Drift Degradation Analysis
A statistical description of the probable block sizes formed by fractures around the emplacement drifts has been developed for each of the lithologic units of the repository host horizon. A range of drift orientations with the drift azimuth varied in 15{sup o} increments has been considered in the static analysis. For the quasi-static seismic analysis, and the time-dependent and thermal effects analysis, two drift orientations have been considered: a drift azimuth of 105{sup o} and the current emplacement drift azimuth of 75{sup o}. The change in drift profile resulting from progressive deterioration of the emplacement drifts has been assessed both with and without backfill. Drift profiles have been determined for four different time increments, including static (i.e., upon excavation), 200 years, 2,000 years, and 10,000 years. The effect of seismic events on rock fall has been analyzed. Block size distributions and drift profiles have been determined for three seismic levels, including a 1,000-year event, a 5,000-year event, and a 10,000-year event. Data developed in this modeling and analysis activity have been entered into the TDMS (DTN: MO0109RDDAAMRR.003). The following conclusions have resulted from this drift degradation analysis: (1) The available fracture data are suitable for supporting a detailed key block analysis of the repository host horizon rock mass. The available data from the north-south Main Drift and the east-west Cross Drift provide a sufficient representative fracture sample of the repository emplacement drift horizon. However, the Tptpln fracture data are only available from a relatively small section of the Cross Drift, resulting in a smaller fracture sample size compared to the other lithologic units. This results in a lower degree of confidence that the key block data based on the Tptpln data set is actually representative of the overall Tptpln key block population. (2) The seismic effect on the rock fall size distribution for all events analyzed is relatively minor. (3) The analysis of thermal and time-dependent effects on rock fall in this study is based on a reduction in the joint cohesion. Joint cohesion has been conservatively reduced from a laboratory test value of 0.86 MPa to a value of 0.01 MPa after 10,000 years. The results from this analysis indicate that time-dependent and thermal effects have a minor impact on rock fall. (4) Both the 75 percentile and the worst-case drift degradation profiles have been provided in this analysis for the current emplacement drift azimuth of approximately 75{sup o}. Most of the emplacement drift openings were not affected by rock fall. For the current emplacement drift alignment, the highest percentage of drift affected by rock fall was 8% in the Tptpmn unit. The Tptpmn unit produced the highest frequency of key blocks per kilometer compared to the other lithologic units (Tables 26 and 41). (5) This key block analysis has shown that the current drift alignment is relatively favorable in terms of reducing the potential maximum size rock block compared to most drift orientations.
- Research Organization:
- Yucca Mountain Project, Las Vegas, NV (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- OSTI ID:
- 790802
- Report Number(s):
- ANL-EBS-MD-000027, Rev. 01, ICN 01; MOL.20011029.0311, DC No. 29317; TRN: US200504%%69
- Resource Relation:
- Other Information: PBD: 28 Sep 2001
- Country of Publication:
- United States
- Language:
- English
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