SW—Soil and Water: Construction of an Artificial Perched Watertable, Part 2: Soil Cavity Production by Air pressure

By constructing an artificial perched watertable which is a horizontal and cylindrical soil cavity with a diameter of 3 m and a height of 0·3 m, at a depth of about 0·8 m from the soil surface in the fields, it was envisaged that the runoff caused in the summer could preferably be held in this layer and, hence, the excess moisture loss could be prevented. The water in the artificial soil cavity could be used as capillary water for plants germinating in the spring. The soil failure experiments by the injection of high-pressure air were conducted to form the artificial perched watertable. In this paper, the size of the underground soil cavity produced by the high-pressure air was determined. The gas energy and gas pressure required for the proper size of the soil cavity were also evaluated. The results show that the energy required for soil-cavity production significantly increased with the larger radius of the soil cavity, the energy of the soil-cavity production being 100 kJ for a cavity radius of 1 m compared with 1000 kJ for a cavity radius of 2 m. When the design point of the soil-cavity radius is 1·5 m (the diameter of the soil cavity is 3·0 m), the required energy is about 300 kJ. The height of the underground soil cavity produced by the high-pressure air injection was always 0·3 m regardless of the working depth of the injector. The radius of the soil cavity produced was 1·5 m on average when the working depth of the injector was more than 0·6 m. When a soil cavity is produced at a depth of 0·8 m in the field of the meadow soil or planosol in China, the tensile strength of 20 kPa is more than the earth pressure of 14 kPa and hence, the air pressure in the charge tank should be at least more than 20 kPa.