Test Study On Engineering Properties And The Constitutive Model Parameters For Soft Clayey Rocks

Dongjiang River-Shenzhen Water Supply Project, a large water basin-diversion engineering system, provides with drinking and irrigation water for Hong Kong, Shenzhen, Dongguan and many towns on the line. In the system, the Jinhu water-lifting pump station is located in a low-relief moser terrain with an elevation of 22~60 m at the eastern of Tangxia town. In order to direct the water to the forebav of the pump station from the original canal, a channel long 135 m is designed. It crosses through the terrain top with a depth of more than 50 m. Soil of the channel slopes is a strongly-weathered silty and sandy mudstone with many well-developed reticular cracks and takes the structural surfaces almost same as the channel slopes. Due to a high content of clay minerals, the soil becomes soft when immersing in water.The stability of high slopes relies directly on the material strength of rock and soil. The strength parameters used in the design are often obtained from the drilling samples before the slopes are excavated. As far as the soft clayey rock, widely distributed in Guangdong, is concerned, it will swell after unloaded and soften during immersion. Its strength decreases with time after excavation. As a result, the slopes probably lose their stability in a long time, and in deed there are some failure cases reported in engineering. Therefore, it is of significance in theoretic research and engineering practice to study the long-term strength of soft clayey rocks under immersion and unload.In this study, the macro structural characteristics of soft clayey rocks were investigated in field. The basic physical and mechanical properties, mineral composition, micro structures, swelling potential, consolidated drained triaxial shear strength, parameters of constitutive model and residual strength of the soft clayey rocks were tested in laboratory with a large number of natural samples. The changing trend of the strength about these rocks is obtained by modeling the condition of softening due to immersion. From the principles of modern soil mechanics, the structural and swelling characteristics of soft clayey rocks were analyzed systematically. By studying the strength behavior to these rocks, their shear strength ranges were given in different engineering environmental conditions. Based on a series of triaxial tests on the soft clayey rocks, parameters of the constitutive model are provided, which are necessary in numerical analysis and engineering computation. According to the results in thisstudy, mechanism of deformation and failure of soft clayey rocks was explored, and the data on their physical and mechanical properties were collected in Guangdong. It can be used for reference in engineering practice.