Abstract
In order to either optimal use of water resource of KELAS river basin and electrical energy generation, Sardasht Dam and power plant are designed. Dam water diversion system includes two tunnels with inner diameter of 7 m. Several collapses have occurred in portal of second diversion tunnel (A2) which has created large cavity in tunnel crown. In order to prevent collapse, various ways such as steel sets installation and also grouting to increase strength of surrounded rock mass, are prescribed but none of technics could not to ban caving in. considering this fact that in order to continue tunnelling process, collapse zone should be passed, a solution or solutions must be suggested to overcome consecutive and dangerous collapses problem. In order to decrease tunnelling risks, in this research, using both experience and knowledge obtained from previous proposed executive solution to similar cases and technically analysis of occurred collapse in current diversion tunnel, it has been tried to suggest a new appropriate solution which defeat the problem. Finally, in order to stabilize of tunnel crown, as an effective and applicable solution, constructing retaining crown by means of rock bolts, was introduced.
Highlights
Underground spaces contain several hazards due to their position in an environment with high uncertainty
Review of accidents and damages occurred in underground structures is a key tool to understand unstable phenomena and processes that we encounter during construction of structures [1, 2]
Placement of fragmented zone resulted from a fault located between diversion tunnels 1 and 2 and dip and strike of that fault, which is approximately parallel to tunnels with a little inclination towards the second diversion tunnel, caused left wall of the second diversion tunnel on 0+18km to come near this fragmented zone and initially suffered from limited collapse
Summary
Underground spaces contain several hazards due to their position in an environment with high uncertainty. This is the reason why several faults and discontinuities formed on tunnel route They designed a support system, after geo-mechanical classification of rock mass of tunnel route [3]. Rock mass classification was done simultaneously with tunnel excavation and proper actions provided caused decreasing risk of hazards such as flood and rock fall in tunnel route [5]. Fraldi and Guarracino conducted studies on analytical solutions for collapse mechanisms in tunnels with desired cross section. Based on the analysis of working face status and review of the construction process for several months, it has been shown that the improper emergency measures adopted were the direct cause for the collapse.
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