Evaluation of discharge capacity of geosynthetic drains for potential use in tunnels

Abstract

Controlling groundwater is always of great concern for tunnel management. A tunnel drainage system may not function properly due to insufficient drain capacity, or because drains become clogged with sediment such as calcium carbonate. In this study, various types of geocomposites were investigated in a laboratory to evaluate their filtration and discharge capacity characteristics for their potential use in tunnels. The drain capacity of the geocomposites was then compared with that of a needle-punched non-woven geotextile, currently used as a drain layer material in tunnels. Based on the results of discharge capacity tests performed on four types of geocomposites found to meet the filtration requirements, the presence of calcium carbonate (CaCO3) in water was found to result in a decrease of approximately 30% of maximum discharge capacity under a confining pressure of 100 kPa. Also, the maximum reduction observed in the discharge capacity was approximately 65% as the confining pressure increased from 50 to 400 kPa. The comparison between the geocomposites and the non-woven needle-punched geotextiles, however, revealed that the geocomposites have a significantly larger discharge capacity than that of non-woven needle-punched geotextiles with similar thickness (i.e., an approximate average of 25 times larger). Moreover, the discharge capacity of the geocomposites is relatively less affected by CaCO3 and confining pressure compared with the non-woven needle-punched geotextile.