ABSTRACT
Soil is one the most extracted natural raw materials. The vast expanses of fertile alluvial soils of the Indo Gangetic Plains have long remained as abundant soil resource pool for brick manufacturing and construction sectors. Unmonitored continuous removal of soil is reported to cause depletion of soil reserves, loss of soil fertility and affect crop yield. Excavation and removal of soil from isolated patches of land creates low lying and elevated degraded areas which disrupts normal crop cultivation pattern. Natural gamma-ray spectrometry (NGS) can be used as a non-destructive and rapid geophysical sensing method, for identification and delineation of areas with suitable soils. During this work brick kiln areas were visited to understand soil's availability and extraction pattern. NGS measurements of samples from soil profiles were carried out to find if gamma-ray intensities varied with soil clay content. Soil texture and plasticity of the same samples were obtained following standard testing procedures. Winkler and Plasticity charts were used to assess suitability of the soils. A strong linear relationship between gamma-ray potassium (K) intensity and clay contents of soil profile samples (R2 = 0.88) was observed. NGS based devices can be used to scan soil samples rapidly and log shallow depth boreholes in grid sampling design. The gathered spectral gamma-ray data can be then used to predict and generate high resolution 3D models of soil properties, based on which resource areas of suitable soils can be delineated for long term soil extraction without affecting cultivated areas. This will help in delineating areas restricted for soil extraction, which will not only make soil mining sustainable but also address soil conservation by setting aside large cultivated fertile soil areas untouched. Adopting NGS methods will prevent unsystematic removal of fertile soil and creation of degraded lands. This will ultimately result in efficient soil resource management.
ABSTRACT
Soils which develop desiccation cracks after drying are unsuitable for the making of earthenware. The present work was carried out to demonstrate the use of Natural Gamma-ray Spectrometry (NGS) as a rapid sensing method to detect the variation of cracking behaviour and types of clay dominant in soil using samples collected from the study region. Natural gamma-ray intensities due to potassium (K) and equivalent thorium (eTh) radioisotopes present in soil were recorded using an NGS device. Circular soil cakes of set diameter were sun-dried to find shrinking and cracking variations. Other tests included measurement of particle size distribution, Atterberg indices, basic soil physico-chemical properties, exchangeable cation contents using ICP-OES and XRD identification of clays. 6 soil varieties were identified from the distribution of data points in the binary plots of gamma-ray potassium (GR-K) and thorium (GR-eTh) counts per sec (C/s). Variation of GR-K was observed to be wider (2.14 C/s to 2.54 C/s) than GR-eTh (0.44 C/s to 0.63 C/s). The measured GR-K counts reflect changes in illite content. The soils displayed 3 categories of shrinking and cracking behaviour. The soil variety which displayed maximum mild shrinkage without fine desiccation cracks on the set surface area has the highest GR-K counts. The soil shrinking and cracking variations were not clearly defined by the classification based on the texture and plasticity chart, though the latter indicated dominant smectites. A strong linear relationship between GR-K and exchangeable K (R2 = 0.84) indicates K+ contribution mainly from illite and dominance of other clay types in outliers. Higher levels of polyvalent cations known for binding clay aggregates were observed in the non-cracking soils. Concomitant higher GR-K levels indicate that shrinking soils lacking fine desiccation cracks are associated with fluvial sediments of the recent past with parental mica. This research concludes that NGS-based portable devices can be used for rapid sensing of soils to detect variation in shrinking and cracking behaviour and dominant clay type and thus can be used for identification of soil suitable for earthenware making.
