Mountain Tunnel Construction Research Articles

Fuzzy Comprehensive Evaluation of Collapse Risk in Mountain Tunnels Based on Game Theory

In view of the problem that mountain tunnel construction is prone to collapse risk and disaster accidents, this paper proposes a fuzzy comprehensive evaluation method based on CRITIC and D-AHP combined weighting, which can effectively improve the accuracy of mountain tunnel collapse risk evaluation and reduce construction risks. This method combines the improved subjective weighting method D-number analytic hierarchy process and the more scientific and reasonable objective weighting method CRITIC method for combined weighting and uses game theory to optimize the weights, which improves its accuracy compared to traditional evaluation methods and makes up for the lack of subjective and objective weighting of a single evaluation method. The results show that the introduction of the D-number theory can reduce the impact of an uncertain environment on the evaluation results. The risk levels of the sample sections are all between three and four, which is consistent with the actual situation of the project, indicating that the evaluation model is feasible.

Study on Risk Management of Rescue Construction of Mountain Tunnels

Study on Risk Management of Rescue Construction of Mountain Tunnels

Study on waterproof and drainage technology of mountain tunnel in high-pressure and water-rich region

High-pressure groundwater brings great challenges to the construction of mountain tunnels. Hence, controlling and discharging groundwater are two key problems that must be addressed before constructing tunnels in high-pressure and water-rich region. Fluid–solid coupling seepage analysis method is used to analyze the variation of displacement, stress and pore water pressure of the tunnel. A waterproof and drainage method suitable for tunnels in high-pressure and water-rich region is proposed. Curtain grouting plays a dual role in waterproof and reinforcing surrounding rock. Decompression drainage holes are designed in order to further reduce the pore water pressure acting on the initial lining. The thickness of grouting circle, the permeability coefficient ratio and the decompression drainage holes distribution rate of the initial lining are the main factors that affect the waterproof and drainage effect of tunnels in high-pressure and water-rich region. Suggested parameters on waterproof and drainage measures for tunnels in high-pressure and water-rich region are given after comprehensive analysis, which can provide basis for the technology on high-pressure groundwater treatments and constructions of underground engineering under complex geological conditions.

Static and dynamic fuzzy assessment methods for the collapse risk of mountain tunnel construction

The static risk assessment method has difficulty tracking variations of the risk level, which is not conducive to the dynamic control of construction. Tunnel collapse during the construction of mountain tunnels has a dynamic evolution law and contains great risk of harm, and the corresponding dynamic risk assessment is extremely important. This study proposes a static and dynamic fuzzy uncertainty assessment method for the collapse risk of mountain tunnels. First, 150 tunnel collapse accidents were investigated and analysed, and the static and dynamic risk assessment index system of mountain tunnel construction collapse was established. Second, the DEMATEL method is processed by applying fuzzy logic, the subjective weight of each index is calculated, and the interaction between the indexes is analysed. Finally, the traditional VIKOR method is improved upon, and the weight of each assessment index is coupled and analysed. A static and dynamic uncertainty assessment model of the construction collapse risk of multiple construction sections is constructed. This method has been successfully applied to the risk assessment of tunnel collapse, and the assessment results are consistent with the actual construction situation. This study provides a new method for the static and dynamic assessment of mountain tunnel collapse risk.

Safety Resilience Assessment of Mountain Tunnel Construction based on Grey Correlation Degree

Safety Resilience Assessment of Mountain Tunnel Construction based on Grey Correlation Degree

Multi-source data integration and multi-scale modeling framework for progressive prediction of complex geological interfaces in tunneling

A reliable geological model plays a fundamental role in the efficiency and safety of mountain tunnel construction. However, regional models based on limited survey data represent macroscopic geological environments but not detailed internal geological characteristics, especially at tunnel portals with complex geological conditions. This paper presents a comprehensive methodological framework for refined modeling of the tunnel surrounding rock and subsequent mechanics analysis, with a particular focus on natural space distortion of hard-soft rock interfaces at tunnel portals. The progressive prediction of geological structures is developed considering multi-source data derived from the tunnel survey and excavation stages. To improve the accuracy of the models, a novel modeling method is proposed to integrate multi-source and multi-scale data based on data extraction and potential field interpolation. Finally, a regional-scale model and an engineering-scale model are built, providing a clear insight into geological phenomena and supporting numerical calculation. In addition, the proposed framework is applied to a case study, the Long-tou mountain tunnel project in Guangzhou, China, where the dominant rock type is granite. The results show that the data integration and modeling methods effectively improve model structure refinement. The improved model's calculation deviation is reduced by about 10% to 20% in the mechanical analysis. This study contributes to revealing the complex geological environment with singular interfaces and promoting the safety and performance of mountain tunneling.

Probabilistic generic transformation model between two rock mass properties: specific fracture energy and P-wave velocity

This study proposed a probabilistic generic transformation model between two rock mass properties, specific fracture energy, Ev, and P-wave velocity, VP. To build the transformation model, 12 pairwise data sets of Ev and VP were collected from six different construction sites involving construction of mountain tunnels in Japan. This database is labeled as “RockMass/2/350”. A probabilistic transformation model was built based on a bivariate standard normal distribution with these 350 data points. The model is generic, because it is based on a variety of sites. The performance of the constructed transformation model was evaluated through a cross-validation. It was found that 98.2% of the validation data fell within the computed 95% confidence interval of the model estimation, and this result provides a preliminary validation of the probabilistic transformation model. Unlike existing deterministic transformation models for estimating VP from Ev, the proposed model can explicitly evaluate the transformation uncertainty with a quantitative metric such as a percentile. For practical application, a 3D model of the spatial distribution for Young’s modulus, E, was visualized based on the proposed transformation model. Since the proposed model is probabilistic, it can provide the spatial distribution for percentiles of E values. The constructed 3D model presented in this paper can be directly used as an input data for finite element or finite difference analysis, and probabilistic evaluation of excavation simulation is feasible based on the proposed probabilistic model. The quantitative information on such uncertainty can be useful in decision-making for tunnel constructions, such as selection of a cautious characteristic value.

BIM-based digital platform and risk management system for mountain tunnel construction

During the construction of mountain tunnels, there are often various intricate and mutable potential hazards, the management and control of which are crucial to ensuring the safety of such construction. With the rapid advancement of engineering information technologies, including Building Information Model (BIM), the internet, big data, and cloud computing, dynamic management of mountain tunnel construction will inevitably become a prevailing trend. This paper proposes a new digital approach to realize the informatization and visualization of risk management in mountain tunnel construction, by combining monitoring measurement with advanced geological prediction based on BIM technology. The proposed approach suggests a BIM-based digital platform architecture for mountain tunnel construction, which is comprised of five layers—basic, model, data, application, and user. The integration of these five layers can realize risk management information during the construction of mountain tunnels. In addition, a set of dynamic risk management systems, including risk monitoring, identification, and assessment, can be established based on the digital platform. The digital platform and dynamic risk management system proposed in this paper have certain advantages in the construction of mountain tunnels, providing a new and significant way for the management of safety risks in such construction projects.

Prediction of the Tunnel Collapse Probability Using SVR-Based Monte Carlo Simulation: A Case Study

Collapse is one of the most significant geological hazards in mountain tunnel construction, and it is crucial to accurately predict the collapse probability. By introducing the reliability theory, this paper proposes a calculation method for the collapse probability in mountain tunnel construction based on numerical simulation, support vector regression (SVR), and the Monte Carlo (MC) method. Taking the Jinzhupa Tunnel Project in Fujian Province as a case study, three-dimensional models were constructed, and the safety factors of the surrounding rock were determined using the strength reduction method. By defining the shear strength parameters of the surrounding rock as random variables, the problem was formulated as a reliability model, and the safety factor was chosen as the reliability index. To increase computational efficiency, the SVR model was trained to replace numerical simulations, and the MC method was adopted to calculate the probability of collapse. The results showed that the cause of the collapse was the change in the excavation method and the very late installation of supports. The feasibility and reliability of the proposed method have been verified, indicating that the method can be used to predict the probability of collapse in a practical risk assessment of mountain tunnel construction.

Evaluation of displacement prediction method for mountain tunnels showing time-dependence characteristics

During construction of mountain tunnels or in service, the ground behavior may show time-dependence characteristics in the acceleration stage. In such cases, in order to quickly consider the scale of displacement suppression, a method that can easily predict future displacement is required. Therefore, we proposed a structural deteriorating type of the Voigt model (called “the D-Voigt model”) that incorporates the structural deterioration mechanism into the Voigt model. When the strain increases, this model assumes that the elastic modulus of the spring and the viscosity coefficient of the dashpot decrease. Three exact solutions are derived from the constitutive equations of this model. These exact solutions can express not only the ground behavior of the deceleration/convergence stage, but also the ground behavior of the constant-velocity stage and the acceleration stage. Next, through an example of actual data from the service tunnel, it was clarified that this model can reproduce measurement results showing time-dependence characteristics in the acceleration stage and is useful as a prediction method of future displacement. At the same time, we devised a method to identify the coefficient of this model from the measurement results and clarified that it is highly effective.

Rock Crushing Analysis of TBM Disc Cutter Assisted by Ultra-High-Frequency Loading

In the construction of mountain tunnels, the increasing proportion of hard rock stratum enhances the difficulty of rock breaking by tunnel boring machine (TBM). As a type of cyclic load with ultrahigh frequency, ultrasonic vibration has the advantages of energy concentration and strong penetration. In the process of rolling and extrusion, the weakening of the rock by ultrahigh-frequency loading can improve the rock crushing efficiency of the TBM disc cutter. In this study, we established a physical model of rock cutting using a disc cutter assisted by ultrasonic vibration and obtained a motion equation. The discrete element software particle flow code (PFC) was selected to construct a heterogeneous granite model to demonstrate the mechanism and development of cracks inside the hard rock under a rolling disc cutter assisted by ultrasonic vibration. The results demonstrate that ultrasonic vibration helps the disc cutter construct a stronger stress field in the shallow layer, which promotes tensile damage of the surface rock. Vibration promotes the development of cracks inside the rock and accelerates the penetration of transverse cracks, which is conducive to the stripping of rock fragments. The addition of ultrahigh-frequency loading also reduces the fluctuation increase of cracks, which makes the operation state of the disc cutter more stable and avoids abnormal damage to tools.

Stability predictions for excavations of mountain tunnels based on [BQ] method and its field verification

In response to the engineering problems often encountered during the construction of mountain tunnels, the aim of this study is to overcome the inability of numerical simulation methods to rapidly predict tunnel construction based on the [BQ] method of classifying surrounding rock grades. Numerical simulations were carried out using FLAC3D6.0 software based on previous empirical formulas for each parameter of the GSI scores and Hoek-Brown criterion. Relying on the Luanlu Highway Tunnel Project, the engineering problems of the Nianpan and Dahongyan tunnels were firstly identified, followed by numerical simulations to quickly obtain construction predictions for the proposed changes, and finally, engineering monitoring was carried out to verify the feasibility of the method. The results indicate that [BQ] = 311 for the water gushing section of the Nianpan Tunnel, which should be changed from Class III to IV surrounding rock and constructed according to the support scheme for Class IV surrounding rock, corresponding to GSI[BQ] = 43. The maximum load-bearing ratios of the secondary lining for ordinary Class III, seepage Class III and Class IV surrounding rocks are 24.2 %, 25.4 % and 34.7 % respectively. For the Dahongyan Tunnel, the change in the length of the anchors should be adjusted to from 3.0 m to 3.5 m and the distance of the secondary lining from the excavation face changes from 40 m to 46 m. Moreover, the secondary lining load sharing ratio at the monitoring point of the maximum load of the section secondary lining generally doesn’t exceed 35 %. The method can be used as a reference for other tunneling problems.

Study on the Mechanical Behavior of Fluid–Solid Coupling in Shallow Buried Tunnels under Different Biased Terrain

In the construction of mountain tunnels, biased and water-rich strata are often encountered. During tunnel excavation, the fluid–solid coupling has a great influence on the stability of the surrounding rock. This effect will be more severe when the terrain is biased. The bias tunnel points out the asymmetric load of the rocks which are surrounding the tunnels through the drilling or construction process due to the topographic situation. These loads can cause inverse actions during tunnel construction. Therefore, the effect of fluid–solid coupling on the displacement field, stress field, and seepage field of the tunnel surrounding rock under different biased terrains are studied in this paper. In the context of the Youzishu tunnel project, the numerical model is established to define the degree of terrain bias. Besides, the concept of bias coefficient is introduced. To achieve what is needed, 10 sets of increasing bias coefficients are obtained, by changing the inclination of the terrain to study the influence of formation bias degree on tunnel excavation in water-rich formations. After an in-depth analysis of the simulation results, it is found that the influence of fluid–structure interaction cannot be ignored. By analyzing ten groups of data under different working conditions, the biased terrain will aggravate this effect. As far as the displacement field of the surrounding rock is concerned, the biased formation has a greater impact on the deeply buried side than on the shallow-buried side, and has a greater impact on the vault than on the arch bottom. In addition, by analyzing the stress field and seepage field of the surrounding rock, a similar result can be obtained: the influence of formation bias on the deeply buried side is greater than that on the shallow-buried side, and the biased terrain will increase the pore pressure outside the tunnel lining and increase the water inflow. Finally, the locations where the displacement, stress, water pressure, and water inflow are the largest during the tunnel excavation process are found by the simulations and analyzed. Thus, attention can be paid to these locations, permitting a focus on protection during the construction process.

Structural failures and geohazards caused by mountain tunnel construction in fault zone and its treatment measures: A case study in Shaanxi

Tunneling in fault zone presents considerable challenges to the engineer, including the unexpected failure of supporting structures and the unpredictable geohazards. This paper provides a case study about the structural failures and treatment measures during the construction of the Shengli tunnel crossing the fault fracture zone. During the fault fracture zone construction, structural failures and geohazards such as large deformation of primary lining, water inflow, and collapse were encountered. Before the collapse, the maximum displacement rate of the surrounding rock was 71.7 mm/d, and the extreme deformation of the lining was characterized by the large vault settlement and asymmetric deformation. Combined with on-site monitoring, laboratory tests, and meteorological investigations, the mechanism of structural failures was analyzed. Rocks with low bearing capacity and strong softening, extremely broken rock mass, and abundant groundwater were the main factors leading to the tunnel structural failures. To reduce the adverse effect of fault fracture zone, a series of comprehensive treatment measures were put forward from the aspects of the treatment of collapse body, advanced support, reinforcement of lining, and adjustment of the construction method. Through the field monitoring data of the processing section, the effectiveness of the adopted countermeasures was verified. Based on the monitoring data and field investigations, the process of failures and the rationality of treatment measures were discussed. These results can provide theoretical and technical experience for future similar projects.

Improved Hybrid Reasoning Approach to Safety Risk Perception under Uncertainty for Mountain Tunnel Construction

AbstractTunnel projects in mountainous areas are considered a kind of high-risk work due to the complexity of geological conditions, as well as the diversity of construction and management factors....

Effect of localized water pressure on mountain tunnels crossing fracture zone

Localized Water Pressure (LWP) on tunnel means water pressure concentrating on partial areas of tunnel periphery instead of distributing evenly all around tunnels. High LWP generally occurs in tunnels crossing mountain areas with faults and fracture zones or results from clogging of the water drainage system of tunnels. High LWP on tunnels could lead to severe structural cracks and leakages. A mountain tunnel in fracture zones with LWP of nearly 2 MPa was taken as an example to investigate the acting mechanism and effect of LWP on the safety of the tunnel lining during the whole process of the tunnel crossing through the fracture zone by a 3D Ground-Structure modeling. The main conclusions drawn from the research work are as follows: (1) The LWP acting on the tunnel lining dynamically changes in both magnitude and distribution (longitudinal and cross-sectional) with the advance of the tunnel face. The magnitude of LWP in the fracture zone is up to 17.9 times higher than that outside the fracture zone and can lead to damage to the tunnel structure. The main distribution scope of the LWP on the lining structure is within 8 m from the boundary of the fracture zone. (2) The actual internal forces of lining near the tunnel face are highest, and the tunnel structure in the fracture zone and within 16 m outside the fracture zone is at risk of crushing induced by high LWP. (3) Cutoff grouting is effective in reducing the LWP and the axial force remarkably with a decrease of 52.4% and 76.8%, respectively. The necessary thickness of the grouting ring for the tunnel crossing fracture zone is set to 6 m. (4) A novel drainage network was proposed to improve the reliability and sustainability of the drainage system of the tunnel in the fracture zone with high water pressure. The results of this study provide practically useful suggestions for the design and construction of mountain tunnels crossing fracture zones of high LWP.

Field testing and numerical modelling of fog production and control in the construction of mountain tunnels

Fog frequently appears in the portal area of mountain tunnels under construction in cold seasons because of the vast air temperature and air humidity differences between the inside and the outside of the tunnel. It consequently reduces visibility and causes accidents in the construction of mountain tunnels. In this study, field test on air temperature, air relative humidity, wall temperature and air velocity was initially performed in an inclined shaft of a mountain tunnel under construction in a typical winter day. The atmospheric temperature was −2 °C and fog was observed within the range of 550 m from the portal in the shaft. The test results show that the longitudinal air and wall temperatures have a linear increase, and the lowest air and wall temperatures are 16.8 °C and 14.9 °C at the portal, respectively. Furthermore, fog disappears when the air relative humidity is lower than 99% in the inclined shaft. Next, a computational fluid dynamics (CFD) model, solving the species transport and energy models, was established to reproduce the test. The comparison of the air temperature shows a good agreement. The fog lengths in the inclined shaft are 550 m for the test and 600 m for the simulation. This CFD model was then employed to study the effects of the inflow air relative humidity and the wall temperature on fog production and distribution in the inclined shaft. The results show that fog is produced when the inflow air relative humidity is above 86.6%, and the fog length increases significantly with the increase of the inflow air relative humidity. Additionally, the fog length also increases with the decrease of the wall temperature when the wall temperature at the portal is lower than 16.9 °C. An insulation layer imposed on the wall is accordingly proposed and its length is suggested over 50 m longer than the fog length to prevent fog production.

Study on Stability of Surrounding Rock of Mechanized Construction in Tunnel Entrance Section

With the development of tunnel construction technology and mechanical equipment, the mechanized drilling and blasting construction of mountain tunnels has gradually developed, but there are still certain problems in the mechanized tunnel entry. Relying on a tunnel project in Yunnan, this article uses FLAC3D software to study the stability of surrounding rock under the condition of mechanized large-section construction of shallow buried section of the tunnel entrance. When the shallow buried section of the cave entrance is constructed by the micro-step method, the surrounding rock displacement and plastic zone changes of the surrounding rock before and after the use of different cyclic footage and the tunnel face reinforcement when the tunnel face is used are compared and analyzed. The results of the study show that when the tunnel face is not reinforced, in order to ensure the safety of construction, the mechanized excavation cycle footage of the tunnel entrance section should be controlled within 1.2m, and the overlap length of the leading pipe shed should be greater than 5m; if the circulation is to be increased for footage, the tunnel face must be reinforced. Under the condition that the tunnel face is reinforced with glass fiber anchors with a length of 10m and a pitch of 1.5m, the cycle footage can be increased to 1.8m at most.

Unascertained Measure-Set Pair Analysis Model of Collapse Risk Evaluation in Mountain Tunnels and Its Engineering Application

Collapse is a major geological disaster that occurs during mountain tunnel construction. However, the accuracy of collapse risk assessment is generally restricted by evaluation factors or methods. This paper proposes a novel integrated collapse risk evaluation method for mountain tunnels based on case-based reasoning, rough set theory, and unascertained measure-set pair analysis (UM-SPA) theory. First, the risk surroundings and risk factors involved in tunnel collapse are summarized by the analytic hierarchy process, and a preliminary risk evaluation index system is established. Then, an attribute reduction algorithm based on the conditional information entropy of a rough set is proposed and applied to cases with similar attribute characteristics as those of the tunnel to be evaluated, to remove the relatively insignificant or redundant indices and improve the reliability of risk assessment. Finally, taking the relationship between tunnel collapse and its evaluation indices as an unascertained system, Set Pair Analysis (SPA) theory is introduced to optimize the credible degree recognition criteria of unascertained measure theory (UMT). Combined with the modified entropy weight method, a UM-SPA model for tunnel collapse risk evaluation is established to calculate the level of collapse risk quantitatively and predict the development trend of risk dynamically. Taking Xiucun Tunnel passing through fault F18 as an example, collapse risk is evaluated and compared with the evaluation results of traditional UMT and field status. The results demonstrate the feasibility and efficiency of the proposed approach and provide a new idea for collapse risk prediction while constructing mountain tunnels.

A novel dynamic impact pressure model of debris flows and its application on reliability analysis of the rock mass surrounding tunnels

Assessing the influence of the impact pressure exerted on surrounding rock mass by potential debris flows is one of the challenges in a mountain tunnel construction project. This paper proposes an effective mathematical model for the assessment of impact pressure exerted by debris flows on obstacles. The characteristics of the new model are analyzed, and the parameters determination method for the new model are deduced. Also, a new method for dynamic reliability analysis of the rock mass surrounding tunnels is proposed and is constituted into three key steps. First, by inputting impact pressure of debris flows generated by the aforementioned new model, the FLAC3D is used as the dynamic analysis engine to obtain the time-varying stress distribution of surrounding rock mass during the impact of debris flow. Second, the factor of safety (FOS) contours of surrounding rock mass are generated based on element states using the maximum tensile stress criterion and the Mohr-Coulomb yield criterion. Third, by using the time-varying contours of the FOS, a failure probability and a reliability index are obtained from a reliability perspective. A case study shows the complete analysis process and confirms the effectiveness of the above methodology. In sum, this paper provides new ideas, new methods, and a reference example for evaluating the influence of dynamic impact exerted by debris flows on the rock mass surrounding tunnels.