Sand geological pit-in-pit dewatering construction method

Abstract

The gravel geology pit-in-pit dewatering construction method comprises the following steps that a foundation pit dewatering tube well is excavated and arranged on the side edge of a large foundation pit, and the water level is lowered to the preset elevation; a local ultra-deep position dewatering well with the preset depth is excavated and arranged on the side edge of the pit in the pit, and a dewatering well protection cage formed by binding a reinforcing steel bar structure in a well pipe shape and densely covering a steel wire net is arranged; a submersible pump is put into the precipitation well protection cage, and the submersible pump is started for pit-in-pit precipitation; keeping rainfall, and carrying out formwork construction of a concrete cushion layer in the pit; and after the concrete cushion layer of the pit-in-pit reaches the strength, form removal is conducted, the submersible pump is taken out, the dewatering well at the local ultra-deep position is backfilled, and cushion layer construction of the large foundation pit is conducted. According to the construction method, formwork erecting construction of the concrete cushion layer in the pit is firstly carried out, then the dewatering well at the local ultra-deep position is backfilled, and then cushion layer construction of the large foundation pit is carried out, so that the integrity is guaranteed; by means of the dewatering well protection cage, the dewatering effect is guaranteed, cost is reduced, the dewatering well protection cage is denser after backfilling, and the structural strength is improved.

Description

Technical Field

[0001] The invention relates to the technical field of foundation pit dewatering construction, and in particular to a pit-in-pit dewatering construction method for a gravel geological pit. Background Art

[0002] Usually, during the dewatering construction of deep foundation pits, there is usually a need to construct super-deep pits such as elevator foundation pits and sump pits. During construction, the water level needs to be lowered to below the pit bottom elevation, and then the overall foundation cushion layer construction, as well as the overall foundation waterproofing and protective layer construction, are carried out. The conventional construction method is to use local small-scale light well point dewatering or pipe well dewatering along the super-deep parts of the foundation pit. When the water level drops below the pit bottom elevation, the overall foundation cushion layer construction, as well as the overall foundation waterproofing and protective layer construction, are carried out.

[0003] However, this construction method cannot backfill or stop the precipitation of the pipe wells around the pit-in-pit when constructing the overall foundation cushion. It is necessary to backfill the pipe wells after the overall foundation cushion is completed, resulting in poor integrity of the cushion and potential leakage. In addition, when this construction method is applied to sand and gravel geological environments, since the pipe wells are mostly cement pipes, their surfaces are basically flat or even smooth. After backfilling, there is always a certain gap between the inner and outer sides of the pipe wells and the backfill soil, which is equivalent to leaving a channel for groundwater, increasing the risk of leakage.

[0004] Therefore, there is an urgent need for a sandstone geological pit-in-pit dewatering construction method to solve the problem of poor construction integrity of the conventional pit-in-pit dewatering construction method. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a pit-in-pit dewatering construction method for sandstone geological areas, so as to solve the problem of poor construction integrity of the conventional pit-in-pit dewatering construction method.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A method for dewatering a gravel geological pit, characterized in that it comprises the following steps: A drainage pipe well is excavated on the side of the large foundation pit, and the water level is lowered to a preset elevation by using the drainage pipe well; a local super-deep drainage well of a preset depth is excavated on the side of the pit-in-pit, and a drainage well guard cage is provided in the local super-deep drainage well, and the drainage well guard cage is composed of a steel bar structure tied in a well pipe shape and densely covered with wire mesh; a submersible pump connected to a drainage pipe is lowered into the drainage well guard cage, and after it is lowered to the bottom of the drainage well guard cage, the submersible pump is started to dewater the pit-in-pit; the submersible pump is maintained to dewater the pit-in-pit, and formwork construction of the concrete cushion layer in the pit-in-pit is carried out; when the concrete cushion layer of the pit-in-pit reaches the expected strength, the formwork is removed, and then the submersible pump is taken out and the local super-deep drainage well is backfilled, and then the cushion layer construction of the large foundation pit is carried out, and the cushion layer of the large foundation pit is made to border the concrete cushion layer of the pit-in-pit.

[0007] To optimize the above technical solutions, the specific measures taken also include: Furthermore, the construction of the concrete cushion layer in the pit-in-pit comprises the following steps: supporting formwork at the bottom of the pit-in-pit and pouring the bottom cushion layer, and during pouring, setting reserved positioning steel bars on the sides of the bottom cushion layer; when the bottom cushion layer reaches the expected strength, the formwork is removed, and then the outer formwork close to the side wall of the pit-in-pit is installed by the reserved positioning steel bars, and then the inner formwork away from the side wall of the pit-in-pit is installed by the outer formwork in combination with the tension screws, and the inner formwork is fixed by the formwork frame set in the center of the pit-in-pit, and then the side wall cushion layer is poured.

[0008] Furthermore, the method of supporting formwork at the bottom of the pit and pouring the bottom cushion layer also includes the following steps: when pouring the bottom cushion layer, a circle of groove is reserved at the upper end of the bottom cushion layer, and the groove is located at the junction of the bottom cushion layer and the side wall cushion layer, for placing the expansion water stop strip.

[0009] Furthermore, the method of fixing the inner formwork by using a formwork frame arranged at the center of the pit in the pit also includes the following steps: placing a counterweight on the upper end of the formwork frame.

[0010] Furthermore, the removing of the submersible pump and backfilling of the local ultra-deep precipitation well specifically includes the following steps: after removing the submersible pump, removing the precipitation well protective cage, and then backfilling the local ultra-deep precipitation well.

[0011] Furthermore, the taking out of the submersible pump and backfilling the local ultra-deep precipitation well specifically includes the following steps: after taking out the submersible pump, the precipitation well protection cage is not taken out, and the local ultra-deep precipitation well is directly backfilled.

[0012] Furthermore, the method also includes the following steps: finally, waterproofing, protective layer and raft construction are carried out on the whole.

[0013] Furthermore, a local ultra-deep drainage well with a preset depth is excavated on the side of the pit in the pit using a backhoe excavator.

[0014] Furthermore, the formwork is removed when the concrete cushion strength of the pit-in-pit reaches 70%.

[0015] Furthermore, triangular supports are respectively provided at the bottom and the middle of the precipitation well cage, and the middle of the triangular supports can allow the submersible pump to pass through.

[0016] The beneficial effects of the present invention are: The present invention can ensure the integrity of the construction by first carrying out formwork construction of the concrete cushion layer in the pit, then backfilling the local super-deep drainage well, and then carrying out the cushion layer construction of the large foundation pit, thereby avoiding the problem of poor construction integrity caused by the conventional construction method that the construction cannot be carried out on the basis of backfilling the local super-deep drainage well, that is, the local super-deep drainage well needs to be backfilled after the overall cushion layer construction; by arranging the drainage well protection cage composed of a steel bar structure tied in a well pipe shape and densely covered with wire mesh in the local super-deep drainage well, it can not only ensure the drainage effect in gravel geology, but also reduce the operation cost. At the same time, the drainage well protection cage composed of steel bars and wire mesh is easier to be compacted with the surrounding sand and gravel after backfilling, which simplifies the construction process, and can increase the structural strength, improve the backfill quality, solve the hidden danger of poor compactness of conventional cement pipes, and increase the stability of the structure.

[0017] The present invention provides reserved positioning steel bars when pouring the bottom cushion layer, which can facilitate the positioning and assembly of the outer formwork and the inner formwork when supporting the side wall cushion layer; and through the provision of expansion water stop strips, the airtightness between the side wall cushion layer and the bottom cushion layer can be increased after the side wall cushion layer is poured.

[0018] The present invention uses a special structural setting of the precipitation well protective cage. When in use, the precipitation well protective cage can be taken out and then backfilled in the local super-deep precipitation well, so that the precipitation well protective cage can be reused; and the precipitation well protective cage can be directly backfilled in the local super-deep precipitation well without taking out the precipitation well protective cage, thereby realizing a streamlined construction process. The precipitation well protective cage composed of a steel bar structure and a steel wire mesh is used to increase the effect of structural strength without hindering the integrity of the sand and gravel geology. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the overall principle of a sandstone geological pit-in-pit dewatering construction method proposed by the present invention; Figure 2 A schematic diagram of a pit-in-pit construction of a sandstone geological pit-in-pit dewatering construction method proposed by the present invention; Figure 3 The present invention provides a schematic diagram of the concrete cushion construction method for a sandstone geological pit-in-pit dewatering construction method.

[0020] Figure numerals: 1. Foundation pit drainage pipe well, 2. Local super-deep drainage well, 3. Drainage well cage, 4. Submersible pump, 5. Drainage pipe, 6. Formwork frame, 7. Counterweight, 8. Inner formwork, 9. Concrete cushion layer, 91. Bottom cushion layer, 10. Expansion water stop strip, 11. Reserved positioning steel bars. DETAILED DESCRIPTION

[0021] The present invention will now be described in further detail with reference to the accompanying drawings.

[0022] As attached Figure 1 As shown, a method for dewatering a gravel geological pit in an embodiment of the present invention comprises the following steps: A foundation pit drainage pipe well 1 is excavated and set at the side of the large foundation pit, and the foundation pit drainage pipe well 1 is used to lower the water level to a preset elevation in the pit-in-pit; a local super-deep drainage well 2 with a preset depth is excavated and set at the side of the pit-in-pit, and a drainage well guard cage 3 is provided in the local super-deep drainage well 2, and the drainage well guard cage 3 is composed of a steel bar structure tied in a well pipe shape and densely covered with wire mesh; a submersible pump 4 connected with a drainage pipe 5 is lowered into the drainage well guard cage 3, and after it is lowered to the bottom of the drainage well guard cage 3, the submersible pump 4 is started to dewater the pit-in-pit; the submersible pump 4 is kept to dewater the pit-in-pit, and the formwork construction of the concrete cushion layer 9 in the pit-in-pit is carried out; when the concrete cushion layer 9 of the pit-in-pit reaches the expected strength, the formwork is removed, and then the submersible pump 4 is taken out and the local super-deep drainage well 2 is backfilled, and then the cushion layer construction of the large foundation pit is carried out, and the cushion layer of the large foundation pit is made to border the concrete cushion layer 9 of the pit-in-pit.

[0023] The present invention can ensure the integrity of the construction by first carrying out formwork construction of the concrete cushion layer 9 in the pit, then backfilling the local super-deep drainage well 2, and then carrying out the cushion layer construction of the large foundation pit, thereby avoiding the problem of poor construction integrity caused by the conventional construction method that the construction cannot be carried out on the basis of backfilling the local super-deep drainage well 2, that is, the local super-deep drainage well 2 needs to be backfilled after the overall cushion layer construction; by arranging the drainage well protection cage 3 composed of a steel bar structure tied in a well pipe shape and densely covered with wire mesh in the local super-deep drainage well 2, it can not only ensure the drainage effect in gravel geology, but also reduce the operating cost. At the same time, the drainage well protection cage 3 composed of steel bars and wire mesh is easier to be compacted with the surrounding sand and gravel after backfilling, which simplifies the construction process, and can increase the structural strength, improve the backfill quality, solve the hidden danger of poor compactness of conventional cement pipes, and increase the stability of the structure.

[0024] As attached Figure 3As shown, the above-mentioned construction of the concrete cushion layer 9 in the pit-in-pit specifically includes the following steps: supporting the formwork at the bottom of the pit-in-pit and pouring the bottom cushion layer 91, and during pouring, setting reserved positioning steel bars 11 on the side of the bottom cushion layer 91; when the bottom cushion layer 91 reaches the expected strength, the formwork is removed, and then the outer formwork close to the side wall of the pit-in-pit is installed by the reserved positioning steel bars 11, and then the outer formwork is used in conjunction with the tension screws to install the inner formwork 8 away from the side wall of the pit-in-pit, and the inner formwork 8 is fixed by the formwork frame 6 set in the center of the pit-in-pit, and then the side wall cushion layer is poured.

[0025] Thus, by setting the reserved positioning steel bars 11 when pouring the bottom cushion layer 91, it is possible to facilitate the positioning and assembly of the outer formwork and the inner formwork 8 when supporting the side wall cushion layer.

[0026] Among them, the above-mentioned method of supporting the formwork at the bottom of the pit and pouring the bottom cushion layer 91 also includes the following steps: when pouring the bottom cushion layer 91, a circle of groove is reserved at the upper end of the bottom cushion layer 91, and the groove is located at the junction of the bottom cushion layer 91 and the side wall cushion layer for placing the expansion water stop strip 10.

[0027] Thus, by providing the expansion water stop strip 10 , the airtightness between the side wall cushion layer and the bottom cushion layer 91 can be increased after the side wall cushion layer is poured.

[0028] As attached Figure 2 As shown, the above-mentioned method of fixing the inner formwork 8 by using the formwork frame 6 set in the center of the pit also includes the following steps: placing a counterweight 7 at the upper end of the formwork frame 6 to prevent the formwork frame 6 and other components from floating and shifting.

[0029] Among them, combined with a relatively light and easy-to-grasp structure composed of a steel bar structure and a steel wire mesh, the above-mentioned removal of the submersible pump 4 and backfilling of the local ultra-deep precipitation well 2 specifically includes the following steps: after removing the submersible pump 4, the precipitation well cage 3 is removed, and then the local ultra-deep precipitation well 2 is backfilled. In this way, the precipitation well cage 3 can be reused. Alternatively, after removing the submersible pump 4, the precipitation well cage 3 is not removed, and the local ultra-deep precipitation well 2 is directly backfilled. In this way, the construction process can be streamlined, and the precipitation well cage 3 composed of a steel bar structure and a steel wire mesh can be used to increase the structural strength without hindering the integrity of the sand and gravel geology.

[0030] Among them, based on the above steps, the following steps are also included: finally, waterproofing, protective layer and raft construction are carried out on the whole.

[0031] Among them, the above-mentioned local ultra-deep position drainage well 2 with a preset depth is excavated by a backhoe excavator on the side of the pit in the pit.

[0032] Wherein, the formwork is removed after the strength of the concrete cushion layer 9 of the pit in the pit reaches 70%.

[0033] The bottom and the middle of the above-mentioned precipitation well cage 3 are respectively provided with triangular braces, and the middle of the triangular braces can be passed through by the submersible pump 4. This can increase the stability of the structure of the precipitation well cage 3.

[0034] A specific implementation of the present invention is as follows: The total construction area of ​​the project is 55,282 square meters. The building 1# that needs to be dewatered has 1 underground floor, 3 podium floors, and 12 main floors. The foundation pit is 124 meters long, 108 meters wide, and the base elevation is 952.5 meters. The partially deepened elevator foundation pit: the upper groove is 9.4 meters × 8.6 meters, and the base elevation is 949.55 meters. During the survey, the groundwater level was about 954.0 meters, and the geological layer section of the dewatering area was a sandstone layer.

[0035] 1. Formulate a precipitation plan 1.1 Investigate the soil distribution and groundwater level of the foundation pit where dewatering is required, and review the geological survey report.

[0036] 1.2 Determine the depth, number, location and spacing of the required foundation pit drainage wells 1 to lower the water level to the -0.5m elevation of the bottom of the large foundation pit. There are a total of 77 drainage wells. The spacing between the drainage wells on the north and west sides of the foundation pit is 6m, and the spacing between the drainage wells on the south and east sides of the foundation pit is 7m. The depth of each well is 22.5m.

[0037] 2. Dewatering construction in the pit-in-pit area 2.1 A backhoe excavator is used to excavate a local ultra-deep dewatering well 2 at a distance of 1m from the upper notch on the south side of the pit in the pit. The depth of the excavated well bottom is 2m lower than the base elevation. A dewatering well cage 3 made of steel bars and wire mesh is installed in the local ultra-deep dewatering well 2. Among them, the diameter of the local ultra-deep dewatering well 2 can be 1.5m. The vertical steel bars of the dewatering well cage 3 are not less than Φ22HRB400 steel bars with a spacing of 100mm as the main steel bars, which are welded into a ring with a diameter of 1m and wrapped with a 5*5*1mm wire mesh on the outside.

[0038] 2.2 Connect the submersible pump 4 to the drainage pipe 5 and lower it into the dewatering well cage 3. After reaching the bottom of the well, start the submersible pump 4 to dewater the pit in the pit. The submersible pump 4 is installed in the dewatering well cage 3, and the pumped groundwater needs to be discharged into the dewatering pipe well around the foundation pit nearby, or discharged outside the foundation pit.

[0039] 3. Construction of the cushion layer and subsequent processes in the pit-in-pit area 3.1 After the water level in the pit drops below the base elevation of 500mm, after the manual cleaning and acceptance, the bottom cushion layer 91 and the side wall cushion layer of the pit are constructed; the bottom cushion layer 91 is cast after the formwork is supported, and the bottom cushion layer 91 is thickened to 400mm. After the inspection is completed, C20 concrete (P6, P8 anti-seepage grade is used according to the situation) is cast. When pouring the bottom cushion layer 91, a 20*20mm annular groove is reserved for the expansion water stop strip 10, and 2 steel bars with a diameter of 25 and a length of 45cm are reserved on the outside of the side wall every 1.5m as reserved positioning steel bars 11 for the inner side. Positioning and fixing of the formwork 8 and the outer formwork; after the bottom cushion layer 91 meets the standard, the formwork is removed and the construction of the side wall cushion layer is carried out, with a thickness of 400mm, the joint part is roughened, and the expansion water stop strip 10 is installed, and the side wall cushion layer formwork is installed. The outer formwork is installed using the reserved positioning steel bars 11, and the inner formwork 8 is positioned and installed using the tension screws; then the scaffolding steel pipe is used as the formwork frame 6 to fix the inner formwork 8, and the longitudinal and transverse spacing of the scaffolding steel pipe is 600mm×600mm. Heavy objects are placed on the upper part of the formwork frame 6 to prevent floating and displacement. After the formwork is installed, concrete is poured. Among them, the formwork can be made of surface-coated plywood and wooden squares.

[0040] 3.2 When pouring the concrete of the bottom cushion layer 91 and the side wall cushion layer in turn, a truck pump is used for pouring. During the pouring process, the cushion layer formwork is monitored and the cushion layer concrete vibration is strengthened to ensure good self-waterproofing.

[0041] 3.3 When the strength of the concrete cushion layer 9 reaches 70%, the formwork is removed and the dewatering of the pit-in-pit is stopped. The completed pit-in-pit cushion layer can effectively form a water-stop curtain, and then the original soil is used to backfill the local ultra-deep dewatering well 2. The upper 600mm high is backfilled with plain concrete and vibrated to make it dense.

[0042] 3.4 After that, a large area foundation pit cushion layer is constructed, which is adjacent to the pit-in-pit cushion layer. After the cushion layer construction is completed, the overall waterproof layer, waterproof protective layer and raft slab are constructed. The subsequent construction is not affected by the precipitation of the pit-in-pit, and the integrity is good. Compared with the conventional construction plan, there is no risk of leakage.

[0043] It should be noted that the terms such as "upper", "lower", "left", "right", "front", "back", etc. cited in the invention are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments in their relative relationships should be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0044] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, it can be understood that various changes, modifications, substitutions, embellishments and variations can be made to these embodiments without departing from the principle and spirit of the present invention, which should be regarded as the protection scope of the present invention. The scope of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for dewatering a gravel geological pit, characterized in that: The steps include: A foundation pit drainage pipe well (1) is excavated on the side of the large foundation pit, and the water level is lowered to a preset elevation by using the foundation pit drainage pipe well (1); a local ultra-deep drainage well (2) with a preset depth is excavated on the side of the pit-in-pit, and a drainage well cage (3) is provided in the local ultra-deep drainage well (2), and the drainage well cage (3) is composed of a steel bar structure tied in a well pipe shape and densely covered with steel wire mesh; a submersible pump (4) connected to a drainage pipe (5) is lowered into the drainage well cage (3) , after reaching the bottom of the dewatering well cage (3), start the submersible pump (4) to dewater the pit in the pit; keep the submersible pump (4) to dewater the pit in the pit, and carry out formwork construction of the concrete cushion layer (9) in the pit in the pit; when the concrete cushion layer (9) of the pit in the pit reaches the expected strength, remove the formwork, then take out the submersible pump (4) and backfill the local super-deep dewatering well (2), and then carry out the cushion layer construction of the large foundation pit, and make the cushion layer of the large foundation pit border with the concrete cushion layer (9) of the pit in the pit.

2. A method for dewatering a gravel geological pit according to claim 1, characterized in that: The construction of the concrete cushion layer (9) in the pit-in-pit comprises the following steps: supporting a formwork at the bottom of the pit-in-pit and pouring the bottom cushion layer (91), and during the pouring, setting a reserved positioning steel bar (11) on the side of the bottom cushion layer (91); after the bottom cushion layer (91) reaches the expected strength, the formwork is removed, and then the outer formwork close to the side wall of the pit-in-pit is installed by the reserved positioning steel bar (11), and then the inner formwork (8) away from the side wall of the pit-in-pit is installed by the outer formwork in conjunction with the tension screw rod, and the inner formwork (8) is fixed by a formwork frame (6) arranged at the center of the pit-in-pit, and then the side wall cushion layer is poured.

3. A method for dewatering a gravel geological pit according to claim 2, characterized in that: The step of supporting a formwork at the bottom of the pit-in-pit and pouring a bottom cushion layer (91) further comprises the following steps: when pouring the bottom cushion layer (91), a circle of grooves is reserved at the upper end of the bottom cushion layer (91), the grooves being located at the junction of the bottom cushion layer (91) and the side wall cushion layer for placing an expansion water stop strip (10).

4. A method for dewatering a gravel geological pit according to claim 2, characterized in that: The method of fixing the inner formwork (8) by using a formwork frame (6) arranged at the center of the pit in the pit also includes the following steps: placing a counterweight (7) at the upper end of the formwork frame (6).

5. A method for dewatering a gravel geological pit according to claim 1, characterized in that: The method of removing the submersible pump (4) and backfilling the local ultra-deep dewatering well (2) specifically comprises the following steps: after removing the submersible pump (4), removing the dewatering well protective cage (3), and then backfilling the local ultra-deep dewatering well (2).

6. A method for dewatering a gravel geological pit according to claim 1, characterized in that: The method of removing the submersible pump (4) and backfilling the local ultra-deep precipitation well (2) specifically comprises the following steps: after removing the submersible pump (4), the precipitation well protection cage (3) is not removed, and the local ultra-deep precipitation well (2) is directly backfilled.

7. A method for dewatering a gravel geological pit according to claim 1, characterized in that: The method also includes the following steps: finally, waterproofing, protective layer and raft construction are carried out on the whole.

8. The method for dewatering a gravel geological pit according to claim 1, characterized in that: A local ultra-deep drainage well (2) with a preset depth is excavated at the side of the pit in the pit using a backhoe excavator.

9. A method for dewatering a gravel geological pit according to claim 1, characterized in that: When the strength of the concrete cushion layer (9) of the pit-in-pit reaches 70%, the formwork is removed.

10. A method for dewatering a gravel geological pit according to claim 1, characterized in that: The bottom and middle of the precipitation well cage (3) are each provided with a triangular support, and the middle of the triangular support can allow the submersible pump (4) to pass through.

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