Abstract
This study was conducted along a tunnel in Crocker Formation. The objectives of this study are to determine the value of Geological Strength Index (GSI) and to predict rock mass properties, very unfavourable discontinuities combination and tunnel support pressure for rock bolts or shotcrete for the tunnel. Engineering geological mapping, rock sampling and estimation of GSI values and the disturbance factor were conducted along the tunnel faces. Laboratory analysis includes Point load and dry density test and data analysis consists of kinematic analysis and limit equilibrium analysis. The rock mass was characterised by 94.88 MPa UCS, 0.024 MN/m3 unit weight, widely space and high persistency of discontinuities. The GSI value is 50 with 0.8 disturbance factor. The cohesion, tensile strength and friction angle are 3.671 MPa, 0.056 MPa and 25.20°, respectively. There are eight possibilities of discontinuities combinations on tunnel roof that have factor of safety (F.O.S) lower than 2 and combination of joints 2, 4 and 6 has the highest maximum wedge volume of 28.37 m3. The maximum support pressure of rock bolts or shotcrete for F.O.S of 2 is 0.04 MN. The individual discontinuity plane has been identified to overestimate friction angle and cohesion values, then the GSI system should be applied in homogeneous or isotropic and not in structurally controlled rock masses.
Highlights
This study was conducted along a tunnel in Tenom, Sabah (Figure 1) as shown in figure 1a
This study has been conducted in the study area because the application of Geological Strength Index (GSI) has never been attempted for the tunnel in Crocker Formation
The surface condition of the tunnel wall is good with structure and composition of type III
Summary
This study was conducted along a tunnel in Tenom, Sabah (Figure 1) as shown in figure 1a. The study area is underlain by the Crocker Formation of Late Eocene to Late Early Miocene ages and consists of tectonically disturbed thick amalgamated sandstone with thin shale layers (figure 1b) [1]. Major applications of this system was done by some researcher for a tunnel of Egnatia Highway in Northern Greece [6]. Another major application was done for the Chenani-Nashri Tunnel which is the longest road tunnel in India [7]. This study has been conducted in the study area because the application of GSI has never been attempted for the tunnel in Crocker Formation.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
