In-situ stress measurement at a candidate repository horizon

The state of in-situ stress under the Hanford Site has attracted attention in recent years because of the core disking phenomenon observed during exploration drilling, an indicator of likely high horizontal stress. Efforts made to elucidate this phenomenon by core analysis and numerical modeling studies have enhanced the understanding of the rock failure mechanism and served to delineate approximate conditions for which disking might occur. The hydraulic fracturing stress measurements conducted in the Umtanum flow in fiscal year 1982 provided, for the first time, direct and quantitative information on the stress state of a candidate repository horizon in basalt. This paper summarizes the measurement method employed, the test results, and future Basalt Waste Isolation Project (BWIP) plans. 4 figures