Application of thermal neutron radiography for the mass transport of moisture through freezing soil

This thesis reports on the development of a technique to evaluate hydraulic conductivities in a soil (Snowcal) subject to freezing conditions. The technique draws on three distinctly different disciplines, Nuclear Physics, Soil Physics and Remote Sensing to provide a non-destructive and reliable evaluation of hydraulic conductivity throughout a freezing test. Thermal neutron radiography is used to provide information on local water/ice contents at anytime throughout the test. The experimental test rig is designed so that the soil matrix can be radiated by a neutron beam, from a nuclear reactor, to obtain radiographs. The radiographs can then be interpreted, following a process of remote sensing image enhancement, to yield information on relative water/ice contents. Interpretation of the radiographs is accommodated using image analysis equipment capable of distinguishing between 256 shades of grey. Remote sensing image enhancing techniques are then employed to develop false colour images which show the movement of water and development of ice lenses in the soil. Instrumentation is incorporated in the soil in the form of psychrometer/thermocouples, to record water potential, electrical resistance probes to enable ice and water to be differentiated on the radiographs and thermocouples to record the temperature gradient. Water content determinations are made from the enhanced images and plotted against potential measurements to provide the moisture characteristic for the soil. With relevant mathematical theory pore water distributions are obtained and combined with water content data to give hydraulic conductivities. The values for hydraulic conductivity in the saturated soil and at the frozen fringe are compared with established values for silts and silty-sands. The values are in general agreement and, with refinement, this non-destructive technique could afford useful information on a whole range of soils. The technique is of value over other methods because ice lenses are actually seen forming in the soil, supporting the accepted theories of frost action. There are economic and experimental restraints to the work which are associated with the use of a nuclear facility, however, the technique is versatile and has been applied to the study of moisture transfer in porous building materials and could be further developed into other research areas.

Buried clay pot irrigation for efficient and controlled water delivery

This study presents water flow (WF) into soil from several pitchers buried in the soil up to their neck and filled with water,under natural atmospheric conditions for a period of two years. Variation in daily WF into soil indicated a direct correlation with moisture deficit (MD) in atmosphere. WF increases linearly with MD for non rainy days. WF without hydraulic head through all pots varied in the order air>soil>water. Base line flow in water with respect to air was < 5%. WF for pots with hydraulic head was also in the order air>soil>water, but with significant increase in WF. Hydraulic conductivity Ks was in the order air>soil>water.Ks in water was independent of MD, whereas for air and soil, Ks increased with MD. Thus total WF is partially under hydraulic head and partly due to pull effect through capillary pores on pot wall either due to MD in air or prevailing soil water tension in soil.