Risk Analysis of Khansar Tunnel Rock Mass Collapse

The purpose of this study is to identify the risk status of Khansar tunnel. Hazard identification and analysis was performed by Reynolds matrix. Aerial images and photographs of coal phyllite rock masses and their outcrops on the ground surface were prepared and collapse sites were shown in aerial photographs along the axis of the tunnel. After field studies, observations and sampling of rock masses, the collected samples were transferred to X-ray diffraction laboratory in the Department of Soil Science of the University of Tehran. Physiographic and morphological status of the area was identified. Climate and humidity conditions of the tunnel were determined using synoptic data. Information on uniaxial compressive strength in both dry and saturated states for coal phyllite rock masses has been measured and a comparison diagram is shown to analyze the risk of collapse. Due to the direction and slope of the stratification of rock masses and the specified angles between 40 and 130 degrees, the mass collapse status for the tunnel was determined. Using Reynolds matrix data and obtained coefficients, the numerical hazard value for Khansar tunnel was in the range of 6, which by placing the number in the hazard matrix, the risk statue of the tunnel host area was assessed very high, therefore taking special safety precautions in Khansar tunnel is considered very important.