Dewatering construction methods for silty clay soil with poor permeability in deep foundation pits

Abstract

This invention provides a method for dewatering silty clay soil layers with poor permeability in deep foundation pits, relating to the field of deep foundation pit construction technology. The method includes the following steps: initial dewatering; foundation pit excavation; sump excavation; deep excavation; partial earthwork replacement, including deep excavation of the sump and replacement of the deep excavated portion of the sump with permeable material; secondary dewatering via a drainage pipe; foundation cushion concrete pouring; waterproof layer construction; waterproof protective layer construction; foundation reinforcement binding; foundation concrete pouring; and cessation of dewatering. By filling the deep excavated portion of the sump with permeable material twice, a portion of the sump in the drainage pipe is buried within the permeable material to guide groundwater from the sump to the municipal pipe network for dewatering. This method not only increases soil infiltration speed and reduces soil erosion during drainage through the permeable material, but also eliminates the need for secondary treatment as the drainage pipe is located below the foundation cushion.

Description

Technical Field

[0001] This invention relates to the field of deep foundation pit construction technology, specifically to a method for dewatering silty clay soil layers with poor permeability in deep foundation pits. Background Technology

[0002] During foundation construction, with the development and application of underground space, deep foundation pit projects frequently occur in various construction projects. Affected by groundwater level, soil quality, and dewatering methods, the dewatering effect often fails to achieve the final goal. In areas such as elevator foundations and sump pits where the groundwater level is higher than the construction elevation than the building foundation, secondary dewatering is required. Most dewatering methods employ lightweight wellpoint dewatering and open drainage systems. These two methods are suitable for different soil types and have varying degrees of impact on foundation construction.

[0003] However, the open drainage method uses open ditches and canals to divert sewage and achieve surface drainage, which requires a lot of waste materials; while the lightweight well point method is suitable for smaller drainage volumes, and if rapid dewatering is desired, the dewatering wells must be dug deep. Therefore, neither of the above two methods can save materials while ensuring dewatering effect and improving construction efficiency. Summary of the Invention

[0004] The purpose of this invention is to provide a dewatering construction method for silty clay soil layers with poor permeability in deep foundation pits, aiming to solve the problem that general dewatering construction methods for silty clay soil layers with poor permeability in deep foundation pits cannot guarantee the dewatering effect while saving materials.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: the dewatering construction method for silty clay soil layers with poor permeability in deep foundation pits includes the following steps:

[0006] Preliminary dewatering involves using dewatering wells to lower the water level in the construction area to the height of the bottom of the foundation pit.

[0007] Excavation of the foundation pit: The foundation pit is excavated according to the design drawings.

[0008] Excavation of the sump pit: The sump pit is excavated on the bottom plane of the foundation pit according to the foundation design elevation, and the bottom of the sump pit is below the water level.

[0009] Deep excavation is carried out, including deep excavation of the bottom of the sump pit;

[0010] Partial earthwork replacement: Permeable materials are used to replace the deep excavated part of the sump pit. The height of the replacement earthwork is flush with the bottom plane of the sump pit so that the upper surface of the replacement earthwork forms the bottom surface of the sump pit.

[0011] Secondary dewatering is achieved by burying the water pipe in the permeable material of the deep excavation layer and connecting the water pipe to a water pump to pump out water from the sump and the deep excavation layer, thereby lowering the water level below the bottom of the sump.

[0012] The foundation cushion layer is formed by pouring concrete on the bottom plane of the foundation pit, the bottom surface of the sump pit and the side walls.

[0013] Waterproofing layer construction: Lay the waterproofing layer on the base layer, and conduct a water tightness test after the waterproofing layer construction is completed;

[0014] Waterproof protective layer construction: The waterproof protective layer shall be poured after the waterproof layer has passed inspection.

[0015] After the foundation reinforcement is tied and the waterproof protective layer is poured, the foundation reinforcement is tied according to the design drawings and specifications.

[0016] After the concealed inspection of the foundation reinforcement is completed, the foundation concrete pouring begins.

[0017] Stop the precipitation. Once the foundation concrete has been poured, turn off the water pumps after the concrete has set.

[0018] The beneficial effects are as follows: by excavating the sump pit deeply and filling the deep part of the sump pit with permeable material twice, a part of the sump pipe in the water guide pipe is buried in the permeable material, and the water delivery pipe connected to the sump pipe is connected to the water pump to guide the groundwater in the sump pit to the municipal pipe network for dewatering. This avoids the need to excavate the dewatering well deeply. Not only can the permeable material increase the soil infiltration rate and reduce soil erosion during drainage, but the water guide pipe is located under the foundation cushion layer and does not require secondary treatment, so it does not affect the normal construction of subsequent procedures.

[0019] A further technical solution of the present invention is that, in the deep excavation step, the height of the water collection pit is 300 mm, and the shape of the deep excavation part of the water collection pit corresponds to the shape of the water collection pit.

[0020] A further technical solution of the present invention is that, in the partial earthwork replacement step, the permeable material is coarse sand, and the permeable material is replaced in two stages. First, the permeable material is laid flat in the artificial soil clearing layer for 150 mm, and then the remaining part is replaced on the flat permeable material.

[0021] A further technical solution of the present invention is that, in the secondary dewatering step of the water pipe, the water pipe is composed of a water collection pipe and a water delivery pipe.

[0022] A further technical solution of the present invention is that the water collection pipe is arranged horizontally in the permeable material, the water collection pipe is arranged horizontally at the bottom of the foundation pit, and part of the water collection pipe extends downward and is buried in the permeable material.

[0023] A further technical solution of the present invention is that a water collection hole for collecting groundwater inside the water collection pit is provided on the outer circumference of the water collection pipe, and a filter cloth is wrapped around the outer surface of the water collection pipe. The filter cloth is used to filter the water introduced into the water collection hole to avoid clogging by sand and gravel.

[0024] The beneficial effect is that it can filter the water entering the water collection pipe to prevent sand and gravel from clogging the water collection holes and affecting its normal operation, thereby affecting the precipitation efficiency.

[0025] A further technical solution of the present invention is that the water delivery pipe is laid out along the outline of the foundation pit to the outside of the foundation.

[0026] A further technical solution of the present invention is that the drainage end of the water supply pipe is connected to a water pump, and the pumping end of the water supply pipe is connected to a water collection pipe, so as to use the water pump to export the groundwater inside the water collection pit and discharge it to the municipal pipe network for dewatering.

[0027] A further technical solution of the present invention is that the water pump is installed outside the foundation pit.

[0028] A further technical solution of the present invention is that, in the waterproof layer construction step, a water tightness test needs to be carried out after the waterproof layer construction is completed, and the next process is carried out after the test is passed. Attached Figure Description

[0029] Figure 1 This is a flowchart of the present invention.

[0030] Figure 2 This is a cross-sectional view of the deep excavation layer of the present invention.

[0031] Figure 3 This is a schematic diagram of the water pipe installation of the present invention.

[0032] In the diagram: 1-Foundation pit, 2-Water collection pit, 21-Deep excavation layer, 31-Water collection pipe, 32-Water delivery pipe, 33-Water pump. Detailed Implementation

[0033] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0034] like Figures 1-3 As shown, the dewatering construction method for silty clay soil layers with poor permeability in deep foundation pits includes the following steps:

[0035] Preliminary dewatering involves using dewatering wells to lower the water level in the construction area to the bottom plane of the foundation pit 1. In this embodiment, multiple dewatering wells are set up around the perimeter of the foundation pit area.

[0036] Excavation of the foundation pit: Once the water level at the location of the foundation pit drops below the bottom of the foundation pit, the foundation pit 1 will be excavated according to the design drawings.

[0037] Excavation of the sump pit: According to the foundation design elevation, sump pit 2 is excavated on the bottom plane of foundation pit 1, and the bottom of sump pit 2 is below the water level.

[0038] The deep excavation layer is formed by continuing to excavate downwards from the bottom of the sump pit 2. In this embodiment, the depth of the deep excavation layer is 300mm, and the cross-sectional shape of the deep excavation layer corresponds to the cross-sectional shape of the sump pit. At this time, the sump pit and the deep excavation layer are located below the water level, resulting in water accumulation in the sump pit and the deep excavation layer.

[0039] For partial earthwork replacement, permeable material is used to replace the deep excavation layer of the sump pit 2. The thickness of the replacement earthwork is 300mm, that is, the height of the replacement earthwork is flush with the bottom plane of the sump pit 2 so that the upper surface of the replacement earthwork forms the bottom surface of the sump pit 2. In this embodiment, the permeable material is coarse sand. The permeable material is replaced in two stages. First, the permeable material is spread evenly in the artificial soil layer for 150mm. Then, the remaining part is replaced on the spread permeable material.

[0040] Secondary dewatering is achieved by burying the water pipe in the permeable material of the deep excavation layer 21 and connecting it to the water pump 33. The water pump 33 then pumps out water from the sump pit 2 and the deep excavation layer 21, lowering the water level below the bottom of the sump pit 2. The water pipe consists of a collection pipe 31 and a delivery pipe 32. The collection pipe 31 is horizontally arranged at the bottom of the foundation pit 1, and a portion of the collection pipe 31 extends downward and is buried in the middle of the permeable material. The outer circumference of the collection pipe 31 has a collection hole for collecting groundwater inside the sump pit 2. The outer surface of the collection pipe 31 is wrapped with a filter cloth to filter the water introduced into the collection hole to prevent sand and gravel from clogging it. The water supply pipe 32 is laid out along the outline of the foundation pit 1 and connected to the water pump 33 outside the foundation pit 1. One end of the water supply pipe 32 located inside the foundation pit 1 is connected to the water collection pipe 31 so that the groundwater inside the water collection pit 2 can be discharged to the municipal pipe network for dewatering through the water pump 33. In this embodiment, both the water collection pipe 31 and the water supply pipe 32 are made of PPR material, and the filter cloth is made of nylon material.

[0041] The foundation cushion layer is poured. Concrete is poured on the bottom plane of the foundation pit 1, the bottom surface of the sump pit 2 and the side walls to form the foundation cushion layer. The water collection pipe 31 is located at the bottom of the foundation cushion layer, and the water delivery pipe 32 is located inside the foundation cushion layer and extends through its side walls to the outside of the foundation pit 1.

[0042] Waterproofing layer construction involves laying the waterproofing layer on the base layer. After the waterproofing layer construction is completed, a water tightness test needs to be carried out to prevent leakage from affecting the next process.

[0043] Waterproof protective layer construction: The waterproof protective layer shall be poured after the waterproof layer has passed inspection.

[0044] After the foundation reinforcement is tied and the waterproof protective layer is poured, the foundation reinforcement is tied according to the design drawings and specifications.

[0045] Stop the precipitation. After the foundation concrete pouring is completed, turn off water pump 33 to stop the precipitation once the concrete has set.

[0046] In a specific embodiment, since the foundation pit is a large-area excavation area, the depth of the dewatering wells should be sufficient to ensure that the groundwater level is below the bottom of the foundation pit. However, if a sump or elevator shaft is excavated at the bottom of the foundation pit, the depth of the dewatering wells will obviously not meet the dewatering level requirements during the excavation of the sump or elevator shaft. In this invention, the sump 2 is deepened to form a deep excavation layer, which becomes the location where groundwater accumulates. The deep excavation portion of the sump 2 is filled with permeable material twice. A portion of the water collection pipe 31 in the water conduit is buried in the permeable material, and the water delivery pipe 32 connected to the water collection pipe 31 is connected to the water pump 33 to connect the sump 2 and the deep excavation layer. The groundwater is drained into the municipal pipe network, thereby dewatering the required depth of the sump pit. In other words, this invention meets the dewatering requirements of large-area excavated foundation pits through dewatering wells, and meets the dewatering requirements of locally excavated sump pits through deep excavation layers and drainage pipes. The combination of dewatering wells and the dewatering method of this application can meet the dewatering level requirements of the excavation depth of foundation pits and sump pits, while also minimizing the depth of dewatering wells. This saves the cost of multiple dewatering wells that would otherwise be caused by deep excavation. At the same time, it can increase the soil infiltration rate and reduce soil erosion during drainage by using permeable materials. Moreover, the water pipe is located below the foundation cushion layer and does not require secondary treatment, so it does not affect the normal construction of subsequent processes.

Claims

1. A method for construction of a deep foundation pit in a silty clay permeable stratum, characterized in that, Includes the following steps: Preliminary dewatering involves using dewatering wells to lower the water level in the construction area to the height of the bottom of the foundation pit. Excavation of the foundation pit: The foundation pit is excavated according to the design drawings. Excavation of the sump pit: The sump pit is excavated on the bottom plane of the foundation pit according to the foundation design elevation, and the bottom surface of the sump pit is below the water level. Deep excavation is carried out, including deep excavation of the bottom of the sump pit; In the deep excavation step, the height of the sump pit is 300mm, and the cross-sectional shape of the deep excavation layer corresponds to the cross-sectional shape of the sump pit. For partial earthwork replacement, permeable materials are used to replace the deep excavated layer of the sump pit. The height of the permeable material is flush with the bottom plane of the sump pit so that the upper surface of the permeable material forms the bottom surface of the sump pit. In the partial earthwork replacement step, the permeable material is coarse sand. The permeable material is replaced in two stages. First, the permeable material is laid flat on the bottom surface of the deep excavation layer with a thickness of 150mm. Then, the remaining part is replaced on the flat permeable material. Secondary dewatering is achieved by burying the water pipe in the permeable material within the excavated layer and connecting the water pipe to a water pump. This allows the water pump to extract water from the sump and the excavated layer, lowering the water level below the bottom of the sump. In the secondary dewatering step of the water pipe, the water pipe consists of a water collection pipe and a water delivery pipe; The water collection pipe is arranged horizontally at the bottom of the pit, and a part of the water collection pipe extends downward and is buried in the permeable material; The foundation cushion layer is formed by pouring concrete on the bottom plane of the foundation pit, the bottom surface of the sump pit and the side walls. Waterproofing layer construction: Lay the waterproofing layer on the base layer, and conduct a water tightness test after the waterproofing layer construction is completed; Waterproof protective layer construction: The waterproof protective layer shall be poured after the waterproof layer has passed inspection. After the foundation reinforcement is tied and the waterproof protective layer is poured, the foundation reinforcement is tied according to the design drawings and specifications. After the concealed inspection of the foundation reinforcement is completed, the foundation concrete pouring begins. Stop the precipitation. Once the foundation concrete has been poured, turn off the water pumps to stop the precipitation after the concrete has set. The water delivery pipe is laid out along the outline of the foundation pit to the outside of the foundation. The drain end of the water supply pipe is connected to the water pump, and the pumping end of the water supply pipe is connected to the water collection pipe, so that the groundwater inside the water collection pit can be discharged to the municipal pipe network for dewatering through the water pump. The water pump is installed outside the foundation pit.

2. The dewatering construction method for silty clay soil layers with poor permeability in deep foundation pits according to claim 1, characterized in that, The outer circumference of the water collection pipe is provided with a water collection hole for collecting groundwater inside the water collection pit. The outer surface of the water collection pipe is wrapped with a filter cloth, which is used to filter the water introduced into the water collection hole to avoid sand and gravel clogging it.

3. The dewatering construction method for silty clay soil layers with poor permeability in deep foundation pits according to claim 1, characterized in that, In the waterproofing layer construction process, a water tightness test needs to be carried out after the waterproofing layer is completed. After the test is passed, the next process can be carried out.

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