4.1
Potential ground-borne noise impacts likely to arise from the proposed Project
during both the construction phase and operation phase have been evaluated and
the results are presented in this section.
4.2
Potential ground-borne noise impacts on Noise Sensitive
Receivers (NSRs) during the construction phase would arise mainly from hydraulic breakers, hand-held breakers,
pipe pile rigs, drill & blast and tunnel boring machine (TBM). Potential ground-borne noise arising from the TBM and Powered
Mechanical Equipment (PME) was assessed, and the predicted noise levels and necessary noise
mitigation measures are presented in this section.
4.3
The drill and blast alternative is not considered with
respect to noise annoyance, as the duration of blasting is very short and
infrequent. As mentioned in section 3.14, no assessment has been carried out
regarding noise annoyance impacts within any of the identified sensitive
receivers. However, it is recommended that if there is a blasting operation, it should be
carried out outside sensitive hours to avoid
nuisance to nearby sensitive receivers.
4.4
When trains operate in tunnels that are located in close
proximity to occupied structures, there is a possibility that vibrations associated
with train passbys will be transmitted through the ground and structure, and be
radiated as noise in the occupied spaces within the structure. The assessment of the ground-borne noise impacts within the structure is presented below.
4.5
Construction ground-borne noise is under the control of the
Noise Control Ordinance (NCO), the Environmental Impact Assessment Ordinance
(EIAO), and their subsidiary Technical Memorandum. With reference to the
Technical Memorandum for the Assessment of Noise from Places Other Than
Domestic Premises, Public Places or Construction Sites (TM-Places) under the
NCO, the criteria for noise transmitted primarily through the structural
elements of the building or buildings should be 10dB(A) less than the relevant
acceptable noise level (ANL). These criteria apply to all residential
buildings, schools, clinics, hospitals, temples and churches.
4.6
The construction ground-borne noise criteria for the
representative ground-borne noise sensitive receivers (GBNSR) along WIL
alignment are tabulated in Table 4.1
below.
Table 4.1 Construction Ground-borne Noise
Criteria
|
Ground-borne Noise Criteria, dB(A) |
||
GBNSR Description |
Daytime (0700-1900 hrs) |
Daytime during general
holidays and Sundays and all days during Evening |
Night |
Churches, School –
Classrooms and |
60/55 [a] |
55 |
[b] |
Domestic premises, clinics[c] and hospitals along WIL alignment |
65 |
55 |
40 |
[a] A
5dB(A) reduction to the ground-borne noise criteria is recommended for school
during examination period.
[b] No sensitive use during this period.
[c] Clinics are considered to be noise sensitive
during daytime and evening time only.
4.7
For construction activities involving the use of TBM and PME
in restricted hours (1900-0700), it is necessary to apply for a CNP. However, there is no guarantee that a CNP
will be issued for the project construction.
4.8
In the projection and measurement of ground-borne noise from
transit trains operating at grade, or in tunnels, to receivers adjacent to the alignment,
it is customary to calculate or measure the impact of a single train passby,
where the noise level from it is rms (root mean square) averaged over the
duration of the passby (Appendix 4.1:
Ref. 1). This is, by definition, the
equivalent noise level of the passby, where duration is defined as the period
between the passage of the front and rear ends of the train pass the closest point on the
alignment to the building foundation.
This measure is assumed in this study and is known as the rms level of
the passby. Given train lengths and
passby frequencies along the WIL, the 30 minutes overall equivalent A-weighted
noise level shall be determined at each GBNSR from the maximum rms level of a
single train passby.
4.9
With reference to the TM-Places under the NCO, the criteria
for noise transmitted primarily through the structural elements of the building
or buildings should be 10dB(A) less than the relevant acceptable noise level
(ANL). The same criteria are applied to
all residential buildings, schools, clinics, hospitals, temples and churches.
4.10
The operational ground-borne noise criteria for the
representative GBNSRs along WIL alignment are tabulated in Table 4.2 below.
Table 4.2 Operational
Ground-borne Noise Criteria
|
Ground-borne Noise Criteria,
dB(A) |
|
GBNSR Description |
Day & Evening |
Night |
Churches, School – Classrooms and |
55 (Leq 30 min) |
[a] |
Domestic premises, Clinics[b] and Hospitals along WIL alignment |
55 (Leq 30 min) |
45 (Leq 30 min) |
Note:
[a] No sensitive use during this period.
[b]
Clinics are considered to be noise sensitive during daytime and evening time
only.
4.11
Under the assumption of
worst-case scenario, two sets of representative GBNSRs were identified for the
assessment of noise impact induced by (1) TBM operation for tunnelling and (2)
PME (e.g. hydraulic breakers, drill rigs and pile rigs) operation at open works
areas and during the construction of adits and vent shaft. Twenty-six GBNSRs identified along the WIL
alignment were designated for the assessment of TBM-induced ground-borne noise
impact. As for the assessment of noise
impact due to the use of PME for rock breaking / drilling, including hydraulic
breakers, drill rigs and pile rigs, at open works areas, adits and vent shaft,
twenty-five representative GBNSRs located in the closest proximity to the
concerned open works areas were identified.
These identified GBNSRs are presented in Tables
Table
Construction GBNSR No. |
Location |
Uses |
Horizontal Distance from NSR to Tunnel (m) |
Vertical Distance from NSR to Tunnel (m) |
1 |
No.153 Queen's Road West, |
Residential |
96 |
29 |
2 |
Sai Ying Pun Jockey Club Polyclinic at |
Clinic |
75 |
40 |
3 |
No.36 Eastern Street, |
Residential |
0 |
43 |
4 |
Sai Ying Pun Community Complex |
Kindergarten, hostel & community centre |
100 |
61 |
5 |
Eastern Street Methadone Clinic |
Clinic |
69 |
65 |
6 |
Nos. |
Residential |
18 |
61 |
7 |
Prewar Buildings Under the Development Project of |
Residential |
15 |
64 |
8 |
No.35 |
Residential |
0 |
43 |
9 |
King's College at |
Educational Institution |
12 |
67 |
10 |
|
Church |
0 |
68 |
11 |
|
Educational institution |
15 |
76 |
12 |
Fung Ping Shan building , the |
Educational institution |
0 |
66 |
13 |
St. Stephen's Church at |
Church |
75 |
84 |
14 |
|
Educational institution |
33 |
84 |
15 |
|
Educational institution |
0 |
84 |
16 |
St. Anthony's Catholic Church at |
Church |
45 |
57 |
17 |
Senior Staff Quarters, Workmen's Quarters and Treatment Works
Building, Elliot Pumping Station and Filters at Pok Fu Lam Road |
Residential |
0 |
90 |
18 |
Lo |
|
0 |
55 |
19 |
|
Education Institution |
0 |
51 |
20 |
Fok Hing Tong, |
|
69 |
48 |
21 |
|
Educational Institution |
129 |
61 |
22 |
|
Hostel |
150 |
15 |
23 |
|
Educational Institution |
120 |
45 |
24 |
|
Church |
120 |
64 |
25 |
Western District Community Centre |
Community Centre |
150 |
58 |
26 |
|
Residential |
0 |
24 |
Table 4.3b Identified NSRs for Assessment of Ground-borne
Construction Noise Impacts due to Construction Works at Open Works Areas
Construction
GBNSR No. |
Description |
Uses |
Horizontal
Distance to the Site Boundary (m) |
Nearest
Site |
KET |
||||
27 |
Hong Kong
Institute of Vocation Education (Kennedy Centre) |
Educational
Institution |
21 |
|
28 |
Luen
Tak Apartment |
Residential |
22 (2
Sites) |
KET
Station site |
29 |
|
Residential |
13 |
Entrance
B |
30 |
|
Residential |
6 |
KET
Station site |
UNI |
||||
31 |
The
Belcher’s Tower 3 |
Residential |
8 |
Entrance
C2 |
32 |
|
Residential |
6 |
Vent
shaft (VS-Y) |
33 |
Western
Court Block 1-4 |
Residential |
4 |
Entrance
B1 |
33a |
The |
School |
11 |
Entrance
A |
SYP |
||||
34 |
|
Residential |
6 |
Entrance
of B3 |
35 |
Bon-Point |
Residential |
6 |
Vent
shaft (VS-Z) and Entrance C |
36 |
Queen’s
Hotel |
Hotel |
6 |
Entrance
A1 and Vent Shaft (VS-Y) |
37 |
|
Residential |
6 |
High
Street Site |
Table
Construction GBNSR No |
Description |
Uses |
Adits / Vent Adits |
Vertical Distance to Adit (m) |
Rock Head ditance to Adits (m) |
UNI |
|||||
38 |
|
Residential |
Adit to
Entrance A |
50 |
35 |
39 |
Intelligent
Court |
Residential |
Adit to
Entrance B1 |
30 |
10 |
40 |
Sik On
Building |
Residential |
Adit to
Entrance B2 |
20 |
20 |
31 |
The
Belcher’s Tower 3 |
Residential |
Adit to
Entrance C2 |
65 |
45 |
41 |
|
Residential |
Construction
Adit |
40 |
20 |
42 |
Wing Fu
Lau |
Residential |
Vent
adit (YS-Y) |
30 |
20 |
SYP |
|||||
34 |
|
Residential |
Adit to
Entrance B3 |
22 |
~20 |
36a |
6-28
Eastern Street |
Residential |
Vent
adit (YS-Z) |
45 |
20 |
43 |
|
Residential |
Adit to
Entrance A1 |
25 |
5 |
44 |
Yee
Shun Building |
Residential |
Adit to
Entrance B1/B2 |
35 |
0 |
45 |
Jade
Court |
Residential |
Adit to
Entrance C |
42 |
32 |
46 |
|
Residential |
Vent
adit (YS-Z) |
49 |
25 |
47 |
|
Residential |
Vent
adit (YS-Z) |
55 |
40 |
4.12
Sensitive receivers along the WIL alignment generally
include educational institution and domestic premises. Domestic premises and hospital are taken into
account during both the daytime and night time periods. School classrooms, churches, clinics and
temples are considered to be noise sensitive during daytime and evening only.
4.13
A total of ten operational phase GBNSRs were identified, and are listed in Table 4.4. Their locations are shown in
Figures 4.6 to 4.9. Information necessary for noise prediction is
also provided in the table below, including the geometry of the closest point
on a GBNSR relative to the alignment, and the structure characterisation. The train speed at each operational phase GBNSR is shown in Appendix
4.11. The maximum allowable acceleration for existing Island Line trains is
Table 4.4 Operational
Ground-borne Noise Sensitive Receivers
GBNSR No (a). |
Location |
Chainage |
Turn- out |
Lowest Sensitive Floor |
Building Type (b) |
Building Height, storey |
Foundat’n Depth, m |
EB Track Dist to G/F Building Edge, m |
WB Track Dist to G/F Building Edge, m |
||||||
Hori |
Rail Depth |
Rock- head Depth |
slant dist to foundat’n |
Hori |
Rail Depth |
Rock- head Depth |
slant dist to foundat’n |
||||||||
1 |
|
SYP-SHW E0+940 |
Y |
1 |
0 |
5 |
2 |
7 |
28 |
28 |
27 |
13 |
28 |
31 |
29 |
2 |
|
SYP-SHW E0+820 |
Y |
2 |
0 |
35 |
5 |
0 |
28 |
28 |
23 |
0 |
28 |
31 |
23 |
3 |
Kian Nan Mansion, 81-85 Bonham Strand West |
SYP-SHW E0+620 |
N |
1 |
0 |
19 |
2 |
0 |
30 |
32 |
28 |
0 |
30 |
32 |
28 |
4 |
No. 36 Eastern Street, |
SYP-SHW E0+150 |
N |
1 |
1 |
5 |
2 |
0 |
42 |
29 |
40 |
2 |
42 |
29 |
40 |
5 |
|
KET-UNI E0+270 |
N |
1 |
0 |
13 |
2 |
0 |
42 |
10 |
40 |
0 |
42 |
10 |
40 |
6 |
Tower 1, |
KET-UNI E0+180 |
N |
3 |
0 |
37 |
2 |
0 |
57 |
20 |
55 |
0 |
57 |
20 |
55 |
7 |
Block D, Kwun Lung Lau |
OVR-KET E0+700 |
N |
>1 |
0 |
20 |
2 |
26 |
44 |
8 |
49 |
22 |
44 |
16 |
47 |
8 |
Kwun Lung Lau New Development Site |
OVR-KET |
N |
5 |
0 |
24 |
0 |
36 |
34 |
8 |
50 |
40 |
34 |
16 |
52 |
9 |
East Terrace, Sai Wan Estate |
OVR-KET E0+560 |
Y |
1 |
0 |
12 |
0 |
17 |
46 |
23 |
49 |
17 |
46 |
23 |
49 |
10 |
Tower 3, Academic Terrace |
KET-UNI E0+310 |
N |
1 |
0 |
26 |
2 |
20 |
72.9 |
Above track |
74 |
0 |
72.9 |
Above track |
71 |
Note: (a) All GBNSR are
residential buildings.
(b) Building Type: 0 – Heavy
Tall Structures, 1 – 2-4 Storeys Medium Height
4.14
Potential ground-borne noise impacts on GBNSRs during the
construction phase will arise mainly from drill & blast and TBM,
as well as PME for rock breaking/drilling including breakers, drill
rigs and pile rigs.
4.15
There are no statutory procedures
and criteria under the NCO and EIAO for assessing blasting noise impacts. Blasting in this Project, if required, would
be carried out underground. Any such
blasting noise, which is transient and short in duration, is not assessed in
this EIA. However, the administrative
and procedural control of all blasting operations in
4.16
When trains operate in tunnels that are located in close
proximity to occupied structures, there is a possibility that vibrations
associated with train passbys will be transmitted through the ground and
structure, and be radiated as noise in the occupied spaces within the
structure. The noise levels within the structure may be high enough to cause
annoyance to the GBNSRs.
4.17
As described above, projections of Peak Particle Velocity
(PPV) assumed worst case assumptions along the WIL alignment. The
projection methodology is empirically based on, and is the same as that used to
determine noise impacts on sensitive receivers from operational trains, as
described in the operation ground-borne noise section. The projection methodology is recommended by
the U.S. Department of Transportation and Federal Transit Administration[1]
. This projection methodology has been
previously used for Ground-Borne Noise & Vibration Assessment for approved
Kowloon Southern Link (KSL) EIA[2]
(EIA Register No. AEIAR-083/2005).
4.18
The main components of the proposed prediction model for
ground-borne noise are:
l
Vibration source level from operation of TBM;
l
Vibration propagation through the ground to the structure
foundation;
l
Vibration reduction due to the soil/structure interface;
l
Vibration propagation through the building and into occupied
areas; and
l
Conversion from floor and wall vibration to noise.
4.19
The empirical based prediction model used to project noise
level within occupied areas of the structures adjacent to the WIL is described
below. The basic equation describing the
model, in decibels, is
L = FDL + LSR + BCF + BVR + CTN + SAF
where
the prediction components are:
L |
ground-borne noise level within
the structure, re: 20 μ-Pascal, |
FDL |
force density level for the TBM in
rock, mixed face or soil, re: 1 lb/in0.5 in English unit and re: 1 N/m0.5 in
SI unit, |
LSR |
unit force incoherent line source
response for the ground, re: 1 μ -in/sec/(1 lb/in0.5) in English unit
and 10-8 m/s/(1 N/m0.5) in SI unit, |
BCF |
vibration coupling loss factor
between the soil and the foundation, relative level, |
BVR |
building vibration reduction or
amplification within a structure from the foundation to the occupied areas,
relative level, |
CTN |
Conversion from floor and wall vibration
to noise, 10-8 m/s or 10-6 in/s to 20 μ Pascal,
and |
SAF |
Safety margin to account for
wheel/rail condition and projection uncertainties. |
4.20
The measurement and analysis equipment used in obtaining these
empirical results is given in operation ground-borne noise section. Predictions are based on assuming the closest
distance along the alignment to the building foundation of the receiver.
4.21
The above methodology has been altered for TBM in the
following ways:
1.
The source vibration level, or force density level (FDL), is
obtained from vibration measurements taken during the passby of a tunnel boring
machine operating in soil and rock along the KCRC Lok Ma Chau extension. A summary of measurement
data is provided in Appendix
4.2: Figure 1. Measurements were
performed underground in an access shaft adjacent to the alignment at 7m
setback from tunnel centreline. The
associated line source response (LSR) was obtained from surface and borehole
impact tests were performed on similar soil and rock geology, as shown in Appendix 4.2: Figure 2. The length of
the LSR along the TBM is assumed to be 10m.
The resulting FDLs are given in Appendix
4.2: Figure 3 and compared to a typical FDL for a heavy rail transit
train. It can be seen that the FDL for
the TBM in rock is considerably higher than that in soil, especially at low
frequencies. The FDL for the TBM in soil
is roughly comparable to the graph of a typical heavy rail transit train. In mixed face geology, the FDL for rock is
assumed, for conservatism.
2.
The LSR along the WIL alignment was taken from borehole
impact tests performed along the WIL, as described in operation ground-borne
noise section, except the line source length is assumed to be 10m.
3.
RMS vibration measurements are used for the ground-borne
noise assessment.
4.22
In all other respects, the components of the projections are
the same as that used for the assessment of operational trains.
4.23
At setback distances characteristic of this study,
ground-borne noise from TBM would have an impact, conservatively, up to about
160 Hz for tunnels situated in soil and up to 500 Hz for tunnels situated in
rock. Above these frequencies, the
material attenuation of the ground would reduce the amplitude of the
propagating waves below which there would be adverse impact. Thus, structure borne noise levels will be
presented in octave bands over the frequency range of 31.5 Hz to 500 Hz.
4.24
The LSR determines the vibration levels or attenuation in
the ground as a function of distance caused by an incoherent line source of
unit force point impacts, with line source orientated along the alignment and
the length of the line source equalling 10m measured from the front of the
TBM. Thus, the basic quantity required
for the determination of the LSR would be the vibration response caused by a
unit point source impact, which is defined as the Point Source Response
(PSR). Given the PSR would be along the
alignment over the length of the train, the LSR would follow directly by
incoherent integration of the PSR over the length of the train.
4.25
However, the determination of the PSR for force point
impacts along the alignment over the length of the train is neither practical
nor affordable. For example, at
underground sections, force impacting would have to be performed in numerous
boreholes drilled to the depth of the alignment and closely spaced along the
alignment over the length of the train just for the determination of the LSR at
one location. Thus, certain assumptions
are invoked, which allow one PSR to be taken as representative along the
alignment near a building receiver and to be used in the determination of the
LSR. These assumptions include:
l
The ground is layer-wise homogeneous,
l
The ground is transversely isotropic along the alignment
over the length of the train
l
The ground is between the alignment segment and the
vibration receivers at which the LSR is to be determined.
4.26
If the ground satisfies these assumptions rigorously, it
would be acceptable to use one PSR in the determination of the LSR. In normal
circumstances, deviation from the idealised assumptions of transverse isotropy
and layer-wise homogeneity is not significant enough to warrant the time,
expense and impracticality of impacting along the entire length of the
train. Also, the flanking effect of
vibration from remote cars towards the front and rear of the train is not very
significant: it is the vibration from the train section opposite to the
shortest distance from the track to the receiver that, in most circumstances,
determines the vibration level at the receiver.
4.27
A detailed description of the PSR testing along the WIL and
the LSR model can be found in operation ground-borne noise section, where the
PSR testing is referred to as borehole impact testing.
4.28
The recommended practice established within the USFTA handbook
is followed. Structures are divided into 4 types, with BCF attenuation given in
the follow:
Type 0 – Large structures with heavy
foundations
Type 1 – 2-4 storeys medium sized
structures
Type 2 – 1-2 storeys complexes
Type 3 – Single family detached
residences
4.29
It can be seen from Appendix
4.2: Figure 4 that, larger and heavier structures have greater vibration
attenuation than smaller and lighter structures. In fact, the extent of the
attenuation is governed by the difference in mechanical impedance between the
soil and the foundation, with impedance being determined by differences in mass
and stiffness within the soil and foundation. For structures founded on rock,
there is no impedance contrast between the soil and the foundation; thus, in
this case, the BCF is zero.
4.30
The building vibration response is generally determined by
three factors:
l
Resonance amplification due to floor, wall and ceiling
spans;
l
Floor-to-floor attenuation; and
l
Attenuation across a structure, in the direction away from
the alignment.
4.31
Resonance amplification due to wall, floor and ceiling spans
is usually an issue for small, lightweight housing, generally single-family
homes constructed of wood. The frequencies
at which resonances occur can vary widely, and the magnitude of the resonance
amplification would depend on the structure. In large, heavy framed structures,
generally multi-floor concrete construction, structural resonances usually
occur at sub-audible frequencies, with small resonance amplification due to
massive structural elements having low mobility.
4.32
The FTA Handbook recommends that the BVR includes no
correction for heavy framed structures, a 3 dB correction for moderate weight
structures and a 6 dB correction for lightweight structures to account for
structural resonances that may be present in smaller and less massive
structures located along the alignment. Lightweight structure refers to hollow
block, lightweight concrete, brick, timber or composite structures of only
several stories high. A moderate weight
structure is generally light weight concrete construction up to 6 or 7 storeys.
As the frequency at which such resonances may occur is not known, these
corrections add either 3 or 6 dB to all frequency bands considered.
4.33
The BVR shown in Appendix
4.2: Figure 5 is applied to all structures conservatively, which is a
modified version of the 6 dB rule across all frequencies, as recommended for
light weight structures.
4.34
Usually, occupied spaces within a structure are assumed to
be located at or above the nearest setback distance from the alignment to the
receiver. However, vibration attenuation across a structure may be relevant
where the noise sensitive area is situated in the back of the building away
from the alignment. Although vibration
attenuation has been measured across a number of structures in
4.35
A floor-to-floor attenuation of 2 dB reduction per floor is
assumed. Where there is a multi-floor
occupancy, only the structure borne noise impact on the lowest occupied floor
is considered.
4.36
A -2 dB correction for conversion of vibration (re: 10-6
in/s) in room walls, floors and ceiling to noise (re: 20 micro Pa) is assumed;
4.37
In the determination of the components of the prediction
model, data undergoes extensive averaging, thus making the overall prediction
of ground-borne noise a sum of averages. In many of our comparisons of
predicted and measured levels, it has been generally found that differences in
overall predicted and measured A-weighted noise levels fall within about ±5dB. Thus if noise criteria are
regarded as simple design guidelines, no safety factor would be appropriate. If
all but a few exceptional passbys are expected to produce noise and vibration
levels below criteria, then a safety factor of 5 dB would be appropriate. If
strict adherence of every passby to noise and vibration criteria is expected,
then a safety factor of 10dB or more would likely be appropriate. In this study, a conservative 10dB safety
factor has been adopted.
4.38
A large safety factor results in higher projected noise and
vibration levels, thus exceeding the criteria in a larger extent. Therefore,
greater requirements for trackform vibration attenuation, both in type and
extent, would be needed.
Adaptation to Hydraulic Breaker, Rock Drill and Pile Rig
4.39
The source terms and transmission factors for the
ground-borne noise assessment of hydraulic breaker, rock drill and pile rig would be different from the TBM
calculation above. Reference was made to
the assessment approach, source terms and transmission factors adopted in the
approved EIA study for the Kowloon Southern Link project. The assumptions adopted in the present
assessment are provided in Appendix 4.3.
Soil
Damping
4.40
Internal losses of soil would cause the vibration amplitude
to decay against the propagation distance and the decay relationship is based
on the equation set out in the Transportation Noise Reference Book[3].
V(R) = V(Ro)
´ e-2pf h R/2c.
The
velocity amplitude V is dependent on the frequency f in Hz, the soil loss
factorh, the wave speed c in m/s, the distance R
from the source to the NSR. The
properties of soil materials are shown in Table
4.5.
Table 4.5 Wave
Propagation Properties of Soil
Soil Type |
Longitudinal Wave Speed c, m/s |
Loss Factor, h |
Density, g/cm3 |
Soil |
1500 |
0.5 |
1.7 |
Rock |
3500 |
0.01 |
2.65 |
4.41
No damping attenuation was applied for propagation in rocks.
All GBNSRs were assumed to have a piling foundation on rockhead
except
4.42
The coupling loss into building structures represents the
change in the incident ground-surface vibration due to the presence of the
piled building foundation. The empirical
values with reference to the “Transportation Noise Reference Book”, 1987 are
given in Table 4.6.
Table 4.6 Loss
factor for Coupling into Building Foundation
Frequency |
Octave Band Frequencies, Hz |
|||||
16 |
31.5 |
63 |
125 |
250 |
500 |
|
Loss factor for coupling into building foundation, dB |
-7 |
-7 |
-10 |
-13 |
-14 |
-14 |
4.43
The coupling loss per floor represents the floor-to-floor
vibration transmission attenuation. For multi-storey
buildings, a common value for the attenuation of vibration from floor-to-floor
is approximately 1 dB attenuation in the upper floor regions and greater than 3
dB attenuation at lower floors. Coupling
loss of 1 dB reduction per floor was assumed in this report for a conservative
assessment to account for any possible amplification due to resonance effects.
4.44
Conversion from floor vibration levels to indoor reverberant
noise levels is based on standard acoustic principles. The conversion factor is dependent on the
surface area S of the room in m2,
the radiation efficiencys, the volume of the room V in m3
and the room reverberation time RT in seconds.
Conversion factors from floor vibration levels to indoor reverberant
noise levels are 27 and 23 dB(A) for residential units and educational
institution respectively.
4.45
The most current and evolved projection methodology recommended
by the FTA Manual is used in this EIA study.
This manual is issued by the US Department of Transportation in 1995 and
is intended to provide guidance in preparing and reviewing the noise and
vibrations sections of environmental submittals to the US Government for grant
applications. The methodology has been
applied on a number of transit systems over the years, including West Rail,
East Rail Tsim Sha Tsui Extension, Kowloon Southern Link and MTR Tseung Kwan O
Line.
4.46
The main components of the proposed prediction model for
ground and structure borne noise are:
l
Vibration source level from operation of MTRC Trains;
l
Trackform vibration attenuation or amplification;
l
Soil-based tunnel vibration reduction;
l
Vibration propagation through the ground to the structure
foundation;
l
Vibration reduction due to the soil/structure interface;
l
Vibration propagation through the building and into occupied
areas; and
l
Conversion from floor and wall vibration to noise.
4.47
The empirical based prediction model used to project noise
and vibration level within occupied areas of the structures adjacent to the
SDTE is described in detail in Appendix
4.1: Refs 2 and 3. A summary is
given below. The basic equation
describing the model, in decibels, is
L = FDL + TIL + TOC + TCF + LSR + BCF + BVR + CTN + SAF
where the prediction components are:
L |
ground-borne noise
level within the structure, re: 20 -Pascal, |
FDL |
force density level for
the KRTC EMU, re: 1 lb/in0.5 in English unit and re: 1 N/m0.5 in SI unit, |
TIL |
trackform attenuation
or insertion loss, relative level, |
TOC |
turnout and crossover
factor, |
TCF |
vibration coupling between
the tunnel and the ground for soil based tunnels, relative level, |
LSR |
unit force incoherent
line source response for the ground, re: 1 -in/sec/(1 lb/in0.5) in
English unit and 10-8 m/s/(1 N/m0.5) in SI unit, |
BCF |
vibration coupling loss
factor between the soil and the foundation, relative level, |
BVR |
building vibration
reduction or amplification within a structure from the foundation to the
occupied areas, relative level, |
CTN |
Conversion from floor
and wall vibration to noise, 10-8 m/s or 10-6 in/s to
20 Pascal, |
SAF |
Safety margin to
account for wheel/rail condition and projection uncertainties. |
4.48
The measurement and analysis equipment used in obtaining
these empirical results is given in Appendix
4.4. Predictions are based on assuming the closest distance along the
alignment to the building foundation of the receiver.
4.49
At setback distances characteristic of this study,
ground-borne noise from transit trains can have an impact, conservatively, up
to about 160 Hz for tunnels situated in soil, and up to 500 Hz for tunnels
situated in rock. Above these
frequencies, the material attenuation of the ground would reduce the amplitude
of the propagating waves below which there would be adverse impact. Thus, structure borne noise levels will be
presented in octave bands over the frequency range of 31.5 Hz to 500 Hz. “Feelable” vibration levels will be presented
in 1/3 octave bands over the frequency range of 3.15 Hz to 500 Hz.
4.50
In the projection and measurement of ground-borne vibration
or noise from transit trains operating at grade, or in tunnels, to receivers
adjacent to the alignment, it is customary to calculate or measure the impact
of a single train passby, where the vibration or noise level from it is rms
(root mean square) averaged over the duration of the passby (Appendix 4.1: Ref. 3).
This is, by definition, the equivalent noise or vibration level of the
passby, where duration is defined as the period between the passage of the
front and rear ends of the train past the closest point on the alignment to the
building foundation. This measure is
assumed in this study.
4.51
The vibration source strength level (Force Density Level
FDL) for train operations on the WIL extension was derived from wayside
vibration measurements taken during operation of eight car MTRC M-stock EMU passbys,
at grade, and in a tunnel structure.
Ground vibration levels were recorded at various setback distances from
the track during train passbys at various speeds between 20 kph and 60 kph and
during impact hammer tests on the trackform.
These measurements are used to determine the vibration source strength
for the passing train. A description of
the measurements and development of the FDL is given in Appendix 4.5.
4.52
In Appendix 4.5, it
is shown that the vibration source level, or the FDL determined for the
Metro-Cammell EMU (M-stock) was obtained from train passby and impact hammer
test on the at grade Up track through Heng Fa Chuen Depot and Down track tunnel
near Po Lam station. The FDL taken for
the WIL EMU is the maximum envelope of FDLs obtained at Heng Fa Chuen Depot
(Island Line) and Po Lam (Tseung Kwan O Line).
Maximum envelope is defined as the maximum levels occurring at all 1/3
octave band frequencies for all passbys considered; it is independent of any
one specific passby. The two FDLs and
the maximum envelope are given in Appendix
4.5: Figure 8.
4.53
It is a well-known fact that the greater the trackform
attenuation, the greater the cost and the engineering complexity. Attenuation has two components: the magnitude
of the attenuation and the frequency above which attenuation occurs (resonance
frequency of the trackform). Generally,
more compliant trackform support and more massive elements in the trackform
will result in a greater magnitude of attenuation occurring at lower
frequencies. Thus floating slab
trackform (FST) will produce significantly more attenuation at lower
frequencies than a resilient baseplate.
However, greater compliance in the trackform support results in greater
mobility of the rail, which requires careful examination of changes in rail
geometry under loading, and consideration of associated fatigue and component
life expectancy. In addition, more massive trackform elements would take up
more space in tunnels and may cause spatial incompatibilities that are
difficult to be overcome in the design.
4.54
The approach taken in this study is to try and reduce the
number of different trackform types to a minimum, whilst providing the
necessary vibration attenuation for satisfaction of the noise and vibration
criteria along the alignment. The type
of vibration mitigating trackform is often grouped into four categories listed
below:
1.
Type 1a: A medium attenuation baseplate or booted dual
sleepers based on a bonded or non-bonded compression style baseplate with a
resilient elastomeric element having static stiffness of about 25 kN/mm, to be
fitted atop the concrete sleepers or atop the invert,
Type 1b: Resiliently supported sleepers whose resilient
support pad is manufactured from natural rubber and has a static stiffness in
the order of 15kN/mm to 20 kN/mm;
2.
Type 2: A high attenuation baseplate or booted dual sleepers
including
i.
a bonded “Egg” style baseplate with a resilient elastomeric
element having static stiffness in the range of 7 kN/mm to 14 kN/mm, to be
fitted atop concrete sleepers or on the invert;
ii.
the Pandrol Vanguard baseplate having static stiffness on the
order of 3kN/mm to 5kN/mm; or
iii.
resiliently supported sleepers whose resilient support pad
is manufactured from natural rubber and has a static stiffness in the order of
8kN/mm to 12 kN/mm - an alternative for tangent, or near-tangent track only.
3.
Type 3: An isolated slab trackform (IST), which is a ballast
mat with bedding modulus in the order of 20N/mm3 placed beneath an
in situ poured concrete slab, with loaded resonance frequency in the order of
20Hz to 25Hz; and
4.
Type 4: A floating mini slab trackform (FST) with loaded
resonance frequency of about 16Hz.
5.
Type 0: Trackform is assumed to be one where no vibration
mitigation is required.
4.55
The details of insertion loss of Type 1a and 1b trackform
are given in Appendix 4.6.
4.56
Vibration attenuation occurs at the interface between a
transit tunnel and the surrounding soil on account of a mismatch in the soil
and tunnel wall impedances. Given the same soil, the heavier and stiffer the
tunnel, the greater the attenuation.
Tunnels borne in rock generally do not exhibit any significant vibration
attenuation across the tunnel rock interface. The TCF was examined in detail in
a measurement study described in Appendix
4.1: Ref. 5. The approach taken was
to measure vibration levels on the ground surface with a linear array of
vibration transducers (Appendix 4.7:
Photos 1-6) in response to impacting within a tunnel. With the linear array in place, additional
measurements were performed during impacting on the ground surface above the
tunnel centreline. By obtaining the LSR
for both the tunnel and surface impact measurements, and correcting for setback
and surface vs. below surface impacting, TCF factors were developed.
4.57
A detailed description of the TCF test utilised in this
study can be found in Appendix 4.7. Interestingly, the TCF curve is similar to
the BCF curve for type 2 (1-2 storeys residential complexes). The TCF taken for the WIL projection is the
maximum envelope of TCF obtained and the type 2 BCF curve (Appendix 4.7: Figure 1).
4.58
No TCF attenuation is applied for rock-founded tunnels. However, with reference to the
FTA Manual, a 3dB(A)
and 5dB(A) reduction in groundborne noise level was assumed for cut-and-cover tunnels and station structures respectively.
4.59
The LSR determines the vibration levels or attenuation in
the ground as a function of distance caused by an incoherent line source of
unit force point impacts, with line source orientated along the alignment and
the length of the line source equalling that of the train. Thus, the basic quantity required for the
determination of the LSR would be the vibration response caused by a unit point
source impact, which is defined as the Point Source Response (PSR). Given the PSR along the alignment over the
length of the train, the LSR would follow directly by incoherent integration of
the PSR over the length of the train.
4.60
However, the determination of the PSR for force point impacts
along the alignment over the length of the train is neither practical nor
affordable. For example, at underground
sections, force impacting would have to be performed in numerous boreholes
drilled to the depth of the alignment and closely spaced along the alignment
over the length of the train just for the determination of the LSR at one
location. Thus, certain assumptions are
invoked, which allow one PSR to be taken as representative along the alignment
near a building receiver and to be used in the determination of the LSR. These assumptions include:
l
The ground is
layer-wise homogeneous,
l
The ground is
transversely isotropic along the alignment over the length of the train,
l
The ground is between
the alignment segment and the vibration receivers at which the LSR is to be
determined.
4.61
If the ground satisfies these assumptions rigorously, it
would be acceptable to use one PSR in the determination of the LSR. In normal circumstances, deviation from the
idealised assumptions of transverse isotropy and layer-wise homogeneity is not
significant enough to warrant the time, expense and impracticality of impacting
along the entire length of the train.
Also, the flanking effect of vibration from remote cars towards the
front and rear of the train is not very significant: it is the vibration from
the train section opposite the shortest distance from the track to the receiver
that, in most circumstances, determines the vibration level at the
receiver.
4.62
A detailed description of the PSR testing along the WIL and
the LSR model can be found in Appendix
4.8, where the PSR testing is referred to as borehole impact testing.
4.63
The recommended practice established within the USFTA handbook
(Appendix 4.1: Ref 3) was followed.
Structures are divided into 4 types, with BCF attenuation given in (Appendix 4.9: Figure 1):
Type 0 – Large structures
with heavy foundations
Type 1 – 2-4 storey
medium sized structures
Type 2 – 1-2 storey complexes
Type 3 – Single family
detached residences
4.64
As shown in Appendix
4.9: Figure 1, larger and heavier structures would have greater vibration
attenuation than smaller and lighter structures. In fact, the extent of the
attenuation is governed by the difference in mechanical impedance between the
soil and the foundation, with the impedance being determined by differences in
mass and stiffness within the soil and foundation. For structures founded on
rock, there is no impedance contrast between the soil and the foundation; thus,
in this case, the BCF is zero.
4.65
The building vibration response is generally determined by
three factors:
1.
Resonance amplification due to floor, wall and ceiling
spans;
2.
Floor-to-floor attenuation; and
3.
Attenuation across a structure, in the direction away from
the alignment.
4.66
Resonance amplification due to wall, floor and ceiling spans
is usually an issue for small, lightweight housing, generally single-family
homes constructed of wood. The
frequencies at which resonances occur can vary widely, and the magnitude of the
resonance amplification would depend on the structure (Appendix 4.1: Ref. 6). In
large and heavy framed structures, generally multi-floor concrete construction,
structural resonances usually occur at sub-audible frequencies, with small
resonance amplification due to massive structural elements having low
mobility.
4.67
The FTA Handbook (Appendix
4.1: Ref. 3) recommends that the BVR includes no correction for heavy
framed structures, a 3 dB correction for moderate weight structures and a 6 dB
correction for lightweight structures to account for structural resonances that
may be present in smaller and less massive structures located along the
alignment. Lightweight structure refers to hollow block, lightweight concrete,
brick, timber or composite structures of only several storeys high. A moderate weight structure is generally
lightweight concrete construction up to 6 or 7 storeys. As the frequency at
which such resonances may occur is not known, these corrections add either 3 or
6 dB to all relevant frequency bands in which building resonance may occur.
4.68
From past experience, structural resonance in the order of 3
to 6 dB occurring in moderate and heavyweight structures, which characterise
most of the buildings along the WIL alignment.
Structural resonance has been observed to be significantly higher than 6
dB in some types of lightweight structures, especially single-family residences
constructed of wood, which are not the types of buildings found along the WIL
alignment. Thus, the BVR given in Appendix
4.10: Figure 1 is applied to all structures, which is an extended version
of the 6 dB rule across the frequencies of 20Hz to 40Hz, as recommended by Appendix 4.1: Ref. 3 for light weight
structures.
4.69
Usually, occupied spaces within a structure are assumed to
be located at or above the nearest setback distance from the alignment to the
receiver. However, vibration attenuation across a structure may be relevant
where the noise sensitive area is situated in the back of the building away
from the alignment. Although vibration
attenuation has been measured across a number of structures in
4.70
A floor-to-floor attenuation of 2 dB reduction per floor is
assumed (Appendix 4.1: Ref. 3). Where there is multi-floor occupancy, only
the structure borne noise impact on the lowest occupied floor is considered.
4.71
At points and crossings, where the wheel transitions from
one rail to another, the sudden loading/unloading of the leading and trailing
rails results in increased broad band vibration levels over that of plain line
continuous rail. In addition, it is not possible to machine grind the rails
through either the points or crossings, so surface deterioration, compared with
that of the place track, is often evident.
4.72
The increase in vibration level at turnouts and crossings is
not easily characterized. For standard level turnouts and crossings receiving
average maintenance, the USFTA handbook (Appendix
4.1: Ref 3) recommends a correction of 10dB. For modern inclined turnouts
in good condition, where impact loads are lessened, it was found through
measurement that a correction of 5dB is often more appropriate. In this study,
5dB(A) and 10dB(A) adjustment were added for inclined and vertical turnouts
respectively. The adjustment factor for
inclined turnout was determined based on measurement
results (refer to Appendix 4.12),
4.73
A +2 dB correction for conversion of vibration (re: 10-6
in/s) in room walls, floors and ceiling to noise (re: 20 micro Pa) is assumed (Appendix 4.1: Ref 3 and 7).
4.74
In the determination of the components of the prediction
model, data undergoes extensive averaging, thus making the overall prediction
of ground-borne noise and vibration a sum of averages. In many of our
comparisons of predicted and measured levels, it has been generally found that
differences in predicted and measured noise levels often fall within about ±5dB, not taking into account variability introduced by the
condition of rail and wheel running surfaces, which in large part determines
the FDL. Occasionally, predictions vary by as much as ±10dB. Thus if noise criteria are regarded as simple design
guidelines, no safety factor would be appropriate. If most passbys were
expected to produce noise levels below criteria, then a safety factor of 5 dB
would be appropriate. If strict adherence of every passby to noise criteria is
expected, then a safety factor of 10dB or more would likely be
appropriate. In this study, a
conservative 10dB safety factor is used that has been adopted for ground-borne
assessment for approved Kowloon Southern Link EIA and strict adherence to
Criteria is expected under the NCO.
4.75
Predicted Noise Level LAeq(30min) = SEL for a passby
+ Tailing Effect + 10*log(number of passby in 30min) – 10*log(1800s)
4.76
SEL (Sound Exposure Level) for a passby is determined by
adding the 10*log(passby duration in seconds) to the LAeq(passby). The passby duration in seconds is obtained by
Train Length (
4.77
In this study, maximum nighttime train frequency was assumed to be 3 minute in each direction and the train types is assumed to
be similar to trains being used in urban line with 8-cars, i.e. total length
200m.
4.78
Ground-borne noise projections associated
with TBM operation have been predicted under the assumption of
worst-case scenario along eight segments of the WIL alignment, and the results
are summarised in Table 4.7 and the
detailed sample calculations for selected receivers are given in Appendix 4.11.
Table 4.7 Predicted
Overall A-weighted Noise Level for Tunnel Boring
Construction GBNSR No. |
Tunnel Founding |
Tunnel Depth(1) (m) |
Predicted Overall Noise Levels (dB(A)) |
Criteria(2) Achieved? |
1 |
Mixed face |
24 |
52.9 |
Yes |
2 & 3 |
Rock |
31 |
54.3 |
Yes |
4*, 5, 6, 7, 8, 21*, 24 & 25 |
Rock |
47 |
45.6 |
Yes |
9*, 10 & 11* |
Rock |
71 |
34.7 |
Yes |
12*, 13, 14*, 15*, 16 & 23* |
Rock |
47 |
41.0 |
Yes |
17, 22 |
Rock |
80 |
27.2 |
Yes |
18, 19* & 20 |
Rock |
40 |
49.1 |
Yes |
26 |
Mixed face |
18 |
60.6 |
Yes |
* GBNSR is an educational
institution.
(1) Tunnel Depth is the depth from ground surface to the top of
tunnel.
(2) Ground-borne noise criteria for educational institution is 60dB(A)
during day time (0700-1900) weekday and 55dB(A) during examination period. For other GBNSR, the criteria is 65 dB(A)
during daytime weekday.
4.79
From Table 4.7, ground-borne construction noise levels at construction
GBNSR No.1-26 would comply with the day time (0700-1900) noise criteria of 60/65 dB(A). Adverse ground-borne construction noise impact
due to the use of TBM would not be envisaged.
4.80
Ground-borne noise impacts from hydraulic breakers, drill rig and pile rig to the
nearby sensitive receivers were predicted, and the prediction results are summarized in Table
Table 4.8a Predicted Construction Ground-borne Noise Impact Associated with the PME Use at Open Works Areas
Construction GBNSR No. |
Description |
Predicted Ground-borne
Noise Levels Leq(30mins), dB(A) |
NCO Criteria for daytime (0700-1900) |
Criteria Achieved? |
||
Breaker |
Drill Rig |
Pile Rig |
||||
27 |
Hong Kong Institute of Vocation Education
(Kennedy Centre) |
48 |
53 |
55 |
60 |
Yes |
28 |
Luen Tak Apartment |
44 |
49 |
50 |
65 |
Yes |
29 |
|
48 |
54 |
55 |
65 |
Yes |
30 |
|
55 |
60 |
62 |
65 |
Yes |
31 |
The Belcher’s Tower 3 |
53 |
58 |
59 |
65 |
Yes |
32 |
|
55 |
60 |
62 |
65 |
Yes |
33 |
Western Court Block 1-4 |
59 |
64 |
65 |
65 |
Yes |
|
The |
50 |
55 |
56 |
60 |
Yes |
34 |
|
55 |
60 |
62 |
65 |
Yes |
35 |
Bon-Point |
55 |
60 |
62 |
65 |
Yes |
36 |
Queen’s Hotel |
55 |
60 |
62 |
65 |
Yes |
37 |
|
55 |
60 |
62 |
65 |
Yes |
Table 4.8b Predicted Construction Ground-borne Noise Impact Associated with the PME Use for Construction of Adits
Construction GBNSR No. |
Description |
Predicted Ground-borne
Noise Levels Leq(30mins), dB(A) |
NCO Criteria for daytime (0700-1900) |
Criteria Achieved? |
|
Breaker |
Rock Drill |
||||
UNI |
|||||
38 |
|
41 |
46 |
65 |
Yes |
39 |
Intelligent Court |
52 |
57 |
65 |
Yes |
40 |
Sik On Building |
46 |
51 |
65 |
Yes |
31 |
The Belcher’s Tower 3 |
39 |
44 |
65 |
Yes |
41 |
|
46 |
51 |
65 |
Yes |
42 |
Wing Fu Lau |
46 |
51 |
65 |
Yes |
SYP |
|||||
34 |
|
29 |
34 |
65 |
Yes |
36a |
6-28 Eastern Street |
46 |
51 |
65 |
Yes |
43 |
|
58 |
63 |
65 |
Yes |
44 |
Yee Shun Building |
37 |
42 |
65 |
Yes |
45 |
Jade Court |
42 |
47 |
65 |
Yes |
46 |
|
44 |
49 |
65 |
Yes |
47 |
|
40 |
45 |
65 |
Yes |
4.81
As shown in Table
4.82
In case of any construction activities during restricted
hours (1900-0700), it is the Contractor’s responsibility to ensure compliance
with the Noise Control Ordinance (NCO) and the relevant technical memoranda. The Contractor will be required to submit construction noise permit (CNP) application to the Noise Control Authority and abide by any
conditions stated in the CNP, should one be issued.
4.83
The predicted operational ground-borne noise results are
summarised in Table 4.9 and detailed
sample calculations demonstrating the predicted ground-borne noise for selected
receivers are shown in Appendix 4.11.
4.84
Exceedance of night-time criterion of 45dB(A) was predicted at Operational GBNSR No. 1, 2, 3, 5 and 9. For Operational GBNSR No. 1, 2 and 9,
exceedance would mainly be due to the turn-out located underneath which would increase the vibration level.
Table 4.9 Summary of Operational Ground-Borne Noise Impact Assessment
(without mitigation measure)
GBNSR No. |
Location |
dB(A) Leq,30mins |
Criteria Achieved? |
|
NCO Nighttime Criteria |
Unmitigated |
|||
1 |
|
45 |
58 |
No |
2 |
|
45 |
59 |
No |
3 |
Kian
Nan Mansion, 81-85 Bonham Strand West |
45 |
49 |
No |
4 |
No. 36
Eastern Street, |
45 |
40 |
Yes |
5 |
|
45 |
55 |
No |
6 |
Tower
1, |
45 |
42 |
Yes |
7 |
Block
D, Kwun Lung Lau |
45 |
43 |
Yes |
8 |
Kwun
Lung Lau New Development Site |
45 |
39 |
Yes |
9 |
East
Terrace, Sai Wan Estate |
45 |
58 |
No |
10 |
Tower 3, Academic Terrace |
45 |
38 |
Yes |
4.85
No cumulative impacts would be expected during the
construction phase and the existing
4.86
During construction phase, the TBM tunnel
construction method would be feasible and designed to achieve the NCO criteria,
with
possible operational prohibition during night time hours near SHW and UNI
stations.
4.87
During the operation of WIL, the groundborne noise levels
predicted at operational GBNSRs No. 1, 2, 3, 5 & 9 would exceed night-time
criterion of 45dB(A) and mitigation measures would be required.
4.88
It is recommended Type
Table 4.10 Summary of Operational Ground-Borne Noise
Impact Assessment (with mitigation measure)
Location |
dB(A) Leq,30mins |
Mitigation |
Criteria Achieved? |
||
Criteria |
mitigated |
||||
1 |
|
45 |
43 |
Inclined Turnout, type
1a resillient baseplate |
Yes |
2 |
|
45 |
44 |
Inclined Turnout, type
1a resillient baseplate |
Yes |
3 |
Kian Nan Mansion, 81-85
Bonham Strand West |
45 |
39 |
Type 1a resillient
baseplate |
Yes |
5 |
|
45 |
44 |
Type 1a resillient
baseplate |
Yes |
9 |
East Terrace, Sai Wan
Estate |
45 |
42 |
Inclined Turnout, type
1a resillient baseplate |
Yes |
4.89
The assessment
results indicated that the ground-borne noise levels at
operational GBNSR No.1, 2, 3, 5 & 9
would comply with the NCO Criteria
after mitigation.
4.90
The currently proposed Type 1a resilient baseplates can be
replaced by Type 1b or Type 2 where practicable and necessary to accomplish a
further 3-6dB(A) noise reduction as a contingency measure (Type 1b and Type 2
baseplates would not be suitable at turnouts due to maintenance and safety
concerns). Changing of the tunnel
dimensions would not be required if these contingency measures have to be in
place. Further measurements would be
conducted to check the accuracy of the noise prediction after the tunnel
construction where necessary.
4.91
An Environmental Monitoring and Audit (EM&A) programme
is recommended to be established according the predicted ground-borne noise
generating construction activities. The
measurement locations shall be above the cutting face of the TBM, and shall be
located as close to the cutting face as practicable. Details of the EM&A
requirements are provided in a stand-alone EM&A Manual.
4.92
Prior to the operation phase of
the Project, a commissioning test should be conducted to ensure compliance of
the operational airborne noise levels with the EIAO-TM noise criteria. Details of the test requirements are provided in a stand-alone EM&A Manual.
4.93
For the construction phase, the drill and blast construction
option is not considered with respect to noise annoyance, as the duration of
blasting is very short and infrequent.
No assessment has been carried out regarding noise annoyance impacts
within any of the identified sensitive receivers.
4.94
The TBM tunnel
construction method would be feasible and designed to achieve the NCO noise
criteria, with
possible operational prohibition during night time hours near SHW and UNI
stations. Ground-borne
construction noise impacts pertinent to the use of breaker, drill rig and pile
rig at open works areas, adits and vent shaft were also found to comply with
relevant criteria of NCO. Overall, no
adverse ground-borne construction noise impacts were predicted.
4.95
During operation phase, projections of ground-borne noise at
identified GBNSR have been performed, based on a methodology recommended by the
US Department of Transportation and assuming an additional 10 dB safety factor,
using vibration measurements taken during operation of eight-car MTRC M-stock
EMU passbys, at grade, and in a tunnel structure. The entire WIL railway design
is predicted to meet the NCO criteria with installation of resilient baseplate
from Luen Yee Building (GBNSR1) to the alignment near West Point (GBNSR4) and
also the alignment starting from Tower 3 of Academic Terrace (GBNSR10) to Sai
Wan Estate (GBNSR9).