Geotechnical Engineering is a branch of Civil Engineering that deals with soil both as a foundation material upon which all types of structures rest and with soil as a structural material. This chapter traces the genesis of Geotechnical Engineering and its development, practice, and importance as a subdivision of Civil Engineering. The chapter further explains the nature, origin, and types of soils, weathering and its agents, and factors affecting it with particular emphasis on tropical weathering and laterization and ends with a brief discussion of soil maps and geotechnical mapping of project sites. The type of maps that may be prepared for engineering or environmental purposes are many and varied and can be categorized on the basis of purpose, content, and scale.
Top1.0 Geotechnical Engineering
Geotechnical Engineering is a branch of Civil Engineering, which embraces many aspects of the established sciences, geology and pedology, engineering mechanics, structures and hydraulics. The term is often used interchangeably with Soil Mechanics but it is much broader. Soil Mechanics embraces the study of all those properties of soils that are related to their behavior, and its application as an engineering material. According to Karl Terzaghi (1948),
Soil Mechanics is the application of laws of mechanics and hydraulics to engineering problems dealing with sediments and other unconsolidated accumulations of solid particles produced by the mechanical and chemical disintegration of rocks regardless of whether or not they contain an admixture of organic constituent.
That is, Soil mechanics is the application of the laws and principles of mechanics and hydraulics to engineering problems dealing with soil as an engineering material. In particular it is concerned with the interaction of structures with their foundation material. This includes both conventional structures and also structures such as earth dams, embankments and roads which are themselves made of soil.
Geotechnical Engineering includes not only Soil Mechanics (soil properties and behavior) but also Soil Dynamics (dynamic properties of soils, earthquake engineering, machine foundations), Foundation Engineering (deep & shallow foundations) which is the science and art of applying the principles of soil and structural mechanics to solve soil-related engineering problems, Pavement Engineering (flexible & rigid pavements: material properties and design), Rock Mechanics (rock stability and tunneling), Geosynthetics (soil improvement) and geo-environmental engineering. Geotechnical engineering problems are usually solved by examining the physical conditions of the soil which are influenced by its geological origin, employing some of the principles of continuum mechanics to model and analyze the problem and then using engineering judgement based on experience to evolve an appropriate solutions.
Geotechnical engineering, in the broadest sense, may be regarded as a subdivision of structural engineering since it deals with soil both as a foundation material upon which all types of structures rest and with soil as a structural material. However, geotechnical engineering, unlike structural mechanics, is not an exact science. The theories of soil mechanics, for example, provide us only with working hypotheses, because our knowledge of the average physical properties of the subsoil and of the orientation of the boundaries between the individual soil strata is always incomplete and often inadequate. This means that the geotechnical engineer must be fully aware of the uncertainties involved in the fundamental assumptions of his computations so as to be in a position to anticipate the nature and importance of the differences, which may exist between reality and his original concept of the situation. The practice of geotechnical engineering therefore involves, among others, the making of appropriate observations during construction in order to adapt the design when necessary to the real soil conditions at the site before it is too late.
Soil Mechanics, an aspect of geotechnical engineering, is a very important field of study because there are very few civil engineering projects, which do not involve soils either as a foundation or as a construction material. Man-made structures like buildings and bridges must rest on foundations, which eventually transfer the load on the superstructure into the soil. The design of retaining walls, culverts, sewers, subways, tunnels and other types of underground structures must take into consideration the pressures exerted by the backfill and the ability of the soil to support the structure. Earth dams, aircraft runways and highway pavements must take into consideration in their design and construction the strengths, gradations, permeabilities and other pertinent engineering properties of the available soils at the site of each project. The design of the foundations of earth structures therefore, requires a thorough knowledge of the principles of soil mechanics.