Zetica Finds 1,000lb WWII Bomb

A 1,000lb unexploded WWII bomb was located earlier this month in Bowers Marsh, Essex.  The sequence of events leading to the disposal of the device will be of interest to clients looking to manage the risk of UXB in a cost effective and low key manner.

Zetica was commissioned by the RSPB to help them safely develop Bowers Marsh into a wetland reserve with visitor centre. The commission followed a European wide pre-qualification and tender process.

The first stage of the project involved conducting a detailed SiteSafe desk study to assess the risk of finding a WWII unexploded bomb (UXB) on the site. The risk was found to be high on the basis of clear evidence that the site had been bombed on a number of occasions, primarily as a result of its location on the north side of the Thames estuary in Essex, close to local strategic targets such as oil refineries and explosive factories. 

The second stage in the risk mitigation process was a surface geophysical survey to detect buried targets which could represent a threat to site works. Zetica utilised its high productivity geophysical scanning system, covering over 8hectares per day.

The third stage consisted of utilising Zetica’s explosive ordnance clearance (EOC) team to expose and identify a number of anomalies which could be UXO. Zetica worked to a standard set of procedures for liaising with the authorities (police and MoD) and the customer to manage the disposal of any UXO found. 

A live 1,000lb bomb was located. The procedures were implemented and the Army disposed of the UXB by detonating it in-situ within 5 hours of discovery with very little fuss or inconvenience to the local area.  The whole operation went like clockwork and didn’t even make the BBC local TV news!

Zetica unveils MagDrill-Plus, a safer, faster and cheaper method of UXB detection.

Zetica has introduced MagDrill-Plus for more efficiently clearing pile or borehole locations of potential unexploded bombs (UXB) where surface based geophysical methods and a CPT-based MagCone technique are unsuitable.

MagDrill-Plus is a result of over 2 years of research and development with the University of Liverpool and involving our drilling partners, Norwest Holst, which has resulted in a wireless detection system which utilises novel magnetometer technology and advanced material technology to scan while drilling.

In soft soil conditions, MagCone is the technology of choice. However, where a thin layer of soft soils overlies dense materials or dense materials occur close to surface, MagCone is not able to penetrate to the required depths to clear a location of the threat of UXB. It is estimated that approximately 40% of the Greater London area is thus affected.

The current alternative to MagCone to locate deep-seated UXB which are beyond the detection range of surface methods, is MagDrill.  This is based on rotary percussive or similar drilling techniques and involves scanning the borehole in stages as it is drilled. The method is relatively slow and costly. 

Alarmingly, some in the industry have compromised on safety by offering a ‘blind’ drilling service.  This involves drilling a borehole without regard to the presence or absence of a UXB within its zone of influence and then scanning the hole for bomb targets only once the borehole has been completed. This is a very dangerous activity no matter what reassurance is provided about the possibility of detonating a bomb if you hit one!

In some cases, where ground conditions are anticipated to be variable, both MagCone and MagDrill techniques are used together.  The big disadvantage is the cost of operating two rigs and the impact on productivity.

MagDrill-Plus is a new service providing a single technique that can cope with dense soils and which offers up to 3 times the productivities achievable using current accepted MagDrill practice.  The improved productivities are based on continuous detection during drilling which also makes the drilling process safer.

For more details contact Mike Sainsbury at mike@zetica.com.

Zetica completes another successful survey at Sellafield

Zetica has completed another specialist ground penetrating radar survey (GPR) at Sellafield. These surveys have been conducted within existing buildings and are used to accurately map the location of reinforcing, utility services and other potential hazards.  This allows any drilling into the building fabric to be conducted safely by avoiding such features.

The key to these surveys is mapping accuracy which has to be centimetre-level.  The Sellafield team are provided with detailed drawings showing the location of the detected features.  The drawing and report is provided in a format which the client has stated is ‘clear and easy to use’.  The surveys have been routinely carried out since 2005 and are ongoing

Example of 3D display of a high resolution GPR dataset (left and middle) collected on a 0.1m orthogonal grid to locate a safe area to drill a hole through a reinforced concrete slab. The location of the recommended drill hole is shown (right) superimposed on the data cube. The final deliverable is a scaled CAD drawing showing the location of relevant features.

New fast electrical resistivity imaging (ERI) system

Zetica has considerable experience in the use of the electrical resistivity imaging technique for a wide range of engineering and environmental applications. Recent projects include mapping the boundaries of in-filled buried pits, delineating the extent of sand/gravel deposits and long term monitoring of a landfill using a permanently installed ERI system. We also authored the acquisition software used by the popular Tigre system 64/128ch system. 

Zetica recently carried out a successful evaluation of a new multichannel ERI system which has the potential to increase ERI productivities by up to 500%!

The new multichannel resistivity imaging / tomography system allows data to be simultaneously collected on 61 potential channels for each current electrode pair. This provides a very high density of resistance data which is ideal for modern 2.5D and 3D resistivity inversion techniques. The system allows monitoring of the full waveform on each channel during data acquisition for QC and later data analysis. Data acquisition is exceptionally fast, with over 62,000 readings taking less than 1 hr to acquire!

The system can easily be deployed for surface, surface to borehole, crosshole and multi-borehole surveys making it extremely flexible with respect to survey design. A new 320 channel version of the system additionally allows acquisition of true 3D surface ERT data.

This system has a proven track record of use in the Far East and Australasia. Zetica were the first UK company to evaluate this system at our test site in Oxfordshire.  

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Lunchtime Seminars

Zetica 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 45 minutes and is case history-based with a 15 minute discussion session following.

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