Karst stratum shield planting disaster prediction method and treatment method

Abstract

The karst stratum shield head planting disaster prediction method comprises the following steps that under the first working condition that a shield tunneling machine travels to one side over a karst cave, a first evenly-distributed load borne by rock soil on the edge of one side of the karst cave is obtained; according to the first uniform load, obtaining a first vertical maximum principal stress borne by rock soil at the bottom depth of the karst cave, obtaining a second maximum principal stress of the rock soil in a limit equilibrium state, and comparing the first maximum principal stress with the second maximum principal stress to judge whether the karst cave is damaged or not; under the second working condition that the shield tunneling machine travels to the position over the karst cave, the evenly-distributed load of middle rock soil between the shield tunneling machine and the karst cave is obtained; the maximum bending moment and the maximum shearing force of the middle rock soil are obtained, and whether the karst cave is damaged or not is judged according to the maximum bending moment and the maximum shearing force; and when it is judged that the karst cave is not damaged under the first working condition and the second working condition, it is judged that no planting disaster occurs, otherwise, the planting disaster occurs, and the method is adopted to avoid the planting disaster.

Description

Technical Field

[0001] The invention relates to the technical field of underground engineering, and in particular to a method for predicting and treating shield tunneling disasters in karst strata. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] With the increasing number of subway constructions, the strata being crossed are becoming more and more complex, and karst strata are often encountered. When encountering underlying karst during shield construction, excavation will disturb the underlying karst, affecting its own stability and causing damage, which will lead to shield head plunge disasters and affect excavation safety. There are two situations for underlying karst. The first is that the shield machine is more likely to cause head plunge disasters when it directly passes through the karst strata; the second is that there is a certain amount of intermediate rock and soil in the underlying karst. When the intermediate rock and soil are thin, the disturbance caused by the shield machine excavation is likely to damage the karst, and then the shield head plunge disaster will occur. When the intermediate rock and soil are thicker and have a certain bearing capacity, they can bear the disturbance caused by the shield machine excavation and will not cause head plunge disasters.

[0004] At present, there is no special prediction method for head plunge disasters. During actual construction, after a full-length shield machine suffers a head plunge disaster, the shield machine's posture is adjusted to overcome the disaster and then the shield construction can be continued, which seriously affects the construction efficiency and causes problems such as construction delays and cost increases. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for predicting shield head plunge disasters in karst strata, which can predict head plunge disasters and thus take corresponding reinforcement measures to avoid the occurrence of head plunge disasters, thereby improving construction efficiency.

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

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

[0008] Under the first working condition when the shield 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; the vertical first maximum principal stress on the rock and soil at the depth of the bottom layer of the karst cave is obtained according to the first uniformly distributed load, the second maximum principal stress of the rock and soil in the limit equilibrium state is obtained according to the first maximum principal stress, and whether the karst cave will be destroyed is judged according to the comparison result of the first maximum principal stress and the second maximum principal stress;

[0009] Under the second working condition when the shield machine travels to the top of the karst cave, the second uniformly distributed load on the rock and soil between the shield machine and the karst cave is obtained; the maximum bending moment and the maximum shear force on the rock and soil in the middle are obtained according to the obtained second uniformly distributed load, and whether the karst cave will be damaged is judged according to the maximum bending moment and the maximum shear force;

[0010] When it is judged that the karst cave will not be destroyed under both the first working condition and the second working condition, it is judged that a head-fall disaster will not occur; otherwise, a head-fall disaster will occur.

[0011] Optionally, the uniformly distributed load on the edge rock and soil on one side of the cave under the first working condition is obtained according to the weight of the rock and soil above the shield machine, the burial depth of the shield machine and the weight of the shield machine itself.

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

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

[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, a second uniformly distributed load on the rock and soil between the shield machine and the cave under the second working condition is obtained according to the weight of the rock and soil above the shield machine, the burial depth of the shield machine and the weight of the shield machine itself.

[0016] Optionally, the intermediate rock and soil between the shield machine and the cave is simplified into a simply supported beam model that is only subjected to the shield machine pressure and the stratum pressure, and then the maximum bending moment and maximum shear force of the intermediate rock and soil are obtained in combination with the second uniformly distributed load based on the simply supported beam model.

[0017] Optionally, the maximum normal stress and maximum shear stress of the intermediate rock and soil are obtained according to the obtained maximum bending moment and maximum shear force, and whether the cave will be destroyed is determined according to 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 cave, and the thickness of the intermediate rock and soil, and the maximum shear stress is obtained based on the maximum shear force, the inertia coefficient, static moment, and thickness of the intermediate rock and soil.

[0019] Optionally, strength verification is performed based on the obtained maximum normal stress and maximum shear stress in combination with the fourth strength theory, and whether the cave will be destroyed is determined based on the verification results.

[0020] In the second aspect, an embodiment of the present invention provides a method for treating shield head plunge disasters in karst strata. First, the method for predicting shield head plunge disasters in karst strata described in the first aspect is used to predict whether a shield head plunge disaster will occur during the shield construction process. If it is predicted that no head plunge disaster will occur, shield construction can be carried out. If it is predicted that a head plunge disaster will occur, grouting reinforcement is carried out on the cave, and shield construction is carried out after the grouting reinforcement is completed.

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

[0022] The prediction method of the present invention can obtain the first maximum principal stress of the rock and soil at the depth of the bottom layer of the cave according to the uniformly distributed load on the rock and soil on one side of the cave under the first working condition, and then obtain the second maximum principal stress according to the first maximum principal stress, and judge whether the cave will be damaged according to the comparison result of the first maximum principal stress and the second maximum principal stress; under the second working condition, the maximum bending moment and the maximum shear force are obtained according to the uniformly distributed load of the middle rock and soil, and the maximum normal stress and the maximum shear stress are obtained according to the maximum bending moment and the maximum shear force. Whether the cave will be damaged is judged by the maximum normal stress and the maximum shear stress, so that it can be predicted whether the cave will be damaged under the two working conditions that the shield machine has not yet traveled to the top of the cave and the shield machine travels to the top of the cave. The prediction of the shield machine head-fall disaster is realized by whether the cave is damaged, so that it is convenient for construction personnel to take targeted reinforcement measures for the cave before shield construction, avoiding the head-fall disaster during shield construction, and can effectively improve the safety of construction under complex geological conditions, and can also significantly improve the construction efficiency, reduce the construction period delay and cost increase caused by geological problems, and thus improve the economic benefits of the project. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0024] Figure 1 is a flow chart of the method of embodiment 1 of the present invention;

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

[0026] Figure 3 It is a schematic diagram of a karst cave destruction model under the first working condition of Example 1 of the present invention;

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

[0028] Figure 5 It is a schematic diagram of a karst cave destruction model under the second working condition of Example 1 of the present invention;

[0029] Figure 6 is the middle rock and soil stress analysis diagram under the second working condition of Example 1 of the present invention;

[0030] Among them, 1. shield tunnel, 2. cave, 3. limestone. DETAILED DESCRIPTION

[0031] Example 1

[0032] This embodiment provides a method for predicting shield tunneling disasters in karst strata. Figure 1 As shown, the following steps are included:

[0033] Step 1: Survey the strata to obtain geological parameters such as the friction angle of the rock and soil. In this embodiment, the rock and soil is limestone 3. Survey and determine the caves, and measure the longest and thickest parts of the cave 2, such as Figure 2 As shown in Figure 2, the cave model is simplified into a regular shape with a rectangular vertical cross-section.

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

[0035] The first failure model corresponds to the first working condition, in which the shield machine travels to a position on one side of the area directly above the cave, but has not yet traveled directly above the cave.

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

[0037] like Figure 3-Figure 4 As shown, the prediction method of whether the cave will be destroyed under the first working condition includes the following steps:

[0038] Step a: Calculate the first uniformly distributed load F on the rock and soil at the edge of one side of the cave according to the bulk density γ of the rock and soil, the buried depth z of the shield machine and the weight P of the shield machine itself.

[0039] Specifically, F = γz + P

[0040] The bulk density of rock and soil is obtained through geological exploration and existing technology can be used, which will not be described in detail here. The buried depth z of the shield machine is obtained according to the construction design requirements. The weight P of the shield machine itself is a parameter of the shield machine and is a known quantity.

[0041] Step b: Calculate the first maximum vertical principal stress of the rock and soil at the depth h of the bottom layer of the cave according to the first uniformly distributed load. Specifically, under the action of the continuous uniformly distributed load F, the first maximum vertical principal stress of the rock and soil unit at the depth h of the bottom layer of the cave is:

[0042] σ1=F+γh (1)

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

[0044] The calculation method of the minimum principal stress σ3 is:

[0045] σ3=σ1K a =FK a +γhK a (2)

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

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

[0048] Specific:

[0049]

[0050] Compare 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, the maximum principal stress required to reach the limit equilibrium state is greater than the actual maximum principal stress, the cave will not be damaged and the cave will remain stable. Otherwise, the soil will be damaged and cause the cave to collapse. At this time, the cave needs to be reinforced by grouting.

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

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

[0053] Specific:

[0054] q=γz+P

[0055] Step (2): Calculate the maximum bending moment M of the intermediate rock and soil during the shield machine's travel based on the second uniformly distributed load q max and the maximum shear force F smax , specifically:

[0056]

[0057]

[0058] Among them, L is the length of the cave, and x is the distance between the front end of the shield machine and the side edge of the cave facing the shield machine.

[0059] When x = L, the maximum bending moment is the largest and the maximum shear force is the largest. At this time:

[0060]

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

[0062]

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

[0064] Step (4): Perform strength verification based on the obtained maximum normal stress and maximum shear stress in combination with the fourth strength theory, and determine whether the cave will be destroyed based on the verification results.

[0065] Specific:

[0066]

[0067] [δ] is the allowable stress; δ b is the tensile strength limit, which is determined according to the actual working conditions; n is the safety factor, which is determined according to the actual working conditions;

[0068] The strength conditions are:

[0069]

[0070] If formula (6) is satisfied, the cave will not be damaged, the cave will remain stable, and no reinforcement is required. If formula (6) is not satisfied, the cave will be damaged and grouting reinforcement is required.

[0071] Step 3: When it is judged that the cave will not be destroyed under both the first and second working conditions, it is judged that there will be no head-fall disaster during the shield construction process; otherwise, it is judged that there will be a head-fall disaster during the shield construction process.

[0072] By adopting the method of this embodiment, the shield machine head-plunge disaster is predicted by determining whether the cave is damaged, thereby facilitating construction personnel to take targeted reinforcement measures for the cave before shield construction, thereby avoiding head-plunge disasters during shield construction. This 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 thus improve the economic benefits of the project.

[0073] In an actual application of the prediction method of this embodiment, the buried depth z of the shield machine is 10m, the strength parameter cohesion c of the rock and soil is 10kPa, and the friction angle The angle is 35° and the gamma is 20 kN / m 3 The weight of the shield machine p is 100kN / ㎡, the depth of the cave h is 3.5m, the length L is 7m, and the thickness of the middle rock and soil is 0.5m.

[0074] Under the first working condition, when the shield machine has not reached the top of the cave, the first uniformly distributed load on the rock and soil at the edge of the cave is F = 20 × 10 + 100 = 300 kPa, and the active earth pressure coefficient is

[0075]

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

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

[0078]

[0079]

[0080] From this we can know that σ 1f >σ1, the cave is stable when the shield machine is at the edge of the cave.

[0081] In the second working condition, when the shield machine passes above the cave, assuming that the shield machine face is close to the edge of the cave, that is, when 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 cave is stable when the shield machine face completely passes over the cave.

[0088] Example 2

[0089] The present embodiment provides a method for treating shield head plunge disasters in karst strata. Firstly, the shield head plunge disaster prediction method in karst strata described in Example 1 is used to predict whether a shield head plunge disaster will occur during the shield construction process. If it is predicted that no head plunge disaster will occur, shield construction can be carried out. If it is predicted that a head plunge disaster will occur, grouting reinforcement is carried out on the cave, and shield construction is carried out after the grouting reinforcement is completed.

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

[0091] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for predicting shield tunneling disasters in karst strata, characterized in that: The following steps are involved: Under the first working condition when the shield 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; the vertical first maximum principal stress on the rock and soil at the depth of the bottom layer of the karst cave is obtained according to the first uniformly distributed load, the second maximum principal stress of the rock and soil in the limit equilibrium state is obtained according to the first maximum principal stress, and whether the karst cave will be destroyed is judged according to the comparison result of the first maximum principal stress and the second maximum principal stress; Under the second working condition when the shield machine travels to the top of the karst cave, the second uniformly distributed load on the rock and soil between the shield machine and the karst cave is obtained; the maximum bending moment and the maximum shear force on the rock and soil in the middle are obtained according to the obtained uniformly distributed load, and whether the karst cave will be damaged is judged according to the maximum bending moment and the maximum shear force; When it is judged that the karst cave will not be destroyed under both the first working condition and the second working condition, it is judged that the head-fall disaster will not occur; otherwise, the head-fall disaster will occur.

2. A method for predicting shield tunneling disasters in karst strata according to claim 1, characterized in that: According to the weight of the rock and soil above the shield machine, the burial depth of the shield machine and the weight of the shield machine itself, the uniformly distributed load on the edge rock and soil on one side of the cave under the first working condition is obtained.

3. A method for predicting shield tunneling disasters in karst strata according to claim 1, characterized in that: 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 rock and soil in the limit equilibrium state is obtained based on the minimum principal stress, the strength parameters of the rock and soil, cohesion and friction angle.

4. A method for predicting shield tunneling disasters in karst strata as claimed in claim 3, characterized in that: The active earth pressure coefficient is obtained based on the friction angle of the rock and soil.

5. A method for predicting shield tunneling disasters in karst strata according to 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.

6. A method for predicting shield tunneling disasters in karst strata according to claim 1, characterized in that: The second uniformly distributed load on the rock and soil between the shield machine and the cave under the second working condition is obtained according to the weight of the rock and soil above the shield machine, the burial depth of the shield machine and the weight of the shield machine itself.

7. A method for predicting shield tunneling disasters in karst strata according to claim 1, characterized in that: The intermediate rock and soil between the shield machine and the cave is simplified into a simply supported beam model that is only subjected to the shield machine pressure and the formation pressure. Then, the maximum bending moment and maximum shear force of the intermediate rock and soil are obtained in combination with the second uniformly distributed load based on the simply supported beam model.

8. A method for predicting shield tunneling disasters in karst strata according to claim 1, characterized in that: The maximum normal stress and maximum shear stress of the intermediate rock and soil are obtained according to the obtained maximum bending moment and maximum shear force, and whether the cave will be destroyed is determined according to the obtained maximum normal stress and maximum shear stress; Furthermore, the maximum normal stress is obtained according to the obtained maximum bending moment, the length of the cave, and the thickness of the intermediate rock and soil, and the maximum shear stress is obtained according to the maximum shear force, the inertia coefficient, the static moment, and the thickness of the intermediate rock and soil.

9. A method for predicting shield tunneling disasters in karst strata according to claim 1, characterized in that: The strength is checked based on the obtained maximum normal stress and maximum shear stress combined with the fourth strength theory, and the results are used to determine whether the cave will be destroyed.

10. A method for treating shield tunneling disaster in karst strata, characterized in that: First, the method for predicting shield head plunge disaster in karst strata as described in any one of claims 1 to 9 is used to predict whether a shield head plunge disaster will occur during the shield construction process. If it is predicted that no head plunge disaster will occur, shield construction can be carried out. If it is predicted that a head plunge disaster will occur, grouting reinforcement is carried out on the karst cave, and shield construction is carried out after the grouting reinforcement is completed.

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