THE EFFECT OF PVD INSTALLED SURROUNDING DJM COLUMNS ON THE COLUMNS QUALITY OF DJM COLUMNS FIELD TESTS FOR QUALITY OF DRY JET MIXED PILES WITH OR WITHOUT PREFABRICATED VERTICAL DRAINS IN SOFT SOILS

With the field testing to single piles and pile groups,the effect of prefabricated vertical drains(PVD) installed in advance surrounding the dry jet mixed(DJM) piles on the pile quality of DJM is presented in this paper.The testing results indicate that the standard penetration test blow counts and the unconfined compression strength of DJM columns with PVD are higher than those of DJM without PVD,especially in deeper layers.The fracturing caused by excess pore pressure during the DJM installation and the drainage provided by the PVC drains increase the permeability of surrounding clay,and thus make the installation of soil-cement columns easier and more uniform,especially in deeper layers.