Reliability of Estimated Anchor Pullout Resistance

In anchor pullout design, conservative soil and rock shear strength parameters are usually adopted. Presumptive values of soil/grout and rock/grout bond strength are available in different design manuals. In this study, in-situ pullout test data for anchors in soil and rock type worldwide were collected from published sources and information provided by specialty wall contractors. The measured pullout test data were compared to estimated pullout resistance using the Post-Tensioning Institute (PTI) presumptive bond strength values. Statistical analysis was performed to determine the probability of success and the corresponding reliability indices using the minimum, average and maximum PTI ground/anchor bond strength values for cohesive soils, cohesionless soils and different rock types. A minimum safety factor of 2 recommended by the PTI to the ground/grout bond strength was found not conservative where the maximum presumptive bond strength values were used in clays and sands, and the average and the maximum presumptive bond strength values were used in rocks. Based on the results of this study, an average minimum factor of safety was recommended for ground/grout bond strength.