Aseismic analyses of underground openings

Abstract

<p>Facilities such as pipelines, tunnels, shafts and some power plant components require safe underground construction and operation. Many of these facilities are also critical from an overall safety viewpoint and/or the provision of relief services after earthquakes. For this reason, such underground structures require reliable and economic procedures for their aseismic analysis and design: a subject which has not received much attention until recently. The aseismic analysis work described herein may be divided into two major parts: the spatial distribution of seismic ground motions; and the dynamic analysis of the structure-medium system. For the first part, a method of computing component responses at the base rock level due to upward and downward propagating shear waves was developed. An improved method for determination of period and phase velocity of R-waves and their contribution to seismic ground motions was also adopted. The size of the problems involved is often too large for efficient computing or design office computers. To overcome this difficulty, methods for substantially reducing the size of the problem and cost of the analysis were applied. For underground structures of considerable length, analysis of a typical portion is often satisfactory. A method for such analysis, with due consideration of the continuity of the system in the axial direction at the transverse ends, was selected from a number of approaches and verified. Parametric studies using a simple, single layer system with a horizontal tunnel were carried out for a number of soil and tunnel properties. The results of these analyses were reasonable and consistent with the behaviour of such structures observed during past earthquakes and field tests. It is considered that the investigation has both contributed to a better understanding of the seismic response of underground structure-medium systems, and provides the necessary methods for the detailed aseismic design of such systems.</p>