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Hydraulic Properties of Glacial Deposits Based on Large Scale Site Investigation
Les propriétés hydrauliques des dépôts glaciaires basées sur une enquête de chantier à grande
échelle
Galaa A., Manzari M.
Coffey Geotechnics, Toronto, Ontario, Canada
Hamilton B.
CH2M Hill, Toronto, Ontario, Canada
ABSTRACT: Glacial deposits by nature comprise variable soil types in relatively short distances. Hydraulic conductivity (K) is the
most important parameter in design of construction dewatering for underground structures. However, determination of proper design
values for K is not an easy task. Due to the inherent variable nature of the glacial deposits, even conventional pumping tests may not
provide reliable design parameter due to its smaller zone of influence compared to that of the actual dewatering for a structure. This
paper describes the methodology created for establishing more representative design values for hydraulic conductivity of glacial
deposits during a large scale subsurface investigation for planned tunnels. The subsurface investigation involved 400 boreholes,
including 88 slug tests and 16 pumping tests. A relation was established between K obtained from the field tests (K
field
) and K
calculated by applying Kozeny-Carman formula (K
KC
). Subsequently, the calibrated K-C formula was applied to 1,200 grain size
analyses conducted on various soil types. The calculated and measured K were used to form statistical analysis of the parameter and
provide more reliable design values for dewatering.
RÉSUMÉ : Les dépôts glaciaires comprennent des sols variables à travers des distances relativement courtes. La conductivité
hydraulique (K) est le paramètre le plus important qui est nécessaire durant la construction des structures souterraines. Cependant, la
détermination des valeurs de calcul appropriées pour K n'est pas une tâche facile. à cause de la nature variable des dépôts glaciaires,
même les essais de pompage peut-être ne fourniront pas des résultats fiables pour une bonne conception pour une bonne conception
parce que les structures déshydratés ont une plus grande zone d'influence. Ce document décrit la méthodologie créée pour établir les
paramètres de conception plus représentatives au cours d'une enquête de chantier à grande échelle pour les tunnels de métro prévues.
L'étude a porté sur 16 essais de pompage avec des puits d'observation associés, et 88 essais de conductivité hydraulique. Une relation
a été établie entre K obtenue à partir des essais sur le terrain (K
field
) et K calculé en appliquant la formule de Kozeny-Carman (K
KC
).
Par la suite, la formule de K-C calibrée a été appliquée à des analyses granulométriques effectuée 1200 échantillons. Les valeurs de K
calculées et mesurées ont été utilisées pour former une analyse statistique, et pour fournir des valeurs plus fiable.
KEYWORDS: Kozeny-Carman formula, hydraulic conductivity, Glacial Tills, dewatering.
1 INTRODUCTION
The Greater Toronto and Hamilton Area (GTHA), located in
southern Ontario, is Canada’s largest and fastest growing urban
region. The Government of Ontario Province through its
transportation authority known as Metrolinx, has embarked in a
massive transportation plan called “The Big Move”, which is a
25-year, $50 billion plan that will transform regional
transportation across the GTHA. The Eglinton Scarborough
Crosstown (ESC) Light Rail Project is part of that Big Move
program. The ESC is a 19-kilometre light rail transit line (LRT)
that will run along Eglinton Avenue, connecting west to east of
the city. Eleven kilometers of the alignment will be tunneled
underground, crossing well established urban areas which are
densely populated and congested. The tunnel construction is
divided in two contract packages: West Twin Tunnels
Construction and East Twin Tunnels Construction, with Yonge
Street the dividing limit. Dewatering operations will be required
for a total of twenty four structures along the tunnel alignment:
sixteen cross passages, four launch and exit shafts, and six
emergency exit buildings.
In order to meet a very tight schedule while properly
managing subsurface risk and support the design of the tunnel,
an aggressive multi-phase geotechnical investigation program
was undertaken. The geotechnical investigation for the west and
east tunnel contracts was conducted during a two-stage program
between 2010 to mid-2012; which followed by a
hydrogeological study for each section. In summary, about four
hundred (400) shallow and deep sampled boreholes were
advanced including three hundred (300) monitoring wells along
the subject alignment to obtain information regarding the
subsurface stratigraphy and groundwater conditions.
Furthermore, eighty eight (88) slug tests and sixteen (16)
pumping tests (150 mm O.D.) were completed as part of the site
specific hydrogeological study. At the time of preparation of
this paper, only the results of eight (8) pumping tests for the
west tunnels are available and used in analyses.
Due to project’s very tight schedule and ongoing progress of
design, the proposed locations of some structures were revised
after completion of the pumping tests. Furthermore, it was not
practical to conduct the pumping tests for all of the structures.
Innovative techniques were developed and used to establish
more representative design value of hydraulic conductivity
while not having pumping test at exact location of each
structure and also consider the inherent variable nature of the
glacial deposits. This paper describes the methodology
developed and summarizes the range of hydraulic conductivity
for various types of glacial deposits obtained from this large
scale subsurface investigation which is generally more refined
than older published range for the same deposits.
2 GEOLOGY SETTING
A detailed regional description of the Quaternary geology of the
project area can be found in the Ontario Geological Survey Map
(Sharpe, 1980). The soil deposits in the project area are result of
glacial depositional systems that took place during various
glacial periods. From the published geological data, the GTHA
experienced three glacial and two interglacial periods. This
