Abstract
Caissons are widely used in foundation preparation in Hong Kong. Typically these caissons are 1 to 4 m in diameter and 10 to 30 m in depth. Because of the hilly terrain, manual digging is the preferred method; furthermore, because of the geology, granite is usually encountered and has to be removed by pneumatic drills. This creates a great deal of crystalline silica-containing dust in a confined space and is extremely hazardous to the drill operators. As high as 2000 times the threshold limit value has been measured in previous studies, and some drill operators contracted silicosis within 1 year. An in situ dust removal system, using wet scrubbing and ventilation methods, was designed, fabricated, and field tested and proved to be effective in removing up to 98 percent of the dust generated in a 1-m diameter caisson.