SLOPE STABILITY STUDY ALONG MURREE - NATHIAGALI ROAD

Abstract

The northern regions of Pakistan have geomorphologically very active mountainous / semi mountainous terrain. Resultantly, population and infrastructure in these areas is vulnerable to hazards like landslides, earthquakes and flash floods. Amongst these hazards landslides are the most frequent and cause extensive damage to life and property. The fast expanding population and unabated deforestation have severely disturbed the fragile natural equilibrium of these areas. Extensive and ill-planned construction activity on barren and disturbed mountain slopes is causing an increase in landslides. Due to their importance the issue of “Landslides in Galiat Areas” is selected for research. The purpose is to investigate the causes of landslides along Murree – Nathiagali Road and suggest remedial measures. In Galliat Area, widening and improvement of Murree – Nathiagali Road has disturbed the natural hill slopes and strata resulting in frequent slope failures. The present study investigates the stability of slopes between Murree and Nathiagali (30 km), and suggests remedial measures to combat landslide phenomena. Extensive survey along with and adjacent to the Murree – Nathiagali Road was carried out and the section was divided into four zones based on slope stability failure potential. Two typical / representative sites in these zones were selected for detailed investigation and analysis. Field investigation plan was formulated to evaluate soil / rock strata and surface / subsurface drainage. Relevant field tests were carried out to find in-situ strength properties of soil / rock. A detailed laboratory testing plan was prepared to determine the geotechnical properties of soil / rock samples in simulated conditions. Based on the material properties and the survey conducted for each potential landslide site, the computer softwares were used for modeling / analysis of slopes. The modeling of slopes was carried out for different scenarios using software like Geo-Slope Office (2002) and Plane Failure Analysis Module. As a result of investigations and analysis it is considered that certain points need to be considered at different stages. For the slopes to be stable along Murree – Nathiagali Road, during construction phase of the road / infrastructure executing agency must take into account stability measures such as proper blasting techniques, proper slope formation, benching and drainage etc. Similarly, local residents must be educated about the land use and its environmental effects. There is need to formulate rational land-use regulations and there strict enforcement. Surface and subsurface drainage needs to be studied in detail and planned accordingly. Various protective measures like hydrological structures, breast walls, retaining walls and reduction in slope face angles are evaluated in the study. Finally, the study recommends preventive / protective measures to mitigate landslides along Murree – Nathiagali Road.