SLOPE STABILITY STUDY OF DHAL - KOHALA ROAD

Abstract

Amongst the northern and mountainous region of Pakistan, Murree - Kohala is considered to be one of the worst slide-affected area. The landslide hazard on the road section Dhal - Kohala has been a cause of great concern affecting the safety of life and property. During last three decades, the extent and severity of the problem has aggravated manifold due to indiscriminate land use and un-planned urbanization. Under this scenario it is pertinent that landslide vulnerability and studies for the area are of utmost need. Landslides and related slope failure phenomenon occur in all parts of the world especially in mountainous areas. A lot of experience and knowledge has been accumulated over years in understanding, recognition and treatment of landslide hazards, however, due to diverse nature of this problem knowledge in this field is still fragmentary. The area requiring particular attention is the proper investigation and analysis for appropriate design and cost-effective remedial measures. This requires a clear understanding of the conditions and processes that cause landslide. Sufficient progress has been made in developing techniques to minimize the impact of landslide through more efficient, quicker and cheaper methods of mitigation. Landslides can generally be controlled by one or combination of any four principle measures i.e. modification of slope geometry, drainage, retaining structures and internal slope reinforcement. There are a number of levels of effectiveness and levels of acceptability that may be applied in the use of these measures, a particular slide may require an immediate and absolute long-term correction, whereas, another may only require minimal control for a short period. In this study the causes for initiation of landslides along the road section Dhal - Kohala are evaluated and remedial measures are suggested. Extensive survey along the route reveals that stable areas are where the grades are mild, vegetative growth is thick and surface / subsurface drainage measures are good. Correspondingly, the slopes with less vegetative growth and improper surface / subsurface drainage and steep grades are found to be more susceptible to slope failure. The study area is divided into zones based upon its stability potential i.e., stable, less stable, meta stable, and unstable zone. Two typical landslides were selected for detailed investigation and analysis. The results obtained can be applied all along the route on areas exhibiting similar conditions. Field investigation plan was prepared to evaluate soil / rock strata and surface / subsurface drainage. Relevant field tests were performed to determine in-situ strength properties of soil / rock. Detailed laboratory testing plan was prepared to determine the strength properties of soil and rock samples in simulated conditions. Computer software GEO-SLOPE office (2002) is used for the analysis of slopes based on the material properties obtained from tests and survey conducted for each potential landslide, under simulated conditions. The analysis of the slopes has been carried out for different scenarios, controlled by material input parameters. Finally, the slopes have been checked for the effects of the recommended solutions.