Deformation Mechanism Of Loose Deposits Gentle Slope Due To The Yushu Earthquake

The State Rd G214Yushu Airport to Jiegu has already interrupted and the Provincial RdS308and S309are basically can maintain access due to the7.1-magnitude earthquake inYushu Qinghai Province on April14,2010. But collapse, cracking deformation and reducedstability of the landslides caused by the earthquake aroused a great deal of threat to roadsafety. At present, slope/landslide seismic stability calculations are still the pseudo-staticmethod based on limit equilibrium theory, which lack of a systematic and comprehensiveevaluation system. As a consequence, conduct slope/landslide earthquake damage survey,collect these information timely and analyze landslide deformation and failure mechanismcaused by the seismic can further provide the solid fundamental data to seismic research ofhighway engineering in China.In this paper, based on the project of State Rd G214Airport to Nangqian to Duo Pumaand Provincial Rd S308and S309reconstruction projects in Qinghai Province, using thecombining research methods of on-site investigation, theoretical analysis and numericalsimulation to study not only the geological characteristics and the choice of parameters of thelandslide in this research area, but also the problem of deformation and instability mechanismof the loose deposits dentle slope in the process of static and earthquake.(1) The spatial distribution of geological disasters in Yushu earthquake has greatrelationship with lithology, geological structure and seismic intensity. Which meansaccumulation area is priority to accumulation landslide, bedrock exposed area primarily highrock slope, while in floodplain areas it is frequently occur foundation liquefactiondeformation in the process of earthquake. Landslides and high slope disease distributionintensive and centralized on both sides of the road due to affected by active faults. The fartherfrom macroscopic epicenter, disaster number decreased significantly.(2) Several typical slope structural models were established according to the landslidegeological structure characteristics, the possible deformation and failure mode were analyzed,and further landslide stability analysis calculation model were established on this basis. Basedon the accumulation landslide structure exist weak clay layer or not, summarized three kindsof earthquake landslide stability calculation model as non-clay model, single-clay andmulti-clay model.(3) Strength test under a variety of moisture content for samples in the research areafound that the peak and residual strength are vary widely, and there is a great influence ofdifferent water content for strength parameters. Also, dynamic strength parameters ofgeotechnical material will significantly reduced on strong ground motion. (4) There is a huge difference deformation mechanism between different stratigraphicstructures in the landslide under the condition of static. For non-clay model, the deformationmechanism is the middle part first started to deform, and then traction the back as well assqueeze the leading of the landslide, which formed a typical three-stage mechanical model.For single-clay model, deformation starting from the back, and then squeeze the leading ofthe landslide formed a driven landslide. While, for multi-clay model, the deformation startedfrom the front of the landslide, and then traction the back, which formed a traction landslide.The landslide displacement is discontinuous in the lithologic interface, and become weak areaof the landslide.(5) In the process of earthquake, displacement of landslide in the lithologic interface iscontinuous, even for single-and multi-clay model, the landslide did not along the clay produceoverall destruction. Researches found that the decrease of strength parameters can make thefront of the landslide more unstable, but the back is less affected. After a period of earthquakeaction, the leading of the landslide starting to yield and become instability, then the back ofthe landslide began appear tensile failure, in addition, the yield range gradually expand andproduce slope creep slip. Finally, the landslide keeps steady state as a whole except forserious deformation and collapse in front of the landslide at the end of the earthquake. As theground motion intensity increases and the instability scope of the landslide become biggeralong with intense group movement; The above statement is the earthquake deformationinstability mechanism of Airport Road landslide group in Yushu earthquake.(6) Study found that the location of the yield elements and the shape of yield surfaceshowed great differences in the process of static and seismic dynamic force. To explain thisphenomenon, this paper puts forward the "vector disorderly mechanism" of seismic action,which can reasonably interpret the discontinuity of displacement in the lithologic interfaceand weak interlayer surface and it become the priority failure plane in the process of staticcalculation. But the destructive effect of which are not obvious in the process of earthquake,which also can explain the landslide slope displacement of ground surface and the free surfaceof the landslide is far great than other areas.