The torque estimation method during helical piles installation

The article presents a torque estimation method during two-bladed helical piles installation. A strain dynamometer was developed to measure the moment generated in real conditions during installation. This structure is made of steel pipe with installed strain gauge transducers (hereinafter referred to as strain gages) set at an angle of 45° to the longitudinal axis of strain dynamometer and connected to the measurement system. The measurement block scheme was used for electrical signals registration from the strain gauges, including dynamometers with glued strain gauges, a strain gauge amplifier 8АНЧ-26, an analog-to-digital converter Е140, jumper cables, and a personal computer. Dynamometer deformation is perceived by the transducers and converted to a voltage change in the measuring diagonal of the bridge circuit. The torque value is defined by calibration dependency M = f(∆U). The studies on torque evaluation were performed in laboratory conditions during installation of two-bladed screw piles in clay soil of soft and stiff consistency. The developed methodology for estimating the torque enables us to come up with recommendations for determining the load bearing capacity of two-bladed helical piles. It’s found out that adding a second blade into the pile shaft provides increased torque in clay soil of soft and stiff consistency by 35-50 %, respectively.