Abstract The origin of the thermal springs of Bath (England) remains unknown. As part of a programme of research into the structure of the thermal aquifer, the Carboniferous Limestone, an urban reflection seismic survey has been carried out to explore the deep geology of the Bath area. Existing gravity data have been used to provisionally identify the seismic reflectors and to map the depth of the (interpreted) Carboniferous Limestone in the area around the springs. The new seismic data show that at a distance of 2.1 km south-west of the springs, the depth of the (interpreted) Carboniferous Limestone surface increases from 0.4 km below Ordnance Datum (OD) to 1.35 km below OD within a distance of 1.8 km, an average apparent dip of nearly 30 degrees. In all other directions from the springs, the Carboniferous Limestone surface is at a depth of 300 m or less below OD. The work described in this paper is part of a continuing research programme.

Abstract The Construction Directorate of the DTI supports the programme of innovation and research to improve the construction industry's performance and to promote more sustainable construction. Its main aims are to improve quality and value for money from construction, for both commercial and domestic customers, and to improve construction methods and procedures. The full potential of geophysics in engineering investigations is still to be realised. The many available techniques can provide important information about the ground, its mass properties, its small-scale variations, and its anomalies of structure or content. The advantage of a geophysical survey is that it enables information to be obtained for large volumes of ground that cannot be investigated by direct methods due to cost. The applications of geophysics in the characterisation Of contaminated land are still developing, but have great potential for example in the distribution and migration of pollutants in the ground and groundwater. Geophysics is still insufficiently or inappropriately used in engineering and the newer capabilities are not appreciated. This report is published in co-operation with the Geological Society and presents a logical guide through the process of using geophysical investigation methods in site characterisation. It explores the roles of geophysical, methods and, provides the back.ground to geophysics as an investigative tool. The procurement, management and reporting frameworks for a geophysical investigation are set out and the underlying science and current practices of the main techniques are explained, as well as the processes of data acquisition, handling and presentation. The different targets determinable by geophysical methods are considered in separate sections for geological, geotechnical, geo-environmental and structural engineering applications. The report concludes with recommendations for practice.

Abstract The full potential of geophysics in engineering investigations is yet to be realised. With investigative capabilities ranging from the detail of well-logging to the long traverses of studies of geological structure, the many available techniques can provide important information about the ground, its mass properties, its small-scale variations, and its anomalies of structure or content. The advantage of a geophysical survey is that it enables information to be obtained for large volumes of ground that cannot be investigated by direct methods because of the costs involved. The applications of geophysics in the characterisation of contaminated land, eg the distribution and migration of pollutants in the ground and groundwater, are still developing, but with great potential. These are still insufficiently or inappropriately used in engineering and the newer capabilities are not appreciated. There is a need for up-to-date guidance about how to apply geophysical investigations. The underlying aims of this report, therefore, are to prepare guidance for civil and geotechnical engineers, and their clients on: the integration of geophysical investigations into the design and construction process the use of geophysics for determining engineering parameters the capabilities of geophysics for investigating ground contamination and grouion.

Abstract Geophysical exploration was probably born in the early 1920s. This was after the successful development of electrical prospecting methods by the brothers Conrad and Marcel Schlumberger in France, and the seismic refraction method in the newly discovered oil fields of the mid-south USA. During the following decade experience was gained using these methods and new techniques were developed, such as seismic reflection, gravity, magnetic and electromagnetic surveying, borehole logging and the use of seismic methods at sea. The exigencies of world War II led to the adaptation of many geophysical methods for use in detecting mines, submarines and enemy fire positions. This encouraged basic research, which led to tremendous advances in electronics, signal processing concepts, and computer methods. Consequently, during the following four decades, the geophysical exploration industry in the non-communist world grew rapidly to having an estimated annual turnover of £3 billion. The bulk of this effort was concerned with the petroleum and mining industries, but there was also a steady growth in the application of various geophysical techniques to civil engineering and groundwater studies. From early applications of the seismic refraction method to the determination of depth-to-bedrock in the 1930s, the practice of engineering geophysics has expanded to encompass a wider range of techniques, applied to more types of problems, than any other branch of geophysics. To a large extent, the techniques and equipment of engineering geophysics evolved from the other sectors. The main differences relate to the relatively shallow depths of investigation required (rarely greater than 100

Abstract This chapter is about how to set up, procure and manage geophysical investigations, to have the best chance of providing information that is useful to an engineering project. There is a perception that geophysical techniques applied to engineering purposes have often been procured inappropriately and managed inadequately. This is particularly so for geotechnical investigations. A summary is given of this background to procurement practices in the UK and some other countries. This leads to a review of what the principal parties in the project want from a geophysical investigation and what this implies for the management framework in which to set the geophysical work. The emphasis for this chapter is on effective management, clear focus, clarity of purpose and definition of deliverables. As in most engineering activities, the more care and thought that is put into the planning of the survey by appropriately qualified professionals, the better the chances of success and of providing a product that will satisfy all parties. To be successful in the selection of an appropriate technique, those involved need appropriate geological training and understanding as well as an adequate appreciation of the nature and impact of the engineering project. Underlying the analysis and proposals of this section, is the intention to examine UK practice and to recommend ways for its improvement. These recommendations are based on the principle that the ground investigation and its component parts should be designed and undertaken in a conscious framework of risk management to achieve greater certainty of outcome. The

Abstract The range of possible subsurface conditions that can be predicted, knowing the geological processes that formed the ground beneath a site, is self-evident to the geological or geotechnical advisor. This information underpins the conceptual ground model. Many construction cost over runs are caused by unforeseen ground conditions. Avoiding this requires a better desk study and ground investigation (including geophysical survey), as well as the development of a ground model that includes the known and suspected features on, below and adjacent to an engineering site. Such a model will assist in identifying the likely implications of the ground for a proposed engineering project. It is helpful to portray the conceptual ground model as a threedimensional block model that allows the scale of the features, in relation to the size of the project, to be appreciated. In addition, the geology should be characterised in engineering terms by the geological/geotechnical advisor, which means that geotechnical properties and their likely lateral and vertical variation, must be assessed within the context of the model. The difficulty in understanding the ground conditions at a construction site has its origin, in part, in the way that geological knowledge advances. Geological mapping has been carried out in Britain since the late 18th century when the canal network was constructed. The process of updating British geological maps is still continuing (see CIRIA Special Publication 149, A guide to British stratigraphical nomenclature, Powell 1998 ). The geologist has to interpret the information as it is made available from boreholes

Abstract Geophysical methods can be used at and below, the ground surface, at sea, in the air, and in the laboratory. In this chapter the advantages and limitations of the main methods used in the civil engineering industry are summarised. Other, less familiar, methods are discussed with the objective of familiarising the reader with the range of possible methods, which might be suggested for the solution to a specific problem. This chapter emphasises land-based geophysical techniques to investigate the ground. There are descriptions of geophysical surveying systems, specifically developed for the marine environment to be rapid and cost-effective. Modern positioning systems, such as the Global Positioning System (GPS) and the Differential Global Positioning System (DGPS), are now in common use and accurate position-fixing of the survey vessel can be achieved. Airborne geophysical methods are widely used in regional surveys associated with hydrocarbon and mineral exploration. They currently have little application in engineering studies because their overall cost would be prohibitive in most cases. However, in a large engineering project, such as the development of a radioactive waste repository, which involves a significant requirement for regional geological information, information from large-scale seismic reflection, gravity, magnetic, and electromagnetic surveys will be required. In this case the use of airborne methods might well be both practical and economically viable. Many of the geophysical methods are widely used in the non-destructive testing (NDT) of civil engineering structures and materials. While not strictly geophysics, the testing employs the same physical parameters that control the effective use

Abstract Geophysics involves the measurement of signals, which are subsequently processed and analysed prior to interpretation and presentation, in terms of a “geophysical” ground-model. Typically, a geophysical method concerns measurements that are in turn controlled by a “geophysical” mass property. For example, if the travel time of seismic waves were the measurement, the controlling ground property would be seismic velocity. Generally, geophysical mass properties are controlled by lithology and rock mass condition. It is important to select geophysical methods that give the greatest response to the variability of geophysical mass properties, of relevance to the civil engineering problem in hand.

Abstract A major use of geophysics in engineering investigations is as a tool in unravelling the subsurface geology. In this fundamental and early application, it is the geology that is the target, and engineering considerations and material properties are secondary. The simplest geological structure, which can be investigated, is a horizontal interface such as that between bedrock and overburden. Geological structures are rarely simple, and surveys have to be designed to tackle complex situations. Geological structure can be considered as lateral variation in the properties of the subsurface rocks. In its simplest form it might be represented by a single dipping or irregular interface such as a bedrock surface. In more complex situations it might include thickness changes, faults, folds, or igneous intrusions. The first section examines the measurement of depth to bedrock, as this is probably the most common boundary problem. Other geological structures are briefly considered under different types of geological hazard.

Abstract Many physical properties of rocks and engineering soils may be determined from geophysical measurements, eg bulk density, porosity and permeability. The most important geophysical parameters, for measuring physical properties, are electrical resistivity (Section 5.1 ) and seismic wave velocity (Section 5.4 ). Others, such as thermal conductivity (Section 5.7 ) are used more directly in engineering studies. Some derived properties need to be modified, usually according to semi-empirical constitutive relationships. For example, the modification of elastic moduli determined by elastic wave propagation methods takes account of larger strains, different mean effective stress and duration. Other geophysical measurements can be translated by empiricism into useful engineering indices (eg rippability from seismic velocity and corrosivity from electrical resistivity). With the improvements in imaging by seismic, electrical and radar methods (Section 5.5 ), the ground may be more readily characterised in terms of the distribution of a geophysical or derived physical property, and this may lead to particular engineering design choices. At the initial stage of site investigation planning, it is often more appropriate to consider the use of geophysical methods in the context of the overall engineering project, rather than in the identification of specific targets or engineering parameters. The main areas of engineering practice, and the associated subject of construction materials, are covered separately in this chapter, but there is a measure of overlap between some areas. For example, the geophysical assessment of bearing capacity is appropriate to bridges, power stations, dams and off shore structures, and

Abstract Environmental applications of geophysical techniques concern the location, delineation and monitoring of subsurface, natural and man-derived hazards. Environmental geophysical surveys are concerned with the near surface, typically to depths of less than 30 m. Natural hazards include dissolution cavities, collapsing soils and earthquakes. Man-made hazards arise from the effects of pollution and previous land usage. Geophysical techniques may be applied in the assessment of the condition of derelict or contaminated land and the monitoring of remedial measures. The use of non-invasive geophysical methods is attractive where contamination is near the ground surface, as they do not penetrate any capping, which minimises the release of gas or the ingress of surface water. In some cases, to find contaminated zones within old landfills and derelict sites, geophysical surveys are the only practical method of investigation.

Abstract This section deals with the application of NDT techniques to buildings and civil engineering structure circumstances. The information is presented as a series of cascading tables (see Figure 10.1 ) supported by case histories. The first table lists the types of information that are sought for structures constructed using: Concrete masonry and stone metals timber composite materials. The subsequent tables link the information sought, with the appropriate diagnostic testing and inspection techniques. In these tables the geophysical methods are in bold text, but also included are alternative methods of investigation and testing, which might supply the required (or complementary) information. The geophysical methods are then summarised after the tables with comments on the effectiveness of the technique to provide the required information. Three case histories illustrate the use of the individual testing/investigation techniques. Table 10.1 provides a simplified guide to the nature of some of the information, which might be sought in various circumstances, for structures constructed using concrete, masonry and stone, metals and composite materials.

Abstract The concluding remarks lead on to some general recommendations for practice, particularly in the way that the geophysical investigation should be planned, staffed and managed integrally with the whole scheme of investigation.

Abstract Identifying the location, size, and characteristics of small aquifers is becoming increasingly important in Scotland with the growing demand for groundwater to supply isolated rural communities. These small, localized aquifers are found within superficial deposits, such as alluvium, blown sands and raised beach deposits, and in fracture zones in the underlying bedrock. Geophysical techniques offer a rapid and inexpensive method of characterizing these aquifers. Electromagnetic techniques using EM34 and EM31 instruments have proved useful in identifying variations in the thickness of superficial deposits and detecting buried channels, for example, at Palnure, SW Scotland. Ground penetrating radar has been used at several locations, including the island of Coll, to detect the boundary between bedrock and alluvium or blown sand. More detailed techniques, such as resistivity soundings, seismic refraction and resistivity tomography have been used to identify fractures in basement rocks and help calibrate the other methods, for example at Foyers, near Loch Ness. Magnetic profiling has also been used to locate dykes (acting as hydraulic barriers) within Permian aquifers in the west of Scotland.