Electronic Thesis and Dissertation Repository


Master of Engineering Science


Civil and Environmental Engineering


Hesham El Naggar


Large diameter helical piles are being utilized increasingly to support large compressive and tensile loads. Both the magnitude of the required installation torque and the pile capacity can be directly attributed to the soil shearing resistance developed over the embedded area of the pile including the shaft and helical plates. Hence, the pile capacity can be correlated to the installation torque. Such correlations are widely used in helical pile industry as a means for quality control/quality assurance. However, the reliability of capacity-torque correlations for predicting the large diameter helical piles is adversely affected by the inaccurate measurement of the installation torque employing hydraulic pressure torque indicators. In the current study, a torque pin was fabricated using strain gauges methodology to facilitate accurate measurement of installation torque. A total of 17 piles, including seven fully instrumented, were installed while monitoring the installation torque continuously with depth using the fabricated device. The results of installation torque monitoring were demonstrated to be accurate and repeatable. In addition, six compressive and four tensile axial load tests were conducted on the test piles. The load test results were analyzed to determine the interpreted ultimate capacity of the test piles. The results demonstrated that the ultimate capacity of large diameter helical piles can be determined from the pile load tests data employing the interpreted failure criteria proposed by Elkasabgy and El Naggar (2015) and Fuller & Hoy (1970).The measured installation torque and the corresponding ultimate capacity values were used to define torque-to-capacity correlation based on embedded pile area, which is suitable for large diameter piles with single and double helices. Furthermore, the results from the seven test piles that were instrumented with strain gauges provided a description of the load transfer mechanism at various levels of axial loading. It was found that significant settlement may be required to mobilize the bearing resistance provided by the lead helix for both compressive and tensile loading conditions. Finally, the rear helix provides significant capacity contribution under compression loading but little contribution under tensile loading.

Cert of Exam - May 4, 2015, 4-34 PM.pdf (229 kB)
Certificate of Examinaion