Study of anisotropic behavior at jointed rocks for big span underground structures with NATM philosophy

Abstract

Underground structures mainly composed in rock environment may be defined as the load-bearing structures under all loading cases. The behavior of the rock environment is the critical component in understanding the behavior of the underground structure and the design procedures. NATM that is accepted as a philosophy rather than a design method is the primary conception in underground rock engineering. The behavior of the rock environment under principal stresses is going to be affected, utilizing secondary and tertiary stresses. The physical dimensions of the technical interference (can be accepted as tunnel structure) which is to be the main issue in the classical design should be designated due to their orientation, joint structures and its surrounding environment properties. The main goal of this study is to examine the relationship between the dimensions of the excavated area with its surrounding environment for anisotropic behavior to define the problem more accurately. Physical and numerical modeling tools were used, and the dimensionless interactions in the design of underground structures were tried to be built. Base friction method was selected and bricks from sugar were used for physical modelling. The ratio of joint openings to tunnel diameter was varied between six to twelve with changing inclination of joints from horizontal to ninety degrees (gradually with 15 degrees each set) with respect to horizontal were provided simultaneously. One of the goals was to determine the influence distance of number of joints at the heading part of the tunnel. Moreover, the variation of influence zone due to the effect of the anisotropy was also studied. The results of total 49 numbers of tests were interpreted, and an analytical variation was derived. The findings of the study were aimed to gain the effectiveness of the excavating strategies in the light of NATM philosophy to find out the correct phenomena in design for big span underground structures.