Investigation of factors affecting vertical drain behavior

Some influencing factors on vertical drain behavior were investigated by la boratory tests as well as by back-analyses of test embankments on vertical drain improved subsoil at Saga Airport, Saga, Japan. Based on the results f rom this study, suggestions are made on determining the design parameters f or vertical drain improvement. For the discharge capacity test of a prefabr icated vertical drain, confining the drain in clay is essential. Also, due to the creep of the filter and the clogging caused by the fine particles en tering the drainage channel. the long-term discharge capacity is significan tly smaller than the short-term one, and this should be considered in desig n. For smear effect, a new equation is proposed for determining the ratio o f the hydraulic conductivity of the natural subsoil to that of the smear zo ne, which considers the fact that laboratory tests normally underestimate t he hydraulic conductivity of natural deposits. Regarding the effect of the sand mat the numerical analysis results in this study show that if the hydr aulic conductivity of sand is larger than 10(-4) m/s, the assumption of a f ree drainage condition in the sand mat may not result in significant error Finally, a methodology of predicting the behavior of vertical drain improve d subsoil is proposed.