Machine for construction of an artificial perched watertable, 1: Hydraulic and mechanical properties of sands to be deposited

By constructing an artificial perched watertable at about an 1 m depth from the soil surface in an area where the annual precipitation occurs only in the summer season, it was intended to retain summer runoff in this watertable and prevent excess moisture loss. The water in the artificially permeable layer could be used for plants as capillary water in the dry spring season. For this purpose, a machine to construct the artificial perched watertable was developed to deposit sand in the horizontal and cylindrical soil cavity underground, produced by high pressure air. This paper deals with the hydraulic and mechanical properties of sand to be deposited as an aid to the development of a sand gun, which is a part of the machine. The results showed that when the soil water content increased from 0 to 35% dry basis (d.b.), the sand bulk density increased from 1250 to 1600 kgmE-3. The specific surface area for each sand type was 3x10**4 - 4x10**4 mE-1 when the soil water content was nearly zero. However, when the soil water content increased and the sand was saturated, the minimum values of the specific surface area decreased to 6x10**3 - 9x10**3 mE-1. The air permeability for each sand type decreased with the greater soil water content because air passed through with more resistance in the sand. The minimum air permeability of the Chinese river sand was the highest at 4 kgMPaE-1sE-1mE- because of its roughness which resisted airflow. This was followed by the Japanese coastal sand at 3 kgMPaE-1sE-1mE-1 and the Toyoura standard sand at 2 kgMPaE-1sE-1mE- because of its fineness and greater resistance to airflow. The cohesion of each sand showed a maximum at a particular soil water content. These soil water contents were about 10% d.b. for each sand. The maximum cohesion for each sand was nearly the same at about 8.0 kPa. The adhesion of each sand also showed a maximum at a particular soil water content. These soil water contents were about 10% d.b., which is the same as that of the cohesion.