Thesis (M. Sc.)--University of Hong Kong, 2001. / Also available in print.

No description available.

No description available.

published_or_final_version / Applied Geosciences / Master / Master of Science

Sandy soils are among the least productive soils because of their inability to store adequate water for plant growth. Their high percolation rate not only allows water to move quickly beyond the root zone, but also washes nutrients below the reach of plant roots. High evaporation occurs from the soil surface. Many acres of these soils around the world are left out of crop production. This study is a contribution to bring these soils into production by increasing their ability to hold more water in the root zone. Several promising methods of enhancing these soils were simulated, surface mulch, buried barrier layer, and a combination of both. The effects of varying texture and thickness of these layers and varying evaporative demand were investigated. The impact of such modifications on solute distribution in the soil was also simulated. A simulation model of water and solute transport in layered soils was developed for this purpose. The Richards equation for one-dimensional water transport in unsaturated soils was modified to account for the water jump between the layers. The solute transport equation was also modified by implementing the same theory of water infiltration in layered soil to the solute convective transport. The Crank-Nicolson scheme was used to solve the transport equations with the help of the Newton-Raphson iteration method. The results of the simulation show that the proposed methods increase water content in the sandy soil by up to 45%. The combination of barriers, which decreases leaching and evaporation was the most effective in conserving water. Most of the contribution came from the influence of the mulch layer in suppressing water losses by evaporation. The combination method traps solute in the root zone, and this decreased solute leaching from the soil may limit plant growth in saline soils. / Graduation date: 1993

published_or_final_version / abstract / toc / Civil Engineering / Doctoral / Doctor of Philosophy

Thesis (M.S.)--Brigham Young University. Dept. of Civil and Environmental Engineering, 2007. / Includes bibliographical references (p. 139-142).

Thesis (M.S.)--Brigham Young University. Dept. of Civil and Environmental Engineering, 2005. / Includes bibliographical references (p. 163-166).

Thesis (Ph. D.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.

No / There is an increasing interest in the use of Ground Source Heat Pumps (GSHPs) as a source of renewable energy in temperate countries. GSHPs coupled with buried heat collectors can harness the thermal energy from near-surface soils to provide the heating required for domestic properties. The performance of a GSHP system depends greatly on the thermal conductivity of the surrounding soils. Near-surface soils undergo cycles of drying and wetting due to, for example, the infiltration of rain water and/or fluctuations of the ground water table. Several parameters - including the properties of soil, suction head and saturation history - affect the thermal properties as well as the retention and flow of water. This paper presents results from a comprehensive laboratory investigation on sand samples with markedly different grain size distribution. Simultaneous measurements of thermal and hydraulic properties of the sands were taken under incremental increase/decrease in the suction head values to simulate cycles of drying and wetting. The results clearly suggest that the thermal conductivity is better expressed as a function of the matric suction head so as to reflect the saturation history. There has been almost five-fold increase in the measured value of thermal conductivity when the soil was wetted to a residual degree of saturation from being dry.