Method for assigning simulation parameters of soft rock tunnel considering surrounding rock unloading and support characteristics

Abstract

The application discloses a soft rock tunnel simulation parameter assignment method considering surrounding rock unloading and supporting characteristics, and specifically comprises the following steps: tunnel excavation and supporting processes are simulated by using FLAC numerical software; in view of the unloading expansion of surrounding rock and the limit characteristics of the supporting structure, the state of the unit is determined in real time in calculation, and the z_prop function in the FISH language is used to assign parameters to the rock mass and the structural unit; the unloading expansion phenomenon of the surrounding rock is simulated by introducing a dynamic elastic modulus, and real-time adjustment is performed in the calculation process; the supporting effect of the structural unit is simulated by introducing a dynamic elastic modulus, and the limit bearing characteristics of the support are considered in the calculation; and a dynamic constitutive relation is introduced to simulate the yielding unit. The application considers the influence of the unloading expansion of the surrounding rock and the limit characteristics of the supporting structure, and realizes relatively accurate numerical simulation calculation of tunnel engineering.

Description

Technical Field

[0001] This invention belongs to the field of computer-aided design of tunnel engineering and geotechnical engineering, and particularly relates to a method for assigning simulation parameters for soft rock tunnels that takes into account the unloading and support characteristics of the surrounding rock. Background Technology

[0002] Accurately predicting tunnel deformation and constructing a reasonable deformation prediction model for soft rock tunnels are of great practical and social significance for analyzing the deformation patterns during tunnel excavation, guiding on-site construction, and ensuring tunnel stability and construction safety.

[0003] Most previous studies have focused on tunnel stability through loading tests, neglecting the fact that actual construction is essentially a process of unloading. Tunnel excavation unloading creates a free face. Due to the localized release of stress, the rock mass is unloaded and deforms into the tunnel, causing stress redistribution. In the loosened rock zone, both stress and strength decrease significantly, and fissure expansion increases, resulting in the phenomenon of "unloading expansion." This phenomenon is crucial to tunnel stability and can alter the final shape and dimensions of the tunnel, especially in soft rock areas where it is more pronounced.

[0004] Numerical calculation is a widely used analytical method for predicting soil deformation and support structure stress after tunnel excavation. When performing numerical calculations, in addition to selecting appropriate calculation software and constitutive models, choosing suitable material property parameters is crucial for the accuracy of the numerical analysis results. In current FLAC software numerical simulations, to simplify calculations, the physical parameters of the rock mass and structure are considered constants, and a suitable average value is taken as the calculation parameter. However, in actual construction, due to stress release, the physical parameter values ​​of the rock mass and structure actually change. By using appropriate modulus parameters that more closely approximate the actual material conditions, actual working conditions can be simulated more effectively, ensuring tunnel construction safety and saving project costs. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for assigning simulation parameters for soft rock tunnels that considers the unloading and support characteristics of the surrounding rock.

[0006] The present invention provides a method for assigning simulation parameters for soft rock tunnels that considers the unloading and support characteristics of surrounding rock. This method introduces "dynamic elastic modulus" to simulate rock mass and structural elements, and "dynamic constitutive model" to simulate pressure relief elements. Specifically, it includes the following steps:

[0007] Step 1: Introduce "dynamic elastic modulus" to simulate the unloading and expansion phenomenon of the surrounding rock. First, assign the elastic modulus of all rock mass elements to E1. Then, perform real-time judgment on the stress values ​​and element states of the rock mass elements in the calculation. When there is a stress less than the critical stress σ, c When the rock mass element is a non-plastic element, adjust the elastic modulus of the rock mass element to E2; otherwise, keep it unchanged.

[0008] Step 2: After simulating excavation, perform iterative calculations and reactivate the support unit, assign the structural unit an elastic modulus E3, and determine in real time whether the stress of the structural unit has reached the corresponding elastic limit σ. e If the elastic limit σ is reached e If the elastic modulus of the structural unit is adjusted to E4, then it remains unchanged; considering the ultimate bearing characteristics of the support structure, when the support stress reaches the stress threshold σ max When a structural unit is given a small elastic modulus of 1 MPa, it indicates that the support structure is in a failure state.

[0009] Step 3: Introduce a "dynamic constitutive" simulation of the yielding element, perform calculations using an elastoplastic constitutive model and assign an elastic modulus E5, and determine the strain magnitude of the element in real time. When the strain of the yielding element exceeds the critical strain ε... c When the calculation mode of the element is changed to elastic constitutive mode, the elastic modulus is adjusted to E6; otherwise, it remains unchanged.

[0010] Furthermore, this invention uses FLAC numerical software to simulate the tunnel excavation and support process. Considering the unloading and expansion of the surrounding rock and the ultimate characteristics of the support structure, the unit state is determined in real time during the calculation, and the z_prop function in the FISH language is used to assign parameter values ​​to the rock mass and structural units.

[0011] Furthermore, the compression unit uses a highly compressible material.

[0012] The beneficial technical effects of this invention are as follows:

[0013] This invention considers the influence of unloading and expansion of surrounding rock and the ultimate characteristics of support structure, introduces "dynamic elastic modulus" to simulate rock mass elements and structural elements, and introduces "dynamic constitutive" to simulate pressure relief elements. The z_prop function of FISH language is used to assign parameters to all elements, thereby achieving a relatively accurate numerical simulation calculation of tunnel engineering. Attached Figure Description

[0014] Figure 1 This is a flowchart illustrating the method for assigning simulation parameters for soft rock tunnels that takes into account the unloading and support characteristics of the surrounding rock, as described in this invention.

[0015] Figure 2 This is a typical stress-strain curve for loading and unloading surrounding rock.

[0016] Figure 3 It is the stress-strain fitting curve of a typical support material under load.

[0017] Figure 4 It is a stress-strain fitting curve of a typical highly compressible material under pressure. Detailed Implementation

[0018] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0019] A method for assigning simulation parameters of a soft rock tunnel considering surrounding rock unloading and support characteristics in the present invention uses FLAC numerical software to simulate the tunnel excavation and support process. Considering the unloading and dilation of the surrounding rock and the ultimate characteristics of the support structure, the unit state is determined in real time during the calculation, and the z_prop function in FISH language is used to assign parameters to the rock mass and structural units. The flow of the method for assigning simulation parameters of a soft rock tunnel considering surrounding rock unloading and support characteristics in the present invention is as Figure 1 shown, and the specific implementation steps are as follows:

[0020] Step 1: Introduce "dynamic elastic modulus" to simulate the unloading and dilation phenomenon of the surrounding rock.

[0021] The stress release caused by unloading makes the rock mass deform towards the tunnel, resulting in a decrease in the surrounding rock stress and an increase in cracks. At this time, the elastic modulus will decrease as the stress decreases. As Figure 2 shown, in the natural state without excavation, the rock mass basically remains in the elastic stage (i.e., the AB segment). However, with the excavation unloading (i.e., the BD segment, where the elastic modulus of the BC segment is marked as E1 and the elastic modulus of the CD segment is marked as E2, and E2 < E1), the lithology changes. The excavation of the tunnel generates a free face, causing the rock mass to change from a three-dimensional six-sided stress state to a three-dimensional five-sided stressed single-sided unloading state. The previously tightly closed cracks reopen to a certain extent, showing a behavior similar to the unloading stage (i.e., the CD segment) in the rock mechanics test. Since this unloading stage is characterized by the reopening of some cracks, the expansion and increase of cracks, and the expansion of volume, it is named the "unloading and dilation" segment. In order to more accurately simulate the tunnel excavation, "dynamic elastic modulus" is introduced to simulate the unloading and dilation phenomenon of the surrounding rock.

[0022] First, the elastic modulus of all rock mass units is assigned as E1, and the stress value and unit state of the rock mass units in the calculation are determined in real time. When there are rock mass units with stress less than the critical stress σ c and the units are non-plastic units, the elastic modulus of the rock mass units is adjusted to E2, and vice versa, it remains unchanged.

[0023] Step 2: Introduce "dynamic elastic modulus" to simulate the support effect of the structural units, and at the same time consider the ultimate bearing capacity characteristics of the support in the calculation.

[0024] During the compression process of the support material, its stress-strain curve is roughly divided into an elastic stage and an elastoplastic stage. (When the stress is small, it is in the elastic stage, and the elastic modulus is marked as E1 at this time; when the stress exceeds the critical stress, it enters the elastoplastic stage, and the elastic modulus is marked as E2 at this time, where E2 < E1). Therefore, in order to more accurately simulate the tunnel support process, the "dynamic elastic modulus" is introduced to simulate the support effect of the structural unit.

[0025] After simulating the excavation, iterative calculations are carried out and then the support units are activated, the elastic modulus E3 is given to the structural unit, and it is determined in real time whether the stress of the structural unit reaches the corresponding elastic limit σ e ; if it reaches the elastic limit σ e , then the elastic modulus of the structural unit is adjusted to E4, otherwise it remains unchanged; considering the ultimate bearing capacity characteristics of the support structure, when the support stress reaches the stress threshold σ max , a small elastic modulus of 1 MPa is given to the structural unit, indicating that the support structure is in a failure state.

[0026] Step 3: Introduce the "dynamic constitutive model" to simulate the yielding unit.

[0027] As Figure 3 shown, generally, when the support material is loaded, it first enters the elastic stage. In this stage, the elastic modulus of the material remains unchanged, and the stress-strain curve is linear; when the pressure exceeds σ1, the material enters the elastoplastic stage. In this stage, the material will slow down the stress increase through deformation; when the load exceeds σ2, the material is crushed. Ordinary support belongs to the "hard resistance" state, and the load is resisted by the strength of the material itself.

[0028] As Figure 4 shown, due to the good ductility of the highly compressible material, it has entered the elastoplastic stage when the load is small. In this stage, the highly compressible material absorbs too much load through deformation, so the strain changes significantly and the stress changes little in this stage; when the load exceeds Figure 4 the σ2 in

[0029] , after the material is completely compacted, it enters the elastic stage until it is crushed. Yielding support allows the surrounding rock to produce a controllable and limited amount of deformation displacement, and allows the "surrounding rock deformation energy" to be appropriately released under the continuous action of the corresponding resistance, so as to achieve the purpose of meeting its reasonable stress state. c Therefore, the "dynamic constitutive model" is introduced to simulate the yielding unit, and calculations are carried out in the elastoplastic constitutive calculation mode and the elastic modulus E5 is given. Since the yielding layer uses a highly compressible material, a large strain will occur under a very small stress change. Therefore, the strain size of the yielding unit is determined in real time. When the strain of the yielding unit is greater than the critical strain ε c , the calculation mode of the unit is changed to the elastic constitutive model, and the elastic modulus is adjusted to E6, otherwise it remains unchanged.

Claims

1. A method for assigning simulation parameters for soft rock tunnels considering surrounding rock unloading and support characteristics, characterized in that, The "dynamic elastic mode" is introduced to simulate rock mass elements and structural elements, and the "dynamic constitutive model" is introduced to simulate pressure relief elements. The specific steps are as follows: Step 1: Introduce "dynamic elastic modulus" to simulate the unloading and expansion phenomenon of the surrounding rock. First, assign the elastic modulus of all rock mass elements to E1. Then, perform real-time judgment on the stress values ​​and element states of the rock mass elements in the calculation. When there is a stress less than the critical stress σ, c When the rock mass element is a non-plastic element, adjust the elastic modulus of the rock mass element to E2; otherwise, keep it unchanged. Step 2: After simulating excavation, perform iterative calculations and reactivate the support unit, assign the structural unit an elastic modulus E3, and determine in real time whether the stress of the structural unit has reached the corresponding elastic limit σ. e If the elastic limit σ is reached e If the elastic modulus of the structural unit is adjusted to E4, then it remains unchanged; considering the ultimate bearing characteristics of the support structure, when the support stress reaches the stress threshold σ max When a small elastic modulus of 1 MPa is assigned to a structural unit, it indicates that the support structure is in a failure state. Step 3: Introduce a "dynamic constitutive" simulation of the yielding element, perform calculations using an elastoplastic constitutive model and assign an elastic modulus E5, and determine the strain magnitude of the element in real time. When the strain of the yielding element exceeds the critical strain ε... c When the calculation mode of the element is changed to elastic constitutive mode, the elastic modulus is adjusted to E6; otherwise, it remains unchanged.

2. The method for assigning simulation parameters for soft rock tunnels considering surrounding rock unloading and support characteristics according to claim 1, characterized in that, The tunnel excavation and support process was simulated using FLAC numerical software. Considering the unloading and expansion of the surrounding rock and the ultimate characteristics of the support structure, the unit state was determined in real time during the calculation, and the z_prop function in the FISH language was used to assign parameter values ​​to the rock mass and structural units.

3. The method for assigning simulation parameters for soft rock tunnels considering surrounding rock unloading and support characteristics according to claim 1, characterized in that, The pressure relief unit is made of a highly compressible material.

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