2815
Improving the capacity of bored piles by shaft grouting
Améliorer la capacité portante des pieux forés par injection de coulis opérée latéralement
Miller M., Potts V., Skinner H.
Donaldson Associates Ltd.
Vaziri M.
Ramboll UK
ABSTRACT: A project in Georgia involved the construction of two towers for residential, retail and hotel use with a two storey
basement. The development was near the Black Sea, with poor ground conditions below basement level. In order to carry the high
loads, the developments used deep bored piles installed by Bauer. The pile capacity was significantly enhanced by shaft grouting from
a number of tubes cast into the piles during construction. Instrumented pile tests were carried out on ungrouted and grouted piles.
Results from the strain gauges showed differences in the behaviour of the piles in different strata depending on the granular content of
the material.
RÉSUMÉ : Dans le cadre d’un projet en Géorgie, deux tours ont été construites pour des logements, bureaux et hôtels ainsi qu’un
sous-sol a deux étages. Le projet est situé près de la Mer Noire, ou les conditions de sol en-dessous de la base du sous-sol sont
mauvaises. Afin de supporter les descentes de charges importantes, des pieux forés ont été installés par Bauer. La capacité portante
des pieux a été considérablement améliorée par injection de coulis de ciment, opérée latéralement a travers plusieurs tubes coulés dans
les pieux pendant la construction. Des essais instrumentés sur des pieux forés avec et sans injection ont été réalisés. Les mesures
fournies par les jauges de déformations ont montrées différents comportements des pieux selon la granulométrie des couches de sols
rencontrées.
KEYWORDS: Batumi, shaft grouting, pile testing
MOT-CLÉS : Batoumi, injection de coulis opérée latéralement, essais sur pieux
1 INTRODUCTION
In the UK there has been significant work carried out on the
benefits of base grouting into Thanet Sand to improve stiffness
and capacity of deep bored piles, but limited information is
available on the use of shaft grouting. This paper will present
and discuss the results of shaft grouting that was carried out to
enhance pile capacity for a project in Georgia.
Ramboll UK provided structural and geotechnical design
services for a new development adjacent to the Black Sea in
Batumi, Georgia in 2009. The development comprised of a 17
storey residential tower and a 23 storey hotel tower surrounded
by a 2 storey podium building. A two storey basement underlay
the entire site footprint.
The findings of the ground investigation and resulting tender
pile design will be presented. The pile testing results will then
be presented giving commentary on the likely factors behind the
pile behaviour and the potential for carrying out shaft grouting
in other situations.
2 GROUND CONDITIONS & SEISMICITY
Tectonic movements, local river systems and the progression
and regression of the Black Sea have influenced the regional
geology.
2.1
Geology & Groundwater
The region is underlain by volcanic rocks reported to weather to
clay dominated strata. Overlying the bedrock are two distinct
quaternary sequences thought to be up to 150m thick. The older
of these is thought to be associated with alluvial-swampy
sediment sequences with the more recent being associated with
marine sequences.
Figure 1. Site location in regional context.
The ground investigation specified by Ramboll revealed
made ground overlying sands and gravels over clayey and sandy
loams. The fines content increased with depth and the test data
and on site observations suggested that the strata generally
decreased in strength and stiffness with depth. Table 1
summarises the ground conditions and Figure 2 presents particle
size distribution against level.
The laboratory testing was carried out to Georgian standards
with some test methods differing from British practices to a
greater extent than others. The laboratory testing of the Loam B
material in particular was inconclusive in determining the
