Geotechnical Engineering

Rock outcrops are defined as visible exposures of bedrock or other geologic formations at the surface of the Earth. Rock outcrops take many different forms within the Park, ranging from the massive granite boulders of Old Rag Mountain, to the sheer cliffs of Little Stony Man, and the jumbled boulder fields of Blackrock.

Most civil engineering projects involve some excavation of soils and rocks, or involve loading the Earth by building on it. In some cases, the excavated rocks may be used as constructional material, and in others, rocks may form a major part of the finished product, such as a motorway cutting or the site f or a reservoir. The feasibility, the planning and design, the construction and costing, and the safety of a project may depend critically on the geological conditions where the construction will take place. This is especially the case in extended ‘greenfield’ sites, where the area affected by the project stretches for kilometres, across comparatively undeveloped ground. Examples include the Channel Tunnel project and the construction of motorways. In a section of the M9 motorway linking Edinburgh and Stirling that crosses abandoned oil-shale workings, realignment of the road, on the advice of government geologists, led to a substantial saving. In modest projects, or in those involving the redevelopment of a limited site, the demands on the geological knowledge of the engineer or the need for geological advice will be less, but are never negligible. Site investigation by boring and by testing samples may be an adequate preliminary to construction in such cases.

Generally, shear strength is a term used in soil mechanics to describe the magnitude of the shear stress that a soil can sustain. The shear resistant of soil is a result of friction and interlocking of particles, and possibly cementation or bonding at particle contacts. Due to interlocking, particulate material may expand or contract in volume as it is subject to shear strength. If soil expands its volume, the density of particles will decrease and the strength will decrease; in this case the peak strength would be followed by a reduction of shear stress.