Developing the ground index (GI) for rock collapse assessment in tunneling

Assessing the possibility of rock collapse is important when tunneling in unfavorable geological conditions because damage can be minimized. A new methodology based on the Rough Set (RS) theory and the Rock Engineering Systems (RES) is proposed to quantitatively identify the tunnel surrounding rock conditions, and to provide the corresponding hazard level. Rock collapse hazards from recent tunnel construction projects in Fujian province, China, were investigated. On the basis of 164 compiled datasets, the ground index (GI) was defined. RS theory was implemented to identify reduct sets associated with the attributes while rock engineering systems (RES) approach was employed to quantify the interactions between the factors affecting the ground conditions. 24 independent cases were selected to validate the proposed GI by comparing predictions given by the GI with the field observations. The final results showed excellent agreement between predictions and observations which suggested that the GI could be used for a quantitative rock collapse hazard assessment of the tunnel surrounding rock. Both methods indicated that the rock quality design, intactness coefficient, groundwater and discontinuity condition, are among the most important parameters controlling the conditions of the surrounding rocks.