Abstract
The improved depth of dry jet mixing (DJM) in China is limited to being less than 15m due to the limitations of DJM machine; and the strength of cement-mixing column reduces with depth. An innovation method to enhance column quality in deeper layers is presented in this study. A remarkable combined method of DJM with prefabricated vertical drains (PVD), termed DJM-PVD combined method, was innovated and successfully practiced in two highway projects on very soft clay in Jiangsu Province, China. The field experiment results indicate that DJM-PVD combined method makes the installation of DJM columns easier and the cement powder can be spouted out better than isthe case without PVD, especially in deeper layers and enabling the mixing of column more homogeneously and, consequently, effectively increasing the strength of DJM column. The procedures used for DJM-PVD combined method, the instrumentation and the field monitoring data about columns strength, such as standard penetration test (SPT) blow counts and the unconfined compression strength (UCS) of DJM columns core samples, are described. Potential reasons for enhancement effect of PVD on DJM column quality are discussed.
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