Excavation of an Instrumented Earthen Liner: Inspection of Dyed Flow Paths and Morphology

Abstract

A small, 3 by 9 by 0.9 m, experimental earthen liner was constructed using full-size compaction equipment. The liner was built utilizing six 15 cm thick compacted lifts. Water containing fluorescein and rhodamine WT dyes was allowed to infiltrate under ponded conditions for 46 days. Dye patterns observed during excavation of the liner indicated that lateral flow occurred between lifts. Although the US EPA hydraulic conductivity criterion for liners (<l×l0−7 cm/sec) was met, the dye experiment shows a need for better bonding between lifts to prevent preferential flow at lift interfaces. Morphological study of two profiles in the liner revealed variation in the degree of compaction within lifts. Vertical and horizontal installation techniques for moisture and solute monitoring devices (tensiometers, gypsum blocks, and soil-water suction lysimeters) were compared. Instruments functioned in either orientation. However, the horizontal instruments, which were installed during liner construction, were necessarily installed at lift interfaces which may be preferential flow paths. In addition, horizontal instruments may be destroyed if the lift thickness is decreased and/or longer compactor feet are used. No evidence of channeling was observed along vertically installed instruments, which were deemed more satisfactory than horizontally installed instruments.