Near-Surface Interface Detection for Coal Mining Applications Using Bispectral Features and GPR

The use of ground penetrating radar (GPR) for detecting the presence of near-surface interfaces is a scenario of special interest to the underground coal mining industry. The problem is difficult to solve in practice because the radar echo from the near-surface interface is often dominated by unwanted components such as antenna crosstalk and ringing, ground-bounce effects, clutter, and severe attenuation. These nuisance components are also highly sensitive to subtle variations in ground conditions, rendering the application of standard signal pre-processing techniques such as background subtraction largely ineffective in the unsupervised case. As a solution to this detection problem, we develop a novel pattern recognition-based algorithm which utilizes a neural network to classify features derived from the bispectrum of 1D early time radar data. The binary classifier is used to decide between two key cases, namely whether an interface is within, for example, 5 cm of the surface or not. This go/no-go detection capability is highly valuable for underground coal mining operations, such as longwall mining, where the need to leave a remnant coal section is essential for geological stability. The classifier was trained and tested using real GPR data with ground truth measurements. The real data was acquired from a testbed with coal-clay, coal-shale and shale-clay interfaces, which represents a test mine site. We show that, unlike traditional second order correlation based methods such as matched filtering which can fail even in known conditions, the new method reliably allows the detection of interfaces using GPR to be applied in the near-surface region. In this work, we are not addressing the problem of depth estimation, rather confining ourselves to detecting an interface within a particular depth range

Electrical properties of road materials and subgrade soils and the use of Ground Penetrating Radar in traffic infrastructure surveys

Abstract This PhD thesis is composed of a synopsis and five published papers that are focused on both the research results of studies on electrical properties of road materials and subgrade soils and their seasonal changes and the use of Ground Penetrating Radar technique in traffic infrastructure surveys. The data for this survey was collected mainly in Finland, Texas, Scotland and Sweden and thus presents many kinds of road materials, subgrade soils and climate conditions. The synopsis of this work begins with a presentation of the theory and basic principles of GPR techniques. Special attention is given to the dielectric properties and seasonal changes of unbound road materials and subgrade soils. The synopsis also presents different kinds of GPR hardware systems as well as recommendations and experiences from different data collection, processing and interpretation techniques. Special attention is given to a method whereby GPR data is integrated with other road survey data and then analysed using a number of structural diagnostic methods. Finally, the synopsis provides an overview of of the various GPR applications on roads and streets, bridges, railways and airports. The laboratory test results presented in this work show that the relationship between dielectric value and increasing water content is not linear or exponential but more likely a series of logarithmic functions. Laboratory results also showed that dielectric dispersion, which can be related to poorly performing subgrade soils and road aggregates, takes place mainly in loosely bound adsorption water and capillary water layer. As such these moisture sensitive problem materials can also be identified during the dry summer seasons when they are stiff. Dielectric value and electrical conductivity can also be related to other technical properties of road materials and subgrade soils such as frost susceptibility, shear strength, plastic limit, compaction degree and voids content. Laboratory tests and field data collected using the Percostation technique also demonstrate that a knowledge of seasonal changes and thermodynamics is very important in understanding and modelling the mechanical behaviour of road structures. Finally, laboratory and field tests indicate that colloids have an important role in the failure mechanism of the road materials. This research demonstrates that the GPR technique not only gives valuable structural information on the different types of structures and subgrade soils but it provides a wide range of information of the electrical properties of the materials under survey which can be further related to their mechanical performance. The best information will be gained if GPR data is analysed together with other non destructive testing data collected form the roads, railways and airports

GPR surveys on a dike near St. Jacobiparochie

In April 2008 Roadscanners Oy survey group from Finland did Ground Penetrating Radar (GPR) surveys on a dike in the Netherlands, in Friesland, near the village of St.Jacobiparochie. The primary goal of these surveys was to test what is the best way to utilise GPR technique in locating areas of disintegrated asphalt and other structural defects in the asphalt layer on the top of dike and the layers beneath it. This survey was a continuation of the tests, done on the Friesland and Hellegatsdam test sections in summer 2007, which produced promising results. An additional goal was to test recently developed signal processing techniques to see if they could be used to improve the test results. The surveys were done utilizing two different types of GPR systems, one a pulse radar horn antenna system with two central frequencies and the other was a stepped frequency 3d GPR system with full 31 antenna setup.Asfaltbekledinge

3D GPR surveys on Friesland dike

In May 2007 Roadscanners did a series of Ground Penetrating Radar (GPR) surveys on two dikes in the Netherlands, one in Friesland and the other in Hellegatsdam. The purpose of these surveys was to determine pavement layer thickness for safety assessment reasons and to produce seed thickness values for FWD back calculation. Another goal was to locate degradation, cracks, voids and other indicators of poor quality structure in the top layers of the dikes. For this task a 3d ground penetrating radar technique was chosen to provide better area coverage over the dike. With a traditional single channel GPR system the limiting factor is that it only gives information along a single narrow line. A 3d GPR collects data from a 2.4 m wide area in a single run, providing a three dimensional view of the dike structures.This report provides a summary of the key research results from the Friesland (Koehool-Westhoek) dike.Asfaltbekledinge