ABSTRACT: This paper describes a method that allows direct use of the Generalized Hoek-Brown criterion in Finite Element (FE) Shear Strength Reduction (SSR) analysis of rock slopes. It describes the generation of shear envelopes for the criterion, lowering of the shear envelope by a factor, and means for determining an equivalent Generalized Hoek-Brown curve that best approximates the lowered envelope. The paper provides two examples that demonstrate the performance of the new method. As well it outlines some of the benefits of the SSR technique for slope stability analysis.
The Finite Element Method (FEM) is increasingly being applied to slope stability analysis. One of the most popular techniques for performing FEM slope analysis is the shear strength reduction (SSR) approach . The SSR is simple in concept: systematically reduce the shear strength envelope of material by a factor of safety, and compute FEM models of the slope until deformations are unacceptably large or solutions do not converge. A factor limiting broader application of the SSR approach to slope stability analysis has been its restriction to Mohr-Coulomb materials. Most discussions of the method found in literature deal with this criterion (the paper by Shukra and Baker  is one of the few known to the authors that examines application to non-linear strength envelopes). For rock masses, the Generalized Hoek- Brown criterion is the most commonly applied strength model. As a result, the authors found it expedient to develop an SSR framework for the Hoek-Brown criterion. The aim of this paper is to outline an approach for applying the Generalized Hoek-Brown criterion in SSR analysis. The paper will also demonstrate the capability and accuracy of the proposed approach through two examples.
Elmo, D. (Camborne School of Mines, University of Exeter in Cornwall) | Coggan, J.S. (Camborne School of Mines, University of Exeter) | Pine, R.J. (Camborne School of Mines, University of Exeter in Cornwall)
Country-scale geology templates have been developed by Defense Threat Reduction Agency (DTRA) contractors and government personnel to provide the Department of Defense and other government agencies with rapid estimates of geology and geotechnical properties. The Geology Templates (GT) are a GIS-based solution that integrates geologic maps, satellite imagery, digital terrain data and a specially developed geotechnical properties database within an easy to use custom application. The geologic maps are approximately 1:500,000 to 1:1,000,000 scale which are digitized and saved as shapefiles. Landsat derived NASA Geocover mosaics are used to adjust lithologic/formation boundaries. Digital Terrain Elevation Data (DTED) is used to determine elevation, slope and slope aspect. The geotechnical database is country specific, derived by consideration of geologic map legend/lexicon lithologic units, geography/terrain and typical or formation-specific physical and engineering properties. Since actual literature properties data are sparse, expert judgment plays a critical role in the assignment of intact and in situ properties and property variability. The geologic profile is modeled as an idealized three layer system composed of soil, weathered rock and underlying fresh bedrock. The soil and weathered rock layer thickness is adjusted as a function of slope. Layer properties include material bulk density, unconfined compressive strength and Rock Mass Rating (RMR).
Geography and geology have long factored into military and intelligence decision making. Country geographic studies have been performed since the WWII era that provided a general treatment of the country geology, geography, soils, groundwater and climate (e.g., National Intelligence Surveys). In the modern era, the most familiar of these studies is broadly referred to as terrain analysis. For example, the U.S. Army Corps of Engineers has historically been responsible for preparing mobility studies and cover and concealment information from terrain analysis that supplies commanders with information on the best routes for cross-country movements and the difficulties that can be anticipated in moving troops and vehicles. A number of field manuals have been developed for these purposes (e.g., FM 5- 33, U.S. Army Field Manual, Terrain Analysis; FM 5-170, U.S. Army Field Manual, Engineer Reconnaissance). The main analytical elements of these studies fall into two general categories, natural and cultural. Natural features include topographic slope, soil type/depth and/or rock exposures, vegetation and surface water features. Cultural or man-made features such as towns, roads, bridges and canals are also critical.
With the increasing complexity, pace, and lethality of the battlefield environment, military and intelligence information requirements have become more diverse and demanding. The Defense Threat Reduction Agency is a Combat Support organization whose research, development, and operational activities directly support threat reduction and military intelligence needs. DTRA has developed fast running, engineering models that are based on extensive field research, development, and testing. Country Geology Templates (GT) have been designed as a compliment to traditional terrain analysis tools in order to provide rapid geological and geotechnical information to support military intelligence requirements. The GT products can also be used by other government agencies requiring general information regarding soil depth, the extent of weathered rock (WX) and material/engineering properties.