A Large-Scale High-Pressure Erosion Apparatus for Studying Internal Erosion in Gravelly Soils under Horizontal Seepage Flow

Internal erosion is a common cause of dam failures, occurring in internally unstable soil strata when the hydraulic boundary reaches some triggering conditions. A large number of high embankment dams are constructed on deep gravelly alluviums, and thus, there is a need to evaluate the internal stability of gravelly alluviums and assess the likelihood of internal erosion for the foundations of high embankment dams. A large-scale seepage apparatus was developed for studying the horizontal internal erosion behavior of compacted gravelly soils under high surcharge pressure. The permeation box can hold a specimen 600 mm long in the seepage path and 400 × 400 mm2 in the cross-section, making the apparatus capable of testing soils with particle sizes up to 60 mm. The water supply system can provide a maximum water head of 30 m and a maximum flow rate of 300 L/min to fit the wide-range variation in gravel’s hydraulic conductivity. The mechanical loading system can provide a surcharge pressure of up to 3.0 MPa. In addition to measuring the common quantities in seepage tests, such as water head loss along the seepage path and total flux, this apparatus was specially designed to allow for observation of the particle outflow at the seepage exit, collection of the eroded fine particles, and measurement of the erosion-induced deformation. Preliminary tests were conducted on gap-graded gravelly alluvium to show the performance of the apparatus. It is shown that the initiation and progression of internal erosion can be better characterized by combining the recorded data and the observed phenomenon of particle outflow at the seepage exit. The influence of surcharge pressure on internal stability was also studied preliminarily to highlight the importance of the apparatus’ capability of imposing a high surcharge pressure.