Design/construction methods – Tunnelling in swelling rocks

Anhydrite and rocks containing clay minerals increase in volume when they come into contact with water. In tunnelling, this can lead to a strong heave of the tunnel floor and even to failure of the invert arch. This paper presents laboratory tests on swelling rocks, methods of monitoring the swelling process in the field, and relevant case histories in tunnel construction. Establishing a characteristic line for the swelling rock is shown to be very useful for discussing the effectiveness of various constructional measures. The design placing the invert arch on yielding supports appears to be the adequate solution for the type of tunnelling problem examined here. With this solution, a drastic reduction in swelling pressure on the lining is achieved by allowing a controlled amount of floor heave.