Packing and strength of sands and sand-kaolin mixtures
This thesis is divided into two distinct parts, each containing a review of the relevant literature. In the first part, the packing of sands at a range of moisture contents was studied using both static loads and impacts provided by a Bruce compactor. Particle shape and particle size distribution were found to determine the maximum and minimum void ratio to which a sand would pack. With sand of greater than 45 Um in size, particle size was not found to exert a major effect on packing. Limitations to the concept of packability or ease of packing are discussed in detail. For narrowly graded sands, air-dry and nearly saturated sands were always foundto pack more closely than the same sand at any other moisture content. For a wide range of intermediate moisture contents, there was practically no effect of moisture content on packing.When saturated mixtures of sand with the addition of a small proportion of calcium-saturated kaolin were allowed to air-dry, they were found to pack to near their minimum void ratio without the aid of any externally applied force.In the second part, the strength of mixtures of sand with 0,0.5, 2 and 8 per cent kaolin was studied as a function of watertension and moisture content. Kaolin did not cause a large increase in strength until water tensions greater than 100 mbar. The concept of effective stress was extended by considering that the kaolin and water acted together within kaolin bridges which were observed to link sand grains up until air-entry occurred into the kaolin itself. In this way it was possible to explain the variation of strength of the mixtures over a range of water tensions from 20 mbar to 10 bar. The relevance of these results to the behaviour of soils and agricultural research is outlined.