D205

Influence of groundwater seepage on the stability of a laterally confined dip slope in centrifuge
models〇Pongsakorn WONGCHANA, Shanzhi TAO, Thirapong PIPATPONGSA, Yosuke HIGO

Abstract
This research aims to investigate seepage-induced

triggered by applying surcharge (2.4kg) first, followedby the supply of water to observe the subsequent failure.

instability in a thrust-loaded dip slope using centrifugalmodeling. The study specifically focused on the failure
mechanism induced by groundwater seepage. Thestudy concluded that the failure mechanism in a dipslope involves losing support at the toe of the slope, andprogressive failure occurring depending on the rise in
groundwater level. Employing centrifuge modeling, it
replicates seepage-induced landslide conditions andFig. 1 Schematic diagram of the experimental setup

utilizes gauges to measure some quantities forassessing slope failure to validate the conceptualframework proposed in the previous study.
Materials and Methods
The slope model utilized Hiroshima sand with apermeability coefficient of 2.4×10-5 m/s, positioned on

Fig. 2 Slope model with instrumentations

a porous stone acting as a permeable rock layer with acoefficient of 5.0×10-5 m/s. This porous stone, withdimensions of 20 mm thick, 400 mm wide, and long,
facilitated more efficient water flow than the soil model.
The Hiroshima sand, compacted to 90% degree ofcompaction and 8% water content, was used. The
model, illustrated in Fig. 1, featured a 40° slope angle,Fig. 3. Laterally confined slope lying on bedding plane
and toe support.

30-mm thickness, 400-mm breadth, and 200-mm

Theocratical Calculation

length, with measuring devices placed for monitoring

This study employs the concept of dip slope with lateralwater seepage and observing slope behavior (Fig. 2).

confinement and toe support. The configuration of the

In the experimental procedure, the slope model wasinclined surface is illustrated in Fig 3, where the slope

triggered by both surcharge, serving as a moving

is stabilized by lateral, and toe supports. Consequently,

boundary to push the slope in the model test, andthe dip slope can be divided into two distinct sections:watering, simulating groundwater seepage. Initially,① the main slope block, and ② the toe segment. The

the centrifugal acceleration was loaded and maintained

gravitational forces acting on the soil are represented

at a constant 20G. Subsequently, the slope failure wasby Eqs. (1) and (2). Furthermore, the components of thesoil's weight in terms of the normal forces, FN,Therefore, total resistance (RT) can be combined asdetermined by Eqs. (5) and (6) and the driving force,

Eq. (18) and the corresponding factor of safety can beFD, determined by Eq. (4), are regulated by the amounts

calculated as Eq. (19)of surcharge (∆𝑊) and water supply (𝑛! , 𝑤𝑎𝑡𝑒𝑟 𝑟𝑎𝑡𝑖𝑜) as

𝑅/ = 𝑅* + 2𝑅, + 𝑃%
FS = 𝑅/ ⁄𝐹'appeared in Eq. (3).
𝑊" = 𝛾𝐵𝑇𝐿
𝛾𝐵𝑇 #𝑊# =cot (𝛼)2𝛾 = 𝛾$ (1 − 𝑛! ) + 𝛾%&$ 𝑛!
𝐹' = 𝑊" sin(𝛼) + ∆𝑊(𝑠𝑖𝑛(𝛼) − 𝑡𝑎𝑛 (𝜙( ) ∙ 𝑐𝑜𝑠 (𝛼))𝐹)" = 𝑊" cos(𝛼)𝐹)# = 𝑊#

(1)
(2)
(3)
(4)
(5)
(6)

Results and discussion
Following Pipatpongsa et al. (2022), rd is computedwith Eq. (20), considering both σh' and σv'. Also, rd canbe derived from earth and water pressures at the samelevel. rd ranges from -1 (active) to +1 (passive).

The shear resistance along the bedding plane (RB) isrd =governed by the contact area of the interface.
Additionally, the lateral shear resistance (RL) is dictated

(18)
(19)

s h' - s v'

(20)

2 (s tan f + c)(s tan f + c)'v

'hIn the comparison of theoretical predictions andby the contact areas of the lateral support and can beexperimental results (Fig. 4), the surcharge weight wascalculated by the frictional force relying on the average

set at 2.4 kg, and rd=1 for a passive slope in thepressure exerted on the laterally confined surface (PL).
Consequently, the equations for determining RB and RL

failure (nw=0.11). Experimental results show a stable
FS with the surcharge(2.4kg), decreasing after water

are provided in Eqs. (7) to (10) respectively.
𝑅* = 𝐹)" 𝑡𝑎𝑛(𝜙+ ) + 𝑐+ 𝐿𝐵𝐹)"
𝑃," =𝐾 + 2𝑐. G𝐾𝐵𝐿 -prediction line. Groundwater was predicted for slope(7)(8)supply (nw=0.15) and reaching collapse when waterincreasing (nw=0.20).

Shear strength reduction ratio (rd), (Dawson et al.,19992)) is defined as follows.
𝑟. =tan(𝜙. ) 𝑐.
=tan(𝜙)𝑐/𝑅, = I (𝑃," 𝑡𝑎𝑛(𝜙% ) + 𝑐% )𝐿𝑑𝑡

(9)
(10)

0

Furthermore, the force that remains (FP) from the upper
portion of the slope exerts pressure on the toe segment,following Eq. (11). The potential for toe sliding
emerges when FP surpasses the resistance of the toesegment. At the termination point of the slope, the toe
support holds the equilibrium of three forces: thenormal force (Np), the shear force (SP), and the lateralresistance (Rs). These three forces can be described by
Eqs. (14), (15) and (13), respectively.

Fig. 4. Comparison between theoretical prediction andexperimental results

Conclusions
This study confirms that groundwater rise significantly
impacts slope failure. The comparison shows good
agreement between predictions and experiments,
highlighting water rise as a destabilizing factor.

𝐹1 = 𝐹' − 𝑅* − 2𝑅,𝐹)#𝑃,# =𝐾 + 2𝑐. G𝐾𝐵𝑇 ∙ 𝑐𝑠𝑐(𝛼) -(11)However, the experimental rd, larger than the predicted(12)

rd=1, leads to larger groundwater seepage triggering the

𝑅% = I (𝑃,# 𝑡𝑎𝑛(𝜙% ) + 𝑐% )𝑡 ∙ 𝑐𝑜𝑡(𝛼)𝑑𝑡(13)

𝑆1 = 𝐹1 cos(𝛼) − 2𝑅%
𝑁1 = 𝐹1 sin(𝛼) + 𝑊#
𝑆1 = 𝑁1 tan(𝜙$ ) + 𝑐$ 𝐵𝑇 ∙ 𝑐𝑠𝑐(𝛼)𝐹1 = 𝑃%(𝑐$ 𝐵𝑇 ∙ 𝑐𝑠𝑐(𝛼) + 2𝑅% )cos (𝜙$ ) + 𝑊# sin(𝜙$ )=cos (𝛼 + 𝜙$ )(14)/0(15)(16)(17)

slope collapse.
Reference
1.
2.

T. Pipatpongsa, K. Fang, C. Leelasukseree and A. Chaiwan(2022): Stability analysis of laterally confined slope lying
on inclined bedding plane, Landslides, 1-19.
Dawson, E.M., Roth, W. and Drescher, A. (1999): Slopestability analysis by strength reduction, Geotechnique,49(6), 835–840.