Fourth International Conference on Ground Penetrating Radar

Subsurface radar is a new undestroied instrument for searching underground structure and buried object. It transmits electromagnetic wave from ground down to underground and identifies target depth, feature and structure of medium according to the delay and shape of return wave which scattered from interface where dielectric feature of underground medium changes.

It is well known that at radio frequencies the electrical properties of rocks are frequency dependent (e.g. Cook 1975, Davis & Annan 1989). As a result, the propagation properties of radiowaves, namely velocity and attenuation, are also frequency dependent. In particular, attenuation increases rapidly with increasing frequency. Ground penetrating radar (GPR) operators trade this property with resolution, which also increases with frequency, to determine the optimum antenna centre frequency to use for a particular application. However, it is often ignored or forgotten that pulsed GPR systems transmit broadband signals+H47 covering two octaves of frequencies or more and so the propagation properties vary significantly over the actual transmission bandwith.

Digitally recorded ground penetrating radar (GPR) data resembles reflection seismic data. Both GPR and the reflection seismic method rely on an impulse-type wave signal, whose length in wavelengths varies with the source. Wave packets are sent into the ground by radio-frequency antennas in the case of GPR and by acoustic sources in the case of reflection seismics. The waves are propagated, attenuated and reflected within the studied material.

The first horizontal jet-drilling machines were imported to Germany in 1986. Since then they have increasingly been used to lay pipes and cables into the ground without trenching. The main features of the horizontal jet-drilling process are illustrated in Figure 1. First a pilot drilling is done (Fig. la); then the expansion and insertion operation takes place (Fig. Ib). Figure lc shows the drilling principle. A high pressure jet of mud excavates the microtunnel. The antisymmetric shape of the drilling head allows the direction of the drilling path to be controlled. Most horizontal drilling projects take place within a depth range of 2 m. A transmitter built into the drilling head allows precise location of the position of the head.

Numerical information on unconsolidated geological materials has use in many geotechnical, hydrogeological and forestry appHcations. Glacial geological mapping, is not based on numerical data, however, but on the morphogenetic interpretation of landforms and visual field checking. The average sampling density for basic map (1 : 20000) production in Finland is less than one sample/km2. One of the practical problems in the mapping is that till, the most common glacial sediment type, has no unambiguous numerical definition, and the conventional dso-classification does not necessarily correspond to the genetic classification. There is a need, therefore, for fast techniques for field data collection, which are consistent with the textural characteristics of glacial materials and allow the differentiation of tills.

Recent advances in subsurface interface radar technology. Geological Survey ojFinland, Special Paper 16, 13-19,5 figures. The acceptance and use of Subsurface Interface Radar (SIR) has increased dramatically over the last five years. During this period, the number of SIR Systems in use worldwide has nearly quadrupled. New and increasingly diverse applications are putting demands on manufacturers to produce systems that can satisfy the growing range of resolution and penetration requirements. Systems must be more flexible yet simple to use and lower in cost.

The limited amount of detailed internal structure of lacustrine (lake) deltas from morphology and widely spaced drill holes has led to the development of simplistic depositional models. To properly understand the geomorphology and internal sedimentology of deltas, it is necessary to determine subsurface sediment facies and their structure. To analyze deltas, other seismic geophysical methods have been hampered by cost, portability and technical limitations (Le. low resolution) and, therefore, has had only limited success. Recent GPR technology has lowered purchase price, maintenance, operating cost, while improved portability, durability and resolution. Published research on the use of GPR in studying subsurface sedimentology and geomorphology is very limited (Ulriksen, 1982; Forgotson et al.1990; Moorman 1990; Moorman et al. 1991; 101 & Smith in press). Our objective is to show and discuss how GPR can be used to better understand subsurface sedimentary structures of different deltas which allows one to improve the construction of depositional models.

A geophysical investigation was conducted at the Parker Landfill Superfund site in Lyndonville, Vermont. The site is underlain by glacial lacustrine deposits primarily comprised of thinly to thickly bedded silty fine sand. Ground penetrating radar (GPR) was utilized in conjunction with other geophysical methods to characterize the site. Three Industrial Waste Sites, IWSI, IWS2, and IWS3, were identified as potential areas where 55 gallon drums containing solvents had been buried. GPR was used to determine the extent of the fill, characterize subsurface materials, locate buried drums and other objects, and identify buried materials which impede intrusive exploration by borings or test pits. A magnetic survey, which delineated the approximate location of ferro-magnetic materials, and test pits were conducted to assess the accuracy of the GPR interpretation.

Contamination of groundwater by DNAPLs, such as chlorinated solvents, is a serious environmental problem. After an accidental spill into the subsurface, a DNAPL will redistribute itself and form both isolated liquid-phase blobs known as residual, and connected-phase zones known as pools. The behaviour of liquid-phase DNAPLs in a sandy aquifer is controlled principally by variations in hydraulic conductivity(Kueper et aI1989). When groundwater flows through zones containing liquid-phase DNAPL, a small amount of the DNAPL dissolves into the water creating a more extensive plume of dissolved-phase contamination that usually poses the most serious threat to drinking water.

The objective of this study was to assess the potential applications of the Ground Probing Radar (GPR) technique to the china clay industry, chiefly through the property of distinguishing variation in degree of argillisation. China clay deposits principally occur in strongly argillised areas of granitic outcrop, where the granite has been totally replaced by kaolinite. The local variations in intensity of kaolinisation of a potential china clay deposit determine the planning, costing and execution of extraction operations. The most intensely kaolinised, highest grade deposits are very soft, and are able to be extracted by ripping and bulldozing, whereas lower grade, harder material is more efficiently mined by drilling and blasting.