Method and device for determining supporting construction opportunity of soft rock tunnel

Abstract

The invention relates to the technical field of tunnel engineering, and discloses a method and device for determining the supporting construction opportunity of a soft rock tunnel, and aims to solve the problem that an existing determination method is poor in accuracy, and the scheme mainly comprises the steps that deformation monitoring is conducted on tunnel surrounding rock under the non-supporting condition, and a first accumulated radial convergence deformation amount is obtained; constructing a first creep constitutive model, and predicting the final radial convergence deformation of the tunnel surrounding rock under the support-free condition; when the first accumulated radial convergence deformation reaches the preset proportion of the final radial convergence deformation, a first layer of support is constructed; and after the first layer of support is constructed, a second accumulated radial convergence deformation amount is detected in real time, and when the radial convergence deformation rate is decreased to a deformation rate threshold value, or when the second accumulated radial convergence deformation amount reaches a deformation amount threshold value and the change speed of the radial convergence deformation rate is smaller than a speed threshold value, a second layer of support is constructed. The method improves the accuracy of support construction time, and is particularly suitable for soft rock tunnels.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering technology, specifically to a method and apparatus for determining the timing of support construction in soft rock tunnels. Background Technology

[0002] Soft rock tunnel engineering faces numerous challenges in actual construction due to the characteristics of low surrounding rock strength, large deformation, and significant time-dependent creep. After tunnel excavation, the deformation of the surrounding rock typically exhibits a rheological characteristic of initially increasing rapidly, then gradually slowing down, and continuing for a considerable period. Currently, determining the timing of initial tunnel support construction mainly relies on the following methods:

[0003] 1. Experience analogy method: This method makes judgments based on the experience of similar projects in the past. However, this method is highly subjective, lacks scientific basis, and is difficult to accurately predict the complex deformation behavior of soft rock. It may lead to support too early (support fails due to excessive early load) or too late (excessive deformation of the surrounding rock leads to instability or difficulty in control of the tunnel face).

[0004] 2. Convergence Constraint Method Based on Static Mechanics Theory: This method, based on elastic or elastoplastic theory, determines the timing of support by calculating the convergence deformation of the surrounding rock. However, this method typically ignores the time-dependent deformation characteristics of the surrounding rock, i.e., the creep effect, leading to discrepancies between the calculated results and the actual deformation development caused by creep. This may result in unreasonable support structure design or increased construction risks. For example, if creep is not fully considered, the support may be applied before the creep of the surrounding rock has fully developed, causing the support structure to bear excessive loads or even fail. Conversely, if it is applied too late, the deformation of the surrounding rock may have become uncontrollable, greatly increasing the construction difficulty and risk.

[0005] 3. Field monitoring method: This method guides support construction by monitoring the convergence deformation of the surrounding rock. Although field convergence deformation monitoring is a common method, there is currently a lack of quantitative models and criteria to accurately correlate monitoring data with the creep characteristics of the surrounding rock and the timing of support construction. This is especially true in double-layer initial support structures, where there is a lack of effective methods to assess the synergistic effect of the two support layers.

[0006] To address the issues of large deformation and creep in soft rock, double-layer initial support structures are widely adopted. The first layer of support is typically more flexible, allowing the surrounding rock to release deformation to some extent and preventing the support from prematurely bearing the full creep load; the second layer of support is relatively rigid, used to control later deformation and provide long-term stability. However, accurately determining the timing of the construction of each of these two initial support layers to fully leverage their synergistic support effect and effectively control the creep deformation of the surrounding rock is a key technical problem that urgently needs to be solved in the field of soft rock tunnel engineering. Therefore, a scientific, rigorous, and quantifiable method is urgently needed to determine the timing of the construction of double-layer initial support in soft rock tunnels. Summary of the Invention

[0007] The present invention aims to provide a method and apparatus for determining the timing of support construction in soft rock tunnels, so as to improve the accuracy of support construction timing, improve support effect, and ensure construction safety and long-term stability of tunnels.

[0008] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0009] In a first aspect, the present invention provides a method for determining the timing of support construction in soft rock tunnels, the method comprising:

[0010] After tunnel excavation, radial convergence deformation monitoring was conducted on the surrounding rock of the tunnel under unsupported conditions to obtain the first cumulative radial convergence deformation of the surrounding rock at different time points.

[0011] A first creep constitutive model of the tunnel surrounding rock is constructed based on the first cumulative radial convergence deformation, and the final radial convergence deformation of the tunnel surrounding rock under unsupported conditions is predicted based on the first creep constitutive model.

[0012] Under unsupported conditions, when the first cumulative radial convergence deformation reaches a preset proportion of the final radial convergence deformation, the corresponding time is taken as the timing for the first layer of support to be implemented.

[0013] After the first layer of support is constructed to form the surrounding rock-support I structure, the second cumulative radial convergence deformation of the surrounding rock-support I structure is monitored in real time. When the radial convergence deformation rate of the surrounding rock-support I structure drops to the deformation rate threshold, or when the second cumulative radial convergence deformation reaches the deformation amount threshold and the rate of change of the radial convergence deformation rate is less than the rate threshold, the corresponding time is taken as the timing for the construction of the second layer of support.

[0014] Furthermore, when the first cumulative radial convergence deformation reaches a preset proportion of the final radial convergence deformation, the corresponding time determination method includes:

[0015] The deformation corresponding to the preset proportion of the final radial convergence deformation is substituted into the constructed first creep constitutive model to calculate the time corresponding to when the first cumulative radial convergence deformation reaches the preset proportion of the final radial convergence deformation.

[0016] Furthermore, when the radial convergence deformation rate of the surrounding rock-support I structure decreases to the deformation rate threshold, the corresponding time determination method includes:

[0017] The second creep constitutive model of the surrounding rock-support I structure is constructed based on the second cumulative radial convergence deformation at different time points, and the corresponding time is calculated based on the second creep constitutive model and the deformation rate threshold.

[0018] Furthermore, the first creep constitutive model and the second creep constitutive model are as follows:

[0019] ;

[0020] in, For time, for The radial convergence deformation over time. This is the instantaneous deformation. This represents the amount of elastic deformation over time. To delay time, For steady-state creep rate, It is a natural constant.

[0021] Furthermore, the corresponding time is calculated based on the second creep constitutive model and the deformation rate threshold, using the following formula:

[0022] ;

[0023] in, The time it takes for the radial convergence deformation rate of the surrounding rock-support I structure to decrease to the deformation rate threshold. The deformation rate threshold, It is the natural logarithm. This represents the time-dependent elastic deformation corresponding to the second creep constitutive model. This represents the steady-state creep rate corresponding to the second creep constitutive model. This represents the delay time corresponding to the second creep constitutive model.

[0024] Furthermore, the final radial convergence deformation is the radial convergence deformation of the tunnel surrounding rock at a preset time, wherein the preset time is greater than or equal to 100 days.

[0025] Furthermore, the preset ratio ranges from 0.1 to 0.3; the deformation rate threshold is less than 1 mm / day.

[0026] Furthermore, the structure of the first layer of support is a flexible support structure or a semi-flexible support structure; the structure of the second layer of support is a rigid support structure or a semi-rigid support structure.

[0027] Furthermore, the method also includes:

[0028] Throughout the tunnel construction process, the preset ratio and deformation rate threshold are dynamically adjusted based on the comparison results of measured deformation data and model predicted deformation data. Furthermore, when the geology of the surrounding rock of the tunnel changes, the creep constitutive model is reconstructed.

[0029] In a second aspect, the present invention provides a device for determining the timing of support construction in soft rock tunnels, used to implement the method for determining the timing of support construction in soft rock tunnels as described in the first aspect, the device comprising:

[0030] The monitoring unit is used to monitor the radial convergence deformation of the tunnel surrounding rock under unsupported conditions after tunnel excavation, and to obtain the first cumulative radial convergence deformation of the tunnel surrounding rock at different time points; and to detect the second cumulative radial convergence deformation of the surrounding rock-support I structure in real time after the first layer of support is constructed to form the surrounding rock-support I structure.

[0031] The prediction unit is used to construct a first creep constitutive model of the tunnel surrounding rock based on the first cumulative radial convergence deformation, and to predict the final radial convergence deformation of the tunnel surrounding rock under unsupported conditions based on the first creep constitutive model.

[0032] The first determining unit is used to determine the timing of the first layer of support when the first cumulative radial convergence deformation reaches a preset proportion of the final radial convergence deformation under unsupported conditions.

[0033] The second determining unit determines the timing of the second layer of support when the radial convergence deformation rate of the surrounding rock-support I structure decreases to the deformation rate threshold, or when the second cumulative radial convergence deformation reaches the deformation amount threshold and the rate of change of the radial convergence deformation is less than the rate threshold.

[0034] The beneficial effects of this invention are:

[0035] 1. Scientificity and Precision: By introducing a constitutive model of surrounding rock creep, the time-dependent deformation characteristics of the surrounding rock are quantitatively described, which elevates the determination of support timing from empirical judgment to a level that combines scientific calculation and real-time monitoring, thereby improving the accuracy and reliability of support timing determination.

[0036] 2. Optimized Support Structure: The timing of the first and second layers of support was rationally determined to ensure that the support structure fully matches the creep deformation characteristics of the surrounding rock. The first layer of support provides flexible support during the large deformation stage of the surrounding rock, allowing for sufficient stress redistribution. The second layer of support is applied when the deformation of the surrounding rock tends to stabilize, providing long-term rigid support. This avoids the support failing due to prematurely bearing excessive loads, and also avoids the instability of the surrounding rock caused by delayed support.

[0037] 3. Improve construction safety: By predicting and controlling the creep deformation of the surrounding rock, safety accidents such as rock instability and face collapse caused by improper support timing are effectively avoided, ensuring the safety of construction personnel and equipment.

[0038] 4. Reduced project costs: It avoids rework or reinforcement due to support failure and reduces unnecessary consumption of support materials. Through precise construction, the amount of support materials used can be optimized, achieving "support on demand" and thus saving costs.

[0039] 5. Extending tunnel service life: Scientific and reasonable support timing helps control long-term deformation of the surrounding rock, reduces continuous stress and fatigue of the support structure, thereby extending the service life of the tunnel lining and reducing later maintenance costs.

[0040] 6. Strong applicability: This invention is applicable to various soft rock tunnel projects with creep characteristics. Through on-site identification and dynamic adjustment of parameters, it has good adaptability and versatility. Attached Figure Description

[0041] Figure 1 A flowchart illustrating a method for determining the timing of support construction in a soft rock tunnel, provided as an example.

[0042] Figure 2 A schematic diagram of the Burgers model provided for the embodiment;

[0043] Figure 3 This is a schematic diagram of the device for determining the timing of support construction for soft rock tunnels provided in the embodiment. Detailed Implementation

[0044] To enable those skilled in the art to better understand the present invention, the technical solutions in this embodiment will be clearly and completely described below with reference to the accompanying drawings.

[0045] In some of the processes described in the specification and accompanying drawings of this invention, multiple operations are included that appear in a specific order. However, it should be clearly understood that these operations may not be executed in the order they appear herein, or may be executed in parallel. The sequence numbers of the operations are merely used to distinguish different operations and do not themselves represent any execution order. Furthermore, these processes may include more or fewer operations, and these operations may be executed sequentially or in parallel.

[0046] The technical solution of the present invention is applicable to application scenarios that require tunnel support, especially for soft rock tunnels requiring two-layer support.

[0047] Since the current methods for determining the timing of initial support construction in tunnels are mainly empirical analogy, convergence constraint method based on static mechanics theory, and field monitoring method, the inventors have found through research that these methods are highly subjective or ignore the creep effect of the surrounding rock, resulting in poor accuracy in determining the timing of support construction.

[0048] To improve the accuracy of support construction timing, this invention proposes a technical solution. In this invention, by using on-site surrounding rock convergence deformation monitoring data and combining it with a surrounding rock creep constitutive model, the long-term deformation behavior of the surrounding rock is predicted, and the construction timing of the first and second layers of support is quantitatively determined accordingly. This avoids subjective influence and enables synergistic matching between the support structure and the creep characteristics of the surrounding rock, improving the support effect and ensuring construction safety and long-term tunnel stability.

[0049] The technical solutions in this embodiment will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0050] Figure 1 A flowchart illustrating a method for determining the timing of support construction in soft rock tunnels is shown. Please refer to [link / reference]. Figure 1 The method includes the following steps:

[0051] Step 1, Surrounding Rock Deformation Monitoring: After tunnel excavation, radial convergence deformation monitoring is carried out on the surrounding rock of the tunnel under unsupported conditions to obtain the first cumulative radial convergence deformation of the surrounding rock at different time points.

[0052] Specifically, after the soft rock tunnel is excavated but before the first layer of support is applied, continuous radial convergence deformation monitoring of the tunnel surrounding rock is conducted. This involves measuring the change in distance between specific monitoring points on the tunnel cross-section over time according to a preset monitoring frequency, thereby obtaining the first cumulative radial convergence deformation of the tunnel surrounding rock at different time points. The monitoring points should be located in representative surrounding rock areas, and the monitoring frequency should be sufficient to capture both early rapid deformation and later slow deformation.

[0053] Step 2: Predict the final radial convergence deformation: Construct a first creep constitutive model of the tunnel surrounding rock based on the first cumulative radial convergence deformation, and predict the final radial convergence deformation of the tunnel surrounding rock under unsupported conditions based on the first creep constitutive model.

[0054] In this embodiment, the creep constitutive model is an improvement upon the Burgers model. Please refer to [link / reference]. Figure 2 The Burgers model is as follows:

[0055] ;

[0056] in, for Total strain over time; The stress is constant. It is the instantaneous elastic modulus; It is the rheological modulus; The viscosity coefficient of Maxwell volume; The viscosity coefficient of Kelvin; For time.

[0057] By replacing strain with cumulative radial convergent deformation, stress with equivalent compressive stress in the surrounding rock, and modifying the model using convergence constraint theory for tunnel lining, a creep constitutive model suitable for predicting the convergence of surrounding rock is obtained:

[0058] ;

[0059] in, Time (unit: days); for Radial convergence deformation over time (unit: mm); The instantaneous deformation (unit: mm) represents the elastic deformation that occurs immediately after tunnel excavation. The amount of elastic deformation over time (unit: mm) represents the delayed elastic deformation that develops over time. The delay time is in days. The smaller the value, the faster the deformation stabilizes. The larger the size, the slower the deformation process; Steady-state creep rate (unit: mm / day) represents the rate at which deformation increases linearly with time after entering the steady-state creep stage; It is a natural constant.

[0060] In this embodiment, the creep constitutive model constructed based on the first cumulative radial convergence deformation of the tunnel surrounding rock is the first creep constitutive model. In practical applications, based on the creep constitutive model and the first cumulative radial convergence deformation of the tunnel surrounding rock at different time points obtained in step 1, nonlinear regression analysis is performed to obtain the instantaneous deformation in the creep constitutive model. , aging elastic deformation Delay time and steady-state creep rate Thus, the first creep constitutive model of the tunnel surrounding rock was obtained.

[0061] In this embodiment, the final radial convergence deformation is the radial convergence deformation of the tunnel surrounding rock after long-term stabilization over a preset time. After obtaining the first creep constitutive model of the tunnel surrounding rock, the preset time is input into the first creep constitutive model to predict the final radial convergence deformation of the tunnel surrounding rock under unsupported conditions, that is, the final radial convergence deformation of the tunnel surrounding rock after a preset time under unsupported conditions. The preset time is greater than or equal to 100 days, which ensures that the final radial convergence deformation of the tunnel surrounding rock after long-term stability under unsupported conditions is obtained.

[0062] Step 3: Determine the timing of the first support application: Under unsupported conditions, when the first cumulative radial convergence deformation reaches the preset ratio of the final radial convergence deformation, the corresponding time is taken as the timing of the first layer of support application.

[0063] Specifically, when the tunnel surrounding rock is under unsupported conditions, the first cumulative radial convergence deformation... To achieve the final radial convergence deformation preset ratio When the corresponding time is met, the timing of the first layer of support will be taken as the implementation time, that is, when the conditions are met... Immediately upon arrival, the first layer of support should be constructed. This includes a pre-set proportion. The value ranges from 0.1 to 0.3, depending on the stability of the surrounding rock, the engineering risk level, and the characteristics of the support material.

[0064] In this embodiment, the deformation amount corresponding to the preset ratio of the final radial convergence deformation amount is substituted into the constructed first creep constitutive model to calculate the corresponding time, thereby realizing the advance determination of the timing of the first support application and providing sufficient preparation time for the first support application.

[0065] In this embodiment, the structure of the first layer of support is a flexible support structure or a semi-flexible support structure, such as initial shotcrete (with steel mesh), anchor bolts, or steel arches that are not closed into a ring. Its main function is to limit excessive deformation of the surrounding rock, allow further stress redistribution and creep deformation release of the surrounding rock, and avoid prematurely bearing excessive loads.

[0066] Step 4: Determine the timing for the second support: After the first layer of support is constructed to form the surrounding rock-support I structure, the second cumulative radial convergence deformation of the surrounding rock-support I structure is monitored in real time. When the radial convergence deformation rate of the surrounding rock-support I structure drops to the deformation rate threshold, or when the second cumulative radial convergence deformation reaches the deformation amount threshold and the rate of change of the radial convergence deformation rate is less than the rate threshold, the corresponding time is taken as the timing for the second layer of support.

[0067] Specifically, after the first layer of support is applied, the rock-support I structure formed by the surrounding rock and the first layer of support still exhibits creep deformation. At this time, the radial convergence deformation on the inner side of the first layer of support is monitored to obtain the second cumulative radial convergence deformation of the rock-support I structure. The timing of applying the second layer of support then satisfies one of the following conditions:

[0068] (a) Deformation rate control: When the convergence deformation rate of the surrounding rock-support I structure Decrease to deformation rate threshold The following can be considered as the rock-support system I being basically stable, with creep deformation largely released. The corresponding time will be taken as the timing for implementing the second layer of support, i.e., when the following conditions are met... Immediately upon arrival, a second layer of support should be constructed. Specifically, according to the "Technical Specification for Construction of Highway Tunnels in Compressible Surrounding Rock," the deformation rate threshold... Less than 1 mm / day, this threshold ensures that creep deformation has been largely released.

[0069] In this embodiment, the method for determining the time when the radial convergence deformation rate of the surrounding rock-support I structure decreases to the deformation rate threshold includes: constructing a second creep constitutive model of the surrounding rock-support I structure based on the second cumulative radial convergence deformation at different time points; and calculating the corresponding time based on the second creep constitutive model and the deformation rate threshold. The calculation formula is as follows:

[0070] ;

[0071] in, The time it takes for the radial convergence deformation rate of the surrounding rock-support I structure to decrease to the deformation rate threshold. The deformation rate threshold, It is the natural logarithm. This represents the time-dependent elastic deformation corresponding to the second creep constitutive model. This represents the steady-state creep rate corresponding to the second creep constitutive model. This represents the delay time corresponding to the second creep constitutive model.

[0072] In this embodiment, the creep constitutive model constructed based on the second cumulative radial convergence deformation of the surrounding rock-support I structure is the second creep constitutive model. Similarly, based on the creep constitutive model and the second cumulative radial convergence deformation of the surrounding rock-support I structure at different time points obtained by monitoring, nonlinear regression analysis is performed to obtain the instantaneous deformation in the creep constitutive model. , aging elastic deformation Delay time and steady-state creep rate This leads to the second creep constitutive model of the surrounding rock-support I structure, and the deformation rate threshold is then used. By substituting the time-dependent elastic deformation, delay time, and steady-state creep rate corresponding to the second creep constitutive model into the above calculation formula, the time corresponding to the radial convergence deformation rate of the surrounding rock-support I structure decreasing to the deformation rate threshold can be calculated. .

[0073] Through calculation This allows for the early determination of the timing of the second support procedure, providing sufficient preparation time for its implementation.

[0074] (b) Control based on cumulative deformation: When the second cumulative radial convergence deformation of the surrounding rock-support I system is monitored... Reaching the deformation threshold Furthermore, the radial convergence deformation rate tends to stabilize, indicating that the surrounding rock-support I system has essentially stabilized and creep deformation has been largely released. The corresponding time is taken as the timing for implementing the second layer of support, i.e., when the following conditions are met... Immediately upon arrival, a second layer of support should be constructed. Among these, the deformation threshold... It can be determined based on the maximum allowable deformation of the support structure.

[0075] In this embodiment, the structure of the second layer of support is a rigid support structure or a semi-rigid support structure, such as thick shotcrete, steel mesh, closed ring steel arch frame, long anchor rod, etc. Its main function is to provide long-term stability, control residual deformation, and form a cooperative force-bearing system with the first layer of support.

[0076] In this embodiment, the method further includes: dynamically adjusting the preset ratio and deformation rate threshold based on the comparison results of measured deformation data and model predicted deformation data throughout the tunnel construction process; and reconstructing the creep constitutive model when the geology of the surrounding rock of the tunnel changes.

[0077] Specifically, radial convergence deformation monitoring of the surrounding rock is conducted continuously throughout the tunnel construction process. Based on the comparison between real-time monitoring data and the prediction model, adjustments are dynamically made. , Parameters such as these are used. When the geological conditions of the surrounding rock change significantly, the parameters of the creep constitutive model are refitted and the model is re-established to ensure the accuracy and adaptability of the support timing determination.

[0078] The following example, taking the determination of the timing of double-layer support construction in a mudstone tunnel, will be used to further illustrate this embodiment in detail.

[0079] 1. Project Overview and Geological Conditions:

[0080] A tunnel traverses a weak mudstone stratum with poor rock integrity, classified as Class V surrounding rock, exhibiting typical creep characteristics. The tunnel cross-section adopts a three-centered circular arch wall structure, with an initial support design of two layers: the first layer consists of 20cm thick C25 shotcrete + Φ8@200 steel mesh + I18 steel arch frames spaced 100cm apart + 4m system anchor bolts (spaced 100cm×100cm); the second layer consists of 30cm thick C25 shotcrete + I25 steel arch frames spaced 100cm apart + 6m long anchor bolts (spaced 100cm×100cm).

[0081] 2. Monitoring of radial convergence deformation of surrounding rock during tunnel excavation:

[0082] The tunnel is excavated using either drill-and-blast or mechanical methods, with an advance of 3 meters per cycle. Displacement gauges are installed at the tunnel arch, arch waist, and sidewalls after excavation to continuously monitor the radial convergence deformation of the surrounding rock in the unsupported state. The monitoring frequency is as follows: once every 6 hours for the first 3 days, once every 12 hours from days 3 to 7, and once daily thereafter.

[0083] 3. Identification of surrounding rock creep parameters and establishment of creep model:

[0084] Collect monitoring data, such as the surrounding rock deformation monitoring data after excavation of a typical cross section, as shown in Table 1.

[0085] Table 1. Monitoring data of surrounding rock deformation after excavation of a typical cross-section.

[0086]

[0087] The above data were fitted to the creep constitutive model using nonlinear regression software (such as MATLAB, Origin, etc.):

[0088] .

[0089] The fitting results may be: , , sky, / day, thus obtaining the first creep constitutive model.

[0090] Based on the fitting results, the long-term final radial convergence deformation of the cross section under unsupported conditions is predicted. In engineering practice, a sufficiently long preset time (such as 100 days) is usually set as the criterion. Therefore, according to the above creep constitutive model, the creep deformation after 100 days is:

[0091] .

[0092] 4. Determine the timing for implementing the first layer of support:

[0093] The timing control conditions for the first layer of support construction in this project are set as follows: preset ratio. (That is, when the cumulative radial convergence deformation monitored reaches 10%~30% of the final radial convergence deformation); given the poor surrounding rock conditions, the first layer of support should be constructed as early as possible. Take 0.1;

[0094] Calculate the target deformation based on the fitted first creep constitutive model:

[0095] .

[0096] Inverse calculation using the first creep constitutive model, when Time Therefore, it can be concluded that the first layer of support can be applied to this section on the 1.5th day after excavation.

[0097] 5. Determine the timing for implementing the second layer of support:

[0098] After the first layer of support is installed, radial convergence deformation monitoring continues for this section. The monitoring points are set inside the first layer of support, and the deformation monitored at this time is the incremental deformation after the first layer of support is installed. Please refer to Table 2 for the deformation monitoring data of this typical section after the first layer of support is installed.

[0099] Table 2 Deformation monitoring data of the surrounding rock and support structure after the first layer of support was constructed.

[0100]

[0101] The above monitoring data were fitted to the creep constitutive model using nonlinear regression software (such as MATLAB, Origin, etc.):

[0102] .

[0103] The fitting results may be: , , sky, =0.0 mm / day, thus obtaining the second creep constitutive model.

[0104] Radial convergence deformation rate The second layer of support shall be constructed when the following conditions are met:

[0105] ;

[0106] Set deformation rate threshold / day, calculate the time it takes for the radial convergence deformation rate to decrease to the deformation rate threshold based on the above conditions. :

[0107] sky;

[0108] If the radial convergence deformation rate is less than 1 mm / day on the 21st day after the first layer of support is applied, the surrounding rock-support I structure can be considered basically stable. Therefore, the second layer of support can be applied to this section on the 21st day after the first layer of support is applied.

[0109] In summary, the method for determining the timing of support construction in soft rock tunnels provided in this embodiment uses on-site monitoring data of surrounding rock convergence deformation, combined with a constitutive model of surrounding rock creep, to predict the long-term deformation behavior of the surrounding rock, and quantifies and determines the timing of the first and second layers of support construction accordingly. This avoids subjective influences and enables synergistic matching between the support structure and the creep characteristics of the surrounding rock, improving the support effect and ensuring construction safety and long-term tunnel stability.

[0110] Based on the above technical solution, this embodiment also proposes a device for determining the timing of support construction in soft rock tunnels, used to implement the method for determining the timing of support construction in soft rock tunnels as described in this embodiment. Please refer to [link to relevant documentation]. Figure 3 The device includes:

[0111] The monitoring unit is used to monitor the radial convergence deformation of the tunnel surrounding rock under unsupported conditions after tunnel excavation, and to obtain the first cumulative radial convergence deformation of the tunnel surrounding rock at different time points; and to detect the second cumulative radial convergence deformation of the surrounding rock-support I structure in real time after the first layer of support is constructed to form the surrounding rock-support I structure.

[0112] The prediction unit is used to construct a first creep constitutive model of the tunnel surrounding rock based on the first cumulative radial convergence deformation, and to predict the final radial convergence deformation of the tunnel surrounding rock under unsupported conditions based on the first creep constitutive model.

[0113] The first determining unit is used to determine the timing of the first layer of support when the first cumulative radial convergence deformation reaches a preset proportion of the final radial convergence deformation under unsupported conditions.

[0114] The second determining unit determines the timing of the second layer of support when the radial convergence deformation rate of the surrounding rock-support I structure decreases to the deformation rate threshold, or when the second cumulative radial convergence deformation reaches the deformation amount threshold and the rate of change of the radial convergence deformation is less than the rate threshold.

[0115] It is understood that since the support timing determination device for soft rock tunnels described in this embodiment is a device for implementing the support timing determination method for soft rock tunnels described in the embodiment, the device disclosed in the embodiment is relatively simple to describe because it corresponds to the method disclosed in the embodiment. For relevant parts, please refer to the description of the method, and it will not be repeated here.

Claims

1. A method for determining the timing of support construction in a soft rock tunnel, characterized in that, The method comprises: After tunnel excavation, the radial convergence deformation of the tunnel surrounding rock under the condition of no support is monitored to obtain a first cumulative radial convergence deformation of the tunnel surrounding rock at different time points; A first creep constitutive model of the tunnel surrounding rock is constructed according to the first cumulative radial convergence deformation, and a final radial convergence deformation of the tunnel surrounding rock under the condition of no support is predicted based on the first creep constitutive model; When the first cumulative radial convergence deformation reaches a preset proportion of the final radial convergence deformation under the condition of no support, a corresponding time is taken as a construction time of the first layer of support; After the first layer of support is constructed to form a surrounding rock-support I structure, a second cumulative radial convergence deformation of the surrounding rock-support I structure is detected in real time, and when a radial convergence deformation rate of the surrounding rock-support I structure decreases to a deformation rate threshold value, or when the second cumulative radial convergence deformation reaches a deformation threshold value and a change speed of the radial convergence deformation rate is less than a speed threshold value, a corresponding time is taken as a construction time of the second layer of support.

2. The method according to claim 1, wherein, The method for determining the corresponding time when the first cumulative radial convergence deformation reaches the preset proportion of the final radial convergence deformation comprises: The deformation threshold value corresponding to the preset proportion of the final radial convergence deformation is introduced into the constructed first creep constitutive model to calculate the corresponding time when the first cumulative radial convergence deformation reaches the preset proportion of the final radial convergence deformation.

3. The method according to claim 1, wherein, The method for determining the corresponding time when the radial convergence deformation rate of the surrounding rock-support I structure decreases to the deformation rate threshold value comprises: A second creep constitutive model of the surrounding rock-support I structure is constructed according to the second cumulative radial convergence deformation at different time points, and the corresponding time is calculated according to the second creep constitutive model and the deformation rate threshold value.

4. The method according to claim 3, wherein The first creep constitutive model and the second creep constitutive model are as follows: ； wherein, is time, is radial converging deformation amount of time, is instantaneous deformation amount, is time-dependent elastic deformation amount, is delay time, is steady-state creep rate, is natural constant.

5. The method according to claim 4, wherein the method is characterized by, The corresponding time is calculated according to the second creep constitutive model and the deformation rate threshold value, and the calculation formula is as follows: ； wherein, is the time corresponding to the deformation rate threshold value when the radial convergence deformation rate of the surrounding rock-supporting I structure decreases to the deformation rate threshold value, is the deformation rate threshold value, is the natural logarithm, is the aging elastic deformation amount in the second creep constitutive model, is the steady-state creep rate in the second creep constitutive model, is the delay time in the second creep constitutive model.

6. The method according to claim 1, wherein The final radial convergence deformation is a radial convergence deformation of the tunnel surrounding rock at a preset time, and the preset time is greater than or equal to 100 days.

7. The method according to claim 1, wherein the method is characterized by, The preset proportion is 0.1 to 0.3, and the deformation rate threshold value is less than 1 mm / day.

8. The method according to claim 1, wherein the method is characterized by, The structure of the first layer of support is a flexible support structure or a semi-flexible support structure, and the structure of the second layer of support is a rigid support structure or a semi-rigid support structure.

9. The method according to claim 1, wherein the method is characterized by, The method further comprises: During the whole tunnel construction process, the preset proportion and the deformation threshold value are dynamically adjusted according to a comparison result of the measured deformation data and the model predicted deformation data, and when the geology of the tunnel surrounding rock changes, the creep constitutive model is reconstructed.

10. A device for determining the timing of support construction in soft rock tunnels, characterized in that, The device for implementing the method for determining the support construction time of a soft rock tunnel according to any one of claims 1 to 9 comprises: A monitoring unit is configured to monitor the radial convergence deformation of the tunnel surrounding rock under the condition of no support after tunnel excavation to obtain a first cumulative radial convergence deformation of the tunnel surrounding rock at different time points, and to detect a second cumulative radial convergence deformation of a surrounding rock-support I structure in real time after the first layer of support is constructed to form the surrounding rock-support I structure. a prediction unit configured to construct a first creep constitutive model of the tunnel surrounding rock according to the first cumulative radial convergence deformation, and predict a final radial convergence deformation of the tunnel surrounding rock under the condition of no support based on the first creep constitutive model; a first determination unit configured to, under the condition of no support, when the first cumulative radial convergence deformation reaches a preset proportion of the final radial convergence deformation, take a corresponding time as a construction time of the first layer of support; a second determination unit configured to, when the radial convergence deformation rate of the surrounding rock-support I structure decreases to a deformation rate threshold, or when the second cumulative radial convergence deformation reaches a deformation threshold and a change speed of the radial convergence deformation rate is less than a speed threshold, take a corresponding time as a construction time of the second layer of support.

Images