Imagine that a drop of water falls on a layer of compacted soil. Water will distribute in the soil. The question, however, is that how the amount of water divided between different particles? In addition, take into consideration that the saturation level decreases from the point of water dropping; is there any law to explain this phenomenon? What happen if another drop of water falls in exactly the same point?
The distribution of water amongst the particles depends on degree of compaction which invariably dictates the pore space available as well as the packing of the particles which also dictates the throats and hence the interconnectivity of the pores. Based thereon, pore-size distribution determination becomes inevitable.
Hello,
in general case, unsaturated soils, the water in pore spaces are divided into three categories, namely, absorbed or hydroscopic water, capillary water and free or bulk water. All soil water types start as free water and are added to the soil by rain or snow. Their final forms depend on different aspects of soil, including chemical state of particles assemblages, physical conditions such as permeability, and the shape of particles. all of these factors can be explained using pore size distribution, soil-water characteristic curve, particle size distribution and etc. The adsorbed water surrounds the soil particles. It can be considered as an inseparable part of particles, particularly in soils with high specific area per unit of mass. The free water, depending on the soil permeability, can move through the pores creating steady state or transient state flow.
as you see, there is no exact explanation for your question since we dont know what category of water we are talking about. if we wish to talk about free water, the seepage and flow analysis can be used. if we wish to talk about capillary water, we enter to the unsaturated state in which suction and surface tension are the main cause and in case of absorbed water, studies will be microscopic and highly dependent on chemical aspects. you have to keep in mind that, we cannot separate these water components or decouple the analysis which makes it really difficult to study.
The type of soil particle is important for the adsorption/absorption of water by a soil particle. Generally the above discussion is limited to clayey /cohesive soil only.. Type of clay minerals, thickness of adsorbed layer etc is also important in this context. Similarly the permeability, which is related to drainage rate.
First, the particle size distribution and air-dried moisture content(in natural condition such as T=15°C, RH=90%) are measured, then different groups of soil particle size separated, and the air-dried moisture contents of different particle size measured. Finally, based the test results, the proportion of water absorption for different particle size in a soil layer determined.
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