1st Line Defence provided case studies and data for a recent paper submitted for CPT’18 regarding a digital CPT system that we utilise called Icone®.
Below is the abstract of the paper and summaries of the two case studies. You can read the full paper here.
ABSTRACT: The paper describes a digital CPT system called Icone®. This system is easily extendable by click-on modules to measure additional parameters and any module is automatically recognized by a digital data logger, thus creating a true plug & play system. By moving to smart digital communication, sufficient bandwidth over a thin flexible measuring cable was created to accommodate additional parameters, without the need for changing cones, cables or data loggers. The following click-on modules are described: seismic, conductivity, magneto and vane. Feedback from fieldwork with the Icone and the magnetometer module (Magneto) highlights the user experience with this approach.
Using the magnetometer module, metal objects in the underground can be detected by interpreting anom-alies of the earth’s magnetic field. The application of this module is illustrated by two unexploded ordnance (UXO) survey projects for clearance ahead of piling.
CASE STUDIES:
Sheerness Bridge
Purpose of Investigation
In February of 2017, a UXO magnetometer survey was carried out ahead of construction piling locations. A detailed UXO risk assessment was carried out earlier, which showed a risk that the site may have been contaminated with items of both German and British unexploded ordnance. The aim of the intrusive survey was to minimize the risk that magnetic anomalies, which may have indicated the presence of unexploded ordnance, were located at proposed pile positions.
Test Method
The positions were set out by a site engineer using the GPS coordinates obtained from the drawing.
Each test was carried out by pushing to the maximum bomb penetration depth (specific to each location depending on the strata). The live data was first quality assurance checked by the on-site Explosive Ordnance Disposal Engineer in attendance, with the interpretation carried out by geophysicists.
Test Results
One investigation at position 372 presented a ferrous anomaly that covered two individual pile locations. The Magneto test shows an anomaly between 5.2 and 6.2m depth. Additional testing was requested in order to collect more data; position 172A and 172B were investigated directly where the piles should be positioned. These tests resulted in the anomaly being present on position 172A.
Due to the depth of the object at approximately 6.5m, a series of temporary works were carried out. Shoring was used, which allows excavations to be completed in a controlled safe manner. This allowed Explosive Ordnance Disposal engineers to locate the anomaly at staged intervals with handheld magnetometers.
The item in turn was identified to be part of a pre-existing old pile location. The item was deemed safe and allowed the customer to carry on with works and proceed with building the bridge.
Royal Wharf
Purpose of Investigation
Royal Wharf, an area in London was assessed as medium UXO risk. Again, the aim of the survey was to minimize the risk that magnetic anomalies were located at proposed pile positions.
Test Method
The same test method as in Case Study 1 was applied.
Test Results
An anomaly was detected during the push of the (Icone®) Magneto module starting at a depth of 2.5m which spanned the entire depth of survey. This particular object presented bomb like characteristics and was required to be investigated to make a visual identification of the object.
The position was investigated using a series of 200mm staged excavations in order to determine the cause of the influence. This was overseen by an Explosive Ordnance Disposal Engineer, who exposed the item at 2.5m which was identified as an existing steel-reinforced concrete pile. This allowed 1st Line Defence and the customer to confirm the ferrous anomaly was not unexploded ordnance and to carry on with the deep intrusive works.
