Effect of Closely Spaced, Non-Persistent Ubiquitous Joint on Tunnel Boundary Deformation: A Case Study from Himachal Him
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ORIGINAL PAPER
Effect of Closely Spaced, Non-Persistent Ubiquitous Joint on Tunnel Boundary Deformation: A Case Study from Himachal Himalaya Ratan Das
. T. N. Singh
Received: 28 September 2020 / Accepted: 7 November 2020 Springer Nature Switzerland AG 2020
Abstract The stability of an underground tunnel excavated in a jointed rock mass is studied using the field investigation and numerical modelling. This research aims to numerically analyze the rockmass behavior as a function of closely spaced non-persistent joints. For this purpose, the Kainchi-mod Nerchowck twin tunnels (Himachal Pradesh, India) is chosen for the in-depth analysis. The host rock encountered is mainly gray sandstone and maroon sandstone with many closely spaced, non-persistent joints, dipping critically into the tunnel. The detailed rockmass properties were collected from the field and intact rock properties were tested in the laboratory. A series of finite element numerical simulations were conducted based on the filed/laboratory data with different values of joint spacing, including the actual values of field joint spacing. It was found that the extent of deformation above the excavation was predominantly controlled by the joint spacing. The results of this study provide an explicit correlation between geometrical features of the rock mass with the total displacement values around the excavation. The study will
R. Das (&) Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur, West Bengal, India e-mail: [email protected] T. N. Singh Department of Earth Sciences, Indian Institute of Technology, Mumbai, Maharashtra, India
help the engineers to design an appropriate support system for heavily jointed rocmkass. Keywords Jointed rock Tunnels FEM Deformation Joint spacing
1 Introduction Stability analysis of tunnel is one of the most crucial requirements for the successful completion of tunnelling projects. The key geological factors that directly influence the stability of tunnels are mechanical properties of the rock mass, in situ stress environment and groundwater influx through the discontinuities (Panthi 2012; Bahaaddini et al. 2016; Sazid and Ahmed 2019). The discontinuities (joints) are the most common type of geological structure found in rockmass and it affects the mechanical behavior of the rock mass (Jia and Tang 2008). Most rock masses are discontinuous over a wide range of scales (from cm to m) and there are two major sources of discontinuities exist in case sedimentary rocks, i.e. the bedding planes and joints, the intersection of which forms the ‘‘blocky’’ rock mass. These discontinuities are fractured surfaces along or across which there has been little or no displacement and many catastrophes during or after tunnel construction are closely related to joints (Das et al. 2017a; Yang et al.
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2019). The mechanical behavior of jointed blocks with non-persistent joints is more complicated than having persistent joints. The m
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