A method for large-section portal demolition operation in pipe jacking construction

Abstract

A large-section hole portal demolition operation method for pipe jacking construction solves the problem of high risk and hidden danger in the current large end hole portal chiseling. It comprises the following steps: S1, according to the shape and size of the hole portal, the to-be-demolished area is divided into several chiseling areas, and different chiseling areas are assigned different serial numbers for distinction; S2, the non-demolition area of the hole portal is reinforced with a steel structure beam; S3, strain gauges are pasted outside the center of each chiseling area; S4, the chiseling area is sequentially broken in the order from top to bottom and left to right symmetry, and the strain data ε of the strain gauge is recorded and analyzed during the breaking process; S5, whether to stop the chiseling operation is judged, when the strain data ε of the strain gauge meets the condition, the hole portal chiseling operation is stopped, S6, after the chiseling operation is stopped, a grouting pipe is obliquely inserted at the hole position formed by the chiseling area; S7, steps S4 to S6 are repeated until the hole portal demolition operation is completed.

Description

Technical Field

[0001] This invention relates to the field of pipe jacking construction technology, and in particular to a method for dismantling large-section tunnel portals in pipe jacking construction. Background Technology

[0002] Pipe jacking is a trenchless construction technology with minimal environmental impact and high economic efficiency, and it has been increasingly widely used in urban underground space development, especially in underground engineering projects in bustling urban areas. Before launching the pipe jacking machine, the tunnel portal must be removed. During the removal of the portal, the ground loses its horizontal support, and the internal soil pressure can easily exceed its shear strength, leading to ground instability and posing significant risks to construction. Furthermore, the portal is often constructed of concrete, and during demolition, the soil pressure can easily cause tension cracks, creating conditions for ground water inrush. If construction control is inadequate, sudden water inrush accidents can easily occur. Summary of the Invention

[0003] In view of the above situation and to overcome the defects of the existing technology, the present invention provides a method for demolishing large-section tunnel portals in pipe jacking construction, which effectively solves the problem of safety hazards and high risks in the current demolition of large-section tunnel portals.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows: a method for demolishing a large-section portal in pipe jacking construction, comprising the following steps: S1. Based on the shape and size of the opening, the area to be demolished is divided into several excavation areas, and different excavation areas are assigned different serial numbers to distinguish them. S2, reinforce the non-demolition area of ​​the tunnel entrance with steel structure beams; S3, attach strain rosettes to the outer center of each excavation zone and connect the strain rosettes to the strain measurement device; S4. Following a top-to-bottom, left-to-right symmetrical sequence, the excavation zone is broken up sequentially, and the strain data of the strain flower is recorded and analyzed during the breaking process. ; S5, determine whether to stop the chiseling operation, based on the strain data of the strain gauge. The tunnel portal removal operation shall be stopped if either of the following two conditions is met: ① Strain data of the strain gauge , ① The ultimate tensile strain of the portal concrete; ② Strain data from the strain rosette. satisfy ;in, The tensile modulus of elasticity of the portal concrete. The sum of the thicknesses of the reinforced strata zone and the tunnel portal. The thickness of the stratum reinforcement zone, To calculate the earth pressure in the strata behind the tunnel portal, The ultimate shear strength of the soil in the stratum; S6. After stopping the chiseling operation, insert grouting pipes at an angle into the holes formed in the chiseled area and use pressure grouting to reinforce the reinforcement area behind the un-chiseled hole. Only when the strain gauge readings are within the safe range during subsequent chiseling operations can the chiseling operation continue. S7. Repeat steps S4 to S6 until the tunnel portal removal operation is completed.

[0005] Preferably, in step S1, the chiseling area is divided according to the principle of larger at the top and smaller at the bottom, and uniform on the left and right.

[0006] Preferably, in step S3, the strain gauge used is a triaxial strain gauge, with the three strain gauges arranged at 0°, 45° and 90° respectively.

[0007] Preferably, in step S5, the ultimate tensile strain of the portal concrete is... The tensile elastic modulus of the portal concrete Ultimate shear strength of soil strata All results were obtained through indoor testing.

[0008] Preferably, in step S6, the grouting material used is selected from reinforcement materials such as cement grout, water glass, and silica sol, based on the properties of the soil and rock mass in the reinforcement area, the setting time of the grouting material, and the required reinforcement strength.

[0009] Compared with existing technologies, this invention has the following advantages: By attaching strain gauges to the outside of the tunnel portal, it is possible to: 1) directly measure the tensile strain of the concrete structure of the tunnel portal, thereby directly determining whether the deformation of the portal under earth pressure exceeds the allowable value and inferring the stability of the portal itself; 2) calculate the magnitude of the earth pressure behind the portal based on the tensile strain of the concrete and the calculation formula of the wall thickness cylinder theory, thus determining the stability of the soil behind it. This method allows for real-time monitoring of the deformation of the tunnel portal and the stress within the soil behind it. Existing technologies typically test the internal pressure of the soil by installing pressure cells inside the soil. These pressure cells are easily damaged during construction and cannot be replaced after damage, making measurement impossible; furthermore, the pressure cells cannot reflect the deformation of the portal itself, which is a significant factor in instability.

[0010] When the cross-section of the portal to be excavated is large, it cannot be excavated all at once. It needs to be excavated in sections in sequence. Since the soil pressure increases with the burial depth, it is smaller at the top and larger at the bottom. Therefore, the principle of dividing the area to be demolished according to the principle of larger at the top and smaller at the bottom and uniform left and right, proposed in this invention, can effectively improve construction efficiency and reduce the risk of instability. Excavating in the order of top to bottom and left and right symmetrical, proposed in this invention, can fully reduce the disturbance caused by construction and avoid instability caused by excessive local soil pressure.

[0011] During the excavation of the tunnel entrance, if the strain is too large, it indicates a potential risk of instability. The method proposed in this invention can be used to further reinforce the soil in areas with excessive deformation, achieving timely and precise reinforcement, thereby greatly reducing the risk of instability. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the division of the removal area according to the present invention; Figure 2 This is a schematic diagram of the grouting reinforcement method of the present invention; Figure 3 This is a schematic diagram of the strain gauge bonding method of the present invention; In the diagram: 1. Portal; 2. Area to be demolished; 3. Excavation area; 4. Steel structure beam; 5. Strain curve; 6. Ground reinforcement area; 7. Grouting pipe. Detailed Implementation

[0013] The present invention will now be described in further detail with reference to the accompanying drawings. The drawings are simplified schematic diagrams, illustrating only the basic structure of the invention in a schematic manner, and therefore only show the components relevant to the invention.

[0014] A method for dismantling a large-section portal 1 used in pipe jacking construction, comprising the following steps: S1, as Figure 1 The portal 1 is rectangular in shape, with dimensions of 13.55m in height and 12m in width. The area to be demolished 2 is divided into 45 different excavation zones 3 according to the principle of being larger at the top and smaller at the bottom, and uniformly spaced left and right, respectively labeled A1, A2, A3, ..., I5. The 45 different excavation zones 3 have the same width, all 2.4m, but different heights: A1 to A5 are 2.25m high; B1 to B5 are 2.25m high; C1 to C5 are 1.75m high; D1 to D5 are 1.75m high; E1 to E5 are 1.55m high; F1 to F5 are 1.25m high; G1 to G5 are 1.25m high; H1 to H5 are 0.75m high; I1 to I5 are 0.75m high.

[0015] S2, the non-demolition area of ​​the portal 1 is reinforced with steel structure beam 4. The steel structure beam 4 is made of high-rigidity steel as a whole to improve its resistance to deformation and prevent damage to the non-demolition area of ​​the area to be demolished during the demolition process.

[0016] S3, attach strain relief 5 to the outer center of each excavation zone 3, such as Figure 3 As shown, the strain gauge 5 used is a triaxial strain gauge, with each strain gauge arranged at 0°, 45° and 90° respectively; the strain gauge 5 is connected to the strain measurement device to record the strain changes at different locations during the demolition of the portal 1 in real time; the strain data of the strain gauge 5 needs to be cleared to zero before the demolition operation.

[0017] S4, following a top-to-bottom, left-to-right symmetrical order, the removal zones 3 are sequentially broken, i.e., first A1 to A5, then B1 to B5, and so on, finally I1 to I5. Within the same horizontal position, the removal zones 3 are broken in a left-to-right symmetrical order; taking A1 to A5 as an example, the removal order is: A1, A5 → A2, A4 → A3; and the process is recorded. The strain data of strain flower 5 is then analyzed. .

[0018] S5, determine whether to stop the chiseling operation, based on the strain data of strain gauge 5. The excavation of tunnel portal 1 shall be stopped if either of the following two conditions is met: ① Strain data of strain gauge 5 , The ultimate tensile strain of the concrete at the portal 1 was obtained through indoor testing; in this embodiment, the concrete at the portal 1 was C35 concrete, as determined by testing. for That is, 500 micro-strains. ② Strain data of strain pattern 5. satisfy: ,in The tensile modulus of elasticity of the concrete at the portal 1 was obtained through indoor testing. In this embodiment, it was obtained through testing. 20 GPa; The sum of the thicknesses of the reinforced zone 6 and the portal 1. The thickness of the formation reinforcement zone 6 in this embodiment is... It is 8m. It is 10m; The calculated earth pressure in the strata behind portal 1; The ultimate shear strength of the soil layer is obtained through laboratory testing. In this embodiment, the strength obtained through testing is... The value is 60 kPa.

[0019] In this embodiment, when the demolition reached C3, it was found that the micro-strain measured in the three regions I2 to I4 increased to 11. At this time, the soil behind the tunnel portal 1 faced the risk of instability due to shear stress exceeding the shear strength. Therefore, the demolition construction was stopped.

[0020] S6, after stopping the chiseling operation, as follows Figure 2 As shown, the grouting pipe 7 is inserted obliquely into the hole formed in the already excavated area 3C3; the grouting pipe 7 should be inserted near I2 to I4; the reinforcement area 6 behind the unexcavated hole 1 is reinforced by pressure grouting; in this embodiment, since the soil and rock in the reinforcement area 6 is silty clay, cement grout is selected as the grouting material, and the grouting pressure is 0.2MPa-0.3MPa; after grouting, after the grout solidifies, it is found that the strain gauge readings in the three areas I2 to I4 are within the safe allowable range (less than the safety threshold of 9 micro-strains), and the excavation construction can continue.

[0021] S7. Repeat steps S4 to S6 until the removal of portal 1 is completed.

[0022] The embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that various variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom remain within the scope of this invention.

Claims

1. A method for dismantling large-section portal tunnels using the pipe jacking method, characterized in that, Includes the following steps: S1. Based on the shape and size of the opening (1), the area to be demolished (2) is divided into several chisel-out areas (3), and different numbers are assigned to different chisel-out areas (3) to distinguish them. S2, reinforce the non-removal area of ​​the portal (1) with steel structure beams (4); S3, attach strain rosettes (5) to the outer center of each excavation zone (3), and connect the strain rosettes (5) to the strain measurement device; S4. Following a top-to-bottom, left-to-right symmetrical order, the chiseling area (3) is broken in sequence, and the strain data of the strain rosette (5) is recorded and analyzed during the breaking process. ; S5, determine whether to stop the chiseling operation, when the strain data of strain flower (5) is available. Stop the excavation of the tunnel entrance (1) when either of the following two conditions is met: ① Strain data of the strain rosemary (5) , ① The ultimate tensile strain of the concrete in the portal (1); ② The strain data of the strain rosette (5) satisfy ;in, The tensile modulus of elasticity of the concrete for the portal (1) is given. The sum of the thicknesses of the reinforced stratum zone (6) and the portal (1) is given. The thickness of the ground reinforcement zone (6) is given. To calculate the earth pressure in the strata behind the tunnel entrance (1), The ultimate shear strength of the soil in the stratum; S6. After stopping the chiseling operation, insert the grouting pipe (7) obliquely into the hole position formed in the chiseled area (3) and use pressure grouting to reinforce the reinforcement area (6) behind the un-chiseled hole (1) so that the strain gauge reading is within the safe range during the subsequent chiseling construction. Only then can the chiseling construction continue. S7. Repeat steps S4 to S6 until the removal of the portal (1) is completed.

2. The method for demolishing a large-section portal in pipe jacking construction according to claim 1, characterized in that, In step S1, the chiseling area (3) is divided according to the principle of larger at the top and smaller at the bottom, and uniform on the left and right.

3. The method for demolishing a large-section portal in pipe jacking construction according to claim 1, characterized in that, In step S3, the strain gauge (5) used is a triaxial strain gauge, with the three strain gauges arranged at 0°, 45° and 90° respectively.

4. The method for demolishing a large-section portal in pipe jacking construction according to claim 1, characterized in that, In step S5, the ultimate tensile strain of the concrete of the portal (1) is measured.

1. Tensile elastic modulus of concrete for the portal (1) Ultimate shear strength of soil strata All results were obtained through indoor testing.

5. A method for demolishing a large-section portal in pipe jacking construction according to claim 1, characterized in that, In step S6, the grouting material is selected based on the properties of the soil and rock mass in the reinforced area (6), the setting time of the grouting material, and the required reinforcement strength.

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