Lining considerations for a circular vertical shaft in generic tuff
This report summarizes some to the classical formulas used in the design of concrete linings for vertical, circular bored shafts and applies them to a generic shaft in tuff. The lining requirements are shown to be highly dependent on the rock mass strength and in situ stress field. For a given stress field, the required lining thickness is analyzed as a function of rock mass strength, which is approximated by various fractions of the laboratory strength. For the cases considered, if the rock mass strength is equal to the laboratory compressive strength, then no lining would be required. If the strength reduction factor is 2, a concrete lining (compressive strength = 35 MPa) having a thickness of 0.3 m would provide a safety factor of at least 1.5. For larger strength reduction factors, the required lining thickness in the different formations is quite variable. An analysis of measured lining pressures for the conventionally sunk (excavated with explosives) Mt. Taylor shaft (Grants, New Mexico) has been included. The results suggest that a substantial damaged (relaxed) zone was created during the excavation process. The lining pressures are much less than would be predicted under the assumption of no damage. Therefore, the recommendations presented sunk, rather than bored, shafts. The approach described and the equations presented may, it is believed, be used with care to analyze different generic shaft scenarios. However, high priority should be placed on obtaining the best estimates possible for rock mass strength and an in situ stress field.
- Research Organization:
- Sandia National Labs., Albuquerque, NM (United States)
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 59565
- Report Number(s):
- SAND--83-7068; ON: DE85005676
- Country of Publication:
- United States
- Language:
- English
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