Study On The Stability Of Highway Loess Cutting Slope

With the development of the Western region, the communication and transportation has been given first priority to development, especially the highway construction in the loess area. A plenty of high cutting loess slopes were built in such a complicated region of the geological background. Because of the long vertical section,the width of the cross section,the vast high slope and the amount of work in the high cutting loess slopes, the stability of slope entirety and slope surface being guaranteed is a technical problem which is difficult to solve in the project under economical reasonable condition. And the behaviors of loess cutting slopes in service been preliminarily understood, the massive examples of high slope engineering have provided reference on studying high loess slopes when highways have been used for nearly ten years. With the backing of West transportation construction science and technology project named"The research on protection techniques of road high slopes in loess area"(200131800020),and by means of a vast amount of investigation data of high cutting loess slopes built or being built,and some experiment inside and outside,theory calculation. etc,the research results have been obtained some as follows in this paper:(1). Based on the origin age, component,structures and water geological condition,etc,8 kinds of geological structure type models were summed up in the cutting loess high slopes. Simultaneously,the feature of shape destroy was examined between surface and slope. these research has the extremely vital practical significance on slope stability analysis as well as the protection engineering design of high loess cutting slopes.(2). 55 typical slopes,which were taken for the case model, were firstly set up the project analogy database by means of Case-based Reasoning method in order to provide the most reference foundation on later slope design. The database, which made use of variable weight thought to calculate in the weight of attribute, gave expression to sensitive that exert weight influent on environment. The results of calculation were close to practice.(3). According to investigation of plenty of materials and the results of rainfall washout experiment on the spot, the suitable style in cutting loess high slope and the guard ways of surface were summed up in light of theory calculation. Slope protection plan recommendable table and the cutting loess high slope design were put forward by different zones and geological structure model with former results.(4). After testing, samples were be turbulent and exist a quiet error in parameter by drill holes technique. A revised formula was set up on the basis of man-excavated well samples testing. A plenty of parameter statistics suggested that water put more influence on the strength indexes c, but more than ? in direction shearing testing. And the variability of physical indexγis small. The large statistic variability of shearing indexes is enough big, but a project statistic variability of shearing indexes is less than it. When kinds of degree of depth in strength indexes were analyst by statistics, the influence of the parameter mutual relation was not considered. The physic indexesωandγsubmitted normal and logarithm normal distribution on the whole, only a few submitted extreme value I distribution. Most of the shearing strength c and ? submitted normal, logarithm normal and extreme value I distribution,a tiny minority submitted Weibull distribution.(5). Using Fredlund non-saturated soil strength formal and matrix suction test,the correlation indexes of strength formal from Xi Yu highway samples were obtained. After regressing between water content and matrix suction,their relation was determined. It was able to calculate matrix suction only using water content without the trouble of suction test.(6). After selected 207 typical stable slopes from 251 loess slopes on investigation and divided into 4 zones and 8 type geology structure models by railway engineering geology,the logarithm liner relation was defined between slope high and the comprehensive slope rate .(7). Based on the simplified Bishop method and Monte-Carlo method,the reliability index of the slope calculation method was established. Altogether 142 computation slopes high spot from 4 zones and geology models of 8 types were simulated calculation with 12 kinds of coefficient variation combination after 1704 times. After analyzing the changing between the failure probability and the reliability index , and given the level of loess strength variability in practical project,δc=0.3 andδ?=0.15 combination was taken as the controlling factor of first-class highway failure probability recommendation,δc=0.5 andδ?=0.2 as the controlling factor of two levels and two level of below roads failure probability recommendation. Finally,different zones, geology structure models and rank highway of failure probability design standard recommendable plan were given in loess cutting high slope.