This paper describes the capabilities of a novel technique to investigate crack formation and propagation in drying soils. The technique is a relatively simple, non-destructive indirect technique using a ground-penetrating-radar (GPR) system to detect cracks that form and propagate inside a soil specimen during desiccation. Although GPR devices have been used for multiple applications, their use in soils for the detection of small desiccation cracks has not been demonstrated yet. The experiment and the methodology used to test the accuracy of a small compact commercial GPR device for crack identification are described. The main objective was to identify what type of signals and what crack width and separation between them can be detected using the GPR device. The results indicate that cracks of 1 or 2mm wide can be detected depending on its position and shape, whereas sub-millimeter cracks are undetectable with the currently existing devices in the market. Regardless of this limitation, the GPR method can be useful to find time-related bounds of when the cracks appear, to point at their location and sometimes at the separation between two of them. Detection of cracks with origin at the bottom or within the specimen was accomplished with this system. Distances of 5 cm or more between cracks can be detected and measured, as well, with accuracy.
This paper presents the results and analysis of cracking tests carried on samples of silty clay which were subjected to a drying-wetting-drying cycle to study the effect of cyclic change of moisture on the cracking behaviour. During tests, temperature, relative humidity, suction, gravimetric moisture content, etc. were continuously monitored
and later cross-referenced with images of the evolving crack pattern characterized with image analysis techniques. The cracking pattern changes clearly with the cyclic change of moisture showing the relationship between the soil's tensile strength and its moisture. The
results provide additional new information about the effect of cyclic moisture changes on crack formation and propagation in soils. They also show the differences between several methods of obtaining water retention curves, and evidence scale effect in soil cracking.
There is a well reported evidence of cracking in clayey or silty soils when drying. Shrinkage in the soil mass and also boundary conditions generate a nonhomogeneous stress state locally producing tensile stresses and eventually cracking. This process has been analysed in detail by several authors. However, the evolution of such cracks due to further relative humidity changes (i.e. wetting and drying again) has been rarely considered in the reported experiments. This paper describes a particular type of experiments developed in an environmental chamber with a cylindrical soil specimen 80 cm in diameter and 10 cm in height, of Barcelona silty clay. Relative humidity was imposed in the chamber by controlling the flows of dry and wet air applied, whereas the main soil and chamber variables were recorded (temperature, suction, water content). A cycle of desiccation, wetting and further desiccation was considered and the paper describes the evolution of the cracking pattern during this process. It is shown that the pattern of cracks changes dramatically when cycles of relative humidity are imposed. In particular, soil cracking increases when soil is wetted after a dry period. An explanation of this behaviour based on Unsaturated Soil Mechanics concepts is also presented in the paper.