STUDIES OF THE SANDS OF A PART OF THE THAR DESERT IN DISTRICT JAISALMER, RAJASTHAN

Abstract

"The Thar desert in India occupies about 155,000 sq.km of western Rajasthan. During recent times it has attracted investigators with varied types of problems including those of defence, traction and geomorphology. However, geological and geotechnical aspects have received scant attention. The present study is an attempt to fill this gap. In this investigation an exhaustive and systematic sedimentological study of desert areas around Sam, Dhanana, Lunar and Murar in Jaisalmer district has been made. Various bedforms,. namely, ripples, barchans, transverse dunes, longitudinal dunes and sand piles have been described and their probable origin is discussed. Samples collected from the various bedforms and sand flats have been analysed for (i) textural attributes of sand grains, (ii) minerological composition and (iii) engineering properties of the desert sands. Grain size distribution, roundness and sphericity of the desert sands have been investigated in detail. For statistical analysis of grain size data, graphical moments for central tendency, dispersion, symmetry and peakedness of the distributions have been calculated with the help of a digital computer, using various formulae given by different workers. Tne intermediate percentile values used in these formulae were calculated by interpolating between the expe rimental points using normal distribution. Plots of the statistical parameters have been made and their correlations discussed and interpreted in terms of grain size populations and modes of transport. In addition, spatial variability of grain size parameters in the area, and also within the barchans, has been studied. Fields of the various environments have been delineated on plots between different grain size parameters by different investigators. Gram size parameters from the area under investigation have been plotted on some of these diagrams such as C-M diagrams, skewness-mean size diagram, mean size standard deviation diagram, Md vs. QDa diagram, QDa vs. Ska diagram etc., with aview to evaluate their efficacy as accurate environment indicators. Heavy and light minerals of the desert sands have been identified and detailed petrographic modal analyses made. Variations of constituent modes with grain size and in space have been studied with aview to determine the provenance of the sands. Determination of the various engineering properties of the sands is an essential step for any engineering project deserts. Representative samples from different localities of the area have been subjected to shear strength and compaction tests. Also maximum dry density and optimum moisture content .ere -videterminod. Further, to investigate the mortar properties of the desert sands, samples were mixed with cement and water for castin, cubes in ratios prescribed by the Indian Standards Code. These sand cement cubes were then autoclaved and tested for compressive strength by Universal Testing Machine. The data so obtained were then analysed and correlated with the grain size parameters. Permeability of afew typical samples has been determined. The soil groups of desert sands of the area have also been determined. In brief, emphasis throughout the study is on a closer understanding of the encrgy-environment relationship which manifests in grain size parameters, bedforms, grain attributes and petrography of the area."