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Contents
Issue #4 | January 2010
Editorial
Latest News
 SafeGround Website goes LIVE
 Housebuilders Conference
 The Science of Forensic Geophysics
 Micro-gravity Special
Geophysical Techniques Explored: Micro-gravity
Courses offered on Geophysics
Geophysics Reference Guide
RSK Group: the one-stop shop for environmental support services
Editorial
Happy New Year and welcome to another edition of Geophysics Focus.
Its that time of year again when the days are shorter than the nights, and the temperatures are subzero. Unlike other outdoor work such as construction, when cold conditions strike, work is stopped,
our intrepid engineers carry on with geophysical surveys throughout the winter ensuring timely project
delivery (see our Picture of the Month below).
With the recent cuts in government spending, and as many organisations also seek to become more
efficient, now is the time to focus on reducing cost, and reducing risk. Geophysics plays an important
part in both of these. There are still huge opportunities in the UK. In 2011 we will hope to see a
modest upturn in the property sector, where RSK has very strong connections, and the energy sector
continues to provide RSK with many opportunities - not least in the nuclear sector, but also in
renewables, gas storage, pipelines and electricity transmission.
In this special edition we highlight the use of the micro-gravity technique, and illustrate it using a
number of case studies.
George Tuckwell, RSK Geophysics director and team-leader
SafeGround website launched
RSK Geophysics recently launched a new utility mapping and detection service to complement the
traditional geophysics portfolio undertaken at RSK. The Safe Ground service functions as a one-stop
shop for everything from the clearance of borehole locations to producing a detailed topographic
drawing that documents underground service locations. The popular service is already undergoing
growth with the recent acquirement of a graduate.
The new website, on-line since last autumn provides pages and resources for the full-spectrum of
buried utility and obstruction site investigation. For more information on SafeGround visit www.safeground.co.uk or contact Gerwyn Leigh.
Figure 1. www.safe-ground.co.uk
Housebuilders Conference success
As part of a series of Autumn property seminars by RSK, the use of geophysics was part of the
agenda in a talk entitled “Reducing the risk of uncovering the unknown”. The seminars include a
variety of talks focused on the environmental challenges facing the property and development sector.
As the property sector carefully manages its way out of recession, control of the environmental
agenda is becoming increasingly complex. Developers are faced with the struggle of dealing
with these issues and the potentially escalating costs within the harsh financial conditions of 2010.
This seminar was set up by RSK to help owners and developers of land understand the complexities
they face and how the problems can be managed in a cost-effective and efficient manner.
Buried obstructions, services, voids, weak ground and contamination can be dangerous and
expensive. The adage “you pay for a site investigation whether you have one or not” is well known
across the industry. Director of RSK Geophysics, George Tuckwell discussed how new
approaches using geophysical mapping techniques can make site investigation more effective.
Geophysical techniques combined intelligently with intrusive investigations can greatly reduce the risk
of expensive unknown issues later in the development. “We are delighted with the success of the
property seminars. There has been much interest and they have already led to a number of follow up
enquires of interested parties” said George.
Quick links:
 Property Seminar flyer (http://www.rsk.co.uk/downloads/RSK_Property_seminars_2010.pdf)
 Geophysics for property sector factsheet (http://www.environmentalgeophysics.co.uk/documents/sectors/RSK_Geophysics_property.pdf)
 Brownfield site geophysical surveys
(links to http://www.environmental-geophysics.co.uk/app_brown.htm)
 Contaminated land geophysical surveys
(links to http://www.environmental-geophysics.co.uk/app_cont.htm)
 Contact George Tuckwell for more info (links to gtuckwell@rsk.co.uk )
Geophysics Photo of the Month
This month saw our engineers battle the cold in the chilliest December on record, and in one case,
the heaviest snowfall in a quarter of a century in Northern Ireland. Below, in a postcard scene from
Narnia (Leicestershire wolds), our engineer is carrying out a magnetic survey at a proposed wind farm
site. “The lying snow has no effect on the data whatsoever, and even aids us walking in perfectly
straight lines!”.
Fig 2.
The Science of Forensic Geophysics
Forensic geophysics is the study of locating and mapping hidden objects or features that are
underground . RSK Geophysics is proud to support ongoing research from Keele University into
conducting new field trials in the area of forensic geophysics.
Geophysical methods have great potential to aid the police and other authorities in the location and
recovery of human remains as they can, non-invasively, very rapidly survey extensive areas where a
suspected clandestine burial has taken place. Anomalies can then be targeted using conventional
intrusive means. Early successes in the 1990s, particularly the Fred West case, raised the profile of
forensic geophysics, particularly Ground Penetrating Radar (GPR), but to-date, geophysics has only
been used sporadically and with varied success.
RSK geophysics had part funded research student John Jervis, who has been conducting trials in the
Midlands over simulated (mock) shallow burials to determine the best, near-surface, geophysical
detection techniques. John’s research has shown that bulk ground electrical methods, particularly
resistivity, is the most promising technique to rapidly survey a suspected area and pinpoint a burial. A
PDF poster showing the results of the research can be viewed here (links to
http://www.environmental-geophysics.co.uk/documents/posters/clandestine_burials_2010.pdf )
For further information or advice, please contact George Tuckwell, Director of RSK Geophysics (links
to gtuckwell@rsk.co.uk) or Dr Jamie Pringle, School of Physical Sciences & Geography (links to
j.k.pringle@esci.keele.ac.uk )
Figure 3. Time-lapse (repeat) bulk ground
resistivity surveys of a simulated clandestine
grave (dotted rectangle) at (A) 2 weeks, (B) 6
weeks and (C) 12 weeks post-burial. From
Jervis et al., (in press).
Micro-gravity Special
The gravity method involves the measurement of variations in the gravity field of the Earth caused by
local differences in the density of the ground. Significant anomalies are recorded in the case of air
filled voids. RSK geophysics has many years experience in undertaking high resolution small and
larger scale gravity surveys, where contoured maps are produced to highlight anomalous areas
associated with fault zones, voids and cavities, mineshafts, buried channels and other low density
ground. We use the latest high precision topographic surveying equipment to ensure that any height
corrections are filtered out effectively. In the current era of cost cutting, a gravity survey may not be
the first thing that comes to a developers mind, however, in settings such as urban environments, the
savings may be immeasurable. Below we summarise results for several of our most recent surveys.
Site 1 shows a microgravity anomaly map across an education institute in Hertfordshire. The dark
blue areas highlight potential voids from chalk quarries at depth. The information was used to aid
future development plans at the site.
Site 2 is an open area of fields with no surface expressions. The blue areas show two capped mine
shafts which were not visible at ground surface level.
Site 3 shows a linear anomaly stretching SW-NE. The anomaly represents voided mine workings in
Cornwall. Subsequent intrusive probes confirmed the void. The work highlighted mineworkings in
order for a future road at the site to be re-routed away from problematic ground.
Click here to view a poster showcasing a number of further successful microgravity case studies.
(links to http://www.environmentalgeophysics.co.uk/documents/posters/RSK_microgravity_case_studies_poster.pdf )
Contact George Tuckwell for more info (links to gtuckwell@rsk.co.uk )
Micro-gravity
This issue we take a look at Micro-gravity. As shown in the section above, it is a particular useful
tool for detected natural and man-made sub-surface voids.
Different subsurface materials have different bulk densities. In microgravity surveying, areas of
contrasting density are located by collecting surface measurements of the variation in the Earth’s
gravitational field. A gravity meter is a highly sensitive spring balance. When positioned above a
dense material it records the acceleration due to gravity (g) as a relative high (a positive gravity
anomaly). When positioned above a low density material (e.g. an air filled cavity) the gravity meter
records a relative gravity low (or negative gravity anomaly).
From our experience we would expect to confidently identify anomalies of the order 10 micro-gals in
amplitude (dependent upon site conditions). This anomaly corresponds approximately to a 5m spherical
air filled void at 10m depth, or a 10m void at 30m depth. It is expected that smaller or deeper voids or
low density ground will also manifest in the data but may not represent an unambiguous anomaly. For a
typical survey we envisage being able to collect approximately 80 point readings covering 25mx25m
area per day per meter (dependent on ground conditions and target type).
The technique can be used for a variety of applications, such as:
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Cavity detection (including bomb shelters, hidden tunnels/adits, old mine workings, sinkholes and
dissolution features)
Mineral exploration
Density determination
Grouting investigations
Figure 5. Working at survey position with the gravity meter and topographic total station (left). In the
above project, RSK were commissioned to undertake a survey along a residential street after a
sinkhole opened up and dramatically swallowed one the houses (centre and right).
For more information, the gravity fact sheet can be downloaded from our site at:
www.environmental-geophysics.co.uk/tech_grav.htm
Remaining sections below same text as per previous Newsletter…
We have developed a number of general and topic specific seminars and short courses on the
application of geophysics, and the services that RSK Geophysical offer to clients. We are pleased to
deliver these on site to interested parties, and can tailor presentations to the specific needs and
interests of a particular audience. Email us for more details.
RSK Geophysics’s manual, A Reference for Geophysical Techniques and Applications, is a first point
of reference for increasing numbers of industry professionals, and as a teaching resource by
university academics.
Find out what all the fuss is about by downloading your free copy here.
Hard copies are available free of charge. Email us for more details
RSK Group is the UK’s largest privately owned environmental consultancy providing over 200
individual services across 17 broad categories. The company employs 750 consultants across 35
worldwide locations, and last year reported a turnover of £63m.
For more information, visit www.rsk.co.uk