3163
Evaluation of Rubber/Sand Mixtures as Replacement Soils to Mitigate Earthquake
Induced Ground Motions
Évaluation du mélange sable-caoutchouc comme sol de remplacement
pour atténuer les mouvements sismiques
Abdelhaleem A.M.
Construction Research Institute, National Water Research Center, Egypt
El-Sherbiny R.M., Lotfy H.
Cairo University, Egypt
Al-Ashaal A.A.
Construction Research Institute, National Water Research Center, Egypt
ABSTRACT: Use of recycled rubber and rubber/sand mixtures (RSM) as lightweight material has been widely growing over the past
decade. The increased damping capacity of RSM leads to considering its use as replacement soils in seismic areas to reduce the
amplitude of earthquake induced ground motions. This paper presents a study on the effect of utilizing a layer of RSM within a
replacement soil on the ground response during an earthquake. Site response analyses were performed using 2D finite element
analyses applying an equivalent-linear constitutive model. Three earthquake ground motions of varying frequency content were
applied to a deposit of sand with replacement soil having different configurations of RSM. Placing a layer of RSM within the
replacement soil resulted in increasing the site natural period causing damping of spectral accelerations at low periods and
amplification of spectral accelerations at high periods. Using a thin layer of RSM at deeper depths was more effective in than using
thick but shallow RSM layers. The results indicate that RSM layers may be effective when the predominant period of the earthquake
is lower than the site natural period, while the configuration is subject to the natural period of the intended structure.
RÉSUMÉ: Le caoutchouc recyclé et les mélanges sable-caoutchouc (MSC) en tant que matériaux légers ont eu une utilisation accrue
au cours de la dernière décennie. L'augmentation de la capacité d'amortissement de MSC conduit à considérer son utilisation en tant
que remplacement des sols dans les zones sismiques afin de réduire l'amplitude des secousses observées pendant les tremblement de
terres. Cet article présente les résultats d’une étude sur l’influence des couches de MSC comme sol de remplacement sur la réponse du
sol au cours d'un tremblement de terre. L’analyses de réponses du site ont été réalisées en utilisant la méthode d’éléments finis 2D
appliquée sur un modèle constitutif du type « linéaire équivalent ». Trois régimes de tremblements de terre de fréquence variable ont
été appliqués à un dépôt de sable avec terres de remplacement ayant différentes formulation de MSC. Placer une couche de MSC dans
le sol de remplacement a eu pour effet d'augmenter la période naturelle du site; et ceci provoque une atténuation des accélérations
spectrales à des périodes faibles et une amplification de la mêm
e accélération aux périodes fortes. L’application d'une mince couche
de MSC à des profondeurs importantes a été plus efficace que d'utiliser des couches épaisses peu profondes. Les résultats indiquent
que les couches MSC ne peuvent être efficaces que si la période dominante du tremblement de terre est inférieure à la période
naturelle du site, et ceci en maintenant la configuration soumise à la même période naturelle de celle de la structure en question.
KEYWORDS: Recycled Material, Rubber-Sand Mixture, Replacement Soil, Earthquake Mitigation
1 INTRODUCTION
The use of recycled rubber and rubber/sand mixtures (RSM)
as lightweight material in civil engineering applications has
been widely growing over the past decade. Processed waste tires
mixed with soils have been introduced as lightweight fills for
slopes, retaining walls, and embankments. The mechanical
properties of the mixture were discussed by (Edil and Bosscher,
1994; Ghazavi, 2004; Zornberg et al., 2004; and Mavroulidou et
al., 2009), while dynamic properties of granulated rubber-sand
mixtures were studied by (Feng et al., 2000; and Anastasiadis et
al., 2012). Xu et al. (2009) performed numerical studies on
protecting buildings from earthquakes hazards by RSM.
The utilization of RSM as replacement soils in seismic areas
to reduce the amplitude of earthquake induced ground motions
is addressed in this paper. The effect of changing the depth and
thickness of the RSM layer will be investigated in this study.
The results will be compared for a range of medium amplitude
ground motions.
Data used in this parametric study is based on a
comprehensive set of torsional resonant column tests performed
for different dry and saturated specimens of sand-rubber
mixture, (Senetakis et al., 2012). Based on these tests, the
modulus reduction and damping curves can be generated for the
sand-rubber mixture as a function of confining pressure. The
parametric study is based on two-dimensional finite element
analyses that can model seismic effects and site response of
multilayered soil profile.
2 PROPERTIES OF PARENT MATERIALS
The properties of parent materials for the RSM used in this
numerical analysis are based on results of the study by
Senetakis et al. (2012). In this study, dry sand of specimen code
(C3D06) and rubber material of specimen code (R3) were used
as parent materials for the RSM of specimen code (C3D06-R3).
The sand is natural of sub-rounded to rounded particles,
whereas the rubber is granulated from recycled tire shreds. The
properties of the parent materials is indicated in Table 1.
Table 1. Properties of sand and granulated rubber
Material
Sand
Granulated rubber
Unit weight,
ɣ (kN/m3)
16.50
6.50
Specific gravity, Gs
2.67
1.10
Max. particle size, D
max
(mm)
0.85
–
2.00
4.75
–
6.35
50% passing size, D
50
(mm)
0.56
2.8
Coefficient of uniformity, Cu
2.76
2.29
Coefficient of curvature, Cc
1.23
1.18
The RSM used in the analyses herein was assumed to
contain 35% rubber content (by weight) and a dry unit weight of
12.5 kN/m
2
.
The modulus reduction and damping curves of dry
RSM (C3D06-
R3) for different confining pressures (σ'
m
) were
generated according to Senetakis et al. (2012). The modulus
