Tunnel surrounding rock pressure determination method based on stratum structure method
阅读说明：本技术 一种基于地层结构法的隧道围岩压力确定方法 (Tunnel surrounding rock pressure determination method based on stratum structure method ) 是由 李斌 尤昭 于 2021-07-05 设计创作，主要内容包括：本发明提供了一种基于地层结构法的隧道围岩压力确定方法,采用了自动迭代算法,首先利用FLAC3D建立隧道的数值模型,并施加支护反力,通过编程实现对支护反力进行自动调整,得到满足安全系数和容许位移的支护反力,最后利用支护反力反算围岩压力,不需要提前确定迭代所需的支护反力的上界和下界,减少分析步骤和计算时间；不需要人为判断计算结果是否收敛,计算结果更加准确；迭代过程可以自动完成,不需要在数值计算和更新支护反力之间来回手动切换。(The invention provides a tunnel surrounding rock pressure determination method based on a stratum structure method, which adopts an automatic iteration algorithm, firstly, a numerical model of a tunnel is established by using FLAC3D, supporting counter force is applied, automatic adjustment of the supporting counter force is realized through programming, the supporting counter force meeting safety factor and allowable displacement is obtained, finally, the surrounding rock pressure is reversely calculated by using the supporting counter force, the upper bound and the lower bound of the supporting counter force required by iteration do not need to be determined in advance, and the analysis step and the calculation time are reduced; whether the calculation result is converged does not need to be artificially judged, so that the calculation result is more accurate; the iterative process can be automatically completed without manually switching back and forth between numerical calculation and updating the support counter force.)
1. A tunnel surrounding rock pressure determination method based on a stratum structure method is characterized by comprising the following steps:
s1: predefining allowable displacement of the tunnel and assigning initial values of vertically uniformly distributed loads;
s2: calculating to obtain a horizontal uniform load initial value according to the vertical uniform load initial value and the side pressure coefficient, calculating a first supporting counter force of each node according to the vertical uniform load initial value, the horizontal uniform load initial value and the tunnel excavation section node coordinate, and applying the first supporting counter force to the excavation section node;
s3: calculating the safety coefficient of the excavated tunnel;
s4: judging whether the safety coefficient is equal to the target value, if so, stopping the iteration and stopping the adjustment of the first support counterforce, otherwise, calculating the first-stage load adjustment proportion according to the ratio of the safety coefficient to the target value;
s5: calculating the vertically uniformly distributed load and the horizontally uniformly distributed load of the next iteration step according to the load adjustment proportion of the first stage, and repeatedly executing the steps S2-S4 until the safety coefficient is equal to the target value, and finishing the iteration of the first stage;
s6: and calculating a displacement result when the first-stage iteration is finished, judging whether the displacement result when the first-stage iteration is finished is less than or equal to the allowable displacement of the tunnel, if so, finishing all iterations, and taking the vertical uniformly distributed load at the moment as vertical surrounding rock pressure and the horizontal uniformly distributed load as horizontal surrounding rock pressure.
2. The method of determining tunnel wall rock pressure of claim 1, wherein when the displacement calculation at the end of the first stage iteration is greater than the tunnel allowable displacement, the method further comprises:
s7: defining a tolerance value, calculating a second-stage load adjustment proportion according to a displacement result obtained when the first-stage iteration is finished and the allowable displacement of the tunnel, and calculating a vertically uniformly distributed load and a horizontally uniformly distributed load of the next iteration step according to the second-stage load adjustment proportion;
s8, calculating second support counter force of each node according to the vertical uniformly distributed load, the horizontal uniformly distributed load and the node coordinates of the excavation section calculated in the step S7, and applying the second support counter force to the node of the excavation section;
s9: and calculating a displacement result of the second stage, judging whether the absolute value of the displacement result of the second stage and the difference value of the allowable displacement of the tunnel is smaller than or equal to the tolerance value or not, if so, terminating the iteration of the second stage, otherwise, repeatedly executing the steps S7-S8 until the absolute value of the displacement result of the second stage and the difference value of the allowable displacement of the tunnel is smaller than or equal to the tolerance value, and taking the vertically uniformly distributed load when the iteration is terminated as the vertical surrounding rock pressure and the horizontally uniformly distributed load as the horizontal surrounding rock pressure.
3. The method for determining the pressure of the surrounding rock of the tunnel according to claim 1, wherein the step S2 of calculating the first supporting counterforce of each node according to the initial value of the vertically uniformly distributed load, the initial value of the horizontally uniformly distributed load and the node coordinates of the tunnel excavation section includes:
obtaining tunnel excavation section node coordinates by using a command stream of FLAC 3D;
determining a node to be calculated;
calculating the vertical supporting force of the node to be calculated according to the initial value of the vertically uniformly distributed load and the distance between two adjacent nodes of the node to be calculated, and calculating the transverse supporting force of the node to be calculated according to the initial value of the transversely uniformly distributed load and the distance between two adjacent nodes of the node to be calculated; the vertical supporting force and the transverse supporting force form a first supporting force.
4. The tunnel surrounding rock pressure determining method as claimed in claim 1, wherein the step S3 includes:
and calculating the safety factor of the excavated tunnel by using an intensity reduction method, wherein the safety factor is defined as:
in the formula: c andrepresenting the cohesion and internal friction angle of the sample input, ccrAndrepresenting the critical cohesion and the critical internal friction angle of the tunnel in extreme conditions.
5. The method for determining tunnel surrounding rock pressure according to claim 1, wherein the first-stage load adjustment proportion includes a tunnel load adjustment proportion in the nth iteration of the first stage, and is used for adjusting the uniformly distributed load of the (n + 1) th iteration of the first stage, and the step S5 calculates the vertically uniformly distributed load and the horizontally uniformly distributed load of the next iteration step according to the first-stage load adjustment proportion, and includes:
calculating the vertical uniform load of the next iteration step according to the load adjustment proportion of the first stage:
wherein the content of the first and second substances,indicating the tunnel load adjustment proportion in the nth iteration of the first stage,representing the vertically uniform load of the nth iteration of the first stage,representing the vertically uniform load of the (n + 1) th iteration of the first stage;
calculating the transverse uniformly distributed load of the next iteration step according to the load adjustment proportion of the first stage:
wherein the content of the first and second substances,indicating the tunnel load adjustment proportion in the nth iteration of the first stage,representing the laterally uniform loading of the nth iteration of the first stage,represents the laterally uniform load of the (n + 1) th iteration of the first stage.
6. The tunnel surrounding rock pressure determining method as claimed in claim 2, wherein the step S7 includes:
s7.1: calculating the load adjustment proportion of the second stage according to the displacement result at the end of the first stage iteration and the allowable displacement of the tunnel,
wherein the content of the first and second substances,indicating the result of the displacement calculation at the end of the first phase,it is shown that the tunnel is allowed to shift,representing the tunnel load adjustment proportion in the nth iteration of the second stage;
s7.2: and calculating the vertical uniform load of the next iteration step according to the tunnel load adjustment proportion in the nth iteration of the second stage:
wherein the content of the first and second substances,representing the vertically uniform load of the nth iteration of the second stage,representing the vertical uniform load of the (n + 1) th iteration of the second stage;
s7.3: and calculating the transverse uniformly distributed load of the next iteration step according to the tunnel load adjustment proportion in the nth iteration of the second stage:
wherein the content of the first and second substances,represents the lateral uniform load of the nth iteration of the second stage,represents the horizontal uniform load of the (n + 1) th iteration of the second stage.
Technical Field
The invention relates to the field of tunnel engineering, in particular to a tunnel surrounding rock pressure determination method based on a stratum structure method.
Background
In the tunnel gauge, the influence of the tunnel burial depth on the surrounding rock pressure is not considered when the surrounding rock pressure of the deeply buried tunnel is calculated, so that the obtained result is not accurate. Two methods for determining the pressure of surrounding rocks are proposed in the prior art.
One method is to study the tunnel surrounding rock pressure based on statistical analysis of a large amount of on-site measured data, so as to fit a surrounding rock pressure calculation formula. However, due to the fact that geological conditions are changed, construction levels are different, supporting parameters are different, and surrounding rock pressure is variable in space-time even if surrounding rock conditions are the same. Therefore, this method cannot be applied to all tunnel surrounding rock pressure calculations.
The other method is to establish a tunnel finite element model, apply support counter force and make the model just converge by manually adjusting the magnitude of the support counter force. And finally, converting the support counter force into uniformly distributed load, wherein the uniformly distributed load at the moment is used as the tunnel surrounding rock pressure. In theory, the method can adopt various constitutive models which accord with actual engineering according to specific geological conditions, and the accuracy of a calculation result is improved.
In the process of implementing the invention, the inventor of the application finds that the following technical problems exist in the prior art:
1. the tunnel support counter force needs to be adjusted manually, a numerical model is built repeatedly for many times to calculate, the calculation process is complex, the consumed time is long, and the efficiency is low. 2. The upper limit and the lower limit for supporting the reaction force need to be determined in advance, and the calculation workload is large.
Therefore, the method in the prior art has the technical problem of low calculation efficiency.
Disclosure of Invention
The invention provides a tunnel surrounding rock pressure determination method based on a stratum structure method, which is used for solving or at least partially solving the technical problem of low calculation efficiency of the method in the prior art.
In order to solve the technical problem, the invention provides a tunnel surrounding rock pressure determination method based on a stratum structure method, which comprises the following steps:
s1: predefining allowable displacement of the tunnel and assigning initial values of vertically uniformly distributed loads;
s2: calculating to obtain a horizontal uniform load initial value according to the vertical uniform load initial value and the side pressure coefficient, calculating a first supporting counter force of each node according to the vertical uniform load initial value, the horizontal uniform load initial value and the tunnel excavation section node coordinate, and applying the first supporting counter force to the excavation section node;
s3: calculating the safety coefficient of the excavated tunnel;
s4: judging whether the safety coefficient is equal to the target value, if so, stopping the iteration and stopping the adjustment of the first support counterforce, otherwise, calculating the first-stage load adjustment proportion according to the ratio of the safety coefficient to the target value;
s5: calculating the vertically uniformly distributed load and the horizontally uniformly distributed load of the next iteration step according to the load adjustment proportion of the first stage, and repeatedly executing the steps S2-S4 until the safety coefficient is equal to the target value, and finishing the iteration of the first stage;
s6: and calculating a displacement result when the first-stage iteration is finished, judging whether the displacement result when the first-stage iteration is finished is less than or equal to the allowable displacement of the tunnel, if so, finishing all iterations, and taking the vertical uniformly distributed load at the moment as vertical surrounding rock pressure and the horizontal uniformly distributed load as horizontal surrounding rock pressure.
In one embodiment, when the displacement calculation result at the end of the first stage iteration is greater than the tunnel allowable displacement, the method further comprises:
s7: defining a tolerance value, calculating a second-stage load adjustment proportion according to a displacement result obtained when the first-stage iteration is finished and the allowable displacement of the tunnel, and calculating a vertically uniformly distributed load and a horizontally uniformly distributed load of the next iteration step according to the second-stage load adjustment proportion;
s8, calculating second support counter force of each node according to the vertical uniformly distributed load, the horizontal uniformly distributed load and the node coordinates of the excavation section calculated in the step S7, and applying the second support counter force to the node of the excavation section;
s9: and calculating a displacement result of the second stage, judging whether the absolute value of the displacement result of the second stage and the difference value of the allowable displacement of the tunnel is smaller than or equal to the tolerance value or not, if so, terminating the iteration of the second stage, otherwise, repeatedly executing the steps S7-S8 until the absolute value of the displacement result of the second stage and the difference value of the allowable displacement of the tunnel is smaller than or equal to the tolerance value, and taking the vertically uniformly distributed load when the iteration is terminated as the vertical surrounding rock pressure and the horizontally uniformly distributed load as the horizontal surrounding rock pressure.
In one embodiment, the step S2 is a step of calculating a first supporting counterforce of each node according to the initial value of the vertically uniform load, the initial value of the horizontally uniform load and the node coordinates of the tunnel excavation section, and includes:
obtaining tunnel excavation section node coordinates by using a command stream of FLAC 3D;
determining a node to be calculated;
calculating the vertical supporting force of the node to be calculated according to the initial value of the vertically uniformly distributed load and the distance between two adjacent nodes of the node to be calculated, and calculating the transverse supporting force of the node to be calculated according to the initial value of the transversely uniformly distributed load and the distance between two adjacent nodes of the node to be calculated; the vertical supporting force and the transverse supporting force form a first supporting force.
In one embodiment, step S3 includes:
and calculating the safety factor of the excavated tunnel by using an intensity reduction method, wherein the safety factor is defined as:
in the formula: c andrepresenting the cohesion and internal friction angle of the sample input, ccrAndrepresenting the critical cohesion and the critical internal friction angle of the tunnel in extreme conditions.
In one embodiment, the first-stage load adjustment ratio includes a tunnel load adjustment ratio in the nth iteration of the first stage, and is used to adjust the uniformly distributed load of the (n + 1) th iteration of the first stage, and step S5 calculates the vertically uniformly distributed load and the horizontally uniformly distributed load of the next iteration step according to the first-stage load adjustment ratio, including:
calculating the vertical uniform load of the next iteration step according to the load adjustment proportion of the first stage:
wherein the content of the first and second substances,indicating the tunnel load adjustment proportion in the nth iteration of the first stage,representing the vertically uniform load of the nth iteration of the first stage,representing the vertically uniform load of the (n + 1) th iteration of the first stage;
calculating the transverse uniformly distributed load of the next iteration step according to the load adjustment proportion of the first stage:
wherein the content of the first and second substances,indicating the tunnel load adjustment proportion in the nth iteration of the first stage,representing the laterally uniform loading of the nth iteration of the first stage,represents the laterally uniform load of the (n + 1) th iteration of the first stage.
In one embodiment, step S7 includes:
s7.1: calculating the load adjustment proportion of the second stage according to the displacement result at the end of the first stage iteration and the allowable displacement of the tunnel,
wherein the content of the first and second substances,to representThe result of the displacement calculation at the end of the first phase,it is shown that the tunnel is allowed to shift,representing the tunnel load adjustment proportion in the nth iteration of the second stage;
s7.2: and calculating the vertical uniform load of the next iteration step according to the tunnel load adjustment proportion in the nth iteration of the second stage:
wherein the content of the first and second substances,representing the vertically uniform load of the nth iteration of the second stage,representing the vertical uniform load of the (n + 1) th iteration of the second stage;
s7.3: and calculating the transverse uniformly distributed load of the next iteration step according to the tunnel load adjustment proportion in the nth iteration of the second stage:
wherein the content of the first and second substances,represents the lateral uniform load of the nth iteration of the second stage,represents the horizontal uniform load of the (n + 1) th iteration of the second stage.
One or more technical solutions in the embodiments of the present application have at least one or more of the following technical effects:
the invention provides a tunnel surrounding rock pressure determination method based on a stratum structure method, which adopts an automatic iteration algorithm of tunnel surrounding rock pressure, calculates first supporting counter force of each node according to a vertical uniformly distributed load initial value, a horizontal uniformly distributed load initial value and tunnel excavation section node coordinates, applies the first supporting counter force to the excavation section nodes, judges whether the safety coefficient is equal to a target value or not, sets a first-stage load adjustment proportion for automatically adjusting the supporting counter force in the iteration process to obtain the supporting counter force meeting the safety coefficient, reversely calculates the surrounding rock pressure by using the supporting counter force, does not need to manually adjust the tunnel supporting counter force, repeatedly establishes a numerical model for calculation for many times, does not need to determine an upper limit and a lower limit for the supporting counter force in advance, and greatly improves the calculation efficiency.
And further, introducing allowable displacement and tolerance of the tunnel, calculating a second-stage load adjustment proportion according to the displacement result when the first-stage iteration is finished and the allowable displacement of the tunnel, performing second-stage iteration, calculating vertical uniformly distributed load and horizontal uniformly distributed load of the next iteration step according to the second-stage load adjustment proportion, automatically adjusting supporting counter force in the second iteration process, finally meeting the supporting counter force of the allowable displacement, and finally reversely calculating the surrounding rock pressure by using the supporting counter force in the second stage. The allowable deformation of the tunnel is considered to cause the obtained tunnel deformation to exceed the allowable value, so that the calculation result is more accurate and reasonable.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
Fig. 1 is a schematic diagram of tunnel node numbering according to an embodiment of the present invention;
fig. 2 is a flowchart of a tunnel surrounding rock pressure determination method based on a stratigraphic structure method in the embodiment of the invention.
FIG. 3 is a schematic cross-sectional view of a ducted valley tunnel according to an embodiment of the present invention;
FIG. 4 is a diagram illustrating how a FLAC3D may be used to create a function valley closing tunnel model in accordance with an embodiment of the present invention;
FIG. 5 is a schematic view of a cross-sectional node of a fun-valley tunnel according to an embodiment of the present invention;
FIG. 6 is a schematic diagram illustrating displacement of monitoring points of a critical steady state tunnel according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of a 350km/h high-speed railway double-track tunnel model established by using FLAC3D according to an embodiment of the invention;
fig. 8 is a schematic diagram illustrating displacement of monitoring points of a critical steady-state tunnel according to another embodiment of the present invention.
Detailed Description
For the design of the tunnel, the surrounding rock pressure is a very important parameter, and the determination of many design parameters, including lining thickness, reinforcement ratio, construction method and the like, depends on the magnitude of the surrounding rock pressure. Under the condition of deep burying, when the tunnel span and the grade of the surrounding rock are determined, the surrounding rock pressure calculated according to tunnel regulations is a fixed value. However, the existing research shows that the pressure of surrounding rocks is different when the tunnel burial depth is different. At the present stage, no surrounding rock pressure calculation method capable of being practically applied exists. The method comprises the steps of firstly establishing a numerical model of the tunnel by using the FLAC3D, applying support reaction force, automatically adjusting the support reaction force by programming to obtain the support reaction force meeting the safety coefficient and the allowable displacement, and finally reversely calculating the surrounding rock pressure by using the support reaction force. .
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment of the invention provides a tunnel surrounding rock pressure determination method based on a stratum structure method, which comprises the following steps:
s1: predefining allowable displacement of the tunnel and assigning initial values of vertically uniformly distributed loads;
s2: calculating to obtain a horizontal uniform load initial value according to the vertical uniform load initial value and the side pressure coefficient, calculating a first supporting counter force of each node according to the vertical uniform load initial value, the horizontal uniform load initial value and the tunnel excavation section node coordinate, and applying the first supporting counter force to the excavation section node;
s3: calculating the safety coefficient of the excavated tunnel;
s4: judging whether the safety coefficient is equal to the target value, if so, stopping the iteration and stopping the adjustment of the first support counterforce, otherwise, calculating the first-stage load adjustment proportion according to the ratio of the safety coefficient to the target value;
s5: calculating the vertically uniformly distributed load and the horizontally uniformly distributed load of the next iteration step according to the load adjustment proportion of the first stage, and repeatedly executing the steps S2-S4 until the safety coefficient is equal to the target value, and finishing the iteration of the first stage;
s6: and calculating a displacement result when the first-stage iteration is finished, judging whether the displacement result when the first-stage iteration is finished is less than or equal to the allowable displacement of the tunnel, if so, finishing all iterations, and taking the vertical uniformly distributed load at the moment as vertical surrounding rock pressure and the horizontal uniformly distributed load as horizontal surrounding rock pressure.
Specifically, the FLAC3D software may be used to model and excavate a multi-center circular railroad tunnel. The first support counter force represents the support counter force obtained by calculation in the first-stage iteration process, and the calculation process of the support counter force of each node is a cycle iteration process.
In one embodiment, when the displacement calculation result at the end of the first stage iteration is greater than the tunnel allowable displacement, the method further comprises:
s7: defining a tolerance value, calculating a second-stage load adjustment proportion according to a displacement result obtained when the first-stage iteration is finished and the allowable displacement of the tunnel, and calculating a vertically uniformly distributed load and a horizontally uniformly distributed load of the next iteration step according to the second-stage load adjustment proportion;
s8, calculating second support counter force of each node according to the vertical uniformly distributed load, the horizontal uniformly distributed load and the node coordinates of the excavation section calculated in the step S7, and applying the second support counter force to the node of the excavation section;
s9: and calculating a displacement result of the second stage, judging whether the absolute value of the displacement result of the second stage and the difference value of the allowable displacement of the tunnel is smaller than or equal to the tolerance value or not, if so, terminating the iteration of the second stage, otherwise, repeatedly executing the steps S7-S8 until the absolute value of the displacement result of the second stage and the difference value of the allowable displacement of the tunnel is smaller than or equal to the tolerance value, and taking the vertically uniformly distributed load when the iteration is terminated as the vertical surrounding rock pressure and the horizontally uniformly distributed load as the horizontal surrounding rock pressure.
Specifically, the safety factor F of the model can be directly obtained by FLAC3D self-carrying strength reduction calculationsHowever, this method only considers the stress characteristics of the model, and does not consider the influence of the displacement generated by tunnel excavation on the stability of the tunnel. The existing railway tunnel design specifications stipulate allowable displacement of the tunnel, and mainly ensure the safety of the tunnel construction process. In order to consider the influence of displacement in the calculation of the tunnel surrounding rock pressure, the displacement of representative positions such as the convergence of the vault and the periphery of the tunnel can be monitored in numerical simulation, and the maximum displacement of the tunnel is checked through a command at the end of each iteration step. When iteration is ended, if the maximum displacement of the monitored tunnel (namely the displacement result when the iteration of the first stage is ended) is smaller than the allowable displacement, the vertically uniform load is distributed at the momentNamely the vertical surrounding rock pressure borne by the tunnel and the horizontally and uniformly distributed loadThe tunnel is subjected to transverse surrounding rock pressure. Otherwise, the supporting reaction force is smaller, the tunnel stability condition is not met, and the supporting reaction force needs to be further increased.
Based on the above consideration, the application adds the iteration process of the second stage on the basis of the iteration of the first stage. And in the first-stage iteration process, calculating a first-stage load adjustment proportion according to whether the safety coefficient is equal to a target value or not, calculating the vertical uniform load and the horizontal uniform load of the next iteration step according to the first-stage load adjustment proportion, and indicating that the first-stage iteration process is finished when the displacement result of the first-stage iteration is less than or equal to the allowable displacement of the tunnel.
And the second stage of iterative process, which is based on the above and takes tolerance as a target to perform similar iterative calculation.
In one embodiment, the step S2 is a step of calculating a first supporting counterforce of each node according to the initial value of the vertically uniform load, the initial value of the horizontally uniform load and the node coordinates of the tunnel excavation section, and includes:
obtaining tunnel excavation section node coordinates by using a command stream of FLAC 3D;
determining a node to be calculated;
calculating the vertical supporting force of the node to be calculated according to the initial value of the vertically uniformly distributed load and the distance between two adjacent nodes of the node to be calculated, and calculating the transverse supporting force of the node to be calculated according to the initial value of the transversely uniformly distributed load and the distance between two adjacent nodes of the node to be calculated; the vertical supporting force and the transverse supporting force form a first supporting force.
In the specific implementation process, firstly, the method utilizes the FLAC3D software to model and excavate the multi-center circular railway tunnel, and the initial value of the vertically uniformly distributed load is designatedThen utilizing the initial value of the vertically uniformly distributed loadCalculating the coefficient of the side pressure to obtain the horizontally distributed loadAccording toAnd calculating vertical support counter force and applying the counter force to a tunnel excavation contour surface. The method comprises the following steps: obtaining tunnel excavation section node coordinates by using a command stream of FLAC3D, and obtaining initial values according to vertically uniform loadAnd calculating the vertical support counter force required to be exerted by each node according to the distance between two adjacent nodes of the point to be calculated. For example, when the computation node is a7, its two neighboring nodes are a6 and A8 (fig. 1). Similarly, the horizontal support counter-force can be obtained by horizontally and uniformly distributing the initial value of the loadThe calculated node numbers are shown in fig. 1.
With A7For example, the method of applying the support reaction force is as follows:
(1) output A6The horizontal coordinates of the points are: a. the6xThe ordinate is: a. the6y；A8The horizontal coordinates of the points are: a. the8x(ii) a The ordinate is: a. the8y；
(2) The lateral pressure coefficient lambda is mu/(1-mu), wherein mu is the Poisson ratio; horizontal uniform load
(1) (3) A7 point vertical support counter force:horizontal support counterforce:
in one embodiment, step S3 includes:
and calculating the safety factor of the excavated tunnel by using an intensity reduction method, wherein the safety factor is defined as:
in the formula: c andrepresenting the cohesion and internal friction angle of the sample input, ccrAndrepresenting the critical cohesion and the critical internal friction angle of the tunnel in extreme conditions.
Specifically, for the established numerical model, the safety coefficient of the tunnel excavation can be calculated through intensity reduction. For a given numerical model and parameters, FLAC3D may be calculated by the intensity reduction method of the belt itself to obtain Fs. The existing research shows that when the safety coefficient is less than 1.15, the model is in a destabilization state, and when the strength reduction coefficient is more than or equal to 1.15, the tunnel is in a stable state. Therefore, the invention uses FsAnd (4) taking the safety coefficient of the tunnel as the limit state as 1.15, and judging whether the surrounding rock is stable after the tunnel is excavated.
In one embodiment, the first-stage load adjustment ratio includes a tunnel load adjustment ratio in the nth iteration of the first stage, and is used to adjust the uniformly distributed load of the (n + 1) th iteration of the first stage, and step S5 calculates the vertically uniformly distributed load and the horizontally uniformly distributed load of the next iteration step according to the first-stage load adjustment ratio, including:
calculating the vertical uniform load of the next iteration step according to the load adjustment proportion of the first stage:
wherein the content of the first and second substances,represents the firstAdjusting the tunnel load proportion in the nth iteration of the stage,representing the vertically uniform load of the nth iteration of the first stage,representing the vertically uniform load of the (n + 1) th iteration of the first stage;
calculating the transverse uniformly distributed load of the next iteration step according to the load adjustment proportion of the first stage:
wherein the content of the first and second substances,indicating the tunnel load adjustment proportion in the nth iteration of the first stage,representing the laterally uniform loading of the nth iteration of the first stage,represents the laterally uniform load of the (n + 1) th iteration of the first stage.
In the specific implementation process, in order to adjust the support reaction force of the tunnel in the iteration process, the method defines a first-stage tunnel load adjustment proportion based on the calculated safety coefficient
Wherein the content of the first and second substances,the safety factor obtained by the nth iteration calculation is shown,indicating extreme state safety factors (i.e. F)s＝1.15)，The tunnel load adjustment ratio (for the (n + 1) th load adjustment) in the nth iteration of the first stage is shown.
With a in fig. 17For example, when the vehicle is walking in an n +1 iteration, the counter force of the vertical support is given Horizontal uniform loadHorizontal support counter-force The principle of the first stage tunnel load adjustment proportion calculation formula is as follows: when the calculated safety coefficient is smaller than the target critical value, the tunnel support reaction force is smaller, so that the current uniformly distributed load needs to be divided by a numerical value smaller than 1; when the calculated safety coefficient is larger than the target critical value, the tunnel support reaction force is larger, so that the current uniform load needs to be divided by a numerical value larger than 1. Through continuous iteration, when the calculated safety factor reaches the target critical valueFirst stage tunnel load regulation ratioThe first supporting counter-force will no longer be adjusted and iteratedAnd (6) terminating.
In one embodiment, step S7 includes:
s7.1: calculating the load adjustment proportion of the second stage according to the displacement result at the end of the first stage iteration and the allowable displacement of the tunnel,
wherein the content of the first and second substances,indicating the result of the displacement calculation at the end of the first phase,it is shown that the tunnel is allowed to shift,representing the tunnel load adjustment proportion in the nth iteration of the second stage;
s7.2: and calculating the vertical uniform load of the next iteration step according to the tunnel load adjustment proportion in the nth iteration of the second stage:
wherein the content of the first and second substances,indicating the tunnel load adjustment proportion in the nth iteration of the second stage,representing the vertically uniform load of the nth iteration of the second stage,representing the vertical uniform load of the (n + 1) th iteration of the second stage;
s7.3: and calculating the transverse uniformly distributed load of the next iteration step according to the tunnel load adjustment proportion in the nth iteration of the second stage:
wherein the content of the first and second substances,represents the lateral uniform load of the nth iteration of the second stage,represents the horizontal uniform load of the (n + 1) th iteration of the second stage.
In the specific implementation process, in order to obtain the support counterforce meeting the allowable displacement of the tunnel, iteration of the second stage is performed, and the load adjustment proportion is redefined in the stage, namely the load adjustment proportion in the second stage:
represents the maximum displacement of the tunnel calculated in the nth iteration,indicating the allowable displacement of the tunnel, for example 12cm,showing the tunnel load adjustment ratio in the nth iteration of the second stage (for the (n + 1) th vertically uniform load adjustment)
Since the calculated displacement value is a fraction and the allowable target value is usually an integer, in order to satisfy the iteration termination condition, the present invention sets a tolerance β, which determines the accuracy of the iteration result. The smaller the value of the tolerance β, the higher the accuracy of the calculation, but the longer the calculation time. Maximum displacement of tunnel obtained from numerical calculation resultAndand when the absolute value of the difference is smaller than the tolerance beta, the iteration termination condition is considered to be reached.
The second stage iteration method is similar to the first stage, and when each iteration step is terminated, if the maximum displacement of the tunnel is calculatedGreater than allowableAt this moment, the tunnel support reaction force is smaller, so that the current uniformly distributed load needs to be multiplied by a numerical value larger than 1; if the maximum displacement of the tunnel is calculatedIs less than allowableAt this time, it is described that the tunnel support reaction force is large, and therefore, the current uniform load needs to be multiplied by a value smaller than 1.
Through a plurality of iterative computations, when the iteration termination condition is satisfied (equation 6), the computation is ended. The uniform load at this time is the tunnel surrounding rock pressure.
Fig. 2 is a flowchart of a method for determining the pressure of surrounding rock of a tunnel based on a stratigraphic structure method in a specific implementation process. The flow shown in the figure comprises a first stage of iteration (above the dashed line) and a second stage of iteration (below the dashed line). The whole process comprises the following steps:
(1) defining allowable displacement of tunnelAnd the numerical value of tolerance beta, appointing the initial value of the vertically uniform load
(2) And calculating the support counter force of each node according to the vertically uniformly distributed load and the node coordinates of the tunnel excavation section, and applying the support counter force to the excavation section nodes.
(3) Calculating the intensity reduction to obtain the safety coefficient
(4) Judging the safety factorWhether or not to equal the target valueIf yes, the iteration is terminated, otherwise, the load adjustment proportion of the next iteration in the first stage is calculated
(5) Calculating the vertical uniform load of the next cycle according to the load adjustment proportion,repeating the steps (2) to (4) untilThe first stage iteration ends.
(6) From the result of the displacement calculation at the end of the first stageJudgment ofWhether or not less than or equal toIf so, finishing all iterations, and taking the uniformly distributed load as the surrounding rock pressure; otherwise, entering the second stage iteration, and changing the iteration target into the tunnel allowable displacement.
(7) According to tunnel displacementAnd tunnel displacement toleranceCalculating new load adjustment ratio (second stage load adjustment ratio)) Calculating the vertically uniform load of the next iteration step by using the new load adjustment proportion
(8) And calculating second support counter force of each node by utilizing the vertically uniformly distributed load and the node coordinates of the excavation section, and applying the second support counter force to the excavation section nodes.
(9) Calculating and obtaining the maximum displacement of the tunnelJudgment ofIf yes, the iteration is terminated; if not, repeating the steps (7) to (8) until the convergence condition is metAnd stopping iteration, wherein the uniformly distributed load is the surrounding rock pressure.
The advantages and the beneficial technical effects of the invention comprise:
1) the upper bound and the lower bound of the support reaction force required by iteration do not need to be determined in advance, so that the analysis steps and the calculation time are reduced;
2) whether the calculation result is converged does not need to be artificially judged, so that the calculation result is more accurate;
3) the iterative process can be automatically completed without manually switching back and forth between numerical calculation and support counter force updating;
4) the iteration time is greatly shortened, and the pressure values of the tunnel surrounding rock under different burial depths in the stratum can be conveniently calculated;
5) the load adjustment proportion is defined simply, and the control programming of the iterative process is more convenient;
6) meanwhile, the structural stress state and the allowable displacement of the tunnel are considered, so that the calculation result is more reasonable and safer.
In order to more clearly illustrate the embodiments of the present invention, the following detailed description is given by way of two examples.
The first embodiment is as follows:
the following example used analysis software FLAC3D, and other numerical software with intensity reduction, all of which involved steps and methods, unless otherwise specified, were conventional. In this embodiment, taking a gateway tunnel of zhengxi passenger dedicated line as an example, the tunnel burial depth is 110m, the grade of surrounding rocks is V grade, and the material parameters are shown in table 1:
TABLE 1 Material parameters
The cross-sectional view of the fun-gu-guan tunnel is shown in fig. 3, and the specific implementation steps are as follows:
(1) specifying initial tunnel radiusThe safety factor target value is Fs *1.15, determining the allowable tunnel displacement according to the design specification of the railway tunnelThe tolerance value is beta-0.5 cm.
(2) As shown in fig. 4, a function valley tunnel model is established by using FLAC3D, the size of the model is required to satisfy the saint-wien law, and the distance between the tunnel and the boundary of the model is larger than 3-5 times of the span of the tunnel. The four sides of the model are normal phase constraints, and the bottom of the model is full constraint. The soil body adopts a mole-coulomb model.
(3) The calculation of the support counter force is not applied after the tunnel is excavated, the safety coefficient is 1.16, the first stage is finished, and the maximum displacement isThe iteration termination condition is not satisfied:and entering the second stage iteration.
(4) Specifying initial vertically uniform loadAnd (5) calculating a support reaction force according to the coordinates of each node of the excavation section (the y direction is divided into 50 grids, and 51 nodes are total). With a in fig. 57For example, the method for applying the supporting reaction force comprises the following steps:
1) outputting coordinates of each node, wherein A6Point abscissa A6x＝4.72m，(A6Point ordinate A6z＝6.15m；A8Point abscissa A8x＝6.40m，A8Point ordinate A8z4.37 m. The lateral pressure coefficient lambda is equal to mu/(1-mu) 0.35/(1-0.35) 0.538
2) Vertical support counter-force Horizontal support counter-force
(5) Performing intensity reduction calculation after applying support counter-force, and calculating the maximum displacement of the tunnel as
(6) Judging that the displacement does not satisfy the iteration termination conditionCalculating load adjustment coefficientCalculating the vertical uniform load of the second iteration step Horizontal uniform load
(7) Repeating the steps (4) to (6), and after the iteration of the step 6, vertically and uniformly distributing the loadHorizontal uniform loadMaximum displacement of the tunnel ofAnd (3) satisfying an iteration termination condition:and (4) finishing iteration, wherein the vertical uniformly distributed load is the vertical pressure of the tunnel surrounding rock, and the horizontal uniformly distributed load is the horizontal pressure of the tunnel surrounding rock.
The data for a specific iteration process is shown in table 2:
TABLE 2 iterative Process data
The displacement of the monitoring point of the critical steady-state tunnel is shown in fig. 6.
The result of the calculation of the surrounding rock pressure in the specification of the railway tunnel and the actual measurement result of the surrounding rock pressure of the funogu tunnel on the zhengxi special line are compared with the calculation result of the present example, as shown in table 3.
TABLE 3 comparison of extreme steady state wall rock pressure values with normative and actual values
As can be seen from table 3, the difference between the surrounding rock pressure obtained according to the railway tunnel specification formula and the measured value is too large, and is not accurate enough. The surrounding rock pressure obtained by the method is closer to the actually measured surrounding rock pressure result, and meanwhile, the calculation results are all larger than the actually measured results, so that certain safety storage can be provided for the tunnel surrounding rock, and the method has reference significance in actual engineering.
Example two:
in order to prove that the buried depth can affect the pressure of the surrounding rock of the deeply buried tunnel, the second embodiment calculates the pressure of the surrounding rock when the buried depth of the tunnel is 200m on the basis of the first embodiment, and the specific implementation steps are as follows:
(1) specifying initial tunnel radiusThe safety factor target value is Fs *1.15, determining the allowable tunnel displacement according to the design specification of the railway tunnelThe tolerance value is beta-0.5 cm.
(2) A350 km/h high-speed railway double-track tunnel model is built by using FLAC3D, as shown in FIG. 7, the size of the model is required to meet the Saint-Venn's law, and the distance between the tunnel and the boundary of the model is larger than 3-5 times of the tunnel span. The four sides of the model are normal phase constraints, and the bottom of the model is full constraint. The soil body adopts a mole-coulomb model.
(3) Initial value of vertically and uniformly distributed load of specified tunnelAnd calculating and applying support counter force according to the coordinates of each node of the excavation section.
(4) Calculating the model by using FLAC3D to obtain a safety factor Fs 1＝1.10。
(5) Judging that the complete coefficient is not equal to the target value of 1.15, calculating the tunnel load adjustment ratio calculated by the second iteration step value as
(6) Calculating the vertically uniform load of the second iteration step, horizontal uniform loadAnd (5) repeating the steps (3) to (5), after the iteration step (20), calculating the safety coefficient to be 1.15, and ending the iteration of the first stage. At the moment, the load is vertically and uniformly distributedHorizontal uniform loadMaximum displacement of the tunnel ofThe iteration termination condition is not satisfied:and entering the second stage iteration.
(7) Calculating load adjustment coefficientCalculating the vertical uniform load of the second iteration stepHorizontal uniform load
(8) Calculating the maximum displacement of the tunnel after applying the supporting counter forceJudging that the displacement does not satisfy the iteration termination condition
(9) Repeating the steps (7) - (8), and after 4 steps of iteration, vertically and uniformly distributing the loadTransversely uniformly distributed loadMaximum displacement of the tunnel ofAnd (3) satisfying an iteration termination condition:and (4) finishing iteration, wherein the vertical uniformly distributed load is the vertical pressure of the tunnel surrounding rock, and the horizontal uniformly distributed load is the horizontal pressure of the tunnel surrounding rock.
The data for the specific iteration process is shown in table 4:
TABLE 4 iterative Process data
The displacement of the monitoring point of the critical steady-state tunnel is shown in fig. 8.
Comparing the calculation results of the first embodiment and the second embodiment, the vertical pressure of the surrounding rock of the ducted valley tunnel at the burial depth of 110m is 53.62kPa, and the transverse pressure is 28.84 kPa; the vertical pressure of the surrounding rock under the buried depth of 200m is 230.9kPa, and the transverse pressure is 124.22kPa, which shows that the tunnel buried depth has great influence on the pressure of the surrounding rock of the tunnel under the deep buried condition.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.