Laboratory experiments on desiccation cracking of thin soil layers H. NAHLAWI and J.K. KODIKARA w Department of Civil Engineering, Monash University, Building 60, Victoria 3800, Australia (Received 6 May 2004; accepted 1 November 2005) Abstract. This paper presents some experimental results on desiccation cracking tests con- ducted on thin layers of clay soils. Observation of the evolution of cracking patterns was examined to clarify the transient mechanisms of the crack formation of clay soils. Laboratory experimentation on desiccation cracking was carried out to examine experimentally the quantitative relationships between the characteristics of soil cracks and the prevailing con- trolling conditions. Five desiccation cracking tests for slurried clay soils were carried out using shrinkage moulds in a humidity chamber, which was capable of controlling relative humidity and temperature. The soil used in the experimental studies was residual basaltic clay and was classified as a highly reactive soil. In order to provide simple conditions for theoretical modelling, the tests were conducted in perspex and metal moulds with rectangular cross- sections. The lengths of the moulds were considerably larger than their widths so that parallel cracking were generated in thin layers. In each cracking test, several rectangular moulds of different thicknesses and widths were used. Some of these tests were used for observation, crack initiation and evolution, and others for moisture content measurement during desiccation. The test results include evolution of the cracking pattern, influences of speed of desiccation and typical crack spacing to depth ratios for soil layers. Key words. clay, cracking, depth, desiccation, evolution, formation, pattern, spacing, thin soil layers. 1. Introduction Clay soils tend to shrink during drying. This occurs due to the development of substantial matric suction in the pore structure of the fine-grained soils. If the suction is uniformly developed within the soil medium, then the soil will develop their full potential shrinkage known as the ‘‘free shrinkage’’ applicable to the prevailing suction change. Commonly, however, the impending free shrinkage may not fully develop due to internal or external restraints acting on the soil. Internal restraints can come from non-uniformity in drying and external restraints can arise from rough interfaces such as boundary friction and/or adhesion. If the shrinkage is restrained, soils can crack during desiccation when the tensile stresses that develop within the soil exceed soil’s tensile strength. The desiccation cracking of clay soils can have a w Corresponding author: tel.: +613 9905 4963; fax: +613 9905 4944; e-mail: J.K.Kodikara@eng. monash.edu.au Geotechnical and Geological Engineering (2006) 24: 1641–1664 Ó Springer 2006 DOI 10.1007/s10706-005-4894-4