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Physical evidence of the effect of vertical cyclic loading on soil improvement by rigid piles: a small-scale laboratory experiment using Digital Image Correlation

Abstract

This paper presents an experimental study focusing on the mechanisms taking place in a granular platform supported by piles in soft soil under vertical cyclic loading. An original three-dimensional laboratory model was developed, with a scale factor of 1/10 on the length. The model contains 20 rigid piles, and the compressible soil is explicitly simulated by a soft material. The case of a thin granular load transfer platform overlaid by a rigid slab is studied. Tests were performed under monotonic or cyclic loading applied on the surface using a pressurized membrane. The analysis is based on a force and displacement sensor instrumentation and application of a Digital Image Correlation technique. The evaluation of the load transfer onto the piles and the settlements in the platform are some of the main points under the scope of this study. The effect of the cyclic loading and the sequence of loading on the structure’s response are examined by a comparative study between the series of cyclic and monotonic tests. Settlement accumulation and increase in the load transmitted to the piles were observed during the cycles. The image analysis gives access to the displacement field within the granular platform, and its evolution during the cycles could be analysed.

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Abbreviations

α :

Recovery ratio (%)

d :

Pile diameter (mm)

l :

Pile height (mm)

s :

Pile spacing

H s :

Height of the soft soil (mm)

H g :

Thickness of the LTP (mm)

γ g :

Unit weight of the LTP (kN/m3)

Ft i :

Vertical force at the top of the pile (kN)

ΣFt i /4:

Average of the forces at top of the four central piles (kN)

D1, D2, D3:

Settlements at the platform base (mm)

w :

Water content of the soft soil (%)

Pm :

Stress applied by the water membrane on the surface (kPa)

φ :

Internal friction angle of the LTP (degree)

c :

Cohesion of the LTP (kPa)

DL:

Dead load: weight of the LPT, rigid plate and water inside the membrane (kN)

LL:

Live load: overload at the surface (kN)

E i :

Pile efficiency: \( E_{i} = \frac{{Ft_{i} }}{{{\text{DL}} + {\text{LL}}}} \)

ΣE i /4:

Average efficiency of the four central piles

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Acknowledgments

The authors are grateful to the French National Federation of Public Work (FNTP) for providing financial support, especially to Philippe Gotteland and the director of the Technique and Research Department. The authors would like to express their gratitude to Gael Combe for his help in the image analysis and in the practice of the programme “Tracker”.

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Correspondence to Orianne Jenck.

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Houda, M., Jenck, O. & Emeriault, F. Physical evidence of the effect of vertical cyclic loading on soil improvement by rigid piles: a small-scale laboratory experiment using Digital Image Correlation. Acta Geotech. 11, 325–346 (2016). https://doi.org/10.1007/s11440-014-0350-z

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  • DOI: https://doi.org/10.1007/s11440-014-0350-z

Keywords

  • Cyclic loading
  • Digital Image Correlation
  • Granular platform
  • Rigid piles
  • Three-dimensional laboratory model