Enhancement of Clay–Sand Liners Using Crushed Limestone Powder for Better Fluid Control

Tunnel boring machine (TBM)-crushed limestone material is a fine powder obtained during tunnel excavations. This material is proposed for use as smart filler in clay–sand liners, which include highly plastic clay and are typically used in waste containment applications and other fields. Replacing a part of bentonite in these liners with an inert, low plasticity material is an efficient way of controlling the compressibility and reducing the swelling index. The objective of this study was to test the water retention capacity under various mixture conditions. The soil–water characteristic curves for mixtures consisting of sand and 15% clay were investigated with regard to three main proportions: clay mixture consisting of one-third of TBM powder and two-thirds of bentonite, clay mixture consisting of two-thirds of TBM powder and one-third of bentonite, and a mixture consisting of only sand and bentonite. The geotechnical properties exhibited a clear improvement in the compressibility and swellability of the clay–sand liner owing to the addition of TBM-crushed limestone filler. The clay–sand mixtures were enhanced by adding crushed filler and could seal off the pores and voids, retain a satisfactory hydraulic conductivity, and prevent or minimize the flow through the layer. Scanning electron microscopy and X-ray investigations were performed for the TBM limestone powder material mixed with commercial bentonite.