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.
Water percolation through a clayey vadose zone
Summary Heavy clay soils are regarded as less permeable due to their low saturated hydraulic conductivities, and are perceived as safe for the construction of unlined or soil-lined waste lagoons. Water percolation dynamics through a smectite-dominated clayey vadose zone underlying a dairy waste lagoon, waste channel and their margins was investigated using three independent vadose-zone monitoring systems. The monitoring systems, hosting 22 TDR sensors, were used for continuous measurements of the temporal variation in vadose zone water-content profiles. Results from 4 years of continuous measurements showed quick rises in sediment water content following rain events and temporal wastewater overflows. The percolation pattern indicated dominance of preferential flow through a desiccation-crack network crossing the entire clay sediment layer (depth of 12 m). High water-propagation velocities (0.4–23.6 m h −1 ) were observed, indicating that the desiccation-crack network remains open and serves as a preferential flow pathway year-round, even at high sediment water content (∼0.50 m 3  m −3 ). The natural formation of desiccation-crack networks at the margins of waste lagoons induces rapid infiltration of raw waste to deep sections of the vadose zone, bypassing the sediment’s most biogeochemically active parts, and jeopardizing groundwater quality.
Combined effect of interblock and interaggregate capillary cracks on the hydraulic conductivity of swelling clay soils
The cracks in swelling clay soils at sufficiently high water content can be presented as the superposition of interblock‐ and interaggregate‐capillary‐crack networks. The objective of this work is the generalization of an earlier proposed model describing the hydraulic conductivity of a soil matrix with only interaggregate capillary cracks. The generalized model describes the hydraulic conductivity of a soil with capillary cracks of both types. For the case of vertical hydraulic conductivity the generalization is based on the available results relative to the geometrical and hydraulic properties of capillary crack networks. The contribution of interblock capillary cracks to the hydraulic conductivity of a soil at a given pressure head changes with depth even for a given matrix structure, contrary to the contributions of interaggregate capillary cracks and soil matrix. For numerical estimates and validation of the model we use literature data on the variation of water content in different soil layers, evaporation, subsidence, and crack volume during a drying period in the course of a laboratory lysimeter experiment. The numerical estimates indicate the essential and even prevailing contribution of capillary cracks of both types to hydraulic conductivity at sufficiently small pressure heads and their negligible contribution to the water retention of clay soil. The validation is based on a comparison between two independent estimates of the summary hydraulic conductivity of the soil matrix and interaggregate capillary cracks. One of these estimates is found as a difference between the total hydraulic conductivity of the soil and the hydraulic conductivity of the interblock‐capillary‐crack network. Another estimate is found by the model describing the hydraulic conductivity of a soil matrix with only interaggregate capillary cracks. The results of the comparison validate the feasibility of the model showing that it is in agreement with the available data of the lysimeter experiment.