Chartered Institution of Civil Engineering Surveyors Technical Presentation

Date08 December 2016
VenueUCL, Medical Sciences G46 HO Schild Pharmacology

The Port of London Hydrographic service has for many years been providing survey support for projects within the Thames and the Thames Estuary. The PLA calls upon its extensive experience of operating within the Thames to support a wide variety of projects ranging from pre dredge surveys to engineering surveys and more recently geotechnical investigations including shallow seismic and shallow intrusive investigations such as Shallow coring and CPTs.

During the pursuit of the shallow investigations, and with the publishing of the recent CIRIA guidelines for marine works, the PLA has increasingly been involved with surveys for UXO clearance. Early works used conventional systems such as Gradiometer, Magnetometer and Magnetometer CPT drives. However the conventional magnetometer/gradiometer approached proved limited within the Thames due to the presence of ferrous rich structures and a proliferation of ferrous detritus.

The PLA has been working with SAND geophysics and Ordtek to augment traditional systems with the use of 3D CHIRP. This system is capable of providing improved target classification and acts to reduce the number of targets which require further investigation. This has been used to great success in support of the Thames Tideway Tunnel Project.

SAND Geophysics Ltd provides geophysical consultancy and support for the Seabed and Near-surface Detection (SAND) of man-made items (e.g. UXO), infrastructure (e.g. cables), and geological properties. Since April 2016 they have been working successfully with the Port of London Authority to bring the Kongsberg GeoChirp 3D system to the Thames for accurate buried UXO detection along the Tideway project that is constructing a 22nd century sewage system for London.

The Kongsberg GeoChirp 3D provides three dimensional acoustic images of shallow sub-seabed structures and buried objects larger than 15cm in dimension. It transfers the well-established principles of conventional 3D reflection seismic used in hydrocarbon exploration, to high-resolution CHIRP sub-bottom profiler technology. The technology was developed by the University of Southampton UK and licensed for commercialisation by Kongsberg GeoAcoustics. The technology has had a massive impact in UXO detection on the Thames where abundant ferrous structures make magnetometers redundant; and for cable routes and monopile sites of wind turbines where boulders can cause millions of pounds of delay.

SAND and the PLA have developed an excellent delivery and acquisition strategy involving the PLA's new survey vessel Maplin, and SAND has developed an efficient processing pipeline to handle and interpret the large amounts of data for acoustic UXO detection on commercial time-scales.

On-going challenges are to provide RTK grade positioning for the system, which it requires to collect an accurate seismic wavefield, for brief transits beneath bridges in the Thames within inner city London. The PLA, SAND and the University of Southampton are looking to have solved this in the first quarter of 2017.

Ordtek's approach to addressing unexploded ordnance (UXO) risk employs an intelligent blend of risk management and geoscience techniques to assess and mitigate the risks posed to development. Their intrinsic understanding of how UXO interacts with the natural and manmade environment is crucial to ensuring that this risk is managed pragmatically, safely and at best value to both land-based and maritime developments

Ordtek have an intimate knowledge of the CIRIA guidelines as well as an exceptional understanding of marine geophysics in the application of the detection of ordnance. They have worked with SAND and the PLA to establish the 3D CHIRP data as an accepted method for UXO detection and classification.

The presentation will introduce the PLA, SAND and Ordtek and examine the limitations of the conventional mechanisms in the detection of UXO in environments such as the Thames. The presentation will introduce the 3D CHIRP then move on to examine the process of establishing the 3D CHIRP as a suitable method for possible UXO detection. Finally the presentation will look at the possibility of additional products attainable from the 3D CHIRP data set. 

This event is being held in conjunction with the Southern Region of The Hydrographic Society UK

All members and visitors welcome

Click here to register 

To secure your place on this event a £10 deposit is required. This is refundable when you sign the register on attendance


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