. Multiple rows of water filtering slits 41 are provided around the wall of the outer steel well pipe 4. The length of the water filtering slits 41 is 100 mm, the slit width is 5 - 8 mm, the circumferential slit center distance of the water filtering slits 41 is 150 mm, and the axial slit center distance of the water filtering slits 41 is 300 mm. The outer diameter of the PVC inner well pipe 2 is 225 mm and the wall thickness is 5 mm. Multiple rows of water filtering holes 21 are provided around the wall of the PVC inner well pipe 2. The water filtering holes 21 are circular water filtering holes with a diameter of 20 mm. Each cross-section of the PVC inner well pipe 2 is provided with 8 water filtering holes 21, and the distance between adjacent cross-section water filtering holes 21 is 80 mm. The water filtering holes 21 of adjacent cross-sections are staggered and arranged in a plum blossom shape. The outer diameter of the pipe shoe 6 is 325 mm, the wall thickness is 15 mm, the height is 30 mm, and the height of the outer steel well pipe 4 is 500 mm higher than the wellhead elevation. The outer diameter of the outer steel well pipe 4 is the same as the outer diameter of the pipe shoe 6. By fixing the pipe shoe 6 at the bottom of the outer steel well pipe 4, when forming the well, the down-the-hole hammer drill is nested on the pipe shoe 6. When the down-the-hole hammer drills, by vibrating and pressing the pipe shoe 6, the outer steel well pipe 4 is driven to synchronously follow and sink. After the down-the-hole hammer drills to the designed elevation, the outer steel well pipe 4 synchronously sinks to the corresponding designed elevation, then the down-the-hole hammer drill is lifted out, and the outer steel well pipe 4 remains in the hole as a retaining wall filter pipe. Then the PVC inner well pipe 2 is inserted into the inside of the outer steel well pipe 4. When inserting, the PVC inner well pipe 2 is kept centered. After insertion, filter material 3 is manually filled into the gap between the PVC inner well pipe 2 and the outer steel well pipe 4. Finally, a submersible pump 8 is placed in the PVC inner well pipe 2 for pumping water.
[0038] This application adopts the down-the-hole hammer pipe-following drilling process. When forming the hole, the steel well pipe is directly used for retaining wall, and no mud is generated during the construction process. After the well is formed, there is no need for well washing, and the submersible pump 8 can be directly placed for pumping water. The PVC inner well pipe 2 is arranged inside, and a filter layer is arranged in the middle, which can effectively reduce the sand content in the water outlet and avoid the problem of high sand content in the water outlet when directly using the outer steel well pipe 4 as the pumping well pipe. After the well-point dewatering of this application is completed, the outer steel well pipe 4 can be pulled out by a pipe extractor and recycled.
[0039] Embodiment 2
[0040] Combined with Figure 9 , the embodiment of the present utility model provides a construction method for a double-well pipe well structure in a deep foundation pit of a pebble layer, including:
[0041] 1) Release the well position and conduct a detailed investigation on the underground obstacles under the well position.
[0042] 2) Process the outer steel well pipe, cut the water filtering slits along the axial direction of the steel pipe. The water filtering slits start to be cut from 500 mm upward from the bottom end. The length of the water filtering slits is 100 mm, the slit width is 5 - 8 mm, the vertical distance between the slit centers is 300 mm, and the circumferential distance is 150 mm.
[0043] 3) Weld a pipe boot at the bottom of the outer steel well pipe. The outer diameter of the pipe boot is 325mm, the wall thickness is 15mm, and the height is 30mm. The pipe boot is fully welded to the bottom of the outer steel well pipe. The outer diameter of the outer steel well pipe is 325mm and the wall thickness is 5mm.
[0044] 4) After the pipe shoe is welded, insert the down-the-hole hammer drill bit into the outer steel well pipe and pass through the outer steel well pipe.
[0045] 5) Lift the down-the-hole hammer drill and connect the top of the drill pipe to the drilling rig power head. After the down-the-hole hammer drill pipe and the power head are connected, move the down-the-hole hammer drill to align with the well position.
[0046] 6) Start the down-the-hole hammer drill and start drilling.
[0047] 7) During drilling, the down-the-hole hammer drill guide clamps the pipe shoe, driving the outer steel well pipe to follow and sink synchronously. The outer diameter of the down-the-hole hammer drill guide is 305mm, slightly larger than the inner diameter of the pipe shoe.
[0048] 8) The down-the-hole hammer drills to the bottom of the hole according to the designed hole depth requirements, and the outer steel well pipe follows to the bottom of the hole simultaneously. After the hole is completed, the outer steel well pipe is 500mm higher than the designed wellhead elevation, and the excess part is cut off with a cutting machine.
[0049] 9) Pull out the down-the-hole hammer drill, remove the drilling rig, and manually lower the PVC inner well pipe into the outer steel well pipe. The PVC inner well pipe is flush with the bottom of the outer steel well pipe. The PVC inner well pipe has an outer diameter of 225mm and a wall thickness of 5mm. Water filter holes are set 500mm upward from the bottom of the PVC inner well pipe. The water filter holes are round holes with a diameter of 20mm. 8 water filter holes are set in each section. The water filter holes in the upper section are staggered by 22.5° with the water filter holes in the lower section. They are arranged in a plum blossom shape, and the distance between two adjacent rows of water filter holes is 80mm.
[0050] 10) When the PVC inner well pipe is lowered, the second centered mortar pad is tied at the bottom. The second centered mortar pad is a mortar block with a size of 40×40×40mm. When the mortar block is made, two 14# fire-burned wires 51 are pre-buried above and below. The fire-burned wires 51 are used to tie the PVC inner well pipe tightly. Four second centered mortar pads are evenly tied around the PVC inner well pipe. After the second centered mortar pad is tied, continue to lower the PVC inner well pipe. After the PVC inner well pipe is lowered to the bottom of the hole, four first centered mortar pads are evenly tied at the top of the PVC inner well pipe to keep it in the center and flush with the outer steel well pipe.
[0051] 11) After the PVC inner well pipe is lowered, the filter material is evenly filled in around the PVC inner well pipe using a trolley. The filter material is round gravel or crushed stone, with a minimum particle size of not less than 20mm and a maximum particle size of not more than 30mm.
[0052] 12) After the filter material is filled, insert the submersible pump 8 into the PVC inner well pipe.
[0053] 13) After the submersible pump 8 is lowered to the designed depth, connect the pump power supply, lay out the pump pipe 7, and arrange the on-site drainage system.
[0054] 14) After all drainage preparations are completed, start the submersible pump 8 to pump water.
[0055] 15) After the foundation pit is dewatered, the outer steel well pipe can be pulled out with a pipe puller for recovery.
[0056] The present application adopts a down-the-hole hammer to synchronously follow up the steel well pipe with vibration impact, and uses the steel well pipe to protect the wall. After the steel well pipe is lowered to the bottom of the hole, the steel well pipe is used as an outer filter pipe, and then a PVC inner well pipe is lowered into the outer steel well pipe, and then filter material is filled between the PVC inner well pipe and the outer steel well pipe. Finally, a submersible pump 8 is lowered into the PVC inner well pipe to pump water, which overcomes the defect of easy hole collapse in the traditional pebble layer pipe well rotary drilling process, and at the same time solves the problem of sand blocking the hole of the outer steel well pipe due to the lack of filter screen and filter layer on the outer layer, and the problem of high sand content in the water output and small water intake when the steel well pipe is directly used as the pumping well pipe.
[0057] In summary, the utility model provides a double well pipe well structure for a deep foundation pit in a pebble layer. The well structure adopts a double well pipe structure, and a filter layer is set between the outer steel well pipe and the inner well pipe for double filtration, so as to reduce the sand content of the effluent as much as possible, which is beneficial to protecting the surrounding environment. The present application cancels the wall protection mud, combines the wall protection steel pipe and the well pipe into one, improves the construction efficiency, and adopts a down-the-hole hammer drill to synchronously follow up the steel well pipe. During the hole-making process, the pebbles are directly crushed by the impact drill bit, and then the pebble debris is blown out of the hole from the gap between the drill rod and the steel well pipe by high-pressure air. After the drilling rig makes the hole to the designed depth, the steel well pipe is lowered to the designed depth accordingly, and then a PVC inner well pipe is set inside the steel well pipe, and then the filter material is backfilled between the PVC inner well pipe and the outer steel well pipe, and finally a submersible pump 8 is placed in the PVC inner well pipe. The present application is applicable to the drilling of pipe wells in pebble formations, and does not require mud wall protection, thereby solving the problem of easy hole collapse in the rotary drilling process of pipe wells in pebble formations. At the same time, the use of double well pipes can better filter groundwater, effectively control the sand content of the effluent water, and avoid the impact of soil erosion in the surrounding strata on the surrounding environment of the foundation pit caused by excessive sand content in the effluent water.
[0058] The above describes in detail the concepts, principles and ideas of the present utility model in combination with specific implementation methods (including embodiments and examples). Those skilled in the art should understand that the implementation methods of the present utility model are not limited to the above-mentioned forms. After reading this application document, those skilled in the art can make any possible improvements, substitutions and equivalent forms to the steps, methods, systems and components in the above-mentioned implementation methods. These improvements, substitutions and equivalent forms should be deemed to fall within the scope of the present utility model, and the protection scope of the present utility model shall be subject only to the claims.
Claims
1. A double - well pipe well structure for deep foundation pits in pebble layers, characterized in that, Including: An outer steel well pipe and a PVC inner well pipe. The outer steel well pipe is embedded in the pebble layer in the deep foundation pit site area. The PVC inner well pipe is sleeved inside the outer steel well pipe. The gap between the outer steel well pipe and the PVC inner well pipe is filled with filter material. A pipe shoe is provided at the bottom of the outer steel well pipe and the PVC inner well pipe. The pipe shoe is fixedly welded to the outer steel well pipe. Four second centering pads are provided between the outer steel well pipe and the PVC inner well pipe and above the pipe shoe. The four second centering pads are evenly distributed along the outer wall of the PVC inner well pipe and are fixedly tied to the PVC inner well pipe. Four first centering pads are provided between the outer steel well pipe and the PVC inner well pipe and above the filter material. The four first centering pads are evenly distributed along the outer wall of the PVC inner well pipe and are fixedly tied to the PVC inner well pipe.
2. The double-well pipe well structure for deep foundation pit in pebble layer according to claim 1, wherein, Multiple rows of water filtering slits are opened around the wall of the outer steel well pipe. The length of the water filtering slits is 100 mm, the slit width is 5 - 8 mm, the circumferential slit center distance of the water filtering slits is 150 mm, and the axial slit center distance of the water filtering slits is 300 mm.
3. The dual-well pipe well structure for deep foundation pit in pebble layer according to claim 1, characterized in that, The outer diameter of the outer steel well pipe is 325 mm and the wall thickness is 5 mm.
4. The pebble layer deep foundation pit double well pipe well structure according to claim 1, characterized in that, The outer diameter of the pipe shoe is 325 mm, the wall thickness is 15 mm, and the height is 30 mm.
5. The double-well pipe well structure for deep foundation pit in pebble layer according to claim 1, characterized in that, The height of the outer steel well pipe is 500 mm higher than the wellhead elevation.
6. The pebble layer deep foundation pit double well pipe well structure according to claim 1, characterized in that, The outer diameter of the PVC inner well pipe is 225 mm and the wall thickness is 5 mm.
7. The pebble layer deep foundation pit double well pipe well structure according to claim 1, characterized in that, Multiple rows of water filtering holes are opened around the wall of the PVC inner well pipe. Each cross-section of the PVC inner well pipe is provided with 8 water filtering holes. The spacing between the water filtering holes in adjacent cross-sections is 80 mm. The water filtering holes in adjacent cross-sections are staggered and arranged in a plum blossom pattern.
8. The pebble layer deep foundation pit double well pipe well structure according to claim 7, characterized in that, The water filtering holes are circular water filtering holes with a diameter of 20 mm.
9. The pebble layer deep foundation pit double well pipe well structure according to claim 1, characterized in that, Both the first centering pad and the second centering pad are mortar blocks with a size of 40×40×40 mm.
10. The double-well pipe well structure for deep foundation pit in pebble layer according to claim 1, characterized in that, The filter material is round gravel or crushed stone, with the minimum particle size greater than or equal to 20 mm and the maximum particle size less than or equal to 30 mm.