Based on GIS Database, this paper presents a new method which take the Slope Unit as study object to search and evaluate the 3D critical slope stability. Assumed the initial slip as ellipsoid. the 3D critical slip surface in the 3D slope stability analysis is performed by the means of a minimization of the 3D safety factor by using Monte Carlo random method to choose the parameters of ellipsoid. The analysis program is developed by VB and is well linked to GIS. especially take advantage of GIS spatial function. It is certain that the spatial data can be easy processed. analyzed, modeled, and showed, the data of layers, underground Water, water table, discontinuous 3D sliding face. and even the water deduced softening can be considered in the 3D slope stability analysis. From the results of example study. it is confirmed that the 3D slope stability assessment method can be used to assess the landslide hazard and its results are rational.


It has been paid attention to the failure of slope in the mOuntainous areas; these failures either initiated by natural or human activity arc a major cause of natural disasters.. In the recent years, Geographic Information System (GIS), wtlh its excellent spatial data process ability has attracted great attention in natural disasters assessment. GIS is a system of hardware, software for data capture, input, manipulation. transformation. visualization. combination. query, analysis, rnodeling and output. GIS provides strong functions in spatially distributed data processing and analyzing. At same time. using GIS can easily and effectively perform the analysis of slope stability. According to Aleotti and Chowdhury (1999). the landslide hazard assessment methods by using GIS can be classified as being showed in Figurc.l, FrOI11 survcying the recent GIS applications to slope stability analysis, it is found that most researches arc C?,"c.entratcd in using statistical method to quantify the ~I;tronship between slope failure and influential factors while f performs regional data preparing and processing. Only very ~\V researches on integrating GIS and deterministic model for ~ Ope stability arc conducted.


Slope-unit, as basic study object in this study, namely. the portion of land surface which contains a set of ground conditions which differ from the adjacent units. possesses an explicit topographical (break line. stream. aspect and slope) and geological concept, and on other hand. grid-unit, which is always exploited in determinate slope stability analysis. does not bear any relation to the geological, geomorphological or other environmental boundaries. Slope units arc basically divided by geomorphological, geological and hydraulic conditions. The appropriate size of slope unit should be dependant on the average size of the landslide bodies presented in the study area. Hovland (1977) appeared to have been the first to analyze a three-dimensional slope using the methods of columns.Ifolland's method is an extension of an assumptions associatedwith the two-dimensional ordinary method

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