Abstract
In this paper experimental investigations on the behaviour of single, double and triple helical screw anchors under the influence of vertical compressive loads are presented. The testing program was conducted on one, two, three and four numbers of model anchors in sand for different depths of embedment keeping shallow and deep mode of behaviour in mind. The experimental setup was instrumented to measure the compressive load and the downward displacement of the anchor. It was observed that the compressive load varied significantly with the installation depth of the anchor and the number of anchors. 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. Ultimate compressive capacity of multiple anchors was plotted against that of single anchor and simple equations were proposed correlating them. Using these equations an anchor foundation for a particular structure can be easily designed. A 3-D finite element model, PLAXIS, was used to confirm the results obtained from laboratory tests and the agreement is excellent.
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Abbreviations
- B:
-
Diameter of the blade of the helical screw anchor
- E:
-
Young’s modulus of elasticity
- H:
-
Embedment depth of the anchor
- N:
-
Newton
- Na :
-
Number of anchors
- nb :
-
Number of blades in the helical screw anchor
- L:
-
Embedded length of the anchor
- Q:
-
Failure load
- Quc :
-
Ultimate compressive capacity of helical screw anchor
- (Quc)1 :
-
Ultimate compressive capacity of one helical screw anchor
- (Quc)2 :
-
Ultimate compressive capacity of two helical screw anchors
- (Quc)3 :
-
Ultimate compressive capacity of three helical screw anchors
- (Quc)4 :
-
Ultimate compressive capacity of four helical screw anchors
- P:
-
Pressure
- z:
-
Depth of the sand fills above the screw of the anchor
- f*:
-
Apparent coefficient of friction between the anchor and the soil
- G:
-
Specific gravity
- c:
-
Cohesion
- emin :
-
Minimum void ratio
- emax :
-
Maximum void ratio
- Cu :
-
Uniformity coefficient
- Cc :
-
Coefficient of curvature
- q:
-
Surcharge intensity
- Φ:
-
Angle of internal friction
- γd :
-
Dry unit weight of soil
- γmin :
-
Minimum unit weight (kN/m3)
- γmax :
-
Maximum unit weight (kN/m3)
- ν:
-
Poisson’s ratio
References
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Elsherbiny ZH, Naggar MHEI (2013) Axial compressive capacity of helical piles from field tests and numerical study. Can Geotech J 50(12):1191–1203
Kumar J, Bhoi MK (2010) Effect of interference of strip footings and strip anchors on their elastic settlements. Int J Geotech Eng 4:289–297
Livneh B, Naggar MHEI (2008) Axial testing and numerical modeling of square shaft helical piles under compressive and tensile loading. Can Geotech J 45(7):1142–1155
Sakr M (2009) Performance of helical piles in oil sand. Can Geotech J 46(9):1046–1061
Acknowledgments
The research is supported by a fellowship to second author from MHRD, Government of India. That support is gratefully acknowledged.
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Mittal, S., Mukherjee, S. Behaviour of Group of Helical Screw Anchors Under Compressive Loads. Geotech Geol Eng 33, 575–592 (2015). https://doi.org/10.1007/s10706-015-9841-4
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DOI: https://doi.org/10.1007/s10706-015-9841-4