Field investigation of the axial resistance of helical piles in dense sand
- Authors: Gavin, Kenneth , Doherty, Paul , Tolooiyan, Ali
- Date: 2014
- Type: Text , Journal article
- Relation: Canadian Geotechnical Journal Vol. 51, no. 11 (2014), p. 1343-1354
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- Description: This paper presents the results of compression and tension load tests performed on a single helical pile installed in dense sand. The pile was instrumented using strain gauges that allowed the shaft and base load resistance to be separated and the distribution of shaft resistance along the pile during the test to be determined. The pile was loaded first in compression, with a maintained load test, followed by a constant rate of penetration load test being performed to assess the effects of creep on the pile’s response to compression loading. The pile was then loaded in tension using a maintained load test procedure. Finite element analyses were performed using Abaqus and these helped to provide additional insights to explain the response of the instrumented pile during loading. The test showed that during compression loading, substantial bearing pressures developed beneath the pile helix, which provided the majority of axial load resistance. During tension loading, uplift pressure mobilized on the helix again provided the majority of axial resistance. The strain gauges suggested that the pile load response to compression loading was ductile. During tension loading, the pile response was brittle. Whilst load tests performed on only one instrumented pile test are presented, the use of instrumentation and finite element analyses allowed important insights into the load–displacement response of helical piles. © 2014, Can. Geotech. J. All right reserved.
An investigation of correlation factors linking footing resistance on sand with cone penetration test results
- Authors: Gavin, Kenneth , Tolooiyan, Ali
- Date: 2012
- Type: Text , Journal article
- Relation: Computers and Geotechnics Vol. 46, no. (2012), p. 84-92
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- Description: Significant research effort has led to improvements in our ability to estimate the ultimate bearing resistance of footings in sand. These techniques often estimate the footing resistance at relatively large displacements, typically 10% of the footing width, q b0.1. Cone Penetration Test (CPT) design methods typically link q b0.1 and q c through a constant reduction factor, α. A range of α factors for shallow footings have been proposed, some methods suggest that α is constant and while others that it varies with footing width and depth (or stress level). There is a dearth of field data with which to compare these correlation factors, in particular where foundation width and depth have been varied in the same ground conditions. For this reason finite element analyses have proven to be a useful tool for performing the parametric studies required to asses factors controlling α. This paper describes the results of numerical analyses performed to investigate α factors for soil profiles which were calibrated using the results of the CPT tests performed at a dense sand test-bed site. The numerical model was first used to perform parametric analyses to consider the effect of footing width, B and footing depth, D on the α factor mobilised in dense Blessington sand. In order to assess the effects of relative density, footing tests in a range of natural sands with variable in situ densities were modeled. The results of the finite element analyses suggest that a direct correlation between q b0.1 and q c can be established at a given test site which is independent of footing width and depth and is relatively weakly dependent on the sands relative density if the zone of influence of the foundation considered is large enough. © 2012 Elsevier Ltd.
Modelling the cone penetration test in sand using cavity expansion and arbitrary lagrangian eulerian finite element methods
- Authors: Tolooiyan, Ali , Gavin, Kenneth
- Date: 2011
- Type: Text , Journal article
- Relation: Computers and Geotechnics Vol. 38, no. 4 (2011), p. 482-490
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- Description: The paper considers two techniques to model the Cone Penetration Test (CPT) end resistance, qc in a dense sand deposit using commercial finite element programmes. In the first approach, Plaxis was used to perform spherical cavity expansion analyses at multiple depths. Two soil models, namely; the Mohr-Coulomb (MC) and Hardening Soil (HS) models were utilized. When calibrated using simple laboratory element tests, the HS model was found to provide good estimates of qc. However, at shallow depths, where the over-consolidation ratio of the sand was highest, the relatively large horizontal stresses developed prevented the full development of the failure zone resulting in under-estimation of the qc value. The second approach involved direct simulation of cone penetration using a large-strain analysis implemented in Abaqus/Explicit. The Arbitrary Lagrangian Eulerian (ALE) technique was used to prevent excessive mesh deformation. Although the Druker-Prager soil model used was not as sophisticated as the HS model, excellent agreement was achieved between the predicted and measured qc profiles.