Geology of the Straight Creek tunnel site, Clear Creek and Summit Counties, Colorado, and its predicted effect on tunnel construction

Robinson, Charles Sherwood; Lee, Fitzhugh T.

doi:10.3133/ofr62111

Cited by 4 publications

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“…To predict the position of the metasedimentary rock inclusions by projection from the surface exposures and drill holes was impracticable because their maximum dimension averages only about 20 feet. However, on the basis of surface and drill-hole information, a prediction was made that 75 percent of the pilot bore would be in granite and 25 percent would be in metasedimentary rocks (Robinson and Lee, 1962).…”

Section: Geologic Predictionsmentioning

confidence: 99%

Engineering geologic, geophysical, hydrologic, and rock-mechanics investigations of the Straight Creek Tunnel site and pilot bore, Colorado

Robinson¹,

Lee²,

Scott³

et al. 1974

Professional Paper

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Tunnels are among the most expensive of engineering structures. They can, and often do, present great difficulties in design and construction. For several decades the techniques used in tunneling have lagged behind those used in other fields of engineering. An engineer, for example, can design a bridge so that it will adequately and economically fulfill its proper function. The design and construction of underground openings commonly is a far different situation. The stresses surrounding a planned underground opening are generally unknown quantities, as are the nature and behavior of the rock mass itself. Therefore, judgment and trial and error prevail; design, in its true sense, becomes impossible; and safety factors can be uneconomically large or dangerously small. Geological factors exert a decisive influence on the difficulties and costs of tunnel construction. Tunnel hazards unanticipated sources of expense and delay are caused largely by the divergence of structural details of a given rock mass from the statistical average for similar rock masses. This variation in rock structure results in erratic tunneling costs; the cost of a tunnel may be considerably higher than the average cost of similar tunnels constructed in similar bodies of rock. A competent experienced geologist usually can predict the kinds of difficulties that would be encountered in different parts of a proposed tunnel, but he seldom can quantitatively evaluate the difficulties. On such a basis, preliminary estimates for materials and equipment for constructing a tunnel commonly involve considerable guesswork. This guesswork usually results in the procurement of unnecessary supplies to offset the possibility effacing an emergency with inadequate provisions. The present (1972) state of tunnel art combines experience and intuition with theoretical and practical principles to design and construct underground openings. We believe that in the future the fullest use of rock-mass information, together with improved theory, will result in greater economy, safety, and confidence in tunnel construction. It is toward this goal that the present report is directed. The Straight Creek Tunnel is about 55 miles west of Denver. The proximity of this tunnel to the research center of the U.S. Geological Survey in Denver offered an unusual opportunity to utilize the personnel and facilities of the Survey on the problems of defining the environment of the proposed tunnel. The authors were able to consult with, and have the services of, experts in nearly every field of geology. As a result, research investigations in the tunnel area were conducted by many survey personnel. The investigations performed in conjunction with the basic geologic investigations, such as geophysical and groundwater research, are described in separate chapters by those who directed the research. At the dedication of the first of the twin bores on March 8, 1973, the Colorado Division of Highways, in accordance with a resolution passed by the General Assembly of Colorado, officially named th...

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Section: Geologic Predictionsmentioning

confidence: 99%

Engineering geologic, geophysical, hydrologic, and rock-mechanics investigations of the Straight Creek Tunnel site and pilot bore, Colorado

Robinson¹,

Lee²,

Scott³

et al. 1974

Professional Paper

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“…The extent of the Loveland Basin landslide is principally controlled by preexisting faults that form a wide shear zone. The shear zone in the area of the landslide was previously mapped by Robinson and Lee (1962) as about 600 feet in width and about 4,000 feet in length. It trends about N. 15° E. and is terminated on the west by the fault that forms the western boundary of the landslide.…”

Section: Structurementioning

confidence: 96%

“…The center of the cut exposed altered metasedimentary rock. Geologic mapping in the vicinity of the tunnel site (Robinson and Lee, 1962) revealed that the bedrock in the tunnel area consisted of about 75 percent granite and about 25 percent metasedimentary rocks; the percentage of the two rock types probably is similar in the landslide area. The metasedimentary rocks occur as inclusions in the granite which range in maximum dimension from less than 1 foot to about 1,000 feet.…”

Section: Bedrockmentioning

confidence: 98%

“…The weight was calculated by multiplying the volume, in cubic yards, by a value of 2.1 tons per cubic yard. The weight per cubic yard was determined, assuming complete water saturation, from density and porosity measurements and density-of-fracture calculations previously made during the study of the geology of the Straight Creek Tunnel pilot bore (Robinson and Lee, 1962).…”

Section: Calculations Of Volume and Weight Of The Landslidementioning

confidence: 99%

“…The geology of the Straight Creek Tunnel site, including the area where the Loveland Basin landslide developed, was mapped at 1:12,000 in 1962 by the authors as part of a research project on the pilot bore for the Straight Creek Tunnel. (See Robinson and Lee, 1962. ) After the development of the landslide, the geology of the landslide area was mapped ( fig.…”

Section: Introductionmentioning

confidence: 99%

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Geological, geophysical, and engineering investigations of the Loveland Basin landslide, Clear Creek County, Colorado, 1963-65

Lee¹,

Moore²,

Carroll³

et al. 1972

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The Loveland Basin landslide occurred in a high mountain valley near the Continental Divide about 55 miles west of Denver during construction of the east portal area for the proposed Straight Creek Tunnel. The landslide developed in Precambrian bedrock, consisting of Silver Plume Granite with inclusions of metasedimentary rocks that are chiefly biotite gneiss and schist. Thin deposits of surficial material, consisting of moraine and soil mixed with talus, overlie the bedrock. The entire area is within the Loveland Pass fault zone. Individual faults within this zone are characterized by masses of breccia and gouge, ranging in width from less than 1 foot to 1,000 feet; these masses are separated by masses of less intensely sheared rock. The preexisting structure partly determined the shape of the landslide. The landslide is outlined by distinct scarps. The upper two-thirds of the landslide is downdropped in relation to the surrounding rock. The lower one-third of the landslide has been thrust upward and outward over the surrounding topography. Within the landslide mass, movement is indicated by tension fractures, which are most numerous near the margins of the mass.

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The relationship of geophysical measurements to engineering and construction parameters in the Straight Creek Tunnel pilot bore, Colorado

Scott

Lee

Carroll

et al. 1968

International Journal of Rock Mechanics and Mining Sciences &am

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Geology of the Straight Creek tunnel site, Clear Creek and Summit Counties, Colorado, and its predicted effect on tunnel construction

Cited by 4 publications

References 0 publications

Engineering geologic, geophysical, hydrologic, and rock-mechanics investigations of the Straight Creek Tunnel site and pilot bore, Colorado

Engineering geologic, geophysical, hydrologic, and rock-mechanics investigations of the Straight Creek Tunnel site and pilot bore, Colorado

Geological, geophysical, and engineering investigations of the Loveland Basin landslide, Clear Creek County, Colorado, 1963-65

The relationship of geophysical measurements to engineering and construction parameters in the Straight Creek Tunnel pilot bore, Colorado

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