The understanding of time dependent effects or creep behavior is important in further development of knowledge in the field of rock mechanics. Increasing pressure on support system because of creep behavior of rock is one of the most important problems in underground structure which surrounded with weak rock mass. This paper presents a time dependent behavior analysis of Kiah Boshes pumped storage powerhouse cavern with complex geometry, available geological formations and diverse geotechnical properties of rocks, is under construction on the Chalks River at the north of Iran. Because of the fractured and jointed rock mass, the Discrete Element method Code 3DEC used to compute convergence and pressure on the support system. The power constitutive creep model which is able to model the primary and secondary creep regions of rock masses is applied. In this paper, results of the Kiah Boshes cavern as a case study dealing with a comparison between long-term deformation data from in situ measurements and obtained data from an analytical solution and numerical simulations with special consideration of anisotropic effects will be presented. The differences between the obtained values might be because of discontinuous media or different inputs parameters were used for analysis.

1. Introduction

The rheology and time-dependent behavior of rock are fundamental mechanical properties of the rock material, which can be used as an important bases in explaining and analyzing the long-term stability for rock engineering. Especially, time dependent deformation of rocks has significant effect on stability of underground structures, such as nuclear waste storage facilities, tunnels and powerhouse caverns. It is particularly common in underground structures excavated in soft rock, heavily sheared weak rock masses or rock masses subjected to high in-situ stresses (German, et al, 1988; Carla, 1995; Basin & Grim stand, 1996). In order to study the stability of the underground structures and designing their support system, time dependent deformations should be highly considered (Salami, 2004; Thai, 2008). Therefore, time dependent behavior of underground structures as well as predicting the long-term behavior, is of great importance. This paper presents a time dependent behavior analysis of Kiah Boshes pumped storage powerhouse cavern with complex geometry. The cavern is being built in a region that is highly prone to sheared and fault zones where their failures could cause severe damages to underground spaces. It is therefore essential to analyze and design underground structures for preventing any serious long-term damages in the region. The rock mass may exhibit continuous or discontinuous deformations due to the existence of large underground openings: shear of joints and creep deformation.

2. Kiah Boshes pumped storage project

The Kiah Boshes pumped storage project is located at the Labors chain Mountains being mainly formed and folded during the Alpine organic phase. The most important tectonic phenomenon of Kiah Boshes area is the fault called as the Main Thrust Fault (MTG), with a dip direction of 78/028 and an almost E-W trend. The site of powerhouse caverns is generally located at the Permian Formation part.

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