An Analysis On The Experiments Of Reinforcing Bridge Head Soft Foundation By DJM Piles

With the development of high way construction in China, Dry Jet Mixing (DJM) has been widely accepted for its excellence while the theoretical understanding of DJM is still far behind.Based on the practical engineering, the article discussed deformations and mechanics capability and reinforced effect of DJM through field measurements. We compared the Plastic Drainage method and DJM combine geotextile method with DJM. The result shows DJM has a great improvement in minimizing foundation settlement and deformation, as well as preventing vehicle jumping on bridge head. The road embankment after DJM treatment has an upper limit of fill height. The maximum deformation place is about 5 meters under ground. Compared to Plastic Drainage method, the road embankment is more stable and the settlement is smaller with DJM. If combined with geotextile, the differential settlement, road embankment extrusion can be better minimized and the stress in foundation can be evenly distributed to improve foundation stability.A study of settlement over time is presented based on the data we collected in our real projects. By adopting a hyperbolic curve fitting method, the amount of settlement can be best predicted over time. The result also shows the overall enhancement of DJM is mostly affected by pile depth and blow out soft clay layer. In the case of not blowing out soft clay layer, 35.7% of settlement comes from soil compression within pile depth and 64.3% from soil compression under pile. And the overall settlement is quite unstable.Finally we discussed the applicability of DJM on soft foundation. We suggest the pile depth of DJM should be shortened and piles should blow out the soft clay layer. According to current technology of construction, pile depth should not be longer than 8m in order to achieve best enhancement effect. For those bridge head areas that require higher stability over settlement, the treatment of preloading or surcharge preloading is very important and the period of preloading should be extended as long as possible.