Rainfall Infiltration and Water-Retention Characteristics of Rockfill Material

Abstract

Comprehending the rainfall infiltration process in rockfill is essential for estimating the strength and unsaturated wetting deformation behaviors of rock structures. This paper presents an experimental study on the rainfall infiltration characteristics and water-retention capacity of a weakly weathered granite rockfill using a newly developed instrument that can generate artificial rainfalls with controllable intensities (0–500 mm/h) and sufficient uniformities. A group of rainfall infiltration tests and drainage tests were carried out using rockfill specimens with a diameter of 600 mm and a height of 1,200 mm. Results show that rainfall infiltration, which is characterized by the downward movement of the wetting front, experiences an unsaturated process even under heavy rainfall conditions. Both the steady-infiltration water content and the velocity of the wetting front increase nonlinearly with increasing rainfall intensity. The unsaturated hydraulic conductivity of rockfill material can be acceptably estimated by classic models for medium-to-fine grained soils. In addition, the drainage process in rockfill is divided into two stages of quick-drainage and slow-drainage by the turning water content. The quick-drainage stage typically lasts for a brief time (e.g., a few minutes), followed by the slow-drainage stage with small decreases (about 2%–3%) in water content. In the end, the concept of water transmission in medium-to-large pores and water retention in small pores were used to characterize the rainfall infiltration and drainage characteristics. The rockfill possesses good seepage/drainage qualities owing to the excellent connectivity of relatively large pores, whereas the water-retention capacity is mainly attributed to the small pores.