In situ reka probe measurements at fran ridge and in the ESF at Yucca mountain

摘要

A thermal probe method,called REKA (Rapid Evaluation of K and Alpha) has been used for determining thermal conductivity (K) and diffusivity (Alpha) both at the Fran Ridge Large Heated Block Tests bed and in the Exploratory Studies Facility (ESF) at yucca Mountain.The REKA method involves a single borehole probe with a heater and a temperature measurement section.An elliptical temperature field is generated by the heater,and the temperature distribution along the length of the probe is recorded at several locations and at given time intervals for a period of 6 to 12 hours.A trial-and-error evaluation procedure is used to determine the unknown thermophysical properties by minimizing the root-mean-square (RMS) error between the measured and the calculated temperature fields.If a conduction-only thermal model is used in the evaluation,the thermophysical properties will include the rockmass and the moisture effects,and the values will represent effective properties.If a hydrothermal model is also used,the difference between the effective and the rock matrix thermophysical properties cna be related to hydrothermal characteristics.A reusable REKA probe can be applied to measure in situ rock properties in a short,open hole,e.g.,in a rockbolt borehole,at low cost.A permanent REKA probe has to be grouted in the insertion hole,if an open hole is not acceptable due to the disturbance it may cause to other site characterization activities.