Point Foundation (PF) method: Principles and recent research findings

Conventionally, cement deep mixing (CDM) columns are designed to have constant diameters over the improved depth as this facilitates the construction procedures. However, this design pattern may be inefficient in cases of spread footings or shallow foundations. This paper first briefly introduces principles, construction procedures and quality control techniques of an innovative CDM method that can create head-enlarged column, named as Point Foundation (PF). The method is practically implemented with a specific binder that is environment-friendly and more effective in strength enhancing compared with the common binder as cement. Static load tests on three instrumented PF columns indicate that the variation trend of induced vertical stress profile along the columns in general is similar to that under the centre of shallow footings on elastic soil medium. However, the stress profile in the (semi-rigid) PF columns is larger than that in elastic soil but less than that in (rigid) PHC pile. This confirms the load transfer mechanism along semi-rigid columns like CDM/PF. Test results also indicate that at the depth of one to two times head diameters the induced stress remains just 20% the applied pressure. Findings on the trend of the induced vertical stress in the columns suggests that the settlement of common shallow footings on CDM/PF column-reinforced grounds should be evaluated using 3D condition taking into account the fact that the induced stress decreases with depth. Keywords: ground improvement; Point Foundation (PF); tapered cross section; load transfer mechanism; load-settlement behavior.