Rock mechanics stability analysis of the shafts and research galleries at the Mizunami Underground Research Laboratory. Japanese Fiscal Year, 2004 (Contract research)

Design of the shafts and tunnels of the Mizunami Underground Research Laboratory and preliminary analysis focuses at the depth of 300m were respectively carried out in FY2002, and FY2003 based on the geological survey results obtained up to that point. We have recently completed the MIZ-1 borehole investigation and obtained the geological data down to the depth of 1,000m. Based on the data, the geological model, rock property, initial stress and other geological characters were reviewed and corrective analysis (two-dimensional) was performed. Also three-dimensional analysis was performed at the connection part of the shaft and sub-stage (horizontal tunnel) located at the depth of 100m and 300m, where the maximum stress is expected. From those analyses, we evaluated the validity of the design. Outlines and the results are as follows: 1) Based on the location of fault predicted from MIZ-1 borehole investigation, the geological structure at the site was revised and then rock classification was established. Also rock properties and initial stress condition for numerical analysis were revised. 2) Corrective analysis at the selected sections which were estimated from the previous analysis was reviewed. As a result, validity of design for shafts and sub-stages (horizontal tunnels) were confirmed. 3) Using three-dimensional elasto-plastic analysis, the stability of support around connection part of shafts and sub-stages (horizontal tunnels) under construction was confirmed. (author)