Abstract: Water retention of undisturbed fully weathered mudstone, from Dayezhen landslide at Cenxi city, Guangxi province, is measured using pressure plate method, filter paper method, and vapor equilibrium technique with saturated salt solution. The water retention curves in a large range of suction are obtained. Mercury intrusion porosimetry is used to measure the pore-size distribution of the intact samples under different suctions. The test results show that the air-entry value of the fully weathered intact samples is about 30 kPa and the water retention curve in the full suction range can be measured by three methods. The undisturbed natural specimens exhibit a unimodal pore-size distribution with a main range of 10-1 000 nm in diameter and a secondary pore diameter distribution of 100-300 μm due to occurrence of primary crack. By comparing the results of the mercury intrusion porosimetry tests on the mudstones experiencing three different suctions, a method for predicting the water retention curve of undisturbed specimens during drying is proposed, and the predicted results are compared with the measured values. The comparison shows that the combination of three predicted curves is closer to measured results of the mudstone in the full suction range. The predicted curve using single pore size distribution curve cannot match measured water retention curve correctly in the full suction range.

Key words: water retention curve, complete-intense weathering mudstone, mercury intrusion porosimetry, pore-size distribution, undisturbed specimen