952
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
vibratory tremie) full scale piles constructed for performance
tests which indicated promising results in comparison to the
piles installed by conventional technique.
16 CONCLUSIONS
The extent of impregnation and smear zone surrounding
borehole is a function of the soil properties and installation
technique. Impregnation of cementitious slurry alters the
physico-chemical characteristics of soil within the impregnated
zone and upon setting strengthens smear zone within the
impregnated depth. Cement-impregnated soil becoming a part
of the cast in-situ deep foundation is almost certain. The
resulting larger effective diameter is causing potential threat
from negative shaft resistance. However, its positive
contribution enhances shaft resistance vis-à-vis design
economy. Due to the opposing nature of smear and cemented-
soil characteristics, soil-structure interface strength depends on
the properties of partially remoulded soil at the potential rupture
surface, location of which is dictated by the depth of
impregnation. Using newly developed simulation device soil
samples from various auger-boreholes were impregnated at 1
and 2 Kg/cm
2
slurry pressure. Microscopic observations on
impregnated samples were not found promising for
determination of the extents of smear and impregnation.
Modified staining technique enabled mapping of impregnation
profile for determination of maximum and average
impregnation depths. Although both impregnation depths
increase with increase in slurry pressure, their plots with
common soil parameters revealed no definite trends. In the plots
of impregnation depth with composite parameter D
50
×e, which
is a measure of both pore size and overall void ratio, no mean
line could be drawn for maximum impregnation, however,
impregnation rendered model of
s location of rupture surface for
onstruction of prototypes, performance of which were found to
be promising..
17 ACKNOWLEDGEMENT
In order to supplement a research (Sarma, 2000), Mr. A. Deb
undertook detailed investigation on impregnation (Deb, 1995)
implementing the scheme and using the device developed by the
Author
1
. His support is gratefully acknowledged. The
experimental investigations referred to in this paper were part of
Author
1
’s PhD work (Sarma, 2000), which were conducted
under the supervision of Prof. P. K. Bora, PhD (Birmingham),
Head of Civil Engineering (Retired), Assam Engineering
College, India. His encouragement is gratefully acknowledged.
regression analysis for average
straight line. The model indicate
auger bored soil-structure interface that can be used for
determination of shaft resistance. Further due to linear
shrinkage the progressive collapse (strain-softening) may occur
at the rupture surface or at the interface when impregnation is
not prominent. This may be detrimental particularly for higher
diameter shafts. The maximum unit shaft resistance is possible
when the depth of smear is less and remains within
impregnation depth. In order to minimise the extent of smear
zone, new equipments were fabricated, patented, and used for
c
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