Rock Tunnel Research Articles

Effect of Pipe Wall Wear Defects on the Flow Characteristics of Slurry Shield Discharge Pipe

During slurry shield tunneling in hard rock or cobble strata, the discharge pipes suffer serve wear and damage. However, the effect mechanism of pipe wall wear defects on the flow characteristics of two-phase flow is unclear. In this study, a three-dimensional slurry particle model of pipeline transport was established using the coupled computational fluid dynamics–discrete element method (CFD-DEM) considering the pipe wall wear defect, and the typical pipeline forms of straight pipe and 90° elbow pipe were selected as the research targets. The results indicated that the localized wear defect of pipes can lead to increased inhomogeneity in the velocity distribution, generating localized low-flow zones and resulting in a reduced flow rate or stagnancy in parts of the pipe. Meanwhile, the wear defect of the pipe results in local shape changes, so that the fluid flow path through the pipe is no longer smooth, causing more vortex/turbulence and secondary flow, where an increased vortex promotes localized kinetic energy reduction and creates larger pressure losses at the elbow. In addition, for the elbow pipe without wear defect, the pressure drop of the elbow increases quadratically from an increase of 6.5% to an increase of 16.9%, with the maximum wear depth increasing from 4 mm to 19 mm. For the straight pipe without wear defect, the pressure drop of the elbow increases linearly, from an increase of 2.2% to an increase of 10.2% with the maximum wear depth increasing from 4 mm to 19 mm. The paper investigates the potential mechanism of pipe flow characteristics influenced by wear defect and provides practical guidelines for the efficient operation of a slurry shield circulating system.

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

Roof stability for rock cavities and tunnels: Revisiting limit state plastic analysis

Roof stability for rock cavities and tunnels: Revisiting limit state plastic analysis

Application and efficacy of excavation compensation method in shallow, large-span hard rock tunnel

Application and efficacy of excavation compensation method in shallow, large-span hard rock tunnel

Study on Evaluation and Control Measures of Large Deformation of Soft Rock Tunnels Considering Unloading Physical Expansion

Study on Evaluation and Control Measures of Large Deformation of Soft Rock Tunnels Considering Unloading Physical Expansion

Study on Deformation Mechanism of Soft Rock Tunnel Under Seepage and Mechanical Response of Prestressed Anchor Cable

Study on Deformation Mechanism of Soft Rock Tunnel Under Seepage and Mechanical Response of Prestressed Anchor Cable

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

Aluminum foam as buffer layer used in soft rock tunnel with large deformation

Aluminum foam as buffer layer used in soft rock tunnel with large deformation

Statistical damage constitutive model of soft rock based on Improved Hoek-Brown strength criterion

It is significant to study the stability of surrounding rock in soft rock tunnels to ensure construction safety and improve efficiency. Through triaxial shear tests on soft rock at various confining pressures, we observed the failure characteristics transitioning from strain softening to strain hardening as confining pressure increases. An improved Hoek-Brown strength criterion has been proposed to characterize the critical confining pressure effect of soft rock, with tensile strength in the tensile zone aligning with experimental results, showing an error of less than 5%. By assuming that the micro-unit strength of soft rock follows a two-parameter Weibull distribution, we constructed a statistical damage constitutive model for soft rock in mountain tunnels. This model provides a more realistic depiction of damage change, failure processes, and stress-strain evolution in soft rock, thereby validating its scientific and rational foundation. The research findings can serve as a valuable reference for mountain tunnel construction.

The impact of extreme rainfall and drainage system failure on rock tunnels: A case study of deep-buried karst tunnel

The impact of extreme rainfall and drainage system failure on rock tunnels: A case study of deep-buried karst tunnel

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.

Study of Seepage Characteristics and Statistical Damage Constitutive Model of Calcareous Mudstone under Different Fluid Pressures

Abstract The ground stress and water pressure together impact the underground water diversion tunnels in plateau regions, which poses a serious threat to the stability of the surrounding rocks and the safety of engineering structures. Typically, the surrounding rock is calcareous mudstone, which is susceptible to weakening by water. This paper presents an experimental study of calcareous mudstone’s mechanical behavior and permeability characteristics under different fluid pressures in a soft rock tunnel of the Central Yunnan Water Diversion Project (CYWDP) in China. The test results show that the fluid pressure affects the calcareous mudstone’s strength and permeability characteristics, leading to its failure and deformation. The fluid pressure promotes the development of internal microcracks, reduces peak stress and damage stress, and influences failure modes. The evolution of permeability with strain is strongly related to the development of microcracks. Based on the statistical damage theory, a rock damage constitutive model considering fluid pressure and porosity is proposed, and experimental data are used to validate its effectiveness. The research results can be used for understanding the mechanical behavior and constitutive model of hydro-mechanical coupling in soft rock underground projects.

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

Analysis on the effect of buried depth-initial water content of the tunnel in expansive rock

There are countless engineering disasters induced by expansive strata in the tunnel project. Nowadays, most of the research focuses on the basic characteristics of expansive rock and soil, while the influence about coupling buried depth and different initial water content of surrounding rock on the tunnel lining is still rarely involved. Based on the principle of temperature and humidity equivalence, this paper discusses the behavior of rock as well as the mechanical properties of lining under the interaction of different buried depth and initial water content by using FLAC3D numerical simulation. It was found that the initial water content show an obvious effect on the evolution about the plastic area of rock compared with the buried depth of the tunnel. For shallow tunnels with a water content of less than 10 %, the plastic zone of the vault will penetrate to the surface after water absorption and expansion. Under the coupling effect, buried depth inhibits the development of the plastic zone to a certain extent. For different initial water contents of the surrounding rock, the displacement of the tunnel adds with the burial depth. The swelling of rock will significantly reduce the safety of the primary support, and when the burial depths of the tunnel increase to 150 m, the security coefficients of some primary support structures are less than 2, which does not meet the need in standard. The safety factor of secondary support is mainly influenced by the expansion force, not the ground pressure (represented by buried depth). The findings may be valuable reference for the analysis as well as evaluation of the security as well as stability of tunnels in expansive mudstone.

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

Characteristics and control techniques of soft rock tunnel lining cracks in high geo-stress environments: Case study of Wushaoling tunnel group

Abstract A high geo-stress environment severely damages tunnel structures owing to the large deformation of the surrounding rock, thereby threatening their safety. In this study, the Wushaoling highway tunnel group, which passes through a high geo-stress environment, is investigated as a case study. The spatial distribution of different types of tunnel cracks is analyzed based on the site observations. The lining crack variations, such as circumferential and longitudinal cracks, with the factors including grade of the surrounding rock, location of buried depth, and design type of the tunnel lining are investigated. Various structural reinforcement technologies are presented based on the damage degrees of the tunnel linings. Several finite element models of supporting structures are established to reveal the mechanism of tunnel crack control technology. The results show that longitudinal and circumferential cracks are the main characteristics of tunnel lining damage in high geo-stress environments, accounting for approximately 29.4 and 53.2% of the total cracks, respectively. SIVb-, SVc-, and SVd-type linings show numerous longitudinal cracks per kilometer. The longitudinal cracks appear primarily on the tunnel crown and hance. In terms of the lining support types in Grade V surrounding rocks, the number of longitudinal cracks per kilometer increases with the lining grade. The number of tunnel cracks per kilometer tends to increase with the buried depth. Four tunnel structure reinforcement treatment measurements for lining cracks in high geo-stress condition were innovatively proposed, which were proved effective in deformation controlling and strengthening the tunnel lining using numerical investigation. The key contribution of this research is to reveal the characteristics and evolution mechanism of tunnel lining cracks in high geo-stress condition, and provide effective treatments for the tunnel lining cracks. In addition, the findings from the study on the tunnel lining cracks also provide industry practitioners with a comprehensive guide regarding the characteristics and control techniques of the tunnel lining cracks, which can serve as a steppingstone to facilitate the construction technology development of the transportation industry.

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.