| Landslide means that under certain terrain and geological conditions,due to various natural or human factors,the unstable body on the slope is moved forward and downward along a certain weak band under the joint action of its own weight or other loads.Rock landslide is an important category in landslides.It has occurred in China in recent years.Landslides are mostly induced by rainfall,such as the Jinxing landslide in Dafang County,Bijie City,Guizhou Province,and the Sucun landslide in Suichang County,Shaoxing City,Zhejiang Province.Etc.Especially in the red zone,this rainfall induces a particularly large number of rock landslides.The red-layered area is distributed between soft and hard rock.The soft rock has low strength and high clay mineral content.It is easy to soften and muddy when it meets water,forming a weak interlayer.Hard rock mass is broken and joint fissures are developed,which is beneficial to water entering the slope.In the face of heavy rainfall,it is prone to mass rock landslides,causing a large number of casualties and property losses.Therefore,strengthening the early warning research on such rock landslides has important theoretical and engineering value for safeguarding people's lives and property and reducing economic losses.At present,domestic and foreign scholars have conducted more research on rainfall warning of rock landslides,and have also achieved good early warning effects.For landslide rainfall warning,the relationship between landslide and rainfall intensity and accumulated rainfall is used to obtain the landslide rainfall threshold for landslide warning at present.However,the rainfall threshold determined by this method does not consider the impact of geology,topographic factors and the type of landslide.The difference between the rainfall thresholds obtained in different regions is large,and the application scope of the early warning model is small.In summary,it is very important to establish an early warning model that is more general,and comprehensively considers various influencing factors of landslides.Through field investigation and data collection of Nanjiang County “9.16” mass rock landslides,Yunyang and Fengjie County “9.1” mass rock landslides and other rainfall-type rock landslides,the landslide topography,geological and rainfall datas were collected.The material composition,genesis and properties of the sliding surface of the rock landslide are studied and classified.Based on the early warning model of rock landslide in the red layer,a rainfall warning model for rock landslide with different sliding surface types is established.Provide a new method for early warning and forecasting of rainfall-type rock landslides,and provide technical support for disaster prevention and mitigation.I have gained the following recognitions and results:?1?The sliding surface is the key to the analysis and evaluation of slope stability.The sliding surface is generally composed of rock mass structural planes.The structural planes reduces the integrity of the rock mass and has a significant impact on the permeability and physical and mechanical properties of the rock mass.The shear strength of the sliding surface is an important mechanical parameter for evaluating the stability of rock slope.The greater the shear strength of the sliding surface,the more stable the landslide.?2?According to the material composition,cause and nature of the sliding surface,the sliding surface of rock landslide is divided into a weak interlayer sliding surface,a rock layer sliding surface and a joint surface sliding surface.The soft interlayer slip surface is formed by softening and mud formation under the combined action of diagenesis,tectonic action and epigenetic action of soft rock such as mudstone and tuff.The sliding surface of the rock stratum is formed by the combination of diagenesis,tectonic action and epigenetic action of the same lithology or different lithology.The sliding surface of the joint surface is composed of one or more joint surfaces combined by structure and surface action.?3?The surface of the sliding surface of the weak interlayer is flat and smooth,the clay mineral content is high,the degree of bonding is extremely poor,the water is easy to soften and mud,and the mechanical properties of the sliding surface are significantly reduced.The shear strength of the sliding surface is closely related to the soaking time.According to the fitting curve and rainfall duration of the red-slip zone in Nanjiang County,the shear strength parameters of the weak interlayer of the red layer in Nanjiang,Yunyang and Fengjie County are taken as the shear strength parameters c = 16.0 kPa,? = 7.2 °.The shear strength of other weak interlayer sliding surfaces investigated in this paper ranges from c = 12.6 to 16.9 kPa and ? = 4 to 9.7 °.The surface of the sliding surface of the rock stratum is relatively flat and smooth,slightly undulating,and the degree of bonding is poor.The hydrophilic minerals are less and only a small amount of clay material is filled in the layer fissure by water.The softening effect of water is limited.The sliding surface of the joint surface is better,the surface is rough,and the degree of bonding is general.The sliding surface contains less hydrophilic minerals,and only a small amount of clay material is filled in the joint crack by water.The softening effect of water is limited.It is difficult to sample the sliding surface of the rock stratum and the joint surface.So,it is difficult to obtain the shear strength value by the test method.In order to reduce the interference of human factors,according to the method of value of structural plane in the technical specification of building slope engineering?GB 50330-2013?,the shear strength of the sliding plane of rock stratum is c=50kPa,?=18°,and the shear strength of the sliding surface of joint surface is c=90kPa,? = 27°.?4?Select the typical rainfall-induced rock landslides,and analyze the geological environment conditions,basic characteristics and genesis of the landslide formation.Based on the early warning model of rock landslide in the red layer,the relationship between topographic factor T,rainfall factor R and geological factor G of the large displacementrock landslide point,small displacement landslide point and rainfall contrast point is compared and analyzed.The rainfall warning model of rainfall-induced rock landslide is obtained : P=RT/G.=(ID0.8/H1?S + 3.33U?/?tan??0.5?Cr.?5?The critical value of the rock landslide in the soft interlayer is 4.8,6.2 and 7.6,and the maximum and minimum thresholds are 58.3%.The model has a good early warning effect.When P is greater than 7.6,the percentage of large displacement landslide points to total is 75.3%;when P is less than 4.8,the percentage of small displacement landslide points and rainfall contrast points respectively is 31.3% and 100%.?6?The critical value of Cr for the sliding surface rock landslide in the rock stratum is 3.2,4.4 and 5.6.The maximum and minimum thresholds differ by 75%.The model early warning result is good.When P is greater than 5.6,the percentage of the large displacement landslide point to the total reaches 100%;when P is less than 3.2,the percentage of the rainfall comparison point to the total is 100%.?7?The critical value of the rock surface landslide of the joint surface is Cr,which is 7,8.3,9.6.The maximum and minimum thresholds differ by 37.1%.The model early warning result is good.When P is greater than 9.6,the percentage of large displacement landslide points accounts for 72.7%;when P is less than 7,the percentage of rainfall comparison points accounts for 87.5%. |
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