Geotechnical Site Investigations for Underground Projects Volume 1 (1984) / Chapter Skim
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2. Geotechnical Site Investigations
2. Geotechnical Site Investigations
Pages 5-15
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From page 5... ...
The development of rock tunnel boring machines in the late 1950s was the precursor of numerous faster, more efficient, and less labor-intensive tunnel construction techniques. A similar development has occurred in tunnel design, bringing, for example, more sophisticated tunnel liner/ ground interactive analysis which permits the use of thinner, stronger, and safer lining systems.
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From page 6... ...
ADVANTAGES, RISKS, AND LIABILITIES A technically sound and thorough geotechnical site investigation program is an essential ingredient in obtaining the lowest fair cost for underground construction. To accomplish that end, the program must not only be optimal in design for the particular conditions at the site, but must also be sensitive to needed refinements in the scope of traditional data, data reporting, and interpretation in order to take full advantage of new cost-reducing construction methods, equipment, and concepts in project design.
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From page 7... ...
For example, an air photo analysis of the site should be conducted, geologic field mapping accomplished, and a boring plan developed identifying the general characteristics of the soil and/or rock and the geologic structure. Borings are usually widely spaced, and laboratory tests on recovered samples emphasize the basic properties of the materials.
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From page 8... ...
Records of specific data can be useful in preventing or settling disputes related to construction conditions or effects, as well as in protecting both owner and contractor fran frivolous claims. USES OF GBOTBCBNICAL DATA The needs for geotechnical data were once relatively unsophisticated, and were keyed primarily to site selection and design.
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From page 9... ...
Constant attention to the application of developing techniques will lead to cost-effective exploration programs (cost-effective in the sense that the programs should be iterative and able to identify and interpret anticipated underground conditions, rather than to simply produce borehole logs) • For example, a study of jointing in a granitic batholith at a tunnel location may show that the two major petrographic facies have different joint orientation maxima because of different cooling conditions (stress history)
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From page 10... ...
, laboratory and field tests, geophysical surveys, and geologic reports fran the project and any neighboring structures have an important status. These data will assist the contractor in identifying the best methods of excavation, choosing the size and type of equipment needed, estimating rates of advance, selecting methods and stages of temporary support systems, calculating anticipated rock overbreak, establishing groundwater control measures, developing the contingencies which should be available for control of fluids or gases, and determining the possible uses of excavated materials.
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From page 11... ...
The degree of confidence in or opinions as to the validity of the individual extrapolations and interpretations should be made explicit. Field data include borehole logs, geologic surface maps, geophysical data, water levels in wells, occurrences of springs, gases, chemicals, etc.
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From page 12... ...
Such a report might be called a •Geotechnical Design Report.• It should be based on (without repeating verbatim) the information contained in earlier geotechnical reports compiled by the investigator responsible for the exploration program.
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From page 13... ...
As an absolute minimum, the geotechnical conditions encountered should be reviewed by the original exploration group to see how and where their techniques and interpretations could be improved. Knowledge of actual construction conditions can assist in identifying the cause of and proper method of correcting problems encountered during the operational life of a tunnel.
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From page 14... ...
As the project moves into the execution phase, costs will vary with conditions encountered. In this respect, geologic conditions are the most significant factor for every underground project.
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From page 15... ...
Last, schedule slippage resulting fran adverse and unexpected geologic conditions delays commencement of service life of the structure. This will cost the public, as well as the owner and contractor.
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