Predicting the behavior of engineering and geologic materials under a variety of complex, random and arbitrary loading and unloading conditions is an essential element to many engineering design problems. Such an understanding comes through both analytical modeling and experimental testing. The multiaxial testing devices and data acquisition system requested will allow for the physical analysis of a broad array of materials including concrete, rock, composite materials, and soil. Within the cubical test cell these materials may be subjected to variable and independent levels of stress along any of the principal axes. This variable and independent loading is what makes the test cell superior to conventional stress analysis along a single axis and therefore more accurate when used to predict behavior over the life of a particular material or composite. The proposed equipment will be used for testing engineering materials under uniaxial, biaxial, or triaxial compressive loading conditions. The devices consist of a cubical steel frame and six walls which function as lids. The load is applied via a hydraulic pressure system whose polyurethane membranes and pressure seals contain the fluid pumped into the system. The deformation of the specimen is measured with a proximitor probe system. This work is proposed to find basic constitutive properties and the stress-strain relationships of tuff rocks (from Yucca Mountain, Nevada) under multiaxial load histories. Yucca Mountain located near the southwest margin of the Nevada Test Site (NTS) in southern Nevada, as show in Figure 1, is being evaluated as a potential site for underground disposal of nuclear waste. Yucca Mountain primarily consists of layered volcanic tuff (Bish et al., 1981). The Topopah Spring Member of the Paintbrush Tuff has been tested (under uniaxial and two dimensional loadings) and reported by References (Olsson and Jones, 1980; Price, Nimick, and Zirzow, 1982; Price, Spence, and Jones, 1984; Price et al., 1985; Nimick et al., 1985; Nimick et al., Price 1986) for physical, thermal, and mechanical properties as part of the Nevada Nuclear Waste Storage Investigations (NNWSI) Project, which is administered by the Nevada Operations Office of the U.S. Department of Energy (DOE). Figure 1 shows the geographic locations of NTS, Yucca Mountain, and Busted Butte, Figure 2 the stratigraphic setting of the Topopah Spring Member, and Figure 3 a measured section of the tuff exposures at the sample location. There is a need for quantitative methods to predict the environmental impact of excavating operations so that preventive and remedial measures can be taken to reduce or eliminate adverse impact. The overall objective of this proposed study is to develop models as quantitative predictive tools to improve the capability of accurately predicting probable subsidence resulting from underground excavating. The specific tasks of this study include: 1. To compile all available relevant data. 2. To develop constitutive and failure models for discontinuous tuff rock based on available uniaxial and triaxial compression test series on Topopoh Spring tuff rocks which have been reported in these Refs. (Olsson and Jones, 1980; Price, Nimick, and Zirzow, 1982; Price, Spence, and Jones, 1984; Price et al., 1985; Nimick et al., 1985; Nimick et al., Price 1986) and other References. 3. To conduct laboratory testing of new core samples and make determination of mechanical properties of tuff rock materials under multiaxial load histories. 4. To develop the finite element computer simulation model to analyze the basic behavior of the underground opening field, including behavior of individual underground opening field, movement of the overburden formation, and dislocation movement between the top of the cavern field and the overburden formations. By using the finite element computer simulation model, the causes of the probable damage will be analyzed and appropriate measures to prevent such damage will be recommended.
