Abstract: Gradient ratio tests of two kinds of plastic vertical drain (PVD) filters (wrapped geotextile) are carried out under the condition of hydraulic gradient increased step by step in the environment of saturated soft clay. Combined with actual vacuum preloading working conditions of soft foundation treatment, the clogging characteristics of two kinds of PVD filters are analyzed. Experimental results show that, with increasing hydraulic gradient，gradient ratio of the anti-clogging effect of the new PVD filter with larger apparent opening size shows upward trend firstly, then downward trend, eventually stability, while gradient ratio of the traditional PVD filter shows upward all the time and is unable to stabilize. Research results show that different hydraulic gradients have a great influence on the clogging features of the PVD filters; and the new PVD filter is better than that of the traditional one in actual vacuum preloading working conditions (the hydraulic gradient is high). The clogging of PVD filters relates to the production technology, pore size of the filter and characteristic of soft clay; it is required to deepen the research of the clogging mechanism of filters.

Key words: vacuum preloading, saturated soft clay, PVD(plastic vertical drain) filter, gradient ratio test, hydraulic gradient