Use of rubber for improving the performance of domestic …paginas.fe.up.pt/~eurodyn2014/CD/papers/034_MS01_ABS_1889.pdf · ground improvement techniques, proved that these techniques

Use of rubber for improving the performance of domestic buildings against seismic

liquefaction.

Georgios Nikitas1, Subhamoy Bhattacharya

1, Masayuki Hyodo

2, Atsuhi Konja

3, Stergios Mitoulis

1

1Department of Civil and Environmental Engineering, University of Surrey, Guildford, United Kingdom

2Department of Civil Engineering, Yamaguchi University, Ube, Japan

3 Hokoku Engineering Corporation, Osaka

email: [email protected], [email protected], [email protected], [email protected],

[email protected]

ABSTRACT: Soil liquefaction as experienced in most of the latest large earthquakes, has left behind permanent large surface

deformations on the soil that set structures unusable and very difficult to repair. Existing mitigation methods, such as deep pile

foundations, gravel drain columns and dynamic compaction can reduce the effects of liquefaction on structures, but their costs

seem prohibitive for most common residential engineering applications. This research provides experimental results from a

series of shaking-table tests carried out at 1g of a new low cost mitigation technique against liquefaction. This technique has

only recently been developed in Japan in order to find immediate application on typical domestic houses following the 2011

Tohoku earthquake. The technique is based on, shredded waste tyres packed in permeable sandbags are used for ground

improvement underneath the structure. A number of parametric scenarios concerning the thickness of the ensuing elastic base

were considered. The experiments indicate that the tyre shreds’ addition can act both as a seismic isolation (i.e. filtering effect)

as well as an efficient drainage method. This mitigation approach also proposes an innovative and sustainable way to reuse

waste tires, which otherwise set a serious environmental problem due to their large volumes produced and their recycling

complications.

KEY WORDS: Liquefaction mitigation, shaking table test, shredded tyre foundation, soil improvement

1 INTRODUCTION

Under moderate to large vibrations, loose to medium density

saturated soil deposits are prone to liquefaction; see for

example the damage to the Tokyo city following the MW 9.0

magnitude earthquake that struck the Tohoku region of Japan

on 11th

March 2011. The earthquake caused great damage to

structures and infrastructures around Tokyo Bay area, due to

liquefaction phenomena. The liquefaction phenomena were

widespread in the area causing damage to the water and

sewerage pipelines, destroying highways and pavements and

making many structures useless due to permanent surface

deformations. Figure 1 shows typical settlement pattern

observed in Urayasu city in Tokyo bay area following the

earthquake. However, the excellent performance of buildings,

such as the International Airport in Tokyo (also known as

Haneda Airport) which was built on reclaimed land, using

ground improvement techniques, proved that these techniques

can actually mitigate liquefaction hazards. In fact, the

earthquake had no effects on the airport, so it was operational

from the very next day of the earthquake. [1]

Many methods for liquefaction mitigation have been

developed throughout the years, but they tend to be used only

in big projects and their cost is prohibitive for domestic

houses (typical one to two storey houses). The current

research considers such an economic mitigation technique

against liquefaction. In the proposed method, shredded scrap

tires are used to minimize the earthquake and liquefaction

impacts on a domestic building, such as a common 1 story

house. The scrap tires are shredded into small pieces (around

2.5 mm wide) and then, after being put inside sandbags, are

placed underneath the foundations of the structure. The layout

of the proposed mitigation technique can be seen in Figure 2.

Figure 1. Differential settlement of a building in Urayasu, in

Tokyo bay area.

The perceived benefits of the proposed technique are:

a) Due to the increased permeability of this resulting sub-

base (because of the larger than sand void ratio), it is

expected to effectively act against the pore water pressure

built up that is a pre-requisite for liquefaction.

b) With the added damping and elasticity of the new

foundation type is supposed to reduce the transmission of

the shear waves, so actually to reduce the acceleration

transmitted to the structure.

For verifying the above hypothesis, a series of 1g shaking-

table experiments were conducted in order to provide

experimental data that could validate and scrutinize the

Proceedings of the 9th International Conference on Structural Dynamics, EURODYN 2014Porto, Portugal, 30 June - 2 July 2014

A. Cunha, E. Caetano, P. Ribeiro, G. Müller (eds.)ISSN: 2311-9020; ISBN: 978-972-752-165-4

259

mailto:[email protected]





performance characteristics of the developed technique. Also

another important aspect of this technique is that it provides

an innovative way to reuse waste tires. The disposal of waste

tires has been a big environmental issue, because of the large

amount of tires produced worldwide and the durability of their

remainder as a waste material.

Figure 2. Layout of the proposed ground improvement

technique.

2 EXPERIMENTAL PROCEDURE

2.1 Test setup

The 1g shaking-table tests were conducted in the

Earthquake and Large Structures Laboratory (EQUALS),

which is part of the Bristol Laboratories for Advanced

Dynamics Engineering (BLADE) in the Faculty of

Engineering at the University of Bristol (U.K.). The actual

shaking table consists of a 3m by 3m cast aluminium platform

weighing 3.8 tonnes, with a 15 tonne capacity and allows

simulating motion in all possible 6 degrees of freedom. The

platform can accelerate horizontally up to 3.7g with no

payload, 1.6g with a 10 tonne payload and vertically up to

5.6g and 1.2g respectively. The shaking table is surrounded by

a strong floor and adjacent strong walls up to 15m high. [2]

For the test arrangement, a rigid plastic container

(1120mm x 920mm x 600mm) was rigidly mounted centrally

on the top of the table. In this design, the shear stiffness of the

end walls is much higher than the stiffness of the soil layers

contained. The end walls and the base of the containers are

designed to be rough, so that the development of shear

stresses is in vertical plane at the interface between container

and soil. [3] The container structure was separated in 2

partitions by a wooden separator (920mm x 550mm x 20mm).

One partition had the model, with the cushion of tire chips

underneath and the other had the model without the cushion.

An identical scaled slab foundation was put on the soil surface

in both cases. The main objective is to assess the qualitative

response differences that emerge when the tire-based

foundation enhancement is in place. Such a technique, of a

single box and single shaking for both alternatives, is

expected to minimize artifacts that may be induced due to

testing differences between two independent testing

arrangements.

Figure 3 illustrates in detail the top and side views of the

model apparatus that was tested. The locations of the

transducers used along with every relevant dimension for

reproducing the setup are also shown. A thorough description

of all the parameters included in the design is given below.

Figure 3. Top and side views of the test arrangement.

2.1 Materials and instrumentation used

The tire chips in Figure 3, were made by shredding ordinary

scrap tires in particle sizes between 1mm and 5mm. The chips

were packed later in small uniformly perforated bags made

out of cellophane with dimensions 89mm x 67mm x 67mm

and total weight of 150 grams. These plastic tire bags, were

evenly arranged underneath the model slab foundation with a

thin layer of soil (67mm) covering the gap between tires and

slab. Some of the properties of the tire chips are listed in

Table 1 and are similar to Hyodo et al [4]

Table 1. Physical properties of Tire Chips.

Material D50

(mm) emin emax

γdmin

(kN/m3)

γdmax

(kN/m3)

Tire

Chips 2.45 1.600 2.320 35.00 45.00

Proceedings of the 9th International Conference on Structural Dynamics, EURODYN 2014

260

The soil was intended to have a low density to ensure the

liquefaction occurrence. The loosely poured liquefiable soil

base consisted of Redhill Sand 110, which is sieved silica

sand with a total quartz content of 98.8%. The typical physical

properties of the sand used are summarized in Table 2. [5]

Table 2. Physical properties of Redhill Sand 110.

Material D50

(mm) emin emax

γdmin

(kN/m3)

γdmax

(kN/m3)

Φ

(o)

Redhill

110 0.12 0.547 1.037 12.76 16.80 36

For the slab foundation models, pieces of MDF wood

(200mm x 200mm x 20mm) were used to form a rigid

uniform base. On each piece of wood, 2 steel weights of 0.6kg

each were mounted centrally and later where covered with the

carton house models. Each model was scaled to weight a total

of approximately 2kg.

Identifying the liquefaction phenomenon necessitates

keeping track of the water pressure and its subsequent rise

inside the soil body. For measuring the water pressure along

the different depths indicated (in Figure 3), six nos Druck

PDCR 811 Pore Pressure Transducers (PPTs) were employed.

Acceleration is the other piece of vital information to be

recorded during dynamic testing. For such measurements 6

ADXL335 MEM accelerometers (3-axis, ±3g), which were

specially modified for underwater use, were employed. Such

instruments were identical to those devised by Bhattacharya et

al. 2012 [6], and were found as previously to produce quality

measurements, comparable to much more expensive uniaxial

instruments for a wide band of frequencies. These

accelerometers were calibrated using SETRA accelerometers

as reference.

2.3 Steps followed

An analytical break down of the testing process includes the

following steps

a) The container is separated in two partitions and marked on

each side with height indications. No mechanical measure

was taken for securing the divider plate (cut to

dimensions) to the box structure. The sand poured inside

the box was the only means of holding the plate in place.

No precautions were taken for addressing wave reflection

from the boundaries and the model is considered to be

representing an infinite space foundation. There is the

provision to use in a follow up improved test foam

coverings on all sides, as in Bhattacharya et al., 2012, but

for the current work no specific study of boundary effects

is pursued.

b) After the container is rigidly mounted on the shaking table,

the Redhill 110 sand is pluviated inside, similarly to dry

deposition method by Isihara[7]. The sand is placed in 4

layers with thicknesses of 150mm, 66.67mm, 83.33mm

and 50mm respectively from bottom to top. During the

process the instrumentation was installed at the locations

shown in Figure 3. An relative density of 45% is achieved.

c) For the saturation process water is poured locally from the

top until full saturation is achieved. This is considered to

be done when the top water level remains unchanged.

Subsequently, the excess water above the sand layer is

soaked so that only a surface of wet sand is visible. Even

minute disturbances of the container could cause a thin

film of water to resurface.

d) The foundation models are placed on the center of each

partition as seen in Figure 3. The bases are leveled to

assure that in both cases a zero initial tilt is the starting

point. An initial recording without any shaking is taken so

that detrending of the data can be later performed.

e) The following shakings were imported to the model:

i. The apparatus is shaken first with low amplitude

white-noise (0 to 80Hz), independently in each of the

x, y and z axes, in order to retrieve all relevant modal

characteristics of the scaled models.

ii. The model ground is shaken with the 40% scaled (in

terms of Peak Ground Acceleration) Christchurch

earthquake of 22 February 2011. A true earthquake is

selected since initially it was thought that a simple

harmonic input motion would clearly favour one over

the other model in terms of resonant response. This

biasing cannot be waived by the use of a true

earthquake recording but in its case this is more natural

and also representative of the full-scale analogue.

iii. Once the above procedure is completed, a second

shaking with the actual non-scaled Christchurch

earthquake takes place. This is an extreme unrealistic

event scenario which only serves to assess the added

magnitude of damage to be incurred.

3 Test results

3.1 Response of the models under white noise test

Before getting into the earthquake response outcomes, it

is interesting to see how the apparatus natural frequencies in

the two cases with and without tire chips under the foundation

would change. Intuitively the less rigid elastic foundation is

expected to respond at a lower fundamental frequency,

because the building supported on tire base will have lower

stiffness and hence lower natural frequency. Additionally this

softening effect is probably expected to be more pronounced

along the z axis where the spring action of the tire chips is

more evident. Yet it is interesting to also uncover whether the

initial white-noise shaking to extract the frequency

characteristics has an impact on them. Figure 4 shows the

acceleration spectra for all 3 axes during their relevant white

noise shaking. Odd number accelerometer names refer to the

tire foundation while their increasing value indicates an

instrument closer to the surface (see Figure 4). Interestingly,

on the x and y axes, the dynamic characteristics seem almost

identical regardless of the foundation type, but in the case of z

axis they are different when comparing their surface (i.e.

above the elastic tire base accelerometers Acc5z, Acc6z)

values. Evidently the stiffness drop appears as expected. Thus

interestingly on x and y axes the two models behave the same

for any input acceleration and the tire inclusion affects only

the vertical movement. Logically such an image is expected to


261

pertain also after the main shaking. It should be noted that all

spectra were calculated based on uncalibrated data.

Figure 4. Acceleration Spectra for white noise dynamic

loading on X (top), Y (middle) and Z axis (bottom).

3.2 Response of the models under Christchurch earthquake

Further the application of the scaled and the actual

Christchurch earthquake accelerations (reproduced along all

directions) is expected to show some changes resulting in the

dynamic characteristics. Identifying these qualitative changes

is the main aspect of the current research work. It should be

mentioned that no additional white noise tests were run with

the completion of the main shaking. Thus the comparison will

not take the form of a simple contrast of spectra alike to the

ones in Figure 4. Rather a more elaborate approach is

pursued, which will not be altered by any extra possible

modifications from additional white noise tests. Figure 5

shows the time histories of excess pore water pressure ratios

ru (PPTs located at 0cm, 15cm and 30cm from the bottom of

the box as illustrated on the inset) and the synchronous input

accelerations on the x and y axes respectively during the 40%

scaled Christchurch earthquake. The instruments correspond

to the case without the ground improvement technique. It is

expected during liquefaction that the pressures start rising

when the dynamic load is applied. It is noted that the pressure

increase varies with different depth, giving an extreme change

closer to the surface. This is a clear indication of the

inhomogeneous liquefaction observed in these experiments.

The relative pressure magnitude has already been scaled with

depth and was expected to rise evenly over all depths. As a

matter of fact different phases in the increasing pressure

evolution can be distinguished as seen also in the literature

even for real-scale field data [8]. The initial shaking seems to

bring a smooth almost linear pressure rise while the

subsequent larger accelerations impose a largely fluctuating

behavior. After the 16s the pressures in all location has

stabilized until the 41s, when their decay which matches the

stop of the ground shaking begins. Indicatively it can be seen

that this decay occurs with different rate again depending on

the depth of the PPT.

Figure 5. Pore pressure rise during the 40% scaled

Christchurch shaking and its acceleration time histories


262

Having observed the pressure effect that the earthquake

has on the ordinary foundation it is time to examine it aside

the tire foundation. In Figure 6 the closer to surface PPTs

from the two models (i.e. PPT 1C and 2C) are plotted

together. As observed in Figure 5, PPT 2C was the instrument

that produced the most extreme pore pressure rise. It can be

seen that when an elastic inclusion is in place the pore

pressure does not rise to high values. This is the best means of

proving the effectiveness of such a foundation solution, which

can effectively eliminate the liquefaction phenomenon, which

is synonymous to pore water pressure rise. Possible

explanations for the attained result could be the higher

permeability of the rubber cushions that do not strongly resist

the water movement. To be more precise Figure 6 is only a

local snapshot of the overall ground condition that centers on

a specific position, the one above the tire base. One may argue

that it could probably be some other change that brings up the

radical differences of Figure 6. Such should well extend

beyond the ground improvement region.

Figure 6. Surface pore pressure rise during Christchurch

shaking.

Figure 7 attempts to address any such implications.

Comparing the next set of PPTs, situated 150mm above the

bottom level, it can be concluded that the liquefaction

phenomenon in the rest of the soil body progresses in a very

similar manner. The correlations plotted for PPTs 1B and 2B

show a very close picture. Namely their autocorrelations

against lag time (nominally a plot analogous to the free decay

response in vibrating systems) decay almost identically.

Further their cross correlation has a very high initial value for

zero lag, close to 0.9, indicating the similarity of conditions in

the two positions. Thus it is natural to state that the local

ground improvement enhances under identical conditions the

impact of the liquefaction phenomenon simply where it is

needed; and this is the actual structure level. Although

liquefaction is better viewed and identified in terms of pore

pressure data, it is equally important to assess the

accelerometer data. After all, these will provide all

information about permanent deformations and the actual

details of the paths for reaching them. As it was earlier noted

the z-axis dynamic characteristics were the ones differing the

most, and as a matter of fact for the real earthquake selected

the motion is expected to be primarily a rocking strongly

influenced by the vertical axis details.

Figure 7. PPT 1B and 2B correlation function during

Christchurch shaking.

Figure 8 shows the autocorrelation of surface

accelerometers, in the z direction against lag time. It can be

witnessed that the two decay functions almost overlap

meaning that the forced response is similar for both cases,.

The harmonic component that can easily be distinguished has

to do with the predominant frequency of the input signal.

When switching the actual constants reached in the

acceleration time signals to tilt values it is concluded that the

ordinary slab foundation reaches 6˚ in contrast to less than 1˚

for the model on the tire cushions. These values were

reconfirmed also by hand height measurements. An

illustration of the vast magnitude of the difference between

remaining deformations can be viewed in all Figures 11-13,

proving the efficacy of the new foundation solution. Most

importantly in the vertical direction the vibration that reaches

the structure is the same for both models implying similar

wave propagation.

Figure 8. Correlation between surface accelerometers in the

two cases x

During testing it was seen that the model on top of the

rubber base was acting like if it was floating, which is

conceptually rather distinct from the normal foundation


263

behavior. Thus differences in the actual motion that reaches

the structure were still sought in other details. Figure 9

correlates the x components of the surface accelerometers in

the two cases (Acc5x and Acc6x) and Figure 10 correlates the

surface accelerometers with the Setra accelerometer, which is

positioned on top of the shake table outside the container (see

Figure 4). Taking into account what was found earlier in

Figures 4 & 8 any changes should be probably unexpected.

Yet the figure actually shows appreciable differences in the

dynamic behavior. Specifically according to the

autocorrelation function of Acc5x and Acc6x when tires are in

place the x surface motion is much more damped and the

harmonic forced character of the earthquake is much more

difficult to make out. The same view is strengthened when the

cross correlation of the two instruments with the Setra

accelerometer is considered. The zero lag values and the

reduced periodicity in the behavior is an indication that on the

x axis movement for the tire base case, the structure behaves

like being more isolated from the imposed ground movement.

The same is also valid for the y axis.

Figure 9 Autocorrelations from surface accelerometers z in

the two cases

Figure 10 Correlations from surface accelerometers z in the

two cases with the Setra accelerometer

Figures 11-13 show actual photos after the Christchurch

shaking test, that can justify the results from the above data

analysis. It is clear from these pictures, that the model with the

tire base underneath was not affected by the shaking as much

as the one without.

Figure 11. View of the models after the shaking of

Christchurch Earthquake (non-scaled).

Figure 12. View of the model with the tire chips underneath

after the shaking of Christchurch Earthquake (non-scaled).

Figure 13. View of the model without the tire chips after the

shaking of Christchurch Earthquake (non-scaled).


264

4 CONCLUSION

The current research work attempts to address and

understand the seismic mitigation measure of using an elastic

sub-base consisting of scrap tire chips just below the slab

foundation. Such a countermeasure resisting permanent

earthquake induced displacements was previously found very

effective for other types of structure e.g. manholes, Yoshida et

al., 2008 [9].

Here it was clearly shown that the tire addition alters the

liquefaction process reducing the close to surface pore

pressure rise and allows the structure to “float” on top of the

water surface that emerges for prohibiting permanent tilts.

More importantly it was shown that the tire action cannot be

realized as a single 1D action modeled e.g. by spring addition

but it rather has a more elaborate 3-dimensional character. It

was found that dynamic characteristics change during the

shaking largely in the horizontal plane isolating the structure

from excessive ground motion.

REFERENCES

[1] Bhattacharya S, Hyodo M, Goda K, Tazoh T, Taylor

CA. Liquefaction of soil in the Tokyo Bay area from the

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Earthquake Engineering 31, 2011, p. 1618-1628.

[2] Dietz M, Dihoru L, Oddbjornsson O, Bocian M, Kashani

M, Norman J, Crewe AJ. Earthquake and Large

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41.

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Earthquake Engineering 22, 2012, p. 135-158.

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mixtures, Scrap tires derived geomaterial. Oportunities

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C.M. Tensile loading of Model Caisson Foundations for

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[6] Bhattacharya S, Murali K, Lombardi D, Crewe AJ &

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[7] Isihara, K. Soil Behaviour in Earthquake Geotechnics.

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Use of rubber for improving the performance of domestic …paginas.fe.up.pt/~eurodyn2014/CD/papers/034_MS01_ABS_1889.pdf · ground improvement techniques, proved that these techniques