Characterization of Deep-Seated Rock Masses by Means of Borehole Investigation. In-Situ Rock Stress Measurements, Hydraulic Testing and Core-Logging. Final Report

摘要

Swedish State Power Board. The main objective of the programme was to test a method of measuring in-situ rock stresses in the deep, water-filled boreholes and to correlate measured rock stresses with the hydraulic and geological properties of the rock mass. The investigations consist of the following activities: - Coredrillin of two main boreholes with a depth of 500 m and 250 m respectively. - Rock stress measurements at 11 and 9 main levels in the boreholes respectively. At each level at least 3 complete measurements were made. - Logging of the cores with respect to rock type, fractures and fracture characteristics. - Water injection tests in the boreholes. The rock mass investigated is composed of a gneiss granite of Svecocarelian age (1500 Ma), with inclusions of younger pegmatites and greenstones of variable ages. The fracture density is as a mean 2 fractures per meter with a marked decrease in frequency with increased depth. The fractures are generally coated with calcite and chlorite as the dominating coating minerals. For the rock stress measurements, the method of Leeman and Hayes was chosen. The result show that there is a very high stress level in the rock mass, recordings of about 70 MPa were taken below a horizontal fracture zone at 320 m depth. In this lower rock masses the high stresses were also illustrated by intense disking of the hollow core which made measur. (Atomindex citation 14:720964)