Geology is the study of earth, the materials of which it is made, the structure of those materials and the effects of the natural forces acting upon them and is important to civil engineering because all work performed by civil engineers involves earth and its features. Fundamental understanding of geology is so important that it is a requirement in university-level civil engineering programs. For a civil engineering project to be successful, the engineers must understand the land upon which the project rests. Geologists study the land to determine whether it is stable enough to support the proposed project. They also study water patterns to determine if a particular site is prone to flooding. Some civil engineers use geologists to examine rocks for important metals, oil, natural gas and ground water.
The investigation of the suitability and characteristics of sites as they affect the design and construction of civil engineering works and the security of neighbouring structures is laid out in British Standard Code of Practice for site investigations (BS 5930:1981, formerly CP 2001). The sections on geology and site exploration define the minimum that a professional engineer should know. The systematic exploration and investigation of a new site may involve five stages of procedure. These stages are:
In a major engineering project, each of these stages might be carried out and reported on by a consultant specialising in geology, geophysics or engineering (with a detailed knowledge of soil or rock mechanics). However, even where the services of a specialist consultant are employed, an engineer will have overall supervision and responsibility for the project. The engineer must therefore have enough understanding of geology to know how and when to use the expert knowledge of consultants, and to be able to read their reports intelligently, judge their reliability, and appreciate how the conditions described might affect the project. In some cases the engineer can recognise common rock types and simple geological structures, and knows where he can obtain geological information for his preliminary investigation. When reading reports, or studying geological maps, he must have a complete understanding of the meaning of geological terms and be able to grasp geological concepts and arguments. For example, a site described in a geological report as being underlain by clastic sedimentary rocks might be considered by a civil engineer to consist entirely of sandstones. However, clastic sedimentary rocks include a variety of different rock types, such as conglomerates, sandstones and shales or mudstones. Indeed it would not be unusual to find that the site under development contained sequences of some of these different rock types—say, intercalated beds of sandstone and shale, or sandstone with conglomerate layers. Each of these rock types has different engineering properties, which could affect many aspects of the development work such as core drilling into, and excavation of, the rock mass, and deep piling into the
The systematic testing of the engineering properties of soils and rocks lies between classical geology and the older disciplines of engineering, such as structures. It has attracted the interest of, and contributions from, people with a first training in either geology or engineering, but has developed largely within departments of civil and mining engineering and is usually taught by staff there. These tests, and the advice about design or remedial treatment arising from them, are more naturally the province of the engineer, and fall largely outside the scope of this book. The reasons for this lie in the traditional habits and practices of both fields. The engineer’s training gives him a firm grounding in expressing his conclusions and decisions in figures, and in conforming to a code of practice. He also has an understanding of the constructional stage of engineering projects, and can better assess the relevance of his results to the actual problem.
These reasons for the traditional divisions of practice between geology and engineering must be qualified, however, by mentioning important developments during the last decade. An upsurge of undergraduate and postgraduate courses, specialist publications and services in engineering geology, initiated or sponsored by departments of geology or by bodies such as the Geological Society of London, has reflected an awakened interest in meeting fully the geological needs of engineers and in closing the gaps that exist between the two disciplines.
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.
Geology is the study of the solid Earth. It includes the investigation of the rocks forming the Earth (petrology) and of how they are distributed (their structure), and their constituents (mineralogy and crystallography). Geochemistry is a study of the chemistry of rocks and the distribution of major and trace elements in rocks, rock suites, and minerals. This can lead to an understanding of how a particular rock has originated (petro genesis), and also, in the broadest sense, to a knowledge of the chemistry of the upper layers of the Earth.
The distribution of rocks at the Earth’s surface is found by making a geological survey (that is, by geological mapping) and is recorded on geological maps. This information about rocks is superimposed on a topographic base map. Knowledge of the nature and physical conditions of the deeper levels of the planet can be gained only by the special methods of geophysics, the twin science of geology; the term ‘Earth sciences’ embraces both. From the theory and methods of geophysics, a set of techniques (applied geophysics) has been evolved for exploring the distribution of rocks of shallower levels where the interests of geologists and geophysicists are most intertwined.
Knowledge of the Earth at the present time raises questions about the processes that have formed it in the past: that is, about its history. The interpretation of rock layers as Earth history is called stratigraphy, and a study of the processes leading to the formation of sedimentary rocks is called sedimentology. The study of fossils (palaeontology) is closely linked to Earth history, and from both has come the understanding of the development of life on our planet. The insight thus gained, into expanses of time stretching back over thousands of millions of years, into the origins of life and into the evolution of man, is geology’s main contribution to scientific philosophy and to the ideas of educated men and women.