GEOTECHNICAL HAZARD EVALUATION AND TUNNEL SUPPORT SYSTEM FOR SAFE AND SUSTAINABLE EXCAVATION OF ZALAM KOT TUNNEL, SWAT EXPRESSWAY

Abstract

The basic aim of this thesis is to asses and analyze the techniques and methods for the safe excavation of Zalam Kot twin tube tunnel. Evaluation of primary support for tunnel is also carried out. This study is also focused to evaluate the geotechnical hazards related to excavation in order to avoid and minimize the damage in case of any hazardous geologic event. This twin tube tunnel site is located in Zalam Kot, District Malakand. This 1300-meter-long tunnel on Swat expressway near Malakand is being constructed by the Frontier Works Organization (FWO). This tunnel is situated at the foothills of MMT, and the formation encountered here is Saidu sharif Formation. This Formation is mainly composed of graphitic schist but at some places traces of mica were also encountered. According to field surveys the lithology encountered is mainly homogeneous, but at some places highly sheared zones, wedges and quartz veins were also encountered which acted as weak zones during the excavation process of tunnel. Rockfall assessment tests and tunnel hazard index is calculated for Geotechnical hazard evaluation of tunnel. During excavation, hazards encountered are of low index while the consequences are comparatively higher. In order to asses and analyze the excavation method, RMR technique was used which specified that rocks of this area had values ranging from 41-60, that classified these rocks of “Fair to Poor” quality. Based on RMR results, New Austrian tunneling method (NATM) is recommended for excavation. The primary support designed for Zalam Kot twin tube tunnel consists of rock bolts, lattice girders, shotcrete, steel ribs, kicker lining and wire mesh. Geosynthetic sheets such as geomembrane and geotextile sheets are installed for water proofing.