Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Model Tests with a Transparent Soil to Observe Behavior of Buried Structuresdue to Neighboring Constructions
Shun-ichi KOBAYASHI
Associate Professor, Department of Science and Technology, Kanazawa University, Kanazawa, Ishikawa, Japan
Email: koba@se.kanazawa-u.ac.jp

Kohei NOGUCHI
Graduate Student, School of Natural Science and Technology, Kanazawa University, Kanazawa, Ishikawa, Japan

Yuki YAMAKURI
Student, Department of Science and Technology, Kanazawa University, Kanazawa, Ishikawa, Japan

Hidekazu MAKI
Graduate Student, School of Natural Science and Technology, Kanazawa University, Kanazawa, Ishikawa, Japan

Tatsunori MATSUMOTO
Professor, Department of Science and Technology, Kanazawa University, Kanazawa, Ishikawa, JapanABSTRACT
Construction works in urban areas must satisfy not only the safety of a newly constructed structure itself but also thesafety of existing structures adjacent to the new one. Visual observation might be a first step to understand the interactionof a newly constructed structure and existing structures adjacent to new one, if a soil would be visible. Recently, Ezzeinand Bathurst (2011) reinvented a transparent soil for laboratory modelling. This technique is fundamental and versatilefor geotechnical model testing. The principle of a transparent soil is to match the refractive indices of transparent grains
and pore-liquid. There have been many combinations of grain-materials and pore-liquids proposed (Ganiyu et al., 2016).
However, though the principle is simple and straight-forward, there seems to be a plenty of know-hows which should bemastered and established to conduct laboratory model tests with transparent soils. In this article, the authors would liketo present such procedural know-hows and the application of them for some demonstrative experiments.
Key words: Transparent Soil, Refractive index matching, Neighboring construction, Buried structure

1. Background and objectives of this study
Construction works in urban areas must satisfy notobservation might be a first step to understand theonly the safety of a newly constructed structure itself butstructures adjacent to new one, if a soil would bealso the safety of existing structures adjacent to the newtransparent and visible, but it is generally impossible.

interaction of a newly constructed structure and existingone. Construction works are always accompanied byRecently, Ezzein and Bathurst (2011) reinvented achange in stresses and deformations of a ground next totransparent soil for laboratory modelling. This techniquethe construction site. For example, change might be

is fundamental and versatile for geotechnical modelcaused due to the loading effect, such as installing

testing. The principle of a transparent soil is to match thestructures with pile-driving or press-in, or due to therefractive indices of transparent grains and pore-liquid.

unloading effect, such as un-installing, excavation,

There have been many combinations of grain-materials

drilling or tunneling. This change of the soil stateand pore-liquids proposed (Ganiyu et al., 2016). However,sometimes induces troubles of the existing buried

though the principle is simple and straight-forward, there

structures, such as piles, foundations and pipelines. Visual

seems to be a plenty of know-hows which should be- 417 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Properties of silica particles

Diameter

0.2 − 1.0 [mm]Density

2.20 [g/𝑐𝑚3 ]Max. void ratio

1.380

Min. void ratio

0.873

Slope of the CSL

M = 1.873

Refraction index

n = 1.4585 (24.7°C)

Deviatoric Stress q [kPa]

Table 1.

900
800
700
600500400300200
10000510
Axial Strain ea(%)

Fig. 1

Axial strain vs deviatoric stress (CD test)

mastered and established to conduct laboratory model
tests with transparent soils.

2.1. Index matching method
In general, two type of the change in direction of lightoccur on the boundary of two different media. One isreflection and the other is refraction. However, if therefraction index of two materials is same, no reflection andrefraction occur.

Volumetric Strain (-)

2. Transparent model ground

This nature directly stands for the possibility of

0.14
0.12
0.1
0.08
0.06
0.04
0.02
0-0.02

c’=50[kPa]510
Axial Strain(%)

combination of transparent solid particles and saturated
Fig. 2pore liquid is selected. Early attempts of this technique forvisualization experiments are summarized in the literature

100[kPa]
200[kPa]

0visualization inside the granular media, if a suitable

1515

Axial strain vs volumetric strain (CD test)

1000

by Ezzein and Bathurst (2011).
Deviatoric Stress q [kPa]

After the intensive quest of a suitable combination ofmaterials which possesses a similar mechanical propertiesof sands, Ezzein and Bathurst also proposed the use of
fused silica as solid transparent particles and mineral oil
as fill liquid.
2.2. Materials for transparent model groundIn this study, transparent silica particles are used astransparent particles, because they can be purchased easily800

CSL (M=1.87)

600
400
2000in Japan. Physical properties of the transparent silica

0200400
Mean Effective Stress p' [kPa]

Fig. 3

Effective stress path (CD test)

particles are summarized in Table 1. CD triaxial tests arecarried out with three densely compacted samples of silica

600

particle deposits saturated with water. Consolidationpore fluids. Such fluids can be divided into two groups:

pressures and relative densities of these samples at theoily fluid and aqueous solution.

start of shearing are ( 50 [kPa] : Dr = 90.3 [%] ),( 100 [kPa] : Dr = 102.0 [%] ) and ( 200 [kPa] : Dr =85.2 [%] ), respectively. Relations of axial strains andIn the oily fluid group, mineral oil refined frompetroleum is cheap and easily handled. Several industrial
products are available in Japan. Density, viscosity anddeviatoric stress q, relations of axial strains and volumetricrefraction index are inter-dependent each other, andstrains (Positive in dilation) and effective stress paths are

refraction index of a mixture of two mineral oils can beshown in Figs. 1, 2 and 3, respectively.

approximated by a linear relation of weight fraction.

On the contrary, there are some feasible options for

Mixture of “Moresco White P-40” (n = 1.4469, at 20.9- 418 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

1.5011, 25 Deg. C, Viscosity 14.9 [cP] at 25 Deg. C:

1.6

Shin-Etsu Chemical Co., Ltd.). Silicon oils are chemicallyRefractive index

1.55

synthesized and have larger variety of refraction index
than mineral soils, but silicon oils are more expensive in

1.5

general.
1.45

In the aqueous solution group, sucrose (roughlyspeaking, sugar) solution is cheap and feasible.

1.4

addition, aqueous solutions are far better than oily liquids

1.35

because they are easy to handle for cleaning of testing

1.3

devices and reuse/disposal of samples and to keep the0

10 20 30 40 50 60 70 80 90 100

laboratory environment clean.

Sucrose (w/w) [%]Fig. 4

InHowever, it should be carefully handled, becausevery dense sucrose solution (67.1 % w/w) should be used

Refractive index of Sucrose solution (20 Deg. C)

to match the refractive index of silica particles ( n =1.4585 ) as shown in Fig. 4. In addition, such dense

1000

sucrose solution is highly viscous as shown in Fig. 5. Once

Viscosity [cP]air bubbles are trapped into a viscous liquid, it is almost
impossible to remove them. A countermeasure to avoid air

100

bubbles and to make fully saturated transparent model
ground with sucrose solution are described later.
102.3. How to make a model ground
Model ground should be completely saturated withpore fluid to avoid any refraction and reflection in a10Fig. 51020 30 40 50
Sucrose (w/w) [%]6070specimen.
In case of mineral oil, viscosity is a little bit higher

Viscosity of Sucrose solution (20 Deg. C)

than that of water. So, liquid pluviation technique can be

Deg. C, Viscosity 3.6 [cP]: Moresco Corp. ) and “Cosmo

applied to make a model ground.

White P-60” ( n = 1.4540 , 21.1 Deg. C, Viscosity
7.9 [cP] : COSMO Oil Lubricants Co., Ltd.) with thetoo viscous to use liquid pluviation technique, because

On the contrary, in case of sucrose solution, liquid isweight fraction 1: 16 is used in this study. Silicon oilsentrapped tiny air bubbles don’t disappear. Therefore, acan be used as alternative, such as, “KF-96-10cs” (n =liquid replacement method as mentioned below is1.4002 , 25 Deg. C, Viscosity 9.35 [cP] at 25 Deg.

proposed to make saturated model ground with sucrose

C :Shin-Etsu Chemical Co., Ltd.) and “KF-56” ( n =solution.

Photo 1.

Preparation procedure of a transparent model ground saturated with sucrose solution(Container size: w=45mm, D=55mm, H=88mm)- 419 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Fig. 6 Plan (Left) and section (Right) views of the testing box, the embedded pipe (Red) and the installed pile (Green)

Vertical deflection [m]Distance from pipe end, x[m]Fig. 7-0.004-0.002 00.200.002
0.004
0.006
0.008
0.01
Deflection distribution of the embedded pipe estimatedby image analysis

the above mentioned preparation procedure of atransparent model ground saturated with sucrose solution.
Water is dyed with red-coloring to monitor thereplacement process easier.
3. Demonstrative experiments
3.1. Behavior of an embedded pipe subject to pile
installation in a near field
In this series of tests, behavior of a horizontally
Photo 2.

Deformation of the embedded pile observed throughthe transparent model ground. Before pile installation (Top) andafter 90 mm-pile installation (Bottom)

A liquid replacement method consists of two steps.
Firstly, a model ground is saturated with water by liquid
pluviation technique. Secondly, heavy sucrose solution isslowly injected from the bottom of a container to makeupward permeable flow and replace water with sucrose
solution. During the second stage, sucrose solution was
warmed to about 60 degrees Celsius to lower the viscosity
and to shorten a preparation period. Photo. 1. illustrates

embedded pipe subjected to pile installation in a near field
is observed. The embedded pipe is made of ABS(Acrylonitrile Butadiene Styrene) with length of 350 mm,
outer diameter of 10.0 mm, thickness of 2 mm and bending
stiffness EI = 1.02 × 106 [N ∙ mm2 ] . 7 pairs of strain
gauges attached to the pipe to measure the bending
moment. A model ground is a mixture of silica particles
and mineral oil prepared by liquid pluviation andcompacted to around Dr = 80[%] . A close-ended
aluminum pipe pile with outer diameter 10 mm, thickness
1mm and Young’s modulus E = 59.0[GPa] is verticallyinstalled.

- 420 -

One demonstrative case is shown here. Plan andProceedings of the First International Conference on Press-in Engineering 2018, Kochi

Fig. 8

Photo 3.

(a)46.6 N (End of this load step)(b)

51.9 N (Start of this load step)Anchor head

Embedded anchor head before pull-out

Photo 4.

(c)51.9 N (After 150 sec.)(d)51.9 N (After 180 sec.)

Anchor failure observed from both sides;(a) End of 46.6N load step, (b) Start of 51.9 N load step, (c)After 150 sec., (d) After 180 sec.

Fig. 9installation is shown in Fig. 7. It should be noted that aTime-Anchor Load, Displacement relations

rigid motion of the embedded pipe cannot be estimated bysectional views of a testing box, an embedded pipe and astrain distributions measured with strain gauges. In thisvertically installed pile are illustrated in Fig. 6. Thesense, the use of a transparent model ground crucial toembedded pipe is horizontally placed at the depth of 90

understand the behavior of the embedded pipe.

mm from the surface. Boundary conditions of the Bothends of the pipe are free. Deformation of the embedded

3.2. Behavior of an embedded anchor head subject topipe can be observed through the transparent modelpull-out

ground as shown in Photo. 2. Transparent thickness fromIn this series of tests, behavior of an embedded flip-the side wall to the embedded pile is about 80 mm.

type anchor head subject to pull-out at a constant load isDeflection distribution of the embedded pile after the pileobserved. A dimension of a testing box is w=200 mm,- 421 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

soil. Among them, combinations of transparent silica
particles and mineral oil / sucrose solution are used in thisstudy. As the laboratory environment, re-use and disposalof testing materials are concerned, an aqueous solution
might be better than oily fluids. However, if such anaqueous solution with high viscosity is used for index
matching, special attention should be paid for complete
saturation of a model ground. To tackle this difficulty, theauthors propose a liquid replacement method. Someexperimental applications to investigate the interactions ofburied structures/objects and surrounding soils are alsopresented to demonstrate the advantage of a transparent
soil.
5. Acknowledgements
This study is partially supported by the Japan Society
for the Promotion of Science (JSPS) KAKENHI Grant
Number 16K06489.
References
Ezzein, F. M. and Bathurst, R.J. 2011. A Transparent Sand
Photo 5.

for Geotechnical Laboratory Modeling. GeotechnicalTrajectory of feature points during the experiment

Testing Journal, Vol. 34, No. 6, pp. 590-601.
d=200mm and h=400mm. A model ground is a mixture of

Ganiyu, A. A., Rashid, A. S. A. and Osman, M. H. 2016.

silica particles and sucrose solution with height of about

Utilisation of transparent synthetic soil surrogates in

250mm. An anchor head made of hard synthetic resin

geotechnical physical models: A review. Journal ofplastic as shown in Fig. 8. This anchor head is horizontallyRock Mechanics and Geotechnical Engineering, 8(4),placed in the transparent model ground at the depth of 217

pp. 568-576.

mm from the surface as shown in Photo. 3. The anchor

Trackpy: Fast, Flexible Particle-Tracking Toolkit, URL

head is subject to constant pull-out loads step by step.

https://soft-matter.github.io/trackpy/v0.3.2

Creep-like behavior is observed just before the pull-out[Accessed: 15- March- 2018]

failure as shown in Fig. 9. Photos of anchor movementfrom both sides of the testing box are summarized inPhoto. 4. Trajectory of feature points using tracking
software “Trackpy” is shown in Photo. 5. This tracking
result is preliminary because real 3D movement is notcorrectly evaluated. However, the movement of the anchor
can be clearly detected.
4. Concluding remarks
In this article, a transparent soil based on therefractive index matching technique and its application togeotechnical model testing are presented and briefly
discussed. There are various combinations of solidtransparent particles and pore fluids to make a transparent- 422 -