Discontinuity geometry characterization in a tunnel close to the proposed permanent shiplock area of the Three Gorges dam site in China

Pinnaduwa Kulatilake, J. Chen, J. Teng, X. Shufang, G. Pan

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Abstract

Discontinuity data from a 400m tunnel located close to the proposed shiplock area were investigated to characterize the discontinuity geometry of the rock mass around the tunnel. Traces of 39 major discontinuities (faults and dykes) were found on the tunnel exposures. Over 2000 minor discontinuity (joint) trace data available showed that the rock mass can be separated into about five statistically homogeneous regions. Three to four joint sets were found to exist in each of these regions. Available theoretical probability distributions were found to be insufficient to represent the statistical distribution of orientation of joint clusters. For about 94% of the joint sets, the gamma distribution was found to be the best probability distribution for representing a joint size distribution. Exponential and gamma distributions were the best probability distributions for representing joint spacing distributions for the joint data studied here. Censored joint trace data showed a significant effect of the trace length biases on the estimated mean trace length. This indicated that the 2m wide exposures which were used for collecting the joint trace data may not be sufficient to produce reliable estimates for joint size parameters for the shiplock area. Different estimates were obtained based on wall data and roof data for the joint size and 3-D intensity parameters. The following may have contributed to this result: (a) the effect of different finite sample sizes used; (b) the effect of sampling biases; and (c) the effect of modelling uncertainties on the estimated parameters. To obtain better estimates, it is suggested to collect joint data for several exposures which are at least 4-5m wide and have different orientations. When such data become available for the Three Gorges region, it is suggested to perform validation studies to check the applicability of the models, in addition to performing the joint geometry modelling.

Original languageEnglish (US)
Pages (from-to)255-277
Number of pages23
JournalInternational Journal of Rock Mechanics and Mining Sciences and
Volume33
Issue number3
StatePublished - 1996

Fingerprint

gorge
Probability distributions
Dams
Tunnels
discontinuity
tunnel
dam
geometry
Geometry
Rocks
Roofs
Sampling
sampling bias
statistical distribution
rock
modeling
roof
distribution
spacing
effect

ASJC Scopus subject areas

  • Economic Geology
  • Engineering(all)
  • Earth and Planetary Sciences(all)
  • Environmental Science(all)

Cite this

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title = "Discontinuity geometry characterization in a tunnel close to the proposed permanent shiplock area of the Three Gorges dam site in China",
abstract = "Discontinuity data from a 400m tunnel located close to the proposed shiplock area were investigated to characterize the discontinuity geometry of the rock mass around the tunnel. Traces of 39 major discontinuities (faults and dykes) were found on the tunnel exposures. Over 2000 minor discontinuity (joint) trace data available showed that the rock mass can be separated into about five statistically homogeneous regions. Three to four joint sets were found to exist in each of these regions. Available theoretical probability distributions were found to be insufficient to represent the statistical distribution of orientation of joint clusters. For about 94{\%} of the joint sets, the gamma distribution was found to be the best probability distribution for representing a joint size distribution. Exponential and gamma distributions were the best probability distributions for representing joint spacing distributions for the joint data studied here. Censored joint trace data showed a significant effect of the trace length biases on the estimated mean trace length. This indicated that the 2m wide exposures which were used for collecting the joint trace data may not be sufficient to produce reliable estimates for joint size parameters for the shiplock area. Different estimates were obtained based on wall data and roof data for the joint size and 3-D intensity parameters. The following may have contributed to this result: (a) the effect of different finite sample sizes used; (b) the effect of sampling biases; and (c) the effect of modelling uncertainties on the estimated parameters. To obtain better estimates, it is suggested to collect joint data for several exposures which are at least 4-5m wide and have different orientations. When such data become available for the Three Gorges region, it is suggested to perform validation studies to check the applicability of the models, in addition to performing the joint geometry modelling.",
author = "Pinnaduwa Kulatilake and J. Chen and J. Teng and X. Shufang and G. Pan",
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T1 - Discontinuity geometry characterization in a tunnel close to the proposed permanent shiplock area of the Three Gorges dam site in China

AU - Kulatilake, Pinnaduwa

AU - Chen, J.

AU - Teng, J.

AU - Shufang, X.

AU - Pan, G.

PY - 1996

Y1 - 1996

N2 - Discontinuity data from a 400m tunnel located close to the proposed shiplock area were investigated to characterize the discontinuity geometry of the rock mass around the tunnel. Traces of 39 major discontinuities (faults and dykes) were found on the tunnel exposures. Over 2000 minor discontinuity (joint) trace data available showed that the rock mass can be separated into about five statistically homogeneous regions. Three to four joint sets were found to exist in each of these regions. Available theoretical probability distributions were found to be insufficient to represent the statistical distribution of orientation of joint clusters. For about 94% of the joint sets, the gamma distribution was found to be the best probability distribution for representing a joint size distribution. Exponential and gamma distributions were the best probability distributions for representing joint spacing distributions for the joint data studied here. Censored joint trace data showed a significant effect of the trace length biases on the estimated mean trace length. This indicated that the 2m wide exposures which were used for collecting the joint trace data may not be sufficient to produce reliable estimates for joint size parameters for the shiplock area. Different estimates were obtained based on wall data and roof data for the joint size and 3-D intensity parameters. The following may have contributed to this result: (a) the effect of different finite sample sizes used; (b) the effect of sampling biases; and (c) the effect of modelling uncertainties on the estimated parameters. To obtain better estimates, it is suggested to collect joint data for several exposures which are at least 4-5m wide and have different orientations. When such data become available for the Three Gorges region, it is suggested to perform validation studies to check the applicability of the models, in addition to performing the joint geometry modelling.

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