Quote from TUST article of 2010, just seen: During tunnel excavation in a jointed rock mass, significant joint closure takes place in the immediate vicinity of tunnel due to joint effective normal stress increase, and the equivalent hydraulic conductivity is largely reduced within a zone approximately one tunnel-radius thick around the tunnel. Do we believe this? What about the four quadrants with joints suffering shear stress? In a larger tunnel unlikely to be correct?
Dear Nick, I cannot give a direct answer to your question but maybe it is a small piece to think about. As you probably already recognized, in my latest paper (A new global database to improve predictions of permeability distribution in crystalline rocks at site scale), I compared the calculated(!) radius of influence derived from a range of hydraulic test methods in crystalline rock. One somewhat puzzeling result has been, that although depth trends of the radius of influence between borehole based tests and tunnel based tests is similar, the depth trend is shifted by 3-4 orders of magnitude towards higher radius, demonstrating that there are significant hydraulic changes for larger excavations. Bests, Peter
Sounds good to me Peter! Thanks a lot for the info. I just found your thesis and look forward to taking a look. The 'size influence' is logical if you allow for the larger potential joint opening, joint shear in specific sectors of large openings in jointed rock. Our UDEC-BB studies in nuclear waste projects have demonstrated reduced inflow in small (Stripa-related) excavations, and larger inflow potential in e.g. large tunnels and storage caverns - due to a wider EDZ of joint shearing. Have a look at QH2O re your (nearer-surface) k-depth trends.
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