Tunnels In Jointed Rock Masses Research Articles

Numerical simulation of rock bursts triggered by blasting disturbance for deep-buried tunnels in jointed rock masses

Frequent dynamic disturbances, such as explosions, vibrations, and earthquakes, may trigger the risk of rock burst disasters around neighbouring deep-buried tunnels. In this study, the PFC software was used to simulate rock bursts triggered by blasting stress waves (dynamic disturbance) to determine their effects on deep-buried tunnels in jointed rock masses. This study investigated the effects of different ground stress values and joint angles on rock bursts in tunnels under intense dynamic disturbance. An analysis of different ground stress values and joint angles revealed the changes in the ejection velocities of damaged rocks and kinetic energy under intense dynamic disturbance. The results show that higher ground stress can alter the proportion of stress waves converted into strain energy and kinetic energy. Joint angles affect the location of the rock burst. The closer the joint angle is to 90°, the greater the damage to surrounding rocks caused by stress waves. Higher ground stress and joint angles increase the risk and intensity of rock bursts, causing significant damage to surrounding rocks, which makes existing tunnels more vulnerable to impact. The findings of this research have important guiding significance to ensure the secure protection of tunnels against rock bursts.

Research on Zonal Disintegration Characteristics and Failure Mechanisms of Deep Tunnel in Jointed Rock Mass with Strength Reduction Method

To understand the fracture features of zonal disintegration and reveal the failure mechanisms of circle tunnels excavated in deep jointed rock masses, a series of three-dimensional heterogeneous models considering varying joint dip angles are established. The strength reduction method is embedded in the RFPA method to achieve the gradual fracture process, macro failure mode and safety factor, and to reproduce the characteristic fracture phenomenon of deep rock masses, i.e., zonal disintegration. The mechanical mechanisms and acoustic emission energy of surrounding rocks during the different stages of the whole formation process of zonal disintegration affected by different-dip-angle joints and randomly distributed joints are further discussed. The results demonstrate that the zonal disintegration process is induced by the stress redistribution, which is significantly different from the formation mechanism of traditional surrounding rock loose zone; the dip angle of joint set has a great influence on the stress buildup, stress shadow and stress transfer as well as the failure mode of surrounding rock mass; the existence of parallel and random joints lead the newly formed cracks near the tunnel surface to developing along their strikes; the random joints make the zonal disintegration pattern much more complex and affected by the regional joint composition. These will greatly improve our understanding of the zonal disintegration in deep engineering.

ESTIMATION OF ROCK JOINT TRACE LENGTH USING SUPPORT VECTOR MACHINE (SVM)

Jointed rock masses modeling needs the geometrical parameters of joints such as orientation, spacing, trace length, shape, and location. The rock joint trace length is one of the most critical design parameters in rock engineering and geotechnics. It controls the stability of the rock slope and tunnels in jointed rock masses by affecting rock mass strength. This parameter is usually determined through a joint survey in the field. Among the parameters, trace length is challenging because a complete joint plane within rock mass cannot be observed directly. The development of predictive models to determine rock joint length seems to be essential in rock engineering. This research made an effort to introduce a support vector machine (SVM) model to estimate rock joint trace length. The SVM is an advanced intelligence method used to solve the problem characterized by a small sample, non-linearity, and high dimension with a good generalization performance. In this study, three data sets from the sedimentary, igneous, and metamorphic rocks were organized, which location of joints on the scanline, aperture, spacing, orientation (D/DD), roughness, Schmidt rebound of the joint’s wall, type of termination, trace lengths in both sides of the scanline and joint sets were measured. The results of SVM prediction demonstrate that predicted and measured results are in good agreement. The SVM model-based results were compared with those obtained from field surveys. The proposed SVM model-based model was very efficient in predicting rock joint trace length values. The actual trace length could be estimated; thus, the expensive, difficult, time-consuming, and destructive joint surveys related to obscured joints could be avoided.

Research on Meso-mechanism of Failure Mode of Tunnel in Jointed Rock Mass

The natural rock that contains micro particles, holes, cracks, impurities, etc. has a complex composition. According to whether the crack is closed or not, kinds of cracks can be divided into two types: open type and closed type. There was a bottleneck in the preparation of the test piece when the indoor test method analyzes the built-in closed cracks of rock materials, so PFC has its unique advantages in simulation analysis of fractured rocks with closed cracks. In order to analyze the influence of the inclination angle, length of the crack above the tunnel and the tunnel spacing on the tunnel failure and crack propagation, the particle was based on the granular flow microscopic parameters. It was shown that with the increase of the inclination of the pre-crack on the upper side of the tunnel, the distance of the tunnel and the length of the crack, the final failure mode of the specimen is similar to that of the non-crack specimen. The initiation of the crack at the end of a certain length of prefabricated crack is mainly affected by its inclination angle. The greater the inclination angle, the earlier the crack initiation is relatively early.

A numerical study on mechanical behavior of jointed rock masses after tunnel excavation

The tunnel in jointed rock masses is prone to be overbroken and then gives rise to collapse, yet the failure modes of jointed rock masses are still poorly understood. This paper investigates anisotropic deformations and failure modes of tunnels in jointed rock masses. For this purpose, five series of numerical models are modeled for a severe tunnel overbreak occurring on the Panlongshan tunnel. The ubiquitous joint model is used to consider the shearing and tensioning effects of the bedding and joint structures. The factors affecting anisotropic deformation and failure of rock masses, such as bedding spacing (s), joint dip angles (θ), and joint spacing (d), are discussed. The results demonstrate that for the stratified rock masses (without joint), the maximum settlement around the tunnel is located at the roof, and the separation of “virtual blocks” along the bedding planes is a basic failure mode; for stratified rock masses containing joints, the maximum deformation surrounding the tunnel appears in the joint position, and failure happens through a combined rotation, sliding, and falling mechanism. Our study can also reveal that with the increase of the number of joints, the plastic zone at the joint positions has a developing tendency towards the deep part. The more complex the joint structures in jointed rock masses are, the more unstable rock masses are formed.

Time and technique of rehabilitation for large deformation of tunnels in jointed rock masses based on FDM and DEM numerical modeling

When large deformation occurs in a tunnel, resulting in the primary lining intruding into the tunnel clearance, an appropriate treatment method is critically important to ensure that the tunnel can be completed on time and safely. This paper investigates the optimal treatment timing and technique for replacing the deformed primary lining. For this purpose, a two-stage numerical approach is employed for a severe tunnel collapse accident occurring on the Jinhong Highway. In the first stage, a global tunnel model is constructed using the finite difference method (FDM). The parameters are calibrated by the synthetic rock mass (SRM) approach, laboratory testing and field data. The continuously yielding (CY) joint model is used in the SRM, and its parameters are derived by the joint direct shear test. In the second stage, a local model encompassing the discrete fracture network (DFN) is constructed using the discrete element method (DEM) in the collapsed zone. Based on the DEM, the influence of the primary lining rehabilitation on the failure of the rock masses is analyzed. The local model is used to study the optimal rehabilitation timing, the optimum rehabilitation duration and the reasonable length of each replacement cycle. The following three conclusions are drawn. (1) The optimal rehabilitation timing is when the deformation of the rock masses reaches 90% of the total deformation. (2) There is a time threshold for the duration of the rehabilitation; if the duration is less than this value, the impact on the surrounding rock is small and almost the same. However, if the duration exceeds this value, the damage to the rock mass will increase as the duration increases. (3) The reasonable length of every replacement cycle should be less than the steel support spacing.

Effects of statistical distribution of joint trace length on the stability of tunnel excavated in jointed rock mass

The rock masses in a construction site of underground cavern are generally not continuous, due to the presence of discontinuities, such as bedding, joints, faults, and fractures. The performance of an underground cavern is principally ruled by the mechanical behaviors of the discontinuities in the vicinity of the cavern. During underground excavation, many surrounding rock failures have close relationship with joints. The stability study on tunnel in jointed rock mass is of importance to rock engineering, especially tunneling and underground space development. In this study, using the probability density distribution functions of negative exponential, log-normal and normal, we investigated the effect of joint trace length on the stability parameters such as stress and displacement of tunnel constructed in rock mass using UDEC (Universal Distinct Element Code). It was obtained that normal distribution function of joint trace length is more critical on the stability of tunnel, and exponential distribution function has less effect on the tunnel stability compared to the two other distribution functions.

Closure to “Two-Dimensional Discrete Element Theory for Rough Particles” by Mingjing Jiang, Serge Leroueil, Hehua Zhu, Hai-Sui Yu, and Jean-Marie Konrad

The discusser was pleased and interested to see the application by Jiang et al. of discrete element method (DEM) technology to rough particles. In particular, the discusser was interested to see the claim by Jiang et al. that in the DEM, with a usual point-contact model, the couple/moment is neither available at the contact nor able to be transferred from one particle to the other. It would be for others more expert in DEM applications to judge the correctness of that claim; the discusser is happy to accept the claim at face value in relationship to the DEM methodology. However, it may be of interest to Jiang et al., and possibly the readership in general, to learn that a numerical model incorporating the couple/moment with the associated rotational mode of deformation was developed and published a very long time ago (Burman 1972). This development occurred as part of a doctoral research program by Burman at James Cook University of North Queensland in Australia under the guidance of well-known discontinuum instigator and long-term proponent, Professor Hugh Trollope. It so happened that at the time when Dr. Cundall was completing his initial work that lead ultimately to the DEM theory (Cundall 1971), Burman was engaged in a similarly directed effort to investigate the mechanics of blocky media, albeit by a different approach and for somewhat different ends. Dr. Cundall, working in the Royal School of Mines at Imperial College, was principally interested in miningrelated activities including dynamic phenomena, such as blasting and mass movements of blocky materials. Meanwhile, with a civil engineering bias, Burman was principally interested in the maintenance of structural integrity within blocky materials, including slopes and tunnels in jointed rock masses. This difference in emphasis was expressed in the greater attention by Burman to modeling rough contacts, whereas Dr. Cundall’s attention was directed to capturing the more spectacular and large block movements. Burman has always felt that the basic point-contact model used by Dr. Cundall was remarkably successful, in spite of its formational simplicity. In Burman’s view, this success demonstrated the power fundamentally involved in having specifically recognized the discrete nature of particles in a discontinuum regardless of the sophistication or otherwise of the micromodel used. The Burman model was developed for a system of rigid blocks interacting through a series of Goodman joint type finite elements (Goodman et al. 1968). The assumption of rigid blocks was necessitated at the time because of the severely restricted capacity of computers to deal with large sets of simultaneous equations. That restriction is no longer relevant, but it is still convenient to assume rigidity, as the writers have done, and to adopt the linearizing assumption of small incremental rotations. The Burman model, which is finite element based, employed the condition of static equilibrium together with the transformation of joint nodal displacements and nodal forces to associated block centroids yielding the basic matrix equation for equilibrium of an individual block (b) as

Numerical study on failure mechanism of tunnel in jointed rock mass

During underground excavation many surrounding rock failures have close relationship with joints. The stability study on tunnel in jointed rock mass is of importance to rock engineering, especially tunneling and underground space development. In this paper, a numerical code called RFPA was used to study the influence of different dip angle of layered joints and the lateral pressure coefficient on the stability of tunnel in jointed rock mass. Numerical analysis indicated that both the dip angle of joints and the lateral pressure coefficient have significant impacts on the failure mode and displacement characters of tunnel. The progressive failure processes of tunnel in jointed rock mass were presented and the mechanisms were discussed. The applicable condition of geographical method by Goodman is also discussed. These results offer a guideline in support design.

界面剥離モデルを組み込んだ複合材料有限要素

Damages in composite materials are mostly governed by interfacial debonding. In order to take this into account, we employ an analytical model considering partial debonding along interface, and formulate a finite element. The model utilizes a concept where a moduli of an inclusion is replaced by an equivalent one of debonded inclusions. By several examples, eligibility of the model is shown. As an application, excavation analysis of a tunnel in jointed rock mass is carried out, and the results are compared with other observations.

The disturbed zone around tunnels in jointed rock Masses

This paper presents an investigation of the effect of joint spacing on the size and shape of the disturbed zone around a tunnel. A two-dimensional distinct element simulation program, UDEC, was used to model the tunnel excavation in a simply jointed rock mass, and an analytical method verified the numerical results. Rock masses were studied, ranging from intact rock to heavily jointed rock, with rock spacing less than 1/16 of the tunnel diameter. Four UDEC models were used to study the effect of joint spacing. The disturbed zone was divided into: (1) the failure zone, where loose rock blocks fall into the tunnel; (2) the open zone, where joints open; and (3) the shear zone. Numerical results were obtained for disturbed zones for different block sizes, boundary conditions, stress state, and joint orientation. An analytical study was made of the shear zones around the tunnel. The failure zone is found in the immediate vicinity of the tunnel; local block falling occurs there only when the joint spacing is small enough to create loose blocks. The open zone enlarges with reducing joint spacing and stress ratio. The shear zone around the tunnel can extend a considerable distance from the tunnel boundary. The division of the disturbed zone into these zones makes it easier to study short-term and long-term tunnel instability.

The disturbed zone around tunnels in jointed rock masses

The disturbed zone around tunnels in jointed rock masses

Site characterisation for tunnels in jointed rock masses : Dhar, Y R; Choubey, V D; Pandalai, H S Proc 6th International Congress International Association of Engineering Geology, Amsterdam, 6–10 August 1990VI, P593–599. Publ Rotterdam: A A Balkema, 1990

Site characterisation for tunnels in jointed rock masses : Dhar, Y R; Choubey, V D; Pandalai, H S Proc 6th International Congress International Association of Engineering Geology, Amsterdam, 6–10 August 1990VI, P593–599. Publ Rotterdam: A A Balkema, 1990