A construction method for tunneling through small karst cave groups, grouting pre-reinforcement and pile forming integration

Abstract

This invention discloses a construction method for integrated grouting pre-reinforcement and pile foundation construction for tunnels traversing small karst cave groups, as follows: Step 1: In the areas on both sides outside the tunnel outline, drill multiple sleeve valve pipe grouting holes vertically downwards from the ground, and vertically insert the sleeve valve pipes to the bottom. Inject rapidly setting single-liquid grout into the sleeve valve pipes, level by level from the bottom upwards. Step 2: Inside the tunnel outline, construct multiple grouting-pile holes vertically downwards from the ground. Upon completion of one grouting-pile hole, vertically insert a grouting pipe to the bottom of the hole, and vertically insert a reinforcing cage into the grouting pipe. Then, inject high-strength cement mortar into the grouting pipe. After solidification, inject cement grout or a two-liquid grout. Using this construction method, during the construction of tunnels traversing karst cave groups, grouting for soil improvement and pile foundation construction at the tunnel bottom are integrated into a single process, providing a guarantee for the long-term operational safety of the tunnel.

Description

Technical Field

[0001] This invention belongs to the field of tunnel engineering technology, specifically relating to a construction method for integrating grouting pre-reinforcement and pile driving for tunnels passing through small karst cave groups. Background Technology

[0002] Karst geology is frequently encountered in tunnel construction, especially when encountering karst cave groups, which poses challenges to the construction and operation safety of tunnels. For large karst formations, it may even be necessary to build bridges inside the tunnels to cross them.

[0003] For common small and medium-sized karst caves with a diameter of less than 5m, grouting is a common treatment method in tunnel engineering. However, due to the insufficient durability of the grout, the filling grout may disintegrate and be lost during the operation of the tunnel after its completion. Alternatively, the karst itself may contain silt and sand, making it difficult for the grout to completely fill the cavity, resulting in the appearance of new cavities. This is a problem that conventional grouting methods cannot avoid.

[0004] When a tunnel passes through a small karst cave system, the treatment of the cave system below the tunnel floor becomes particularly critical. If the treatment is insufficient, or if the old fill material is lost and new cavities develop later, the bearing capacity of the surrounding rock at the bottom of the tunnel will be severely reduced, endangering the operational safety of the tunnel. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a construction method for grouting pre-reinforcement and pile driving integrated for tunnels passing through small karst cave groups, which addresses the shortcomings of the prior art. In the construction process of tunnels passing through karst cave groups, grouting to improve the strata and pile driving at the bottom of the tunnel are carried out in an integrated manner, which provides a guarantee for the long-term safe operation of the tunnel.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is a construction method for integrating grouting pre-reinforcement and pile driving for tunnels passing through small karst cave groups. The construction method is as follows:

[0007] Step 1: Construct the grouting hole for the sleeve valve pipe:

[0008] In the areas on the left and right sides outside the tunnel outline, multiple sleeve valve grouting holes are drilled vertically downward from the ground and inserted vertically into the sleeve valve pipe to the bottom. Rapidly solidifying single-liquid grout is injected into the sleeve valve pipe from the bottom upward in stages. The bottom of each grouting hole is located below the tunnel floor. In each side area, multiple sleeve valve grouting holes are arranged in a row and spaced apart along the tunnel excavation direction.

[0009] Step 2: Constructing Grouting-Combined Pile Holes: Within the tunnel outline, construct multiple grouting-combined pile holes vertically downwards from the ground. When constructing these holes, begin at the points on the left and right sides closest to the tunnel outline, constructing multiple holes at each starting point, and then proceed sequentially towards the outline area. The bottom of each grouting-combined pile hole should be below the tunnel floor. Upon completion of one grouting-combined pile hole, vertically insert a grouting pipe to the bottom of the hole, and then vertically insert a reinforcing cage into the grouting pipe. The height of each reinforcing cage should be close to the lowest point of the tunnel outline. Then, inject high-strength cement mortar into the grouting pipe up to the top of the reinforcing cage. After the high-strength cement mortar has solidified, inject cement slurry or a two-component grout into the grouting pipe. Grout from bottom to top, step by step, until reaching the top of the grouting pipe.

[0010] Furthermore, in step two, when constructing the grouting-bonded pile hole, if the area below the tunnel floor is a karst zone, drilling continues until the bottom of the grouting-bonded pile hole vertically penetrates the karst zone; and a grouting pipe is vertically placed inside the grouting-bonded pile hole, and then a reinforcing cage is vertically inserted into the grouting pipe to the bottom, with the upper part of the reinforcing cage at the same horizontal level as the other reinforcing cages.

[0011] Furthermore, multiple grouting pile holes are arranged in a horizontal row, aligned along the tunnel excavation direction.

[0012] Furthermore, each grouting pipe is made of PVC pipe, and multiple overflow holes are arranged along the length of the side wall of the grouting pipe. When grout is injected into the grouting pipe, the grout overflows from each overflow hole and is injected into the surrounding rock and karst.

[0013] Furthermore, the bottom of each grouting pile hole is located 5m below the tunnel floor slab, and after grouting, it reinforces the area on both sides of the tunnel outline.

[0014] Furthermore, excluding the grouting pile holes located in the karst cave area, the bottom of each other grouting pile hole is located 5m below the tunnel floor. After grouting, the soil from 5m below the floor to 5m above the roof within the tunnel excavation area is reinforced.

[0015] Furthermore, in the same column, the distance between two adjacent sleeve valve grouting holes is 2m.

[0016] Furthermore, the spacing between two adjacent grouting pile holes is 2m.

[0017] This invention has the following advantages: 1. When traversing karst cave sections, a dense network of reinforced mortar piles is formed under the tunnel floor, providing further assurance for its long-term operational safety. 2. The surrounding rock within the tunnel excavation area is reinforced, and without the obstruction of reinforcing steel, the tunnel can be excavated safely and quickly, making it suitable for shield tunneling. 3. The ground grouting reinforcement process is completed in one integrated step. Attached Figure Description

[0018] Figure 1 A schematic diagram of the cross-section of a tunnel equipped with sleeve valve pipes and overflow pipes;

[0019] Figure 2 A top plan view of a tunnel equipped with sleeve valves and overflow pipes;

[0020] Figure 3 A schematic diagram of overflow pipes laid out within the tunnel excavation area;

[0021] Figure 4 A schematic diagram of a grout overflow pipe equipped with a reinforcing cage;

[0022] Among them: 1. Grouting and pile hole; 2. Sleeve valve grouting hole; 11. Grout overflow pipe; 12. Grout overflow hole; 13. Reinforcing cage; a. Tunnel outline; b. Reinforcement boundary line. Detailed Implementation

[0023] This invention provides a construction method for integrating grouting pre-reinforcement and pile driving in tunnels traversing small karst cave groups, such as... Figure 1 , 2 As shown in Figures 3 and 4, the construction method is as follows:

[0024] Step 1: Construct grouting hole 2 in sleeve valve pipe:

[0025] In the area on the left and right sides outside the tunnel outline a, multiple sleeve valve pipe grouting holes 2 are drilled vertically downward from the ground and inserted vertically into the sleeve valve pipe to the bottom. Rapidly solidifying single liquid grout is injected into the sleeve valve pipe from the bottom upward in stages. After the construction is completed, a grouting reinforcement range is formed on the left and right sides of the tunnel outline a, between the tunnel outline a and the reinforcement boundary line b on the respective side.

[0026] In each side area, multiple sleeve valve grouting holes 2 are arranged in a row and spaced apart along the tunnel excavation direction; the bottom of each sleeve valve is located below the tunnel floor; the inner diameter of the sleeve valve grouting hole 2 is 90mm, and the drilling depth is 5m below the tunnel floor.

[0027] Step 2: Constructing the grouting and pile hole 1:

[0028] Constructing grouting pile holes 1: Within the tunnel outline a, construct multiple grouting pile holes 1 vertically downward from the ground. When constructing grouting pile holes 1, take the left and right sides near the tunnel outline a as the starting point, and construct a row of grouting pile holes 1 at each of the two starting points. Then, construct them row by row towards the outline area.

[0029] Upon completion of a grouting-convertible pile hole 1, a grouting pipe 11 is vertically inserted into the hole to the bottom, and a reinforcing cage 13 is vertically inserted into the grouting pipe 11, with the height of the reinforcing cage 13 approaching the lowest point of the tunnel outline a. High-strength cement mortar is then injected into the grouting pipe 11 up to the top of the reinforcing cage 13. After 24 hours, once the injected high-strength cement mortar has solidified, cement grout or a two-component grout is injected into the grouting pipe 11. Each grouting-convertible pile hole 1 forms a group of reinforced mortar piles below the tunnel floor.

[0030] Then, grouting is carried out step by step from bottom to top in the grouting pipe 11, injecting ordinary cement grout or two-component grout until it reaches the upper end of the grouting pipe 11. The grout overflows from the overflow hole 12 and is injected into the surrounding rock and karst to reinforce and fill the area.

[0031] The inner diameter of the grouting-convertible pile hole 1 is 150mm, and the horizontal and vertical spacing is 2m. The amount of cement mortar injected is equivalent to the volume of a cylinder with a diameter of 150mm and a height equal to that of the reinforcing cage 13.

[0032] Multiple grouting pile holes 1 are arranged in a horizontal row along the tunnel excavation direction; the bottom of each grouting pile hole 1 is located 5m below the tunnel floor.

[0033] Ultimately, a group of reinforced mortar sleeve piles was formed 5m below the tunnel floor, providing long-term and stable support for the tunnel bottom. Above the floor, extending up to 5m above the tunnel, a grouting reinforcement and improvement zone was formed, ensuring safe and rapid tunnel excavation.

[0034] The aforementioned steel cage 13 includes three 5m long Ф20 main bars, i.e., 20mm diameter steel bars surrounded by Ф8 stirrups, i.e. 8mm diameter steel bars. The cross-section of the steel cage 13 is distributed in an equilateral triangle, and the stirrup spacing is 150mm, which is used to enhance the long-term load-bearing performance of the pile.

[0035] If a 150mm grouting and pile hole 1 is constructed, and the hole is drilled to 5m below the tunnel floor and reaches the designed depth, and then encounters karst, the drilling continues until it passes through the karst area and penetrates more than 1m into the stable bedrock. The hole is then marked, and a separate reinforcing cage 13 is prefabricated for the hole. The length of the reinforcing cage 13 is equal to the designed length of 5m plus the additional drilling depth. After that, the reinforcing cage 13 is inserted and high-strength cement mortar is poured in.

[0036] Using the method of this invention, a group of reinforced mortar sleeve piles is finally formed at a depth of 5m below the tunnel floor and in the karst area, providing long-term and stable support for the tunnel bottom. A grouting reinforcement and improvement zone is formed above the floor up to 5m above the tunnel, which can ensure safe and rapid tunnel excavation.

Claims

1. A construction method for integrated grouting pre-reinforcement and pile forming of small karst cave groups for tunnel crossing, characterized in that, The construction method is as follows: Step 1: Construct the grouting hole (2) in the sleeve valve pipe: In the left and right areas outside the tunnel outline (a), multiple sleeve valve pipe grouting holes (2) are drilled vertically downward from the ground and inserted vertically into the sleeve valve pipe to the bottom. Rapidly solidifying single liquid grout is injected into the sleeve valve pipe from the bottom upward in stages; the bottom of each grouting hole (2) is located below the tunnel floor slab. In each side region, multiple sleeve valve grouting holes (2) are arranged in a row and spaced apart along the tunnel excavation direction; Step 2: Constructing grouting pile holes (1): Within the tunnel outline (a), construct multiple grouting pile holes (1) vertically downwards from the ground. When constructing the grouting pile holes (1), starting from the left and right sides near the tunnel outline (a), construct multiple grouting pile holes (1) at each of the two starting points, and then proceed sequentially towards the outline area. The bottom of each grouting pile hole (1) is located below the tunnel floor. Upon completion of one grouting pile hole (1), vertically insert a grouting pipe (11) into the grouting pile hole (1) until... At the bottom, a steel cage (13) is vertically inserted into the grouting pipe (11), with the height of each steel cage (13) close to the lowest point of the tunnel outline (a); then high-strength cement mortar is injected into the grouting pipe (11) up to the upper end of the steel cage (13); after the injected high-strength cement mortar solidifies, cement slurry or two-component slurry is injected into the grouting pipe (11); grouting is carried out step by step from bottom to top until the upper end of the grouting pipe (11); a steel mortar sleeve pile group is formed below the tunnel floor slab, and a grouting reinforcement and improvement zone is formed above the floor slab; In step two, when constructing the grouting pile hole (1), if the area below the tunnel floor is a karst area, drilling continues until the bottom of the grouting pile hole (1) vertically passes through the karst area; and a grouting pipe (11) is vertically placed in the grouting pile hole (1), and then a steel cage (13) is vertically inserted into the grouting pipe (11) to the bottom, with the upper part of the steel cage (13) at the same horizontal position as the height of the other steel cages (13).

2. The construction method for integrated grouting pre-reinforcement and piling of small karst cave groups for tunnel crossing according to claim 1, characterized in that, Multiple grouting pile holes (1) are arranged in a horizontal row along the tunnel excavation direction.

3. The construction method for integrated grouting pre-reinforcement and pile driving of a tunnel traversing a small karst cave group according to claim 2, characterized in that, Each of the grouting pipes (11) is made of PVC pipe. Multiple overflow holes (12) are arranged along the length of the side wall of the grouting pipe (11). When grout is injected into the grouting pipe (11), the grout overflows from each of the overflow holes (12) and is injected into the surrounding rock and karst.

4. The construction method for integrated grouting pre-reinforcement and pile driving of a tunnel traversing a small karst cave group according to claim 3, characterized in that, The bottom of each of the grouting pile holes (1) is located 5m below the tunnel floor slab. After grouting, the area on both sides of the tunnel outline is reinforced.

5. A construction method for integrating grouting pre-reinforcement and pile driving in tunnels traversing small karst cave groups according to claim 4, characterized in that, Except for the grouting pile holes (1) located in the karst cave area, the bottom of each of the other grouting pile holes (1) is located 5m below the bottom plate of the tunnel. After grouting, the soil from 5m below the bottom plate to 5m above the top plate within the tunnel excavation range is reinforced.

6. A construction method for integrating grouting pre-reinforcement and pile driving in tunnels traversing small karst cave groups, as described in claim 5, is characterized in that... In the same column, the distance between two adjacent sleeve valve grouting holes (2) is 2m.

7. A construction method for integrated grouting pre-reinforcement and pile driving of a tunnel traversing a small karst cave group according to claim 6, characterized in that, The distance between two adjacent grouting pile holes (1) is 2m.

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