Site monitoring of suction and temporary pore water pressure in an ancient landslide in the Three Gorges reservoir area, China

Rainfall is the main factor influencing the stability of landslides, but the precise mechanisms and processes are still poorly known. Unsaturated soil mechanics can be used to study how suction and temporary pore water pressure affect landslide stability. During rainfall, the groundwater level in the landslide will change, and the suction and temporary pore water pressure will also change with time and rainfall. Construction of a field observation well is an effective method of studying changes in suction. An observation well was constructed in an ancient landslide in the Three Gorges reservoir area in China. The well has a depth of 20 m, a diameter of 2 m, and is the largest observation well for monitoring of suction and temporary water pressure in the world. Suction, temporary water pressure, and rainfall were measured between October 2002 and December 2004; this is the longest observation period for this type of study. Analysis of the results shows that the distribution of suction is determined by the depth, soil materials, gradation, and structure of the landslide. The changes in suction are related to the intensity and duration time of rainfall, the season, and the climate. If the suction does not change promptly after rain, there is a time difference between the timing of rainfall and of suction change. The suction varied between 0 and 15 kPa. These conclusions form a basis for further scientific studies on how rainfall affects landslides.