Mobile Ground Penetrating Radar for M25 Pavement Survey

19th November, 2019

Project Overview

LandScope were commissioned to complete a large-scale pavement survey on the M25 utilising mobile ground penetrating radar (GPR) to remove the need for road or lane closures.

We were required to survey an approximate 25km section of the M25 (both clockwise and anti-clockwise) over all 4 running lanes. This meant in total that approximately 200km of carriageway was required for pavement analysis and characterisation. The survey was completed at road speed in our Chapter 8 approved vehicle with no formal road/lane closures. LandScope worked with the relevant highways authorities and completed the works under two-night shifts to negate disruption to the general public and other road users.

LandScope’s survey vehicle has a single channel 1GHZ antenna mounted to the vehicle’s underside – located in the driver side wheel track. The GPR antenna was set at its optimum data sampling rate to ensure, even at full road speed, a dense sampling interval was ascertained. The GPR antenna was combined with a mobile mapping system to provide high accuracy positioning. The mobile mapping system has the benefit of an inertial measurement unit (IMU), GNSS receiver and odometer. This allows the standard GPR GNSS trajectory to be replaced by a much higher precision trajectory that gives a very high positional confidence even in challenging environments, such as passing under bridge, tunnels, tall tree lines etc.

All data was processed within Road Scanners, Road Doctor software. This software is designed specifically to handle mass data sets and allows for easy extraction of sub-surface layers with sophisticated automatic reporting functions.

Fig.1. GPR Pavement Data Processing in Road Doctors Software. Layer Thickness Analysis and Interpretation.

Technique Overview

Mobile GPR is an effective non-intrusive data collection platform that can provide valuable information on a carriageway make up.

The collected data can be used to analyse the pavement layer thicknesses. A carriageway is typically made up of multiple layers that can either be flexible or rigid in nature. A typical flexible pavement may consist of; sub-base, base course and several layers of asphalt. Understanding the layer properties/thickness can be essential to calculating a carriageway life expectancy and be used to plan effective repair and maintenance works.

Mobile GPR processing packages allow for the incorporation of intrusive core results. This enables true on-site data values to be used to calibrate the GPR results – providing a high level of confidence and vastly minimising the amount of intrusive work required.