A construction technology for deep foundation pit excavation and support of pipe jacking wells

Abstract

This invention discloses a construction process for deep foundation pit excavation and support of pipe jacking wells, relating to the field of foundation pit protection. The process includes earthwork excavation, first-layer excavation, construction of ring beams and layer wall panels, progressive excavation of each layer and construction of ring beams and layer wall panels at each layer, waterproofing treatment at the bottom of the foundation pit, pouring of the bottom slab, and construction of the rear support wall. This invention prevents water accumulation in the foundation pit by setting intercepting ditches and sump pits at each layer, and avoids groundwater inflow into the foundation pit later by waterproofing the bottom of the pit.

Description

Technical Field

[0001] This invention belongs to the field of floor decking structure construction, specifically relating to a deep foundation pit excavation and support construction process for pipe jacking wells. Background Technology

[0002] In existing technologies, the most widely used support structures for working shafts are concrete support, caisson support, and plate bracing. With concrete support, the concrete strength of the formwork must reach a suitable level before the next stage of excavation can proceed. The caisson support construction process requires prefabrication of the caisson structure, with wooden supports or a subbase placed underneath. After the caisson structure is prefabricated, the wooden supports or subbase are removed, and the plain concrete layer is broken up before sinking.

[0003] Chinese patent CN112431225A discloses a reverse construction method for a brick-built working well with pipe jacking. However, this patent does not divert groundwater from the working well during construction, nor does it waterproof the bottom of the pit. Drainage is only carried out when the underground foundation layer is poured. During the process of deepening or partially deepening the foundation pit, the infiltration of groundwater under the soil lateral pressure may cause the foundation pit to collapse.

[0004] Therefore, providing an effective waterproof construction process for deep foundation pit excavation and support of pipe jacking wells has become a technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a construction process for deep foundation pit excavation and support of pipe jacking wells. The present invention prevents water accumulation in the foundation pit by setting up intercepting ditches and sump pits on each layer, and avoids groundwater from flowing into the foundation pit later by waterproofing the bottom of the foundation pit.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A construction technique for deep foundation pit excavation and support of pipe jacking wells, employing a reverse construction method, includes the following construction steps:

[0008] S01. Before construction, the area within 3m around the foundation pit shall be hardened with concrete, and a tool-type edge protection facility with a height of not less than 1.2m shall be set up around the working well.

[0009] S02. Earthwork excavation: Earthwork excavation is carried out vertically in layers. The excavation is carried out according to the principle of vertical layering, from top to bottom, layer excavation, and excavation of the middle first and then the surrounding area. After excavating to the design elevation of each layer, intercepting ditches and sump pits are manually excavated. Drainage systems are promptly set up on the upper, lower and surrounding parts of the working pit. When excavating the first layer, the foundation pit is initially shaped like the bottom of a pot, and the work is gradually expanded.

[0010] S03. After the first excavation to the set depth, construct the ring beam and the first layer of wall panels in a timely manner. Tie steel bars, set up formwork and pour concrete around the foundation pit. After the concrete strength is ≥85% of the design strength, proceed with the excavation of the next layer.

[0011] S04. The second layer and subsequent layers are excavated using the full-section excavation method. Reinforcing bars are tied, formwork is erected and concrete is poured for each layer. The next layer is excavated after the concrete strength of the second layer reaches 80% of the design strength. This gradual process is to prevent the well wall from suddenly sinking.

[0012] S05. After the sidewall of the last working well is poured, the reserved pipe jacking inlet and outlet are temporarily sealed with brick walls.

[0013] S06. After reaching the design elevation, waterproof the bottom of the foundation pit, lay a 3:7 lime-soil cushion layer, lay two layers of waterproof geotextile and one membrane on top of the 3:7 lime-soil cushion layer, and pour concrete on top of the geotextile for the cushion layer.

[0014] S07. After the plain concrete foundation has initially set, various steel reinforcement installation positioning lines are marked on the foundation and reinforcement is arranged. Spacers are placed under the bottom reinforcement of the foundation slab to ensure that the bottom reinforcement has sufficient protective layer. The bottom and top reinforcements are supported by stirrups. The stirrups must be firmly tied to the steel reinforcement to ensure its stability. After the reinforcement is tied, the foundation slab is poured. When the foundation slab is poured, a groove for the back wall is reserved.

[0015] S08. After the base plate is poured and reaches the design strength, the rear seat wall is constructed in the insertion groove of the rear seat wall to ensure the integrity of the rear seat wall and the base plate. A thick steel plate is attached to the side of the rear seat wall away from the side wall.

[0016] Furthermore, the formwork adopts a single-sided template, with tie rods installed on the inner side of the template. The tie rods are welded firmly to the side wall steel bars to form the template as a whole. Tenons are installed at both ends of the outer side of the template, and square timber with mortise grooves is inserted into the tenons. The square timbers are tightened and fixed together by adjustable steel support columns.

[0017] Furthermore, during concrete pouring, the vertical bars of the upper two layers of reinforcing bars are reserved 35cm downwards for connection with the next layer. The ends of the reserved reinforcing bars should not be at the same cross section, so that the concrete retaining wall forms a whole.

[0018] Furthermore, during the excavation process, soil layers with high water content and poor self-supporting capacity are fixed with soil nails and steel mesh, and pre-reinforced with a 2-3cm thick concrete surface layer.

[0019] Furthermore, the entrance to the working pit on the side wall and the exit of the receiving pit are reinforced by adding ring reinforcement.

[0020] Furthermore, a funnel-shaped pouring opening 20cm high is set on the upper part of the post-pouring formwork. When the concrete is poured to this height, the concrete gaps are filled and compacted by the pouring pressure and vibrator. After the concrete in the funnel part hardens, the surface is chiseled smooth.

[0021] Furthermore, the vertical inclination angle of the funnel-shaped pouring inlet is 30°.

[0022] Furthermore, to prevent leakage at the joints, after pouring and vibrating, the funnel opening is tapped with a wooden mallet to discharge air bubbles and water outside the funnel opening. If leakage occurs at local joints, polyurethane injection is used for repair.

[0023] The beneficial effects of this invention are as follows:

[0024] This invention features a simple structure. By installing a drainage system at each layer during excavation, it prevents water accumulation in the foundation pit, thus avoiding water soaking. Waterproofing the bottom of the pit prevents groundwater infiltration and potential collapse. The funnel-shaped pouring opening in the formwork, along with pre-reserved steel reinforcement ends, solves the problem of sealing gaps in the formwork during reverse construction, improving the overall integrity of the pit sidewalls. The formwork uses a mortise and tenon structure, facilitating the disassembly and installation of the square timber. The adjustable steel support columns facilitate the fixing and tightening of the formwork. Attached Figure Description

[0025] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0027] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "horizontal," "inner," "outer," and "one side," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0028] Example

[0029] like Figure 1 As shown, this embodiment provides a construction process for deep foundation pit excavation and support of pipe jacking wells, which adopts the reverse construction method and includes the following construction steps:

[0030] S01. Before construction, the concrete within a 3m radius around the foundation pit shall be hardened, and a tool-type edge protection facility with a height of not less than 1.2m shall be set up around the working well. The distance between the piled soil and the upper edge shall not be less than 2m, and the height of the piled soil shall not exceed 1.5m.

[0031] S02. Earthwork excavation: Earthwork excavation is carried out vertically in layers. The excavation is carried out according to the principle of vertical layering, from top to bottom, layer excavation, and excavation of the middle first and then the surrounding area. After excavating to the design elevation of each layer, intercepting ditches and sump pits are manually excavated. Drainage systems are promptly set up on the upper, lower and surrounding parts of the working pit, with a clear slope for water flow to ensure that there is no standing water in the pit. When excavating the first layer, the foundation pit is initially shaped like a pot bottom and is gradually expanded for operation.

[0032] S03. Upon excavation to the designated depth, promptly construct the ring beam and the first layer of wall panels. Tie reinforcing bars around the perimeter of the pit, erect formwork, and pour concrete. Use single-sided formwork with tie rods on the inner side, welded securely to the side wall reinforcement to form a unified structure. Tenons are provided at both ends of the outer side of the formwork, with mortised square timber inserted into them. The square timbers are then secured together using adjustable steel support columns.

[0033] In this embodiment, the inner formwork of the pit retaining wall is made of plywood. Sponge tape is applied to the formwork joints to prevent grout leakage. A release agent must be applied to all formwork before use; a water-based release agent is required, and paint-based release agents are prohibited. The release agent must not contaminate the reinforcing steel or concrete joints. The formwork dimensions are 1220mm × 2440 × 15mm. The rear beams are 40mm × 60mm square timber, arranged vertically at 0.2m intervals. The main beams are Ф48 × 3.0mm double adjustable steel support columns, arranged horizontally at 0.5m intervals. Ф48 × 3.0mm adjustable steel support columns are fixed with top supports, with a horizontal spacing of 0.7m and a vertical spacing of 0.5m.

[0034] When pouring concrete, the vertical bars of the upper two layers of steel bars should be reserved 35cm downwards for connection with the next layer. The ends of the reserved steel bars should not be on the same cross section, so that the concrete wall can form a whole. The next layer of excavation can be carried out after the concrete strength is ≥85% of the design strength.

[0035] S04. From the second layer downwards, full-section excavation shall be used. Reinforcing steel shall be tied, formwork shall be erected and concrete shall be poured for each layer. The next layer shall be excavated only after the concrete strength of the second layer reaches 80% of the design strength. This gradual process shall be used to prevent the well wall from suddenly settling downwards. The excavation depth of each layer shall be determined according to the soil conditions and shall generally not exceed 1.5 meters. The construction of each side of the well wall shall not take more than 2 days from excavation to concrete pouring. The excavation depth of each layer of the foundation pit shall not exceed 2 meters.

[0036] S05. After the sidewall of the last working well is poured, the reserved pipe jacking inlet and outlet are temporarily sealed with brick walls.

[0037] S06. After reaching the design elevation, waterproof the bottom of the foundation pit, lay a 3:7 lime-soil cushion layer, lay two layers of waterproof geotextile and one membrane on top of the 3:7 lime-soil cushion layer, and pour concrete on top of the geotextile for the cushion layer.

[0038] S07. After the plain concrete foundation has initially set, various steel reinforcement installation positioning lines are marked on the foundation and reinforcement is arranged. Spacers are placed under the bottom reinforcement of the foundation slab to ensure that the bottom reinforcement has sufficient protective layer. The bottom and top reinforcements are supported by stirrups. The stirrups must be firmly tied to the steel reinforcement to ensure its stability. After the reinforcement is tied, the foundation slab is poured. When the foundation slab is poured, a groove for the back wall is reserved.

[0039] S08. After the base slab is poured and reaches the design strength, the rear wall is constructed in the rear wall insertion groove. The bottom end of the rear wall is inserted into the soil to ensure the integrity of the rear wall and the base slab. The reverse support force on the upper part can be transferred to the ground and the base slab through the lower part, which is conducive to the dispersion of force. A thick steel plate is attached to the side of the rear wall away from the side wall to improve the surface strength and wear resistance of the rear wall.

[0040] To prevent the exposed soil on the sidewalls of the foundation pit from collapsing, soil layers with high water content and poor self-supporting properties are fixed with soil nails and steel mesh and pre-reinforced with a 2-3cm thick concrete surface layer during excavation.

[0041] Preferably, the entrance to the working pit and the exit of the receiving pit on the side wall are reinforced by adding ring reinforcement.

[0042] Preferably, since this embodiment uses the reverse construction method, the joint treatment is very important. Therefore, a funnel-shaped pouring opening with a height of about 20cm is set on the upper part of the post-poured formwork. The vertical inclination angle of the funnel-shaped pouring opening is 30°. When the concrete is poured to this height, the concrete gaps are filled and compacted by the pouring pressure and vibrator. After the concrete in the funnel part hardens, the surface is chiseled smooth. To prevent leakage at the joint, after pouring and vibrating, the funnel opening is tapped with a wooden mallet to discharge air bubbles and water outside the funnel opening. If leakage occurs at local joints, polyurethane injection is used for repair.

[0043] The above are merely preferred embodiments of the present invention and do not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A construction technology for deep foundation pit excavation and support of pipe jacking wells, employing a reverse construction method, characterized in that... The construction steps include the following: S01. Before construction, the concrete within a 3m radius around the foundation pit shall be hardened, and a tool-type edge protection facility with a height of not less than 1.2m shall be set up around the working well. S02. Earthwork excavation: Earthwork excavation is carried out vertically in layers. The excavation is carried out according to the principle of vertical layering, from top to bottom, layer excavation, and excavation of the middle first and then the surrounding area. After excavating to the design elevation of each layer, intercepting ditches and sump pits are manually excavated. Drainage systems are promptly set up on the upper, lower and surrounding parts of the working pit. When excavating the first layer, the foundation pit is initially shaped like the bottom of a pot, and the work is gradually expanded. S03. After the first excavation to the set depth, construct the ring beam and the first layer of wall panels in a timely manner. Tie steel bars, set up formwork and pour concrete around the foundation pit. After the concrete strength is ≥85% of the design strength, proceed with the excavation of the next layer. S04. The second layer and subsequent layers are excavated using the full-section excavation method. Reinforcing bars are tied, formwork is erected and concrete is poured for each layer. The next layer is excavated after the concrete strength of the second layer reaches 80% of the design strength. This gradual process is to prevent the well wall from suddenly sinking. S05. After the sidewall of the last working well is poured, the reserved pipe jacking inlet and outlet are temporarily sealed with brick walls. S06. After reaching the design elevation, waterproof the bottom of the foundation pit, lay a 3:7 lime-soil cushion layer, lay two layers of waterproof geotextile and one membrane on top of the 3:7 lime-soil cushion layer, and pour concrete on top of the geotextile for the cushion layer. S07. After the plain concrete foundation has initially set, various steel reinforcement installation positioning lines are marked on the foundation and reinforcement is arranged. Spacers are placed under the bottom reinforcement of the foundation slab to ensure that the bottom reinforcement has sufficient protective layer. The bottom and top reinforcements are supported by stirrups. The stirrups must be firmly tied to the steel reinforcement to ensure its stability. After the reinforcement is tied, the foundation slab is poured. When the foundation slab is poured, a groove for the back wall is reserved. S08. After the base plate is poured and reaches the design strength, the rear seat wall is constructed in the insertion groove of the rear seat wall to ensure the integrity of the rear seat wall and the base plate. A thick steel plate is attached to the side of the rear seat wall away from the side wall.

2. The construction technology for deep foundation pit excavation and support of pipe jacking wells according to claim 1, characterized in that: The formwork uses a single-sided template. Tie rods are installed on the inner side of the template and are firmly welded to the side wall steel bars to form a whole. Tenons are installed at both ends of the outer side of the template, and square timber with mortise grooves is inserted into the tenons. The square timbers are fixed together by adjustable steel support columns.

3. The construction technology for deep foundation pit excavation and support of pipe jacking wells according to claim 1, characterized in that: When pouring concrete, the vertical bars of the upper two layers of steel bars should be reserved 35cm downwards for connection with the next layer. The ends of the reserved steel bars should not be on the same cross section, so that the concrete wall can form a whole.

4. The construction technology for deep foundation pit excavation and support of pipe jacking wells according to claim 1, characterized in that: During the excavation process, soil layers with high water content and poor self-supporting capacity are fixed with soil nails and steel mesh, and a 2-3cm thick concrete surface layer is sprayed for pre-reinforcement.

5. The construction technology for deep foundation pit excavation and support of pipe jacking wells according to claim 1, characterized in that: The working pit entrance and receiving pit exit on the side wall are reinforced by adding ring reinforcement.

6. The construction technology for deep foundation pit excavation and support of pipe jacking wells according to claim 1, characterized in that: A funnel-shaped pouring opening 20cm high is set on the upper part of the post-pouring formwork. When the concrete is poured to this height, the concrete gaps are filled and compacted by the pouring pressure and vibrator. After the concrete in the funnel part hardens, the surface is chiseled smooth.

7. The construction technology for deep foundation pit excavation and support of pipe jacking wells according to claim 6, characterized in that: The vertical inclination angle of the funnel-shaped pouring inlet is 30°.

8. The construction technology for deep foundation pit excavation and support of pipe jacking wells according to claim 6, characterized in that: To prevent leakage at the joints, after pouring and vibrating, tap the funnel opening with a wooden mallet to discharge air bubbles and water outside the funnel opening. If leakage occurs at local joints, use polyurethane injection for repair.

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