MI-ECku: A novel methodology for estimating unsaturated hydraulic conductivity of porous media

Acta Geotechnica - Numerous applications of hydraulic conductivity of porous media (e.g., soils, clay liners, rocks, concrete, ceramic filters, etc.) in their unsaturated state are well established...     

Analytical representation of spatial and temporal variations of the geomagnetic field in the Indian region

The magnetic measurements of declination (D), horizontal (H) and vertical (Z) components of earth’s magnetic field, collected from ground surveys between 1962 and 1966, are used to develop an analytical model of geomagnetic field variations over Indian region for the epoch 1965. In order to reflect spatial features with wavelengths of approximately 1000 km, sixth degree polynomial as a function of differential latitude and longitude is calculated by the method of least squares. The root mean square fit of the model to the input data is better than that accounted by the International Geomagnetic Reference Field for 1965.0. Isomagnetic charts drawn forD, H, Z and total force (F) reflect more details than that shown on world magnetic charts. Further, the values of the field at common repeat stations recorded between 1962 and 1974, after eliminating the field values for the epoch 1965.0, are used to get the secular variation as well as its spatial dependence again by means of polynomial which now includes coefficients which are functions of time and of geographical locations. The accuracy of coefficients is tested against the behaviour of secular variation at permanent magnetic observatories. The merits and limitations of the model are discussed.     

Some investigations to quantify hysteresis associated with water retention behaviour of fine-grained soils

The soil water retention characteristics curve (SWRC) has been reported to be quite useful for estimation of unsaturated soil properties. However, the uniqueness of SWRC is questionable due to hysteresis associated with the drying- and wetting-path SWRCs and this poses great challenge in utilising the SWRC for reliable estimation of unsaturated soil properties. Although hysteresis associated with SWRCs has been extensively studied for coarse-grained soils, due to limited studies on wetting-path SWRC for fine-grained soils, the hysteresis for fine-grained soils is not well understood. The present work attempts to address this gap, by studying the drying- and wetting-path SWRCs for eight different fine-grained soils by employing Dew point Potentiameter (WP4C®), Environmental Chamber and Controlled Water Sprinkling method. The study employs the concept of ‘Suction Hysteresis’, ψ_h, for quantification of hysteresis. Further, the influence of various soil-specific properties on the variation of ψ_h-water content relationship (viz., slope of variation of suction hysteresis, S_ψh) has also been studied and demonstrated. The findings of the study are quite encouraging and it has been realised that extensive studies on soils of different characteristics would be quite useful in quantifying the variation of SWRC during drying and wetting cycles.     

Water retention characteristics of swelling clays in different compaction states

The soil–water retention (SWR) characteristics of the clays play an important role in controlling their engineering behaviour, particularly, in the unsaturated state. Although, researchers have attempted to understand the water retention characteristics of the clays in their reconstituted or remoulded state, such studies are rare for the clays in their intact state. In this context, it becomes important to understand the influence of initial state of compaction, which would create different pore and fabric structure (viz., microstructure), on the water retention characteristics of the clays. With this in view, SWR behaviour was experimentally determined for the swelling clays (dried from different compaction states, viz., intact, reconstituted and remoulded) by employing Dewpoint PotentiaMeter (WP4C®). The changes in the pore size distribution of the clays at different stages of drying cycle were also studied by employing the Mercury Intrusion Porosimetry. The study reveals that the SWR curves for the intact and reconstituted specimens of the clays converge beyond a certain stage of drying. Also, a critical analysis of changes in the pore structure of the swelling clay specimens, during drying, indicates that the progressively deforming pore structure plays an important role in controlling its water retention characteristics to a great extent.     

Anomaly map ofZ component of the Indian sub-continent from magnetic satellite data

An anomaly map of the Z component has been produced for the region of the Indian sub-continent for the first time by the Survey of India usingmagsat data. Data of thousands of kilometres of satellite tracks of varying altitude have been reduced to a common elevation of 400 km by removing the external field and linear trend. The entire data was plotted on a map of 1:6 M and mean values of 2°×2° blocks then accepted for contouring. A prominent magnetic low is reflected over the Himalayas and a prominent high over the Indian peninsula. The dividing line of positive and negative anomalies between the Himalayas and Deccan Traps falls along the Narmada lineament.