Rock Tunnel Research Articles

Numerical simulation of fracture evolution behaviors in deep roadway surrounding rock containing discontinuous joints

To explore the internal bearing characteristics and fracture evolution laws of discontinuous jointed rock mass in deep roadways, the −600 m main roadway in Xin ’an Coal Mine was used as the research background. The fracture fractal dimension D was employed to characterize the joint density, and an intermittent jointed roadway model, both without support and with anchor cable support, was modeled using the particle flow software PFC2D. The internal stress, deformation, and fracture characteristics of intermittent jointed surrounding rock in tunnels with different support methods and joint densities were studied from a microscopic perspective. The results indicate that during the bearing process of the bolt anchor support and unsupported roadway discontinuous jointed rock mass model, the main bearing area of both models transferred from the surface rock mass to the deep rock mass. The tensile cracks of the anchor cable support model were reduced by 57.7% compared with the unsupported model, effectively suppressed the tensile failure of the surrounding rock, and the convergence of the surrounding rock was substantially reduced. The density of intermittent joints was negatively correlated with the bearing capacity of the surrounding rock mass of roadways, and the increase of joint density the overall failure of the surrounding rock, and the possibility of roadway destabilization was increased. Importantly, the number and distribution of intermittent joints in the surface surrounding rock were closely related to the rupture characteristics of the roadways. When the load exceeded the ultimate load of the deep surrounding rock, stress fluctuation occurred due to the stress drop caused by its destruction. This fluctuation promoted the development of intermittent joints in the surface surrounding rock, increasing the risk of roadway destabilization.

The Control Effect of Directional Rock Bolt on Asymmetric Deformation of Layered Soft Rock Tunnel with Different Grades of Large Deformation

The Control Effect of Directional Rock Bolt on Asymmetric Deformation of Layered Soft Rock Tunnel with Different Grades of Large Deformation

A data-driven evaluation method for tunnel rock stability based on multi-core support vector regression

A data-driven evaluation method for tunnel rock stability based on multi-core support vector regression

Research on the influence of curtain grouting parameters on the stability of tunnel surrounding rock and lining structure under the action of local high water pressure

Choosing the reasonable and economical grouting parameters is crucial for controlling the seepage field of surrounding rock and tunnel stability. This paper adopted the fluid–solid coupling theory based on FLAC3D to establish numerous simulations on the stability of surrounding rock and lining structure in karst tunnels under the different grouting conditions. The influences of grouting layer thicknesses and their permeability coefficients on the mechanical behaviors of lining structure, seepage, and stress properties of surrounding rock were investigated. The results show that with the increase of grouting thickness and its ratio of permeability, the maximum flow velocity and flow rate per liner meter in surrounding rock, the bending moments and axial forces, and the horizontal and vertical displacements of the lining structure all exponentially decrease, but safety factors at different positions of the lining structure first rapidly and then slowly increase. The changes in safety factor and uplift displacement at the inverted arch are more significant, and the minimum safety factor occurs at the left arch foot. As the grouting thickness and its ratio of permeability increase, the plastic zone range in surrounding rock decreases and expands, respectively. Through considering the improvement effect and economy of grouting comprehensively, choosing a grouting layer thickness of 7–9 m and a ratio of permeability of 20–50 is an ideal configuration parameter to ensure the stability and safety of karst tunnels under the conditions of this paper. The research results could provide references for choosing the reasonable grouting parameters in karst tunnels.

Experimental and numerical analysis of polyurethane spraying materials as a compressible layer in deep soft rock tunnels

Experimental and numerical analysis of polyurethane spraying materials as a compressible layer in deep soft rock tunnels

Theoretical analysis of additional surrounding rock pressure in shallow buried bias tunnel

The existing calculation method for the surrounding rock pressure of shallow buried bias tunnel fails to account for the impact of the progressive failure characteristics of the surrounding rock and slope creep, thereby neglecting the additional pressure arising from slope creep. Therefore, the progressive instability failure mode of the surrounding rock of shallow buried bias tunnel was obtained by numerical simulation. Based on this, the theoretical analysis model of the additional pressure of shallow buried bias tunnel was established, and the calculation formula of the additional pressure was derived. Further analysis revealed that the larger the deformation rate of the surrounding rock, the shorter the time it takes for the additional pressure to reach its maximum value. When the deformation rate of surrounding rock increases to a certain value, there will be no additional pressure on the liner, that is, the pressure will be released when the surrounding rock is excavated. In such scenarios, if the strength of the first lining is inadequate, cracking or even collapse of the first lining may occur during excavation.

Research on Support Control of New Materials and Structures for Deep Buried Complex Soft Rock Tunnel with Large Deformation

Research on Support Control of New Materials and Structures for Deep Buried Complex Soft Rock Tunnel with Large Deformation

Application of FDEM in the study of large deformation mechanisms in deep-buried soft rock tunnels: A case study

The Hutou Beishan Mega Tunnel frequently experiences significant deformation and instability collapse when passing through weak and fractured rock strata, leading to frequent design modifications and adversely impacting the construction progress and costs. This paper employs the finite-discrete element method (FDEM) to investigate the mechanisms and characteristics of large deformations in soft rock and analyzes the effects of in-situ stress and lateral pressure coefficients on the stability of soft rock tunnels. The results indicate that: (1) Once the compressive stress concentration exceeds the shear strength of the surrounding rock, shear failure occurs, with the resulting cracks predominantly forming X-shaped conjugate fractures. The shape of the excavation damage zone (EDZ) corresponds to the stress state; (2) Under hydrostatic stress conditions, the extent of damage to weak surrounding rock is influenced by the in-situ stress. At lower in-situ stress levels, only a few cracks appear at the edges of the surrounding rock, and deformation is minimal. At higher in-situ stress levels, cracks extend deeper into the tunnel, crushing shallow rock; (3) The failure characteristics of the tunnel vary with different lateral pressure coefficients. As the lateral pressure coefficient changes, the shape of the EDZ also changes, and the concentrated damage zone shifts from the arch waist to the crown as the lateral pressure coefficient increases.

Pressure relief for drilling (trenching) and support technology in deep soft rock tunnels

Controlling surrounding rock stability in deep soft rock tunnels solely by increasing the support strength is challenging. The key areas where the surrounding rock of a roadway is prone to “instability” should be treated with comprehensive measures, such as drilling to relieve pressure, grouting of the surrounding rock, floor trenching technology, and secondary support, to achieve overall stability of the roadway surrounding rock. In this paper, based on a typical straight wall semi-circular arch roadway project in the Huaibei mining area of Anhui Province, mechanical parameters, such as cohesion, internal friction angle, Poisson’s ratio, and elastic modulus of the surrounding rock, were measured. Displacement stress distribution in surrounding roadway rock were simulated and analyzed using FLAC 3D, and the key parts of the surrounding rock prone to instability under the original roadway support conditions were determined. A suitable arrangement and parameters of the borehole pressure relief in the side roadway, floor grouting, floor trenching, and floor bolt secondary support were selected. Engineering measurements indicated that the engineering techniques were successful. It provided a significant reference for the comprehensive management and treatment of the surrounding rock stability in deep soft rock roadway on a global scale.

Technology for Treatment and Reinforcement of Soft Rock Tunnel Floor Using Sealing Material

To maintain the stability of soft rock tunnels, the research team proposed a support scheme involving “floor grouting + floor anchors + sealing material”. This scheme incorporates a new sealing material with excellent mechanical properties, airtightness, and cost-effectiveness. To develop the sealing material, a series of proportioning tests and optimization designs were conducted to investigate how various experimental factors influence material performance. Based on these experiments, a regression prediction model was established to reveal the characteristics of factor interactions and determine the optimal mix ratio. Practical engineering validation confirmed that this support scheme effectively controls floor heave in soft rock tunnels.

Solution of plastic zone range in soft rock tunnel surroundings considering joint damage

Based on the Hohai model, a creep constitutive model of viscoelastic-plastic soft rock with joint fracture damage is proposed to solve the rheological failure problem in soft rock tunnels surrounding rock. Based on the proposed creep model of rock with joint damage and the current analytical analysis method of circular tunnel, the analytical formulas of viscoelastic-viscoplastic stress and displacement of circular tunnel with joint damage surrounding rock are derived. ABAQUS finite element software is used to simulate the excavation of surrounding rock with different joint angles. The numerical solution is compared with the analytical solution to verify the accuracy of the theoretical formula. The results show that when the joint inclination is 45°, the displacement values of the two are 16.36 mm and 16.87 mm respectively. The error of the two is 3.02%. The theoretical calculation is in good agreement with the numerical simulation results, verifying the rationality of the derived analytical formula of viscoelastic-viscoplastic stress and displacement of soft rock tunnel with joint damage.

Risk classification assessment and early warning of large deformation of soft rock in tunnels based on CNN-LSTM model

Tunnels in the Western Plateau region of China often face numerous problems of high ground stress, as well as highly fractured and weak rock masses in deep sections of the tunnel, which results in an increased risk of large soft rock deformation in tunnels, posing substantial challenges to safe and efficient construction. Hence, risk assessment and establishment of an early safety warning system are essential. By examining factors affecting the large soft rock deformation in tunnels, a set of index system consisting of three primary indicators (i.e., hydrogeological conditions, design factors, and construction factors) and eight secondary indicators (i.e., strength-to-stress ratio, rock mass index, groundwater influence, groundwater influence, etc.) for assessing these risks is constructed, while the risk classification and identification criteria are also established. As an example, a tunnel on the Xicheng Railway is adopted for regression prediction of rock mass deformation and risk warning classification based on CNN-LSTM model. The results indicate that the model is effective in predicting rock mass deformation with minimal fluctuations in settlement data, a MAPE of 0.29525, and a RMSE of 6.1311. The model demonstrates a high accuracy rate of 91.67% for early risk warning prediction of soft rock deformation in the tunnel, moreover, when applied to 10 cross-sections of the Xicheng Railway Tunnel for deformation risk early warning, the model demonstrated a high prediction accuracy of 90%. which serves as a reference for the assessment and prediction of large deformation risks in similarly complex and challenging tunnels in the western region of China.

Effect of Lateral Pressure on the Stability of Inclined Layered Rock Tunnel: A 3D-printed Model Investigation by Cement-based Materials

The inclined layered rock tunnel engineering in the alpine canyon area subject to tectonic stress will be influenced by high lateral stress. Currently, there are scarce reports on the impact of the lateral pressure coefficient on the stability of inclined layered rock tunnels. Hence, the mechanical response of the inclined layered tunnel model was investigated based on the 3D-printed model test, supplemented by acoustic emission (AE) and digital image correlation (DIC) monitoring methods under three cases of lateral pressure coefficients of 1.2, 1.5 and 1.8. The results reveal that for the tunnel model with a 60° bedding inclination, the bearing capacity is negatively correlated with the lateral pressure coefficient. The normal deformation of the bedding of the tunnel model is prominent, exhibiting significant asymmetric deformation characteristics. When the lateral pressure coefficient k increases from 1.2 to 1.5, the failure of the tunnel model changes from shear-slip failure along the layer to bedding cracking and buckling failure of the sidewall. The test results have enlightenment significance for the stability evaluation of inclined layered surrounding rock tunnels in the alpine canyon area.

Study on the heat and moisture coupling transfer characteristics with surrounding rock in subway tunnel under fluctuation boundary condition

Study on the heat and moisture coupling transfer characteristics with surrounding rock in subway tunnel under fluctuation boundary condition

Research on the Cutting Control Method of a Shield-Type Cutting Robot

With problems of low cutting efficiency, poor forming quality, and low control accuracy in large-section semi-coal rock roadway tunneling, comprehensive coal tunneling seriously lags behind fully mechanized mining. A fuzzy PID control method was proposed, taking the cutting robot in a shield-type tunneling system as the research object. Using mathematical analysis and other methods, a kinematic model of the cutting robot was established, and the pose transformation matrix of the cutting robot during the cutting process was obtained. A limit model for the motion space of the cutting robot cutting drum was established, and the motion relationship between the driving cylinder and the cutting drum was obtained. A fuzzy PID cutting robot control scheme was designed. The feasibility of the model was validated by simulation methods, and the correctness of the model and simulation was verified through on-site experiments. The results indicate that the established cutting robot model is correct, and the proposed fuzzy PID control method for the cutting robot is feasible. The maximum error of the center control of the cutting drum was 5.5 mm, and the average date was 0.89 mm, which was far less than the standard of 50 mm for engineering of the cross-section cutting of the roadway. This study enriches the control theory of shield-type cutting robots by improving control accuracy, enhancing the cutting efficiency of large-section semi-coal rock tunnels, ensuring the quality of section forming, and narrowing the gap between comprehensive coal tunneling and fully mechanized mining.

Experimental and numerical analysis of high-pressure gas-driven rock particle impact and fragmentation rock technology

Aiming at the problems of fast tool wear and low tunneling efficiency in hard rock tunneling process, a granite particle impact rock breaking technology is proposed to impact the rock mass of the tunneling face in advance to reduce tool wear. By simulating the process of granite particle impact rock breaking, the feasibility of granite particle impact rock breaking is verified. The impact velocity and new surface area of granite were obtained by high-speed camera and three-dimensional scanner test. The influence factors of gas pressure and granite particle quality were analyzed. It is concluded that increasing gas pressure can effectively increase the new surface area of rock failure and improve the failure effect. Improving the quality of granite particles does not continuously increase the impact kinetic energy. When the product of granite particle quality and impact kinetic energy reaches a critical value, continuing to increase the quality will not improve the impact damage effect of granite. The impact kinetic energy of granite particles impacting granite shows a linear relationship with the new surface area.

Phase field modelling of tunnel excavation damage in transversely isotropic rocks

Layered rocks, prevalent in geological formations, exhibit complex failure behaviours driven by pronounced anisotropy in their mechanical properties. However, the intricate failure mechanisms remain inadequately understood due to the spatial complexity of these mechanical responses. To address this challenge, this study proposes a novel phase field model tailored for layered rocks. A new strain energy decomposition method is introduced, uniquely formulated based on stress components and designed for transversely isotropic constitutive models. Numerical solutions to the coupled stress-phase field equations are obtained using user-defined element and material subroutines, implemented through a staggered solution scheme. The accuracy and robustness of the numerical approach are validated through simulations of a composite panel with a central hole under tensile loading. Additionally, the model is applied to the excavation of the layered soft rock tunnel, revealing the significant influence of bedding plane angles on displacement and stress field distributions, as well as post-excavation failure modes. Notably, the model captures the predominant shear-slip failure along bedding planes following excavation, effectively reflecting the complex mechanical interactions in layered rocks. This proposed model represents a significant advancement in understanding the failure mechanisms of layered rocks, providing a valuable tool for future geotechnical applications.

More accurate theoretical prediction of mechanical behavior of viscoelastic–viscoplastic rock tunnels using combined supporting system

The combined supporting system of rockbolts and linings is one of the most common methods for controlling the deformation of surrounding rock in tunnels. However, current theoretical analyses typically consider the deformation control effect of only one support type. Consequently, the bearing capacity of rockbolts or linings is not fully utilized as their combined effect is not considered. Thus, this study analyzes the mechanical responses of a “rockbolts + lining” combined supporting system for large deformation tunnels. For theoretical derivation, a viscoelastic–viscoplastic constitutive model is employed to describe the time-dependent behavior of surrounding rock. To satisfy the actual deformation development law, the effect of the stress path in the plastic zone of the surrounding rock is considered. An analytical solution is provided for predicting the tunnel behavior, where the installation time of the rockbolts and lining is considered sufficiently. Furthermore, the proposed analytical solution can be reduced to a viscoelastic solution and is well applied in a tunnel project. The superiority of the proposed solution is demonstrated by comparing it with previous solutions. Finally, a comprehensive parametric investigation is conducted, which considers the cohesion and internal friction angle of rock, the linear stiffness coefficient and installation time of rockbolts, and the stiffness and installation time of the lining. The results show that the cohesion and internal friction angle of the rock dominate the plastic deformation of the surrounding rock, thus further affecting tunnel deformation. The installation of rockbolts and lining can effectively restrict the deformation of the surrounding rock. Generally, better deformation control can be achieved by installing rockbolts (lining) earlier or by improving the stiffness of the rockbolts (lining). However, the stiffness of the rockbolts (lining) is limited to a certain range, in which significant deformation control can be achieved. After determining the installation time of the rockbolts and lining based on the actual construction level, the reasonable design parameters of the rockbolts and lining can be determined using the proposed solution such that their bearing capacities can be fully utilized in this combined supporting system.

Analysis of elastic and rheological properties of tunnel anchorage support structure under the action of seepage flow

The large deformation and strong rheological characteristics of the underground rock body under complex geological conditions have led to the failure of the support system and even the instability of tunnels from time to time. Based on the theory of groundwater seepage, the elastic solution of the mechanical model of the tunnel anchorage support system under seepage is solved, which reveals the influence of seepage on the peripheral rock and the support parameters of the anchorage support system; the viscoelastic solution is solved according to the corresponding principle of elasticity—viscoelasticity, which analyses the influence of seepage on the rheological process of the anchorage support system; and the model is simulated with the help of finite element software, which analyses the agreement and discrepancy of the numerical solution and the theoretical solution. The results show that the analytical and numerical solutions are basically consistent. This study can provide important guidance for controlling long-term stability of water-rich tunnel rocks.

Influence of variation in construction parameters on the stability of the surrounding rock in soft rock tunnels

Influence of variation in construction parameters on the stability of the surrounding rock in soft rock tunnels