Geotechnical Site Investigations for Underground Projects Volume 1 (1984) / Chapter Skim
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5. Special Purpose Projects
5. Special Purpose Projects
Pages 35-45
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From page 35... ...
Case histories of such projects as underwater taps, steep inclines, and deep underground chambers are so few and the data so limited that they were not collected for this study; by the same token, limited data were obtained for shafts. However, the geotechnical factors are equally important to site selection, design, and construction of these projects.
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From page 36... ...
Factors in Site Selection Chambers excavated for resource recovery are sited on the basis of exploration that has defined the dimensions of the resource body and the hazards and exigencies associated with extraction. Chambers excavated for resource storage or waste disposal are sited, insofar as possible, to maximize their ability to provide containment and isolation and to avoid or minimize conditions adverse to safe performance.
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From page 37... ...
As a part of the geologic site investigation, all of these conditions must be evaluated through careful laboratory and insitu tests prior to actual emplacement. Depending on the depth and geologic complexity of the proposed facility, an exploratory shaft and test chamber may be the only practical method of obtaining the quality of insitu data needed for final design.
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From page 38... ...
Factors in Site Selection In most cases, geotechnical factors dictate the location of an underground facility such as a nuclear-waste repository or a powerhouse. However, shaft site may be prescribed by the position of such an accompanying underground facility, rather than from an optimum geotechnical standpoint.
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From page 39... ...
The shaft exploration should include, as a minimum, a cored borehole or holes near the shaft site or within its area,, because geologic and hydrologic conditions may vary considerably over a short distance, even in flat-lying sedimentary formations or strata. With nonhorizontal geologic features, and especially in areas where potentially near-vertical features occur, more than a vertical hole is required.
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From page 40... ...
In cases where freezing is to be used, ultrasonic readings should be taken between freeze holes before ground freezing starts, in order to provide a comparative background for later ultrasonic testing to detect windows in the freeze wall. When grouting is anticipated, laboratory tests should be conducted to determine the ground characteristics related to grout-curtain design and grout selection, such as grain size and distribution, porosity, and permeability.
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From page 41... ...
ROof support methods are probably the most frequent deviation from the construction specifications. The bonding of formations is perhaps the most critical rock characteristic in determining proper roof support in an incline.
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From page 42... ...
The raise drill is therefore limited to what can be achieved on a single pull. If machine boring or excavating is contemplated, site investigations require an assessment of both rock strength and abrasiveness.
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From page 43... ...
Because of the expanding need and its implications for the future, site selection procedures and planning of underwater taps based on geological study are increasingly important. Frequently the tap is constructed between a vertical, or steeply inclined shaft and a horizontal tunnel.
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From page 44... ...
In the case of an underwater tap, a second opportunity for specific site investigation occurs when construction nears the point of breakthrough. Given the penalty for error if the crucial tap is performed carelessly, this opportunity should not be ignored.
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From page 45... ...
When blasting the final plug wet, a sump or trap may be built downstream to catch and permanently store the rock from the final blast or spread it evenly along the floor of the tunnel.
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