| Located in the hinterland of the Three Gorges reservoir area,Wan Zhou District of Chongqing city is one of the the worst landslides regions.According to the investigation results of geological disasters about Wanzhou in2010, there are a total of1193geological disasters points and925landslides points in this region.Near Wanxian syncline axis, there are several huge landslides, in the area with width of8km and length of45km, although the strata dip is relatively flat which is generally less than10°,the main Wanzhou city is located in the old landslide with the nearly horizontal rock strata environment.In recent years, influenced by the global warming climate, extreme preternatural heavy rain in Wanzhou District appears more and more frequently, therefore, formation probability of rainfall-induced landslide will also rise, lots of translational gliding landslides have happen in this region,this kind of landslides are in small quantities compared with a large number of accumulation landslides wich take creep as the main damage mode,but generally more landslides occur suddenly with large cracks in the ground in trailing edge and seriously damaged houses on the landslide,so it can cause public panic and have a great impact on society.Therefore, to summarize development and distribution rules of the nearly horizontal strata landslide in Wanzhou District and bring forward economical, simple,and easily spreaded control measures in rural areas are important to that carrying out more targeted prevention of geological disasters,avoiding resurrection of old landslides induced by the irrational human construction activities, preventing new translational gliding landslide from appearing,ensure people’s lives and property safe, reducing damage losses. Because the distribution of nearly horizontal strata landslide in Wanzhou District is relatively concentrated,and it has some specificity, based on the data of correlative landslide investigations, landslide survey and the on-site investigations collected at different times in Wanzhou District,according to the statistical analysis of14similar landslides,firstly, starting with geological environment conditions of nearly horizontal strata landslide in Wanzhou District, it is studied one by one on the factors such as meteorology and hydrology, topography and spatial distribution, geological structure,lithology, hydrological and geological conditions, human engineering activities,then the basic development and distribution rules is obtained.Secondly landslides are analyzed combined with two typical examples.Among them, fujiayan landslide is representative of nearly horizontal strata old landslides in Wanzhou District. In this instance, it is focused on that how fujiayan landslide comes into being in special geological environments of Wanzhou District,at the same time it is explored that how river incision and human engineering activities and other factors affect the stability of such old landslide;dabaoliang landslide is representative of nearly horizontal strata new landslides in Wanzhou District. in this instance, development characteristics of new translational gliding landslide has been focused on, then it is gived rise to the development trend of nearly horizontal strata landslides in Wanzhou District.Finally, economical and easily achieved countermeasure are given for similar landslides in Wanzhou District. Therefore, this paper’s research content and innovative work are as follows:(1)The landslide investigation, survey results are summarized and analyzed in Wanzhou District at different times for the past, the development and distribution rules of nearly horizontal strata landslides in Wanzhou District is summarized;(2)There are two-stage landslides about old landslides in the studied area, the grade with higher level distribution place remains eomorphology of translational gliding landslide, with typical landscape characteristics such as rupture groove, depression, pond, rockery in trailing edge,with slow and wide landslide platform in the middle place, and with a high range of scarp in the first part of the landslide,and the whole is stable.The grade with lower level distribution place is more generally into a gently slope-shaped,and the front edge stretches from the river bed.As the continuous erosion by the river at the foot of the slide,it is in a less stable state with long-term creep deformation;(3)Translational gliding damage is the core formation mechanism of old landslide at beginning, in geological history, caused by tectonic effects and long-term effects of groundwater, mudstone in the slope is softened or mudded, then become weak intercalation. Weak intercalation has plasticextrusion in the overhead direction under the overlying gravitypressure, and gradually lead to rupture, disintegration, and subsidence of overburden. In the Case of heavy rainfall, tension cracks are filled with water. Groundwater percolats through the top surface of weak interlayer. On the one hand,it reduces the soft interlayer shear strength, on the other hand it produces uplift, coupled with the hydrostatic pressure in the tension cracks of the trailing edge. Because of the three combined effects, overlying rock is moved horizontally along the soft interlayer, finally translational gliding landslide is formed. After the landslide starts, tension cracks in the trailing edge widen and become tension groove and waterlogged depression, at the same time, hydraulic head lowers quickly,and the landslide body breaks quickly.But at present,it shows traction damage of the leading edge. Though The new nearly horizontal strata landslides in the studied area is small,they are typical translational gliding landslides;(4)On the basis of conclusion of the development and distribution rules, a complete set of control measures is proposed. First of all, similar slopes in the studied area should be to investigated, the key control areas should be pointed out,and then disaster prevention and mitigation should be carried out in targete;at the same time, disaster prevention and mitigation knowledge should also be spread to avoid unreasonable engineering activities which can induce landslides; against nearly horizontal strata landslides occurred, it should be taken the the management idea that water control is the main thing, and the retaining is the second thing. |
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