Zetica - e-news
December 2006 Volume 2, Number 8

In this issue

 

Useful Links & Recent Publications:

Benefits of high speed GPR to manage trackbed assets and renewal strategies
PWI paper presented in Sydney, June 2006

Solution matrix for road or motorway applications
The US Federal Highways Dept has published a very useful matrix of geophysical and NDT methods for solving engineering problems during SI, construction and maintenance of road infrastructure.

WW2 bomb risk maps
Download risk maps for your region (28 regions across the UK)
WW2 bomb risk maps image

Limits of detection of unexploded ordnance – are you getting what you paid for?
White paper on physical limits of detection for surface- and borehole-based geophysical methods

Statistical assessment of the risk of unexploded bombs
Paper published in Ground Engineering, May 2006

UXO frequently asked questions
Download a list of FAQ demystifying various aspects of unexploded ordnance

Holly image Thames Gateway Forum – 22nd and 23rd November 2006 Stand E5, Excel, London

The award-winning Thames Gateway Forum is the annual meeting place for all those involved in the regeneration of The Thames Gateway and Olympic region. It will be "the largest ever gathering of the people and organisations responsible for delivering the most exciting regeneration project in the world."

Zetica has designed a custom stand for the event based on the theme:

Zetica exhibition stand animation
Reduce risk through smart site investigation

Traditional methods for investigating brownfield sites deal inadequately with the mitigation of risks. Desktop studies are only as useful as the records upon which they rely. Intrusive borehole / trial pit investigations may not offer a representative view of the subsurface.

Little wonder that over 50% of construction project delays are due to in-ground surprises. Zetica will reduce the risk of delays to your project by carrying out unexploded ordnance (UXO) surveys, Landsweep™ geophysical surveys eg to locate waste tips and buried storage tanks, detailed Utility surveys, and engineering geophysical surveys to determine the shear modulus or depth to bedrock.

We look forward to seeing you at this event.

Banner image for exhibition

Click here to request a reduced rate (£30) ticket to the exhibition (normal price is £80). Deadline for this offer is end of business on Wednesday 15th November 2006.

Holly image On-line probability calculation of the risk of detonating a UXB

A formalised statistical approach (UXB-PC) developed by Zetica to assess the risk of UXB for land owners, developers and consultants was published in Ground Engineering in May 2006. This introduced a statistically rigorous method for quantifying risks so that the potential impact of a few boreholes on a site or a dense grid of clustered piles can be accurately quantified.

Click here to view Zetica’s paper on the statistical assessment of the risk of detonating unexploded bombs.

We are pleased to announce that we will make available a website applet on the 8th December 2006, to facilitate calculation of the probability of detonation based on user inputs including estimated density of UXB/ha, no of boreholes/ha or pile grid separation. An analytic solution is derived including an option to allow for the fact that a UXB detonation can in theory be initiated without a direct strike by impacting the surrounding ground with significant shock forces as caused by piling and drilling.

The on-line probability calculator (UXB-PC) coupled with our freely available regional risk maps will allow users to accurately quantify order of magnitude of risk levels to help decide whether to proceed with any specific risk mitigation work.

Click here to access Zetica’s UXB-PC applet.

Holly image Desk study services for assessing the risk of UXO

Some UK UXO specialists seem to confuse and alarm developers through their misunderstanding or misrepresentation of the risk from WWII bombing or past military activity. We recognised that a fresh approach to that currently being offered in the UK was required to assess the risk from Unexploded Ordnance (UXO).

Zetica has updated the look of its reports from the outside, but more importantly the style of the report inside. The reports offer a clearer appraisal of risk and hopefully more understandable conclusions.

zetica sitesafeWe have made the assessments clearer by detailing the sources of information and most importantly, the deficiencies and peculiarities of the sources of data consulted. By pointing out the discrepancies between differing sets of data, it has made the reasoning behind any conclusions clearer to the reader.

We also think we have a much more realistic view of risk. For example, you won’t find us ‘blighting’ an entire site because it happened to be a former military airfield. We would aim to zone the site and give regions a risk ranking, thus providing the client with options for development.

Our experience and practical understanding of a developer’s needs, means that Zetica’s Sitesafe desk studies offer a pragmatic view of UXO risk. This combined with Zetica’s new online UXB-PC applet demonstrates our continual improvements to make the assessment of UXO risk more transparent.

'Zetica's approach has enabled us to progress the scheme in a pragmatic manner. The main problem with UXO, is that once its potential presence is identified it is very difficult to reduce the perceived risk to an acceptable manner. Zetica were able to undertake the desk top searches and isolate the areas where it was felt that a significant risk may exist. ' Client: FaberMaunsell

Click here to request more information.

Holly image Integrated Topography, Utilities and Landsweep™ surveys

Zetica Ltd carries out integrated Topography, Utilities and Landsweep™ surveys for house builders and other developers prior to purchase decisions on a site or to provide input for tender documentation for contractors.

The cost savings in outsourcing site mapping services to one company can be considerable. Zetica offers in-house specialist desktop studies, detailed topographic surveys, Landsweep™ geophysical surveys, detailed utility surveys and engineering geophysical surveys. Our multifunction crews are trained to carry out all site-works thus saving on mobilising separate teams.

An example of an integrated survey is provided below:

Landsweep surveys 3D graphic

Click here to request more information.

Contact Us:
Zetica logo

www.zetica.com
info@zetica.com
Tel: 01993-706767
Tel: 01322-612140

CEO:
Asger Eriksen

Managing Director:
Mike Sainsbury

Technical Manager:
Jon Gascoyne

Rail Services Manager:
Ben Venables

Copyright © 2006

Holly image Landsweep™ survey detects source of contamination

Zetica Ltd was asked to carry out a Landsweep™ survey to map unknown buried structures which may be the source of contamination leaking into an adjacent water course.

Work previously carried out to investigate the site using multiple Geoprobe locations with soil sampling had proved inconclusive.

A combined electromagnetic (EM) and magnetic profiling survey with follow-up ground penetrating radar (GPR) was carried out over the 3,000m2 site during the course of a single day. The results of the work verified the location of many known services and buried foundations but also showed an unknown non-ferrous pipe leading to a buried rectangular structure. The latter was investigated and found to be the source of the contamination. The non-ferrous pipe was a previously unmapped waste material feeder pipe.

Colour-coded results image

Colour-coded results of apparent conductivity (top) with interpretation of waste pipe and buried structure overlaid in green, and total field magnetics (bottom). Vector lines are from historical plans of previous structures on the site.

The logical order of events for investigating brownfield sites where the risk of the unknown is high, should be a site wide Landsweep™ survey to verify historical plans and locate unknown features which would then target the intrusive phase of investigation using more expensive methods.

Recommended brownfield site investigation methodology chart
Recommended brownfield site investigation methodology

Click here to request more information on Landsweep™.

Holly image Drainage surveys in the rail environment

Zetica has recently been awarded various contracts to characterise drainage in the rail environment. Clients include Network Rail, Grant Rail, and Metronet Alliance. The general objective of the works is to map and assess the condition of subsurface drainage systems.

A typical work sequence includes:

  • Visual site inspection to evaluate existing drainage system, working practice restrictions and other site risks
  • Develop work plan and method statement and undertake risk assessment
  • Investigate visible drain system using CCTV to establish condition, visible blockages, drainage spurs etc
  • Define drain depths using Cat scan and sonde, tied into rail and invert level survey
  • Trace drainage beyond blockages using GPR antennae to identify pipe position
  • Trace drainage covers using EM scanner (to detect metal grids of catchpits)
  • Topography survey of all catchpits and key rail features, such as bridges, rails, junctions etc
  • Plot topography results and produce level cross sections of drain system
  • Write a report with recommendations on remedial work priorities

Contact Ben Venables, Rail Services Manager to discuss your requirements.

Holly image Technical note – Optimising the design of geophysical surveys

Problem:
The client specified the target which was a 2m diameter air-filled cavity at up to 5m depth. Microgravity was highlighted as the most likely geophysical method for detection. What is the most cost effective survey design that should be used to meet the objective? A good understanding of the physical limitations of the chosen method must be combined with budget considerations to achieve the desired result.

Solution:
A desktop 3D modelling exercise was carried out to determine the signal to noise characteristics expected in the actual burial setting (5 microgal noise envelope). Examples of these are provided below (red box is noise envelope).

Models of response of target assuming 1m, 3m and 5m grid spacing diagram
Models of response of target assuming 1m, 3m and 5m grid spacing (left to right)

The 5m station scenario has the highest risk of non-detection due to <3 points defining the target. The 1m scenario provides highest probability of detection but at greatest cost. Based on the above, the most cost effective option (3m grid spacing) was highlighted.

Microgravity survey to locate buried tunnel – 1m radius at 5m depth.

Duration (0.4ha area)

Budget Cost (£)

Result (tick indicates high probability of detection)

Station interval 1m

50 days

40,000

Station interval 3m

6 days

6,000

Station interval 5m

3 days

3,000

x

Click here to request more information.

Problem:
Most companies take an unquestioning view of the service offerings of UXO contractors. It is assumed that if a company says that they will ‘clear’ an area of UXO, that this is sufficient basis for letting a contract without quality assurance conditions. All UXO ‘clearance’ contractors should be obliged to provide detection assurance levels for UXO of expected size and estimated range of burial depth. This can easily be achieved.

Solution:
The geophysical fingerprint of an item of UXO can be modelled to give an indicative order of magnitude of signal strength (amplitude) and wavelength. This can be used to determine whether a particular measurement system and survey design is capable of detecting the target.

Next a signal to noise measure for locating UXO buried in particular settings (eg made ground or natural ground) needs to be derived on a site by site basis. It may be relatively straight forward to detect a 6” shell at 1m depth in ‘quiet’ ground conditions but if the site has geophysically ‘noisy’ soils and/or is overlain by made ground containing materials which interfere with the signal from the target, then detection may not be possible.

The figure below shows the results of characterising detection assurance levels for targets at various depths. In one case detection assurance levels for a 6” shell at 1m depth was close to 100% but assurance levels for 2m and 3m depths was <50% and 0% respectively.

Zetica also provides a methodology for physically measuring the effect of burial setting on detection assurance levels. The arrangement of inclined pipes shown in the figure can be installed on any site.

Click here to request more information.

Click here to access Zetica’s white paper on the physical limits of detection of surface- and borehole-based geophysical methods.

Holly image Zetica is moving

2006 has seen a significant expansion in Zetica’s service portfolio. Increased staff numbers and a growing equipment pool has meant that after 10 years in a listed building in the heart of Witney, we’ve decided to move our head office to a fit-for-purpose industrial unit at Long Hanborough, 5 miles up the road. The extra space and closer proximity to the M40 motorway, and a mainline train station 2 minutes walk away will be welcomed. The move is expected to take place in December and new address and contact details will be circulated soon.

New Zetica location map

Holly image Lunchtime Seminars

Lunchtime seminars imageZetica offer a popular seminar on the uses and abuses of geophysics. Engineers are brought up to date on the latest geophysical methods available in the market place and interesting areas of research and development. The presentation normally lasts 30 – 40 minutes and is case history-based with a 15 minute discussion session following.

Click here to email Ellen Stevens to discuss your requirements and arrange a seminar at your offices.