Assessing Soil Disturbance while Installing Vertical Drains

Soil disturbance (smear zone) can be created while installing vertical drains, within which changes in horizontal permeability and the compressibility of in-situ soil can be observed. Previous studies on different aspects of soil disturbance due to driving vertical drains are limited, so extensive soil characterisation was carried out while installing drains at Ballina, NSW to obtain a more realistic smear zone. Soil disturbance was evaluated by determining the change in the coefficient of permeability, the water content, and volume compressibility away from the drain. The characteristics of the smear zone were compared to the data available from past literatures and indicated that the radius of the smear zone was about 6.3 times the equivalent mandrel radius, which was larger than that observed in the laboratory using reconstituted specimens.