Extensions Of Three-dimensional Discontinuous Deformation Analysis And Its Application In The Initiation Mechanism Of Earthquake-induced Landslides Considering Pulse-like Ground Motions

Slopes tend to become unstable when they are impacted by earthquakes,thus inducing landslide movements.Strong pulse characteristics are usually found in ground motion recordings of stations near faults.Under the influence of strong pulse ground motions,the travelling speeds and distance of sliding masses are higher and larger than those triggered by earthquakes with weaker pulse effects,thus causing huge damages to human lives,properties as well as resources.Therefore,researches concerning the effects of the pulse components in earthquake recordings have on the motion characteristics of landslides are of great imminence and importance.For rocky sliding masses where joints and fractures develop,the contacts between each blocks are highly discontinuous.Therefore,Discontinuous Deformation Analysis(DDA),a numerical tool for analyzing discontinuous and large deformation,was chosen for the study of seismic landslide movements.Three-dimensional deformation analysis(3-D DDA)is an extension of Two-dimensional deformation analysis(2-D DDA)in the dimensional concept.Compared to 2-D DDA,3-D DDA is capable of considering seismic loadings along both directions of the horizontal plane.What's more,the motion paths as well as deposit areas of three-dimensional blocks in the three-dimensional space can also be simulated and studied by using 3-D DDA.Therefore,3-D DDA is a useful numerical tool for studying the motion characteristics of landslides.Earthquake loadings cannot be functionally considered in the original 3-D DDA program,which sets an obstacle for the study.Therefore,a seismic model was built into original main 3-D DDA program to achieve the purpose of loading earthquake records into the program and transforming the seismic accelerations into block body force.Thus the shaking motion of the base block can be simulated by the new developed program.The two blocks model were used for studying the seismic loading accuracy of the new program.And the sliding block model was used for verifying the calculating accuracy of dynamic sliding blocks.The results show that the newly developed program is capable of dealing with the problems concerning 3-dimensional block dynamic motion.The motion characteristics of sliding block,which is considered as the simplest form of landslides,was further studied by using the updated program on the basis of its correct verifications.The results show that the changing behaviors of sliding distance are in highly relation with the orderly harmonic waveform,which also verifies that correct transmission of seismic loading from the base block to the sliding block can be achieved in the new program.The simulation results of the three-layer sliding blocks model show that the drawback of theoretical method,which is only capable of considering one sliding block,can be well overcomed by using the 3-D DDA numerical simulation method.The sliding-triggering mechanism of the pulse components in earthquake recordings as well as the pulse effect of two certain near-fault earthquakes along different directions were studied through an eight sliding blocks model by using the updated 3-D DDA program.The results show that the block started sliding right at the time when the main pulse was applied to the base,and the block travelled with high velocity during the main pulse period.It is considered that stronger pulse components often cause longer traveling distances and higher velocities of sliding blocks compared with those with weaker pulse components,which can be explained as the sliding-triggering mechanism of pulse-like earthquakes.The simulation results of motion process of the eight blocks in eight different directions further verify the strong pulse effects vertical to the strike directions of geological faults,which is one of the major achievements of former studies.After the studies of simple sliding blocks,the motion process of a real landslide on complicated topography was simulated and the results show that motion of blocks in the front side of the sliding masses is more sensitive to seismic loadings than those in the rear side.Under the influence of earthquakes with stronger pulse effects,more rock blocks started sliding earlier and traveled faster and longer than those caused by earthquakes with weaker pulse effects,causing great damages to human architectures nearby.Therefore when predicting disasters and making corresponding counter measures for seismic landslides,due attention should be paid to the sliding-triggering mechanism of strong pulse components vertical to the faults striking directions in mountainous areas with tense geological faults distribution and frequent earthquake events.