Vibration Assessment

3 Hawthorn Park, Holdenby Road, Spratton, Northampton, NN6 8LD, UK. Tel: 01604 842888 Fax: 01604 842666 E-mail: [email protected] www.hydrock.com Vibration Assessment at Garston Road, Frome Final Report Prepared by

SPL Acoustics & Claire Ringrose for Bloor Homes (Newbury) Limited Hydrock Ref: R/07378/003

August 2008

Bloor Homes (Newbury) Vibration Assessment at Garston Road, Frome R/07378/003

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DOCUMENT CONTROL SHEET Issued by: Hydrock Consultants Limited

3 Hawthorn Park Holdenby Road Spratton Northampton NN6 8LD Tel: 01454 619533 Fax: 01454 614125 www.hydrock.com

Client: BLOOR HOMES (NEWBURY) Project: GARSTON ROAD, FROME Title: VIBRATION ASSESSMENT Status: FINAL Date: August 2008 Document Production Record

Issue Number: 1 Name Signature

Prepared SPL Acoustics & Claire Ringrose

Checked Allan Bell

Approved Allan Bell

Document Revision Record

Issue number Date Revision Details

1 26th August 2008 Original issue

Hydrock Consultants Limited has prepared this report in accordance with the instructions of the above named Client for their sole and specific use. Any third parties who may use the information contained herein do so at their own risk. The interpretation, conclusions and recommendations provided represents only our assessment and shall not be taken to indicate a preferred or accepted method of working nor restrict in any way whatsoever any tenderers or any contractor’s own interpretation and determination of the most appropriate method of working.


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CONTENTS

1.0 INTRODUCTION ............................................................................................................................1

1.1 Terms of Reference ........................................................................................................................1 1.2 Objectives .......................................................................................................................................1 1.3 Scope..............................................................................................................................................1 1.4 Site Description...............................................................................................................................1 1.5 Limitations.......................................................................................................................................2

2.0 VIBRATION CRITERIA ..................................................................................................................3 3.0 VIBRATION SURVEY ....................................................................................................................5 4.0 VIBRATION ASSESSMENT ..........................................................................................................6 5.0 CONCLUSIONS .............................................................................................................................7 APPENDICES

Appendix A SITE LOCATION PLAN AND VIBRATION MONITORING LOCATIONS

APPENDIX B DESCRIPTION OF VIBRATION UNITS


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1.0 INTRODUCTION

1.1 Terms of Reference

In August 2008, Hydrock Consultants Limited (Hydrock) was commissioned by Bloor Homes (Newbury) (e-mail approval Mr. Rob Clarke to Mr. Allan Bell, dated 15th August 2008) to undertake a vibration survey and assessment at the proposed residential development site known as ‘Garston Road’, Frome.

The site is located north of Frome Station and the A362. Two railway lines run adjacent to the northern boundary and the eastern boundary.

A site location plan is provided in Appendix A (07378/D001) and Figure 1 (Appendix A) shows the site in relation to the above vibration sources.

1.2 Objectives

The objectives of this investigation are to establish whether existing vibration levels at the site pose a constraint to the development with particular regard to the residential aspect of the site.

1.3 Scope

The scope of work for this commission comprises:

• a vibration survey;

• reporting on findings of the vibration survey.

1.4 Site Description

The site is currently derelict land, bordered to the east and to the north by railway lines. The eastern line is on a steep embankment that rises progressively from around 2m above site level at the northeastern corner of the site to 5m above site level at the south east corner of the site. The northern line is on less of an embankment, which remains approximately 2m above site level along its length. Both railway lines execute tight radius turns along the boundary of the site as they diverge from a set of points that lies to the northeast of the site.

The existing access to the site is from the southeast corner, via the A362. This is a moderately heavily trafficked road that is on a gradient and is in a deep cutting at the site access point. The southeastern line railway crosses the A362 on a 4.6m clearance bridge at the southeast corner of the site.


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To the east of the site, over the eastern line there is an existing residential development. The roofline of this development appears to be approximately 3m above the level of the eastern line embankment.

To the north of the site is a further residential development, set back from the railway by approximately 20m. The closest properties to the northeastern line are bungalows, the rooflines of which are below the level of the railway line. Further from the railway line are two storey residential properties. Only freight movements were observed on the northern line, all of which passed the application site at low speed.

The land sandwiched between the southern boundary of the application site and the A362, much of which is raised above the level of the application site, generally comprises terraced housing. For the majority of the application site, this land and housing completely obscure the A362 from sight.

1.5 Limitations

This report details the findings of work carried out in August 2008. The report has been prepared by Hydrock and SPL Acoustics on the basis of available information obtained during the study period.

The report has been prepared for the exclusive benefit of Bloor Homes (Newbury) and those parties designated by them for the purpose of providing a vibration assessment for the site. The report contents should only be used in that context. Furthermore, new information, changed practices or new legislation may necessitate revised interpretation of the report after the date of its submission.

Hydrock and SPL Acoustics have used reasonable skill, care and diligence in the design of the survey of the site.


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2.0 VIBRATION CRITERIA

BS6472-1: 2008 Guide to evaluation of human exposure to vibration in buildings (Part 1: Vibration sources other than blasting) contains a methodology for assessing the human response to vibration in terms of either the vibration dose value, or in terms of the acceleration or the peak velocity of the vibration, which is also referred to as peak particle velocity.

The advice contained in BS6472 states that when the vibration is intermittent, as is the case at this site, the vibration dose value, or VDV, may be used to assess the potential for impacts. The way in which people perceive vibration depends on various factors, including the vibration frequency and direction. Different frequency weightings are required for different axes of motion (e.g. x, y and z).

This 2008 version of BS6472 has only recently been published. There are a number of significant changes from the current version to the previous 1992 version (BS6472: 1992 Evaluation of human exposure to vibration in buildings (1 Hz to 80 Hz)). In measurement and evaluation terms, the 2008 version applies different frequency weightings to derive the VDV along with the use of a geocentric coordinate system as opposed to the previous basicentric coordinate system. In effect the coordinate system is now earthcentred, as opposed to being oriented to the human body in the 1992 version.

Unfortunately, at present equipment manufacturers have yet to implement the above mentioned BS6472-1: 2008 changes to their equipment (‘Vibrock’ or high volume equipment hire providers, ‘Gracey & Associates’ will not have the relevant equipment for perhaps as long as 1-2 months). Discussions were held with the local authority and it was agreed that due the lack of available monitoring equipment compatible with BS6472-1:2008, the 1992 version of BS6472 should be applied for this site.

The vibration dose value, as set out in BS6472:1992, is determined over a 16 hour daytime period or 8 hour night-time period and compared with the following guidance:

Table 2.1 Vibration dose values (ms-1.75) above which various degrees of adverse comment may be expected in residential buildings (BS6472:1992).

The above guidance relates to vibration measured at the point of entry into the human body, which is usually taken to mean the ground surface or at a point mid-span of an upper storey floor, rather than the point of entry into the building, for example a foundation element.


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Where the vibration is measured at another location, BS6472:1992 states that a transfer function should be applied; however, BS6472:1992 does not contain any guidance on suitable transfer functions. BS6472:2008 does not contain specific transfer functions but notes that applying simplified transfer functions previously measured at similar buildings should be treated with care.

Transfer functions, after a correction for geometric spreading is applied, take into account the vibrational energy losses that occur with ground and foundations together with an amplification factor as the energy travels through the building to the mid-span of an upper storey floor. The value of the transfer functions will therefore depend on the soil, the type of foundations and the type of building (e.g. wooden framed, masonry etc) and the type of flooring.

The proposed foundations of the proposed housing adjacent to both railway lines are a mixture of deep trench foundations or piled on earth foundations (see Appendix B). All housing will be masonry with wooden upper storey floors.

Transfer functions have been referenced from the following sources:

• Handbook of Urban Rail Noise and Vibration Control (HURNVC), published by the Federal Transit Administration, USA, written by H J Saurenam, J T Nelson and G P Wilson (also reproduced in the Transportation Noise Reference Book (1987));

• Methods for Predicting Groundborne Noise & Vibration From Trains In Tunnels, LARIF 1999 by Richard Greer;

• Transmission of Ground-borne Vibration in Buildings by Jorgen Jakobsen, Journal of Low Frequency Noise and Vibration, Vol. 8 No. 3, 1989.

In assessing the effect that the foundations may have, guidance has been sought from HURNVC. The HURNVC sets out attenuation factors that can be applied to calculate the transfer function between vibrations measured on unloaded ground and vibration at a foundation. It is noted that the multiplication factor for strip deep trench foundation is approximately -6 dB and for a piled foundation approximately –8dB (both based on the 31.5 Hz frequency band). For a conservative worst case scenario, -6 dB has been applied for foundation losses.

Greer advocates +10.2 dB and Jakobsen suggests a value of +15.5 dB for amplification on an upper storey suspended floor. For a conservative worst case scenario, +15.5 dB has been applied for amplification at the upper storey mid span floor level.

Taking the above into account gives an overall multiplication factor of 2.98 for a worst case scenario (a best case scenario would be 1.29).


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3.0 VIBRATION SURVEY

Vibration levels were sampled during both the day and night-time between 21st and 22nd August 2008, using two Vibrock 901 Geophone Systems. One system was located at the northern boundary (along proposed façade line of plot 157, approx 8m from the railway line) whilst the other system was located on the eastern boundary) along the proposed façade line of plot 174, approx 11m from the railway). Measurement locations are shown in Figure 1 in Appendix A.

The V901 is a self-calibrating meter capable of simultaneously measuring vibration in the three orthogonal axes. The equipment, which has a frequency range of 1Hz to 200Hz, was set to record vibration dose values over representative 16 hour day and 8 hour night-time.

Vibration dose value (VDV) measurements taken at the above locations are as follows (it was noted that vibration levels were not perceptible at the above locations due to mainly to the tight radius of the both tracks slowing the trains down):

Table 3.1 Summary of VDV measurements

It is noted on site that there were significantly more passenger trains than freight (mainly mineral laden) traffic. However, the measured daytime values indicate more vibrational energy on the northeast boundary. This is probably due to the heavier minerals traffic as well as the distance to the nearest railhead. At night, there are more passenger trains than fright trains (with little or no traffic along the northeast railway line, and consequently more vibrational energy is recorded for the southeast boundary.


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4.0 VIBRATION ASSESSMENT

The below-ground structure of a building or hard surface will affect the levels of vibration present due to a remote source. Different types of foundation will affect the amount of vibration that is transferred from the ground to either the building or the hard surface.

Assuming the residential buildings are constructed no closer than the vibration measurement position, the vibration levels at the proposed properties should be no greater than those that were measured. This assumes that there are no geological faults or other peculiarities that affect the propagation of vibration. Properties located further away from the railway line than the measurement position, should be subject to lower levels of vibration, again assuming there are no geological faults or other peculiarities that affect the propagation of vibration.

As discussed in section 2 of this report, it is necessary to use a transfer function that would represent the likely effect that a different foundation would have on the transfer of vibration from the ground into the proposed dwellings.

The table below shows the likely vibration level within a habitable room located on the upper storey of a residential property at the measurement position. The figures presented below equate to the measured values amplified by a transfer function of 2.98:

Table 4.1 Estimated Vibration Dose Values (eVDV) at Upper Storey, ms-1.75

It can be seen that the above values indicate a less than low probability of adverse comment during both the day and night-time periods, when compared to the guidance contained in BS6472:1992. Mitigation measures are therefore not deemed to be necessary.

Due to the different frequency weightings used by the 2008 version of BS6472 and the frequency weightings used in the measurements (in accordance with BS6472:1992) which may double or halve the measured values, we do not deem it appropriate to link the above assessment with the guidance now contained in BS6472-1: 2008.


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5.0 CONCLUSIONS

In order to evaluate vibration levels from the railway lines running along the eastern and northern boundaries of the development site that could potentially affect the nearest proposed dwellings on the site, a vibration survey and assessment was undertaken.

The assessment considered the potential impact on future residents by taking into account the different vibration energy interactions between the ground and the foundations as well as the amplification of the vibration energy as it propagates to the upper storey suspended floors.

The vibration assessment, in accordance with relevant British Standards methodology, has shown that the likelihood of adverse comment would be low. Existing vibration levels therefore should not be considered a constraint to the residential aspects of the development.

Hydrock Consultants Limited


Appendix A

Appendix A

SITE LOCATION PLAN AND VIBRATION MONITORING LOCATIONS

Garston Road, FromeSPL Acoustics Limited

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FIGURE 1:

Vibration Monitoring Locations

Vibrationmonitoring location

2, approx 11mfrom Railway

Vibrationmonitoring location1, approx 8m from

Railway


Appendix B

APPENDIX B

DESCRIPTION OF VIBRATION UNITS


Appendix B

Vibration

Vibrating sources, such as motor vehicle engines, railway engines/wagons or the movement of vehicles over road surface irregularities, can produce not only displacement of the air molecules which we perceive as noise, but also displacement within the material components of the source or materials in contact with the source. These energy waves can travel through the ground in a similar manner to air pressure waves through the atmosphere and, dependent on the amount of energy being transmitted, be perceived as vibration.

• Vibration can produce three effects:

o at levels above the threshold of perception it may cause human annoyance;

o at extreme levels it may cause building damage (e.g. during construction activity); and

o it may be re-radiated as audible noise.

• Vibration can be defined as an oscillating motion about a fixed reference position. The number of times that a complete oscillation takes place during one second is called the 'frequency' measured in hertz (Hz) or cycles/second. The movement of an oscillating body can be described in terms of its displacement, velocity or acceleration.

• For a simple oscillating signal, the peak-to-peak value measures the maximum excursion of the vibration about the stable reference position; it is particularly useful for measuring the vibratory displacement of machine parts. The peak value is the highest positive excursion from the stable reference position and is used to measure the energy level of short duration shocks; these are commonly measured as peak particle velocity (ppv) in mm/s.

• For a complex vibration signal, the peak measures described above will not take account of the fluctuations that occur with time; this is called the signal's 'time history'. The RMS or 'root mean square' value is the most appropriate unit for measuring either the destructive abilities of a vibration or its potential for causing human annoyance because it takes account of the full time history of the signal and provides an amplitude value which is directly related to the energy content. Values are commonly measured as rms accelerations in m/s2.

• For a symmetrical signal the positive and negative excursions are equal, therefore, if the signal were to be averaged a ‘zero’ value would be obtained. This effect can be countered by first squaring the signal values before taking a mean. (The square of a negative value produces a positive value.) This squaring action will of course overestimate the vibrational energy and needs to be countered in turn by finally taking a square root of the mean, hence the term ‘root mean square’.

• The probability of adverse comment due to a given vibration time history can be determined by using the rms frequency weighted acceleration and the duration of exposure to calculate a Vibration Dose Value (VDV). The VDV has ‘fourth power’ time


Appendix B

dependency; therefore, unlike the rms value (which uses the square root of a squared value) the VDV is derived from the fourth root of the integral of the fourth power of the acceleration, in units of m/s1.75. It provides a time dependent and frequency weighted unit of vibration that correlates with human response.

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Vibration Assessment