Stress based safety evaluation of tunnel liners situated in swelling rock masses

The liners of tunnels excavated in swelling rocks are vulnerable to the expansive behaviour of surrounding rock masses. To look into this issue, this paper performs a study on a tunnel situated in silty mudstone rock mass with sufficiently humid condition. The swelling behaviour of this strata is investigated based on indoor laboratory tests using samples drilled from field representative rock mass layer. The mineral content test shows there are considerable clay, which contribute to the exhibition of medium expansibility of rock mass. To estimate the stresses in tunnel liners and optimize the design schemes, numerical calculations are done to consider various loads, including swelling pressure, excavation load and ground water pressure. The results show that the differences of tunnel profile and liner thickness yield remarkable variations of stresses in liners. By summarizing the results, an optimized tunnel liner design scheme is proposed. The work of this paper gives a general guideline for safety evaluation of tunnel liners situated in swelling rock masses.