Complexity of the Ground Conditions and Non Compliance with Basic Assumptions in the Trench Stability Analysis: A Case Study in Iran

Basic Insufficient Geological and geotechnical studies will be caused the inaccurate parameters for trenchstability analysis. Therefore, as the first step, in the trench design, the special considerations forinvestigations and primary studies are very important. In the Portal of Sabzkuh Water Conveyance Tunneldesign, despite the adequate geotechnical investigations, field studies have not been performed withappropriate accuracy, consequently a landslide and collapse is occurred in a part of the portal because oftunnel excavation. The site geology was predicted by taking soil samples from trench soil withunderground and surface surveying inside of tunnel as well as trench site, that the Alternating layers ofCL, CH, CL-ML, SC-SM and GP-GM with more than 55 degrees slope as well as a buried slide surfaceunder alluvium was observed. But the primary assumptions used in the design by engineers were differentfrom the results that were noted at the recent lines. In this paper, the importance of having a precise andpredetermined schedule for selecting site location, Complexities of the ground conditions and its effectson the stability of the trench has been investigated.