Axial and Lateral Behavior of Helical Piles under Static Loads

Weidong Li
Helical piles have been used extensively in Western Canada to support the superstructures particularly with applications in power transmission towers, commercial buildings, camps, and so on. Extensive research in helical piles has been conducted using physical testing methods; however, there has been insufficient research in the numerical modeling soil-helical pile interaction in axial or lateral directions. The present research is thus carried out to bridge the knowledge gap. The first part of
more » ... present research is aimed to investigate the behavior of helical piles subject to axial static loading using field load tests and numerical simulation based on Beam-on-Nonlinear-Winkler-Foundation (BNWF) methodology. Field load tests were conducted on 26 single-helix piles including 15 compression tests and 11 tension tests in two types of soils in Alberta, Canada. The soils in the two selected sites were classified as medium to stiff clay, and medium to dense sand respectively. Three sizes of helical piles whose shaft diameters varied from 7.3 cm to 11.4 cm were tested according to the same test procedures. The load-displacement curves were obtained to show the axial behavior of the helical piles under axial static load. Installation torque was recorded per foot penetration into the ground to portrait the correlations between the installation torque and bearing or uplift capacity. Cone penetration tests (CPT) were applied to develop soil profiles of the test sites to provide input parameters to the numerical models. The field tests provide case studies to the subsequent finite element analyses of axial soilpile interaction. A BNWF model was developed on the platform of Open System for Earthquake Engineering Simulation (OpenSees). Soil reaction springs (p-y, q-z and t-z) were adopted by the developed model to simulate the integrated behavior of piles. It was iii found that the existing soil reaction spring implemented in OpenSees were capable of simulating the axial behavior of helical piles. The second part of present research is aimed to investigate the lateral soil-pile interaction using the BNWF model developed in OpenSees. In the literature, the effects of helix on the lateral capacity of helical piles have not been quantified. The numerical model was calibrated against published results of lateral load tests of helical piles. Systematic parametric analyses of helical piles using the BNWF models were conducted to observe the lateral capacity improvement due to the change of size and embedment depth of the helix, diameter and length of the bucket (partially enlarged pile shaft), and the soil classification (clay and sand). The effect of these geometric factors on the lateral capacity of helical piles was quantified, and the results of the parametric studies may be used for the practical design of lateral capacities of helical piles. iv
doi:10.7939/r39k4617b fatcat:td2sjvpsgfdm7bubey57gfi2ri