Karst stratum shield tunneling head disaster prediction method and treatment method

Abstract

The present application relates to a kind of karst stratum shield head disaster prediction method and treatment method, comprising the following steps: shield machine travels to the first working condition under the side of karst cave directly above, obtains the first uniform load that one side edge rock-soil of karst cave is subjected to;According to the first uniform load, the vertical first maximum principal stress that rock-soil is subjected to at the depth of karst cave bottom is obtained, the second maximum principal stress of rock-soil in limit equilibrium state is obtained, and the comparison of first maximum principal stress and second maximum principal stress is to determine whether karst cave is damaged;Shield machine travels to the second working condition under the side of karst cave directly above, obtains the uniform load of intermediate rock-soil between shield machine and karst cave;The maximum bending moment and maximum shear force of intermediate rock-soil are obtained, and whether karst cave is damaged is determined according to maximum bending moment and maximum shear force;When karst cave is not damaged in the first working condition and the second working condition, it is judged that head disaster will not occur, otherwise head disaster will occur, and the method of the present application avoids head disaster.

Description

Technical Field

[0001] This invention relates to the field of underground engineering technology, specifically to a method for predicting and treating shield tunneling head disasters in karst formations. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] With the increasing number of subway constructions, the geological strata they traverse are becoming more complex, often encountering karst formations. When tunnel boring machines (TBMs) encounter underlying karst during construction, excavation disturbs the karst, affecting its stability and potentially causing damage, leading to TBM head-down accidents and compromising tunneling safety. There are two scenarios involving underlying karst: first, the TBM directly traverses the karst strata, which is more prone to head-down accidents; second, the underlying karst contains a certain amount of intermediate rock and soil. When this intermediate rock and soil is thin, the disturbance generated by the TBM excavation can easily damage the karst, leading to head-down accidents. However, when the intermediate rock and soil is thick and has sufficient bearing capacity, it can withstand the disturbance generated by the TBM excavation and prevent head-down accidents.

[0004] Currently, there is no specific method for predicting head-down disasters. In actual construction, after a head-down disaster occurs on a long tunnel boring machine, the machine's posture is adjusted to overcome the disaster and continue tunneling. This seriously affects construction efficiency and causes problems such as project delays and increased costs. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for predicting tunnel head falls in karst formations. This method can predict tunnel head falls and take corresponding reinforcement measures to avoid their occurrence, thereby improving construction efficiency.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] An embodiment of the present invention provides a method for predicting shield tunneling head disasters in karst strata, comprising the following steps:

[0008] In the first working condition where the tunnel boring machine travels to the side directly above the karst cave, the first uniformly distributed load on the rock and soil at the edge of the karst cave is obtained; based on the first uniformly distributed load, the first maximum vertical principal stress on the rock and soil at the bottom depth of the karst cave is obtained; based on the first maximum principal stress, the second maximum principal stress on the rock and soil in the limit equilibrium state is obtained; based on the comparison between the first maximum principal stress and the second maximum principal stress, it is determined whether the karst cave will be damaged.

[0009] In the second working condition where the tunnel boring machine travels directly above the karst cave, the second uniformly distributed load on the intermediate rock and soil between the tunnel boring machine and the karst cave is obtained; based on the obtained second uniformly distributed load, the maximum bending moment and maximum shear force on the intermediate rock and soil are obtained, and the karst cave is judged to be damaged based on the maximum bending moment and maximum shear force.

[0010] If it is determined that the karst cave will not be damaged under both the first and second working conditions, then it is determined that no head-down disaster will occur; otherwise, a head-down disaster will occur.

[0011] Optionally, the uniformly distributed load on the edge of the karst cave under the first working condition can be obtained based on the unit weight of the rock and soil above the tunnel boring machine, the burial depth of the tunnel boring machine, and the weight of the tunnel boring machine itself.

[0012] Optionally, the minimum principal stress is obtained based on the first maximum principal stress and the active earth pressure coefficient, and the second maximum principal stress of the soil and rock under the limit equilibrium state is obtained based on the minimum principal stress, the strength parameters of the soil and rock, cohesion, and friction angle.

[0013] Optionally, the active earth pressure coefficient is obtained based on the friction angle of the soil mass.

[0014] Optionally, if the second maximum principal stress is greater than the first maximum principal stress, the cave will not be destroyed; otherwise, the cave will be destroyed.

[0015] Optionally, the second uniformly distributed load on the intermediate rock and soil between the tunnel boring machine and the karst cave under the second working condition can be obtained based on the unit weight of the rock and soil above the tunnel boring machine, the burial depth of the tunnel boring machine, and the weight of the tunnel boring machine itself.

[0016] Optionally, the intermediate soil and rock between the tunnel boring machine and the karst cave can be simplified into a simply supported beam model subjected only to the pressure of the tunnel boring machine and the ground pressure. Then, the maximum bending moment and maximum shear force on the intermediate soil and rock can be obtained based on the simply supported beam model and the second uniformly distributed load.

[0017] Optionally, the maximum normal stress and maximum shear stress of the intermediate soil and rock can be obtained based on the obtained maximum bending moment and maximum shear force, and the potential for damage to the karst cave can be determined based on the obtained maximum normal stress and maximum shear stress.

[0018] Furthermore, the maximum normal stress is obtained based on the maximum bending moment, the length of the karst cave, and the thickness of the intermediate rock and soil; the maximum shear stress is obtained based on the maximum shear force, the inertia coefficient of the intermediate rock and soil, the static moment, and the thickness of the intermediate rock and soil.

[0019] Optionally, the strength can be checked by combining the obtained maximum normal stress and maximum shear stress with the fourth strength theory, and the results can be used to determine whether the cave will be damaged.

[0020] Secondly, embodiments of the present invention provide a method for treating shield tunneling head-down disasters in karst strata. First, the method for predicting shield tunneling head-down disasters in karst strata described in the first aspect is used to predict whether a head-down disaster will occur during the shield tunneling process. If it is predicted that a head-down disaster will not occur, shield tunneling can proceed. If it is predicted that a head-down disaster will occur, the karst cave is reinforced by grouting. After the grouting reinforcement is completed, shield tunneling is carried out.

[0021] The beneficial effects of this invention are as follows:

[0022] The prediction method of this invention, under the first working condition, can obtain the first maximum principal stress of the soil and rock at the bottom depth of the karst cave based on the uniformly distributed load on one side of the karst cave, and then obtain the second maximum principal stress based on the first maximum principal stress. The comparison between the first and second maximum principal stresses determines whether the karst cave will be damaged. Under the second working condition, the maximum bending moment and maximum shear force are obtained based on the uniformly distributed load of the intermediate soil and rock, and the maximum normal stress and maximum shear stress are obtained based on the maximum bending moment and maximum shear force. The maximum normal stress and maximum shear stress determine whether the karst cave will be damaged. Thus, it is possible to predict whether the karst cave will be damaged in two working conditions: before the tunnel boring machine (TBM) has traveled directly above the karst cave and when the TBM has traveled directly above the karst cave. By predicting whether the karst cave will be damaged, the prediction of the TBM head-down disaster is realized. This makes it easier for construction personnel to take targeted reinforcement measures for the karst cave before the TBM construction, avoiding the head-down disaster during the TBM construction process. It can effectively improve the safety of construction under complex geological conditions, significantly improve construction efficiency, reduce the delay and cost increase caused by geological problems, and thus improve the economic benefits of the project. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0024] Figure 1 This is a flowchart of the method in Embodiment 1 of the present invention;

[0025] Figure 2 This is a simplified schematic diagram of the karst cave model constructed in Embodiment 1 of the present invention;

[0026] Figure 3 This is a schematic diagram of the karst cave failure model under the first working condition of Embodiment 1 of the present invention;

[0027] Figure 4 This is a stress analysis diagram of the rock and soil on one side of the karst cave under the first working condition of Embodiment 1 of the present invention;

[0028] Figure 5 This is a schematic diagram of the karst cave failure model under the second working condition in Embodiment 1 of the present invention;

[0029] Figure 6 This is a stress analysis diagram of the intermediate soil and rock under the second working condition in Embodiment 1 of the present invention;

[0030] Among them, 1. shield tunnel, 2. karst cave, 3. limestone. Detailed Implementation

[0031] Example 1

[0032] This embodiment provides a method for predicting shield tunneling head disasters in karst strata, such as... Figure 1 As shown, it includes the following steps:

[0033] Step 1: Conduct geological surveys to obtain geological parameters such as the friction angle of the rock and soil. In this embodiment, the rock and soil are limestone 3. The karst caves are surveyed and identified, and the longest and thickest parts of karst cave 2 are measured. Figure 2 As shown, the cave model is simplified into a regular shape with a rectangular vertical cross-section.

[0034] Step 2: Predict and judge whether the karst cave will be damaged during the advance of the tunnel boring machine. In this embodiment, a karst cave damage model is constructed. There are two damage modes of the karst cave during the advance of the tunnel boring machine. Two damage models are established respectively. The first damage model is the karst sidewall damage, and the second model is the intermediate rock and soil damage between the tunnel boring machine and the karst cave.

[0035] The first failure model corresponds to the first working condition, which is when the tunnel boring machine has traveled to one side of the area directly above the karst cave, but the tunnel boring machine has not yet traveled directly above the karst cave.

[0036] The second failure model corresponds to the second working condition, which is when the tunnel boring machine travels to the area directly above the karst cave.

[0037] like Figures 3-4 As shown, the method for predicting whether a karst cave will be damaged under the first working condition includes the following steps:

[0038] Step a: Calculate the first uniformly distributed load F on the soil and rock at one edge of the karst cave based on the unit weight γ of the soil and rock, the burial depth z of the tunnel boring machine, and the weight P of the tunnel boring machine itself.

[0039] Specifically, F = γz + P

[0040] The unit weight of the soil and rock is obtained through geological exploration and can be achieved using existing technology, so it will not be described in detail here. The burial depth z of the tunnel boring machine is obtained according to the construction design requirements. The weight P of the tunnel boring machine itself is a parameter of the tunnel boring machine and is a known quantity.

[0041] Step b: Calculate the first maximum vertical principal stress on the soil and rock at a depth of h in the bottom layer of the karst cave based on the first uniformly distributed load. Specifically, under the action of a continuous uniformly distributed load F, the first maximum vertical principal stress on the soil and rock element at a depth of h in the bottom layer of the karst cave is:

[0042] σ1=F+γh (1)

[0043] Step c: Obtain the minimum principal stress σ3 based on the calculated first maximum principal stress.

[0044] The method for calculating the minimum principal stress σ3 is as follows:

[0045] σ3=σ1K a =FK a +γhK a (2)

[0046] in, K a The active earth pressure coefficient, The friction angle of the rock and soil is obtained through geological exploration.

[0047] Step d: Based on the calculated minimum principal stress σ3 of the soil and rock element and the strength parameters of the soil and rock obtained through geological exploration, namely cohesion c and friction angle... The second maximum principal stress σ of the soil and rock under the limit equilibrium state is obtained. 1f

[0048] Specifically:

[0049]

[0050] Comparing the second maximum principal stress with the first maximum principal stress, if the second maximum principal stress is greater than the first maximum principal stress, then the maximum principal stress required to reach the limit equilibrium state is greater than the actual maximum principal stress, and the karst cave will not be damaged and will remain stable. Otherwise, the soil will be damaged, causing the karst cave to collapse. In this case, grouting reinforcement of the karst cave is required.

[0051] like Figures 5-6 As shown, the method for predicting whether the karst cave will be damaged under the second working condition includes the following steps:

[0052] Step (1): When the tunnel boring machine travels to the top of the karst cave, the intermediate rock and soil between the tunnel boring machine and the karst cave is simplified into a simply supported beam model, that is, the intermediate rock and soil between the tunnel 1 and the karst cave 2 is simplified into a simply supported beam model. Based on the unit weight γ of the rock and soil, the burial depth z of the tunnel boring machine and the weight P of the tunnel boring machine, the second uniformly distributed load q on the intermediate rock and soil is obtained.

[0053] Specifically:

[0054] q=γz+P

[0055] Step (2): Calculate the maximum bending moment M of the intermediate soil and rock during the tunnel boring machine's movement based on the second uniformly distributed load q. max and maximum shear force F smax Specifically:

[0056]

[0057]

[0058] Where L is the length of the karst cave, and x is the distance between the front end of the tunnel boring machine and the edge of the karst cave facing the tunnel boring machine.

[0059] When x = L, the maximum bending moment and the maximum shear force are both at their maximum.

[0060]

[0061] Step (3): Based on the obtained maximum bending moment M max and maximum shear force F s max The maximum normal stress δ and maximum shear stress τ of the intermediate soil and rock are obtained, specifically:

[0062]

[0063] Where W is the bending coefficient of the intermediate soil and rock, and I z S represents the inertia coefficient of the intermediate soil and rock. z Here, is the static moment of the intermediate soil and rock, and h is the thickness of the intermediate soil and rock. All of these parameters can be obtained through geological exploration and will not be described in detail here.

[0064] Step (4): Based on the obtained maximum normal stress and maximum shear stress, the strength is checked in conjunction with the fourth strength theory. Based on the check results, it is determined whether the cave will be damaged.

[0065] Specifically:

[0066]

[0067] [δ] represents the allowable stress; δ b The tensile strength limit is determined based on the actual working conditions; n is the safety factor, determined based on the actual working conditions.

[0068] The strength condition is:

[0069]

[0070] If formula (6) is satisfied, the karst cave will not be damaged and will remain stable without the need for reinforcement. If formula (6) is not satisfied, the karst cave will be damaged and will need to be reinforced by grouting.

[0071] Step 3: If the karst cave is determined not to be damaged under both the first and second working conditions, it is determined that no head-down disaster will occur during the shield tunneling construction; otherwise, it is determined that a head-down disaster will occur during the shield tunneling construction.

[0072] The method in this embodiment predicts the risk of tunnel boring machine (TBM) head-down disaster by checking whether the karst cave is damaged. This allows construction personnel to take targeted reinforcement measures for the karst cave before TBM construction, thus avoiding head-down disaster during the TBM construction process. It can effectively improve the safety of construction under complex geological conditions, significantly improve construction efficiency, reduce construction delays and cost increases caused by geological problems, and ultimately improve the economic benefits of the project.

[0073] In a practical application of the prediction method in this embodiment, the tunnel boring machine is buried at a depth z of 10m, the soil and rock strength parameters cohesion c is 10kPa, and the friction angle is... The angle is 35°, and the specific gravity γ is 20 kN / m. 3 The weight of the tunnel boring machine is p = 100 kN / m², the depth of the karst cave is h = 3.5 m, the length is L = 7 m, and the thickness of the rock and soil in the middle is 0.5 m.

[0074] In the first working condition, before the tunnel boring machine reaches the top of the karst cave, the first uniformly distributed load on the rock and soil at the edge of the karst cave is F = 20 × 10 + 100 = 300 kPa, and the active earth pressure coefficient is...

[0075]

[0076] At the bottom of the cave, the first maximum principal stress σ1 = F + γh = 300 + 20 × 3.5 = 370 kPa, then the minimum principal stress σ3 = σ1K a =370 × 0.27 = 99.9 kPa

[0077] The second maximum principal stress σ1f of the soil and rock under limit equilibrium state is obtained.

[0078]

[0079]

[0080] Therefore, σ 1f >σ1, the karst cave is stable when the tunnel boring machine is at the edge of the karst cave.

[0081] In the second scenario, when the tunnel boring machine (TBM) passes over the karst cave, assuming the TBM face is close to the edge of the cave (i.e., x is L), the maximum bending moment and maximum shear force are:

[0082]

[0083] The maximum normal stress is:

[0084] The maximum shear stress is:

[0085]

[0086]

[0087] The karst cave is stable when the tunnel boring machine face passes completely over it.

[0088] Example 2

[0089] This embodiment provides a method for dealing with shield tunneling head-down disasters in karst strata. First, the method for predicting shield tunneling head-down disasters in karst strata described in Embodiment 1 is used to predict whether a head-down disaster will occur during the shield tunneling process. If it is predicted that a head-down disaster will not occur, shield tunneling can proceed. If it is predicted that a head-down disaster will occur, the karst cave is reinforced by grouting. After the grouting reinforcement is completed, shield tunneling can proceed.

[0090] The grouting reinforcement construction method can be implemented using existing technology, and will not be described in detail here.

[0091] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for predicting shield tunneling head-climbing disasters in karst strata, characterized in that, Includes the following steps: In the first working condition where the tunnel boring machine (TBM) has not yet reached the top of the karst cave, the first uniformly distributed load on the rock and soil at the edge of the karst cave is obtained. Based on the first uniformly distributed load, the first maximum vertical principal stress on the rock and soil at the bottom depth of the karst cave is obtained. Based on the first maximum principal stress, the second maximum principal stress of the rock and soil in the limit equilibrium state is obtained. Based on the comparison between the first maximum principal stress and the second maximum principal stress, it is determined whether the karst cave will be damaged. The minimum principal stress is obtained from the first maximum principal stress and the active earth pressure coefficient. The second maximum principal stress of the soil and rock under the limit equilibrium state is obtained from the minimum principal stress, the strength parameters of the soil and rock, cohesion, and friction angle. In the second working condition where the tunnel boring machine travels directly above the karst cave, the second uniformly distributed load on the intermediate rock and soil between the tunnel boring machine and the karst cave is obtained; based on the obtained uniformly distributed load, the maximum bending moment and maximum shear force on the intermediate rock and soil are obtained, and the karst cave is judged to be damaged based on the maximum bending moment and maximum shear force. The intermediate soil and rock between the tunnel boring machine and the karst cave is simplified into a simply supported beam model that is only subjected to the pressure of the tunnel boring machine and the pressure of the ground. Then, based on the simply supported beam model and the second uniformly distributed load, the maximum bending moment and the maximum shear force on the intermediate soil and rock are obtained. If it is determined that the karst cave will not be damaged under both the first and second working conditions, then it is determined that no head-down disaster will occur; otherwise, a head-down disaster will occur.

2. The method for predicting shield tunneling head disasters in karst formations as described in claim 1, characterized in that, The uniformly distributed load on the rock and soil at one edge of the karst cave under the first working condition is obtained based on the unit weight of the rock and soil above the tunnel boring machine, the burial depth of the tunnel boring machine, and the weight of the tunnel boring machine itself.

3. The method for predicting shield tunneling head disasters in karst strata as described in claim 1, characterized in that, The active earth pressure coefficient is obtained from the friction angle of the soil and rock mass.

4. The method for predicting shield tunneling head disasters in karst formations as described in claim 1, characterized in that, If the second maximum principal stress is greater than the first maximum principal stress, the cave will not be destroyed; otherwise, the cave will be destroyed.

5. The method for predicting shield tunneling head disasters in karst formations as described in claim 1, characterized in that, The second uniformly distributed load on the intermediate rock and soil between the tunnel boring machine and the karst cave under the second working condition is obtained based on the unit weight of the rock and soil above the tunnel boring machine, the burial depth of the tunnel boring machine, and the weight of the tunnel boring machine itself.

6. The method for predicting shield tunneling head disasters in karst formations as described in claim 1, characterized in that, The maximum normal stress and maximum shear stress of the intermediate soil and rock are obtained based on the maximum bending moment and maximum shear force, and the maximum normal stress and maximum shear stress are used to determine whether the karst cave will be damaged. Furthermore, the maximum normal stress is obtained based on the maximum bending moment, the length of the karst cave, and the thickness of the intermediate rock and soil. The maximum shear stress is obtained based on the maximum shear force, the inertia coefficient of the intermediate rock and soil, the static moment, and the thickness of the intermediate rock and soil.

7. The method for predicting shield tunneling head disasters in karst formations as described in claim 1, characterized in that, The strength is checked by combining the obtained maximum normal stress and maximum shear stress with the fourth strength theory, and the results are used to determine whether the cave will be damaged.

8. A method for treating shield tunneling head failure in karst formations, characterized in that, First, the method for predicting tunnel head-down disasters in karst formations as described in any one of claims 1-7 is used to predict whether a tunnel head-down disaster will occur during the tunnel construction process. If it is predicted that no tunnel head-down disaster will occur, tunnel construction can proceed. If it is predicted that a tunnel head-down disaster will occur, the karst cave is reinforced by grouting. After the grouting reinforcement is completed, tunnel construction can proceed.

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