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Numerical Investigation of the Inclined Pullout Behavior of Anchors Embedded in Clay

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Abstract

Two-dimensional plane strain finite element analysis has been used to simulate the inclined pullout behavior of strip anchors embedded in cohesive soil. Previous studies by other researchers were mainly concerned with plate anchors subjected to loads perpendicular to their longest axis and applied through the centre of mass. This paper investigates the behavior of vertical anchors subjected to pullout forces applied at various inclinations with respect to the longest anchor axis, and applied at the anchor top and through the centre of mass. The effects on the pullout behavior of embedment depth, overburden pressure, soil–anchor interface strength, anchor thickness, rate of clay strength increase, anchor inclination, load inclination and soil disturbance due to anchor installation were all studied. Anchor capacity is shown to increase with load inclination angle for anchors loaded through the centre of mass; greater effects are found for higher embedments. The results also show that anchor capacity improves at a decreasing rate with higher rates of increase of soil shear strength with depth. In addition, the capacity of vertically loaded anchors is shown to approximately double when the soil–anchor interface condition changes from fully separated to fully bonded. Similarly, disturbed clay strengths adjacent to the anchor following installation cause a significant reduction in anchor capacity. The results showed a significant effect of the point of load application for anchors inclined and normally loaded. The effects of other parameters, such as anchor thickness, were found to be less significant.

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Abbreviations

B :

Anchor length (m)

C u :

Clay undrained shear strength (kN/m2)

C interface :

Shear strength at anchor interface (kN/m2)

D :

Caisson diameter (m)

E :

Young’s modulus (kN/m2)

H :

Embedment depth (distance from ground surface to anchor tip) (m)

H c :

Critical depth (m)

H :

Distance between ground surface and anchor centre of mass (m)

K o :

Lateral earth pressure coefficient

L :

Caisson length (m)

N c :

Breakout factor

N c :

Breakout factor for unbonded condition

N c * :

Breakout factor for fully bonded condition

N coρ :

Inhomogeneous breakout factor

N coψ :

Breakout factor for inclined anchor in weightless soil

N co90 :

Breakout factor for vertical anchor in weightless soil

N v :

Breakout factor in the vertical direction

N h :

Breakout factor in the horizontal direction

P :

Ultimate load/unit length (kN/m)

q h :

Overburden pressure (kN/m2)

q u :

Applied pressure required to cause undrained failure (kN/m2)

S :

Coefficient for the effect of overburden pressure on anchor capacity

S t :

Soil sensitivity

t :

Anchor thickness (m)

β :

Anchor inclination to the vertical (°)

γ :

Soil unit weight (kN/m3)

φ :

Angle of internal friction (°)

ρ :

Rate of increase of undrained shear strength per unit length (kN/m2/m)

ν :

Poisson’s ratio

σ v :

Effective overburden stress (kN/m2)

α :

Adhesion factor

ψ :

Angle between the vertical plane and the pullout direction (°)

θ :

Load inclination angle to the vertical (°)

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Acknowledgments

The authors would like to acknowledge the financial support of the Natural Sciences and Engineering Research Council of Canada (NSERC).

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Authors and Affiliations

  1. Department of Civil and Environmental Engineering, The University of Western Ontario, London, ON, N6A 5B8, Canada

    Ahmed M. Fahmy & T. A. Newson

  2. Department of Physics and Astronomy, The University of Western Ontario, London, ON, N6A 3K7, Canada

    John R. de Bruyn

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  1. Ahmed M. Fahmy
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Correspondence to John R. de Bruyn.

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Fahmy, A.M., de Bruyn, J.R. & Newson, T.A. Numerical Investigation of the Inclined Pullout Behavior of Anchors Embedded in Clay. Geotech Geol Eng 31, 1525–1542 (2013). https://doi.org/10.1007/s10706-013-9676-9

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