The stability of scarp slopes

I. Purpose: With the investigation and development of large-scale engineering projects the engineering geologist is faced with problems, the solution of which may well determine the economic feasibility of those projects. Among the most vital problems, particularly in the field of hydro-electric engineering, are those concerning the stability of slopes. The purpose of this thesis is to outline the investigation of one such problem, to state the observed facts and to offer interpretations of these facts. II. The problem: The problem: The proposed construction of hydro-electric installations on the face of the Western Tiers of Tasmania necessitated a study of the stability of slopes on this actively retreating scarp. Abundant evidence of rock slips and extensive scree and talus deposits reflect the general instability of the Tiers face. Any structure contemplated must be located to minimise the danger of extensive rock slides from higher levels. A study of the mechanisms of retreat and an assessment of the stability of cliffs and rock-slide material is undoubtedly the major problem of the geology of this scheme. III. Investigation methods: The investigations were carried out in two phases: Phase 1: The compilation of a detailed geological map with appropriate contour information over an area broad enough to include all the salient features of the Western Tiers. Geological boundaries were plotted on aerial photos and transferred to map squares prepared from aerial photos by the Hydro-Electric Commission. At the same time barometric traverses were carried out and from these, with the help of steroscopic inspection of the aerial photos, a rough contour map was prepared. (Note: After the field work was completed the Mapping Branch of the Tasmanian Lands and Survey Department produced a contour map of the southern portion of the area chosen. These contours have been substituted for the Author's in maps included in this thesis.) The stratigraphic succession was established from field mapping and core logging of diamond drilling carried out by the Hydro-Electric Commission. Phase 2: A close examination of structures, superficial deposits and vegetation which provides evidenCe of recent and imminent scarp retreat. Plane-Table mapping of selected areas with the recording of the physical characters and disposition of scree blocks, joint patterns in outcrops and vegetation data provided the \control areas\" for photo interpretation of the scarp face generally. Diamond drill cores provided subsurface information on scree and talus deposits. IV Presentation: The thesis is presented in three parts: Part A: Genereal description of the area. The location access and climate of the area and the broader aspects of its physiography and geology are intended as a general introduction to the more detailed treatment in subsequent parts of this thesis. PART B. HISTORY AND CHARACTER OF THE WESTERN TIERS. The origin and subsequent history preface a detailed description of the scarp in terms of slope elements. PART C. STABILITY ANALYSIS OF SCARP SLOPES. An analysis of the data presented in Part B. is attempted with a view to its general application to problems of stability of scarp slopes."