Experimental Study On Fissure Evolution Of Silty Mudstone Under Hygro-thermo-mechanical Conditions

With the rapid development of the automobile industry and the vigorous promotion of urbanization,expressways with a series of advantages,such as expanding the scope of activities,promoting economic and cultural exchanges between urban and rural areas,and reducing the pressure of transportation have become an inevitable product of social development.According to the economical principle of taking local materials according to local conditions,the silty mudstone widely distributed in South China has become the main material for excavation and filling in the process of highway construction,and a large number of silty mudstone slopes are exposed.Because most of the southern part of our country belongs to the subtropical monsoon climate zone,it has the characteristics of hot summer,cold winter,sufficient light and heat,and abundant rainy seasons.The silty mudstone exposed in these environments is prone to fissures and reduce the slope strength,thus leading to the occurrence of disaster events.Therefore,this paper do an experimental study on the fracture evolution of silty mudstone under hygro-thermo-mechanical conditionsunder,hoping to provide some theoretical basis for the subsequent maintenance of silty mudstone slopes.The main research contents and final conclusions are as follows:(1)According to the literature review,it is known that the silty mudstone sampling site in Liuyang is hot in summer,cold in winter,and relatively vast in water area because of abundant rainy days.The surface layer of mudstone slope has water storage and recharge.At the same time,basic physical tests were carried out on the silty mudstone samples to obtain the parameters such as natural water content,block density,water absorption and saturated water absorption.(2)The relationship between the acoustic amplitude of silty mudstone and the vertical projection length,number of fractures,and the water content of the sample itself is explored through the sonic detection and characterization test.And by using the results,the crack propagation inside the silty mudstone sample was studied to a certain extent.With the help of Avizo software,the three-dimensional reconstruction of the interior of the sample can also be roughly restored.Finally,it is concluded that the generation of cracks under the role of humidity,temperature,and load mostly starts from the top surface of the sample,and gradually expands to the middle with the increase of the number of cycles.(3)By setting up a series of control experiment,it is found that the expansion rate of the crack of silty mudstone is the largest when the temperature and humidity work togetherit.The temperature causes different dehydration rates in different parts of the sample,which accelerates the migration of water in the sample.Water again becomes a medium for the rapid transfer of temperature in the sample,and the two complement each other.The loading effect brought by the shallow covering soil can only promote the expansion of the existing micro-cracks,but cannot bring about the initiation of the cracks.(4)Through the scanning test of SEM electron microscope,it is known that the internal units of silty mudstone are mostly layered aggregates.In the wet state,the relative position will be reversed due to the action of the water flow.At the same time,due to the swelling of clay minerals due to water absorption,the cementing ability will also be weakened.In the end,the internal structure of the sample becomes no longer compact and the strength decreases,which provides conditions for the generation of cracks.When the particles shrink when dehydrated,the cracks are gradually revealed.The presence of temperature accelerates the above process.