Tunnels In Rock Masses Research Articles

A LightGBM-based strategy to predict tunnel rockmass class from TBM construction data for building control

Identification of rockmass class before construction is crucial to the safe and high-efficiency building of underground tunnels and has been a challenge for long water diversion tunnels. This paper is devoted to developing the LightGBM-based strategy for on-site rockmass class prediction in long tunnels from TBM construction data. The LightGBM-based strategy optimizes the input features and hyperparameters automatically by combining the tree-structured Parzen estimator (TPE), the light gradient boosting machine (LightGBM), and Shapley Additive exPlanations (SHAP) and establishes rockmass prediction models with data of various structures in 7505 TBM tunneling cycles in the Yinsong tunnel of 17.488 km long. The LightGBM-based strategy has an accuracy of 92% on the testing set, outperforms the random forest and support vector machines on the Yinsong tunnel data, and shows good generalization ability in the TBM7 tunnel in Xingjiang. The work contributes to the intelligent and efficient construction of long TBM tunnels.

Influence of Anisotropic Stress Conditions on Tunnel Deformation and Sequential Excavation Performance in Rock Mass

Abstract This study looks at how anisotropic stress conditions affect the mechanical response of circular tunnels in rock mass using a finite element plane strain model. The deformation response and evolution of the yield zone are evaluated using a non-linear Hoek-Brown failure criterion. The results show that predictions made under the widely employed assumption of isotropic stress conditions significantly underestimate the deformations for in-situ stress ratios greater than 1.0 and overestimate the values for in-situ stress ratios less than 1 under full-face excavation. The pattern of the yield zone changes noticeably as the in-situ stress ratio changes. With stress anisotropy, the yield zone becomes asymmetric. When the in-situ stress ratio is less than 1.0, the yield zone concentrates on the sidewalls and transitions to the crown when the in-situ stress ratio assumes values greater than 1.0. Also, the effect of anisotropic stress conditions on the performance of two commonly used excavation support schemes is studied. The results emphasize the importance of consideration of the in-situ stress ratio for prediction of tunnel deformation and selection of sequential excavation schemes.

Study on cyclic blasting failure characteristics and cumulative damage evolution law of tunnel rock mass under initial in-situ stress

Although in-situ stress significantly affects tunnel rock mass excavation blasting, the crack propagation law of the rock mass under both in-situ stress and cyclic blasting load has not been adequately evaluated. The blasting failure mechanism of rock mass and the cumulative damage evolution effect of cyclic blasting load under different ground stress conditions are systematically studied herein through theoretical analyses, laboratory tests, and numerical analyses. First, the Riedel–Hiermaier–Thoma (RHT) constitutive model is modified and calibrated, and its reliability is improved via an indoor split Hopkinson pressure bar splitting test. Second, the blasting failure analysis model of the dynamic and static load coupling field is established and verified via numerical simulation. Finally, a numerical simulation of the smooth blasting excavation of a rock tunnel is conducted, and the blasting failure mode of a rock tunnel subjected to ground stress is discussed. Notably, the modified and calibrated RHT model can adequately simulate dynamic crack propagation in limestone specimens. Due to the effect of ground stress, the maximum principal stress side is the most favourable direction for blasting crack propagation. The direction of blasting crack propagation is mainly determined by the loading conditions of ground stress, and the number of blasting cycles does not significantly affect the law of rock crack propagation. Smooth blasting during rock tunnel excavation can effectively reduce the dynamic response of surrounding rock in the unexcavated area. Optimizing the cutting-hole and delayed-blasting parameters can improve the blasting quality of tunnel rock mass under in-situ stress.

Effect of horizontal stress on the mesoscopic deformation and failure mechanism of layered surrounding rock masses in tunnels

The deformation and failure behaviors of layered surrounding rocks under high in-situ stress are important indicators for tunnel stability evaluation. The attitude of bedding planes is too complex, which impedes the understanding of the rock deformation mechanism under different horizontal stress, especially from the microscopic perspective. In this study, high-precision and easy-to-prepare 3D printing materials are used to simulate layered rock masses. The biaxial loading test system is adopted to explore the creep properties of layered rocks during tunnel excavation in the case of different horizontal stress. The mesoscopic deformation field and failure evolution mechanism of the layered surrounding rocks are revealed using digital image correlation technology. The test results are verified with the numerical simulation method. The shear displacement and plastic strain zone of surrounding rocks in the case of different layer dip angles are studied, and the plastic failure region is given. This paper provides significant experimental and theoretical guidance for the excavation and support of layered soft rock tunnels.

Quantitative granitic weathering assessment for rock mass classification optimization of tunnel face using image analysis technique

Weathering degree is one of the key criteria used to determine tunnel support with the main difficulty is in assessing the weathering grade of the tunnel face. This study applied CIEL*a*b colour space and image analysis to a rock mass tunnel face. The authors used the Japanese Highway (JH) Rock Mass Classification System to classify the rock mass tunnel face. JudGeo converted the RGB photographs to L*a*b values. This study compared the quantitative evaluation system's performance to manual tunnel face mapping by geologists using six JH Rock Mass Classification samples (Class B, CI, CII, DI, DII, and E). The analysis showed good correlations between four (B; CI; CII; DI) of six rock mass classes. The tunnel face mapping showed two rock mass classes above grade (DII and E). This technique can effectively identify the degree of weathering grades of the tunnel face, especially for fresh to moderately weathered tunnel faces.

Prevention and Control Analysis of Rockburst Using Drilling Pressure Relief in Surrounding Rock Mass of Deep Tunnel

Prevention and Control Analysis of Rockburst Using Drilling Pressure Relief in Surrounding Rock Mass of Deep Tunnel

Elasto-plastic analysis of the surrounding rock mass in circular tunnel using a new numerical model based on generalized nonlinear unified strength theory

It is proposed a new numerical model based on the generalized nonlinear unified strength theory (GNUST). Based on the modified continuous multi-segment plastic flow rule, the proposed model considers how confining stresses influence plastic flow on the premise of ensuring the continuity of plastic flow. In a finite-difference code, the proposed numerical model was successfully implemented, and it was validated by simulating the stress distribution in an elastoplastic ring subjected to circumferential pressure in the plane strain state, and the role of the constitutive parameters was investigated. Finally, two rock tunneling projects were analyzed using the proposed numerical model: excavation plastic zone (EPZ) distribution in a deep-buried diversion tunnel and construction displacements in a shallow-buried highway tunnel. The numerical results obtained with the proposed numerical model based on the GNUST criterion agreed well with those from on-site measurements, emphasizing the significance of the intermediate principal stress. The empirical formula for determining the parameter b has been verified by practical engineering, ensuring the application of the numerical model even without triaxial test data. Thus, the proposed numerical model has good applicability to practical rock engineering and can provide guidance and reference for similar rock projects.

Structural stability analysis and deformation control of constraint-anchorage support system in soft rock mass tunnel

The primary support of the soft rock mass tunnel is prone to lose its bearing capacity in advance due to the buckling instability. To solve it, the buckling critical load formula was derived in combination with structural stability theory. It is found that the stability can be improved by strengthening or increasing the constraint conditions for the structure. Consequently, a constraint-anchorage support system was proposed inspired by this conclusion. It provides effective constraints for the primary support by anchoring the pipes in deep rock mass with grouting high-performance material, and connecting with the primary support by I-beam connector. Reasonable support parameters were presented by analyzing the influence of support parameters on the deformation and stress of the tunnel structure. Finally, this support system was applied to the actual the tunnel construction. It was found that the stability of the primary support was improved and the tunnel deformation was effectively controlled.

Blasting Damage of Tunnel Rock Mass Based on Cumulative Effect

Blasting Damage of Tunnel Rock Mass Based on Cumulative Effect

Design Equations for Predicting Stability of Unlined Horseshoe Tunnels in Rock Masses

This paper aims to propose new stability equations for the design of shallow, unlined horseshoe tunnels in rock masses. The computational framework of the upper- and lower-bound finite-element limit analysis is used to numerically derive the stability solutions of this problems using the Hoek–Brown failure criterion. Five dimensionless parameters including the width ratio and the cover-depth ratio of the tunnels, as well as the normalized uniaxial compressive strength, the geological strength index, and the yield parameters of the Hoek–Brown rock masses, are considered in the study. Selected failure mechanisms of the horseshoe tunnels in rock masses are presented to portray the effect of all dimensionless parameters. New design equations for stability analyses of horseshoe tunnels are developed using the technique of nonlinear regression analysis and the average bound solutions. The proposed stability equations are highly accurate and can be used with great confidence by practitioners.

Data-Driven Prediction of Stability of Rock Tunnel Heading: An Application of Machine Learning Models

In this paper, Artificial Neural Networks (ANN) have been utilized to predict the stability of a planar tunnel heading in rock mass based on the well-defined Hoek-Brown (HB) yield criterion. The HB model was developed to capture the failure criterion of rock masses. To provide the datasets for an ANN model, the numerical upper bound (UB) and lower bound (LB) solutions obtained from the finite element limit analysis (FELA) with the HB failure criterion for the problem of tunnel headings are derived. The sensitivity analysis of all influencing parameters on the stability of rock tunnel heading is then performed on the developed ANN model. The proposed solutions will enhance the dependability and preciseness of predicting the stability of rock tunnel heading. Note that the effect of the unlined length ratio has not been explored previously but has been found to be of critical importance and significantly contributes to the failure of rock tunnel heading. By utilizing the machine learning-aided prediction capability of the ANN approach, the numerical solutions of the stability of tunnel heading can be accurately predicted, which is better than the use of the classic linear regression approach. Thus, providing a better and much safer assessment of mining or relatively long-wall tunnels in rock masses.

Investigation on the evolution mechanism of water and mud inrush disaster in fractured rock mass of mountain tunnel

Water inrush is one of the major disasters during tunnel construction. Due to its characteristics of great harm and difficult prediction, it has always been the focus of research. In order to reveal the mechanism of fault water inrush, a laboratory experiment is adopted to simulate tunnel excavation. The results show, firstly, the pore water pressure and soil pressure of model are unchanged before the fault is exposed; after the fault is exposed, the pore water pressure and soil pressure of vault decrease first, followed by the arch and haunch, and the decline of arch and vault is greater than that of haunch. Secondly, excavation has the greatest impact on the displacement of rock mass directly above the tunnel axis, and the farther away from the axis, the smaller the impact. Thirdly, the seepage channel around vault begins to expand, and clear water begins to seep out after the fault exposure. As the sediment in the crack is carried out by water flow, the clear water gradually becomes turbid, seepage channel changes from pore flow to fissure flow and then to pipe flow. Finally, Comsol is used to analyze the fault water inrush mechanism from the perspective of permeability change, and the correctness of model test is verified by comparing with engineering practice.

Numerical Simulation of Long-Term Deterioration of Rock Mass Supported by Shotcrete Lining

The deterioration of rock mass and shotcrete lining has major consequences on the long-term performance of tunnels in the weak rock mass. In this study, the long-term behavior of rock mass and shotcrete in tunnels was simulated by using the three-dimensional finite difference method, considering the nonlinear deterioration mechanism. The degradation of rock mass was simulated by weakening the mechanical parameters, while the deterioration of shotcrete was modeled by decreasing the thickness. The support pressure, internal force, and displacement of the secondary lining were monitored with the gradual degradation of rock mass and shotcrete. As a consequence, the factor of safety (FoS) evolution with time was discussed. The results indicated that 1) the deterioration of both rock mass and shotcrete would significantly increase the rock pressure on the secondary lining, leading to an increase in the displacement (0–14 mm). The FoS of the secondary lining was reduced by 85%. 2) The influence of shotcrete’s deterioration on the secondary lining was relatively less, and the rock pressure on the secondary lining increased from 0 kPa to 13.8 kPa. The long-term safety of the tunnel is remarkably affected by the deterioration of rock mass, depending on the deterioration characteristics of the rock mass. Therefore, the deterioration characteristics of rock mass should be fully considered in tunnel maintenance.

Prediction of the Stability of Various Tunnel Shapes Based on Hoek–Brown Failure Criterion Using Artificial Neural Network (ANN)

In this paper, artificial neural network (ANN) models are presented in order to enable a prompt assessment of the stability factor of tunnels in rock masses based on the Hoek–Brown (HB) failure criterion. Importantly, the safety assessment is one of the serious concerns for constructing tunnels and requires a reliable and accurate stability analysis. However, it is challenging for engineers to construct finite element limit analysis (FELA) algorithms with the HB failure criterion for tunnel stability solutions in rock masses. For the first time, a machine-learning-aided prediction of tunnel stability based on the HB failure criterion is proposed in this paper. Three different shapes of tunnels, i.e., heading tunnel, dual square tunnels, and dual circular tunnels, are considered. The inputs include four dimensionless parameters for the heading tunnel including the cover-depth ratio, the normalized uniaxial compressive strength, the geological strength index (GSI), and the mi parameter. Moreover, dual square and circular tunnels include one more additional parameter namely the distance ratio. The results present the best ANN models for each tunnel shape, providing very reliable solutions for predicting the tunnel stability based on the HB failure criterion.

Prediction of Final Displacement of Tunnels in Time-Dependent Rock Mass Based on the Nonequidistant Grey Verhulst Model

Time-dependent deformations of rock are important factors for the design and construction of tunnels in the rock masses with time-dependent strength and deformation properties. Therefore, determination displacement and stable time of tunnel are an indispensable task in geotechnical engineering, especially during the design and construction of underground structures. However, in some types of rock masses, the tunnel displacement may increase for months or years after the excavation owing to the rheological behavior of the surrounding rock masses, which greatly influences the selection of the initial tunnel support system, the excavation layout, and the determination of its load-carrying capacity. In this paper, we present a method to quickly predict the final displacement and stable time of tunnels in time-dependent rock mass using the improved nonequidistant grey Verhulst model (INGVM) with Fourier series, which is used to reduce the periodic residual error. The proposed method is validated fairly via a test for a newly excavated roadway of −600 m level in a coal mine, Democratic People’s Republic of Korea. These results are useful references for similar projects in the future.

Monitoring of Tunnel Rock Mass Deformations During Provisional Support Stage: A Case Study

Abstract The present study evaluates on site the effects of provisional support on the rate of deformation (convergence) of clay-stone of a twin-tube tunnel. The combination of shotcrete, steel lattice, steel retaining, pre-supporting iron bar and Rock bolts can act as structural support in the form of provisional support for new or existing tunnels. Applications of provisional supports as confinement mechanisms to decrease the capacity of convergence can be helpful for distressed rock mass during tunnels digging. Real-size and real-time field monitoring over a period of approximately one (01) year was carried out with a Tachometer “Leica, TS 09” and 3D Displacement Monitoring Objectives fixed on the top heading and on the invert/bench. Wherefore; a sketch of the same cross-section of the tunnel was used in order to define the deformations of the rock mass of the tunnel measured in 3D in successive periods in all directions along the weak rock mass of the fourth class (IV) after the installation of the provisional support. The study shows good results in terms of deformation of the rock mass of the tunnel and satisfactory stability in terms of confinement. Consequently; it was noticed, that there is a relation between the deformations (convergence) in the two tubes along tunnel - when the deformation of the left tube increases the deformation of the right tube decreases -, and that the deformation of the tunnel is a deformation overall of the rock mass and it is the same along the tunnel relative to its rock mass. It can be concluded that there is a reciprocal effect between the two tunnel tubes, which can be considered as a conservation principle of the rock mass.

Application of Artificial Neural Networks for Predicting the Stability of Rectangular Tunnels in Hoek–Brown Rock Masses

An artificial neural network (ANN) model for predicting the stability of rectangular tunnels in rock masses based on the Hoek–Brown (HB) failure criterion is presented in this study. Since the safety assessment of the tunnel stability is one critical issue for civil engineers during the construction, it is very important to develop a reliable and accurate stability analysis of such problems. The finite element limit analysis (FELA) with the HB failure criterion is used to develop the numerical upper and lower bound solutions of the problem of rectangular tunnels in rock masses. A novel machine learning-aided prediction of this problem is then developed based on the datasets of the numerical bound solutions obtained from the FELA. The inputs consist of six dimensionless parameters including the cover-depth ratio of tunnels, the width ratio of tunnels, the normalized uniaxial compressive strength, the geological strength index, the mi parameter, and the degree of disturbance of rock masses. The results show that the optimal ANN models provide very great accuracy in predicting the stability of the rectangular tunnels based on the HB failure criterion. The solutions will provide a prompt assessment of tunnel stability in rock masses for geotechnical engineers during the construction of rock tunnels.

Microseismic characteristics of rockburst development in deep TBM tunnels with alternating soft–hard strata and application to rockburst warning: A case study of the Neelum–Jhelum hydropower project

The rockbursts that occur when tunneling through deep, hard rock can result in serious harm to workers, mechanical damage, delays, and economic losses. As a result, obtaining a warning of impending rockburst remains a challenge in rock engineering around the world. Unfortunately, the rockbursts that occur in deep tunnels with alternating soft–hard strata have development laws and mechanisms that are unclear and so are particularly difficult to predict. This paper focuses on the characteristics of the microseismicity occurring in deep tunnels constructed within alternating soft–hard strata and using the data to warn of rockburst occurrence. The study uses the Neelum–Jhelum hydropower project in Pakistan (tunnels with a maximum burial depth of 1,890 m) as an engineering background. The temporal evolution of the microseismicity and the fracturing mechanism involved in the rockburst development process in alternating soft–hard strata were thus revealed. Thresholds for six microseismic (MS) parameters that can be used to warn of rockbursts of different intensities in different lithologies were thus found based on 58 recorded cases (recorded during a month-long period of MS monitoring). These thresholds were subsequently used (together with MS monitoring) to warn of rockbursts of a certain intensity in the corresponding lithology during the excavation of subsequent tunnels. The warning results obtained agree with the actual situation when the right thresholds for the corresponding lithologies were used. The characteristic values of the six MS parameters used for rockburst warning in different lithologies were also discussed. Our results provide a useful reference for understanding and warning of rockbursts in deep tunnels in rockmasses with similarly complex lithologies.

Research on Seepage of Jointed Rock Mass of Tunnel and Limited Discharge of Grouting

In underground engineering such as tunnel engineering, the condition of surrounding rock such as water-containing jointed rock mass is a common engineering geology. For broken, water-containing surrounding rock, the reasonable measures to prevent and drain water has always been a key issue. Based on the statistical information of the structural surface of the surrounding rock of the Hongtuzhang tunnel, DIPS software was used to classify the structural plane of the tunnel. Based on the statistical analysis of the occurrence, size, and density of the structural plane, the two-dimensional structural plane network model of the rock mass was established, and the permeability tensor (K1 = 1.61 × 10−6 m/s, K2 = 5.78 × 10−7 m/s) was calculated. Consider the worst orientation, the permeability tensor (K1 = 1.61 × 10−6 m/s) was selected to calculate the grouting design. Based on the theory of limited discharge, the influence of parameters of permeability coefficient ratio n and thickness of grouting layer Tg on the tunnel water inflow and lining external water pressure was analyzed. The recommended value of tunnel drainage was 3.0 m3/m∙d, then the corresponding grouting circle parameters were put forward (permeability coefficient ratio n = 100, thickness of grouting layer Tg = 8 m).

DLSM Simulation Analysis of the Influence of Blasting Construction on Adjacent Tunnels in Rock Mass with Discontinuities

In order to study the influence of blasting construction of rock mass with discontinuities on adjacent tunnels, a feasible blasting scheme is formulated to ensure the safety of adjacent tunnels during construction. Based on the water resources allocation project in the Pearl River Delta, a tunnel construction model is established by using continuous‐discontinuous medium mechanics calculation model, Distinct Lattice Spring Model (DLSM), to simulate the impact of blasting construction of the left tunnel on the right adjacent tunnel. According to the numerical simulation results, the stress wave transmission process of the left tunnel with blasting time t = 18 ms is analyzed. Furthermore, the effects of the positions of the discontinuity, the width of the discontinuity, and the angle between the discontinuity and the horizontal direction on the adjacent tunnel are studied. The modelling results show that the existence of discontinuities plays a certain role in improving the safety of adjacent tunnels in the blasting stage. The farther the distance between the discontinuity and the adjacent tunnel is, the smaller the impact of blasting on the adjacent tunnel is. In the process of blasting, the larger the width of discontinuity is, the more effective it is to block the influence of blasting stress wave on the adjacent tunnel. The smaller the angle between discontinuity and horizontal direction, the smaller the impact of blasting on adjacent tunnels.