Proceedings of the 45th Annual Conference on Deep Foundations, 2020 - ONLINE , (DFI)
Use of Reinforced Concrete Drilled Shafts for Landslide Control in Pakistan - A Case Study
Sohail Kibria, Asim Masud, Obaid Rehman
The northern part of Pakistan is generally mountainous, having low hills in soft rocks to high rocky peaks of the Himalayas. Landsliding of mild as well as steep slopes is a common phenomenon in these formations. There are numerous natural as well as anthropogenic causative factors for the triggering of landslides in these slopes. A notorious landslide was stabilized a few years ago, in Murree area in soft rocks at Jhika Gali, Pakistan. The site is characterized by steep and deep slopes, high rainfall, poor drainage, high seismicity and poor geology, making it quasi-stable. A combination of natural and anthropogenic causes led to the formation of two large slides which took out about half the width of a very important road. A combination of earth embankment and reinforced concrete drilled shafts in multiple rows at the toe of the slope, helped curb further slope movement totally. The design of drilled shafts was based on extensive deep drilling, seismic refraction survey, characterization of complex geology, back-analysis of failed slope, laboratory testing and analysis of slope stability by Geo-studio - Slope/W. The drilled shafts were embedded deep into bedrock below the sliding surface to behave as long elastic elements and designed to carry lateral thrust of large sliding mass. The construction of these 4 ft diameter and up to 80 ft long shafts posed a serious challenge as the steeply sloping ground with difficult access was very weak. Rotary bucket auger was employed for the construction of shafts in very difficult geology. The behavior and stability of site during and after construction was continuously monitored with a set of instrumentation including surface markers, inclinometers and hydraulic piezometers. This paper describes the design and construction procedures as well as the issues involved during the execution of drilled shafts and the stability of slopes, as witnessed by monitoring afterwards.
|article #3692; publication #1073 (AM-2020)|