Investigating the reactivation of historical landslides during the 2022 Luding M_(S)6.8 earthquake

On September 5,2022,a strong earthquake with a magnitude of MS6.8 struck Luding County in Sichuan Province,China,triggering thousands of landslides along the Dadu River in the northwest-southeast(NW-SE)direction.We investigated the reactivation characteristics of historical landslides within the epicentral area of the Luding earthquake to identify the initiation mechanism of earthquake-induced landslides.Records of the two newly triggered and historical landslides were analyzed using manual and threshold methods;the spatial distribution of landslides was assessed in relation to topographical and geological factors using remote sensing images.This study sheds light on the spatial distribution patterns of landslides,especially those that occur above historical landslide areas.Our results revealed a similarity in the spatial distribution trends between historical landslides and new ones induced by earthquakes.These landslides tend to be concentrated within a range of 0.2 km from the river and 2 km from the fault.Notably,both rivers and faults predominantly influenced the reactivation of historical landslides.Remarkably,the reactivated landslides are characterized by their small to medium size and are predominantly situated in historical landslide zones.The number of reactivated landslides surpassed that of previously documented historical landslides within the study area.We provide insights into the critical factors responsible for historical landslides during the 2022 Luding earthquake,thereby enhancing our understanding of the potential implications for future co-seismic hazard assessments and mitigation strategies.

Simple approach for solution of the quasi-plane-strain problem in a circular tunnel in a strain-softening rock mass considering the out-of-plane stress effect

The out-of-plane stress is sometimes the major or intermediate principal stress in a circular tunnel opening.The influences of the outof-plane stress and axial strain are often neglected in the stability analyses of tunnel excavation,which can induce significant errors in the determination of surrounding rock deformations.In this paper,the use of a simple approach is proposed to solve the quasi-plane-strain problem of circular tunneling considering the effect of the out-of-plane stress,which is deformation-dependent and influenced by the in situ stress.As the intermediate principal stress is deformation-dependent,to obtain the numerical solution of the intermediate principal stress,the quasi-plane-strain problem is defined based on assumptions that the initial axial total strain is a nonzero constant(e0)and that the axial plastic strain is nonzero.With the numerical solution for the plastic strain,obtained using the plastic potential functions based on the three-dimensional failure criteria,the formula for the intermediate principal stress can be derived using Hooke’s law.The proposed approach can be utilized to obtain the numerical solution for the intermediate principal stress,which is deformationdependent,and the numerical results can be simplified as the solution presented by Pan and Brown.The proposed approach can also be used to obtain the solution for the strain softening of the surrounding rock.To verify its validity and accuracy,the results obtained using the proposed approach are compared with the solution of Pan and Brown.In addition,parametric studies are performed to address the influences of the out-of-plane stress on the stress and displacement in the circular tunnel.