Numerical Simulation of Surrounding Rock Deformation and Grouting Reinforcement of Cross-Fault Tunnel under Different Excavation Methods

Tunnel construction is susceptible to accidents such as loosening, deformation, collapse, and water inrush, especiallyunder complex geological conditions like dense fault areas. These accidents can cause instability and damageto the tunnel. As a result, it is essential to conduct research on tunnel construction and grouting reinforcementtechnology in fault fracture zones to address these issues and ensure the safety of tunnel excavation projects. Thisstudy utilized the Xianglushan cross-fault tunnel to conduct a comprehensive analysis on the construction, support,and reinforcement of a tunnel crossing a fault fracture zone using the three-dimensional finite element numericalmethod. The study yielded the following research conclusions: The excavation conditions of the cross-fault tunnelarray were analyzed to determine the optimal construction method for excavation while controlling deformationand stress in the surrounding rock. The middle partition method (CD method) was found to be the most suitable.Additionally, the effects of advanced reinforcement grouting on the cross-fault fracture zone tunnel were studied,and the optimal combination of grouting reinforcement range (140°) and grouting thickness (1m) was determined.The stress and deformation data obtained fromon-site monitoring of the surrounding rock was slightly lower thanthe numerical simulation results. However, the change trend of both sets of data was found to be consistent. Theseresearch findings provide technical analysis and data support for the construction and design of cross-fault tunnels.

Frost heaving force considering synchronous damage to tunnel lining and surrounding rocks under freeze—thaw cycles

In areas with seasonal freezing,when the tunnel lining concrete is saturated with water infiltrating the interior,the lining and the surrounding rocks will simultaneously freeze.However,the current calculation of the frost heaving force fails to consider the synchronous damage to the lining and surrounding rocks under freeze-thaw cycles.Therefore,as per the elastic calculation model of the frost heaving force and model of steady-state heat transfer of circular tunnels,this study introduces the frost heaving rate of lining and surrounding rocks.First,the analytical solution of frost heaving force is obtained for simultaneous frost heaving of lining and surrounding rocks under any steady-state temperature field.Then,based on the fracture theory and meso-damage mechanics,the damage variables of lining and surrounding rocks under freeze-thaw cycles are extracted,representing their elastic modulus and porosity.Finally,the formula of frost heaving force for synchronous damage to the lining and surrounding rocks at any steady-state temperature field is obtained.The calculation results demonstrate that the lower the temperature inside the lining,the greater the frost heaving force.With the increasing number of freeze-thaw cycles,frost heaving force tends to gradually increase initially,reaching a peak value at 85 freeze-thaw cycles,decreasing to 80%of the peak value at 140 cycles before reaching a constant value.The lining participates in frost heaving,increasing the frost heaving force.The initial increase rate of frost heaving force is 15.7%.Changing the fitting coefficients s1 and s2 of the lining and surrounding rocks can effectively control the magnitude of the frost heaving force in the tunnels.

Forward prediction for tunnel geology and classification of surrounding rock based on seismic wave velocity layered tomography

Excavation under complex geological conditions requires effective and accurate geological forward-prospecting to detect the unfavorable geological structure and estimate the classification of surround-ing rock in front of the tunnel face.In this work,a forward-prediction method for tunnel geology and classification of surrounding rock is developed based on seismic wave velocity layered tomography.In particular,for the problem of strong multi-solution of wave velocity inversion caused by few ray paths in the narrow space of the tunnel,a layered inversion based on regularization is proposed.By reducing the inversion area of each iteration step and applying straight-line interface assumption,the convergence and accuracy of wave velocity inversion are effectively improved.Furthermore,a surrounding rock classification network based on autoencoder is constructed.The mapping relationship between wave velocity and classification of surrounding rock is established with density,Poisson’s ratio and elastic modulus as links.Two numerical examples with geological conditions similar to that in the field tunnel and a field case study in an urban subway tunnel verify the potential of the proposed method for practical application.

Heterogeneity identification method for surrounding rock of large-section rock tunnel faces based on support vector machine

Purpose–The purpose of the study is to quickly identify significant heterogeneity of surrounding rock of tunnel face that generally occurs during the construction of large-section rock tunnels of high-speed railways.Design/methodology/approach–Relying on the support vector machine(SVM)-based classification model,the nominal classification of blastholes and nominal zoning and classification terms were used to demonstrate the heterogeneity identification method for the surrounding rock of tunnel face,and the identification calculation was carried out for the five test tunnels.Then,the suggestions for local optimization of the support structures of large-section rock tunnels were put forward.Findings–The results show that compared with the two classification models based on neural networks,the SVM-based classification model has a higher classification accuracy when the sample size is small,and the average accuracy can reach 87.9%.After the samples are replaced,the SVM-based classification model can still reach the same accuracy,whose generalization ability is stronger.Originality/value–By applying the identification method described in this paper,the significant heterogeneity characteristics of the surrounding rock in the process of two times of blasting were identified,and the identification results are basically consistent with the actual situation of the tunnel face at the end of blasting,and can provide a basis for local optimization of support parameters.

Failure mechanism and control countermeasures of surrounding rock at deep large section chamber intersection in the Wanfu Coal Mine

In order to solve the problem of large deformation at the intersection of deep large section soft rock roadway,this paper takes the intersection of kilometer-deep roadway in the Wanfu Coal Mine as an engineering example and applies Negative Poisson’s Ratio(NPR)steel anchor cable in roadway support for the first time.By combining numerical simulation indoor test,theoretical analysis and field test,the deformation mechanism of surrounding rock at the intersection of deep-buried roadway was analyzed,and the control strategy with micro NPR steel anchor cable as the core was put forward.Through numerical simulation,the numerical analysis model of roadway intersection with different intersection angles and excavation sequence was constructed,and the impact of two key variables of rake angle and excavation sequence on the stability of surrounding rock at roadway intersection was studied.The optimal dip angle is 90°and the optimal excavation sequence was determined as pump house-pump house passage-substation.The mechanical properties of the micro-NPR steel anchor cable were studied through the static tensile test in the laboratory.The results showed that the micro-NPR steel anchor cable showed high constant resistance,uniform tensile,no yield platform,and no obvious necking phenomenon during breaking.Through theoretical derivation,it was calculated that the vertical stress of roadway intersection is 45 MPa,and the bearing capacity of superposed arch composed of micro NPR steel anchor cable is 1257 kN,which is enough to guarantee the overall stability of intersection.Support application test and monitoring were carried out on site,and it was verified that the combined support strategy of short and long micro NPR steel anchor cable has a good control effect on large deformation of surrounding rock at intersection,which provides a new support material and support means for the safety and stabilization control of surrounding rock at intersection.

Propagation characteristics of vibration waves induced in surrounding rock by tunneling blasting

The effect of blasting vibration waves on surrounding rock and supporting structures is an important field in underground engineering. In this paper, the separation variable method is used to solve the displacement potential function for the propagation of the blasting vibration waves. In the axis coordinate system, the particle motion and stress change with axial distance, radial distance and time is obtained in surrounding rock. The peak particle velocity law in surrounding rock under different blast loads and surrounding rock parameters is discussed.In addition, the particle vibration characteristics in the surrounding rock are studied using numerical simulations method. The results shows that the peak particle velocity in surrounding rock appears negative exponent attenuation with the increase of axial distance, but it appears positive and negative fluctuations in radial direction. This phenomenon is a new discovery and it has been rarely investigated before. Moreover, the peak particle velocity attenuates more quickly and intensely in the near blasting field,which means that the supporting structure in a shorter distance away from the heading face is vulnerable to the impact of blasting vibration. Theattenuation of blasting vibration velocity is closely related to charge length, blasting load amplitude,attenuation index and rock elastic modulus. The numerical simulation accomplishes the same results and then demonstrates the validity of theoretical results.

Study on calculation of rock pressure for ultra-shallow tunnel in poor surrounding rock and its tunneling procedure

A computational method of rock pressure applied to an ultra-shallow tunnel is presented by key block theory, and its mathematical formula is proposed according to a mechanical tunnel model with super-shallow depth. Theoretical analysis shows that the tunnel is subject to asymmetric rock pressure due to oblique topography. The rock pressure applied to the tunnel crown and sidewall is closely related to the surrounding rock bulk density, tunnel size, depth and angle of oblique ground slope. The rock pressure applied to the tunnel crown is much greater than that to the sidewalls, and the load applied to the left side-wall is also greater than that to the right sidewall. Mean-while, the safety of the lining for an ultra-shallow tunnel in strata with inclined surface is affected by rock pressure and tunnel support parameters. Steel pipe grouting from ground surface is used to consolidate the unfavorable surrounding rock before tunnel excavation, and the reinforcing scope is proposed according to the analysis of the asymmetric load induced by tunnel excavation in weak rock with inclined ground surface. The tunneling procedure of bench cut method with pipe roof protection is still discussed and carried out in this paper according to the special geological condition. The method and tunneling procedure have been successfully utilized to design and drive a real expressway tunnel. The practice in building the super-shallow tunnel＆amp;nbsp;has proved the feasibility of the calculation method and tunneling procedure presented in this paper.

Deformation mechanism and collapse treatment of the rock surrounding a shallow tunnel based on on-site monitoring

When tunnels are constructed at shallow depths in areas with poor geological conditions,such as portal sections,valleys and hillsides in regions with granitic bedrock,considerable excavation-induced deformation of the surrounding rock may occur,potentially resulting in tunnel collapses.The main reason for these problems is the lack of understanding of the deformation mechanism and evolution of the soft granitic rock surrounding the tunnel and the adoption of inappropriate construction technology and methods.This article analyzes the deformation mechanism of the rock surrounding a shallow tunnel based on in situ monitoring data as a case study and suggests that certain measures should be taken to effectively control the deformation of the surrounding rock and to minimize the potential for tunnel collapse.The results show that the deformation of the granitic soil surrounding the tunnel can be divided into three stages:the rapid deformation stage,the slow deformation stage and the stabilization stage.Appropriate construction methods should be carefully selected to ensure safety during tunnel excavation in the first stage.To avoid secondary disasters caused by tunnel collapses,three treatment measures may be implemented as part of safety management:enhancing the monitoring of the surrounding rock deformation,adjusting the construction methods and optimizing the support systems.In particular,accurate monitoring data and timely information feedback play a vital role in tunnel construction.Therefore,engineers with considerable engineering experience and professional knowledge are needed to analyze the monitoring data and make accurate predictions of tunnel deformation to ensure that reasonable measures are taken in the process of shallow tunnel excavation.

Non-contact monitoring and analysis system for tunnel surrounding rock deformation of underground engineering

It is very important to monitor surrounding rock deformation in tunnel construction. The principle, function, development and application of the system composed of a total station and computer for monitoring and analyzing surrounding rock deformation were discussed. The new methods of two free station of 3D measurement and its mathematic adjustment mode were presented. The development of software for total station on-board and post for computer were also described. Without centering it and measuring its height, the total station controlled by the software on-board can fulfill the whole measurements to target points. Monitoring data can be processed by the post software and results of regression analysis, forecasting information of the tunnel surrounding rock deformation can be provided in time. The practical use shows that this system is practicable, highly accurate and efficient. It satisfies the needs of safety and information construction in tunnel construction of underground engineering.

Vibration Effect and Damage Evolution Characteristics of Tunnel Surrounding Rock Under Cyclic Blasting Loading

Model test studies based on the similarity theory were conducted to investigate vibration effect and damage evolution characteristics of tunnel surrounding rock under push-type cyclic blasting excavation.The model was constructed with a ratio of 1∶15.By simulating the tunnel excavation of push-type cyclic blasting,the influence of the blasting parameter change on vibration effect was explored.The damage degree of tunnel surrounding rock was evaluated by the change of the acoustic wave velocity at the same measuring point after blasting.The relationship between the damage evolution of surrounding rock and blasting times was established.The research results show that：（1）In the same geological environment,the number of delay initiation is larger,the main vibration frequency of blasting seismic wave is higher,and the attenuation of high frequency signal in the rock and soil is faster.The influence of number of delay initiation on blasting vibration effect cannot be ignored;（2）Under push-type cyclic blasting excavation,there were great differences in the decreasing rates of acoustic wave velocity of the measuring points which have the same distance to the blasting region at the same depth,and the blasting damage ranges of surrounding rock were typically anisotropic at both depth and breadth;（3）When blasting parameters were basically kept as the same,the growth trend of the cumulative acoustic wave velocity decreasing rate at the measuring point was nonlinear under different cycle blasting excavations;（4）There were nonlinear evolution characteristics between the blasting cumulative damage（D）of surrounding rock and blasting times（n）under push-type cyclic blasting loading,and different measuring points had corresponding blasting cumulative damage propagation models,respectively.The closer the measuring point was away from the explosion source,the faster the cumulative damage extension.Blasting cumulative damage effect of surrounding rock had typically nonlinear evolution properties and anisotropic characteristics.

Numerical simulation on deformation character of surrounding rock masses of Changjiashan tunnel through the gob of coalmine

Based on the construction project of the Changjiashan tunnel of the freeway,the variety rule of surrounding rock masses of the tunnel through the gob of coalmine wasstudied by using of finite element methed(FEM).The status of the stress and strain,thevariety of the plastic area were simulated in the whole rock mass before and after thetunnel was excavated.The characters of stress and deformation of surrounding rockmasses were analyzed when the tunnel was built.It concluded from the numerical simula-tion that the influence on the tunneling is great when the tunnel passing through the gob ofcoalmine is excavated,and the relative measures should be taken.

Tunnel Surrounding Rock Deformation Characteristics and Control in Deep Coal Mining

In order to study the failure characteristics and control method of deep tunnel surrounding rock, based on the stress test, the structure and stress state of the main transportation tunnel surrounding rock in Mine Zhaogezhuang level 14 was analyzed, and it shows that the surrounding rock is exposed to an interphase hard and soft disadvantageous structure state and complex high stress repeated addition area;Through the theoretical analysis and the statistical data, the relation between the tunnel stress transformation and the surrounding rock deformation was proposed;Through the numerical simulation of the tunnel surrounding rock failure process with the help of RFPA procedure, the results show that the damage of the transportation tunnel level 14 mainly occurs in the bottom and the two coal ribs, and the failure process is spreading from the bottom to the two coal ribs, and the effect of the surrounding rock deformation control is obvious by using the way of 2.5 m anchor with 1.0 m grouting strengthening.

Influence of underground water seepage flow on surrounding rock deformation of multi-arch tunnel

Based on a typical multi-arch tunnel in a freeway, the fast Lagrangian analysis of continua in 3 dimensions(FLAC3D) was used to calculate the surrounding rock deformation of the tunnel under which the effect of underground water seepage flow was taken into account or not. The distribution of displacement field around the multi-arch tunnel, which is influenced by the seepage field, was gained. The result indicates that the settlement values of the vault derived from coupling analysis are bigger when considering the seepage flow effect than that not considering. Through the contrast of arch subsidence quantities calculated by two kinds of computation situations, and the comparison between the calculated and measured value of tunnel vault settlement, it is found that the calculated value(5.7-6.0 mm) derived from considering the seepage effect is more close to the measured value(5.8-6.8 mm). Therefore, it is quite necessary to consider the seepage flow effect of the underground water in aquiferous stratum for multi-arch tunnel design.

Numerical analysis and field monitoring tests on shallow tunnels under weak surrounding rock

The Jianpudong No. 4 tunnel is a shallow tunnel, which belongs to Shaoshan County scenic highway in Hunan province, China and whose surrounding rock is weak. According to its characteristics, the field monitoring tests and numerical analysis were done. The mechanical characteristics of shallow tunnels under weak surrounding rock and the stress-strain rule of surrounding rock and support were analyzed. The numerical analysis results show that the settlement caused by upper bench excavating accounts for 44% of the total settlement, and the settlement caused by tunnel upper bench supporting accounts for 56% of the total settlement. The maximum axial force of shotcrete lining is 177.2 k N, which locates in hance under the secondary lining. The maximum moment of shotcrete lining is 5.08 k N·m, which locates in the arch foot. The stress curve of steel arch has three obvious stages during the tunnel construction. The maximum axial force of steel arch is 297.4 k N, which locates in tunnel vault. The axial forces of steel arch are respectively 23.5 k N and-21.8 k N, which is influenced by eccentric compression of shallow tunnel and locates in hance. The results show that there is larger earth pressure in tunnel vault which is most unfavorable position of steel arch. Therefore, the advance support should be strengthened in tunnel vault during construction process.

New methods of safety evaluation for rock/soil mass surrounding tunnel under earthquake

The objective of this work is to obtain the seismic safety coefficient and fracture surface and proceed with the seismic safety evaluation for the rock mass or soil mass surrounding a tunnel,and the limitation of evaluating seismic stability is considered using the pseudo-static strength reduction.By using the finite element software ANSYS and the strength reduction method,new methods of seismic safety evaluation for the rock mass or soil mass surrounding a tunnel are put forward,such as the dynamic finite element static shear strength reduction method and dynamic finite element shear strength reduction method.In order to prove the feasibility of the proposed methods,the results of numerical examples are compared with that of the pseudo-static strength reduction method.The results show that 1) the two methods are both feasible,and the plastic zone first appears near the bottom corners; 2) the safety factor of new method Ⅱ is smaller than that of new method I but generally,and the difference is very small.Therefore,in order to ensure the safety of the structure,two new methods are proposed to evaluate the seismic stability of the rock mass or soil mass surrounding a tunnel.A theoretical basis is provided for the seismic stability of the rock mass or soil mass and the lining surrounding a tunnel and also provided for the engineering application.

Mechanical response features and failure process of soft surrounding rock around deeply buried three-centered arch tunnel

Due to the extreme complexity of mechanical response of soft surrounding rock(SR) around a tunnel under high geostatic stress conditions, the integration of physical and numerical modeling techniques was adopted. Based on the similarity theory, new composite-similar material was developed, which showed good agreement with the similarity relation and successfully simulated physico-mechanical properties(PMP) of deep buried soft rock. And the 800 mm×800 mm×200 mm physical model(PM) was conducted, in which the endoscopic camera technique was adopted to track the entire process of failure of the model all the time. The experimental results indicate that the deformation of SR around a underground cavern possessed the characteristics of development by stages and in delay, and the initial damage of SR could induce rapid failure in the later stage, and the whole process could be divided into three stages, including the localized extension of crack(the horizontal load(HL) was in the range of 130 k N to 170 k N, the vertical load(VL) was in the range of 119 k N to 153.8 k N), rapid crack coalescence(the HL was in the range of 170 k N to 210 k N, the VL was in the range of 153.8 k N to 182.5 k N) and residual strength(the HL was greater than 210 k N, the VL was greater than 182.5 k N). Under the high stress conditions, the phenomenon of deformation localization in the SR became serious and different space positions show different deformation characteristics. In order to further explore the deformation localization and progressive failure phenomenon of soft SR around the deeply buried tunnel, applying the analysis software of FLAC3 D three-dimensional explicit finite-difference method, based on the composite strain-softening model of Mohr-Coulomb shear failure and tensile failure, the calculation method of large deformation was adopted. Then, the comparative analysis between the PM experiment and numerical simulation of the three centered arch tunnels was implemented and the relationship of deformation localization and progressive failure of SR around a tunnel under high stress conditions was discussed.

Research on the stability analysis and design of soil tunnel surrounding rock

The paper first analyzes the failure mechanism and mode of tunnel according to model experiments and mechanical calculation and then discusses the deficiency of taking the limit value of displacement around the tunnel and the size of the plastic zone of surrounding rock as the criterion of stability. So the writers put forward the idea that the safety factor of surrounding rock calculated through strength reduction FEM(finit element method) should be regarded as the criterion of stability,which has strict mechanical basis and unified standard and would not be influenced by other factors. The paper also studies the safety factors of tunnel surrounding rock (safety factors of shear and tension failure) and lining and some methods of designing and calculating tunnels. At last,the writers take the loess tunnel for instance and show the design and calculation results of two-lane railway tunnel.

Engineering Geological Classification of Surrounding Rock Stability in Coal Mine Tunnels and Its Engineering Applications

The stability type and spatial distribution of surrounding rock are an important basis for the layout of hae tunuels and the selection of support patterns in a mine design. Based on a lot of investigations and testing studies,a new engineering geological classification scheme of surrounding rock stability is put forward,which is easy to be applied,and reliable verified by examples. According to the classification system,the spatial divisions of surrounding rock stability can be delineated in an exploration progamme, providing relevant engineering geological informations for mine designers to prevent them from making the uurealistic tunnel layout and support

基于Bayes-LSTM的公路隧道围岩变形预测方法研究

在公路隧道施工过程中,围岩的稳定性对隧道施工的影响较大。因此公路隧道围岩变形的监控量测与准确预测是保障隧道施工安全的关键。针对当前隧道围岩变形的预测精度较低以及泛化能力较差等问题,该文提出一种基于贝叶斯(Bayes)优化长短期记忆网络(LSTM)的方法,该方法首先对拱顶沉降和周边收敛的原始监测数据进行预处理,而后构建公路隧道拱顶沉降与周边收敛的初始LSTM模型,并利用Bayes优化模型中的超参数,最终得出预测结果。利用该模型对某公路隧道拱顶沉降和周边收敛进行预测,将预测结果以均方根误差为评价指标与神经网络(CNN)和支持向量回归(SVR)进行对比。预测拱顶沉降时,Bayes-LSTM模型的平均预测精度相较于CNN与SVR模型分别提高了1.0与1.26;预测周边收敛时,Bayes-LSTM模型平均精度相较于CNN与SVR分别提高了0.3与0.32。表明Bayes-LSTM模型的预测精度较高,同时其能在训练模型过程中对历史信息进行判断和取舍,极大地提高了时序数据处理的效率,为公路隧道围岩变形预测提供了新的思路和探索。

Time-dependent safety of lining structures of circular tunnels in weak rock strata

Following tunnel excavation and lining completion,fractured surrounding rock deforms gradually over time;this results in a time-dependent evolution of the pressure applied to the lining structure by the surrounding rock.Thus,the safety of the tunnel lining in weak strata is strongly correlated with time.In this study,we developed an analytical method for determining the time-dependent pressure in the surrounding rock and lining structure of a circular tunnel under a hydrostatic stress field.Under the proposed method,the stress–strain relationship of the fractured surrounding rock is assumed to conform to that of the Burgers viscoelastic component,and the lining structure is assumed to be an elastomer.Based on these assumptions,the viscoelastic deformation of the surrounding rock,the elastic deformation of the lining structure,and the coordinated deformation between the surrounding rock and lining structure were derived.The proposed analytical method,which employs a time-dependent safety coefficient,was subsequently used to estimate the durability of the lining structure of the Foling Tunnel in China.The derived attenuation curve of the safety coefficient with respect to time can assist engineers in predicting the remaining viable life of the lining structure.Unlike existing analytical methods,the method derived in this study considers the time dependency of the interaction between the surrounding rock and tunnel lining;hence,it is more suitable for the evaluation of lining lifetime.