Long-term Lateral Resistance of Helical Piles in Cohesive Soils

Bien Dinh, John Liu, John Dunn, Justin Zhang, Peter Huang

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Earth Walls and Foundations

ABSTRACT: The results of ten lateral pile load tests for both helical piles and driven piles with the same shaft diameter and wall thickness are presented in this paper. The long term lateral load tests were conducted four years after the piles were installed. The test program was consisted of 6 long-term and 2 short-term helical pile loads tests and 2 long-term driven pile load tests. The test results show that both helical and driven piles have similar long-term lateral behavior. This study confirmed the previous research findings that shaft diameter and embedment depth primarily control the lateral resistance of both helical piles and driven piles. The long-term lateral resistance of the helical piles was equal to or exceeded that of the driven piles. In comparing the short-term and long-term lateral resistance of the helical piles, the long-term test results showed an average of 10% to 20% increase in lateral resistance, four years after installation. RÉSUMÉ Les résultats de dix tests de résistance latérale pour pieux vissés et battus, utilisant le même diamètre de tuyau et la même épaisseur de mur sont présentés dans ce document. Ces tests de résistance latérale ont été complétés quatre ans après l'installation des pieux. Ces résultats démontrent que les pieux vissés ont le même comportement à long-terme que les pieux battus. L'étude a reconfirmé les résultats des recherches précédentes qui démontrent que le diamètre du pieu est le principal point de résistance du contrôle latérale des pieux vissés et battus. Par ailleurs, les résultats des tests ont aussi démontrés que la résistance latérale à longue durée des pieux vissés est égale, ou même plus élevée que celle des pieux battus. En comparant la résistance à courte et à longue durées des pieux vissés, les résultats indiquent une augmentation moyenne de 10 à 20% de la résistance latérale, quatre ans à la suite de l'installation. 1 INTRODUCTION Recent development of hydraulic torque motors, coupled with advances in manufacturing techniques, now allows for the use of large diameter helical piles (up to 42' shaft diameter). Large diameter helical piles can be used in a wide variety of applications that require combined high compressive and tensile loading, as well as large lateral loading. Deep foundation application examples include wind turbines, power transmission towers, pipeline anchor blocks, and many others. Many publications have focused on the compression and uplift capacity of helical piles, while few studies have examined short-term lateral resistance, and none have examined long-term lateral resistance. Investigation of the long term lateral performance of helical piles is necessary in order to evaluate any improvement in lateral resistance over time. G. Padros et al. (2012) evaluated the lateral load performance of screw piles in cohesive soils by considering the soil disturbance from pile installation in terms of soil sensitivity. Continuing from that research, the results of a series of helical pile lateral load test programs, for both long-term and short-term durations after pile installation, are presented. The results for helical piles were also analyzed and compared to results for the long term lateral capacities of driven piles with the same shaft diameter. In November 2008, 6 helical piles and 2 driven piles were installed, to be used as long-term test piles (-LT). In July 2012, 2 helical piles were installed, to be used as short-term test piles (-ST). The lateral load tests were conducted in July 2012, only a few days after the two short-term screw piles were installed, and almost 4 years after the long-term piles were installed. 2 TEST SITE AND GEOTECHNICAL CONDITIONS The test site is located about 11.0 km (7 miles) to the north of Ponoka, Alberta (Figure 1). The subsurface investigation was conducted using cone penetration testing (CPT) and a mechanically augured test hole to a depth of 15.0m. The soil stratigraphy consists of an upper 1.0m thick layer of organic silt, underlain by 2.0m of stiff clay, followed by a 1.5m layer of very stiff silty clay, and followed by a 7.5m thick layer of hard clay till. The ground water level was measured at 1.2m below the existing ground surface. The soil properties are summarized in Table 1:

RÉSUMÉ: -term Lateral Resistance of Helical Piles in

Access this article:
Canadian Geotechnical Society members can access to this article, along with all other Canadian Geotechnical Conference proceedings, in the Member Area. Conference proceedings are also available in many libraries.

Cite this article:
Bien Dinh; John Liu; John Dunn; Justin Zhang; Peter Huang (2014) Long-term Lateral Resistance of Helical Piles in Cohesive Soils in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper267,author = Bien Dinh; John Liu; John Dunn; Justin Zhang; Peter Huang,title = Long-term Lateral Resistance of Helical Piles in Cohesive Soils,year = 2014}