Soft rock tunnel simulation parameter assignment method considering unloading and supporting characteristics of surrounding rock

Abstract

The invention discloses a soft rock tunnel simulation parameter assignment method considering unloading and supporting characteristics of surrounding rock, and the method specifically comprises the steps: simulating a tunnel excavation and supporting process through FLAC numerical software, considering the unloading capacity expansion of the surrounding rock and the limit characteristics of a supporting structure, judging the state of a unit in real time in calculation, and determining the state of the unit in real time; performing parameter assignment on the rock mass and the structural unit by using a zprop function in the FISH language; a'dynamic elastic modulus' is introduced to simulate the unloading expansion phenomenon of the surrounding rock, and real-time adjustment is carried out in the calculation process; a dynamic elastic modulus is introduced to simulate the supporting effect of a structural unit, and meanwhile the ultimate bearing characteristic of supporting is considered in calculation; and a'dynamic constitutive 'simulation yielding unit is introduced. According to the method, the influence of surrounding rock unloading capacity expansion and supporting structure limit characteristics is considered, and accurate tunnel engineering numerical simulation calculation is achieved.

Description

Technical Field

[0001] The invention belongs to the field of computer-aided design of tunnel engineering and geotechnical engineering, and in particular relates to a method for assigning simulation parameters of soft rock tunnels taking surrounding rock unloading and support characteristics into consideration. Background Art

[0002] Correctly predicting tunnel deformation and building a reasonable soft rock tunnel deformation prediction model are of great practical engineering and social significance for analyzing the deformation law of tunnel excavation, guiding on-site construction, and ensuring tunnel stability and construction safety.

[0003] In most previous studies, tunnel stability is often studied through loading tests, while ignoring the fact that actual construction is essentially a process of unloading. Tunnel excavation unloading produces an empty surface. Due to the local release of stress, the rock mass is unloaded and deforms into the tunnel, causing stress redistribution. The stress and strength in the loose area of ​​the surrounding rock are significantly reduced, the crack expansion increases, and the "unloading expansion" phenomenon occurs. This phenomenon is crucial to the stability of the tunnel and may change the final shape and size of the tunnel, especially in soft rock areas, where this phenomenon will be more obvious.

[0004] Numerical calculation is an analysis method widely used in predicting soil deformation and support structure stress after tunnel excavation. When performing numerical calculations, in addition to selecting appropriate calculation software and constitutive models, selecting appropriate material physical parameters is also particularly important for the accuracy of numerical analysis results. In the current numerical simulation of FLAC software, in order to simplify the calculation, the physical parameters of the rock mass and structure are regarded as constants, and a suitable average value is taken as the calculation parameter. In actual construction, due to the release of stress, the physical parameter values ​​of the rock mass and structure actually change. By adopting appropriate modulus parameters that are closer to the actual material, the actual working conditions can be simulated more effectively, ensuring the safety of tunnel construction and saving engineering costs. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for assigning simulation parameters of a soft rock tunnel taking into account surrounding rock unloading and support characteristics.

[0006] The present invention provides a method for assigning simulation parameters of soft rock tunnels taking into account surrounding rock unloading and support characteristics, which introduces a "dynamic elastic modulus" to simulate rock mass units and structural units, and introduces a "dynamic constitutive" to simulate yielding units, and specifically includes the following steps:

[0007] Step 1: Introduce the "dynamic elastic modulus" to simulate the unloading expansion phenomenon of the surrounding rock. First, assign the elastic modulus of all rock units to E1, and make real-time judgments on the stress value and unit state of the rock unit in the calculation. When there is a stress less than the critical stress σ c When the rock unit is a non-plastic unit, the elastic modulus of the rock unit is adjusted to E2, otherwise it remains unchanged.

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

[0009] Step 3: Introduce the "dynamic constitutive" simulation of the yielding unit, calculate it in the elastic-plastic constitutive calculation mode and assign the elastic modulus E5, and determine the strain of the unit in real time. When the strain of the yielding unit is greater than the critical strain ε c When , the calculation mode of the unit is changed to elastic constitutive and the elastic modulus is adjusted to E6, otherwise it remains unchanged.

[0010] Furthermore, the present invention adopts FLAC numerical software to simulate the tunnel excavation and support process, takes into account the unloading expansion of the surrounding rock and the limit characteristics of the support structure, determines the unit state in real time during the calculation, and uses the z_prop function in the FISH language to assign parameters to the rock mass and structural units.

[0011] Furthermore, the compression unit is made of a high compressibility material.

[0012] The beneficial technical effects of the present invention are:

[0013] The present invention takes into account the influence of surrounding rock unloading expansion and the limiting characteristics of the supporting structure, introduces a "dynamic elastic modulus" to simulate rock mass units and structural units, and introduces a "dynamic constitutive" to simulate yielding units, and assigns parameters to all units through the z_prop function of the FISH language, thereby achieving relatively accurate numerical simulation calculations of tunnel engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The present invention is a flow chart of the soft rock tunnel simulation parameter assignment method taking into account surrounding rock unloading and support characteristics.

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

[0016] Figure 3 It is the stress-strain fitting curve of general support material loading.

[0017] Figure 4 It is the stress-strain fitting curve of general high compressible materials under pressure. DETAILED DESCRIPTION

[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 according to 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 judged 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 according to the present invention is as Figure 1 shown, and the specific implementation steps are as follows:

[0020] Step 1: Introduce the "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 section). However, with the progress of excavation and unloading (i.e., the BD section, where the elastic modulus of the BC section is marked as E1 and the elastic modulus of the CD section is marked as E2, and E2 < E1), the lithology has changed. 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 one-sided unloading state of three-dimensional five-sided stress. The previously tightly compressed cracks are reopened to a certain extent, showing a behavior similar to the unloading stage (i.e., the CD section) 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" section. In order to more accurately simulate the tunnel excavation, the "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 judged 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 the "dynamic elastic modulus" to simulate the support effect of the structural units, and at the same time consider the ultimate bearing 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, and 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 to reactivate the support unit, 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 the elastic limit σ e is reached, 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 will first enter 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 it, 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, so that the "deformation energy of the surrounding rock" is appropriately released under the continuous action of the corresponding resistance, so as to achieve the purpose of meeting its reasonable stress state.

[0029] Therefore, the "dynamic constitutive model" is introduced to simulate the yielding unit, and it is calculated 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 be generated 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 of soft rock tunnels considering surrounding rock unloading and support characteristics, characterized in that: The "dynamic elastic modulus" is introduced to simulate the rock mass unit and structural unit, and the "dynamic constitutive" is introduced to simulate the yielding unit, which specifically includes the following steps: Step 1: Introduce "dynamic elastic modulus" to simulate the unloading expansion phenomenon of surrounding rock. First, assign the elastic modulus of all rock units to E1, and make real-time judgments on the stress value and unit state of the rock unit in the calculation. When there is a stress less than the critical stress σ c When the rock mass unit is a non-plastic unit, the elastic modulus of the rock mass unit is adjusted to E2, otherwise it remains unchanged; Step 2: After simulating excavation, perform iterative calculations and reactivate the support unit, assign the elastic modulus E3 to the structural unit, and determine in real time whether the stress of the structural unit reaches the corresponding elastic limit σ e ; If the elastic limit σ is reached e , the elastic modulus of the structural unit is adjusted to E4, otherwise 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 1MPa is given to the structural unit, indicating that the support structure is in a failed state; Step 3: Introduce the "dynamic constitutive" simulation of the yielding unit, calculate it in the elastic-plastic constitutive calculation mode and assign the elastic modulus E5, and determine the strain of the unit in real time. When the strain of the yielding unit is greater than the critical strain ε c When , the calculation mode of the unit is changed to elastic constitutive and the elastic modulus is adjusted to E6, otherwise it remains unchanged.

2. A method for assigning simulation parameters of soft rock tunnels considering surrounding rock unloading and support characteristics according to claim 1, characterized in that: The FLAC numerical software is used to simulate the tunnel excavation and support process. Taking into account the unloading expansion of the surrounding rock and the limit 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 parameters to the rock mass and structural units.

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

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