Rock-support Interaction Research Articles

Reliability analysis of tunnels considering the rock-support interaction using a metamodel-based reliability method

The convergence-confinement method (CCM) is an important approach to analysis the rock-support interaction and to design tunnel and its support. To make an effort on efficient reliability analysis of tunnels integrated with CCM, of which performance functions are mostly highly nonlinear and implicit, a hybrid intelligent algorithm combing uniform design (UD) and Gaussian process regression (GPR) is proposed. Based on the generated UD samples, GPR-parameter metamodels to predict the important parameters of CCM and GPR-probability metamodels to approximate the real performance functions are constructed consequently. Then sensitivity analysis, determination of the optimal preliminary support timing and failure probabilities calculations can be performed in conjunction with Monte Carlo simulation (MCS) based on the constructed GPR-parameter metamodels and GPR-probability metamodels. To verify the efficiency and accuracy of the proposed method, a typical circle tunnel is analyzed and good results are achieved. Finally, a practical hydraulic tunnel is analyzed using the proposed method and some beneficial conclusions are drawn.

Experimental investigation on the load-bearing capacity and deformation behaviour of the composite lining with polyurethane compressible layer

Lining structures for tunnels in rheological rocks are susceptible to large deformations and damage. Installation of a polyurethane (PU) compressible layer between the primary and secondary lining provides a potential solution to mitigate large deformation hazards. Although the capability of PU-enhanced composite lining in adapting and absorbing large deformation has been found, its underlying load-bearing mechanism and deformation behaviour remain less understood. To fill the gap, large-scale model tests were conducted using a self-designed loading test setup, primarily focusing on the mechanical response of PU-enhanced composite lining. Ten lining specimens with varying thicknesses (25, 37.5, and 50 mm) and densities (50, 100, and 150 kg/m3) of the PU compressible layer were investigated. The digital image correlation (DIC) analysis technique was used to detect real-time deformation and strain fields under loading conditions. Results demonstrated that the PU compressible layer enhanced the ultimate load, toughness, and deformation capacity of the composite lining by an average of 17.6 %, 164.6 %, and 157.4 %, respectively. The load-displacement response of the specimens with PU compressible layer could be categorized into four stages: pre-cracking, post-cracking, strain-hardening, and failure. The primary lining experienced the largest vertical displacements among the specimens with the PU compressible layer, followed by the compressible layer and the secondary lining. Although the specimens exhibited similar progressive failure modes, there were variations in crack distribution and propagation. The analysis of rock-support interaction indicated that increasing the thickness of the PU compressible layer mainly affects the deformation capacity when the secondary lining reaches its elastic limit.

Theoretical and Numerical Studies of Rock-Support Interaction by Considering Imperfect Rock-Lining Interface

Theoretical and Numerical Studies of Rock-Support Interaction by Considering Imperfect Rock-Lining Interface

Design of deep rock tunnels using hyperstatic reaction and convergence confinement methods

Tunnel lining is usually installed with delay behind the tunnel face excavation, which requires that a displacement is considered at the tunnel boundary before the support structure installation. This delayed installation comes with a release and redistribution of stress in the rock mass. Internal tunnel lining forces significantly rely on the stress relaxation process taking place in the rock mass surrounding the excavated tunnel. One of the difficulties when designing tunnel supports is, therefore, to analyse the rock–support interaction considering the tunnel lining convergence caused by the stress redistribution. Here, a simple and effective calculation process based on the combination of two methods, the hyperstatic reaction method (HRM) and convergence confinement method, is presented to analyse the interaction of rock mass and support structure. The rock mass is assumed to obey the Hoek–Brown criterion. The stress release is also taken into consideration. The present method is validated by comparing results of the HRM in terms of tunnel lining forces against the analytical ones. Thereafter, the effect of the stress release coefficient, the tunnel depth and the Hoek–Brown criterion parameters (the geological strength index and σci) on the lining internal forces are presented and discussed.

Physical model simulation of rock-support interaction for the tunnel in squeezing ground

The existence of squeezing ground conditions can lead to significant challenges in designing an adequate support system for tunnels. Numerous empirical, observational and analytical methods have been suggested over the years to design support systems in squeezing ground conditions, but all of them have some limitations. In this study, a novel experimental setup having physical model for simulating the tunnel boring machine (TBM) excavation and support installation process in squeezing clay-rich rocks is developed. The observations are made to understand better the interaction between the support and the squeezing ground. The physical model included a large true-triaxial cell, a miniature TBM, laboratory-prepared synthetic test specimen with properties similar to natural mudstone, and an instrumented cylindrical aluminum support system. Experiments were conducted at realistic in situ stress levels to study the time-dependent three-dimensional tunnel support convergence. The tunnel was excavated using the miniature TBM in the cubical rock specimen loaded in the true-triaxial cell, after which the support was installed. The confining stress was then increased in stages to values greater than the rock's unconfined compressive strength. A model for the time-dependent longitudinal displacement profile (LDP) for the supported tunnel was proposed using the tunnel convergence measurements at different times and stress levels. The LDP formulation was then compared with the unsupported model to calculate the squeezing amount carried by the support. The increase in thrust in the support was back-calculated from an analytical solution with the assumption of linear elastic support. Based on the test results and case studies, a recommendation to optimize the support requirement for tunnels in squeezing ground is proposed.

Safety Evaluation of Anchoring-Grouting Rock-Support Interaction in Deep Underground Excavation Based on Support Vector Machine Learning

Safety Evaluation of Anchoring-Grouting Rock-Support Interaction in Deep Underground Excavation Based on Support Vector Machine Learning

Modeling the behavior of a coal pillar rib using Bonded Block Models with emphasis on ground-support interaction

Rib spalling is a major hazard in the mining industry and in absence of coal rib support guidelines, accidents have continued to occur in recent years. Developing effective support guidelines requires a complete understanding of pillar damage mechanisms as well as the rock-support interaction mechanism. Bonded Block Models (BBMs) represent a convenient tool for this purpose, as they can reproduce the rock fracturing process reasonably well, but it is not known whether this modeling technique can quantitatively replicate the impact of reinforcement (bolts) on otherwise unsupported ground. To bridge this gap in research, we employed the BBM approach to simulate the behavior of a supported coal pillar rib located in a longwall mine in Australia. This case study presents a unique opportunity in that two otherwise identical chain pillars with different support densities adjacent to one another were instrumented. After calibrating a model against displacement and stress measurements made over the course of mining in one pillar, the support in the calibrated BBM was modified to match that of the adjacent chain pillar. This model could predict the rib displacement to within 6 mm of what was measured in-situ. Given the ability of the BBM to match field-measured displacements and stresses and also field observations for varying support densities, it seems that such a model has the potential to aid in the development of a support design tool. Lastly, the effect of block shape was investigated by replacing the elongated blocks with isotropic polygonal blocks. This model could not reproduce the ground-support interaction very well, likely due to the inaccurate geometric representation of an anisotropic rock like coal.

Surrounding RockSupport Interaction MechanismConsidering Effect of TunnelAdvance Supports

Surrounding RockSupport Interaction MechanismConsidering Effect of TunnelAdvance Supports

Application of the convergence-confinement method to excavation response of roadway in rock mass considering large deformation

For mining operations in a rock mass with high deformability and low strength, large deformation is one of the primary manifestations of roadway failure, which easily occurs when the construction techniques and support measures cannot accommodate the geological environment. Therefore, the ground response to excavation disturbance and control technology of squeezing behavior should be analyzed based on large deformation theory. This study presents an elasto-plastic theoretical model for a circular roadway in the finite strain framework using a hypoelastic-plastic theory and convergence-confinement method to provide a rigorous approach for large deformation prediction and weak rock-support interaction analysis. A novel numerical procedure for the strain-softening rock mass subjected to large deformation is proposed based on an existing brittle-plastic analytical formula, which is simple but precise. Furthermore, suggestions on analysis of weak rock-support interaction based on large deformation method are presented, which may be beneficial to understanding deformation prediction and support design more rigorously.

The Reliability-Based Design Optimization of considering Rock-Support Interaction for Rock Tunnels

Uncertainty is critical to the tunnel design. In this study, a novel reliability-based design (RBD) method was developed by integrating the rock-support interaction and its uncertainties for rock tunnels. In this method, the rock-support interactions were analyzed based on a convergence-confinement method. Uncertainties were estimated by reliability analysis using Excel Solver. Chaotic particle swarm optimization (CPSO) was adopted to search the optimal tunnel design parameters based on the rock-support interaction analysis. The proposed method for estimating the reliability index and determining the tunnel support parameters was introduced in detail. To illustrate the proposed method, it was applied to two tunnels with rock-bolt and combined support systems. The results indicated that the method could obtain accurate solutions with a dramatically improved computing efficiency, guaranteeing the tunnel stability at the same time. The developed method provides an excellent way to deal with the uncertainty in tunnel design. It was proved to be an efficient and effective method for the support designs of rock tunnels.

Experimental Study on Rock-Support Interaction in Deep Tunnel Under Complex Geological Conditions

Rock-support interaction is one of the most core issues in underground engineering, which is of major interest to supporting structure design, construction safety and cost, as well as environmental protection. In order to study the rock-support interaction in deep tunnel under complex geological conditions, taking Xianglushan Tunnel of Yunnan Water Diversion Project in China as the engineering background, two true three-dimensional physical model tests were conducted. The model test results show: (1) the surrounding rock and support are a pair of opposite and united contradictions, which are both antagonistic and cooperative; (2) the rock-lining interaction and rock-bolt interaction are distinctly different. The lining is a type of outside supporting structure to bear the load from surrounding rock and the bolt is a kind of inside supporting structure to reinforce and protect surrounding rock; (3) the impacts of weak fault on mechanical behavior of surrounding rock and supporting structure are significant. The load bearing effects of surrounding rock and support system exhibit different characteristic depending on the corresponding geological conditions. The results can contribute to the development of construction scheme and optimization of support design, and also provide an ideal data set for the calibration and validation of numerical models to simulate the rock-support interaction.

Investigation of pillar damage mechanisms and rock-support interaction using Bonded Block Models

In this study, Bonded Block Models (BBMs) are used to investigate the pillar damage mechanisms and rock-support interaction in massive-to-sparsely-fractured rockmasses. Hypothetical granite pillar models of width-to-height (W/H) ratio of 1, 2 and 3 are developed, and the input parameters are constrained by matching the stress-strain response of the BBMs to the stress-strain curves from FLAC3D models that were previously calibrated to an empirical pillar strength database. Two different block representations are also considered – elastic and inelastic. It was found that inelastic blocks are necessary to capture the behavioral transition from strain-softening to pseudo-ductile with increase in pillar W/H.Post-calibration, different rockbolt combinations are tested in the BBM and their influence on the pillar strength and lateral deformations are analyzed. It was found that as the support density is increased, the peak pillar strengths also increase but the effect is dependent on the W/H. Deformation of the outer stress-fractured region and bulking systematically decreased with increasing support density, but the exact trend evolved as the pillars were loaded to various points on their stress-strain curves. Lastly, a BBM pillar was developed with explicit intra-block fracturing capability (i.e., individual blocks could break) and the support analysis was repeated. The goal was to understand if the continuum representation of damage within the inelastic blocks led to some underestimation of the rock-support interaction mechanism. It was ultimately concluded that the continuum inelastic representation of smaller-scale damage within individual blocks allows for a more appropriate representation of the rock-support interaction than the explicit intra-block representation.

The influence of the two-component grout on the behaviour of a segmental lining in tunnelling

Filling material is present around the segment lining when a shielded Tunnel Boring Machine is used to excavate a tunnel. The two-component grout is becoming lately one of the most used filling materials. Its mechanical properties evolve over time. Unfortunately, there are not many studies in the literature on the specific mechanical characteristics of these materials. This work presents the results obtained from an extensive laboratory test campaign that allowed to fully characterize the two-component filling material during the setting period. In particular, the values of the stiffness and resistance parameters were obtained over time, where uniaxial compression tests and oedometer tests were carried out. A detailed study of the effect of the presence of the filling material on the behavior of the support system (segmental lining + filling material) was developed for two of the most widespread analytical methods for the analysis of the behavior of tunnels and structures of support: the convergence-confinement method and the Einstein and Schwartz method. Subsequent parametric analyses made it possible to consider the variability of the influencing parameters within the typical variability ranges obtained from the laboratory test campaign or known from the available scientific literature. From the study carried out, it was possible to note that it is necessary to consider the presence of the filling material in the evaluation of the stiffness of the support system, when using the convergence-confinement method to estimate the loads acting on segmental lining. In this regard, it is necessary to have a reliable estimate of the elastic modulus of the filling material in the period of loading of the segmental lining. On the other hand, the presence of the ring of filling material is negligible when evaluating the state of stress of the segmental lining with specific methods capable of considering the rock-support interaction. In particular, adopting the Einstein and Schwartz method, it is possible to define the bending moments and normal forces acting in the support structure, referring to the stiffness parameters of the segmental lining alone.

Integration of three-dimensional continuum model and two-dimensional bonded block model for studying the damage process in a granite pillar at the Creighton Mine, Sudbury, Canada

Bonded block model (BBM) has shown potential in replicating rock mass behavior as well as the rock–support interaction mechanism, but their practical application is limited to two dimensions due to the high associated computational demand. To allow for the use of BBM in simulating three-dimensional (3D) problems, this study proposes an integrated 3D continuum–two-dimensional (2D) discontinuum approach, in context of rock pillars. A cross-section of a granite pillar was simulated using a BBM with a load path from a calibrated mine-scale FLAC3D model. Pillar support as employed in the mine was also incorporated in different stages during the simulation. The model was calibrated by varying the input parameters until the displacements at six locations within the pillar matched those measured by a multi-point borehole extensometer (MPBX) in the field. The calibrated model was subsequently used to understand how the support and load path influenced the damage evolution in the pillar. The shear component of the load path was found to have a major effect on the severity and extent of the damaged regions. When the support density was increased in the model, the lateral displacements along the pillar walls were significantly suppressed in a somewhat unpredictable manner. This was explained by the interaction between the supports and the damaged regions at the corners, which ultimately modified the stresses along the pillar periphery. The amount of displacement reduction obtained by increasing the support density illustrates the potential of BBM to be used as a support design tool.

Understanding continuum and discontinuum models of rock-support interaction for excavations undergoing stress-induced spalling

Although the design of underground structures is becoming increasingly dependent on modeling-based analysis approaches, ground control systems continue to be designed primarily using a site-specific trial and error approach. This discrepancy is related to the difficulty of reproducing rock-support interaction behavior in its entirety using commonly applied modeling methods. To help bridge this gap, this study has conducted a comparison of continuum and discontinuum models with a focus on their ability to realistically capture the support effect generated by rock bolts with or without wire mesh. It was found that continuum models can adequately replicate the damage processes and deformation of reinforced rockmasses, but show a negligible change in ground behavior when support elements are explicitly considered within the models. We propose a ‘strain-continuity’ hypothesis where the inability of the modeling method to allow discrete block separation after failure is thought to be responsible for this unrealistic behavior. Two discontinuum bonded-block modeling approaches (Voronoi Tessellation and Trigon) were subsequently tested; realistic behavioral differences between the supported and unsupported model conditions that are consistent with empirical data were exhibited by the Voronoi model. Finally, a conceptual framework has been presented that combines field data from the literature with the modeling results to provide an understanding of how support responses in the continuum and discontinuum models compare to reality.

Applicability of the Convergence-Confinement Method to Full-Face Excavation of Circular Tunnels with Stiff Support System

The ConVergence-ConFinement (CV-CF) method is widely used in conventional tunneling at a preliminary stage of the design. In this method, the rock–support interaction is simplified by means of a two-dimensional plane-strain assumption. However, when the ground exhibits large deformation and/or when the support is very stiff and installed close to the tunnel face, the results obtained with the CV-CF method may significantly differ from those obtained using 3D numerical computations. The strong interaction taking place between the rigid lining and the rock mass is not considered in the most common use of the CV-CF method. Some improvements of the CV-CF method as the so-called implicit methods have been developed to better account for this interaction. In this paper, the applicability of the CV-CF methods is discussed for full-face excavation tunneling with a stiff support system. An in-depth comparison between plane-strain closed form solutions and numerical results which properly accounts for the 3D effects at the vicinity of the tunnel face is carried out. The range of application of the different approaches of the CV-CF method is discussed. Finally, some simple empirical formulae which can be used in preliminary design for a large range of ground conditions are proposed.

Displacement-Based Estimation of the Best Time for Secondary Lining Construction Using Grey Model GM (1,1)

Large deformation or collapse often occurs in tunnels due to the high ground stress and rock rheology. When it cannot be effectively curbed by primary support, the secondary lining construction at a reasonable time comes to be particularly important in maintaining the stability of surrounding rock. In this paper, an efficient approach to estimating the best time for secondary lining construction in circular tunnels is presented based on Grey Prediction Model GM (1,1). Taking the tunnel in Hunan Province as an example, according to the classic rock-support interaction model, the limit displacement of tunnel roof is determined by investigating the stress–strain relationship of the surrounding rock in the framework of elastic–plastic theory. Subsequently, the GM (1,1) is employed and modified by optimizing the weight coefficient of background value μ and boundary condition D to predict the time sequence of the displacement of tunnel roof. Accordingly the best time for secondary lining construction is reasonably predicted. The results show that the greater μ is, the higher the model precision will be. The dispersion of the predicted results can be significantly reduced with the optimized D. The predicted displacement of tunnel roof reaches 55.840 mm in the 23rd observation period while the theoretical limit displacement of surrounding rock is 55.33 mm. Hereby, it is suggested that the secondary lining construction should be completed just before the 23rd observation period. The biggest advantage of the proposed approach is that it can be efficiently performed with resort to less parameters, and proves to be practical and feasible in tunnel design and construction.

Post Crack Behavior of Shotcrete in Rock Support Interaction Curve

Post Crack Behavior of Shotcrete in Rock Support Interaction Curve

Optimum Support Design for Openings Considering Intact Rockmass in Production Level of Maddhapara, Granite Mine, Maddhapara, Dinajpur, Bangladesh

Maddhapara Granite mine is the only Hardrock underground mine, which is contributing to infrastructure development of Bangladesh. It was established in 1995 by the North Korean contractor (NAMNAM).Over the past few years it was observed that in some of the vital area of the pit bottom, appears to be vulnerable, where needs to be taken special consideration to make sure the safe working environment for the miners and equipment machinery as well. The authors of this research have taken an attempt to identify and overcome such problem by a research program. In this research, our outcome has been established that the, optimum support have to be determined by using Rock Support Interaction Analysis for rock mass in production level. During design stage, it was considered that the total rock mass is intact (based on initial geological survey data), means there are no wedges along the opening. However a little amount of geological abnormality anticipated in the production level during construction phase. Due respect to that, our research recommended that, there has to be a little amount of support is needed for any kinds of openings in first category of rock, in second category it has to be considered by shotcreting of different thickness of lining in roof and the sidewall. In third category of rock, support system has to be considered by rock bolting and latter shotcrete the roof and side wall. Finally 2.3, 4.6 and 10.73 m openings in third category of rock there needs to be 0.0095m 0.015m and 0.026m fiber reinforced shotcrete and 3m bolt length and blot spacing with 1.5, 1, 0.95m respectively in roof and inside wall 0.006m, 0.015 and 0.045m shotcrete lining have to be considered for safe mining work.

Application of the Convergence-Confinement Approach to Analyze the Rock-Lining Interaction in Tunnels (Case Study: Shimizu Tunnel)

The Convergence-Confinement approach is a procedure in which the ground-liner interaction is analyzed by considering the behavior of the ground and the lining independently. This method enables calculation of average radial pressure applied to the support by the intersection of two curves representing the radial stresses as a function of radial strain, one for the ground and the other for the liner. This paper discusses the application of the Convergence-Confinement method of tunnel analysis to rock masses that satisfies the Hoek-Brown failure criterion. The Shimizu Tunnel has been studied using this method to analyze the structural interaction between rock and different types of individual support systems such as; steel ribs, shotcrete, rock bolts and compound systems of these supports. The equations that govern the behavior of the rock-support interaction are given through two basic components of the Convergence-Confinement method which are, Ground Reaction Curve (GRC) and Support Characteristics Curve (SCC). According to the analytical results, a comparison has been conducted between the different support systems according to the maximum capacity pressure of the support and the estimated lining load based on the Convergence-Confinement method. The value of this load depends on the timing of lining installation and consequently the value of the ground radial displacement due to the releasing of stresses.