Fengdian high cutting slope is a typical one in Sichuan section of the expressway from Chengdu to Shanghai. It is 78.5 meters high. The slope consists of interbedded strata of rock mass of purplish red mudstone and grey-brown arkosic sandstone of Jurassic age. The mudstone is soft while the sandstone is hard and contains two sets of opening joints. One is nearly parallel and the other is nearly decussated with the trend of the slope. The stability and support method to be taken is important for successful construction of the expressway. In this paper, the stability and deformation of the slope is studied. The results indicated that the slope is stable as a whole, but near the surface of the slope foot is unstable because of the deformation and fracture of mudstone and slip of sandstone blocks. Retaining at the foot and anchoring on the top of slope is an effective support method.
The Fengdian high cutting slope in the section from Chengdu to Nanchong of national expressway from Shanghai to Chengdu locates at l.0km southwest of Fengdian town of Zhongjiang county, Sichuan Province. The slope is 78.5m high and 320m long and its' designed grade is 52°. The undisturbed natural slope inclines to NW357° with 20° grade and is a consequent slope. It is consists of interbedded strata of purplish red mudstone and grey-brown arkosic sandstone of Jurassic age. The mudstone is soft. A lot of micro-cracks are well-developed in these strata. The sandstone is hard. Two sets of relaxed or opening joints with high dip angle, whose attitude are dip to NW276° <84° and dip to NW 353° <87° respectively, are well-developed in the sandstone strata. Mean length of the joint trace is more than 40m, mean space between joints is 1.2m and the aperture of the joints ranges from 5mm to 260mm. One set of joint is parallel to the trend of the slope and the other is perpendicular to it. Roadbed width of the expressway is 26m, The structure and lithologic character of the slope is shown by Fig. I. The dimension, the lithologic character and structure of the cutting slope are typical in Sichuan basin. Because there is a Qingzishan Slide of I6x 10 6m3 in volume creeping along the mudstone bedding plane with a dip angle only 7°, appropriate evaluation of deforming stability and reasonable selection of support and designing parameters for the cutting slope are the key of the slope project. Presently, the rigid body model and the arm Skewing model are adopted in analysis of the slope down the dip.
If the slope is cutting in a natural slope with small gradient and in the strata with small dip angle, it will act like surrounding rock of the underground chamber. Firstly, stress-release and rebound deformation will occur. Then, time-dependent creeping deformation.
