Location: Madhya Bharath HEP, Sikkim
What: Brief of the Problem: Global Instability of Road near Dam Area
National Highway 31-A runs between Siliguri and Gangtok. Construction activities for the dam lead to settlement and global failure of road parallel to it. Activities for dam construction include blasting, excavation, submergence of the region; this is in turn leads to the generation of faults/fracture in the surrounding geological region due to blasting and excavation events. This (faults/fractures) may cumulatively go on widen with respect to time. Stress accumulation due to the movement of mass along fault and shear region leads to the issue of global instability.
This is same occurred for the HEP, Sikkim. Where the road was on the verge of global failure. This requires some rigid geotechnical stability measures to address the global instability issue.
How: Engineered Solution: Addressing the Global Instability Issue using Cable Anchors
Since, Stress accumulation due to movement of mass along fault and shear region leads to the issue of global instability. In addition, any seismic event can cause a disastrous event.
So, there was a need to provide the system which confines the zone to restrict lateral movement, which will also add the road strengthening and address the issue of global instability.
To serve the above purpose a system of cable anchors was used. Anchors prestressed at the load of 100-ton. Holes of 125mm diameter were drilled with 30 m depth for the installation of cable anchors. This resulted in to increase in road stability and provided resistance against lateral deformation.
Difficulties Faced during Execution:
Since the strata were extremely difficult in terms of implementation of the stability measure. Mass excavation resulted in collapsible strata. In addition seismic events also added the disturbance in the geological profile of the surrounding mass. So drilling and installation of cable anchors have to be done with extreme care.
Fragile geology created obstruction in maintaining the direction of drilling holes. The presence of the tough geological strata like boulders in anchoring direction led to repeated changing of drill bits.
The technology used for Execution:
Emerging and latest technology of passive ground anchors for the purpose of providing stability to the roadway was used. The implementation of this new technology served not only the purpose of providing stiffness around the excavated mass and road passing through a zone of disturbance but also provide global stability and safe path for vehicle movements.
All issues were overcome after the successful implementation of the cladding wall with cable anchors.
Geo Spar’s mission to provide fast and efficient services with lasting solutions was achieved.