Vibration Isolation Performance of Concrete Filled Trench Type Wave Barriers

Abstract

High speed trains, manufactories, machines and traffic generate ground vibrations during their activities. Induced vibrations are propagated through the soil and may disturb the environment. Different screening methods have been developed in order to reduce the ground borne vibrations. Among these screening methods, open and in-filled trench type wave barriers are frequently preferred ones for isolating the vibrations. Previous studies showed that the isolation performance is controlled by Rayleigh wave length and the trench depth. Moreover, dynamic properties of soil and the in-filled material affect the screening efficiency of the wave barriers. Considering these parameters, a series of analyses are conducted by utilizing the finite element method. Isolation performance of open and concrete filled trench are assessed and the results are compared with the previous experimental and numerical studies.

Full text

3rd International Soil-Structure Interaction Symposium-Izmir, Turkey
589
Vibration Isolation Performance of Concrete Filled Trench Type
Wave Barriers
Selda Durmaz 1,*, Deniz Ülgen 2, Mohammad Mouaz Hassoun3,
Onur Toygar4, Recep Birgül5
1 Res.Assist., Muğla Sıtkı Koçman University,
seldadurmaz_22@hotmail.com
2 Assist.Prof.Dr., Muğla Sıtkı Koçman University,
denizulgen@gmail.com
3 MSc.Student., Muğla Sıtkı Koçman University,
elcengstu@gmail.com
4 Res.Assist., Muğla Sıtkı Koçman University,
onur.toygar@hotmail.com
5Prof.Dr., Muğla Sıtkı Koçman University, rbirgul@gmail.com
ABSTRACT: High speed trains, manufactories, machines and traffic
generate ground vibrations during their activities. Induced vibrations
are propagated through the soil and may disturb the environment.
Different screening methods have been developed in order to reduce
the ground borne vibrations. Among these screening methods, open
and in-filled trench type wave barriers are frequently preferred ones
for isolating the vibrations. Previous studies showed that the isolation
performance is controlled by Rayleigh wave length and the trench
depth. Moreover, dynamic properties of soil and the in-filled material
affect the screening efficiency of the wave barriers. Considering these
parameters, a series of analyses are conducted by utilizing the finite
element method. Isolation performance of open and concrete filled
trench are assessed and the results are compared with the previous
experimental and numerical studies.
Keywords: Vibration isolation, Wave barrier, Trench
ÖZET: Yüksek hızlı trenler, fabrikalar, makineler ve trafik,
faaliyetleri sırasında zeminde titreşimler üretir. Bu titreşimler zemin
içinde dağılır ve çevreyi rahatsız edebilir. Zeminde oluşan titreşimleri
azaltabilmek için birçok yöntem geliştirilmektedir. Bu yalıtım
yöntemleri arasında, içi boş ya da dolu hendek tipi dalga bariyerleri en
çok tercih edilen yöntemlerdendir. Daha önce yapılan çalışmalar,
yalıtım performansının Rayleigh dalga boyu ve hendek derinliği
tarafından kontrol edildiğini ortaya koymuştur. Bunlara ek olarak,
zeminin ve dolgu malzemesinin dinamik özellikleri de dalga

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bariyerlerinin yalıtım verimliliğini etkilemektedir. Bu parametreler
göz önünde bulundurularak, sonlu elemanlar metoduyla bir dizi
dinamik analiz yapılmıştır. Boş ve beton dolgulu hendeklerin yalıtım
performansları değerlendirilmiş ve sonuçlar mevcut sayısal ve
deneysel çalışmalarla karşılaştırılmıştır.
Anahtar Kelimeler: Titreşim yalıtımı, Dalga bariyeri, Hendek
INTRODUCTION
Vibration isolation studies focus on mitigating or minimizing the
disturbance of generated waves by any source. Using wave barriers
between vibration source and effected zone yields satisfactory results
in terms of absorption of diffused dynamic energy. This method is
applicable for both passive (far field) and active (near field) isolation.
Wave barriers vary as open and in-filled (geofoam, concrete, water,
bentonite, gas cushion, and rubber chip) type trenches or sheet pile
walls. There are many researches to evaluate the screening
performance of available barriers and according to the findings,
utilizing open trench gives best results. However, open trench is not
applicable in terms of likely stability problems and safety. Thus, in-
filled type trenches should be used with suitable filling materials.
Herein, the important parameter is selection of barrier material in
terms of impedance difference. Impedance difference indicates the
difference of shear wave velocity and density of materials and
impedance ratio (Z) is defined as multiplication of wave velocity (VR)
and density of material (ρ). While El Naggar and Chehab (2005) were
indicating the better performance of softer barriers, many numerical
and site studies were conducted on concrete barriers. In the latest
studies, Wang et al. (2009) reported that effect of concrete wave
barriers are limited for isolation of vibrations. Çelebi et al. (2009)
observed 50% reduction with open trench and 35% with concrete
filled. Likewise, Zoccali et al. (2015) stated the reduction ratio with
concrete barrier as 20%.
Since a big fraction of generated vibrations travel through the
geological formations in Rayleigh wave form, the concept of
decreasing transmitted energy by utilizing trench is based on
refraction and reflection of Rayleigh waves. Relations between
Rayleigh wave length (λR), Rayleigh wave velocity (VR), trench
geometry and material properties of soil become effective at this
point. Barkan (1962) conducted full scale tests on open trench and
sheet piles and reported that screening performance is higher for

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591
higher vibration frequencies. For comparisons, Woods (1968)
recommended a new definition that is based on dividing vibration
amplitudes, measured before and after trench installation. This ratio is
called amplitude reduction ratio (Ar). According to his study, upper
limit of this value should be selected as 0.25 for an effective
application. Moreover it is also stated to select the trench depth at
least 0.6λR and 1.19λR for active and passive isolation.
NUMERICAL ANALYSES
In the present study a series of numerical analyses are conducted to
evaluate the screening performance of open and concrete filled trench
type wave barriers. For the installation of trench with the dimensions
of 5m depth and 0.8m width, a homogeneous soil model with 0.03
damping ratio is used. Although the damping ratio of soils generally
vary between 0.03 and 0.07, to obtain upper bounded results 0.03 is
preferred. Generated vibrations are applied as a continuous point load
and their frequencies vary from 10Hz to 75Hz, increasing by 5Hz.
Thus, effects of vibration frequency can be observed. Besides, mesh
size of finite elements is calculated considering the vibration
frequencies (f) and Rayleigh wave velocity (VR). Defining wavelength
(λR) as Rayleigh wave velocity over frequency, recommended mesh
size is 8 elements per wavelength (λR/8) (Kuhlmeyer and
Lysmer,1973). Amplitude of vibrations are recorded at 10 points as
seen in test set up (Figure 1), in terms of acceleration. Soil profile and
geometry of trench remained same during the analyses. The material
properties are summarized in Table 1. Finite element method is
preferred for the dynamic analyses and carried out with QUAKE/W.
Initially, analyses are conducted to obtain the attenuation performance
of field and then open trench and concrete filled ones are carried out.
Figure 1. Test model

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592
Table 1. Material and trench properties
Density
of soil
(t/m3)
Density
of
concrete
(t/m3)
Trench
depth
(d)(m)
Trench
width
(m)
Wave
velocity
of
concrete
(m/s)
Rayleigh
wave
velocity
of soil,
VR (m/s)
1.73 2.40 5.00 0.80 2200.00 250.00
Figure 2. Mesh properties of finite element model
Figure 3. Closer view of trench and data points
RESULTS
This study aims to investigate the isolation performance of open and
concrete filled trench type wave barriers. A series of numerical
dynamic analyses are conducted for this purpose. Finite element
method is preferred for the analyses. As previously defined,
measurements of vibration amplitudes are given in terms of amplitude
reduction ratios. Attenuation of vibrations are obtained by drawing the
variation of normalized accelerations with distance. In Figure 4 and 5,
analyses results of no trench case, open and concrete filled trench are
given for 25 Hz, 50 Hz and 75 Hz. Herein, location of trench is
demonstrated with a red line in the figures. As seen in the figures, the

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normalized accelerations are lower at higher frequencies. When the
frequency is high, the wavelength is short and at shorter wavelengths
barriers show a better isolation performance. Screening efficiency of
trenches can be compared by utilizing the amplitude reduction ratio.
In Figure 6 and 7, variation of amplitude reduction ratio is given for
different relative depths (D). Assuming d is depth of trench and λR is
Rayleigh wave length, relative depth (D) can be defined as d/λR. The
vibration amplitudes are reduced by the open trench more than
concrete filled one. This difference can be attributed to the impedance
ratio. When the density difference between soil and filling material is
high, screening is more effective. Moreover, it can be deduced that
isolation efficiency is higher just behind the wave barrier. Screening
performance is reducing with increasing distance, thus the design
engineer should be careful when selecting the location of wave
barrier. Figure 8 show the comparison of previous numerical studies
with the present study for open trench. Results of this study follow an
overestimated trend. This can be related with the damping ratio of the
soil. For higher damping ratios, illustrated curves shift to lower
values. Furthermore, the findings are plotted in Figure 9 and compared
with site test results. When the results are examined, it is seen that the
numeric study performed higher than the field tests. Therefore,
recommended curve can be used as the upper bound of initial estimate
at the preliminary design step of open trenches. Likewise, Figure 10
shows the comparison of open and concrete filled trench type wave
barriers. Amplitude reduction ratio, Ar, remains almost constant when
relative depth is equal or more than 1, thereof, there is no need to use
higher values. When relative depth (D) is equal to 1, open trench
screens 60% of vibration (Ar =0.4) and concrete filled one screens
30% (Ar =0.7). Thus, utilizing open trench gives satisfactory isolation
performance, however, for the situations that the open trench is not
applicable, utilizing light filling materials (EPS-Expanded Polystyrene
Foam) may provide an effective isolation.

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594
0.01
0.10
1.00
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0
Normalized Acceleration
Distance (m)
no trench-25hz no trench-50hz
no trench-75hz concrete filled-25hz
concrete filled-50hz concrete filled-75hz
Figure 4. Variation of normalized acceleration with distance for
open trench
Figure 5. Variation of normalized acceleration with distance for
concrete filled trench
0.01
0.10
1.00
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0
Normalized Acceleration
Distance (m)
no trench-25hz no trench-50hz no trench-75hz
open trench-25hz open trench-50hz open trench-75hz

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595
Figure 6. Variation of amplitude reduction ratio (Ar) with
distance for open trench
Figure 7. Variation of amplitude reduction ratio (Ar) with
distance for concrete filled trench
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0
Ar
Distance (m)
D=0.5
D=1.0
D=1.5
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0
Ar
Distance (m)
D=0.5
D=1.0
D=1.5

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0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 0.5 1 1.5 2
Ar
D (d/λ
R
)
Woods (1968)
Haupt (1981)-Close to trench
Alzawi and El Naggar (2011a)
Ulgen and Toygar (2015)
Present study-open trench
Figure 8. Comparison of previous numerical studies with present
study for open trench
Figure 9. Comparison of previous site test results with present
study for open trench
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 0.5 1 1.5 2 2.5
Ar
D (d/λ
R
)
Dolling (1965)
Beskos et al. (1986a) (W=0.1)
Beskos et al. (1986a) (W=0.4)
Al-Hussaini (1992) (W=0.1)
Al-Hussaini (1992) (W=0.3)
Tsai and Chang (2009)
Saikia and Das (2014)
Present study-open trench

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Figure 10. Comparison of trenches for present study
CONCLUSIONS
This study aims to reveal the screening performance of open and
concrete fill trench type wave barriers. According to the finite element
test results, following comments can be made:
- Trench depth has a significant importance for the screening
performance and one wave length is recommended for the depth
of trench to obtain an efficient isolation. For the values of D more
than 1, Ar remains almost constant. Thus, assuming D=1 can be
the upper bound of preliminary design.
- When the isolation performance of open trench and concrete
filled one are compared, open trench with 60% isolation is nearly
two times more effective than concrete filled trench. This finding
shows the importance of impedance ratio. When the difference
between density of soil medium and fill material is high, isolation
performance is better.
- Results of present study are quite consistent with the results of
previous site and numerical studies. Since the damping ratio is
preferred lower, analyses yield upper bounded results.
- In this study, a homogeneous and isotropic soil profile is used. In
order to clarify the isolation mechanism of wave barriers,
different soil profiles and layering effects should be examined in
the future studies.
ACKNOWLEDGEMENT
This study is funded by Muğla Sıtkı Koçman University Scientific
Research Projects with the BAP Code: 17/080.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 0.5 1 1.5 2
Ar
D (d/λ
R
)
Present study-open trench
Present study-concrete filled trench

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