Abstract:With a review of disadvantages of ordinary deep mixing techniques in China,the bi-directional mixing technique is developed and presented. In order to investigate the improving effect and economic benefits of slurry bidirectional mixing column for soft ground improvement in expressway engineering,comparison tests between bidirectional and ordinary deep mixing column sites were conducted in the same geological condition field of Shanghai—Jiangsu—Zhejiang expressway,Jiangsu Province,China. The strength characteristics of columns and behaviors of the composite ground under embankment filling were analyzed. It is indicated from the in-situ standard penetration tests(SPT) and unconfined compression tests on coring samples taken from the column that the strength along the columns with bidirectional mixing technique is almost uniform,while strength with the ordinary deep mixing method decreases rapidly with depth. The bearing capacity of bidirectional mixing column composite ground is higher than that of ordinary deep mixing column composite ground. At the same embankment height,the load sharing ratio of bidirectional mixing column is higher than that of ordinary deep mixing column. The ground surface settlement and the maximum lateral displacement at embankment toe of bidirectional mixing testing section are less than those of ordinary deep mixing method. It is also shown that the excess pore water pressure caused in bidirectional mixing composite ground during the embankment filling is less than that in ordinary deep mixing ground,which is benefit for speeding up the filling in the bidirectional mixing ground. In addition,the bidirectional mixing technique can eliminate grout spill phenomena,decrease the disturbance to surrounding soil and save construction time. The results show that bidirectional mixing technique is an efficient and economic method for soft ground improvement in expressway engineering.