Abstract: Curves of water absorption process of gypsum rocks are obtained by using one-dimensional water absorbing method. Gypsum rocks from Shiziya tunnel are taken as research object. The water absorption processes are divided into two stages rapid absorption stage and constant speed stage. Water absorption is mainly concentrated in the first stage and different specimens have different absorption durations. With the increase of time, the water absorption velocity decreases and the decreasing slows down as well. Water absorption characteristic curves in 0.4 hour, 4 hours and the rapid absorption stage are all polynomial. After dry-wet cycling, the accumulated water absorption volume and average absorption velocity both increase, the absorption in early stage increases, and the rapid absorption stage is shortened. Through mercury injection experiment, it is found that the maximum diameter of gypsum rock is 2.85μm and average diameter is 0.88μm, indicating poor degree of sorting. After wetting-drying cycles, maximum diameter and average diameter increase and the sorting improves. Finally, a simple approach to obtain the range of effective pore diameter is presented using saturated absorption, capillary water absorption and mercury injection data.

Key words: gypsum rocks, capillary water absorption, dry-wet cycling, porosity character