EXPERIMENTAL RESEARCH ON QUALITY ASSESSMENT OF CEMENT-SOIL MIXED PILE IN SEPARATE SOIL LAYERS USING SPT

The most common barrier to the use of cement deep mixing technology is the lack of effective approach to assess the quality of finished piles. Based on previous works and the comparisons between common assessment techniques, SPT with the assistant of visual examination is believed to be able to assess the continuity and strength quality of the whole pile in separate soil layers. The quality assessment system is investigated through a series of SPts on the cement-soil piles from a real project in Shanghai. This research shows that soil properties impact on both SPT blow counts and improvement effect in correspondence with depth and age, and thus should be taken into account in the system. In addition, the maximum probability intervals and the suggested reasonable ranges of pile SPT blow counts are obtained from the statistical analysis in separate soil layers. The suggested reasonable intervals in the third layer is 10-18,while 5-12 in the forth layer and 11-23 in the interlayer. Accordingly, the assessment specifications for cement-soil mixed piles in Shanghai are established so as to provide a reference for future works.