4
Vibration from tunnelling
Excavation of more competent chalk at Ramsgate
Vibration magnitude as PPV is determined by the geology, not the tunnelling method
Excavation of weak chalk at Ramsgate
Attenuation appears not to be significantly geology dependent over this range of distances
Res
ulta
nt P
eak
Par
ticl
e V
eloc
ity
(PPV
)
6
Vibration from tunnelling
45m
0.2 mm/s2x10-4 m/s200µm/s At 45m, tunnelling vibration
would give ~200µm/s peakOr ~ 50µm/s rms
7
Residential (day)
Operating theatre
VC-A
VC-B
VC-C
VC-D
VC-E
NIST-A1NIST-A
Vibration Criteria – Where do we sit?
50µm/s
8
Overall figure or an octave or 1/3
octave or narrow band rms?
Over what frequency range?
Duration over which measurement
should be determined?
Max-hold or time averaged rms?
Measured where – eg on the floor,
on the equipment?
Worst case or a spatial average?
Single (any?) axis or resultant?
Residential (day)
Operating theatre
VC-A
VC-B
VC-C
VC-D
VC-E
NIST-A1NIST-A
Vibration criteria – but what do they mean?
10
Vibration impacts and assessment criteria
Vibration at source Attenuation with distance Transfer function – ground to
building Equipment / process sensitivity
12
Vibration Criteria for Hospitals
Tunnelling alongside and 30m below a hospital
Radiotherapy suites, scanners, microsurgery, etc all potentially
vulnerable
Predict tunnelling vibration and compare with established criteria and
manufacturers’ specifications
Criteria not available for all equipment or every process
Tests carried out to establish criteria where there was none
13
Vibration Criteria for Hospitals
“Theoretical models are not sufficiently reliable to predict vibration
propagation from different sources of construction activities through
geological formations. Therefore, predictions of vibrations and
groundborne noise presented in the EIS [Environmental Impact Statement]
are preliminary in nature and must be verified by field vibration
measurements. Prediction models need to be calibrated against and
updated based on field trials.”
Expert’s Report to the Dublin Metro North public enquiry (Massarsch, 2010:58)
15
Vibration Criteria for Operating Theatres
Neurosurgeon’s observations:
At the floor natural frequency, vibration
became perceptible through the
microscope such that at 108 and 133μm/s
(two measurement positions; rms 1/3
octave band) the surgeon would not be
happy to work.
At the resonance frequency of the
microscope, vibration became perceptible
at around 20μm/s rms and would be
clearly a problem at 33μm/s (rms 1/3
octave band).
Operating theatre
16
Vibration Criteria for Operating Theatres
Surgeon Discipline Microscope
Vibration at perception 1/3 octave rms vel (µm/s)
Vibration at perception overall rms vel (µm/s)
Vibration a problem 1/3 octave rms vel (µm/s)
Vibration a problem overall rms vel (µm/s)
Comments
Highest† Next to
microscope base
Highest†Next to
microscope base
Highest†Next to
microscope base
Highest†Next to
microscope base
Mr O’Laoire
Neuro Leica M525/ULT500 at c.75% of maximum magnification
47 43 56 51 81 74 92 84
Mr Colreavy
Ear Nose and Throat
Zeiss OPMI 1-FC. Magnification x2.5
44 40 52 47 101 92 121 110 Problem for fine work
Ms Pat Logan
Eye Surgeon
Leica F40 x8 magnification (c.50% of range)
61 54 72 64 70 62 85 74
Kevin O’Malley
Vascular Loops x3.5 magnification
N/A – loops used
N/A – loops used
N/A – loops used
N/A – loops used
No problem at highest 1/3 oct rms vel – 90 µm/s; highest overall rms vel – 112 µm/s
Mr O’Dwyer
Ear Nose and Throat
Zeiss set at x2.5 x 10
23 20 29 25 30 26 38 33
Ciaran Bolger
Neuro Leica M525/ULT500 *
N/A N/A N/A N/A 51 48 64 60
Gavin Quigley
Neuro Leica F40* 19 18 24 23 19 18 24 23 Problem as soon as perceptible
Michael O’Keeffe
Eye Leica F40 x9 magnification*
12 11 17 17 21 20 27 25
Marcus Timlin
Orthopedic Zeiss on lowest magnification
N/A N/A N/A N/A (98) (87) (119) (105) No problem these levels (maximum vibration achieved given in brackets)
Jim McCarthy
Cardiac Loops x3 magnification
11 N/A – loops used
15 N/A – loops used
18 N/A – loops used
24 N/A – loops used
Prof. Ciaran Bolger
Neuro Wild Heerbrugg (Wild M691)
17 16 21 20 78 75 92 87 Deep cavity simulation – spatula in mouth to test light and shadow
17
Conclusions
In many cases there are no established vibration guidelines or they are poorly understood, leading to a need to define vibration criteria
Established criteria and manufacturers’ specifications can be ambiguous in any case.
Need to know:- Vibration at source – seems to be defined by geology, so probably cannot
appreciably reduce- Vibration at the instrument – measured where; which elements? Any critical
frequencies?- What are the actual assessment criteria – both for operational and non-operational
times- ‘Not above ambient’ may be unduly restrictive
Analytical approach – works well for structural analysis (eg Extreme Light Infrastructure Laser Hall, Prague) but less well where there are complex unknowns