groundborne vibration from percussive piling
DESCRIPTION
Groundborne vibration induced by piling operation may sometimes attract complaints from the public due to human discomfort perceived by the occupants in the surrounding building or structural damage or distress to a building. The amount of groundborne vibration depends on three elements: input driving energy, attenuation rate and attenuation distance between the source and the receptor. Empirical formulae that have been devised and published overseas have been used in Hong Kong to predict the maximum vibration induced by piling operation. One of the widely adopted formulae is that in BS 5228-2: 2009, which relates the peak particle velocity (ppv) with the parameter kp, depending on the types of soils and the types of piles. This paper presents the in-situ measurements for the ground vibration induced by percussive steel H-piles in some recent projects in Hong Kong. It was found that rather than to designate soil in a particular site into different types, this paper suggests correlating the values of kp with the Standard Penetration Test (SPT) N-values of the soil from the ground investigation.TRANSCRIPT
14th Asia Pacific Vibration Conference, 5-8 December 2011, The Hong Kong Polytechnic University
Groundborne Vibration from Percussive Piling
Chi-tong WONG* Man-kit LEUNG* Man-kie WONG* and Wing-chi TANG* * Architectural Services Department, Hong Kong SAR Government,
38/F Queensway Government Offices, Hong Kong SAR
E-mail: [email protected]
Abstract
Groundborne vibration induced by piling operation may sometimes attract
complaints from the public due to human discomfort perceived by the occupants in
the surrounding building or structural damage or distress to a building. The
amount of groundborne vibration depends on three elements: input driving energy,
attenuation rate and attenuation distance between the source and the receptor.
Empirical formulae that have been devised and published overseas have been used
in Hong Kong to predict the maximum vibration induced by piling operation. One
of the widely adopted formulae is that in BS 5228-2: 2009, which relates the peak
particle velocity (ppv) with the parameter kp, depending on the types of soils and
the types of piles. This paper presents the in-situ measurements for the ground
vibration induced by percussive steel H-piles in some recent projects in Hong
Kong. It was found that rather than to designate soil in a particular site into
different types, this paper suggests correlating the values of kp with the Standard
Penetration Test (SPT) N-values of the soil from the ground investigation.
Key words: Ground vibration; percussive piling; in-situ measurements
1. Introduction
Ground vibration and noise induced by percussive piling are commonly considered as
nuisance to the public in the neighbouring area. The vibration induced by piling operation
from time to time attracts complaint from the public due to human discomfort felt in a
building or distress caused to a building. Though percussive steel H-pile is one of the most
economical foundation types among different types of deep foundation systems if the site
and geological condition permits, it is unfortunate that many practicing engineers avoid
using this system just because of the fear of potential social resistance without the
conduction of a detailed study of the genuine vibration effects beforehand. This paper
reviews criteria on human perception and response, structural damage, and statutory
acceptance level of ground vibration to structures and utilities. It presents the actual ground
vibration data induced by percussive piling in some Architectural Service Department
(ArchSD) projects.
2. Generation of Groundborne Vibration
When a hammer hits a pile, there is resistance at the pile toe which will generate
vibration to the ground. The ground vibration can be divided into body waves and surface
waves. Body waves propagate through rock or soil and can be further divided into shear
wave (S-wave) and compressive wave (P-wave). Both P-waves and S-waves travel
outward from the tip of the pile on spherical wave fronts. When P-wave and S-wave
encounter the ground surface, part of their energy is converted to Rayleigh waves (R-wave)
(Figure 1) (Woods 2004)
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14th Asia Pacific Vibration Conference, 5-8 December 2011, The Hong Kong Polytechnic University
The proportion of total energy propagated in P-wave, S-wave and R-wave are
approximately 10%, 25% and 65% respectively (Head and Jardine 1992). The energy
density of both P-wave and S-wave attenuates rapidly with distance from the source.
R-wave has the slowest propagation velocity and its effect decreases rapidly with depth.
However, R-wave propagation is planar, rather than hemispherical, and as a result, the
decay of energy is much slower and will therefore contribute the highest proportion of total
energy transmission (Head and Jardine 1992).
Besides the spherical (P wave) / shear wave (S wave) generated from the resistance at
the toe, the resistive shear forces on the pile shaft will induce vertically polarized shear
waves which would propagate outwards as cylindrical wave fronts centred on the pile shaft
(Figure 1).
The commonly accepted criterion for quantifying ground vibration and human
evaluation of transient vibration is Peak Particle Velocity (PPV). The measuring unit of PPV
is in “mm/s”.
Fig. 1 Composite of waves emanating from driven pile (Source: Woods 2004)
3. Prediction of Groundborne Vibration Induced by Driving of Pile
The amount of groundborne vibration depends on three elements: input driving energy,
attenuation rate and attenuation distance between the source and the receptor. Empirical
formulae (e.g. Attewell and Farmer 1973, Head and Jardine 1992, Jongmans 1996, Hope
and Hiller 2000, and Massarsch and Fellenius 2008) have been proposed to predict the
maximum vibration induced by piling operation. One formula that is widely used
nowadays to predict ground vibration induced by percussive piling is given by BS
5228-2:2009. In BS 5228-2:2009 Appendix E, information from Hiller and Crabb
regarding the prediction of vibration levels from construction activities is reported. The
empirical formula derived by Hiller and Crabb (Equation [1]), which has been validated
against a number of other parameters from field measurements, was then adopted by BS
5228-2:2009 to estimate the ground vibration induced by percussive piling.
1.3pr
Wkv (1)
where W is the hammer energy and r is generally accepted as the slope distance
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14th Asia Pacific Vibration Conference, 5-8 December 2011, The Hong Kong Polytechnic University
BS 5228-2:2009 recommends the range of kp to be adopted for different driving
conditions and soil types (Table 1). One of the limitations in employing the suggested kp
value is that the hammer energy W shall lie within 1.5kJ and 85kJ (BS 5228-2:2009 Table
E.1).
Table 1: Recommended values of kp for use in predicting vibration from percussive piling
Ground Conditions Value of
All piles driven to refusal 5
Pile toe being driven through:
3
Very stiff cohesive soils
Dense granular soils
Fill containing obstructions which are large relative to
the pile cross-section
Pile toe not being driven through:
1.5 Stiff cohesive soils
Medium dense granular soils
Compacted fill
Pile toe being driven through:
1
Soft cohesive soils
Loose granular soils
Loose fill
Organic soils
(Source: BS 5228-2:2009 Table E.2)
4. Relationship between the Value of kp and Equivalent SPT N-Value
The results of groundborne vibration induced by driving steel H piles with hydraulic
hammers from six numbers of ArchSD projects, including Sun Yet Sen Swimming Pool,
Tseung Kwan O Velodrome, Kwun Tong Swimming Pool, Kai Tak Cruise Terminal
Development, Joint Users Complex at Bailey Street, and Victoria Park Swimming Pool,
were collected. Field data of groundborne vibration (mm/s) and horizontal distances (m)
of the projects, Sun Yet Sen Swimming Pool, Tseung Kwan O Velodrome and Kwun Tong
Swimming Pool, were plotted in Figure 2 through 4.
Fig. 2 Sun Yat Sen Memorial Park and Swimming Pool Complex ground vibration data
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14th Asia Pacific Vibration Conference, 5-8 December 2011, The Hong Kong Polytechnic University
Fig 3: Indoor Velodrome-cum-Sports Centre in Tseung Kwan O ground vibration data
Figure 4: Kwun Tong Swimming Pool ground vibration data
With the measured PPV (mm/s) and the known energy input together with the radial
distance, the constant kp can be calibrated and validated using the Equation [1] (with W =
90% of the rated energy). Measurements of groundborne vibration of 26 piles at 6
different ArchSD sites were carried out. Measurements were carried at different distances
from each pile to obtain an average kp value for each pile. The kp values were found within
the range of 0.24 to 1.50 ( Table 2).
The results reveal that the values of kp stated in BS 5228-2:2009 may not be
applicable to ground conditions in Hong Kong. Furthermore, it is also difficult to classify
a site by single type of soil for the full depth of a pile. In view of the difficulty in the
estimation of the value of kp, this paper has therefore correlated the values of kp against the
equivalent Standard Penetration Test (SPT) N-values from the ground investigation results.
SPT N-value is basically a measure of the compactness of the soil, and this is, in turn, a
measure of the soil shear strength as well as its deformation characteristics. It is the most
commonly available soil testing data that is adopted in deep foundation design. In order to
correlate the values of kp against the different N-values of the actual soil profile, the
equivalent N-value is computed as illustrated in Figure 5.
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14th Asia Pacific Vibration Conference, 5-8 December 2011, The Hong Kong Polytechnic University
Equivalent N
n321
nn332211
D....DDD
)DN....DNDNDN(
Fig 5: Computation of equivalent N-value
Table 2 and Figure 6 summarise the relationship between average kp and equivalent
N-value of each of the 26 piles at 6 different ArchSD sites. The results show that the
value of kp increases with the increase in equivalent SPT N-value. This is in line with the
trend shown in Table 1 (BS 5228-2:2009).
Table 2: Relationship between average kp and equivalent N-value
Site Pile No Depth Avg k p Eq. N G.I. No.
FC123 P1 34.86 0.24 22.2 BH 16
FC99 P1 34.19 0.39 18.7 BH 16
FC85 P1 34.25 0.40 19 BH 16
FC127 P1 33.81 0.68 51.8 BH 15
FC103 P1 33.66 0.55 51.1 BH 15
P99 54 1.240 57.5 BH 4
P217 54 0.6 57.5 BH2
P186 57.6 0.5 57.5 BH1
PC151 P1 18.2 0.36 13.7 KSB19
PC107 P1 17 0.33 13.7 KSB19
PC94 P2 15.2 0.28 13.7 KSB19
PC107 P2 17.2 0.43 12.8 KSB19
PC97 P1 14.2 0.49 10.2 KSB23
H71 53 1.50 44.55 ABH9
H208 59 1.14 50.4 ABH17
H16 24 0.75 12 ABH9
C12E 4 59.8 0.97 59.2 BH8
C12H 1 57.3 1.10 53.1 BH8
C12B 2 56.7 0.89 59.4 BH12
C9A 1 58.6 0.66 70.3 BH11
C5A 3 60.3 1.36 59.7 BH10
C4A 3 60.35 1.10 59.8 BH10
C6B 3 60 0.65 73.4 BH11
C8A 3 66 0.49 84.2 BH11
C11D 2 63.3 1.03 80 BH11
Victoria Park Swimming
Pool ComplexP245 58.3 1.44 103 DH5
Velodrome TKO
Kwun Tong Swimming
Pool
Cruise Terminal
Sun Yat Sen Memorial
Park
Bailey Street
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14th Asia Pacific Vibration Conference, 5-8 December 2011, The Hong Kong Polytechnic University
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0 20 40 60 80 100 120
Avg.
kp
Equivalent. N
Relationship between Average kp and Equivalent N
Velodrome TKO Bailey Street
Kwun Tong Swimming Pool Cruise Terminal
Sun Yat Sen Victoria Park Swimming Pool Complex
Upper Limit
Mean kp value
Fig 6: Relationship of average kp versus equivalent N-value
For the best and conservative estimate of the vibration effect, this paper suggests
adopting the upper limit line ( with the odd data excluded) (Figure 6). In Figure 6, the upper
limit of kp values vary linearly from 0.5 to 1.8 as the equivalent SPT N-values increase from
20 to 80. The suggested range also matches with the values 0.1 to 1.5 as quoted in CIRIA
Technical Note 142 and those quoted by Sarsby (2000) which suggested values 0.25 and 1.5
for loose and very stiff or dense soil respectively.
It should further be noted that kp is in fact an empirical parameter which has lumped
all the factors not properly addressed in the empirical energy formula, including interaction
between P-, S-, R- and cylindrical waves, the pile/soil impedances, the distribution of pile
shaft and toe resistance, and propagating distances. The accuracy of the prediction of
groundborne vibration therefore tends to be crude and the method is subject to further
research.
It should further be commented that the prediction of vibration using the empirical
formula Equation [1] is not very accurate for the vibration within a distance less than 10m.
As noted from Figure 2 to 4, the measured vibrations show abnormal variation at this
distance and it is difficult to predict the vibration by a single formula for such close
vibration.
5. Relationship between Peak Particle Velocity and Horizontal Distance from Pile for a given Soil Condition and Pile Depth
Based on the upper limit of kp values as suggested in Figure 6, the relationship between
the peak particle velocity and horizontal distance from a pile can be established for a given
soil condition (equivalent N-value) and pile depth (Figure 7). It is observed that a higher
equivalent N-value will give a higher groundborne vibration and a shallower pile will also
give a higher groundborne vibration than a deeper pile if same equivalent N-value is
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14th Asia Pacific Vibration Conference, 5-8 December 2011, The Hong Kong Polytechnic University
encountered. For the case illustrated in Figure 7, it is noted that a lower equivalent
N-value (N = 30) for a shallow pile (25m) will have a higher ground vibration than a high
equivalent N-value (N = 60) for a deeper pile (60m) from a distance less than 30m. A
possible reason is that there would be a higher degree of R-wave measured at the ground
surface within a shorter travel distance.
Fig 7: Predicted ground vibration versus plan distance for different soils conditions and pile depths
(with all measured vibration in the six ArchSD sites )
From Figure 7, it can also be seen that the magnitude of groundborne vibration depends on
equivalent N-value, depth of pile and the distance from the pile.
In driving of steel H piles, it is not usual to use a single size of hammer throughout the
whole installation process. For example, contractors tend to use a lighter hammer for
pitching of piles at shallow depth, and then use a heavier hammer to drive near the final set.
The input hammer energy is therefore smaller during pitching and the induced groundborne
vibration will be smaller . During the final set, the input hammer energy will be larger and
the induced groundborne vibration will be increased.
6. Conclusions
This paper presents a new and simple approach in estimating the groundborne vibration
effect due to percussive piling. From the results of groundborne vibration measurements of
driven steel H-piles installation using hydraulic hammers of 26 piles at 6 different ArchSD
sites, an upper limit of kp values for groundborne vibration prediction correlated with the
equivalent SPT N-values is developed. The kp values vary linearly from 0.5 to 1.8 as
equivalent SPT N-values increase from 20 to 80. The suggested range matches with
various research studies and is applicable in prediction of groundborne vibration in soil
conditions of Hong Kong.
It is noted that the prediction of vibration using the empirical formula Equation [1] is
not very accurate for the vibration within a distance less than 10m. For such a close
vibration, abnormal variations are observed and it is difficult to predict the vibration by a
single formula.
It is also observed that a higher equivalent SPT N-value gives a higher groundborne
vibration and a shallower pile also gives a higher groundborne vibration than a deeper pile
if same equivalent SPT N-value is encountered.
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14th Asia Pacific Vibration Conference, 5-8 December 2011, The Hong Kong Polytechnic University
References
(1) Athanasopoulos, G.A. and Pelekis, P.C. (2000), “Ground vibrations from sheetpile driving
in urban environment: measurements, analysis and effects on buildings and occupants”,
Soil Dynamic and Earthquake Engineering, 19, pp 371-87.
(2) Amick, H. and Gendreau, M. (2000), “Construction Vibrations and Their Impact on
Vibration-Sensitive Facilities”, Presented at the ASCE Construction Congress 6, Orlando,
Florida, 22 February 2000.
(3) Attewell, P.B. and Farmer, I.W. (1973), “Attenuation of ground vibrations from pile
driving”, Ground Engineering, 6(4), pp. 26–9.
(4) BSI (1990), BS 7385-1:1990 - Evaluation and Measurement for Vibration in Buildings –
Part 1: Guide for measurement of vibration and evaluation of their effects on buildings
(London: BSI).
(5) BSI (1993), BS 7385-2:1993 - Evaluation and Measurement for Vibration in Buildings –
Part 2: Guide to damage levels from groundborne vibration (London: BSI).
(6) BSI (2009), BS 5228-2:2009 - Code of Practice for Noise and Vibration Control on
Construction and Open Sites – Part 2: Vibration (London: BSI).
(7) Clough, G. W. and Chameau, J. (1980), “Measured effects of vibratory sheet pile driving”,
Journal of the Geotechnical Engineering Division, ASCE, 106(GT10), pp. 1080 - 99.
(8) Federal Transit Administration (2006), Transit Noise and Vibration Impact Assessment
(Washington DC: Department of Transportation).
(9) Hope, V.S., Hiller, D.M. (2000), “The prediction of groundborne vibration from percussive
piling”, Canadian Geotech. Journal, 37, pp 700-11
(10) Head, J.M. and Jardine, F.M. (1992), Construction Industry Research and Information
Association (CIRIA) Technical Note 142 - Ground-borne Vibrations Arising from Piling
(London: CIRIA).
(11) Jongmans D. (1996), “Prediction of ground vibration caused by pile driving: a new
methodology”, Engineering Geology, 42, pp. 25-36.
(12) Lacy, H.S. and Gould, J.P. (1985), “Settlement from pile driving in sands”, in Michigan, G.
Gazetas and E.T. Selig (eds) (1985), Proceedings of ASCE Symposium on Vibration
Problems in Geotechnical Engineering, ASCE, Detroit, pp. 152-73.
(13) Massarsch, K. R. (2000), “Settlements and damage caused by construction-induced
vibrations”, Proceedings, Intern. Workshop Wave 2000, Bochum, Germany 13–15
December 2000, pp. 299 – 315.
(14) Massarsch K. R. and Fellenius, B.H. (2008), “Ground Vibrations Induced by Impact Pile
Driving”, International Conference on Case Histories in Geotechnical Engineering,
Arlington, Virginia, 12-18 August 2008.
(15) Mohamed, R. and Dobry, R. (1987), “Settlements of cohesionless soils due to pile
driving”, Proceedings, 9th Southeast Asian Geotechnical Conference, Bangkok, Thailand,
pp. 7-23 – 30.
(16) Sarsby, R.W. (2000), Environmental Geotechnics (London: Thomas Telford Ltd).
(17) Saurenman H.J., Nelson J.T. and Wilson G.P. (1982), Handbook of Urban Rail Noise and
Vibration Control (Report UMTA-MA-06-0099-82-1) (Oakland, California: Wilson, Ihrig
& Associates).
(18) Wiss, J. F. (1981), “Construction Vibrations: State-of-the art,” Journal of the Geotechnical
Engineering Division, ASCE, 107(GT2), pp. 167-81.
(19) Woods, R.D. and Sharma V.M. (2004), Dynamic Effects of Pile Installations on Adjacent
Structures (Washington, DC: Balkema Publishers).
(20) Yeung, A.T., Tham, L.G., Yang J. and Li, K.S.V. (2005), “Ground vibration induced by
percussion piling”, Proceedings of the 16th International Conference on Soil Mechanics
and Geotechnical Engineering, 4, pp. 2205-8.
(21) Zapfe J.A., Saurenman H.J. and Fidell S.A. (2009), Contractor’s Final Report for TCRP
2014
14th Asia Pacific Vibration Conference, 5-8 December 2011, The Hong Kong Polytechnic University
Project D-12 - Ground-Borne Noise and Vibration in Buildings Caused by Rail Transit
(Washington, DC: Transportation Research Board).
Acknowledgements
The authors would like to record their thanks to the Director of Architectural Services
for her kind permission of publishing the paper. The authors would also like to record their
thanks to the staff in Division One of the Structural Engineering Branch in the Architectural
Services Department, Hong Kong SAR Government for their help in preparing the
manuscript.
2015
14th Asia Pacific Vibration Conference, 5-8 December 2011, The Hong Kong Polytechnic University
Building Vibration Induced by Percussive Piling
Chi-tong WONG* Man-kit LEUNG* Wing-chi TANG* and Heung-ming CHOW* * Architectural Services Department, Hong Kong SAR Government,
38/F Queensway Government Offices, Hong Kong SAR
E-mail: [email protected]
Abstract
Due to the complex phenomenon of propagation of vibration from the ground
through the foundation to the building, modelling and predicting building vibration
due to piling operation is always a difficult task. Empirical formulae are therefore
used to predict the vibration amplitude. However, few publications have been
documented for the applicability of these empirical formulae in Hong Kong. This
paper presents a prediction method and in-situ measurements for building vibration
induced by installation of percussive steel H-piles from a construction site. The
prediction makes use of calibrated Hong Kong soil data and the empirical method
proposed by the US Federal Transit Administration. The results show that the
approach provides a reasonable estimate of the building vibration due to percussive
piling work.
Key words: Building vibration; percussive piling; in-situ measurements
1. Introduction
Vibration and noise induced by percussive piling are commonly considered as nuisance
to the public in neighbouring areas. The vibration induced by piling operation from time to
time attracts complaint from the public due to human discomfort felt in a building or
cosmetic damage or structural distress caused to a building. For example, on 31 January
2011, when the foundation work was being carried out on a Wan Chai redevelopment site in
Hong Kong, more than a dozen residents on the nearby six-storey building was asked by the
police to evacuate, as many of them felt the shaking of the building and the furniture for at
least twice in three days (The Standard, 1 February 2011). Therefore, though percussive
steel H-pile is one of the most economical foundation types among various types of deep
foundation if the site and geological condition permits, it is unfortunate that many projects
avoid using this system just because of the fear of potential social resistance without
carrying out an estimation of the genuine vibration effects beforehand.
The vibration on the ground surface due to percussive piling has extensively been
studied and documented. However, the interaction between the ground and the foundation
causes reduction in vibration amplitude. The amount of reduction depends on the building
mass and stiffness of the foundation. A more massive building has lower response to the
ground vibration. The vibration amplitude also decreases as the vibration energy propagates
through the building to upper floors. However, in some cases, amplification of the vibration
amplitude may occur due to resonance of the floor systems. Because there are so many
factors to be considered in the estimate of building vibration due to piling operation, the
propagation of vibration from the ground through the foundation to the building is a
complex phenomenon that is difficult to model and predict accurately. Hence, empirical
formulae are widely used to predict the vibration amplitude. However, few publications
have been documented for the applicability of these empirical formulae in Hong Kong. This
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14th Asia Pacific Vibration Conference, 5-8 December 2011, The Hong Kong Polytechnic University
paper therefore presents a prediction method and the in-situ measurements for the building
vibration induced by percussive piling work from a construction project of the Architectural
Services Department of Hong Kong SAR Government.
2. Generation of Groundborne Vibrations
When a hammer hits a pile, there is resistance at the pile toe which will generate
vibration to the ground. The ground vibration can be divided into body waves and surface
waves (Woods, 2004). The amount of groundborne vibration depends on three elements:
input driving energy, attenuation rate and attenuation distance between the source and the
receptor. It is further subdivided between the energy (resistance) generated from the pile
shaft and toe, which depends on the pile and soil impedance (Massarsch and Fellenius,
2008). The rate of attenuation depends on the ground condition and the distance. Vibration
level is affected by the penetration resistance, and will be increased when dense strata or
boulder are encountered. In stiff or dense soils, smaller amount of energy is dissipated, as
elastic deformation of the soil and penetration is small, resulting in higher groundborne
vibration. In soft soils, most of the energy is used in overcoming soil friction and in
advancing the pile, resulting in low level of ground vibration.
The commonly way for quantifying ground vibration is Peak Particle Velocity (“PPV”).
The measuring unit of PPV is in “mm/s”. Extensive studies (Attewell and Farmer, 1973;
Head and Jardine, 1992; Jongmans, 1996; Hope and Hiller, 2000; and Massarsch and
Fellenius, 2008) have been carried out on correlating the ground vibration against different
piling installation methods. Most methods are based on energy approach and are basically
empirical. There have been many such formulae in slightly different format developed over
the years. One of the wisely used formulae for percussive piling was proposed by Hiller and
Crabb (2000), as shown in Equation 1:
1.3pr
Wkv (1)
where W is the hammer energy; r is the slope distance (i.e. pile toe and the receiver, rather
than the horizontal distance); and kp is the most important parameter, which varies with
different ground condition (and is greater in stiff, dense soils than in loose, soft soils).
Though there are numerous values proposed for kp (e.g. BS 5228), there are no such data for
Hong Kong soil. Wong et al (2011), based on a number of piling sites in Hong Kong,
summarizes the relationship between average kp and equivalent N-value as shown in Figure
1. The result shows that the value of kp increases together with the increases in equivalent
SPT N-value. With the availability of SPT N-value, kp can be determined readily for the
prediction of PPV on the ground.
Equation 1 was adopted in BS 5228 in predicting the ground vibration due to percussive
piling, and BS 5228 Part 4 also specifies limits on the ground vibration. For residential
premises, the limit on PPV for continuous vibration is 5mm/s and for transient vibration is
10mm/s. The PPV can also be expressed in terms of vibration velocity level (Lv) which is
defined as shown in Equation 2 (Harris Miller, 2006):
ref
10vv
vlog20L (2)
where Lv is the velocity level in decibels, v is the PPV, and vref is the reference velocity
which is usually taken as 2.54x10-5 mm/s (Harris Miller, 2006).
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14th Asia Pacific Vibration Conference, 5-8 December 2011, The Hong Kong Polytechnic University
3. Vibration of Buildings
The previous paragraph discusses the prediction of ground vibration due to percussive
piling. However, occupants of a neighbouring building are more concerned about the
resulting building vibration due to the percussive piling. The limits specified by BS 5228
represent that for structural damage. However, far before structural damage, occupants will
have experienced annoyance and discomfort well below such limits. BS 6472 gives detailed
guidance on human response to vibration in buildings. For residential premises, human will
start to feel vibration with magnitude of 0.3 mm/s and 1.0 mm/s for continuous vibration
and transient vibration, respectively (Sarsby, 2000). When considering the effects of piling
vibration on buildings, foundations are initially excited by the ground vibration. For a
typical reinforced concrete floor, the fundamental resonance is usually in the range of 20-30
Hz. Amplification is negligible if the excitation frequency is well below that of the
fundamental floor resonance. However, typical vibration produced by percussive piling is in
the range of 10-30Hz, and hence the potential of amplification is not negligible.
The prediction of building vibration is therefore even more difficult than for ground
vibration. Most numerical approaches are still in the early stages of development. The
approach presented by the US Federal Transit Administration (FTA) (Harris Miller, 2006) is
widely employed in the industry. The method basically follows that suggested in the
Handbook of Urban Rail Noise and Vibration Control (Saurenman et al., 1982). It relies on
a heuristic predictive model for predicting train-induced vibrations in buildings. As the
method is devised for vibration from mass transit projects, it may not be entirely applicable
for piling work. Yet it is difficult to find a handy method and there are no available
numerical methods to compute the vibration. Hence, though the method is very crude,
designers prefer this method, especially that it is very easy to use and able to give the
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Avg.kp
Equivalent. N
Relationship between Average kp and Equivalent N
Velodrome TKO Bailey Street
Kwun Tong Swimming Pool Cruise Terminal
Sun Yat Sen Victoria Park Swimming Pool Complex
Upper Limit
Mean kp value
Fig. 1 Relationship of average kp versus Equivalent N-value
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14th Asia Pacific Vibration Conference, 5-8 December 2011, The Hong Kong Polytechnic University
estimate quickly. Hence, it was determined to validate its applicability in Hong Kong with
the project site in this paper.
One-third-octave analysis is commonly used to analyze the vibration signals. In such an
analysis, the time domain vibration signal is passed through a series of band-pass filters
whose upper and lower frequency bands are defined by the American National Standards
Institute (ANSI, 2004). FTA’s method consists of adding a number of adjustments, including
building coupling loss (Figure 2), transmission through the building and floor resonances, to
the 1/3-octave band spectrum of the projected ground-surface vibration. For estimating
floor-to-floor vibration attenuation, -2dB/floor (1-5 floors above ground) and -1dB/floor
(5-10 floors above ground) are suggested. The FTA manual also points out that some floors
may exhibit resonant behaviour, amplifying vibrations by up to 6dB. According to the Study
Report for TCRP Project D-12 sponsored by FTA (Zapfe et al., 2009), there are a number of
areas where there is less confidence in the data and assumptions. These areas include: (1)
the attenuation of vibration as the vibration energy travels from the ground into the building
foundation and then propagates throughout the building, and (2) the amplification resulting
from resonances of floors and other structural elements. Hence, the current practice in the
US is that the resulting predictions are augmented with a factor of safety to account for
these uncertainties. An allowance of up to 5 dB is therefore commonly adopted (Zapfe et
al., 2009).
Fig. 2 Building coupling loss (extracted from FTA 2006)
4. Case Study
In-situ measurements in one project at Bailey Street, Hung Hom, Hong Kong (location
plan in Figure 3) were carried out to validate the predicted vibration level using FTA
method. Percussive steel H-piles were used as the foundation system in the project. Field
measurements were performed on the site and the building nearby (Peninsula Square),
during the installation of the steel H-piles. Peninsula Square is a high-rise commercial
reinforced concrete building with piled foundation.
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14th Asia Pacific Vibration Conference, 5-8 December 2011, The Hong Kong Polytechnic University
Fig. 3 Location plan of Joint-User Complex at Bailey Street
The following is the information of the pile at the time of measurements:
Hammer weight = 16t
Height of drop = 1.5m
Pile size = 305×305×180kg/m Grade S460J0 H-pile
Efficiency = 90%
Depth of pile at final set = 54m below ground
Distance of the building from the pile = 25m
Ground vibration is measured using vibrograph (Figure 4), which houses triaxial geophones
of sensitivity and frequency range of 0.127-254mm/s and 2-250 Hz, respectively. Histogram
mode was used for recording
ground vibration under piling
operation. In order to have better
contact between the triaxial
geophones and the ground
surface, a sand bag was put on
top of the vibrograph during
measurement.
5. Prediction and Verification of Building Vibration
Typical frequency spectra of the measured velocity are shown in Figure 5. It can be
observed that the dominated frequency due to percussive piling is around 10-20Hz. The
spectral vibration magnitude corresponding to vertical direction is the largest one among the
three orthogonal directions. However, the translational velocities should not be ignored
when considering vibration problem due to piling operation. PPV taken as the vector sum of
the three orthogonal components is therefore used in the measurement.
Tables 1 and 2 summarize the mean value estimate and the upper limit estimate of the
vibration level against the measured vibration levels respectively. There is no amplification
due to floor resonance at span of G/F, as G/F slab is on-grade. The measured PPV is the
mean values of the measured data. There are four cases in total. Case 1 considers the “mean
kp” value without any allowance for the uncertainty, while Case 2 uses the same kp value but
with +5dB allowance for the uncertainty. For Case 3, the “upper limit of kp” value is applied
with no allowance for the uncertainty. Case 4 is same as Case 3 except allowing only +2dB
instead of +5dB as the upper limit of kp value has been chosen.
Fig. 4 Vibrograph.
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14th Asia Pacific Vibration Conference, 5-8 December 2011, The Hong Kong Polytechnic University
Table 1. Mean value estimate (building coupling loss=6dB)
Location Measured
PPV (mm/s)
Case 1 (kp=1.0)
Attenuation 2dB per storey
Case 2 (kp=1.0)
Attenuation 2 dB per storey
+ 5dB (allowance)
Outside
building1.4 2.3 mm/s (99dB) 2.3 mm/s (99dB)
Attenuation
/
resonance
( /+ dB)
dBPPV
(mm/s)
Attenuation
/
resonance
( /+ dB)
dBPPV
(mm/s)
G/F column 0.9 6 93 1.1 1 98 2.0
span 1.0 6 93 1.1 1 98 2.0
1/F column 0.9 8 91 0.9 3 96 1.6
span 2.3 2 97 1.8 3 102 3.2
2/F column 0.9 10 89 0.7 5 94 1.3
span 2.8 4 95 1.4 1 100 2.5
Table 2. The upper limit estimate (building coupling loss=6dB)
Location Measured
PPV (mm/s)
Case 3 (kp=1.3)
Attenuation 2dB per storey
Case 4 (kp=1.3)
Attenuation 2 dB per storey
+ 2dB (allowance)
Outside
building1.4 2.9 mm/s (101dB) 2.9 mm/s (101dB)
Attenuation
/
resonance
( /+ dB)
dBPPV
(mm/s)
Attenuation
/
resonance
( /+ dB)
dBPPV
(mm/s)
G/F column 0.9 6 95 1.5 4 97 1.9
span 1.0 6 95 1.5 4 97 1.9
1/F column 0.9 8 93 1.2 6 95 1.5
span 2.3 2 99 2.3 0 101 2.9
2/F column 0.9 10 91 0.9 8 93 1.2
span 2.8 4 97 1.9 2 99 2.3
Fig. 5 Typical frequency spectra of measured
velocity induced by percussive piling (transverse
PPV=1.28mm/s; vertical PPV=3.18mm/s;
longitudinal PPV=1.14mm/s )
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14th Asia Pacific Vibration Conference, 5-8 December 2011, The Hong Kong Polytechnic University
6. Discussions
In Case 1, the calculated PPVs are quite close to the measured data except mid-span of
2/F where the predicted vibration level is only half of the measured one. In Case 2, +5dB
allowance is added to cater for the uncertainty in the reality. It is found that the large
discrepancy between the calculated and the measured vibration level at mid-span of 2/F is
greatly reduced. The relatively large uncertainty in the empirical parameter of kp justifies an
allowance of +5dB. In Case 3, where the upper limit of kp is used, most of the estimated
vibration levels are slightly larger than or equal to those measured except mid-span of 2/F.
It is observed that the amplification of vibration level at mid-span of 2/F is quite large
that +5dB allowance of uncertainty may not be enough if mean value of kp is adopted (e.g.
Case 2). However, the estimated vibration level in Case 4 is 3.2mm/s (102dB) if +5dB
instead of +2dB is employed. In this case, the estimated vibration level (3.2mm/s) is slightly
larger than the measured value (2.8mm/s), which is conservative. Therefore, it can be
concluded that +5dB allowance is generally good enough to cover the uncertainty provided
that the upper limit of kp is used.
7. Conclusions
The measured field data match quite well with the estimated results based on FTA
method, if adequate allowance has been made for the uncertainty. It is concluded that the
approach suggested by FTA, although crude, provides a reasonable estimate of the building
vibration due to percussive piling work. For the allowance of uncertainties, 0-5dB is well
representing the uncertainty, provided that the upper limit of kp (Figure 1) is used. In this
particular case-study, the amplification of vibration level at mid-span of 2/F is relatively
large, and the limit of +6dB suggested by the FTA manual may not be enough to cater for
the amplification. More data should be collected for further investigation in this area.
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Acknowledgements
The authors would like to record their thanks to the Director of Architectural Services
for her kind permission of publishing the paper. The authors would also like to record their
thanks to the staff in Division One of the Structural Engineering Branch in the Architectural
Services Department, Hong Kong SAR Government for their help in preparing the
manuscript.
2023