Landslides Susceptibility Assessment Along Karakorum Highway In Besham-dasu Northern Pakistan

Landslide is a major global problem.If landslide occurs in densely populated areas,it may cause serious damage to infrastructure and threaten the safety of people's lives and property.Therefore,how to effectively assess the risk of landslide and corresponding failure mechanism of typical geohazards are very important.However,the risk assessment of landslide is not easy.In the area where landslide may occur,numerical study on slope instability and landslide impact can be carried out better,which provides a useful reference for risk assessment of landslide.Karakorum Highway is an important channel of China Pakistan Economic Corridor.Under the strong geological tectonic movement and rainfall,there are widespread collapse and unstable slopes along the corridor.Therefore,Besham-Dasu section in Karakorum highway,Pakistan,which belongs to typical landslide-prone area,was adopted as study area.The mainly works contain: 1.To clear spatial distribution of landslides,a landslide inventory was established according to field investigation;2.To clear landslide susceptibility in study area,the using logistic regression model(LR)was to assess the landslide susceptibility of study area;3.To clarify failure mechanism and dynamic response of typical landslides,multiple numerical simulation methods were adopted.The results are listed as follows.(1)For landslide inventory and corresponding typical characteristics,the Google earth was used to interpret landslides preliminary,then a detail field investigation was carried out to verify them.The results show total 112 landslides were identified including 17 rockfalls;the geology,distance to the river,distance to the faults,slope angle,and rainfall are the most important factors for the occurrence of the landslides in the study area.The field results also show the main characteristics of existing rockfalls and vulnerable slopes in the study area mainly consist rock shapes rounded-cylindrical rock shakes,steep slopes and moderate weathering.The failure modes were confirmed finally.(2)For landslide susceptibility,9 conditioning factors i.e.,elevation,curvature,annual mean rainfall,slope angle,slope aspect,distance to the road,distance to river,distance to the faults,and geology were adopted as influence factors;the logistic regression model(LR)was used and inventory dataset was divided into 70% and 30% for training and testing.The final susceptibility map was divided into four classes from low to very high,(Low 22.46%,moderate 29.05%,high 21.50%,very high 26.99%).The accuracy of success and prediction rates are 83.40% and 82.10% respectively.(3)For failure mechanism and dynamic response of typical landslides,two most vulnerable slopes have been chosen to demonstrate its failure mode,the rockfall damage impact,factor of safety of the slopes and provide recommendation to develop their countermeasures.Dips software,Georock 2D software and SLIDE software were adopted.The main achievements are as follows:1)The results of stereographic projection analysis show that both slopes are prone to plane failure and wedge failure.2)The dynamic process of rockfall shows that the rebound height of the slope in section 1 and the slope in section 2 is 33 m and 29 m respectively.The total kinetic energy of rockfall in the section 1 is1135.099 k J and the velocity is 0.5m/s-44m/s.The kinetic energy of rockfall in the section 2 is 973.012 k J and the velocity is 0.5m/s-40.90m/s.3)The results of limit equilibrium calculation show that the stability coefficient of the section 1under static and dynamic condition are less than the critical factor of safety within(Bishop simplified method,Janbu corrected,Janbu simplified,and spencer method)which indicates that the slope is unstable,and the stability coefficient of the section 2 under static condition is greater than the required FOS.Whereas,under dynamic condition the FOS values are lower than 1,indicating that the stability of the slope under static condition is slightly stable while under dynamic condition the slope has lost its stability.This study showed a great damage potential of the rockfalls and landslides along KKH in Jijal-Pattan area,which would be a reference for the design of the countermeasures of rockfalls and landslides.