Performance of Hollow Bar Micropiles under Monotonic and Cyclic Lateral Loads

Hollow bar micropiles are becoming a popular option for foundation retrofitting because of their fast installation and effectiveness as both a foundation system and ground improvement at the same time. This paper presents a field study and numerical investigation of the lateral behavior of single hollow bar micropiles embedded in stiff silty clay deposits. Two monotonic and six cyclic lateral load tests were conducted on four micropiles, and the results were used to calibrate/verify a numerical model that was then used in a numerical investigation. The observed load-displacement curves demonstrated that the micropile behavior was flexible and was governed by the properties of soil along a depth equal to 10 times the pile diameter. The parametric study suggested that hollow bar micropiles can carry moderate lateral loads with proper reinforcement configurations and pile head fixity condition. During cyclic loading, the micropile head stiffness degraded initially as the number of load cycles increased. However, the stiffness reached a constant value after a specific number of cycles at the same load amplitude and at different cyclic load amplitudes.