Research And Engineering Application Of Shear Strength Characteristics Of Bedding Weak Intercalation In Marl Of Southwest Hubei

With the rapid development of China's economy and the continuous advancement of national strategies such as the Rise of Central China and the Development of the Western Region,engineering activities in southwestern Hubei province along the Three Gorges Reservoir area of the Yangtze River have rapidly increased,and landslides and geological disasters in the region have occurred frequently,causing a large number of casualties and property.At the same time,heavy rainfall caused by extreme weather around the world will induce more landslide geological disasters.The weak interlayer is a special structural surface,which has the characteristics of low shear strength and easy to soften in contact with water.Rock landslides with weak interlayers are common geological disasters in southwestern Hubei and northeastern Chongqing.At present,there are few researches on the shear strength characteristics of weak interlayers in the Badong Formation T₂b₂ marl.It is a big problem in the engineering community to obtain more accurate shear strength indexes in engineering practice.For this reason,this paper has carried out related researches.The content of the research and the results obtained are as follows:(1)On the basis of sufficient literature research,the classification of weak interlayers was carried out,followed by the geological origin of weak interlayers,the occurrence of weak interlayers,the relationship between the principal compressive stress and the slope,the particle composition and the degree of fragmentation of the weak interlayers.,The geological characteristics of the weak interlayer,the lithology of the rock mass occurring around the weak interlayer,the state of the weak interlayer when it absorbs water,and the classification of the weak interlayer in other ways.(2)A medium-sized direct shear test was carried out.A total of 20 samples were prepared with the weak interbedded layer of marl in southwestern Hubei,and the water content was 8%,13%,18%,23%and 28%.of the remolded specimens were tested under the conditions of Normal normal stress of 50 k Pa,100 k Pa,150 k Pa,and 200 k Pa.The test shows that when the moisture content is gradually increased from 8%to 28%,the internal friction angle?decreases from 29.3°to 16.4°,a decrease of 44.02%;the cohesive force c decreases from 55k Pa to 15.2k Pa,the decrease rate Reached 72.36%.The test shows that the change of water content has a significant weakening effect on the shear strength index of the weak intercalation in the marl in southwest Hubei.At the same time,the relationship between the interlayer shear strength index and the moisture content is also quantified.(3)The particle flow PFC simulation software was used to simulate the medium-sized direct shear test.The meso-parameters in Model 8 were used to simulate the shear strength index and shear displacement properties of the weak interlayer.On this basis,the water content was predicted.The cohesion c when the ratio is 33%is 13.4 k Pa,and the internal friction angle?is 15.2°.(4)Apply the predicted shear strength of the weak interlayer when the water content is 33%to the treatment of the Shijiapo slope,and use the finite element numerical simulation software ABAQUS to study the slope stability.Research shows that the slope safety factor before treatment is 1.105,and the safety reserve is insufficient.After adopting anti-slide pile treatment,the slope safety factor is 1.385,and the slope safety reserve has been greatly improved compared with before treatment.The calculation shows that the treatment plan is reasonable.