GIS (geographical information system), with its capacities range from conventional data storage to complex spatial analysis and graphical presentation, is becoming a powerful tool for geotechnical engineers too. In this study, combining the GIS grid-based data with four proposed column-based 3D slope stability analysis models, a GIS extension, 3DSlopeGIS, has been developed to implement the algorithm in which all the input data are in the same form of GIS dataset. A widely addressed example and an actual landslide have been evaluated and a actual 3D slope problem has been analyzed in this paper, the results show the correction and usability of this GIS-based tool for assessing the 3D stability of a slope. Because all related data are in the GIS database, this new database approach will be very convenient for data renewing and for multiple cases studying.
Most slope stability analyses are performed using a two-dimensional (2D) limit equilibrium method in the practice of geotechnical engineering. The safety factor is commonly assessed through a 2D idealization of the slope: for example, an equivalent plane-strain problem is postulated and analyzed. The results of the 2D analysis are usually conservative though more expensive, since threedimensional (3D) analysis tends to increase the safety factor. It is implicitly assumed that the failure surface is infinitely wide in the 2D model, and thus 3D effects are negligible because of the infinite width of the slide mass. By summering studies of 3D slope stability, Duncan [3] had concluded that the 3D safety factor is greater than 2D result, provided that the 2D safety factor is calculated for the most critical 2D section. It will be shown herein that the percentage of the difference between 2D and 3D analysis can be as large as 30% (the difference is about 3%-30% and the average is 13.9%, by [6]), and thus a 3D analysis should be conducted for slope stability analyses. Since the middle of the 1970s, increasing attention has been directed toward the development and application of 3D stability models [3]. Several 3D methods of analysis have been proposed in geomechanical literature [1-2, 7-12, 19 ]. With the development of the 3D approach for slope stability analysis, a number of computer programs have be developed. Commercially available 3D slope stability softwares are briefly illustrated that: CLARA [11] can conduct limit equilibrium slope stability analysis in two or three dimensions. It uses 3D extensions of Bishop's Simplified, Janbu, Spencer and Morgenstern-Price [15] methods, with circular sliding surfaces, ellipsoids, wedges, compound surfaces, fully specified surfaces and searches; TSLOPE3 is 3D slope stability analyses of arbitrary slip surfaces using the LA County method which is similar to the Simplified Janbu method. Here the safety factor is calculated simply as the sum of the resisting forces divided by the sum of the driving forces; 3D-PCSTABL [18] can only be used in the analysis of slopes with a symmetrical failure surface. This limitation prevents the use of this software.