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Improvement in strength characteristics of soft marine clay by Bidirectional Dry Mixing Method

Dry Jet Mixing (DJM) is a commonly used in-situ soil improvement approach for increasing the strength and reduction on compressibility of soft marine clayey soils. However, the possibility of DJM improved soil achieving designed strength is largely dependent on the mixing process in that strength distribution of DJM improved soils is often scattered. This discreteness has been attributed to less homogeneity characteristic of mixed soil mass during the procedure of DJM. Given the discrete strength distribution of mixed soils, the strength of DJM improved soil applied in design is usually much lower than that obtained from the laboratory tests so that the security of geotechnical engineering projects can be guaranteed. Recently, with modifications of traditional DJM drill machine, it has become more likely that higher mixing homogeneity be achieved. “Double-Pole and Bidirectional Mixing” technology is just one of these modifications through which the strength of improved cement soil column can be increased. In this study, strength characteristics of column body were investigated both in laboratory using unconfined compressive strength test and in the field using standard penetration test. The test results reveal that bidirectional DJM method tends to attain a higher homogeneity thus increase bearing capacity of soft sediment. On the other hand, the strength of the bottom of column and the quality of column shaft can be improved as well. Due to potential advantages of bidirectional DJM technology above, the prospect of its application is promising.