Development Of Excavation Damaged Zone Research Articles

Numerical Analysis of Tunnel Design Effect of Excavation Damaged Zone on Principal Stresses and Total Displacement

The development of Excavation damaged zone (EDZ) in an underground opening can significantly affect the overall performance of the opening. Generally, it is believed that the presence of such zone in any kind of underground opening can pose big problem to seepage flow, stability and subsequently impair the general performance and functionality of the excavation. In order to assess the influence of EDZ on excavation, the behavior of the principal stresses and the total maximum displacement was observed in the present study. Therefore, this study is aimed at numerical design of underground tunnel and determining the effect of EDZ on the principal stresses (sigma 1 and sigma 3) and total maximum displacement surrounding the excavation. The principal stresses (sigma 1 and sigma 3) were observed to decrease with increasing EDZ thickness and corresponding increase in elastic modulus, while the shear stress was observed to increase. The total maximum displacement was also observed to decrease with increasing EDZ thickness and corresponding increase in permeability. The general conclusion drawn from the analysis is that mechanical properties principal stresses and (total maximum displacement) decrease with the development of EDZ around the tunnel.

Contributions of In-Situ Stress Transient Redistribution to Blasting Excavation Damage Zone of Deep Tunnels

With the background of construction of the headrace tunnels with the deepest buried depth in China at present, by means of carefully acoustic velocity detection and analysis of Excavation Damage Zone (EDZ), the contributions to damage zones made by the effect of in situ stress transient redistribution are studied and compared with the extent of damage caused by the explosive load. Also, the numerical simulation was adopted to verify detecting the results. It turned out that the in situ stress transient redistribution during blasting has great influence on the development of EDZ of deep tunnels. The blasting excavation-induced damage zone of deep tunnels can be divided into the inner damage zone and the outer damage zone from the excavation surface into surrounding rocks. Although this damage zone dividing method is similar to the work of Martino and Chandler (2004), the consideration of developing a mechanism of the inner damage zone, especially the contribution of in situ stress transient redistribution, is totally different. The inner damage zone, which accounts for 29–57 % of the total damage zone, is mainly caused by explosive load and in situ stress transient adjustment, while the outer damage zone can be mostly attributed to the static redistribution of in situ stress. Field tests and numerical simulation indicate that the in situ stress transient redistribution effect during blasting contributes about 16–51 % to the inner damage zone in the 2# headrace tunnel of Jinping II Hydropower Station. For general cases, it can be concluded that the in situ stress transient redistribution is one of the main contributors of an excavation damage zone, and damage caused by in situ stress transient redistribution effect may exceed the damage caused by explosion load and become the main inducing factor for damage with the rise of in situ stress levels.

Influence of bedding planes to EDZ-evolution and the coupled HM properties of Opalinus Clay

Field observations at the Mont Terri site demonstrate an excavation damage zone (EDZ) around tunnels consisting of a complex crack network related to the bedding and the existing stress field. To separate the different impacts of the rock mass and bedding planes laboratory investigations were performed on Opalinus Clay samples including triaxial strength and direct shear tests. During the deformation tests monitoring of ultrasonic wave velocities, permeability and volumetric strain measurements facilitates the detection of stress induced onset of damage. Two stress dependent criteria were estimated, referring to various damage states, i.e. (1) to initial onset of damage and (2) occurrence of dilatancy. Based on the experimental results a new modelling approach for a prognosis of the evolution of the EDZ is developed consisting of two parts: (1) a (visco-)elasto-plastic constitutive model, comprising the hardening/softening behaviour and dilatancy effects of the rock mass, and (2) a specific friction model, which described displacement- and velocity-dependent shear strength softening for the bedding planes. The capability of the new approach is demonstrated by recalculating the spatial development of EDZ around a drift at the Mont Terri site.

Numerical simulation of the excavation damaged zone around an opening in brittle rock

The micromechanics-based damage model proposed by Golshani et al. [A micromechanical model for brittle failure of rock and its relation to crack growth observed in triaxial compression tests of granite. Mech Mater 2006;38:287–303] is extended so that time-dependent behavior of brittle material can be taken into account, with special attention to the numerical analysis of an excavation damaged zone (EDZ) around an opening, which is a major concern in assessing the safety of underground repositories. The present model is capable of reproducing the three characteristic stages of creep behavior (i.e., primary, secondary, and tertiary creep) commonly observed in the laboratory creep tests. The sub-critical microcrack growth parameters (i.e., n and A) can be determined for Inada granite by fitting the numerical results of elapse time to failure versus the creep stress ratio curve with the experimental data under both dry and wet conditions. It is found that moisture has a significant influence on the parameter A rather than the parameter n. Use of the extended model makes it possible to analyze not only the extension of microcrack length, but also the development of EDZ around an opening as a function of time. The damaged zones mainly develop in the sidewalls of the opening in the case that the vertical stress σ 22 is larger than the horizontal stress σ 11.