Determination of volumetric shrinkage of an expansive soil using digital camera images

The volume change during drying of compacted expansive soils occurs in the form of reduction in overall volume and development of cracks. Accurate determination of volume of shrunken soil specimens becomes essential to understand the shrinkage behaviour of compacted expansive soils. Mercury displacement method available for the bulk volume measurement of cylindrical small samples suffers from the serious limitations such as the restrictions of using the mercury as it is a hazardous material and the size of specimens is limited to small samples/portions. In the past few years, the digital camera images have been successfully utilised in studying the crack pattern and various parameters associated with reconstituted soils dried from slurry state. Fewer works have been carried out to quantify the cracks in the compacted soils, especially in compacted expansive soils. In this paper, simple methods for the determination of the volume of shrunken soil specimens excluding the volume of cracks are proposed based on the digital camera images captured on thin oedometer shrunken soil specimen along with the vernier calliper method. The results were compared with the mercury displacement method. Cracks which extended from top to bottom of the shrunken specimen during drying assisted in employing these methods. The effect of cracks on shrinkage deformations during second drying cycle and at the end of five drying cycles under a vertical stress of 12.5 kPa was studied.