An experimental scale-model study of seismic response of an underground opening in jointed rock mass

Abstract

NRC Job Code B6643 ST For sale by the U.S. Government F'rinting Office Superintendent of Documenb, M a i l Stop: SSOP, Washington, DC 20402-9328 ISBN 0-16-048982-2 Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. ABSTRACTThis report describes an experimental investigation conducted by the Center for Nuclear Waste Regulatory Analyses (CNWRA) to (i) obtain a better understanding of the seismic response of an underground opening in a highly-fractured and jointed rock mass and (ii) generate a data set that can be used to evaluate the capabilities (analytical methods) to calculate such response. This report describes the design and implementation of simulated seismic experiments and results for a 1/15 scale model of a jointed rock mass with a circular tunnel in the middle. The discussion on the design of the scale model includes a description of the associated similitude theory, physical design rationale, model material development, preliminary analytical evaluation, instrumentation design and calibration, and model assembly and pretest procedures. The thrust of this discussion is intended to provide the information necessary to understand the experimental setup and to provide the background necessary to understand the experimental results. The discussion on the experimental procedures and results includes the seismic input test procedures, test rum, and measured excitation and response time histories. The closure of the tunnel due to various levels of seismic activity is presented. A threshold level of seismic input amplitude was required before significant rock mass motion occurred. The experiment, though designed as a two-dimensional representation of a rock mass, behaved in a somewhat three-dimensional manner, which will have an effect on subsequent analytical model comparison.iii

Preclosure seismic design methodology for a geologic repository at Yucca Mountain. Topical report YMP/TR-003-NP

“…The welded tuffs at Yucca Mountain, including the welded Topopah Spring tuff that would be the host rock for emplacement drifts, are highly fractured. Through research conducted by the Center for Nuclear Waste Regulatory Analyses and others, significant progress has been made recently in understanding the seismic behavior of jointed rock masses and in developing rock joint models for cyclic loads (e.g., Fishman 1988;Jing et al 1992;Huang et al 1993;Qiu et al 1993;Wibowo et al 1993;Hsiung et al 1994a;Hsuing et al 1994b;Ghosh et al 1995;Kana et al 1995;Souley et al 1995). However, this research has also clearly shown that dynamic joint behavior is a complex nonlinear phenomenon that depends on the joint boundary conditions, joint surface characteristics, and joint slip history.…”

Seismic response of rock joints and jointed rock mass

“…both cyclic pseudostatic and dynamic loadings. A detailed discussion regarding the design of this scale-model experiment is given by Kana et al (1995).…”

“…In and p represents the model and the prototype parameters, where k is equal to 2.0, which was determined by comparison of the shear test results of the simulated rock interfaces and actual rock joints. For a detailed discussion regarding the shear tests of the simulated rock interfaces, readers are referred to a separate report prepared by Kana et al (1995). Finally,…”

“…The results of this experimental investigation show that a threshold level of seismic input amplitude is required before any significant amount of permanent rock mass deformation will occur and begin to accumulate. Kana et al (1995). Thus, lower amplitude seismic events will not have much effect on underground opening stability.…”

“…in length that were instrumented with strain gages and tested in uniaxial compression test machines. A list of the ingredients that were ultimately found to provide a material having the appropriate properties is given by Kana et al (1995).…”