– the anchor for civil engineering design, construction and project implementation
This article, first in the series, intends to introduce readers to a very important subject area in civil engineering. The content will be addressed under the following headings or titles:
- What is Geotechnical Engineering?
- History of Geotechnical Engineering
- Who is a Geotechnical Engineer in Ghana?
- Areas of application
What is Geotechnical Engineering?
One of the better definitions of the subject is extracted from http://www.whatisgeotech.org/. It simply puts “Geotechnical engineering is the science that explains mechanics of soil and rock and its applications to the development of human kind”. This means, any civil engineering infrastructure that is supported by soil or rock is the responsibility of Geotechnical Engineering. Geotech, for short, applies the principles of soil and rock mechanics to investigate subsurface characteristics by providing information such as relevant physical, chemical and mechanical properties, known as geotechnical parameters. Geotechnical engineering determines the type of foundations, earthworks, pavement among others of the artificial structures to be built.
History of Geotechnical Engineering
In ancient Egypt, Mesopotamia and the like, dating back at least 2000BC, soil material was used to build foundation, for irrigation purposes, in control flood and as construction materials. For example, in irrigation works and flood control soil material was used in canals, dykes and dams. Foundation systems became significant as these ancient cities expanded; the ancient Greek constructed pad and raft or mat footings for buildings. Before the 18th century, there was no scientific approach or understanding to design for these activities as the subject area was more of an art based on experience. Just after the 18th century several foundation related problems emerged. For example, the Leaning Tower of Pisa in Italy alerted Scientists to use scientific approach to investigate the subsurface. The earliest attempts using scientific approach to study soil mechanics was in the area of earth pressure theories for the construction of retaining wall. In 1717 a French royal engineer, Henri Gautier, observed natural slope of different soils and this gave the idea of soil’s angle of repose. In classifying soil a basic approach based on its unit weight, which later not considered as good indicator, was used. In 1773 Charles Coulomb (an army captain, physicist and engineer) applied the principles of mechanics on soils and determined a better approach for earth pressures against military fortifications. In the 19th century another great man, Henry Darcy, developed the Darcy’s law that describes the flow of fluids in porous media and Joseph Boussinesq propounded theories of stress, which are being used to estimating stresses at depth within the ground. William Rankine and Albert Atterberg developed an alternative to the Coulomb’s earth pressure and clay consistency indices for soil classification respectively. In 1885 Osborne Reynolds observed that shearing results in volumetric changes in granular soils. For example, there is dilation for dense, and contraction for loose, coarse grain soil. The 20th century saw the advent of modern geotechnical engineering with Karl Terzaghi as a key pioneer. He developed the principle of effective stress, theories on bearing capacity, and settlement of clay layers due to consolidation. In 1958 critical state soil mechanics emerged with studies on volume change behaviour (dilation, contraction and consolidation) in relationship with shearing behaviour by Wroth, Roscoe and Schofield. In fact critical state soil mechanics has become the backbone for many advanced constitutive models in geotechnical engineering practice.
Who is a Professional Geotechnical Engineer in Ghana?
A Geotechnical engineer is a typical graduate who has completed a Bachelor’s Degree in Civil/Geological Engineering and with geotech as one of the majors. A good background in geology during the coursework is very important and advantageous. A typical individual with solid background in Engineering Geology could also support geotechnical activities because both subject have large areas of overlap. One can develop capacity in education by obtaining a Master’s Degree in Geotechnical Engineering. To practice, in Ghana, the graduate has to be certified or recognized by a licenced professional body such as the Ghana Institution of Engineering (GhIE). The entry point is a Trainee Professional Engineer and, at least, after 3-years of practice the individual is a qualified candidate to sit for the professional exams. Passing the professional exams qualifies you to practice as a Professional Geotechnical Engineer. In Ghana there is the Geogroup of the Civil Technical Division, which comprises Ghana Geotechnical Society (GGS) and International Geosynthetic Society Ghana Chapter (GhIGS). The group promotes geotechnical and related activities among professionals and students in Ghana.
Areas of Application
Geotechnical engineering is one of the broadest application for civil engineering infrastructure development. The key areas include the following:
- Transportation – geotechnical engineering supports railway and general pavement (road, runway, harbour, waterways etc.) engineering in the areas of design, construction, maintenance, monitoring, and upgrade. Geotechnical aspects of transportation considers the following:
- Earthwork design, construction and quality control.
- The use of non-geomaterial (geotextile, geogrid etc.) in embankment and structural layers of pavement and railway.
- Site investigation of pavement and railway carriageways including immediate environs.
- Improvement and use of marginal geomaterial (soil and rock) for such construction.
- Deep & Shallow foundation – the geotechnical engineering focus is to design, install and testing of piles under different loading conditions. Also the design of pad, strip and mat or raft footing (shallow) are subset of geotechnical engineering.
- Landslide – here the geotechnical capability is to design slopes that is stable against such occurrence. In addition, it assesses risk of such environment before the general land-use.
- Earthquake – geotechnical engineering assesses the risk of a subject site and characterizes it in line with earthquake including its rippling effects such a liquefaction. The assessment aids in the choice for site locations and type of infrastructure to implement including general spatial planning. In addition, it will provide an input for structural design and general costing for projects. There is also the support for the development of seismic codes.
- Underground infrastructure – underground infrastructures include tunnels, subways, pipelines, underground highway, and waste storage among others. Geotechnical engineering assess the sites for such infrastructural needs and provides geotechnical parameters for design and construction. For example, it provides anticipation for underground challenges during construction.
To be continued……
About the writer: The writer is Ing. Joseph K. Oddei, a Fellow of the Ghana Institution of Engineering and Chairman for the Civil Technical Division. He is the Secretary of the Ghana Geotechnical Society and deeply involved in geosynthetic issues. He holds a BSc (Hon) degree in Geological Engineering and an MPhil in Geotechnical Engineering from KNUST with over 17-yrs of professional practice.