Method for judging fault activation caused by tunnel excavation

Abstract

The invention discloses a method for discriminating fault activation caused by tunnel excavation, and relates to the field of tunnel and underground engineering design and construction, and the method specifically comprises the following steps: S1, surveying or looking up site geological parameters, and obtaining rock mechanical parameters of a fault and surrounding rock strata, a fault plane friction coefficient [mu], and stress state parameters representing fault plane feature points; and S2, establishing a numerical model of fault site tunnel excavation, endowing the fault plane slippage weakening friction constitutive, and appointing the weakening relationship between the fault plane friction coefficient mu and variables such as the slippage rate or the contact pressure. According to the method, the surrounding rock stress field evolution process in the tunnel excavation process is calculated, the fracture surface friction constitutive structure is introduced to achieve the bonding weakening process of the fault so as to describe the slippage instability of the fracture surface, the coulomb instability criterion for describing rock shear fracture is used for judging the activation behavior of the fracture surface, the mechanical mechanism of fault slippage is met, and the method is suitable for tunnel excavation. The method is simple and easy to use, and still has high accuracy.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel and underground engineering design and construction, and in particular to a method for determining fault activation caused by tunnel excavation. Background Art

[0002] In the process of earthquake development, in addition to the slowly and steadily changing tectonic stress caused by plate movement and other tectonic processes, earthquakes are also affected by transient and periodic stress disturbances caused by surrounding strong earthquakes, reservoir water storage and engineering activities. These stresses act on the faults and cause the fault stress state to adjust, which will change the characteristics of seismic activity on the faults and cause strong earthquakes to occur earlier or later.

[0003] Faults in the long-term creep process accumulate huge energy, but they still remain stable under the bonding effect of the fracture. The excavation of large underground spaces such as tunnels will inevitably cause changes in the surrounding rock stress field. When there are faults in or near the excavation space, stress disturbances may break this balance and cause fault activation. The fault will instantly change from a bonding state to a slip state, inducing disasters such as rock bursts and earthquakes.

[0004] However, there is currently no unified mechanistic understanding of the fault activation caused by construction stress disturbance, and the earthquake source is far away from the tunnel excavation surface, making it impossible to accurately predict and take timely measures. Summary of the invention

[0005] The purpose of the present invention is to provide a method for determining fault activation caused by tunnel excavation, to calculate the evolution of surrounding rock stress field during tunnel excavation, and to introduce fault plane friction constitutive model to describe the slip instability of the fault plane. When defining the friction constitutive model in the finite element, it is still based on the Coulomb friction theory, that is, the friction force is proportional to the normal compressive stress acting on the friction surface, and the adhesion weakening process of the fault is realized by assigning the fault plane slip weakening friction constitutive model, so as to further use the Coulomb instability criterion describing rock shear fracture to judge the activation behavior of the fault plane, so as to solve the problem mentioned in the above background technology that there is no unified mechanistic understanding of fault activation caused by construction stress disturbance, and the earthquake source is far away from the tunnel excavation surface, and cannot be accurately predicted.

[0006] In order to achieve the above-mentioned invention object, the present invention adopts the following technical scheme:

[0007] The present invention provides a method for determining fault activation caused by tunnel excavation, comprising the following steps:

[0008] S1. Survey or check the geological parameters of the site to obtain the rock mechanics parameters of the fault and surrounding rock formations, the friction coefficient μ of the fault surface, and the stress state parameters characterizing the characteristic points of the fault surface;

[0009] S2. Establish a numerical model for tunnel excavation in fault sites, assign a slip-weakened friction constitutive model to the fault surface, and specify the weakening relationship between the friction coefficient μ of the fault surface and variables such as slip rate or contact pressure;

[0010] S3, calculate the evolution of the surrounding rock stress field during tunnel excavation, obtain the fault plane shear stress increment Δτ and normal stress increment Δσ, and the pore pressure increment ΔP;

[0011] S4. Draw the Mohr circle according to the Coulomb instability criterion Δτ=μ(Δσ-ΔP) to determine the fault activation instability state.

[0012] Preferably, the rock mechanics parameters in step S1 are the parameters required by the numerical model of tunnel excavation in the fault site S2, and the parameters are adjusted according to the established model constitutive law.

[0013] Preferably, the selection of the fault plane feature points in step S1 should be representative, such as being uniformly selected from top to bottom on the fault plane and appropriately encrypted near the tunnel excavation surface to improve the accuracy of the method.

[0014] Preferably, the characteristic points of the fault plane in step S1 should also be appropriately encrypted according to the stress increment extreme value points of the surrounding rock stress field evolution in step S3.

[0015] Preferably, the slip-weakening friction constitutive model in step S2 may select the weakening relationship between the friction coefficient and the slip rate or contact pressure etc. as required, or may adopt other friction constitutive models that can reflect the fault slip instability process, and its parameters shall be adjusted accordingly.

[0016] Compared with the prior art, one or more of the above technical solutions have the following beneficial effects:

[0017] 1. The physical meaning of each step in the present invention is clear, simple and easy to use, well-organized and novel in conception;

[0018] 2. The present invention describes the shear fracture of rocks by using the Coulomb instability criterion, thereby judging the activation behavior of faults, which is consistent with the mechanical mechanism of fault sliding. Its calculation method is reasonable and the calculation results are reliable.

[0019] 3. The present invention realizes the slip weakening instability of the fault by defining the friction constitutive structure of the fault plane, which conforms to the mechanical mechanism of fault instability and more accurately describes the change of stress state of the fault plane. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] 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.

[0021] Figure 1It is a schematic diagram of the fault site tunnel excavation calculation model of the present invention;

[0022] Figure 2 It is a schematic diagram of the Mohr circle for judging fault activation using the Coulomb instability criterion of the present invention. DETAILED DESCRIPTION

[0023] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0024] See also Figure 1 - Figure 2 , a method for determining fault activation caused by tunnel excavation, comprising the following steps:

[0025] S1. Survey or check the geological parameters of the site to obtain the rock mechanics parameters of the fault and surrounding rock formations, the friction coefficient μ of the fault surface, and the stress state parameters characterizing the characteristic points of the fault surface;

[0026] S2. Establish a numerical model for tunnel excavation in fault sites, assign a slip-weakened friction constitutive model to the fault surface, and specify the weakening relationship between the friction coefficient μ of the fault surface and variables such as slip rate or contact pressure;

[0027] S3, calculate the evolution of the surrounding rock stress field during tunnel excavation, obtain the fault plane shear stress increment Δτ and normal stress increment Δσ, and the pore pressure increment ΔP;

[0028] S4. Draw the Mohr circle according to the Coulomb instability criterion Δτ=μ(Δσ-ΔP) to determine the fault activation instability state.

[0029] The present invention calculates the evolution of the surrounding rock stress field during tunnel excavation and introduces the fault plane friction constitutive method to realize the bonding weakening process of the fault, which is used to describe the slip instability of the fault plane. The Coulomb instability criterion for describing rock shear fracture is used to judge the activation behavior of the fault plane, which conforms to the mechanical mechanism of fault sliding. The method is simple and easy to use, while still having high accuracy.

[0030] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for determining fault activation caused by tunnel excavation, characterized in that: The following steps are involved: S1. Survey or check the geological parameters of the site to obtain the rock mechanics parameters of the fault and surrounding rock formations, the friction coefficient μ of the fault surface, and the stress state parameters characterizing the characteristic points of the fault surface; S2. Establish a numerical model for tunnel excavation in fault sites, assign a slip-weakened friction constitutive model to the fault surface, and specify the weakening relationship between the friction coefficient μ of the fault surface and variables such as slip rate or contact pressure; S3, calculate the evolution of the surrounding rock stress field during tunnel excavation, obtain the fault plane shear stress increment Δτ and normal stress increment Δσ, and the pore pressure increment ΔP; S4. Draw the Mohr circle according to the Coulomb instability criterion Δτ=μ(Δσ-ΔP) to determine the fault activation instability state.

2. The method for determining fault activation caused by tunnel excavation according to claim 1, characterized in that: The rock mechanics parameters in step S1 are the parameters required by the numerical model of tunnel excavation in the fault site S2, and the parameters are adjusted according to the established model constitutive law.

3. The method for determining fault activation caused by tunnel excavation according to claim 1, characterized in that: The selection of the fault plane feature points in step S1 should be representative, such as being uniformly selected from top to bottom on the fault plane, and appropriately encrypted near the tunnel excavation surface to improve the accuracy of the method.

4. The method for determining fault activation caused by tunnel excavation according to claim 1, characterized in that: The characteristic points of the fault plane in step S1 should also be appropriately encrypted according to the stress increment extreme value points of the surrounding rock stress field evolution in step S3.

5. The method for determining fault activation caused by tunnel excavation according to claim 1, characterized in that: The slip-weakening friction constitutive model in step S2 may select the weakening relationship between the friction coefficient and the slip rate or contact pressure etc. as required, or may adopt other friction constitutive models that can reflect the fault slip instability process, and its parameters shall be adjusted accordingly.

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