Stability Analysis and Remedial Measures Design for Landslide Mitigation Below Nagaland Legislative Assembly, Kohima - Thizama Road
A Three-dimensional reinforced erosion control mat with a self-drilling anchor was used for the protection of hill side-slope and in the valley side shotcrete along with Secured Drapery System which comprises DT mesh, Ring Net (GPS-H7) and self-drilling anchor is used for rockfall protection and slope stabilization work. The products are globally used by many countries. Materials are provided by OST Slope Protection Engineering India Pvt. Ltd. of standard specification as per the Indian and International codes.
Problem Definition
The road from Kohima to Thizama in the North-eastern Region of Nagaland passed through the mountainous region. The Slope is highly weathered and the joints orientation is forming wedge failure patterns whose probability of failure is high. Rainfall intensity is high in the particular region that’s why Slope is highly weathered and landslide has occurred formerly.
The chances of occurrence of disasters are very high, as the route is used for various transportation activities, it is necessary to provide remedial measures.
Protection Measures
After collecting the site data and analyzing it, slope protection measures are provided for the upside slope and downside slope of the road. The stabilization and rockfall protection system for upside rock slope consists of Self Drilling Anchors (SDA) of 32 mm dia., length 10 m along with a 3D reinforced erosion control mat. SDA provides the stability to the slope and 3D-Mat will prevent the slope from weathering. For the valley side of the road, stabilization work is carried out by providing a Secured Drapery system along with shotcrete. For secured drapery system DT mesh (60 x 80 mm), Ring net GPS-H7 along with SDA is used along with SDA is used. The mesh is made up of 3.0 mm dia. of high tensile steel wire. The steel wire is of high-carbon steel wire processed by the Galfan coating (Zn+Al). The tensile strength for GPS-H7 is >215 KN and ultimate bursting strength >380 KN.
The shotcrete of grade M25 (50 mm thick) is used to further protect the slope. Fiber-reinforced shotcrete with steel wire mesh reinforcement shall be provided to prevent exposure to weathering. Shotcrete is a pneumatically applied, fine aggregate mortar that is usually placed in a 50 mm layer and is often reinforced for improved tensile and shear strength. For the present slope the drainage pipes were provided at 8 m intervals longitudinally and 5 m laterally. The depth of drainage holes was 4 m with a diameter of 100 mm.
Installation
The area for protection has been prepared by removing loose and unstable rock fragments. For the upside slope of the road, SDA was installed and then 3D-Mat was provided. The top row of anchors was installed initially. For the valley side, first, the SDA was installed then DT mesh was provided. After that shotcrete of grade M25 and thickness of 50 mm was provided. Horizontal and vertical rope wires were installed properly at required places. Then the GPS-H7 (Ring net) system is installed. The total area for protection is greater than 2100 sq. m.
Concluding Remark
It is observed that the use of a 3D Reinforced Erosion Control Mat for highly weathered slopes and use of Secured Drapery System along with Shotcrete for stabilization, work soundly and can be provenly used for such conditions in future.
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