Environmental Engineering Reference
In-Depth Information
5. Geotechnical logging and photographing of the cores of drill holes and of exposures
in the exploratory excavations;
6. Logging of drill holes using video imaging, cameras, impression devices, etc;
7. Permeability testing in drillholes;
8. Field and/or laboratory testing of soils;
9. Field and/or laboratory testing of rocks;
10. Plotting of all geological and test data, as soon as it is obtained, onto plans, sections
and 3-dimensional models (physical or computer generated). In this way it is possible
to visualise and analyse the surface and subsurface data, progressively filling in gaps
in the subsurface picture until the required degree of detail is obtained. All plans, sec-
tions and models show the proposed works, at least in outline. The end results of this
activity are the geotechnical model and geotechnical design parameters;
11. Assist in the design and analysis to assess the behaviour of proposed structures and
their foundations, under construction and operating conditions.
4.5
REPORTING
It is important during all stages, that the geotechnical facts, interpretations, conclusions and
decisions made from them are recorded regularly by a system of formal progress reports.
A comprehensive report is essential at the end of each stage, setting out the answers to the
questions of that stage and with recommendations for the next stage.
In general terms, a geotechnical report should consist mainly of a carefully planned and
ordered sequence of drawings (and preferably some photographs) with relatively short
explanatory text, and appended tables and calculations. The drawings and photographs
should convey a clear threedimensional picture of the surface and subsurface conditions
at the site, and the geotechnical properties of the foundation and construction materials.
A clear distinction should be made between factual data and inferences made from them.
The report (or a separate one) should include the results of analysis and design e.g. stability
analysis, design of filters.
A formal system for checking and certification is needed for all drawings and reports.
4.6
FUNDING OF GEOTECHNICAL STUDIES
In the opinion of the authors, it is most important that dam projects receive adequate
funding at the feasibility stage. This is because the question 'Is it economically feasible to
build and maintain a safe structure at this site?' is the really vital and difficult one. Usually
there are alternative sites but finally one must be adopted and the above question must be
answered in relation to it.
Unfortunately, some organisations may not have (or seek?) large amounts of money
until they believe they have shown a project to be feasible. Also, they may not wish to, or
cannot, acquire the site until feasibility is assured. Because of these matters, and the
inevitable pressure from landowners and conservation groups, the investigations at this
vital stage often tend to be less logical and less thorough than necessary - too much
reliance is placed on indirect methods (geophysical) and drilling of small diameter bore-
holes. The advantage of these methods is that they cause minimal disturbance of the land.
However, without an adequate understanding of the geological situation, which often can
be obtained only by large, continuous exposures in deep bulldozer trenches or access track
cuttings, the results of geophysical studies and drilling can be difficult to interpret. For
major, high hazard dams at geologically complex sites, exploratory adits are often the
most appropriate method for answering the feasibility questions.
