Abstract: Due to the large deformation and its long time dependent characteristic of high rockfill dams, a method of using composite grout to increase the compression modulus and reduce creep deformation of rockfill materials is proposed for high rockfill dams. The composite grout is a mixture of fly ash and cement with the characteristics of easy flow and post hardening. The composite grout was first sprinkled on the surface of rockfills, which later infiltrated into the rockfills during the process of rolling compaction. Flow tests on glass balls were conducted to study the effects of mixture ratios and contents of composite grout on its flow characteristics. Confined compression tests and creep tests were finally carried out to investigate the compression modulus and creep deformation of rockfills with composite grout. The results show that the flow property of composite grout is related to the fly ash content, water-to-binder ratio, maximum sand size and mixed content. The filling of composite grout can effectively increase the compression modulus and decrease creep deformation of rockfills, especially for soft rock materials and poorly-graded rockfills. The composite grout mainly plays the role of filling, cementation and lubrication in rockfills.

Key words: composite grout, rockfill, flow characteristics, compression modulus, creep