Method for dewatering combined foundation pit under geological condition of water-containing interlayer

Abstract

The invention discloses a combined foundation pit dewatering method under the geological condition of a water-containing interlayer, which belongs to the field of building construction and comprises the following steps of: opening a drainage deep well and a decompression deep well, ensuring that a phreatic water level is 1m below an excavation surface, and opening the decompression deep well according to a calculated water head; when the foundation pit is excavated to reach 0.5-1.0 m of a water-containing interlayer, a vacuum drainage deep well is additionally arranged in the longitudinal direction of the foundation pit, and the drainage deep well and the pressure reduction deep well are synchronously operated; every 10 downcast pipes are provided with a vacuum pump to form a downcast section; the downcast pipes are exposed out of the ground by 30-50 cm, each downcast pipe is connected into the water pumping main pipe through a second hose, and the joints are wrapped with plastic films. The vacuum pump is connected with a drain pipe which is connected to a ground drainage ditch; the multiple vacuum drainage deep wells are additionally arranged, the dewatering speed is increased through the pipelines in the vacuum drainage deep wells, meanwhile, the foundation pit excavation time is shortened, and the excavation efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the field of building construction, and in particular relates to a combined foundation pit dewatering method under water-containing interlayer geological conditions. Background Art

[0002] At present, in the deep foundation pit construction in Nantong City, the excavation depth is mainly the phreatic aquifer, and there is confined water below the excavation surface. The phreatic water is mainly stored in the shallow silt and silt sand layers (1st, 2nd and 3rd layers). The 4th layer of silty clay has good water-proof performance and is a micro-permeable layer. The first confined water is generally stored in the sand and silt layers below a depth of about 30m, that is, the 5th layer of silt sand and silt soil, the 6th layer of silt sand and the 7th layer of medium sand. The dewatering design and construction of similar foundation pit projects generally adopts deep wells for drainage and deep wells for decompression to carry out targeted dewatering in layers. The foundation pit waterproof curtain is inserted into the decompression target aquifer, and it is more preferred to use the pit to reduce the confined water. The surrounding conditions of the foundation pit are complex and the environmental protection requirements are high. It is necessary to monitor the changes in the water level outside the pit in real time, and a water level observation well needs to be arranged outside the pit. The number of drainage and dewatering wells is generally determined by the ratio of the total drainage and dewatering area of ​​the foundation pit to the effective drainage area of ​​a single well. The pressure relief and dewatering wells are confirmed based on the safety verification results of the sudden surge stability of the foundation pit. Generally, a circular hole filter is used for the drainage well, a bridge filter is used for the pressure relief well, and a 60-mesh filter is used for the net. Due to the existence of four layers of silty clay, this dewatering method is applicable before the foundation pit is excavated to the four layers of silty clay. When the four layers of silty clay are excavated, the water content of this layer is relatively high, and it seeps through the excavation section to the excavated working surface, causing the base to be soaked in water, making it difficult for excavation equipment to dig and move, and it is difficult to form the downturned structure trench. The foundation pit is difficult to close the bottom, which is labor-intensive and time-consuming. The foundation pit is exposed for a long time, and the deformation of the surrounding structure increases, posing a safety hazard.

[0003] Existing devices have poor precipitation efficiency and are prone to safety hazards;

[0004] The patent with the announcement number CN103758144A discloses a pipe well for simultaneous drainage and pressure reduction and precipitation, including a well pipe, the well pipe including a sedimentation pipe, a pressure reduction filter pipe, a pressure reduction well wall pipe, a drainage filter pipe and a drainage well wall pipe which are sequentially arranged from bottom to top, a sealing plate is arranged at the junction of the pressure reduction well wall pipe and the drainage filter pipe, a gravity pipe is installed on the sealing plate, the gravity pipe has an inlet pipe section extending to the bottom of the sealing plate and a water outlet pipe section extending to the top of the sealing plate, a water inlet is arranged on the inlet pipe section, a plurality of water outlets are arranged at intervals along the axial direction on the water outlet pipe section, each water outlet is an openable and closable structure, the sedimentation pipe, the pressure reduction filter pipe and the pressure reduction well wall pipe form a lower pressure reduction well pipe, the drainage filter pipe and the drainage well wall pipe form an upper drainage well pipe, the inner diameter of the lower pressure reduction well pipe is smaller than the inner diameter of the upper drainage well pipe, the lower pressure reduction well pipe and the upper drainage well pipe are respectively sealed and connected to the sealing plate to form a stepped reducer.

[0005] The dewatering effect of the foundation pit dewatering method disclosed in the above patent is still very low, which is prone to potential safety hazards. Therefore, how to provide a combined foundation pit dewatering method under water-containing interlayer geological conditions is an urgent problem that technical personnel in this field need to solve. Summary of the invention

[0006] The main purpose of the present invention is to provide a combined foundation pit dewatering method under water-bearing interlayer geological conditions to solve the above technical problems. The device is equipped with multiple vacuum dewatering deep wells, and the dewatering speed is increased through the pipelines in the vacuum dewatering deep wells, while shortening the foundation pit excavation time and improving the excavation efficiency.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for combined foundation pit dewatering under water-bearing interlayer geological conditions comprises the following steps:

[0009] S1, open the drainage deep well and the decompression deep well, and ensure that the water level is 1m below the excavation surface. The decompression deep well is opened according to the calculated water head; when the foundation pit is excavated to the water-bearing interlayer of 0.5-1.0m, add a vacuum drainage deep well along the longitudinal direction of the foundation pit, and operate the drainage deep well and the decompression deep well synchronously;

[0010] S2, one end of the water pumping main pipe on the excavation surface of the foundation pit is connected to the pipes in the decompression deep well and the drainage deep well; the end of the water pumping main pipe away from the decompression deep well and the drainage deep well is connected to the vacuum pump through a hose;

[0011] S3, insert the downpipe into the vacuum drainage deep well, the downpipe is exposed 30-50 cm above the ground, and the end of each downpipe away from the vacuum drainage deep well is connected to the pumping main pipe through hose 2, and the connection is wrapped with plastic film;

[0012] S4, the vacuum pump is connected to the drain pipe, and the drain pipe is connected to the ground drain ditch.

[0013] Furthermore, the diameter of the downcomer is 30 mm, and within a 3-meter-long range from the bottom of the vacuum drainage deep well to the ground, two holes with a diameter of 8 mm are opened in a circumferential direction every 10 cm, and the downcomer is wrapped with a 60-mesh filter.

[0014] Furthermore, the diameter of the water pumping main pipe is 50 mm, and a hole with a diameter of 32 mm is opened in the circumferential direction of the water pumping main pipe every 2 m.

[0015] Furthermore, each of the plurality of downcomer pipes is equipped with a vacuum pump to form a downcomer section.

[0016] Furthermore, the distance between each row of vacuum pumps is 6 to 8 meters.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention adds a plurality of vacuum drainage deep wells, and the speed of precipitation is increased through the pipes in the vacuum drainage deep wells, while shortening the foundation pit excavation time and improving the excavation efficiency; the present invention occupies a small construction area, can be flexibly arranged, and has light materials, fast construction speed, short construction time for each section, and simple dismantling; in addition, the present invention can precipitate water while under construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0020] Figure 1 It is a structural schematic diagram of the present invention.

[0021] Figure 2 Schematic diagram of the water level control and excavation depth curve of the deep well for dewatering the main station foundation pit.

[0022] Figure 3 Schematic diagram of the block excavation of the foundation pit for the main station.

[0023] Figure 4 Schematic diagram of layered excavation of the foundation pit for the main station.

[0024] Figure 5 Schematic diagram of the water level control and excavation depth curve of the deep pressure relief well for the main station foundation pit.

[0025] Among them, 1-vacuum pump, 2-drain pipe, 3-hose one, 4-downflow pipe, 5-hose two, 6-pumping main pipe, 7-foundation pit excavation surface. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] like Figure 1 As shown, the present invention provides a method for combined foundation pit dewatering under water-bearing interlayer geological conditions, comprising the following steps:

[0028] S1, open the drainage deep well and the decompression deep well, and ensure that the water level is 1m below the excavation surface. The decompression deep well is opened according to the calculated water head; when the foundation pit is excavated to the water-bearing interlayer of 0.5-1.0m, add a vacuum drainage deep well along the longitudinal direction of the foundation pit, and operate the drainage deep well and the decompression deep well synchronously;

[0029] S2, one end of the water pumping main pipe 6 on the foundation pit excavation surface 7 is connected to the pipelines in the decompression deep well and the drainage deep well; the end of the water pumping main pipe 6 away from the decompression deep well and the drainage deep well is connected to the vacuum pump 1 through a hose 3;

[0030] S3, insert the downpipe 4 into the vacuum drainage deep well, the downpipe 4 is exposed 30 to 50 cm above the ground, and the end of each downpipe 4 away from the vacuum drainage deep well is connected to the pumping main pipe 6 through a hose 2 5, and the connection is wrapped with a plastic film to prevent water leakage;

[0031] S4, the vacuum pump 1 is connected to the drain pipe 2, and the drain pipe 2 is connected to the ground drain ditch. The drain pipe 2 is used to drain the water in the pumping main pipe.

[0032] In this embodiment, the downcomer 4 is a PVC pipe with a diameter of 30 mm. The downcomer 4 has two holes with a diameter of 8 mm opened every 10 cm in a circumferential direction within a 3-meter length from the bottom of the vacuum drainage deep well to the ground for water seepage, and is wrapped with a 60-mesh filter screen to prevent clogging of the seepage holes and ensure drainage efficiency. The role of the opening holes: the size of the holes is first for convenience of operation, and second, if the size is too large, it is easy to cause the filter screen to sink and the suction pressure at the hole mouth is too small; if the hole mouth is too small, it is easy to be blocked and the pumping efficiency is low.

[0033] In this embodiment, the diameter of the water pumping main pipe 6 is 50 mm, and holes with a diameter of 32 mm are provided in the circumferential direction of the water pumping main pipe 6 every 2 m for connecting the hose 2 5 . The water pumping main pipe 6 is used for pumping water.

[0034] In this embodiment, one vacuum pump 1 is configured for every 10 downpipes 4 to form a downpipe section, and the downpipe effect inside the foundation pit is ensured through multiple downpipe sections.

[0035] In this embodiment, the spacing between each row of vacuum pumps 1 is 6 to 8 meters, and the vacuum pumps 1 can provide power for pumping water.

[0036] Before the dewatering method of the present invention was adopted, the excavation took about 10 days. After the dewatering method of the present invention was adopted, each section of excavation can save 6 days of construction period. The entire foundation pit is divided into 7 sections, which can shorten the excavation period by 42 days. The total cost of station excavation is saved by about 300,000 yuan; the stability and safety of the foundation pit excavation retaining structure is greatly enhanced, the project cost is saved, the quality of foundation pit excavation and land acquisition is ensured, and the construction progress is accelerated.

[0037] 1. Dewatering deep well operation

[0038] 1. Deep well dewatering should be carried out 7 days or earlier before foundation pit excavation to ensure that the water content in the excavated soil is effectively reduced and the foundation pit excavation construction is carried out smoothly.

[0039] 2. According to the excavation progress, the water level in the drainage deep well should be controlled within a certain depth below the foundation pit excavation surface. Before the drainage deep well is officially pumped, the monitoring unit should construct a phreatic level observation hole outside the pit as soon as possible. After the construction of the phreatic level observation hole is completed, the drainage deep well should be opened in time for drainage and precipitation. Under normal circumstances, the drainage deep well basically maintains continuous pumping for 24 hours. When abnormal precipitation occurs, adjustments should be made as needed.

[0040] The excavation depth of the drainage well and the water level in the drainage well need to be based on Figure 2 The main station foundation pit dewatering deep well water level control and excavation depth curve are used to control the process.

[0041] 2. Decompression Deep Well Operation

[0042] The number of deep pressure relief wells and the amount of water pumped should be controlled according to the excavation depth of the foundation pit and the buried depth requirements of the pressure head. The dewatering work should be stopped only after the underground structure is constructed to the balance between the overburden pressure and the supporting force of the groundwater head. The time to stop dewatering is determined by the calculation results of the balance between the overburden pressure and the supporting force. The calculation results should be submitted to the design and approved by the design before the construction site can stop dewatering. During the dewatering operation, the observation wells inside and outside the foundation pit should be monitored manually. In the case of abnormal water level, the frequency of manual monitoring should be carried out according to actual needs.

[0043] For decompression deep wells, in order to reduce the impact of precipitation on the surrounding environment, precipitation must be carried out on demand, and the water level control is strictly carried out according to the foundation pit excavation depth and pressure safety water level burial depth curve in the foundation pit qualitative analysis. According to the excavation conditions, the time, number and water output of the decompression deep wells opened during precipitation operation should correspond to the excavation depth of the foundation pit.

[0044] In order to ensure that the north and south end wells are completed according to the shield receiving and starting node targets, the station arranges two excavation faces and arranges the excavation of the two end wells first, so as to complete the bottoming of the foundation pits of the north and south end wells as soon as possible. The station foundation pit is divided into 2 working faces and a total of 8 sections for excavation. The standard section of the station is divided into 6 layers for excavation, and the end section is divided into 7 layers for excavation. Figure 3 , 4 Schematic diagram of the block and layer excavation of the main station foundation pit.

[0045] Excavation in sections and segments: The standard section of the Sports Park Station has 6 supports, and the end section has 7 supports. The excavation and support erection of the station are carried out in sections and layers according to the principle of "time and space effect". The longitudinal excavation and support erection of this station are divided into eight sections: the first to the eighth section; the vertical excavation of the east and west end shield shaft sections is divided into seven layers, and the standard section is divided into six layers (except for surface earth excavation). Each layer of soil in each construction section is excavated in small sections. The width of the platform for each small section of excavation is determined according to the horizontal distance of the support, not less than 6m; the excavation depth is determined according to the vertical spacing of the support, and the soil at the steel support is constructed by the method of grooving; each small section of soil must be excavated within 16 hours, and then the support erection and prestressing are completed within 8 hours.

[0046] According to the progress of layered excavation, Figure 2 The water level control and excavation depth curve of the deep well for dewatering the foundation pit of the Central Main Station shows that when the excavation reaches the designed depth, it is required to open the ④1st, ⑤1st and ⑤3rd layers of decompression deep wells. The numbers of the decompression deep wells opened according to the requirements in Tables 1, 2 and 3 can control the actual head of the pressurized water to meet the requirements of the calculated head in the table, thereby ensuring the safety verification of the sudden surge stability of the foundation pit and ensuring the safety of the bottom of the foundation pit.

[0047] The excavation depth of the decompression well and the water level in the decompression well need to be determined according to Figure 5 The water level control of the decompression well in the main station foundation pit is controlled by the excavation depth curve chart.

[0048] Table 1: Block and layer excavation of the main station foundation pit and water level control table of ④1 layer

[0049] Section Paragraph 1 Paragraph 2 Paragraph 3 Paragraph 4 Paragraph 5 Paragraph 6 Paragraph 7 Paragraph 8 The third track: 11.9m 3.2 3.2 3.2 3.2 3.2 3.2 3.2 3.2 Number of operations (ports) 1 1 1 Running Hashtag Y41t-1 Y41t-5 Y41t-9 The fourth track is 14.65m 7.96 7.96 7.96 7.96 7.96 7.96 7.96 7.96 Number of operations (ports) 1 1 1 Running Hashtag Y41t-1 Y41t-5 Y41t-9 Fifth track 18.599m 14.78 14.78 14.78 14.78 14.78 14.78 14.78 14.78 Number of operations (ports) 1 1 1 1 1 Running Hashtag Y41t-1 Y41t-3 Y41t-5 Y41t-7 Y41t-9 The sixth track is 21.901m 20.49 20.49 20.49 20.49 20.49 20.49 20.49 20.49 Number of operations (ports) 1 1 1 1 1 1 1 Running Hashtag Y41t-1 Y41t-3 Y41t-5 Y41t-7 Y41t-8 Y41t-9 Standard section bottom plate 24.19m 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 Number of operations (ports) 1 1 1 1 1 1 1 Running Hashtag Y41t-1 Y41t-3 Y41t-4 Y41t-5 Y41t-6 Y41t-7 Y41t-8 Y41t-9 Shield area bottom plate 25.95m 27.00 27.00 27.00 27.00 27.00 27.00 27.00 27.00 Number of operations (ports) 1 1 1 1 1 1 1 Running Hashtag Y41t-1 Y41t-3 Y41t-4 Y41t-5 Y41t-6 Y41t-7 Y41t-8 Y41t-9

[0050] Table 1 Table 2 Block and layer excavation of the main station foundation pit and water level control table of layer ⑤1

[0051]

[0052] Table 2 and Table 3 are the block and layer excavation of the main station foundation pit and the water level control table of layer ⑤3

[0053]

[0054] Table 3

[0055] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0056] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for combined foundation pit dewatering under water-bearing interlayer geological conditions, characterized in that: The following steps are involved: S1, open the drainage deep well and the decompression deep well, and ensure that the water level is 1m below the excavation surface. The decompression deep well is opened according to the calculated water head; when the foundation pit is excavated to the water-bearing interlayer of 0.5-1.0m, add a vacuum drainage deep well along the longitudinal direction of the foundation pit, and operate the drainage deep well and the decompression deep well synchronously; S2, one end of the water pumping main pipe (6) on the excavation surface (7) of the foundation pit is connected to the pipelines in the deep decompression well and the deep drainage well; the end of the water pumping main pipe (6) away from the deep decompression well and the deep drainage well is connected to the vacuum pump (1) through a hose (3); S3, inserting the downpipe (4) into the vacuum drainage deep well, with the downpipe (4) exposed 30 to 50 cm above the ground, and connecting the end of each downpipe (4) away from the vacuum drainage deep well to the pumping main pipe (6) through a hose 2 (5), and wrapping the connection with a plastic film; S4, the vacuum pump (1) is connected to the drainage pipe (2), and the drainage pipe (2) is connected to the ground drainage ditch.

2. The method for combined foundation pit dewatering under water-bearing interlayer geological conditions according to claim 1, characterized in that: The diameter of the downcomer (4) is 30 mm. The downcomer (4) has a length of 3 meters from the bottom of the vacuum drainage deep well to the ground, and has two holes with a diameter of 8 mm opened every 10 cm in the circumferential direction, and is wrapped with a 60-mesh filter.

3. The method for combined foundation pit dewatering under water-bearing interlayer geological conditions according to claim 1, characterized in that: The diameter of the water pumping main pipe (6) is 50 mm, and holes with a diameter of 32 mm are provided in the circumferential direction of the water pumping main pipe (6) every 2 m.

4. The method for combined foundation pit dewatering under water-bearing interlayer geological conditions according to claim 1, characterized in that: Each of the plurality of downpipes (4) is equipped with a vacuum pump (1) to form a downpipe section.

5. The method for combined foundation pit dewatering under water-bearing interlayer geological conditions according to claim 1, characterized in that: The distance between each row of vacuum pumps (1) is 6 to 8 m.

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