Integrated geophysical and geotechnical investigations of selected landslide along China Pakistan Economic Corridor (CPEC)

Abstract

China Pakistan Economic Corridor (CPEC) is a regional network of connectivity (roads, physical infrastructure) between Central Asian and European countries through Pakistan. It is a milestone initial investment of USD 46 billion towards trade and industry development in a digital world. Due to the active tectonics of the northern region of Pakistan followed by several recent disastrous earthquakes, the existed Highways network of CPEC in north Pakistan, i.e. Karakoram Highway (KKH) is highly vulnerable to fluid mountain hazards and poorly designed infrastructures built along the CPEC Highways network from Khunjerab to Gwadar in Pakistan. It is time to assess the stability of potentially hazardous sites that can destroy the existed CPEC Highways network in north Pakistan and deliver the seismic structural design for all kinds of infrastructure built along with the Highways network of the CPEC project. Probabilistic seismic hazard assessment (PSHA) of the Highways network of CPEC from Khunjerab to Gwadar in Pakistan is carried out by using an Areal seismic source model. The seismic hazard maps of the Highways network of CPEC are derived, using the standard Cornell-McGuire (1968-1976) methodology by considering all the earthquakes (25AD-2020) incurred in Pakistan and surrounding regions. The final ground motions are attained as peak ground acceleration (PGA) and 5% damped spectral acceleration (SA) at T=0.2 s and T=1.0 s for 475-, and 2475- years Return Periods (RPs) (for engineering rock site conditions, i.e., Vs30 of 760 m/sec). Results of the analysis are displayed as color-coded maps that signify the amplitude deviation of ground motion parameters. The ground motion intensity values (i.e., PGA and SA) obtained in this study can be utilized for all kinds of infrastructure, particularly the spectral intensity values explicitly for the seismic design of the bridges along with the Highways network of the CPEC under AASHTO guidelines and can make this USD 46 billion investment secure and productive. The ground motion hazard assessment has categorized various CPEC routes susceptible to the highest peak ground acceleration. Therefore, the existed CPEC route that is passing nearby Mayoon village, Hunza-Nagar District, Gilgit Baltistan is considered as the potential site that has the capability to create an artificial dam like Atabad Lake. The stability of Mayoon landslide is assessed using an integrated geophysical and geotechnical approach. It is a slowly developed, non-catastrophic landslide that has gained importance in the last few years after its rapid activation and fast slip rate. The present study has characterized the area by high earthquake hazards (with peak ground acceleration value of 0.32-0.52 g for 475-years return period) due to frequent earthquakes. The non-invasive geophysical techniques, including Ground Penetrating Radar (GPR) and Electrical Resistivity Soundings (ERS), are deployed to evaluate the Mayoon landslide subsurface. The subsurface is interpreted into a two-layer model. Bright reflectors and highly variable resistivity characterize the top layer (Layer-1). Hyperbolic reflections and intermediate resistivity characterize the bottom layer (Layer-2). The hyperbolic reflections show faults/fractures within the bedrock. The intermediate resistivity shows that the bedrock is weathered and foliated. Reflections within Layer-1 have disrupted directly above the fractures/faults suggesting a possible movement. A bright reflection between the two layers highlights the presence of the de bonded surface. Loose material within Layer-1 coupled with de-bonding possesses a significant hazard to generate a landslide under favorable conditions such as an intense rainstorm or earthquake activity. Mayoon landslide eastern and western exposed rock stability is assessed using an empirical method and kinematic analysis (stereo net plots). The Slope Mass Rating (SMR) has quantified the eastern exposed rock as stable, whereas the Western exposed rock as partially stable. The Kinematic analysis has predicted the potential of toppling in the eastern side, whereas the Western side has potential of wedge failure. The numerical modelling has provided the factor of safety for Mayoon eastern, central and western sections based on material properties and landslide geometry. The recommended mitigation measures based on geophysical and geotechnical investigations can save the existed CPEC Highway in north Pakistan, i.e., KKH and community residing under these fluid mountains.