Dewatering construction structure of confined water depth foundation pit

Abstract

The utility model provides a pressure-bearing water depth foundation pit dewatering construction structure, which belongs to the technical field of foundation pit construction and comprises a sheath arranged in a drill hole, a filter material layer arranged in the sheath, and a well casing arranged in the filter material layer. The sheath comprises a lower section located at the bottom end of the drill hole and an upper section close to the top end of the drill hole. According to the utility model, the upper section and the lower section are formed through the reserved sleeve, and the upper section and the lower section do not influence normal underground water overflow and can also ensure the stability of the pressure-bearing water depth foundation pit, so that the construction difficulty can be reduced in the construction process of the deep foundation pit.

Description

Technical Field

[0001] The utility model relates to the technical field of foundation pit construction, in particular to a pressure-bearing deep foundation pit dewatering construction structure. Background Art

[0002] Foundation pit dewatering technology is of great significance in current engineering construction, especially during the period of rapid urban development. With the continuous development and utilization of underground space, the problem of pressurized water in foundation pit construction has become increasingly prominent. Confined water, with its high pressure, can cause disasters such as water and sand inrush in the foundation pit, seriously threatening construction safety and the surrounding environment.

[0003] Traditional foundation pit dewatering methods can be inefficient, ineffective, and significantly impact the surrounding environment. For example, some methods can cause the groundwater level to drop excessively, impacting the safety of surrounding buildings; or the dewatering effect can be unstable, failing to meet construction requirements. Deep foundation pits, due to their depth and complex soil conditions, also make dewatering operations more difficult.

[0004] To this end, the utility model proposes a construction method for dewatering a deep foundation pit under pressure water, which improves the safety and stability of the foundation pit construction and also minimizes the impact on the surrounding environment. Utility Model Content

[0005] In order to solve the problems of low efficiency, poor effect and great impact on the surrounding environment in traditional foundation pit dewatering methods, the utility model provides a construction method for dewatering deep foundation pits with pressurized water, which realizes the effective control and utilization of pressurized water, improves the safety and stability of construction, and reduces the impact on the surrounding environment. It has the characteristics of accuracy, safety and stability, and can be widely used in construction in the field of foundation pit dewatering technology.

[0006] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0007] The construction structure for dewatering deep foundation pits under pressure water includes:

[0008] A sheath is provided inside the borehole, a filter material layer is provided inside the sheath, and a well pipe is provided inside the filter material layer;

[0009] The protective sleeve comprises a lower section located at the bottom end of the borehole and an upper section close to the top end of the borehole.

[0010] Preferably, the sheath further comprises an orifice inner support located at the top end of the drill hole.

[0011] Preferably, the filter material layer comprises, from bottom to top, medium-coarse sand and melon seed slices, medium-coarse sand, yellow pure fine sand, and clay balls.

[0012] Preferably, the well pipe comprises, from bottom to top, a lower sedimentation pipe, a middle bridge filter pipe, and an upper seamless steel pipe.

[0013] Preferably, the lower part of the middle bridge filter tube is a 60-mesh filter screen, and the upper part is an 80-mesh filter screen.

[0014] Preferably, the wall thickness of the well pipe is 14 mm.

[0015] The beneficial effects of the present utility model are as follows: the casing is lowered after the hole is formed, which can prevent the well wall from collapsing and ensure the safety of the well. After the filter material filling process is completed, the casing is partially pulled out, and part of the casing is reserved to form upper and lower sections. The upper and lower sections will not affect the normal overflow of groundwater, and can also ensure the stability of the deep foundation pit under pressure. During the construction of the deep foundation pit, the difficulty of construction can be reduced. The well washing, installation of pumping equipment and the pumping test steps can monitor the working status of the well pipe in real time, discover and solve problems in time, and ensure the quality of construction. Through well pipe sealing, construction monitoring and emergency measures, it is possible to respond quickly when abnormal situations occur and effectively deal with possible risks. Through the above series of construction steps and technical means, the stability and reliability of the precipitation construction are ensured, and the safety of the project is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the construction method of dewatering a deep foundation pit under pressure, the following drawings are shown;

[0017] Figure 1 This is a schematic diagram of a pressure relief well / observation well in a foundation pit of the present utility model;

[0018] Figure 2 This is a schematic diagram of the plan layout of the observation well and pressure relief well of the utility model;

[0019] Figure 3 It is a schematic diagram of the casing of the present utility model.

[0020] wherein the reference numerals in the accompanying drawings;

[0021] 1. Well pipe; 101. Lower sedimentation pipe; 102. Middle bridge filter pipe; 103. Upper seamless steel pipe; 2. Medium-coarse sand and melon seed slices; 3. Medium-coarse sand; 4. Yellow pure fine sand; 5. Clay balls; 6. Mortar; 7. Casing; 701. Short section; 702. Long section; 702a. Flange; 703. Welded inner strip; a. First-order pressure relief well; b. Second-order pressure relief well; c. Third-order pressure relief well; d. Observation well. DETAILED DESCRIPTION

[0022] Taking a sluice and ship lock project as an example, the construction method of pressurized water deep foundation pit dewatering is explained. In the construction of deep foundation pit, how to effectively control and utilize pressurized water, improve the safety and stability of construction, and reduce the impact on the surrounding environment, and it has the characteristics of accuracy, safety and stability.

[0023] Please refer to the attached Figure 1-Figure 3 This embodiment provides a construction method for dewatering a deep foundation pit under pressure, comprising the following steps:

[0024] Step 1: Measure and lay out to ensure the accuracy of construction, as follows:

[0025] According to the well pipe position Figure 2 Based on the benchmarks provided by the owner, a control network was established within the project using a combination of traverse and triangulation. Control points were re-surveyed and approved before use. Well casing positioning was performed using the polar coordinate method with a total station and marked with "gantry piles."

[0026] Step 2: The drilling rig is in place to facilitate subsequent construction, as follows;

[0027] To ensure the well casing can be lowered smoothly to the desired depth, the ground around the pile hole must be cleaned and leveled, and the foundation must be compacted before the drilling rig is placed. The drilling rig must be placed stably. When the drilling rig is in place, the center of the drill bit and the center of the pile must be aligned on the same plumb line, with a centering error of less than 10mm. Once the drilling rig is in place, the leveling must be adjusted to maintain verticality, and the floor elevation must be measured. A verification form must also be completed. Drilling may only proceed after the supervising engineer has inspected and accepted the drilling rig's centering and drill pipe verticality. Before formal drilling, the drilling rig must undergo a test run to check its stability and condition, ensuring continuity of subsequent drilling operations.

[0028] Step 3: bury the casing to protect the wellhead and prevent the influx of groundwater, as follows;

[0029] The casing should be placed in the same position as the pile. The pile position is located using the polar coordinate method using a total station, and crosshairs are used to verify the location of the casing in conjunction with the "gantry pile" method. A 450 drilling machine is used to lower the casing. The casing is made of 14mm thick steel plate, is 11.5m long, and has a slurry discharge port at the top.

[0030] To ensure the quality of the borehole, the casing should meet the following requirements: Onshore casing is buried by manually digging a pit directly on the ground, filling the bottom of the pit with 0.5m thick clay, and then burying the casing; the casing is not less than 30cm above the ground; when there is pressurized water in the borehole, it should be 1.5 to 2.0m higher than the stabilized pressurized water level; after the casing is sunk into the stratum, use a cross line to check whether the center of the casing is consistent with the center of the pile, and ensure that the plane position deviation of the casing after burial is <5cm; to increase rigidity and prevent deformation, a stiffening rib is welded on the outer side of the upper and lower ends and the middle of the casing.

[0031] Step 4: Mud preparation and use, in order to ensure stability during the drilling process and reduce pollution to the environment, the details are as follows;

[0032] The wellbore mud wall is primarily constructed with purchased bentonite. The mud density, viscosity, and sand content should be regularly measured during the drilling process. The ideal mud density is 1.05-1.10. On-site testing personnel are responsible for maintaining original records of the drilling and cleaning mud quality inspections and communicating the inspection results to relevant personnel for timely adjustments.

[0033] Step 5: Soil excavation and hole formation is to use drilling equipment to dig out the soil to form a hole in preparation for the subsequent well pipe installation, as follows;

[0034] After the drilling rig is leveled and the pile position has been verified, drilling can begin. The 360 rotary drilling rig begins drilling, advancing slowly at first and then faster, with an initial feed rate of 0.4-0.5 m / min. Check for unfavorable underground strata. Once the feed reaches the clay layer and drilling proceeds normally, the feed rate can be increased appropriately. A drop hammer grab removes the soil from the casing and unloads it onto the surface. A loader loads the soil into a dump truck and transports it to the drying area. After drying, it is transported to a designated waste disposal site. When drilling, the elevation of the aquiclude and gravel layers should be recorded in detail, and a histogram of the drilled holes should be generated to facilitate control of the backfill elevation for filter material, clay balls, and other materials. Once the hole reaches the designed elevation, the hole depth, diameter, and verticality of the hole wall should be checked. Inspection tools, measuring ropes, and other tools should be prepared before testing. During drilling, the drill rig instrument should be monitored at all times. If the instrument indicates any change in verticality, adjustments should be made immediately before drilling.

[0035] Step 6: Hanging and lowering the casing. The purpose of hanging and lowering the casing is to prevent the well wall from collapsing and ensure the safety of the well. The details are as follows;

[0036] After the soil is excavated, a 75t crawler crane is used to lower the entire casing. The entire casing is made of φ610 seamless steel pipe with a wall thickness of 14mm. The overall length of the casing is the same as the hole depth, and the hole mouth uses a pre-made flange.

[0037] The sleeve includes a short section 701 and a long section 702. The bottom end of the long section 702 is aligned with the top end of the short section 701. A plurality of welded inner strips 703 are connected between the short section 701 and the long section 702. The top end of the long section 702 has a flange portion 702a.

[0038] The plurality of welded inner strips 703 connect the short section 701 and the long section 702 into a whole, so that the casing can be hoisted and lowered smoothly.

[0039] Step 7: Hole cleaning: Hole cleaning is to remove debris and sediment in the hole to ensure that the well is unobstructed. The details are as follows;

[0040] The hole is cleaned before the well pipe is lowered into the well. The hole is cleaned by injecting clean water for displacement, using a mud pump to pump out the sediment, and measuring the hole depth.

[0041] Step 8: Hoisting the well pipe is to hoist the prepared well pipe into the hole for installation, as follows:

[0042] The well pipe is divided into three parts: the upper seamless steel pipe 103, the middle bridge filter pipe (10m) 102, and the lower sedimentation pipe (1m) 101. It is slowly lowered using a 75t truck crane. Each section of steel pipe is welded at the orifice, and the welding quality meets the specifications and design requirements. To prevent the upper and lower sections from being misaligned, the well pipe should be straightened in the direction before lowering. The well pipe should be hoisted vertically and kept in the center of the wellbore to prevent rainwater, mud, sand, or foreign matter from flowing into the well. The well pipe should be at least 20cm above the ground, and the wellhead should be covered. When lowering the well pipe, it should not be rotated or moved up and down to prevent damage to the filter screen, which will cause mud and sand to flow into the precipitation well.

[0043] Step nine, filling the filter material. Filling the filter material and clay is to filter out impurities and suspended matter in the water. The details are as follows;

[0044] S1: Filling filter material: After the well pipe reaches the designed depth, the mud in the well is appropriately diluted, and then gravel is immediately filled around the well pipe. The gravel material is: medium-coarse sand + 10% melon seed slices. The gravel is filled into a pebble layer. Clay balls are used to backfill the 1m connecting area between the pebble layer and the aquiclude, and clay is used to backfill the rest.

[0045] You can also use the method of having the following layers from bottom to top: medium-coarse sand and melon seed slices, medium-coarse sand, yellow pure fine sand, and clay balls.

[0046] S2: When backfilling filter material, it should be evenly distributed around the well pipe to ensure uniform filter layer thickness. The backfill volume should meet regulatory requirements. After the well pipe is lowered, the water seepage performance should be promptly checked. When the sand filter material is poured into the wellbore around the well pipe, muddy water should emerge from the well pipe. Alternatively, if clean water seeps quickly when injected into the well pipe, the well pipe is considered to be in good condition. If water does not seep, immediate action should be taken. After the well pipe is buried, a test pumping and flushing should be conducted promptly.

[0047] S3: The filter media for the wellbore is graded gravel and medium-coarse sand. It should be evenly distributed to prevent separation of coarse and fine aggregates, and the filter media should be densely packed. After the filter media is filled, clay balls should be added. When filling with clay balls, the balls should be evenly distributed around the wellbore, with a height of at least 1m. After this filling is completed, clay filling should be added.

[0048] Step 10: Pull out part of the casing, and the part of the casing remaining in the hole forms upper and lower sections.

[0049] Specifically, during the process of pulling out part of the casing, the welded inner strip 703 at the short section 701 and the long section 702 is broken, so that the short section 701 is completely left at the bottom of the hole. After the long section 702 is raised to a suitable height, the long section 702 is cut off at a height 2m below the ground elevation. After the long section 702 is cut off, the upper part of the long section 702 is raised out of the hole or 0.5-1m is reserved at the hole mouth.

[0050] Step 11: Well washing, installation of pumping equipment and pumping test: The well pipe is inspected and tested to ensure that it is working properly, as follows:

[0051] S1: Well washing: After completing the backfill filling, wash the well according to the regulations. The well washing should be sufficient and timely. Within 8 hours after the well is completed, put the sludge pump into the bottom of the well for repeated pumping and washing to ensure the water seepage effect. During the well washing process, observe the changes in water level and water output.

[0052] S2: Install pumping equipment:

[0053] ① The pumping test should be carried out after the well washing quality meets the requirements, and the maximum drawdown should be performed. The water output should be calculated using the steady flow principle, and the static water level and drawdown should be measured.

[0054] ②Install the submersible pump and piping system: Check the motor and pump body before installation. The water pump should be of P=7.5KW, H=50m, and flow rate 50m3 / h. The equipment can be installed only after inspection. The insulation of the submersible motor, cables and connectors is safe and reliable, and equipped with protective switch control to ensure safe operation. During the installation process, ensure that all connection parts are sealed reliably and leak-proof.

[0055] ③ When lowering the water pump, it should be tied firmly with steel rope or wire, and the water pipe mouth should be tied firmly. After the water pump is installed, a cover plate must be installed at the wellhead to prevent foreign objects from falling into the well.

[0056] S3: Lock pumping test:

[0057] The ship lock foundation pit is set as one area, and the pressure relief well is constructed in three sequences.

[0058] ① Before constructing the relief well, complete the observation well. Before the relief well is completed, to prevent overflow of pressurized water, drainage can be conducted through the observation well if necessary. Tests should be conducted to ensure the effectiveness of the observation well. If the water flow from the observation well is normal, proceed to step ②. Otherwise, the design will make decisions based on the situation on site.

[0059] ②Construct a first-order pressure relief well and conduct tests to ensure the effectiveness of the pressure relief well. If the water output is normal, proceed to step ③. Otherwise, the designer will make decisions on site based on the situation.

[0060] ③ Pump water from the completed pressure relief wells in ② and observe all observation wells within the sluice foundation pit: if the dewatering of all observation wells meets the design requirements and can be stable for three days, the dewatering well design plan needs to be optimized; if the dewatering of only some observation wells meets the design requirements or all observation wells do not meet the design dewatering requirements, continue the dewatering test according to ④, and the dewatering of the pressure relief wells in ② will not be interrupted.

[0061] ④Construct the second-order pressure relief well and conduct tests to ensure the effectiveness of the pressure relief well. If the water output is normal, continue to step ⑤. Otherwise, the designer will make decisions based on the situation on site.

[0062] ⑤ Pump water from the completed pressure relief wells in ②④ and observe all observation wells within the sluice foundation pit: if the dewatering of all observation wells meets the design requirements and can be stable for three days, the dewatering well design plan needs to be optimized; otherwise, three-sequence pressure relief wells need to be added according to the situation.

[0063] Step 12: Well plugging, construction monitoring, and emergency measures to prevent groundwater from gushing out again and ensure construction safety are as follows:

[0064] S1: Well pipe plugging: Before sealing the well after the dewatering operation is completed, the well pipe should be cleaned to remove the garbage and gravel, etc. After cleaning the debris, the well pipe should be cleaned and the water should be drained to avoid affecting the subsequent construction, and the pump should be pulled out. A 40mm grouting pipe is lowered into the pipe, and the bottom of the grouting pipe enters the bottom of the well pipe. The well pipe is initially filled with melon seed slices, and the melon seed slices should be backfilled to more than 9.0m above the grouting pipe mouth. Before the formal grouting, the grouting pipe position should be fixed at the well pipe mouth, and the cement slurry should be pre-mixed according to the size of the well, with a water-cement ratio of 0.6 to 0.7. Then start grouting. After grouting about 50cm to 100cm of slurry, lift the grouting pipe up 0.5 to 1.0m to continue grouting; after the grouting pipe is lifted 3.0m, pull out a section of the grouting pipe, and continue in sequence until the plugging is completed.

[0065] S2: Construction Monitoring:

[0066] ① Surrounding environment monitoring: including monitoring of settlement, tilt, crack generation and development of surrounding buildings and roads, generally one every 10m;

[0067] ②Monitor the settlement, tilt, crack formation and development of surrounding pipelines (gas pipes, water pipes, rainwater pipes, sewage pipes, fire pipes, power pipes, etc.), generally one crack every 10 meters. Excavate and expose the pipeline joints for monitoring;

[0068] ③ Lateral displacement of deep soil layer on foundation pit slope;

[0069] ④ Groundwater level observation hole;

[0070] ⑤ Foundation settlement detection.

[0071] S3: Emergency measures:

[0072] ① The retaining wall project is extremely complex and there are many factors that affect safety. A certain number of emergency equipment and materials should be available on site, such as sand bags, channel steel or steel pipes, grouting machines, etc. The equipment and materials must be in place before excavation. The construction unit must take corresponding emergency measures in a timely manner to ensure safety. When the foundation pit displacement is too large, additional supports can be added to the parts where conditions permit, or soil nails can be driven in, soil can be unloaded from the top of the slope, and bagged soil can be used for counter pressure at the foot of the slope. When the foundation pit leaks, emergency measures such as compaction grouting or rotary jet piles can be taken. When the situation is critical, excavation should be stopped immediately, and backfill should be carried out when necessary, and emergency measures such as unloading soil outside the pit should be taken. When the situation is critical, backfill should be carried out inside the pit.

[0073] Type ② mechanical construction should ensure that the ground has sufficient bearing capacity, and measures should be taken to ensure the stability of the machinery to avoid overturning and slope instability during operation.

[0074] ③ During the excavation of the foundation pit, pay close attention to the changes in the groundwater level outside the pit. If water seepage or sand flow is found, the designer should be notified in time and leakage prevention measures should be taken.

[0075] ④ The treatment of waste soil, slag and waste mud during the construction process should comply with the regulations of relevant departments and pay attention to environmental protection.

[0076] ⑤ During the foundation pit excavation process, excavation should be carried out in layers according to the design requirements. Excavation can only be continued after each support construction reaches the design strength. "Big pot bottom" excavation is strictly prohibited, and drainage work in the foundation pit must be done well. If construction is carried out during the rainy season, sufficient pumping equipment must be prepared to ensure that the base is not soaked for a long time.

[0077] ⑥ After the foundation pit is excavated to the designed depth, drainage ditches and collection wells should be built at the bottom of the foundation pit, and the accumulated water in the collection wells should be removed in time.

[0078] ⑦ When cracks appear on the ground surface, grouting is used to seal the cracks to prevent surface water from seeping in.

[0079] Specifically, the above-mentioned pressurized water deep foundation pit dewatering construction method forms: a pressurized water deep foundation pit dewatering construction structure, which includes: a casing arranged inside the borehole, a filter material layer arranged inside the casing, and a well pipe 1 arranged inside the filter material layer; the casing includes: a lower section located at the bottom end of the borehole and an upper section close to the top end of the borehole.

[0080] The sheath also includes an inner support at the top of the borehole; the filter material layer includes, from bottom to top: medium-coarse sand and melon seed slices 2, medium-coarse sand 3, yellow pure fine sand 4, and clay balls 5; the well pipe 1 includes, from bottom to top: a lower sedimentation pipe 103, a middle bridge filter pipe 102, and an upper seamless steel pipe 103; the lower part of the middle bridge filter pipe 102 is a 60-mesh filter screen, and the upper part is an 80-mesh filter screen; the wall thickness of the well pipe 1 is 14 mm.

[0081] Those skilled in the art will readily envision other embodiments of the present invention after considering the specification and practicing the disclosure herein. This application is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered as exemplary only, with the true scope and spirit of the present invention being indicated by the following claims.

[0082] It should be understood that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. The present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from the scope of the present invention. The scope of the present invention is limited only by the appended claims.

Claims

1. Construction structure for dewatering deep foundation pit under pressure water, characterized by: include: A sheath is arranged inside the borehole, a filter material layer is arranged inside the sheath, and a well pipe (1) is arranged inside the filter material layer; The protective sleeve comprises a lower section located at the bottom end of the borehole and an upper section close to the top end of the borehole.

2. The construction structure for dewatering a deep foundation pit under pressure water according to claim 1, characterized in that: The sheath also includes an orifice support located at the top end of the drill hole.

3. The construction structure for dewatering a deep foundation pit under pressure water according to claim 1, characterized in that: The filter material layer comprises, from bottom to top, medium-coarse sand and melon seed slices (2), medium-coarse sand (3), yellow pure fine sand (4), and clay balls (5).

4. The construction structure for dewatering a deep foundation pit under pressure water according to claim 1, characterized in that: The well pipe (1) comprises, from bottom to top, a lower sedimentation pipe (103), a middle bridge filter pipe (102), and an upper seamless steel pipe (103).

5. The construction structure for dewatering a deep foundation pit under pressure water according to claim 4, characterized in that: The lower part of the middle bridge filter tube (102) is a 60-mesh filter screen, and the upper part is an 80-mesh filter screen.

6. The construction structure for dewatering a deep foundation pit under pressure water according to claim 1, characterized in that: The wall thickness of the well pipe (1) is 14 mm.

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