2253
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
Landslide stabilization by piles: A case history
Stabilisation des glissements de terrain par des pieux: Un cas d’étude
Mahmut Y. ŞENGÖR
Yuksel Project Co. Inc., Ankara, Turkey,
M. Ufuk ERGUN
Middle East Technical University, Ankara, Turkey,
Nejan HUVAJ
Middle East Technical University, Ankara, Turkey,
ABSTRACT: During the foundation excavation of an industrial plant in Eskişehir, Turkey, a landslide occurred in the neighbouring
slope, and consequently, the excavation had to be stopped. The instability occurred in a natural slope which had an average slope
angle of 9-13 degrees. The aerial extent of the slide mass was 400 m by 115 m. The material in the slope was 7 to 20 meter-thick
colluvium (slide debris), which constitutes a historic landslide mass, underlain by a gravelly sandy silty clay matrix containing
limestone blocks, weathered tuff and tuff. Soil profile and location of the slip surface were determined through a site investigation
program including nine boreholes and inclinometers. A back analysis was carried out and shear strength parameters of the slope
forming materials were determined. Slope stability analyses were carried out, stabilization alternatives were evaluated and slope
stabilization by piled retaining walls was considered as the most feasible alternative. The analyses and design procedure for the piles
will be presented together with a summary of existing analyses and design methods for landslide stabilizing piles.
RÉSUMÉ : Pendant les excavation des fondations d’un site industriel à Eskisehir, en Turquie, un glissement de terrain a eu lieu dans
un talus voisin, et par conséquent, les travaux ont été arrêtés. L’instabilité s’est produite dans un terrain naturel présentant une pente
moyenne de 9 – 13 degrés. Les dimensions en plan du glissement étaient de 400 m par 115 m. Le matériau du glissement était
composé de colluvions, sur 7 à 20 m d’épaisseur, qui constituaient une masse de glissement postérieur. Les colluvions reposaient sur
une argile graveleuse et sablo-limoneuse contenant des blocs de calcaire, du tuf sain et du tuf altéré. La coupe géotechnique du site et
la localisation de la surface de glissement ont été mises en évidence par une campagne d’investigations incluant neuf forages et
inclinomètres. Les paramètres de résistance au cisaillement des terrains en place ont été déterminés par une rétro-analyse. Suite aux
études de stabilité des pentes et à l’examen des systèmes de renforcement alternatifs, la solution de stabilisation par une paroi en pieux
s’est avérée comme la plus judicieuse. Les analyses et la procédure de dimensionnement pour ces pieux vont être présentées en même
temps qu’un résumé des analyses et des méthodes de calcul existantes sur la stabilisation des glissements par pieux.
KEYWORDS: landslide, piles, inclinometer.
1
INTRODUCTION AND SOILS AT THE SITE
Instability occurred in a natural slope which had an average
slope angle of 9-13 degrees, during excavation works near the
toe. The aerial extent of the slide mass was 400 m by 115 m.
The construction site was located at the toe of this sliding mass
(Figure 1). The slope movement had a NW-SE direction. The
material in the slope was 7 to 20 meter-thick colluvium (slide
debris), which constitutes a historic landslide mass, underlain
by gravelly sandy silty clay layers with limestone blocks,
weathered tuff and unweathered tuff at different borehole
locations. The colluvium was also composed of pieces of
limestone cobbles and blocks in a clayey silty matrix.
It was observed that the slide debris lies on tuff. The pliosen
age tuffs are approximately 100 m thick and lies on limestone.
In the borehole descriptions the tuff layer at the upper levels are
weathered to highly weathered condition and can be considered
as a transition between rock and soil and identified as a layer of
stiff clay. Samples from this weathered tuff had natural water
content 19-43% (high natural water content such as 43% was
obtained near the shear surface at about 20 m depth at borehole
SK9). Since this material can be considered clay-like, Atterberg
limits are determined LL=45-49%, PI=11-28% (for the material
near the shear surface LL=49-66% and PI=27-36%), fines
content=34-74% and clay-size fraction was 23-57%, and the
material can be classified as CL, ML, GC and SC. The natural
unit weight of samples were 20-21 kN/m
3
. Unconfined
compressive strength of this material was 30-240 kPa and UU
triaxial tests gave c
u
=13-44 kPa and
u
=11-22°. Since the
residual shear strength will be of interest in this reactivated
landslide case, direct shear tests were carried out on limited
number of undisturbed samples taken from near the shear
surface in order to find the residual friction angle. 46 mm
diameter specimens were sheared undrained without
submerging in water, then sheared continuously and slowly to
reach residual condition. From the lab tests it was concluded
that the 100 and 250 kPa undrained shear strength for tuffaceous
clay and clayey tuff are reasonable values. Drained friction
angle of slope debris/colluvium was 15-20 degrees, and
tuffaceous clay taken from near the shear surface had 10.2
degrees residual friction angle.
1.1
Soil Profile and The Mechanism of the Slope Movement
The sliding mass has grown progressively backward into the
slope as multistage rupture surfaces from the toe of the landslide
developed. First, the tension crack (scarp) C1 has been observed
while excavation works were going on. Then, within about 15
days, there were total of four major tension cracks (visible
scarps) (C1 to C4 in Figures 1 and 2) and one meter horizontal
and vertical movements have been observed at the ground
surface. Fifty days after the start of the first scarp, a small road
located at the slope was observed to move 15 m downslope and
4 m in vertical direction.
Nine boreholes are opened at a line of NW-SE direction
which is also the direction of the movement and inclinometers
are also placed in these boreholes. In all boreholes except SK7,
SK8 (at the toe) and SK6; the top layer is slope debris and
Landslide stabilization by piles: A case history
Stabilisation des glissements de terrain par des pieux : un cas d’étude
Şengör M.Y.
Yuksel Project Co. Inc., Ankara, Turkey
Ergun M.U., Huvaj N.
iddle East Technical University, Ankara, Turkey
