Engineering Geology

Chapter 7
purpose, have a larger scale. Engineering geological maps may serve a special purpose or
a multipurpose (Anon, 1976). Special-purpose maps provide information on one specific
aspect of engineering geology, for example, the engineering geological conditions at a dam
site or along a routeway or for zoning for land use in urban development. Multipurpose maps
cover various aspects of engineering geology.
Engineering geological maps should be accompanied by cross sections, and explanatory
texts and legends. Detailed engineering geological information can be given, in tabular form,
on the reverse side of the map (Fig. 7.31; Tables 7.7a and b). For example, a table of rock
and soil characteristics summarizing the various rock and soil groups, listing their mode of
occurrence, their thickness, their structure and their hydrogeological and geotechnical properties,
may be provided. More than one map of an area may be required to record all the
information that has been collected during a survey. In such instances a series of overlays or
an atlas of maps can be produced. Preparation of a series of engineering geological maps
can reduce the amount of effort involved in the preliminary stages of a site investigation, and
may indeed allow site investigations to be designed for the most economical confirmation of
the ground conditions.
Geotechnical maps and plans indicate the distribution of units, defined in terms of engineering
properties. For instance, they can be produced in terms of index properties, rock quality
or grade of weathering. A plan for a foundation could be made in terms of design parameters.
The unit boundaries then are drawn for changes in the particular property. Frequently,
the boundaries of such units coincide with stratigraphical boundaries. In other instances, as
for example, where rocks are deeply weathered, they may bear no relation to geological
boundaries. Unfortunately, one of the fundamental difficulties in preparing geotechnical maps
arises from the fact that changes in physical properties of rocks and soils frequently are
gradational. As a consequence, regular checking of visual observations by in situ testing or
sampling is essential to produce a map based on engineering properties.
Geographical Information Systems
One means by which the power, potential and flexibility of mapping may be increased is by
developing a geographical information system. Geographical information systems (GIS) represent
a form of technology that is capable of capturing, storing, retrieving, editing, analyzing,
comparing and displaying spatial information. For instance, Star and Estes (1990) indicated
that a geographical information system consists of four fundamental components, namely, data
acquisition and verification, data storage and manipulation, data transformation and analysis,
and data output and presentation. The GIS software is designed to manipulate spatial data in
order to produce maps, tabular reports or data files for interfacing with numerical models.
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