Using the Reference Shrinkage Curve to Estimate the Corrected Crack Volume of a Soil Layer
To estimate the correct soil crack volume based on the shrinkage geometry factor, in addition to measurements with core samples, one also needs to know the shrinkage curve of the soil matrix without cracks. For such a curve one can use the soil reference shrinkage curve that is only stipulated by intraaggregate clay shrinkage without interaggregate cracking. The objective of this work is to illustrate such use of the reference shrinkage curve and, in addition, to argue the necessity to correct the usual estimates of the shrinkage geometry factor in order to correctly estimate the soil crack vol- ume. The illustration is based on available data and reference shrinkage curves for eight soils.
An approach for estimating the shrinkage geometry factor at a moisture content
Soil shrinkage is characterized, along with the shrinkage curve, by a partition of the volume change of the soil matrix between contributions of cracks and soil subsidence. This partition is determined by the shrinkage geometry factor (r s ). Knowledge of the value of r s is important for the consideration of water and solute transport in swelling and cracking soils. The r s concept was recently used for the generalization of flow equations in the case of the axially symmetric two-dimensional deformation of shrink-swell soils. Sufficient accuracy of the r s value is very essential for all these applications. However, the theoretical definition and available measurement method of the r s factor include some implicit assumptions that are disturbed in real conditions. These disturbances, which are not accounted for in r s measurements, can lead to distortion of the r, value. The objectives of the work are: to explicitly formulate the assumptions; to introduce a new presentation of the r s concept based on a comparison between different shrinkage curves of a soil; to suggest an approach for estimating the r s values corrected by taking into account the disturbance of one of the assumptions; and to experimentally illustrate the approach using the simplest case of pure-clay paste samples when they dry, shrink, and crack. The results show the necessity and practical possibility of considering the r s factor as a function of soil moisture and introducing to the factor the multiplicative correction that is connected with accounting for possible macrocracks in soil samples to be used for experimental estimation of the r s factor.
Shrinkage of Dutch clay soil aggregates.
Shrinkage characteristics and COLE and PLE values of undisturbed natural aggregates of clay soils from the Netherlands were measured. The course of the shrinkage process upon drying varied strongly between soils, and very often the measured characteristics diverged from the theoretical curve. Some Dutch clay soils are amongst the strongest swelling and shrinking soils in the world, with volume decreases of aggregates up to 49% between saturation and oven-dryness, and 42% between saturation and a pressure head of -16 000 cm. Potential subsidence of a Dutch field soil due to shrinkage is up to 15 cm. In some Netherlands clay soil, as a result of normal shrinkage, the aggregates remain saturated throughout the whole year; only inter-aggregate pores such as shrinkage cracks, contain air. (Abstract retrieved from CAB Abstracts by CABI’s permission)