Back analysis of an earthquake triggered landslide in Mansehra district, Pakistan
Keywords:
Back analysis; Slope failure; Limit equilibrium analysis; Slope mass rating (SMR); Slope stability evaluation; Sensitivity analysisAbstract
This paper investigates the slope failure along the Karakorum Highway near Sim Elahi Jung Village, District Mansehra Khyber Pakhtunkhwa, Pakistan by using numerical back analysis method. The slope face was ~80m high with a cut angle of 80 degree in quartz mica schist of Tanawal formation. The failure was triggered by 26th October 2015 earthquake of moment magnitude (Mw) of 7.5. The slope was investigated thoroughly for the geological conditions, slope geometry and the slid mass. During field studies, discontinuity surveys were conducted for onward assessment of the rock mass quality and orientation data for kinematic analyses. In view of rock mass quality determined from discontinuity surveys, back analyses were conducted considering slope material as Hoek-Brown material with the help of computer code Slide 6.0. The rock mass input parameters were adopted in the light of field and laboratory studies at the verge of failure. Back analysis conducted using estimated value of peak ground acceleration (PGA) have indicated that the geological strength index (GSI) value and the uniaxial compressive strength of the slope forming material were 24.0 and 29.0 MPa respectively at the time of failure. The analyzed slip surface and the observed ground slip surface were found consistent with each other, thus, confirming the validity of the model. The derived rock mass parameters are presented here for the evaluation of remaining slopes in the area having similar geological conditions and geometries.
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