Reliability Applied To Stability Analysis Of Loess Slope

Based on investigation of plenty of natural loess slopes and detail examination of the style and rate of the slopes in the middle of the Loess Plateau from An'sai to Guanzhong, Shanxi province, the author proposed the concept of "limit slope" and gave the criteria for the limit slope determination consequently. Then the longitudinal sections of the 79 investigated limit slopes and 16 topographic outline of loess slides were surveyed in the field. The research area is divided into 3 zones on the diffractions of topographies and soil properties, which are Tonghuang zone, from Fuxian to Guanzhong; Ganquan zone, from Fuxian to the divide of Yanhe River and Luohe River; Jin'an zone, to the north of the divide. By using of the sections of limit slopes, liner regression model and logarithmic liner regression model of the correlation between height vs ratio of the limit slope were set up, the statistic parameters under various degree of confidence were achieved in the three zones respectively. Comparison of the statistic results and the excavated loess slopes on highway suggests that it is reasonable to apply the natural limit slope in slope reliability analysis and engineering slope design.The two-dimensional Bishop's simplified method is improved. The slices method is changed into integral method that working trouble is prevented and accuracy is approached. If the slice is thin enough, the stability factor what slices method is computed is approximated to the results that integral method computed. A kind of method used in hunting most possible slide face is put forward. Comparing to the open method, this way is systematic and accurate so as suitable to program. Large amount of reliability analysis is done by it. Groundwater largely influence on slope stability. It is discussed in detail of processing method and open question of groundwater in slope stability computing and engineering feasibility and error source of the commonly used "method of substitution". Further a slope stability model is established by the edge condition of split trailing and soft layer in loess bottom.There are 1635 groups of loess physical and mechanical data collected in the investigation reports of Tongchuan to Huanglin, Huanglin to Yan'an and Jinbian to An'sai expressways. While 22 groups of samples extracted on the slopes along the research zones were tested with the physical indexes, granular composition, shearing strengths of direct shearing test and tri-axial shearing test. Detail examination of the loess physical and mechanical indexes of the samples collected from drill holes suggests that the samples were compressed while sampling with static compressing or hitting way. Therefore the dry density and the natural density of the drill hole samples are modified based on the data of man-excavated well samples. The shearing strengths of direct shearing and tri-axial shearing in the conditions of unconsolidated un-drained, consolidated un-drained and saturate consolidated un-drained were tested in laboratory. The factor of safety of the slopes recovered by the surveyed topography of the slopes is supposed to be 1.0, then the shearing strengths of the slopes were calculated by the way of back-up analysis. Comparison of the shearing strengths tested and those calculated shows that the strengths tested in the condition of unconsolidated un-drained direct shearing is close to the results of back-up analysis which represent the realistic situation. So the strengths by quick test is applied to the analysis of the loess slope reliability. Comparing the data of drill hole samples, well samples and back-up analysis, the quick test results of drill hole samples in Tonghuang zone can be used directly,...