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Abstract

Since 1993, when a new radar technique for pavement investigation was developed by Impulse Geophysics, many thousands of kilometres of data have been collected in the United Kingdom and elsewhere. The technique, in the following years, has been refined and improved with regard to data collection, processing, interpretation and easy of client use. Using a radar survey continuous thickness measurements of the construction layers, the detection of structural anomalies, moisture content and the presence of voiding in the road pavement, are readily established. An effective radar survey, therefore, offers high quality and accuracy for monitoring and scheduling road maintenance. In Italy most engineering road departments still request the traditional, locally limited, coring method to measure the thickness of bituminous and granular layers. An application of the radar technique was carried out in the “Dino e Enzo Ferrari” autodrome with the intention of integrating the 20 material core locations (see Figure 1) chosen by the Formula 1 Circuit Management Consultants, who maintained the circuit. The Ground Penetrating Impulse Radar Survey (GPR) consisted of three lane investigations placed on the right, central and left track of the road, starting and ending on the finish line. The data were collected along the three tracks using three antennae; a 500 and 900 MHz and a 2.5 GHz. The recording system used was a GSSI SIR 2. The antennae and a distance encoder were mounted behind a vehicle (see Figure 2) travelling at an average speed of about 40 kilometres/hour resulting in a sample at 20 cm intervals. Additional markers were located every 500 metres on the total length of 4,920 metres. The three antennae gave good results to the following depth: 2.5GHz = 30cm, 900MHZ = 1m, 500 MHz = 2m. During data processing, the radargrams were horizontally scaled and filtered using band-pass filtering. The processing software, WinRAS, developed by Impulse Geophysics, allowed easy and rapid tracking of the wavelets relevant to the pavement layers. Matching the two-way travel time of the radar events with the core samples, the impulse radar velocities were depth calibrated and the time cross-sections were converted into depth-sections. The combination of the results obtained using the three types of antennae gave the required resolution and penetration down to 2 metres from the surface. The average sequence of the layers, from the surface, was as follows: 4cm wearing course, 6cm asphalt, 10cm bound bituminous, 20cm granular sub-base, 40cm granular sub-base, natural gravel and sand. Using the high speed radar system, a large amount of data is normally collected, resulting in extensive paperwork if the depth cross-sections are printed in a readable size. To avoid this inconvenience and to be able to readily view the radar data, Impulse Geophysics has developed the “Roadshow” software. The Roadshow may be run on a normal Personal Computer and examples will be shown, by the authors, at the meeting. Also to be demonstrated will be a Digital Video Survey of the Circuit, recorded using 4 S-video cameras for front, rear, left and right views. Both Roadshow systems together allow engineers to view the surface and subsurface of a road from their desktop PC.

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/content/papers/10.3997/2214-4609.201406439
1999-09-06
2020-04-09
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http://instance.metastore.ingenta.com/content/papers/10.3997/2214-4609.201406439
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