D16

Effect of side frictions in a centrifuge model of slope sliding along a bedding plane〇Krit AROONWATTANASKUL, Thirapong PIPATPONGSA, Takafumi KITAOKA, Hiroyasu OHTSU

To understand more about the effect of side

The physical models were made of moist Edosakifrictions, this study examines an empirical estimation

sand. The basic properties of Edosaki sand and itsof the side frictions effect on a slope sliding along ainterface with Teflon sheet are shown in Table 1. The

bedding plane by using a failure envelope. Two seriesmodel configuration and structure of the instrument isof experiments; slope width 20 cm and 40 cm, wereshown schematically in Fig. 1(a). The model wasconducted with a variation of thickness, slope length,

divided into two parts, basal support, and slope part.

and slope angle. The results of the slope width 40 cm

Basal support and slope part were placed on a rigid

were employed to predict centrifugal acceleration atplane covered by a Teflon sheet for simulating the low

the failure of the slope width 20 cm model. The

friction interface plane. Moist sand with an optimumrelationship between normal force and driving force

water content of w =15.1% was compacted to achieve

was obtained experimentally to validate the former

a bulk density of ρ =1860 kg/m3. Pressure gauges

predictive value.

were installed in the slope part during the compaction.
Testing conditions were varied by thickness, slope
width, slope length and slope angle.

1. Introduction
In the process of studying the behavior of soil
structures using centrifuge modeling, the model
boundaries provide side frictional supports the model,
and this effect may lead to an uncertain prediction
when extrapolated to a prototype scale. The
lubrication systems in laboratory tests, i.e., grease
method and plastic sheet method (Fang et al., 2003)
have been studied to improve aforementioned problem.

(a) Model configuration

However, these systems could not eliminate lateral
friction

duetodifficultyincontrolling

theexperimental procedures; a better understanding of theeffect of side frictions is still necessary.
2. Methodology
Table 1 Basic properties of Edosaki sand and interface
Bulk unit weight (γ)

18.2 kN/m3

Unconfined compressive strength (σc)

5.8 kN/m2

Interface friction angle (ϕi)14.7°(b) Instrumented slope modelFig. 1 Slope model with instrumentations

Apparent adhesion (ci)

0.2 kN/m2

After the preparation of basal support and slope part,

Internal friction angle (ϕ)

44.2°

a uniform displacement boundary using surcharge wasapplied at the slope top edge by using the fabricated

The gaps between each line represent the effect ofwooden roller with a deadweight container. Four laser

resistance on each part. An example of the predictedsensors were installed in various positions (Fig.1(b))

and experimental value in the slope width 20 cm

for different objectives, e.g., investigating themodel is listed in Table 2. The prediction of an

upheaval at basal support and monitoring slope
displacement.

Duringthetest,thecentrifugal

unknown value calculated by using a constant value ofother parameters in the following equations.

acceleration was gradually increased until 50g at eachsurcharge load while monitoring the initial collapse of
the model. The centrifugal acceleration was increased
until the first failure occurrence.
3. Results and discussions

where FN: Normal force per unit area, FD: Driving
force per unit area, Δm: surcharge, ϕr: roller’s friction
angle, n: centrifugal acceleration, g: gravitational
acceleration, c1: gradient and c2: y axis-intercept.
Table 2 Predicted and experimental value
Parameters
Centrifugal acceleration (n)Predicted

Experimental

value

value

23.3

28.4

The failure mode in a long slope length model(30cm) occurred Pop-up wedge failure (Fig.3(a))
while those in a short slope length model (20cm)
occurredFore-thrust

failureonly(Fi.g.3(b)).

Experimental results confirm that different failuremodes would occur caused by variation of slope
Fig. 2 Experimental result with linear regression
The equilibrium of a slope was simply evaluated by
the equilibrium of force along the bedding plane. The

length. Therefore, the length of the slope needs to beconsidered in the design purpose because it also
affects slope stability.

forces applying to the slope are the normal and thedriving forces. The failure envelope can be determinedand plotted in terms of the normal and driving forces
per unit contact area of a model along a bedding planein prototype scale as shown in Fig. 2. Using dataobtained from slope width 40 cm experiments (circlesymbol) to approach the linear regression (blue line)
for predicting the test results in slope width 20 cm.
The

derivedexpressionshowsana) Slope length 30 cm

acceptableb) Slope length 20 cm

Fig. 3 Modes of failure

agreement with the experiments. Some data which lie

Referenceout of the range represents testing results which either

Fang, Yung-Show, et al. "Reduction of boundary friction in

failed by different failure mode or retest many times.

model tests." Geotechnical Testing Journal 27.1 (2004): 3-12