Frost Action in Granular Materials

Abstract

This thesis presents an experimental study of frost action in granular materials. A highly frost susceptible matrix, consisting of sand and ground chalk was produced. Its freezing behaviour was modified by the addition of selected coarse aggregates - Slag, Basalt and Limestone - which were each sub-divided into two groups of particles - 37.5 to 20mm and 20 to 3.35mm. The initial experimental work was concerned with assessing the frost susceptibility using the standard TRRL frost heave test. Heaving pressures were measured using equipment developed during the investigation. It proved to be reliable and permitted an assessment of the effects of the boundary conditions on the heaving pressure. Both heave and heaving pressure were reduced by the introduction of coarse particles, so such inclusions modified the frost susceptibility of the matrix. These reductions were dependent on both aggregate type and aggregate content, with particle size being less influential, and they have been attributed to changes in pore structure, porosity and thermal characteristics that accompanied the additions of coarse aggregate. Similar behaviour was obtained when the coarse aggregates were added to a natural soil, demonstrating that mechanical stabilisation is effective in controlling frost susceptibility. A Controlled Heave Unit (CHU) was developed to provide close control of the boundary temperatures during heave tests. It produced reliable heave values, after approximately 100 hours freezing, which were compatible with those obtained from the cold room tests, and so provided a basis for the rapid assessment of frost susceptibility. Heave tests were performed under different levels of restraint. The results clearly demonstrated the role of surcharge loading in controlling heave. Whilst low surcharges significantly reduced the heave, complete elimination was not achieved even at high surcharges. The reductions in heave were clearly related to the ratio between surcharge loading and heaving pressure.