The Coupling Relationship Of Permafrost Hydrology And Geological Hazards In Yushu, Qinghai Province

The area of permafrost in Qinghai-tibet plateau is as much as one and a half millionsquare kilometers, accounting for about70%of the total area of permafrost in China, andespecially the permafrost in Yushu State is almost throughout the whole area. The permafrostregion has its own special hydrogeological characteristics, and develops into the special typeof groundwater in frozen zone, which is one of the factors leading to the special freeze-thawgeological disasters. Under the background of global weather warming up today, thepermafrost presents the tendency to degenerate, and with the development of the westernregion and post-disaster reconstruction project, the original insulating layer in frozen soilslope is destroyed, resulting in the decrease of slope stability in frozen soil. So the research onsoil slope stability in permafrost area is imminent. A study on this issue areas follows:(1) Basic on Geological environment survey in permafrost regions in Yushu, find out themain types of freezing and thawing slope disasters are: landslide, collapse, debris flow, thereare74landslide,205collapse,578debris flow, distribution in the high altitude basin andconcave and linear gradient of20~40on the slopes; The main factors affecting the stabilityof the slopes are: Topography, Lithology, Climate, precipitation, surface water andgroundwater; Under the effect of freezing and thawing by freeze-thaw weathering effect andfrozen stagnant water, frozen heaving and role of geological disasters.(2) Through30years of meteorological data from Yushu weather station analyzedvariation of soil temperature and moisture in permafrost area. In the melting season of the soilincreases with decreasing depth, but in the freeze season showed a reverse trend. Afterthawing of soil moisture increase than before freezing.(3)The shear strength is studied for the tested soil in six kinds of differenttemperature(-20℃、-15℃、-5℃、0℃、2℃、4℃) and five kinds of different moisturecontent(5%、10%、15%、20%、25%), and by simulating the process of frozen soil from a totalfreeze on to complete melt with temperature up, the conclusion is drawn that Shear strengthdecreases with water content increasing and drops with the temperature rising.(4)Based on the effective stress analysis method, the slope stability analysis diagramsunder different water conditions and different melting depth are drawn, and from safetycoefficient calculation chart, we can see that the security coefficient in the zone of dry slope isonce more than that in zone of saturation slope; thaw slumping occurs when the ramp is meltdepth of44-80cm; Under the frozen slope the safety coefficient is higher, through the melting process, the slope safety coefficient is increases with the increase of water content, the slopewhen the slope under the temperature0℃, the safety coefficient of slope is minimum.(5) Based on continuous medium explicit Lagrangian finite-difference method, authoruses Fish language of FLAC3Dto get access to the temperature item, to simulate the meltingprocess of slope. Simulation results show that: Soil temperature, pore water pressure andsafety coefficient are presents the seasonal change rule.In May, slope stability is the worst among one year, and the reason is that the activelayers of seasonal permafrost melt completely, and the value of pore water pressure andthe scope also increases. The minimum slope safety coefficient is0.91.(6) Choose typical prone month (May) to analysis the stress and shear strain of the slope,analyzed the most unfavorable position and damage from unstable slope in permafrost regions,provides the reference to the stability of the soil slope.