Bearing characteristics of long enlarged head ultra-deep T-shaped bidirectional mixing column

T-shaped bidirectional cement mixing column has unique advantages in improving mixing quality and foundation bearing capacity. However, field test research on the bearing characteristics of more than 15 m ultra-deep column with long enlarged head is insufficient. In this paper, vertical load tests were carried out to test the bearing capacity of single column and composite foundation with long enlarged head ultra-deep T-shaped bidirectional mixing column. Distribution characteristics of additional stress and axial force along depth were investigated. The results show that bearing capacity characteristic values of single pile and composite foundation are much higher than the designed. Axial force not only disperse to foundation soil through lateral friction resistance, but also transfers to the lower foundation soil beneath enlarged head at variable section. Therefore, the new column type work well in improving deep mucky silty soft soil foundation above karst bearing layer.