Some aspects of soil shrinkage and the effect of cracking upon water entry into the soil.

Abstract

The shrinkage of natural soil aggregates that accompanies water withdrawal has been examined. Four main stages operate: (1) structural shrinkage, (2) normal shrinkage, (3) residual shrinkage, (4) no shrinkage: The pF ranges over which these stages operate and the fraction that they constitute of the total shrinkage has been measured for a range of soils. The influence of structure and texture upon shrinkage was assessed. These affect both the shrinkage phase and the range over which it operates. Structural development affects shrinkage markedly, giving a very different shrinkage pattern from that found for puddled soil or remoulded soil blocks. The difference in porosity between a natural aggregate and a puddled block of the same soil corresponding to a definite pF value is suggested, therefore, as a means of assessing the degree of structural development in the soil. It provides a suitable index for assessing the rate of structure improvement under various ameliorative treatments. The influence of cracking in increasing the rate of water entry into fine textured soils is discussed. In the particular cases of irrigated soils, where soil water contents are maintained at relatively high levels (above wilting point), it seems that cracking may not have progressed sufficiently to compensate for the low inherent permeability of such soils. Cultivation of the surface soil to form a mulch before irrigation tends to eliminate any contribution to conduction by the smaller cracks which are present at higher soil water contents. Large increases in permeability, due to the presence of gross soil cracks, are attained only when water contents are reduced to levels which are not practicable in continuous irrigation culture.

Il Comportamento Di Suoli Agrari Rigonfiabili

“…Secondo le proposte di Stirk [42] a seguito di perdita graduale dell'umidità a partire da un campione di terreno saturo nelle condizioni in situ ha inizio un campo di variazione, che indicheremo come dominio (2) di umidità strutturale, durante il quale la perdita di acqua in volume, spesso irregolare, è in genere superiore alla riduzione del volume del suolo (dw > dV map ; ciò in generale implica pendenza media della curva di contrazione <1). Il contributo di questo dominio al contenuto idrico del terreno può raggiungere anche il 60-80% di quello totale ( fig.…”

Utilisation of Sepidrud dam basin sediments in fired clay bricks: laboratory scale experiment

“…Soil shrinkage is defined as the specific volume change of soil relative to its initial water content and this is Utilisation of Sepidrud dam basin sediments in fired clay bricks • 5 thought to be mainly due to clay swelling properties (28)(29). However, recent research has clearly ruled out the possibility of considering the drying shrinkage as one of the plasticity characteristics of a soil.…”

Pore Volume Changes in a Structured Silt-Loam Soil During Drying

“…Nos r6sultats montrent clairement la d6pendance de la densit6 upp-"nte d,, sol et de la porositd sur le potentiel de.l'eau et tendent i confrrmer I'hypothbse qui veut qu'aux fins de comparaison, la densit6 apparente et la porosit6 doivent 6tre exprimees en fonction d'une valeur de r6f6rence de la teneur en eau ou du potentiel de I'eau du sol. (Stirk 1954 Various phases of soil shrinkage were described by Haines (1923) and Stirk (1954).…”

“…Subsequently the cores were subjected to controlled air drying and finally oven drying. Various phases of soil shrinkage were described by Haines (1923) and Stirk (1954).Drying a fully saturated pedal soil results in an initial structural shrinkage (Stirk 1954) in which water loss is from large, stable pores and soil volume change is less than the volume of water removed. The second phase was termed "normal shrinkage" (Haines 1923) Fig.…”

“…Drying a fully saturated pedal soil results in an initial structural shrinkage (Stirk 1954) in which water loss is from large, stable pores and soil volume change is less than the volume of water removed. The second phase was termed "normal shrinkage" (Haines 1923) (Aitchison and Holmes 1953;Mclntyre et al 1982).…”