Soil Slope Stability Analysis Of The Improvement And Implementation Of The Arc Method

In the methods of slope stability analysis, circle slices method is used widely as it is simple and effective. The computation process has two basic steps: at the first, a slip surface is assumed and the factor of slope stability to this slip surface is calculated; second, after calculating a series of factors of assumed slip surfaces, the minimum one is token as the critical slip surface.On the former study, a integral formula has been deduced instead of slices dividing in calculating factor of stability. Some further improvements of the method have been completed in this paper as follow:(1) Computation of factor of slope stability in dip variable landform. Generally the slope surface is simplified to a straight line. Actually the slope surface is dip variable, and also many artificial slopes are step-shaped. So in this paper, the author use straight line to simulate the slope surface in subsections. The formula of factor of slope stability to analyse the slope with dip variable landform is deduced.To some slopes with dip variable landform, some assumed slip surfaces may intersected with slope surface, the situation could not be calculated correctly. So the slip surface is limited within the slope by adjusting the parameter t, t is the x-axis intercept of the tangent which passed through the upper extremity of the circular arc. Passed through the two extremity and the down-protruded inflexion of slope surface, the circular arc is searched which the radius is minimum, t0 correspond to this circular arc. Then the interval of t is confined in (t0,xb), then all circular arcs are within the slope corresponding t in this interval.This method can also be applied to the case that the lower extremity of he circular arc is not at the foot-point of the slope.(2) The determination of the critical slip surface and the corresponding stability factor. When t varied successively in interval (t0,xb), it is indicated that the curve of k-t is a segment of a parabola, so the minimum of k can be calculated by means of numerical method; when xb varied on upper ground of the slope or xa varied in front of the foot of the slope successively, the value of k have the same rule and the minimum can also be obtained by numerical method. So the minimum can be calculated at last if t, xb and xa is changed in turn. Computer program has been designed based on this method, which reduced the quantity of calculating and systematized the process of critical slip surface searching.(3) When there is some underlying aquiclude stratum, the interface is softened because of long-term soaked in water, so the shear failure may occur along the interface. Slip surface is made up of two segments: straight line and circular arc, and the slope can be divided into two segments correspondingly. Formulas of stability factor of the two segments by equilibrium of forces and equilibrium of moment could be set up respectively. The stability factor can be calculated by solving the simultaneous equations.Changing t, xa and xb in turn, the minimum stability factor and corresponding critical slip surface are worked out at last.To above-mentioned improvements, a program is designed and some examples are computed by this program. It is indicated that these results are credible by comparing these results with other results which had been worked out by former scholar.