Vertical flow of soil moisture, in situations with water application, drainage and evapo-transpiration, is investigated through theory in which the dynamic effects of both water and air are taken into account. The hydro-pneumatic properties of two model soils - a fine-grained loam and a medium-grained sand are derived from publications by investigators worldwide. A system of equations for defining soil characteristics is descriptionbed, which can be applied to any soil tested in a specified manner. Lacking sophisticated laboratory service, complete data lor a project soil,lor which two specific readily determined properties are known, can be estimated from those of the model soils by interpolation. A method of analysis utilizing finite differencing is developed and its application demonstrated by numerical examples in aquifer recharge and irrigation. The complex analytical problems arising from the hysteresis phenomenon in matrix potential, in situations where there is cyclic change in soil moisture content, are solved.
This paper reports on a qualitative experimental programme on model silos. The objective was to study the flow patterns in a silo of given proportions, with either a concentric or an eccentric outlet, as well as the susceptibility to buckling of a steel silo with either of the two types of outlet. It was found that a thinwalled silo with a concentric outlet tends to be surprisingly well behaved, and one with an eccentric outlet equally surprisingly susceptible to buckling and collapse. It is concluded that none of the existing theories adequately address the issue of buckling of an eccentrically-emptied silo.
Concretes containing two types of aggregate, crushed granite and crushed andesite from the Witwatersrand area, were studied in order to quantify the influence of aggregate stiffness and volume concentration on elastic properties. Representative paste and mortar mixes were extracted from the basic concrete mixes, and elastic properties of these materials, as well as of rock core specimens from the two aggregate types, were determined.