Mechanism of water and air flows through unsaturated soil

Abstract

Laying of aeration slabs is an essential requirement for construction of open space car parks in Singapore as imposed by National Parks Board. The intended objectives of the aeration slabs are to improve air flow to the rooting zone, to improve water infiltration to the rooting zone, and to reduce the harshness of the environment by planting turf in car park areas. However, there are no local empirical data to indicate whether aeration slabs confer significant benefits to trees in car parks. A systematic assessment is therefore required to evaluate the efficacy of aeration slabs in open space car parks. Soil layers below road, parking lot, and tree pit areas were instrumented to study water and air flows in the soil layers below the asphalt, aeration slab, and root zone surface covers. In addition, variations in soil temperature were also monitored. Measurements of local climatic conditions, such as air temperature, relative humidity, potential evaporation, and rainfall above the ground surface were conducted to relate dynamics processes above and below the ground surface. Numerical analyses were conducted to assess the water-air-heat flows through different surface covers using assumed soil properties. Results of the numerical analyses provide better understanding of the mechanisms of water-air-heat flows under the asphalt, aeration slab, and root zone surface covers as affected by tropical climate of Singapore.