Yingchao Wang

Set pair analysis for risk assessment of water inrush in karst tunnels

Considering the uncertain characteristics of water inrush in karst tunnels, the set pair analysis (SPA) method was newly applied in this study for risk assessment of water inrush. First, karst hydrology and engineering geological conditions were considered, and several main influencing factors were selected as evaluation indices, such as formation lithology, unfavorable geology, groundwater level and contact zone of dissolvable as well as other factors. Second, a set pair was established with the combination of the evaluation indices and the standards of risk grade. Then, the evaluation indices of water inrush were divided into two main types: economic and cost indices. Based on set pair analysis (SPA), the graded connection degrees of evaluation indices were calculated. Finally, the established risk evaluation model of water inrush with set pair analysis was applied to the Jigongling tunnel on the line of the Fanba expressway in China. The results not only are consistent with the results of the attribute mathematical theory, but also agree well with practical situations. In addition, the method of set pair analysis used in this study could provide relatively high accuracy when applied to risk assessment of water inrush in karst tunnels. Meanwhile, SPA is simple, feasible and easy to implement. The presented method has been validated as an effective method of risk assessment for water inrush, which also has good prospects for further engineering applications.

A novel cloud model for risk analysis of water inrush in karst tunnels

Water inrush is a serious geological hazard in underground engineering. The prediction of possibility and classification of water inrush risk has long been a global problem for the construction of deep-buried tunnels in karst areas. To solve the randomness and fuzziness in the evaluation process of water inrush risk, a novel comprehensive evaluation model was established based on the normal cloud theory. According to the systematic analysis of the influence factors of water inrush, seven factors were selected as evaluation indices, including formation lithology, unfavourable geological conditions, groundwater level, landform and physiognomy, modified strata inclination, contact zones of dissolvable and insoluble rock, and layer and interlayer fissures. Meanwhile, a hierarchy model of the influence factors was established for water inrush, and the analytic hierarchy process was adopted to determine the weighting coefficients for each evaluation index. The normal cloud theory was used to describe the cloud numerical characteristics for each evaluation index of risk classification for water inrush. Normal cloud droplets were generated to reflect the uncertain transformation between the risk levels of water inrush and the evaluation indices. Then, the synthetic degrees of certainty were calculated, and risk level of water inrush was determined. Finally, the proposed model was applied to two typical deep-buried tunnels in karst areas: Jigongling tunnel and Xiakou tunnel. The obtained results were compared with the relevant analysis results and the practical findings, and reasonable agreements were gained. The normal cloud model was found to be more accurate, feasible and effective for risk classification of water inrush prediction. It can not only meet the requirement of tunnel engineering, but also be extended to various applications.

Elastic Analysis for Subaqueous Tunnel Surrounding Rock via the Complex Variable Method

Generally speaking, the subaqueous tunnels can be regarded as the shallow-buried ones. Consequently, the classical problem of an elastic half plane with a round cavity, loaded arbitrarily along the surface boundary, can be used to obtain the stress and displacement fields of the surrounding rock for this type of tunnels. The solution uses the complex variable method, with a conformal mapping onto a circular ring in the image plane. Because of the convergence of the complex potentials throughout the annular region, the coefficients in the Laurent series expansion form for complex functions can be determined by a system of liner recurrent equations, obtained from both the horizontal and the cavity boundary conditions. The stresses and deformations of the surrounding rock can then be calculated via some relevant equations. The whole calculation program should be coded by Fortran language. As an example, the case of a specific underwater tunnel is considered in some detail eventually.

Prediction of Collapse Scope of Deep-Buried Tunnels Using Pressure Arch Theory

Tunnel collapse remains a serious problem in practice. Effective prediction methods on tunnel collapse are necessary for tunnel engineering. In this study, systematic study on the pressure arch was presented to predict tunnel collapse. Multiple factors under different conditions were considered. First, the pressure arch was described as a certain scope in comparison with the lowest pressure arch line. Then, a deep-buried circular tunnel was selected as the investigated object. Its collapse scope was analyzed using the lowest pressure arch line. Meanwhile, the main influence from the ground stress field was considered. Different modes of ground stress fields were investigated in detail. The results indicate that the collapse scope varies with different ground stress fields. Determination on the collapse scope is strongly affected by the judgment standard of the pressure arch. Furthermore, a selected case was analyzed with the pressure arch. The area and the height of tunnel collapse were calculated with multiple factors, including ground stress field, judgment standard, and lateral pressure coefficient. Finally, selected results were compared with relevant previous researches, and reasonable results were obtained. The present results are helpful for further understanding of the tunnel collapse and could provide suitable guidance for tunnel projects.

Effect of a Fault Fracture Zone on the Stability of Tunnel-Surrounding Rock

AbstractThe fault fracture zone is vital to the stability of the surrounding rock of tunnels in geological engineering. In this study, a three-dimensional numerical model was established for Wuzhuling Tunnel of Zhuji-Yongjia Highway in Zhejiang Province, China. The dynamic processes of tunnel excavation were simulated through the fault fracture zone. The deforming performance and stress distribution of surrounding rock were investigated. Moreover, the stability of surrounding rock in tunnels was analyzed with consideration of the slope angle and the width of the fault. The simulation results indicate that the fault fracture zone in the tunnel can reduce the stability of surrounding rock. The slope angle and the width of the fault all have obvious influences on the stability of surrounding rock in tunnels. Furthermore, the collapse processes of a tunnel in the construction steps were investigated in a laboratory model. Reasonable agreements can be obtained to validate the model presented here and the simul...

Strength degradation and anchoring behavior of rock mass in the fault fracture zone

Rock mass in the fault fracture zone has some characteristics such as low strength and poor self-stability, so the control mechanism of stability has been a difficulty in the research of underground engineering. A set of laboratory simulation method of fault fractured rock mass is developed to reflect the natural forming process of fault fracture zone. Compared with intact rock mass, the fault fractured rock mass has an obvious degradation in strength and deformation parameters, and the degradation index is between 22.79 and 84.06%. The bolt has a certain supporting effect on the fault fractured rock mass, and in the situation of end anchoring, the greater the pretightening force is, the better the enforcement effect will be. The stress field produced by high pretightening force can relieve the stress concentration around the bolt hole and make the initial cracks of rock mass away from the bolt plate. The evolution curve of bolt axial force in the process of uniaxial compression of large-scale specimen shows four stages, which are the initial compression stage, pre-peak joint load-bearing stage, post-peak joint load-bearing stage and the residual stage. Research results could provide some theory reference for the stability control of rock mass in the fault fracture zone.

A Novel Model of the Ideal Point Method Coupled with Objective and Subjective Weighting Method for Evaluation of Surrounding Rock Stability

The classification of surrounding rock stability is the critical problem in tunneling engineering. In order to decrease engineering disasters, the surrounding rock stability should be accurately evaluated. The ideal point method is applied to the classification of surrounding rock stability. Considering the complexity of surrounding rock classification, some factors such as rock uniaxial compressive strengthen, integrality coefficient of rock mass, the angle between tunnel axis and the main joint, joints condition, and seepage measurement of groundwater are selected as evaluation indices. The weight coefficients of these evaluation indices are determined by the objective and subjective weighting method, consisting with the delphi method and the information entropy theory. The objective and subjective weighting method is exact and reliable to determine the weights of evaluation indices, considering not only the expert’s experiences, but also objectivity of the field test data. A new composite model is established for evaluating the surrounding rock stability based on the ideal point method and the objective and subjective weighting method. The present model is applied to Beigu mountain tunnel in Jiangsu province, China. The result is in good agreement with practical situation of surrounding rock, which proves that the ideal point method used to classify the surrounding rock in tunnels is reasonable and effective. The present model is simple and has very strong operability, which possesses a good prospect of engineering application.

A predictive model correlating permeability to two-dimensional fracture network parameters

This study presents a predictive model of permeability with correlation to parameters of two-dimensional fracture networks, including mass density of fractures (dm), average number of intersections per meter at the inlet and outlet boundaries (din), and connectivity (Cr). The fracture networks were constructed by considering the influence of fracture number density, fracture length, orientation, and variance of fracture length. A total of 86 discrete fracture network (DFN) models were established using the Monte Carlo technique, and the relationships between permeability and dm, din, and Cr were analyzed. By fitting these calculated results, a multi-variable regression function was proposed for predicting permeability. The results show that the number density of fractures plays a more significant role in permeability than fracture length. Fracture orientation can change the connectivity of fracture networks robustly, and thereafter influence the permeability. Although variance of fracture length can affect the pattern of cumulative frequency – fracture length curves, the variance has negligible influence on the permeability of fracture networks. A necessary condition to form connected flow paths from inlet boundary to outlet boundary is: dmu2009>u20090.27xa0m/m2, dinu2009>u20090.19 /m, and Cru2009>u20091.20. The proposed regression function can predict permeability with a correlation coefficient larger than 0.87, and its validity is verified by comparisons with results reported in the literature. Finally, the potential future works that can facilitate the predictive models of permeability are pointed out as open questions.