A soft soil foundation pit support structure and support method

Abstract

The present invention relates to the technical field of foundation pit support, and discloses a foundation pit support structure and a support method for soft soil. A plurality of groups of cast-in-place piles (6) are arranged at the connection between each level of slope (2) and the ground (1) or a platform (5) or a base (3). The tops of the plurality of groups of cast-in-place piles (6) located at the same cross section are sequentially connected with zipper structures (7). An anchor rod (8) is provided between two groups of cast-in-place piles (6) located at the same level of slope (2) cross section to form a triangular stable configuration. A steel mesh (9) is laid on the zipper structure (7) and concrete is poured for reinforcement. The support structure and the support method are suitable for soft soil. By combining traditional slope excavation and cast-in-place pile technology, the cost of foundation pit support is effectively reduced, and the maintenance cost is also very low.

Description

Technical Field

[0001] The present invention relates to the technical field of foundation pit support, and in particular to a soft soil foundation pit support structure and a support method. Background Art

[0002] Foundation pit support is a measure of support, reinforcement and protection for the side walls of the foundation pit and the surrounding environment to ensure the safety of underground structure construction and the surrounding environment of the foundation pit. Forms of foundation pit support include slope excavation, soil nailing wall (composite soil nailing wall), cement-soil gravity retaining wall, steel-cement-soil mixing wall (SMW method), pile rows, ground walls, etc. In order to increase urban living space, the development of underground space is becoming more and more popular. Coastal areas are mostly soft soil. Excavating foundation pits under soft soil, high groundwater levels and other complex site conditions can easily cause soil slippage, foundation pit instability, pile displacement, pit bottom uplift, serious water leakage in retaining structures, soil flow and damage, etc., posing a great threat to the safety of surrounding buildings, underground structures and pipelines. Foundation pit support for soft soil foundations has become a hot spot and difficulty in current foundation engineering.

[0003] Chinese patent publication number CN207436069U discloses a deep foundation pit support structure, including a foundation pit and an anchor wall arranged in the foundation pit slope. A plurality of anchor rods are arranged in the foundation pit. The anchor rods are obliquely inserted into one end of the foundation pit slope and anchored to the anchor wall. The anchor rods include an anchor rod body, to which an anchor rod sleeve is detachably connected. The anchor rod body is a hollow tube. The side wall of the anchor rod body is provided with a plurality of support rods distributed along the circumference and located in the anchor rod sleeve. The support rods are fixedly connected to the anchor rod body. An anchor rod tip is fixedly connected to the end of the anchor rod body away from the foundation pit slope. The anchor rod tip is arranged in a conical shape. In the above-mentioned support structure, the anchor rod tip is inserted into the anchor wall and anchored to the anchor wall. Although an external thread is provided on the anchor rod tip to increase the friction between the anchor rod tip and the anchor wall, the anchoring between the anchor rod tip and the anchor wall is still unstable and needs further design improvement.

[0004] The applicant later applied for a slope support structure with Chinese patent publication number CN210031841U. By setting up an anchoring component, the structure is deployed and anchored to the anchoring wall after passing through the anchoring wall, ensuring the stability of the anchoring between the anchor rod and the anchoring wall, and can support the slope more stably. However, under the same conditions, the cost of the support form is from low to high: slope excavation < soil nail wall (composite soil nail wall) < cement soil gravity retaining wall < steel cement soil mixing wall (SMW method) < pile row < ground wall. Therefore, the cost of setting up an anchoring wall is relatively high, and the maintenance cost is also relatively high. The applicant further studied low-cost support forms suitable for soft soil. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a foundation pit support structure and support method for soft soil. The support structure and support method are suitable for soft soil. Combined with traditional slope excavation and cast-in-place pile technology, the foundation pit support cost is effectively reduced and the maintenance cost is also very low.

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

[0007] A soft soil foundation pit support structure and support method, comprising a ground surface, a slope surface, a base, and a foundation pit, wherein the base surface is arranged around the foundation pit, the slope surface connects the ground surface and the base surface, the slope surface comprises at least one level of slope surface, a platform is provided between two adjacent levels of slope surface, and a plurality of groups of cast-in-place piles are provided at the connection between each level of slope surface and the ground surface, the platform, or the base surface, the tops of the plurality of groups of cast-in-place piles located in the same cross-section are sequentially connected with zipper structures, and anchor rods are provided between the two groups of cast-in-place piles located in the same level of slope surface cross-section to form a triangular stable configuration; a steel mesh is laid on the zipper structure, and concrete is poured for reinforcement.

[0008] Preferably, the cast-in-place piles include outer cast-in-place piles and inner cast-in-place piles, the outer cast-in-place piles include steel mesh tubes, the inner cast-in-place piles include hollow steel pipes located inside the steel mesh tubes, concrete is poured between the steel mesh tubes and the hollow steel pipes, and the hollow steel pipes also serve as water holes.

[0009] Preferably, a fixed depth rod is provided in the hollow steel pipe, and its depth is .- times the depth of the external cast-in-place pile to ensure the depth of the cast-in-place pile.

[0010] Preferably, the zipper structure includes a hook member located on the ground, platform or base and a lock hook member located on the slope, the hook member includes a horizontal pipe section and a C-shaped hook located at at least one end of the horizontal pipe section, and U-shaped tubes are provided at both ends of the lock hook member, which are placed in the hook to lock and fasten each other.

[0011] Preferably, a positioning hole is provided on the horizontal pipe section, and the depth-fixing rod passes through the positioning hole to prevent the zipper structure from shifting.

[0012] Preferably, the steel mesh located on the same slope or ground or platform or base is fixed to the hook pieces or lock hook pieces in the corresponding area by steel wires or cable ties, so as to further improve the stability of the support structure.

[0013] A soft soil foundation pit support method comprises the following steps:

[0014] S1. Determine the depth of the foundation pit and the geological conditions. Based on the depth of the foundation pit and the ground level, determine the number of slope levels, slope, platform width, number of cast-in-place piles, and depth. Drill holes in the ground, platform, and base. Lower the steel mesh cylinder and hollow steel pipes within the steel mesh cylinder. Concrete is poured 5-10 cm below the horizontal plane to form cast-in-place piles. The hollow steel pipes are trimmed where they extend above the horizontal plane.

[0015] S2. Dig a 5-10cm deep groove between adjacent cast-in-place piles, place the hook member located on the ground or platform or base and the lock hook member located on the slope, the hook member and the lock hook member zipper each other and pass through the hollow steel pipe;

[0016] S3 is located at the same level of the slope and at the bottom of the cast-in-place pile at the top of the slope to the bottom of the cast-in-place pile at the top of the slope interspersed with anchor rods, the tip of the anchor rods inserted into the cast-in-place pile to form a stable triangular configuration;

[0017] S4. Lay steel mesh, reserve water-permeable holes on the slope, and pour concrete.

[0018] Preferably, in step S1, the hollow steel pipe is penetrated with a fixed depth rod, and the depth of the fixed depth rod is 1.2-2 times the depth of the external cast-in-place pile.

[0019] Preferably, in step S2, a positioning hole is provided on the horizontal pipe section of the hook member, and the depth-fixing rod passes through the positioning hole to prevent the zipper structure from shifting.

[0020] Preferably, in step S4, the steel mesh is fixed to the hook members or locking hook members in the corresponding area by steel wires or cable ties.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The invention is suitable for soft soil. It combines traditional slope excavation and cast-in-place pile technology to form a triangular stable configuration on the slope surface through a zipper structure and anchor rods. A steel mesh is laid on the zipper structure and concrete is poured for reinforcement, which effectively reduces the cost of foundation pit support and has low maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a structural diagram of traditional foundation pit support and slope excavation.

[0024] Figure 2 This is the structural diagram of the foundation pit support structure.

[0025] Figure 3 This is a schematic diagram of the local structure of this foundation pit support structure.

[0026] Figure 4 This is a structural schematic diagram of the zipper structure in this foundation pit support structure.

[0027] In the accompanying drawings: 1-ground, 2-slope, 3-base, 4-foundation pit, 5-platform, 6-cast-in-place pile, 61-steel mesh tube, 62-hollow steel pipe, 63-fixed depth rod, 7-zipper structure, 71-hook, 711-horizontal pipe section, 7111-positioning hole, 712-hook, 72-lock hook, 721-U-shaped pipe, 8-anchor rod, 9-steel mesh, 10-permeable well. DETAILED DESCRIPTION

[0028] Example 1: A preferred embodiment of the present invention provides a soft soil foundation pit support structure and support method, including ground 1, slope 2, base 3 and foundation pit 4, wherein the base 3 is arranged around the foundation pit 4, the slope 2 connects the ground 1 and the base 3, the slope 2 includes at least one level of slope 2, and a platform 5 is provided between two adjacent levels of slope 2. It is characterized in that a plurality of groups of cast-in-place piles 6 are provided at the connection between each level of slope 2 and the ground 1 or platform 5 or base 3, and the tops of the multiple groups of cast-in-place piles 6 located at the same cross-section are connected in sequence with zipper structures 7, and anchor rods 8 are provided between the two groups of cast-in-place piles 6 located at the same level of slope 2 cross-section to form a triangular stable configuration; and a steel mesh 9 is laid on the zipper structure 7, and concrete is poured for reinforcement.

[0029] The cast-in-place pile 6 includes an outer cast-in-place pile and an inner cast-in-place pile. The outer cast-in-place pile includes a steel mesh tube 61 , and the inner cast-in-place pile includes a hollow steel pipe 62 located inside the steel mesh tube 61 . Concrete is poured between the steel mesh tube 61 and the hollow steel pipe 62 .

[0030] Traditional foundation pit support and slope excavation methods Figure 1 As shown, this method is primarily suitable for areas with good soil conditions, and natural slopes should be preferred. It is not suitable for soft soil areas. However, it is low-cost, lacks protection, and leaves the site open. Furthermore, if the excavation surface of the traditional foundation pit support and slope excavation method is below the groundwater level, well-point dewatering measures, such as permeable wells 10, should be implemented at the top of the slope and on the platform to improve slope stability. A water retaining dam or drainage ditch should be installed at the top of the slope to prevent water from accumulating outside the pit from flowing into the pit and eroding the slope.

[0031] This technology combines the traditional slope excavation and cast-in-place pile 6 process, and forms a triangular stable configuration on the slope surface through the zipper structure 7 and the anchor rod 8. The zipper structure is laid with a steel mesh 9 and reinforced with concrete, which effectively reduces the cost of foundation pit support and the maintenance cost is also very low.

[0032] At the same time, the design of the hollow steel pipe 62 is also used as a water permeable hole, and there is no need to take additional well point dewatering measures. It can prevent water outside the pit from flowing into the pit and eroding the slope, and the construction cost can be further reduced.

[0033] Example 2: A preferred embodiment of the present invention provides a soft soil foundation pit support structure and support method, which differs from the above embodiment only in that:

[0034] The zipper structure 7 includes a hook member 71 located on the ground 1, platform 5, or base 3, and a locking hook member 72 located on the slope 2. The hook member 71 includes a horizontal pipe section 711 and a C-shaped hook 712 located at at least one end of the horizontal pipe section 711. Both ends of the locking hook member 72 are provided with a U-shaped tube 721, which is positioned within the hook 712 to secure the two ends. The horizontal pipe section 711 is provided with a positioning hole 7111, through which the depth-fixing rod 63 extends to prevent the zipper structure 7 from shifting.

[0035] Example 3: A preferred embodiment of the present invention provides a soft soil foundation pit support structure and support method, which differs from the above embodiment only in that a fixed depth rod 63 is provided in the hollow steel pipe 62, and its depth is 1.2-2 times the depth of the external cast-in-place pile to ensure the depth of the cast-in-place pile 6.

[0036] Example 4: A preferred embodiment of the present invention provides a soft soil foundation pit support structure and support method, which differs from the above embodiments only in that the steel mesh 9 located on the same slope 2 or ground 1 or platform 5 or base 3 is respectively fixed to the pull hook part 71 or lock hook part 72 in the corresponding area through steel wire or cable tie, thereby further improving the stability of the support structure.

[0037] A soft soil foundation pit support method comprises the following steps:

[0038] S1. Determine the depth of the foundation pit 4 and the geological conditions. Based on the depth of the foundation pit 4 and the height of the ground 1, determine the number and gradient of the slope 2, the width of the platform 5, and the number and depth of the cast-in-place piles 6. Drill holes in the ground 1, the platform 5, and the base 3. Lower the steel mesh tube 61 and the hollow steel pipe 62 located within the steel mesh tube 61. Concrete is poured 5-10 cm below the horizontal plane to form the cast-in-place piles 6. The hollow steel pipe 62 is trimmed where it extends upward beyond the horizontal plane.

[0039] S2 adjacent piles dug 5-10cm depth of the groove between 6, into the ground or platform 5 or base 3 at the hook member 71 and the slope 2 at the lock hook member 72, the hook member 71 and the lock hook member 72 zippered with each other and inserted through the hollow steel pipe 62;

[0040] S3 is located at the same level of the slope 2 and at the bottom of the cast-in-place pile 6 at the top of the slope to the bottom of the cast-in-place pile 6 is interspersed with anchor rods 8, the tip of the anchor rod 8 is inserted into the cast-in-place pile 6 to form a stable triangular configuration;

[0041] S4. A steel mesh 9 is laid, water-permeable holes are reserved on the slope 2, and concrete is poured.

[0042] In step S1, the hollow steel pipe 62 is penetrated by a depth-fixing rod 63, and the depth of the depth-fixing rod 63 is 1.2-2 times the depth of the external cast-in-place pile.

[0043] In step S2 , a positioning hole 7111 is provided on the horizontal pipe section 711 of the hook member 71 , and the depth-fixing rod 63 passes through the positioning hole 7111 to prevent the zipper structure 7 from shifting.

[0044] In step S4, the steel mesh 9 is fixed to the hook members 71 or the lock hook members 72 in the corresponding area by steel wires or cable ties.

Claims

1. A soft soil foundation pit support structure, comprising a ground surface (1), a slope surface (2), a base (3) and a foundation pit (4), wherein the base (3) is arranged around the foundation pit (4), the slope surface (2) connects the ground surface (1) and the base (3), the slope surface (2) comprises at least one level of slope surface (2), and a platform (5) is provided between two adjacent levels of slope surface (2), characterized in that: A plurality of groups of cast-in-place piles (6) are provided at the connection between each level of the slope (2) and the ground (1) or the platform (5) or the base (3); the tops of the multiple groups of cast-in-place piles (6) located at the same cross section are sequentially connected with zipper structures (7); anchor rods (8) are provided between two groups of cast-in-place piles (6) located at the same cross section of the slope (2) to form a triangular stable configuration; and a steel mesh (9) is laid on the zipper structure (7) and concrete is poured for reinforcement; The cast-in-place pile (6) includes an outer cast-in-place pile and an inner cast-in-place pile, the outer cast-in-place pile includes a steel mesh tube (61), and the inner cast-in-place pile includes a hollow steel pipe (62) located in the steel mesh tube (61), concrete is poured between the steel mesh tube (61) and the hollow steel pipe (62), and the hollow steel pipe (62) also serves as a water-permeable hole; A depth-fixing rod (63) is provided in the hollow steel tube (62); The zipper structure (7) includes a hook member (71) located on the ground (1) or the platform (5) or the base (3) and a lock hook member (72) located on the slope (2), wherein the hook member (71) includes a horizontal pipe section (711) and a C-shaped hook (712) located at at least one end of the horizontal pipe section (711), and both ends of the lock hook member (72) are provided with a U-shaped tube (721), and the U-shaped tube (721) is placed in the hook (712) to be locked and fastened to each other; The horizontal pipe section (711) is provided with a positioning hole (7111), and the depth-fixing rod (63) passes through the positioning hole (7111) to prevent the zipper structure (7) from deflecting; The steel mesh (9) located on the same slope (2) or ground (1) or platform (5) or base (3) is fixed to the pull hook piece (71) or lock hook piece (72) in the corresponding area through steel wire or cable tie, thereby further improving the stability of the supporting structure.

2. A soft soil foundation pit support structure according to claim 1, characterized in that: The depth of the depth-fixing rod (63) is 1.2-2 times the depth of the external cast-in-place pile to ensure the depth of the cast-in-place pile (6).

3. A soft soil foundation pit support method, characterized in that: The soft soil foundation pit support structure according to claim 1 or 2 comprises the following steps: S1. Determine the depth and geological conditions of the foundation pit (4), determine the number of levels and slopes of the slope (2), the width of the platform (5), the number and depth of the cast-in-place piles (6) according to the depth of the foundation pit (4) and the height of the ground (1), drill holes on the ground (1), the platform (5) and the base (3), lower the steel mesh tube (61) and the hollow steel pipe (62) located in the steel mesh tube (61), and start pouring concrete at a position 5-10 cm below the horizontal plane to form the cast-in-place piles (6), and trim the hollow steel pipe (62) where it extends upward beyond the horizontal plane; S2. Dig a 5-10 cm deep groove between adjacent cast-in-place piles (6), place a hook member (71) located on the ground (1) or platform (5) or base (3) and a lock hook member (72) located on the slope (2), and the hook member (71) and the lock hook member (72) are mutually locked and inserted through the hollow steel pipe (62); S3. An anchor rod (8) is inserted from the top of the cast-in-place pile (6) at the same level of slope (2) and at the bottom of the cast-in-place pile (6) at the top of the slope, and the tip of the anchor rod (8) is inserted into the cast-in-place pile (6) to form a triangular stable configuration; S4. A steel mesh (9) is laid, water-permeable holes are reserved on the slope (2), and concrete is poured.

4. A soft soil foundation pit support method according to claim 3, characterized in that: In step S1, the hollow steel pipe (62) is penetrated by a fixed depth rod (63), and the depth of the fixed depth rod (63) is 1.2-2 times the depth of the external cast-in-place pile.

5. The soft soil foundation pit support method according to claim 3, characterized in that: In step S2, a positioning hole (7111) is provided on the horizontal pipe section (711) of the hook member (71), and the depth-fixing rod (63) passes through the positioning hole (7111) to prevent the zipper structure (7) from deflecting.

6. The soft soil foundation pit support method according to claim 3, characterized in that: In step S4, the steel mesh (9) is fixed to the hook piece (71) or the lock hook piece (72) in the corresponding area by means of steel wire or cable ties.

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