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Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
from the Figure, the normalized neutral depth increases with the
increase of the pile length embedded in the clay layer.
The explanation of the effect of the pile length on the neutral plane is
due to the compressibility of the pile length. When negative skin
friction is induced in a short pile, most of the downdrag is transmitted to
the pile tip in the form of penetration to the bearing layer. Whereas, for
long pile the downdrag is partly taken by the pile compressibility, and
partly transmitted to the tip.
3.4 Determination of the Neutral Plane
Shong approach is adapted to locate the neutral plan. This
approach is outlined in Section 1. The factor of safety of pile
capacity against ultimate pile capacity, Fs is considered two,
and
is taken 0.3.
Fig. 7 Monitored and Calculated Location of the Neutral Plane
Figure 7 depicts the normalized neutral depth from both the
monitored data and Shong approach. The pile diameter is
1.5cm. Two cases; I, and II, of tested pile are shown in the
Figure. As can be seen from the Figure, the calculated
normalized neutral depth is having the same trend as the
monitored ones. The approach results into very good agreement
with the normalized neutral depth.
4 CONCLUSION
This paper presents a study on the behavior of pile during soil
consolidation. In order to carry out the investigations,
experimental program was designated. A special rig was
designed and constructed for this purpose. Based on test results
the following conclusions are reached:
Consolidation of the soil surrounding the pile due to
surcharge loads induces negative skin friction on piles.
The monitored strains along the pile length reflect the
consolidation process with time. Strain increases from the
pile top until it reaches a peak value at the location of the
neutral plane.
Sand layers, at the pile tip, offer resistance to the pile
movement; end bearing. This increases stresses in the
bottom portion of the pile. Hence, there is increase in the
monitored strain, when compared with piles ended in clay,
or floated.
Shear stress is initiated from zero value at the surface of the
soil and increases until it reaches a peak negative value at
an intermediate depth. Then, it decreases down to zero at
the elevation of the neutral plane where the positive skin
friction develops.
The neutral plane is located closer to the end of the pile as
the base layer getting stiffer.
The normalized neutral depth increases with the increase of
the pile length.
Shong approach
for ND results into very good agreement with the
monitored ones.
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