Several creep tests (lasting more than one year) were performed to study the delayed mechanical behavior of Boom clay under the hydro-mechanical coupling effect. To prevent the soil from swelling as much as possible during resaturation, the samples were submitted to a confining pressure close to the in situ effective mean stress (2.5MPa) at a room temperature of 21°C. Creep tests highlight the creep potential of Boom clay. Delayed behavior became significant as the deviatoric stress increased. A deviatoric stress threshold (approximately 1.0MPa), below which only primary creep occurred, was proved to exist. If we introduce a quasi-steady state creep rate, the average creep rate after the creep deformation becoming stable, it can be found that the quasi-steady state creep rate of Boom clay is on the order of 10_6 ε/h under low deviatoric stress (1.5MPa) in the laboratory. However, In situ measurements of the tunnel diameter reduction show that steady creep state was not reached even after five years after construction. The in situ quasi-steady state diameter reduction rate calculated from the average of 10 years of stable deformation of thetunnel linings is on the order of 10_8 ε/h.
|Journal||International Journal of Rock Mechanics & Mining Sciences|
|State||Published - Jun 2015|