Study On Hazard Mechanism And Prevention Technology Of Cutting Slope In Red Beds Soft Rock

This article,In view of the prominent cutting slope hazards of construction projects in the area of red beds soft rock, combining a number of high-grade highway construction projects of Sichuan, Chongqing, Yunnan Province, using the methods of survey research, geology mechanical model experiment, laboratory research, field testing research and long-term monitoring, numerical simulation and experience analogy, studied the rock mass structure and mechanical properties of red beds soft rock, and on the basis of it,studied the hazards formation mechanism and the control technique of cutting slopes in approximately horizontal stratum and inclined stratum, and also the weathering and erosion mechanism, control technique of cutting slope. The main research results include:(1) The hazard mechanism and the failure mode of cutting slope in red beds soft rock are studied with classification by the geological features in this paper. Based on wide range of investigation on the red beds soft rock highway slopes in Si chuan province, Chong qing city, Yun nan province and Gan su province, according to the geological features, three main categories are divided: approximately horizontal strata, inclined strata and faults-broken folding strata, and 12 sub-categories. According to the characteristics of the slope engineering, this article further put forward the classification of rock mass structure of slopes, which is classified into 5 categories and 11 sub-categories. This article discusses the characteristics of rock mass structure, controlling structure surface and the deformation and failure mode of slopes of each kind of the structure.(2) Carried compression, shear and creep test study on the typical rock sample. Through laboratory tests and large on-site shear tests, studied the shear strength characteristics of the structure plane. According to the nature of filling of structure plane, it is divided into four categories:open and less filling, closed without filling, thin filling and thick filling. Various types of structure plane was selected to carry out the shear strength test, the characteristics of deformation of typical structure plane in the shear load has been summed up. The reference value of the strength and deformation parameters of typical structure plane has been raised.(3) The structure plane of red beds soft rock, especially the soft interlayer, is very significant in rheology. By the analysis of the long-term shear strength and the short-term shear strength experimental information, advised that long-term strength is about 75% of short-term strength.(4) By mudstone indoor weathering test, on-site monitoring and investigation, revealed the mechanism of weathering and disintegration of red beds soft rock.The weathering and disintegration of red beds soft rock is caused by temperature and water together, only the change of water environment or temperature can not causes rapid weathering and disintegration.(5) The in-site monitoring of mudstone slope weathering and denudation shows that, high-temperature and large temperature difference, the weathering rate of mudstone on slope is rapid, the contrary is small. The number of rainfall over moderate rain has a great impact on the weathering and denudation volume of the mudstone, there was a relationship of negative exponent function between the two parameters, the light rain does not affect significantly. Mudstone watered repeatedly in the high-temperature is in high nature of weathering and disintegration. Therefore the weathering and collapse of mudstone on slope usually occurres in the summer,when is in high temperatures and has more rainfall.The data of in-situ monitoring work shows that from May to September the amount of weathering and denudation is 19.19kg/m2, accounting for 64.2% of the amount of weathering all a year(29.9 kg/m2).(6)The major hazard modes of the cutting slope in approximately horizontal red beds include:landslide, ripping deformation and rock collapse, and so on. The geomechanics model test and numerical analysis shows that, the landslide is taking the weak intercalation as slip plane and the steep joint as the back boundary, water pressure in fissure has an aggravating function to the slipping destruction. The method of conforming loose zone caused by cutting is put forward. On the basis of the analysis that how the rheology of the red beds soft rock affect the stability of slope, the method of decision-making using rheological mechanics resolving the problem of the slope stability is put forward.(7)The main hazard modes of cutting slope in inclined stara are the sliding of rockmass cutting by the plane and joints, which is according to the spatial relations between the plane and the slope. In allusion to the slipping-ripping damage for bedding slope, the method of conforming loose zone caused by cutting with the terrane unstable length is put forward.(8) A dynamic design method of high way deep excavation slope is advanced, which is make engineering geology survey to find out the slope rockmass structure, analysis the main structure plane which control the stability of slope, made correct judgment of slope stability and design the slope defending engineer, then carry construction supervise and design dynamically during the construction, analysis and summarize after construction.(9)Through the on-site rainfall simulative test before and after the ecological protection, the long-term monitoring and research of the water and temperature of slope, it reveals a mechanism that the ecological protection of slopes in red beds soft rock can prevents weathering and denudation effectively. The slope of red beds adopting eco-protection technology can effectively eliminate the splash erosion and surface erosion, delay the beginning time of run-off, reduce rainwater penetration depth of the slope. And it also can reduce the impactful depth of the day temperatures, the temperature difference (including the temperature difference a day and the temperature difference a year). It also can maintain the content of shallow water of the slope at a relatively stable state. These advantages make the ecological protected slope in red beds soft rock prevent soil erosion and surface weathering effectively.(10)According to the hazard-causing mechanism and destruction modes of the cutting slope in red beds soft rock, the different forms of the reinforced and protective engineering technology, including the method of combined ecological protections with projects techniques have been put forward. The design principles of the ecological protections applying to the slope in red beds soft rock, and the eco-protection technology based on reasonable gradient of the slope have been put forward.