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Vertical Uplift Capacity of a Group of Helical Screw Anchors in Sand

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Abstract

In this paper experimental investigations on the behavior of single, double and triple helical screw anchors under the influence of vertical uplift loads are presented. The testing program was conducted on three model anchors having single, double and triple helical screws installed in sand. The experimental setup was instrumented to measure the pullout load and the upward displacement of the anchor. It was observed that the pullout load varied significantly with the installation depth of the anchor and the number of anchors. A mathematical model was developed using the limit-equilibrium method of analysis. Based on experimental results, non-dimensional graphs were plotted normalizing the deformation and load axis both and simple equations are proposed correlating load and deformation. Using these equations an anchor foundation for a particular structure can be designed. Comparison of the pullout load values obtained from the theory developed and the present experimental results showed good agreement.

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Abbreviations

A:

Cross sectional area of the screw blade the anchor (m2)

B:

Diameter of the helical screw of the anchor (m)

B′:

Width of footing in plate load test (m)

Cu :

Uniformity coefficient

Cc :

Coefficient of curvature

G:

Specific gravity

H:

Depth of the bottom of the anchor from the soil surface (m)

Kp′:

Modified coefficient of passive earth pressure

L:

Length of the anchor (m)

Na :

No. of anchors

Nγ :

Bearing capacity factor

P:

Failure load (N) (obtained from laboratory plate load test)

Pp :

Passive earth pressure on the assumed failure surface (N/m2)

Pp′:

Passive earth pressure for unit perimeter of the inverted cone (N/m2)

Q:

Pullout capacity of anchor (N)

T:

Shear stress (N/m2)

V:

Volume of the assumed inverted cone (m3)

c:

Cohesion (kN/m2)

emin :

Minimum void ratio

emax :

Maximum void ratio

ep :

Passive earth pressure (N/m2)

f* :

Apparent coefficient of friction

nb :

No. of screw blades in the anchor

q:

Surcharge intensity (N/m2)

z:

Depth of the sand fill above the screw of the anchor (m)

γd :

Dry unit weight of soil (kN/m3)

Φ:

Angle of internal friction

γmin :

Minimum unit weight (kN/m3)

γmax :

Maximum unit weight (kN/m3)

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Acknowledgments

The research is supported by a fellowship to second author from MHRD, Govt. of India. This support is gratefully acknowledged.

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Authors and Affiliations

  1. Department of Civil Engineering, Indian Institute of Technology Roorkee, Roorkee, 247667, India

    Satyendra Mittal & Sanjeev Mukherjee

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  1. Satyendra Mittal
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  2. Sanjeev Mukherjee
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Correspondence to Sanjeev Mukherjee.

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Mittal, S., Mukherjee, S. Vertical Uplift Capacity of a Group of Helical Screw Anchors in Sand. Indian Geotech J 43, 238–250 (2013). https://doi.org/10.1007/s40098-013-0055-5

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