Effect of open-framework gravel on suffusion in sandy gravel alluvium

Abstract

Some accidents of dams are attributed to suffusion around open-framework gravel (OFG) in sandy gravel alluvium. However, whether OFG can be really an internal seepage exit of fine particle migration in the field or not? How much the effect of OFG on suffusion is? These problems have not been investigated yet. This paper presented a list of flume-scale suffusion tests to investigate suffusion at the tip of a cutoff wall in sandy gravel alluvium with OFG. The results indicate that suffusion first initiates at the downstream side of the tip of the cutoff wall in the test without OFG, while in the tests with OFG, it initiates at the upstream side of OFG, and then both mainly progress backward to the upstream side. OFG significantly decreases the hydraulic gradients at the initiation of suffusion and at blowout. In addition, the experimental results also confirm that OFG is likely to be an internal seepage exit of fine particle migration in the field. A large number of fine particles and some coarse particles in the sandy gravel are eroded into OFGs in the tests, and OFG significantly increases the settlement induced by blowout; meanwhile, it makes the settlement unstable after blowout.