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.
