66

SECM/13/113

RISK ASSOCIATED WITH NOISE AND VIBRATION EXPOSURES AND THEIR

EFFECTS ON HEALTH OF WORKERS IN CONSTRUCTION SITES

V.H.P.Vithrana1, G.H.M.J. Subashi De Silva

2 and G.S.Y. De Silva

3

1Department of Civil & Environmental Engineering, University of Ruhuna, Sri Lanka

Telephone: +94 712767575; Fax: +94 912245762

E-mail: vhashi@yahoo.com1,subashi@cee.ruh.ac.lk

2 and sudhira@cee.ruh.ac.lk

3

Abstract

Construction industry is one of main hazard industries, due to the nature of activities involved in

construction. In Sri Lanka, there are several research works investigating this hazardous nature based

on statistical data analysis of death and injuries caused by the risk factor having acute effect such as

working in higher places. However, no attention has been paid on health effects of construction

workers due the risk factors having chronic effects such as noise and vibration exposures. Objective

of this study is to investigate workers awareness on the risk associated with construction activities,

noise and vibration exposure levels in Civil Engineering Construction sites and the effects of noise

and vibration exposures on the health of workers. A questionnaire survey was conducted among

workers in building construction sites in the Southern Province, Sri Lanka. In addition, noise

exposure was measured by using noise level meter while vibration exposure was measured by using a

seat pad accelerometer attached to tri-axial vibration meter. The Relative Important Index (RII) was

determined to rank workers awareness on risk factors. RII values for “exposure to noise” and

“exposure to vibration” were 0.22 and 0.21, respectively. It was found that, although these two values

indicate that the workers are less aware about risk of noise and vibration exposures, exposing to

severe noise and vibration for a prolonged time can lead to adverse health effects. Noise and vibration

exposure levels prevailing in construction sites and their effects on the health of workers are

discussed in this paper.

Key words: Civil engineering construction sites, Construction worker, Noise, Vibration

1.0 Introduction

Construction workers do not generally have formal education such as college or degree acquired

skills, and belongs to lower strata of economy and privileges. There are many research on developing

new building technologies and economical factors on construction industry. Although the construction

worker, for the fruition of a project, does animportant work, there are no many research works

regarding construction workers. It has been reported that the construction workers are three times

more likely to be killed and twice as likely to be injured as workers in other occupations (Okela,

2009). This may be because of construction workers are at risk of exposure to various health hazards

that can result in injury, illnesses, disability or even death. Factors affecting this severe nature of

construction industry and possible methods to overcome them have been investigated recently (

Sawacha etal., 1999;Rameezdeen etal., 2003;Ismail et al., 2011;Ahamaed etal., 2011 ).

Sawacha et al., (1999) have investigated how historical factors (background and characteristics of the

individual such as age and experience), economic factors (monetary values which are associated with

Special Session on Construction Management, 4th International Conference on Structural Engineering and Construction Management 2013, Kandy, Sri Lanka, 13th, 14th& 15th December 2013

67

safety such as hazard pay), psychological factors (safety behavior of fellow workers on site including

supervisors), technical and procedural factors (the provision of training and handling of safety

equipment on site) and the organizational and environmental factors (type of policy that management

adopts to site safety) are linked with the level of site safety. The study (Sawacha et al., 1999) has

analyzed the factors using accidents of 120 operatives in construction industry and found that the most

dominant factors influencing safety performance are organizational policies: management talk on

safety, provisions of safety booklets, provision of safety equipments, providing safety environment

and appointing a trained safety representative on site.

Rameezdeen et al., (2003) examined the accidents that were taken place at Sri Lankan construction

sites as recorded in the Industrial Safety Division (ISD) of the Ministry of Labour. The study also

certifies that age affects on construction safety, as workers over 60 years of age and less than 20 years

of age have been found to be over represented among fatalities. A survey conducted in Malaysia by

Ismail et al (2011) and a survey conducted in Sri Lanka by Ahamaed et al., (2011) found that the most

influential safety factor was personal awareness. In addition, Ahamaedet al, (2011) recommended to

provide a site plan for the safe access to the site, provide fences to keep the unauthorized persons

away, display warning signs at places to instruct workers to be cautions, declare proper walking and

vehicle paths to lead safe access to working place, keep the site tidy and clean, provide sufficient light

during dark in order to improve site safety.

A few research studies on fatal accidents and non-fatal accidents in Sri Lanka have been published

(Rameezdeen et al., 2003; Ahamaed et al., 2011). However, it is very hardly found a survey on

chronic effects from the risk factors such as noise and vibration exposures. Risk factors such as noise

and vibration exposures affect the worker, although the worker is less aware about these risk factors

than the other risk factors such as working in higher places. Eger et al., (2007) measured Whole Body

Vibration (WBV) exposure levels at the vehicle -seat interface and the operator- seat interface, during

the operation of both small and larger Load-Haul-Dump (LHD) vehicles. WBV levels have been

recorded during loading and unloading and mucking tasks of 16 different LHD vehicle models at

eight underground mining sites in Ontario and compared to the ISO 2631-1 health guidance caution

zones to determine safe exposure durations. Preliminary test results have indicated that LHD

operators were exposed to whole-body vibration levels putting them at risk for injury. ISO 2631-1

exposure guidelines for the health caution zone were exceeded during the operation of several

different vehicles. Although the situation in Sri Lanka might be the same as above, it is hardly found

any research on investigation about safety of construction workers exposed to severe vibration

exposures.

It seems that there are several noise sources in construction sectors and the noise levels are different in

each stage of a construction work. The report (Department of Environmental and Occupational Health

Science), which has been produced based on six years research in construction trades, stated that

repeated exposure to noise levels about 85 dB(A) (such as years of working around construction noise

without hearing protection) or from as little as one noise exposure above 140 dB(A) can damage

nerves in the inner ear, loosing permanent and irreversible hearing loss. Department of Environmental

and Occupational Health Sciencefurther stated that construction workers in Washington are more

likely to claimworkers’ compensation for hearing loss than that for workers in all occupations.

68

Therefore, it is very important to investigate the workers awareness about the risk associated with

severe noise and vibration exposures in construction sites. In addition, it is necessary to have

quantitative estimation on possible exposure level of noise and vibration of construction workers in

Sri Lanka as it will be useful to make workers and contractors aware on possible health effects. The

relationship between the workers awareness about the risk factors and the exposing level of noise and

vibration is very important to minimize the bad health effects of construction worker. Objectives of

this study are to investigate the workers awareness about risk factors including the noise and vibration

exposure in Sri Lankan construction sites. In addition, a relationship between the noise and vibration

exposure levels and their bad health effects will be discussed.

2.0 Methodology

Workers’ awareness of risk factors wasinvestigated by conducting a questionnaire survey. Noise and

vibration exposure levels prevailing in construction sites and possible health effects were investigated

by measuring noise and vibration exposure levels in construction sites (i.e., objective responses) and

interviewing construction workers (i.e., subjective responses).

2.1 Workers’ awareness about risk factors in construction sites

A questionnaire survey form was developed for the workers in construction sites. Ten risk factors of

construction sites were identified using a literature survey and were considered in preparing the

survey form of worker. These risk factors were categorized into two, according to the time of

affecting them on the workers. Working in higher places, lifting heavy materials and electricity were

considered as risk factors having acute effects while dust, ionizing radiation and direct sunlight, hot

environments, vibratory tools, noisy environment and skin sanitizers were considered as risk factors

having chronic effects (Table 1). Each risk factor wasassessed by using three-point risk assessment

scale: high risk, medium risk and low or no risk.

Table 1: Categorization of risk factors

Risk factors

Chronic effects Acute effects

Dust Working in higher places

Ionizing radiation Lifting heavy materials

Direct sunlight Electricity

Hot environment

Vibratory tools

Noisy environment

Skin sanitizers’

69

Construction sites in Galle and Matara districts were selected for this survey. The contractor of each

selected construction site is in grading M1. The survey was conducted within the period of three

months. The workers were interviewed for about ten minutes and the survey was performed in the

morning (i.e., between 9.00 am to 12.00 noon). Number of participants of the study is 100. The age of

workers, participated in the survey, is in the range between 18-67 years. Ninety percent of the workers

have studied only for G.C.E. (O/L) or less than that.

2.1.1 Relative Important Index (RII)

The Relative Important Index (RII) was determined to rank risk factors in an order of workers

awareness in particular risk factor.RII is given by Eq.(1);

(1)

where,w is the weighting assigned to each risk factor by the respondents, ranging from 1 to 5, and A is

the highest weight and N is the total number of samples. The RII was normalized as in Equation (1)so

that RII value will fall between 0 and1.

2.2 Noise and vibration exposure levels, and their effects on workers

A building construction site, in the Galle district, operated under a construction company having

grading M1 was selected. Foundation work was the major construction activity going on this building

site at the time when it was selected for measuring noise and vibration exposure levels.

Vibration exposure levels of Excavator operator and Soil Roller Compactor operator were measured

for a period of 30 minutes and 15 minutes, respectively. The excavator operator excavated the

construction site and the soil roller compactor operator leveled the ground of the construction site

when the measurements were recorded. Vibration exposure levels of the operators were measured at

the driver-seat interface during actual operating conditions according to the recommendations of the

International Standard ISO 2631-1997(International organization for standardization, 1997).Tri-axial

vibration meter and seat pad accelerometer were used to measure the vibration exposure level of

worker. The seat pad accelerometer was placed on the seat of the operators (Figure 1(a)) and it was

connected to tri-axial vibration meter (Figure 1(b)). Then, the operator was instructed to sit on the seat

pad accelerometer (Figure 1(c)).

In the tri-axial vibration meter, frequency weighting of Wd, Wk, and measurement range of 10 ms-2

were selected. As the worker is in seated position, frequency weighting,Wd, was used to weight the

vibration in X and Y directions. Frequency weighting, Wk., was used to weight the vibration in Z

direction. Figure 2 shows the basic centric axis (X,Y and Z axis) at seat back, seat surface and feet of

the human body in seated position.

70

Figure 1: Procedure of measuring vibration exposure level of an operator (a) Seat pad

accelerometer on the seat of the operators, (b) Seat pad accelerometer with the tri-axial

vibration meter, (c) Operator sit on the seat pad accelerometer

Figure 2: Basic centric axes of the human body in seated position (ISO 2631-1, 1997)

Directional factors kx, ky and kz were set as 1.4, 1.4 and 1.0, respectively. Measured vibration

exposure levels were assessed by limit boundaries of vibration exposures as defined by the ISO -2631

(International organization for standardization, 1997) (Figure 3).

SL-1350(CUSTOM) sound level meter, which is capable in measuring noise in frequency range of

31.5 Hz to 8 kHz, was used to measure the noise level of construction sites and the noise exposure

level of operators. The sound level of the construction site was measured during two days for a period

of 20 minutes in randomly selected locations within daytime and was considered as an ambient noise.

During measuring the ambient noise level, an excavator, a soil roller compactor, an electric wood

cutter and an electric bar cutter were operated in the site.

Noise exposure level of Excavator operator, Soil Roller Compactor operator, Concrete mixing

operator, electric wood cutter operator and bar cutter operator was separately measured for twenty

minutes during the operation of their assigned tasks. “A” frequency weighting was selected in the

instrument to measure sound levels, as the human ear is less sensitive to low audio frequencies.

71

Figure 3: Limit boundaries of vibration exposures as defined by the ISO -2631 (International

organization for standardization, 1997)

In practice, when measuring noise it is possible to take Leq (Equivalent Continuous Sound Pressure

Level)readings, with instrument, of short duration, i.e. <5 minutes, providing all variations of noise

emissions are covered.

Adding Leq values requires taking an anti-log of each value. The addition can be performed as shown

in Eq. (2) and the average noise level can be calculated. (Castle group, 2013)

10 Leq1/10

+10 Leq2/10

+10 Leq3/10

+…+10 Leqn/10

) / (2)

Here n is the total number of samples.

A questionnaire form was developed for the equipment operators in construction sites so as to record

subjective responses. Noise or vibration exposing hours per day, working experience and noise or

vibration related symptoms of the worker were found through the questionnaire survey. It was

recorded whether the workers have worn Personal Protective Equipments also.

3.0Results and discussion

3.1 Workers’ awareness about risk factors in construction sites

Figure 4 shows the Relative Important index (RII) of risk factors determined based on workers

responses. It verifies that the workers’ perceptions of the risk factors are poor as none of RII value of

risk factors percept by workers exceeded the limit 0.5. It has been identified that “working in higher

places” and “hot environment” are the most significant risk factors in construction sites: RII values

are 0.42 and 0.45, respectively.

The workers have the least awareness about risk of sever noise and vibration exposures. The RII value

corresponding to risk factors of noise and vibration are 0.22 and 0.21, respectively.The workers tend

to believe that when these vibratory tools are familiar for them, the risk is reduced. This is possibly

because they are mainly concern about acute effects due to injuries caused by vibratory tools.

72

Although the noise of construction sites is generally high, workers have the same idea as for the effect

of vibratory tools: as these equipments are familiar with them there is no risk for the worker.

However, workers should be educated with the possible health effects of severe noise and vibration

exposure and most of health effects are irreversible.

Figure4: RII values of perception of workers

3.2 Noise and vibration exposure levels, and their effects on workers

Vibration exposure levels

Table 2(a) shows root mean square value, peak value,crest factor, vibration dose value, maximum

transient vibration value for X, Y and Z-axis.

It can be seen from Table 2(a) that for Soil Roller Compactor operator, the RMS value of vibration

exposures in Z-axis and X-axis exceeds 2.00 ms-2

. This magnitude of vibration (measured in RMS)

should be extremely uncomfortable for the worker (Mansfield, 2005). RMS value of X, Y and Z-axis

for both Excavator operator and the Soil Roller Operator exceeds the value 0.8 ms-2

. So that the

operators are in uncomfortable condition when they are operating the equipments (Mansfield, 2005).

However, operators judgment on “discomfort” would be highly subjective, as this may be mainly

depend on personal level of expectation.

0 0.05

0.1 0.15

0.2 0.25

0.3 0.35

0.4 0.45

0.5

RII

Val

ue

Perciption of the worker

73

Table2 (a): Vibration exposures of the two operators

Op

erat

or

Ax

is o

f v

ibra

tion

Fre

qu

ency

-wei

gh

tin

g

Ro

ot

Mea

n S

quar

e

val

ue(

RM

S)

m/s

2

Pea

k v

alu

e

m/s

2

Cre

st f

acto

r

Vib

rati

on

Do

se V

alue

(VD

V)

m/s

1.7

5

(Max

imum

Tra

nsi

ent

Vib

rati

on

Val

ue

(MT

VV

)

m/s

2

Excavator

operator

X Wd(a) 1.24 20.00 16.13 20.00 4.83

Y Wd(a) 0.86 14.74 17.21 11.35 3.77

Z Wk(a) 0.61 7.19 11.88 13.28 3.95

Soil Roller

Compactor

operator

X Wd(a) 2.74 20.00 7.31 19.79 4.98

Y Wd(a) 1.19 18.45 15.45 10.58 4.25

Z Wk(a) 2.12 11.37 5.37 15.37 5.57

The RMS method of assessing vibration underestimates the effects of vibration with substantial peaks

(International organization for standardization, 1997).So that, it is recommended to use the crest

factor and it is defined as the ratio between the peak value and RMS value for the period of

measurement, T. For a more impulsive vibration, its crest factor is high. Health assessment based on

crest factor may be more appropriate for impulsive vibrations, because impulsive vibrations are

considered as more harmful than non-impulsive vibrations. The crest factor is often considered as a

good indicator of the harmful content of a vibration. It was found that the crest factor is greater than 9

for all the axis of Excavator operator. Vibration Dose Value (VDV) of each axis is greater than 9.1

ms-1.75

(exposure action value (Mansfield, 2005)). For the excavator operator, the crest factor of Y-axis

is greater than 9 and VDV value also exceeds the exposure action value of 9.1 ms-1.75

.

Mansfield (2005) explains .although there is a way to calculate MTVV; no guidance has been given

on how to interpret it. Therefore, the combined vibration value was calculated for each operator to

assess the vibration exposure based on the guidelines given in ISO 2631-1. Calculated combined

vibration value (av)for each operator is presented in Table 2(b). This value is also known as the

vibration total value of weighted RMS acceleration.

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Table 2(b): Calculated Combined Vibration Value for the two operators

Operator Excavator

operator

Soil Roller Compactor

operator

kx(directional factor for x axis) 1.4 1.4

ky(directional factor for y axis) 1.4 1.4

kz(directional factor for z axis) 1.0 1.0

Calculated combined vibration value

av[ (kxawx)2 + (ky awy)2 +(awz)2]1/2

m/s2(International organization for standardization,

1997)

2.20 4.69

Calculated Combined Value of Excavator operator and Soil Roller Compactor operator are 2.20 ms-2

and 4.96 ms-2

, respectively. Comparison of these values and limit boundaries of vibration exposures

as defined by the ISO -2631 (Figure 2), it can be identified that the both excavator operator and the

soil roller compactor operator are in caution zone according to the ISO 2631 guidelines if they are

exposed to 30 minutes and 15 minutes, only.

It was found that the daily exposure value for excavator operator is 0.55 ms-2

while the daily exposure

value for soil roller compactor operator is 0.8291 ms-2

. Both exposing level of excavator operator and

the soil roller operator exceed the daily exposure action value, which is 0.5ms-2

(European Agency for

Safety and health at work, 2008).

Noise exposure levels

The ambient noise level of the construction site was 71.17 dB (A), implying that the noise exposure

level of a general worker might not cause for any hearing loss, although it can be an annoyance to

workers (i.e., exceed the recommended level of environmental noise in commercial area, 65 dB (A))

(The Ministry of Transport, Environmental and Women’s Affairs; 1996).Noise exposure levels of

Electric wood cutter operators’ helper, Electric wood cutter operator, Electric bar cutter operator, Soil

Roller Compactor operator and Concrete mixture machine operator exceeded 85dB(A). This may

imply that all operators are at health risk due to severe noise exposures.

Noise exposing hours per day, working experience and whether they had wore earmuffs or not are

presented in Table 4. Any of the operators have not worn earmuffs. However, each worker exposes

higher level of noise (Table 3). These workers are exposing noise for a considerable period. As an

example Excavator Operator, Electric woodcutter operators’ helper, Electric woodcutter operator and

Soil Roller Compactor operator expose to noise for 8- 9 hours per day.

75

Table 3: Noise exposure levels of operators

Equipment Operator Position of the sound level

meter Noise Level dB(A)

Excavator operator

0. 3 m away from the

operators’ ear

80.26

Electric wood cutter

operators’ helper 93.09

Electric wood cutter operator 101.5

Electric bar cutter operator 94.38

Roller operator 87.12

Concrete mixture machine

operator

1m away from the operators’

ear

At the side of

the engine

Other side

from the

engine

93.26 87.04

Table4: Working environment and the behaviour of the workers

Equipment Operator

Daily duration of

noise exposure (hr/

day)

Working Experience Wearing ear

muffs

Excavator Operator 8 8 years No

Electric wood cutter

operators’ helper 9 6 years No

Electric wood cutter

operator 9 3 years No

Electric bar cutter

operator 2-3 3 years No

Roller operator 8 6 years No

Concrete mixture machine

operator

The operator did not

provide the data

The worker did not provide

the data No

76

Health effects

None of the operators did complain about hearing lose and about back pains (Table 5).

Table 5: Subjective responses about hearing lose and back pain

Equipment Operator Complains about Back pain Complains about hearing

lose

Excavator Operator No No

Electric wood cutter operators’ helper Not relevant No

Electric wood cutter operator Not relevant No

Electric bar cutter operator Not relevant No

Roller operator No No

Concrete mixture machine operator Not relevant No

According to Table 2(b), Calculated Combined Value of vibration exposures of Excavator operator

and Soil Roller Compactor operator are 2.20 ms-2

and 4.96 ms-2

, respectively. Comparison of these

values and limit boundaries of vibration exposures as defined by the ISO -2631 (Figure 2), it can be

identified that the excavator operator is in caution zone but Soil Roller Compactor operator might not

be in the caution zone , according to the ISO 2631 guidelines. Nevertheless both the Excavator

operator and the Soil Roller Compactor operator did not report any back pain (Table 4).

When vibration exposure levels exceed the limit boundaries, workers are at risk. Vibration induced

from construction machines may affect on major part of the worker’s body or only a particular organ

to vibrate. As a result, workers exposed to two different types of vibrations: segmental vibration and

whole- body vibration. When the Whole Body Vibration (WBV) energy enters the body through a

seat or a floor, it affects the entire body or a number of organs in the body (Griffin, 1996). Both

operators of excavators and soil roller compactors exposed to WBV mainly through the seats. The

symptoms of WBV are not so readily recognizable and are often mistaken for other unrelated

conditions. The health outcomes are non-specific and can be difficult to identify, manage and control.

Although the frequency of vibration exposures were not measured in the current study, the back of the

human body is especially sensitive to the vibration in the frequency range of 4-12 Hz then the spinal

column disease and complaints are most common. When the stomach exposes to frequencies between

4 and 5 Hz, digestive system diseases are often observed in persons. Prolonged exposure to WBV, at

frequencies below 20 Hz, caused for cardiovascular system problem. These result in hyperventilation

increased heart rate, oxygen intake, pulmonary ventilation and respiratory rate.The frequency of

vibration exposures of the operators, who work in construction sites, will be investigated in future

studies.

77

As a general rule, workers are advised to used earmuffs whenever they are exposed to noise levels of

85dB (A) (Department of Environmental and Occupational Health Sciences; 2004). In this site, the

electric wood cutter operator, concrete mixture operator, concrete mixture operator, electric wood

cutter operator and soil roller compactor operators are exposed a noise level above 85 dB(A),

although they were not wearing earmuffs. Earmuffs can be used to control worker’s exposure to noisy

equipment and work areas.Exposing to 100 dB (A) for 1 hour is leading to hearing lose (Department

of Environmental and Occupational Health Sciences; 2004). However, the electric wood cutter has

been exposed to the noise level of 101.5 dB (A) for 9 hoursper day since 6 years and did not complain

about hearing lose, possibly because the worker has less awareness on health risk, often identifies as

annoyance or discomfort until permanent damage to hearing has occurred.

Permanent hearing loss is usually caused by long-term exposure to excessive noise. Excessive noise

causes to physical damage to the human hearing mechanism, which is incontrovertible (European

Agency for safety and health at work, 2005). This hearing impairment is known as Noise Induced

Hearing Lose (NIHL) that often progress slowly over many years and may go unnoticed until

permanent damage has occurred. The report (European Agency for safety and health at work, 2005)

further explains that excessive exposures to noise are probably the most common cause of hearing

loss due to damage of the inner ear. Prolonged exposure to sound level of more than 85dB (A) is

potentially hazardous although the important factor is total amount of exposure given by the level and

length of exposure time.

Noise can cause more harm than hearing loss, it can be a casual factor in work related stress, work

related voice disorders loss and can be a factor in work place accidents.

4.0 Conclusions

Most of the construction workers are not well educated although they are at risk of exposure to

various health hazards that can result in injury, illnesses, disability or even death. Although

construction workers make significant contribution to succeed engineering projects, less attention has

been paid for safety and health effects of the workers. .

In this study, site visits were made, questionnaire survey and interviews were conducted among 100

workers in construction sites to determine workers’ awareness of possible risk factors during their

construction tasks. Relative Importance Index (RII) was used to rank the possible risk factors. Noise

exposure level and vibration exposure level of construction workers were measured and their effects

on health risk were investigated through a questionnaire survey.

It was found that RII values for “Working in higher places” and “exposure to hot environment” were

0.42 and 0.45, respectively, implying that these two risk factorsare the most significant risk factors in

construction sites identified by workers. RII values for “exposure to noise” and “use of vibratory

tools” were 0.22 and 0.21, respectively, implying that workers were less aware about risk factors

having chronic effects.

Combined Vibration Value of Excavator operator and Soil Roller Compactor operator are 2.20 ms-2

and 4.96 ms-2

, respectively. Comparison of these values and limit boundaries of vibration exposures

as defined by the ISO -2631 standard, it can be identified that the both excavator operator and the soil

78

roller compactor operator are in caution zone, although further investigations with many number of

operators are necessary. Construction workers who are operating electric woodcutter, electric bar

cutter, soil roller compactor operator and concrete mixture operator expose to a noise level greater

than 85dB(A) implying these operators are at risk, although any worker did not wore earmuffs.

Despite, being a well- known hazard, construction workers who are exposing to noise and vibration

are in risky. However prolonged exposure to vibration may cause cardiovascular system problem,

hand arm vibration syndrome while prolonged exposure to noise may cause Noise induced hearing

loss and even permanent hearing loss.

Acknowledgement

The study presented in this paper was conducted under the financial support received from

Transforming University of Ruhuna into International States (TURIS) project. The authors wish to

express their special thanks to TURIS for providing necessary funds to carry out this research work.

In addition, special thanks go to site engineers and the construction workers of the sites, which were

selected for this research, for their support and corporation.

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