Field test on stiffened deep mixed columns

Abstract

A composite column, referred to as Stiffened Deep Mixed (SDM) column, can be used to improve the soft soils. It consists of a Deep Mixed (DM) column inserted by a small-sized precast concrete pile (called core pile as well) in center. The past study (citation) shows that the SDM column can provide high bearing capacity as compared with the pile with the same material of the core pile and same configuration of the SDM column under the same geological conditions. Therefore, the technique of SDM columns has a significant effect on saving construction material and budget. The previous projects indicate that the SDM column can reduce 20-40 % of budget at least. However, its mechanical behaviors have not been well understood yet. To investigate the mechanical behaviors of SDM column, a series of plate loading tests including nine Prestressed High Strength Concrete (PHC) piles and 30 SDM columns in total are conducted in field. Axial strains of two columns are measured during tests by the Fiber Bragg Grating (FBG) Sensor Technology. The axial force distributions of the core piles can be obtained based on the axial strains. The test results show the bearing capacity of SDM column is extremely high and the side resistant ratio between SDM columns and PHC piles is approximately in a range from 1.3 to 2.5.