Behavior Of Helical Piles Research Articles

THE COMPRESSION AND UPLIFT BEARING CAPACITIES OF HELICAL PILES IN COHESIONLESS SOIL

Helical piles have been used widely in engineering application .They can be used to provide structural stability against axial compression ,uplift and lateral forces. . In recent years, helical pile foundations have become more widely used in many countries. There are few studies about helical piles, for this reason the aim of the present paper is to study how to improve the prevision of the compression and uplift capacities of helical piles, and study the effect of embedded depth and helical area of helical piles in sand soil on the compression and uplift bearing capacities. Studies of helical piles with different areas of helices provided are in continuation. Compression and uplift loads were applied at different height within the soil. The embedment length of screw anchor piles was also varied to study the behavior of helical piles under compression and uplift loads. Various size and numbers of helices have been used in the laboratory tests with diameters 5 ,6.7 , 8.2 and 10cm with varying lengths. The embedment ratios for each ,D/d are 1 ,2 ,3 ,4 ,5 ,6 and 7 . An experimental setup instrumented to allow the measurement of the compression and pullout loads which affect on the helical pile installed into prepared layers of sand until failure. The results show that the compression and pullout resistance of helical anchors is strongly affected by the area and composition of helical plates welded to the pile steel shaft . The compression and uplift loads are increased with increasing of the embedment ratios, D /d and helix diameter, d. In addition to some other useful results are indicated in this paper.

Dynamic response of vertically loaded helical and driven steel piles

The dynamic performance of helical piles is of significant interest because such piles can offer an efficient alternative to conventional piling systems in many applications where the foundation is subjected to dynamic loads. This paper presents the results of full-scale dynamic vertical load tests on a 9.0 m double-helix, large-capacity helical pile and a driven steel pile of the same length and shaft geometry. Comparing the results is considered necessary to evaluate, qualitatively and quantitatively, the dynamic performance characteristics of large-capacity helical piles. The test piles were closed-ended steel shafts with an outer diameter of 324 mm. The piles were subjected to harmonic (quadratic) loading of different force intensities acting within a frequency range that covered the resonant frequencies of the tested pile–soil–cap systems. The dynamic and static properties of the subsurface soil adjacent to the test piles were determined using the seismic cone penetration technique and the conventional soil boring and testing methods. In addition, field observations are compared with calculated responses using the program DYNA 6 to better understand the pile–soil interaction for the case of helical piles. The effects of soil nonlinearity and pile–soil separation were accounted for in the analysis by employing a weak boundary zone around the piles in the analytical model. The experimental results show that the dynamic behaviour of helical piles is essentially the same as that of driven steel piles with the same geometric properties (without the helix plates). In addition, it was demonstrated that the program DYNA 6 can accurately simulate the behaviour of both helical and driven piles.

Lateral Capacity of Helical Piles in Clays

In this paper, the behavior of helical piles under lateral loads in clayey soils is examined through an experimental investigation on model piles. Tests were conducted on rigid helical piles with different numbers of plates. Model anchors were made of 13.8 mm diameter mild steel shafts to which mild steel plates of 33 mm diameter were welded. For comparison, a single straight shaft with a diameter of 13.8 mm was also tested. Test results revealed that the lateral capacity of helical piles is greater than that of straight shaft piles. A simple theoretical model is suggested to estimate the lateral capacity of rigid helical piles. The theoretical model suggested incorporates lateral resistance of the soil on the shaft, bearing resistance on the bottom of the helical plate, uplift resistance on the top of the helical plate, and frictional resistance on the surface of the helical plate. The validity of this model is examined.