1947
Performance of Soil Nails in Weathered Granite and Fill
Performance de renforcement par clouage du granite altéré et du remblai
Chow C.-M., Chee-Meng, Tan Y.-C.
G&P Geotechnics Sdn Bhd, Kuala Lumpur, Malaysia (
ABSTRACT: Soil nail is increasingly common in Malaysia for infrastructure works where high cut slope is often formed to
accommodate road alignment, facilities, etc. In recent years, soil nailing has also proven to be a viable, cost-effective and
environmental friendly alternative solution for deep excavation of basement to replace conventional solutions using vertical retaining
wall such as contiguous bored pile, secant pile or diaphragm wall. Applications of soil nail for basement construction of up to 30m
deep have been successfully designed and constructed where performance of the soil nailing works have been verified based on
monitoring results. Design assumptions for the skin friction between the soil and grouted body of soil nail were also verified using
instrumented preliminary and working pull-out tests on the soil nails. This paper discusses results of the pull-out tests on the soil nails
and based on analysis of the test results, recommendations on the skin friction applicable for soil nail design are presented.
RÉSUMÉ : Les clous de sols sont de plus en plus communs en Malaisie pour les travaux d'infrastructure où une forte pente de talus
est souvent créée pour le tracé de la route, pour accueillir les installations, etc. Ces dernières années, le clouage de sol s'est également
avéré être une solution alternative viable, rentable et écologique pour remplacer les solutions classiques utilisant un mur de
soutènement vertical tels que les pieux forés contigus, les pieux sécants ou les parois moulées pour les excavations profondes des
travaux de fondations. Les applications du clouage de sol dans la construction
d’excavations
de plus de 30m de profondeur ont été
correctement conçues et mises en œuvre et leurs performances ont également été vérifiées sur la base de mesures répété
es. Les
hypothèses de calcul des efforts
d’adhérence
entre le sol et les clous de sols avec injection ont également été vérifiées par des tests
d’arrach
ement. Cet article présente les résultats des tests d'arrachement sur des clous de sol et sur la base de l'analyse de ces résultats,
propose des recommandations sur la capacité en de scellement à prendre en compte lors de la conception des clous de sol.
KEYWORDS: Soil nail, skin friction, pull-out tests, deep excavation.
1 INTRODUCTION
Soil nails are increasingly common in Malaysia for
infrastructure works where high cut slope is often formed to
accomodate road alignment, facilities, etc. Soil nail is
advantageous compared to other retaining wall system as the
soil nails are installed directly onto the final slope/wall profile
and as such, minimises earthworks compared to conventional
retaining wall. Furthermore, soil nails installation also does not
required heavy machineries compared to system such as
contiguous bored pile (CBP), diaphragm wall/secant pile.
Malaysia’s experiences in soil
nail design and construction have
been discussed by Chow & Tan 2006 and Chow & Tan 2011.
In recent years, the use of soil nails as alternative solution to
vertical retaining wall for basement excavation is also gaining
popularity and has been successfully designed and constructed
for basement excavation of up to 30m deep. This paper
discusses the design and construction of a soil nailed slope for
basement excavation of a commercial development in Mont’
Kiara, Kuala Lumpur, Malaysia with excavation depth of up to
20m.
2 GENERAL GEOLOGY AND SUBSURFACE
INFORMATION
The site is underlain by the Kuala Lumpur Granite formation.
The granite rocks are generally whitish grey and dark grey in
colour except certain parts with iron stained markings that gives
orange and dark red colours to the rocks. The texture and
composition of the granitic rock generally ranges from coarse to
very coarse-grained.
A total of twenty nine boreholes were carried out at the site
to facilitate retrieval of undisturbed soil samples for laboratory
testing (e.g. Atterberg limits tests, Isotropically Consolidated
Undrained Triaxial
–
CIU tests, etc.) and also in-situ tests such
as Standard Penetration Tests (SPT). The interpreted borehole
profiles relevant to the soil nail slope showing the SPT-N
values, major/minor components of soil and Rock Quality
Designation (RQD) for rock are shown in Figure 1. Some of the
materials near to the surface, especially for materials with low
SPT ‘N’ values (< 5) are
filled materials.
Generally, the subsoil consists mainly silty SAND and
sandy SILT with Liquid Limit (LL) ranging from 25% to 71%
and Plastic Limit (PL) ranging from 15% to 42% and can be
classified as low to high plasticity silty/clayey materials.
A total of eleven Isotropically Consolidated Undrained
Triaxial (CIU) tests and four Direct Shear Box tests were
carried out to determine the shear strength of the soil. The shear
strength parameters of the subsoil adopted for design are
c’=3.5kPa,
’=30
.
3 DESIGN OF SOIL NAIL SLOPE FOR BASEMENT
EXCAVATION
The soil nail slope with retained height of up to 20m is designed
to ensure minimum long-term factor of safety of 1.4 as the soil
nail slope will be permanent.
