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...

Transmissibility estimated from specific capacity is subject to error, because the effects of duration of pumping and specific yield are not evaluated. Rearrangement of the Theis equation provides a mathematical relation for evaluating drawdown during nonequilibrium conditions and delayed yield from storage at any time after pumping begins. This relation is obtained from type curves of u plotted against u[W(u)] where u[W(u)] is equal to 1.632 × 10−2 [(Sy) r2s/Qt]. The only term that needs to be assumed is specific yield. The error of the estimated transmissibility will be 30 to 40% of the error made in assuming the apparent specific yield for u = 10−2 and 10 to 15% for u less than 10−4. The curves presented in the paper were used to construct a transmissibility map of the valley‐fill aquifer in the Arkansas River valley of Colorado. The map was the foundation for an analog‐model analysis of the aquifer system. The transmissibilities estimated from the type curves correlate well with transmissibilities determined from aquifer tests and estimated from test‐hole logs.

Accidental releases of contaminants resulting from the operation of the U.S. Energy Research and Development Administration T s nuclear-processing and recovery plant located on Rocky Flats will move at different rates through different parts of the hydrologic system. Rates of movement are dependent upon the magnitude of the accidental release and the hydrologic conditions at the time of the release. For example, during wet periods, a contaminant resulting from a 5,000-gallon (19,000-litre) release on the land surface would enter the groundwater system in about 2 to 12 hours. Groundwater flow in the Rocky Flats Alluvium might move the contaminant eastward at a rate of about 3 to 11 feet (0.9 to 3.4 metres) per day, if it remains dissolved. Maximum time to a point of discharge would be about 3 years; minimum time could be a few days. A contaminant entering a stream would then move at a rate of about 60 feet (18 metres) per minute under pool-and-riffle conditions. The rate of movement might be about 420 feet (128 metres) per minute under open-channel-flow conditions following intense thunderstorms. R.71W.

The water supply for the Pueblo Army Depot, 15 miles east of Pueblo, Colo., is obtained from wells that tap an aquifer in terrace alluvium. Withdrawals have resulted in a water-level decline of 27 feet, which adversely affects the discharge rate ot individual wells. Furthermore, excessive pumpage has resulted in progressive deterioration o f water quality. Over a 20-year period, hardness has increased from 70 milligrams per i er to 135 milligrams per liter and dissolved-solids content has increased from 250 milligrams per liter to 370 milligrams per 1i ter.Two new supply wells were drilled in the southern part of the Depot and were tested to determine aquifer properties and probable production rate. The hydraulic conductivity determined from these tests ranged from about 350 to nearly 600 gallons per day per square foot. The transmissivity for the full thi c kness of the aquifer is in ~he range of 7,500 to 12,000 gallons per day per foot.The two new s upply wel ls can be pumped at a combined rat e of about 140 gallons pe r minute. If pumpage in the existing well field is reduced by the same amount, some re co ve ry of water levels in the field will occur and th e trend in wat e r quality deterioration may slow or e ven reverse.

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