1901
Experimental analyses on detection of potential risk of slope failure by monitoring of
shear strain in the shallow section
Analyses expérimentales sur la détection d'un risque potentiel de rupture de pente par la
surveillance de la contrainte de cisaillement en pied du talus
Tamate S., Hori T.
National Institute of Occupational Safety and Health, Tokyo, Japan
Mikuni C., Suemasa N.
Tokyo City University, Tokyo, Japan
ABSTRACT: A large scale model test was carried out in this study to investigate the relationship between the potential risk of slope
failure and an increase of the shear strain in the shallow section. A model slope made of soft deposit of Kanto-loam with 30 degrees
inclination and 3.5m height was prepared. Compact shear strain meters as well as inclinometers and extensometers were installed to
measure the movements of slope prior to failure. Seven steps of cuttings were carried out from the toe to make the slope unstable. The
model slope did not fail soon after completion of the final cutting, and it lasted 7 minutes before it finally failed. Clear increases in
the shear strain
had been measured as the cuttings progress. The obtained data of
and the displacement showed good agreement
in their reactions. Accordingly, it is proven that the potential risk of slope failure was detectable by monitoring of the shear strain in
the shallow section for simplicity.
RÉSUMÉ : Un essai sur modèle à grande échelle a été réalisé dans cette étude pour étudier la relation entre le risque potentiel de
rupture de pente et une augmentation de la déformation de cisaillement dans la partie peu profonde. Une pente modèle composée de
dépôts mous de Kanto-limoneux a été préparée avec une pente de 30 degrés et une hauteur de 3,5 m. Des capteurs de déformations de
cisaillement compacts ont été développés et installés avec des inclinomètres et des extensomètres pour mesurer les mouvements de
pente avant la rupture. Sept phases d’excavation ont été réalisées au pied pour rendre la pente instable. Le modèle de la pente ne s’est
pas écroulé tout de suite après la coupe finale, et il y a eu un intervalle de 7 minutes avant la rupture. Une nette augmentation de la
déformation de cisaillement
a été mesurée lors des excavations. Les données de
obtenues et le déplacement montrent un bon
accord dans leurs comportements. Ainsi, il a été montré que le risque potentiel de rupture d’une pente est détectable par le suivi de la
déformation de cisaillement au pied du talus pour la simplicité.
KEYWORDS: slope failure, monitoring, shear strain in shallow section, large scale model test.
1 INTRODUCTION
Slope failures frequently cause occupational accidents at
construction sites. It is also known that even a small collapse
can cause serious injury to workers. Therefore, slope failures
must be avoided for safety reasons, and temporary retaining
walls are needed to support slopes at worksite. In addition, the
practice of immediate escape is also important to save human
lives, and warning must be given prior to failure. Consequently,
monitoring of the slopes is needed to detect increase of the
potential risk of failure.
This paper will first summarize hazards that exist in the
slope works. Next it will explain a large scale model test
carried out to simulate the slope failure. It will also introduce a
compact shear strain meter developed to measure increase of
shear strain in the shallow section of slopes. Finally, its
applicability will be discussed in consideration of results from
the test.
2 HAZARDS IN WORKS ON SLOPES
Excavations and cuttings are frequently performed in many
aspects of slope works. Cuttings at the toe of slopes are
common in the building of retaining walls. However, cuttings
may cause the slope to be unstable even though its duration is
only short term. Itoh et al. (2005) reported that the volume of
collapsed soil blocks in almost 60 % of all accidents was less
than 50m
3
. Accordingly, serious damage to the workers are
caused by small amount of collapsed soil blocks. In addition,
safety must be maintained at the recovering operation after
disasters. Collapsed soil deposited is soft and loose after seismic
failure, and shear strength of remaining soil slopes was also
reduced by seismic acceleration. Therefore, slopes will become
unstable after earthquakes. Meanwhile, when quick operations
are also required to save refugees, sufficient time for both
installation of temporary structures to support the unstable
slopes and survey of the ground conditions in detail will not be
given.
Hazards exist to people who work on the slopes as well as
under the slopes. Moreover, the time for escape may be not
given to the adjacent workers. Consequently, warning prior to
the failures is important to save workers as well as an
installation of temporary supports.
3 A LARGE SCALE MODEL TEST
3.1
Preparation of model ground and method of model test
A model slope of 3.5m height, 4.0m width and 30 degrees
inclination was made by filling soil material as shown in Figure
1. Any compaction was not provided to simulate loose deposit
of collapsed soil after seismic disasters. Several sheets of
tarpaulins are placed to lubricate the friction between the
retaining wall and the soil so that the plane strain condition was
undertaken.
Soil material used in the test was Kanto loam that has soil
properties as shown in Table 1. Figure 2 shows the relationship
between the cone penetration resistance
q
c
and the depth from
the top of slope
d
. Values of
q
c
roughly show a linear increase
to
d
because the self-weight was loaded for consolidation.
