Land evaluation and site investigation

Land evaluation and site investigation are undertaken to help determine the most suitable use of land in terms of planning and development or for construction purposes. In the process the impact on the environment of a particular project may have to be assessed, this is especially the case for large projects. Obviously, there has to be a geological input into such assessments. This may be with regard to earth processes and geological hazards, mineral resources and the impact of mining, water supply and hydrogeological conditions, soil resources, ground conditions or disposal of waste. The impact of the development of land is most acute in urban areas where the human pressures on land are greatest. In addition, the redevelopment of brownfield sites can present difficult problems such as derelict heavy industrial sites with extensive foundations, severely contaminated ground and abandoned mineral workings at shallow depth (Bell, 1975; Bell et al., 2000). Investigations in relation to land-use planning and development obviously can take place

at various scales, from regional to site investigations. Regional investigations generally are undertaken on behalf of government authorities at, for example, state or county level, and may be involved with the location and use of mineral resources, with the identification of hazards, with problems due to the past types of land use or with land capability studies and zoning for future land use. In this context, it is necessary to recognize those geological factors that represent a resource or constitute a constraint. A constraint imposes a limitation on the use to which land can be put, so that a particular locality that is so affected is less suited to a specific activity than another. Site investigations tend to be undertaken for specific reasons, for instance, to obtain the necessary information for the location of a suitable site for a landfill, for the site of a routeway, a tunnel, or of a reservoir and dam, or for the development of a large brick pit and works. A site investigation may form part of a feasibility study or is undertaken to assess the suitability

of a site and surroundings for a proposed engineering structure. As such it involves exploring the ground conditions at and below the surface (Anon., 1999). The data that is obtained from a site investigation for a feasibility study is used to help determine whether a project is feasible. A site investigation carried out prior to the construction of an engineering project is a pre-requisite for the successful and economic design of engineering structures and earthworks. Insufficient or inadequate geotechnical data may lead to unsatisfactory design, which subsequently may result in serious damage to, or even failure of an engineering structure. Any attempt to save costs by allocating a low budget to a site investigation may be the cause of additional expenditure later if unfavourable ground conditions are encountered during construction, which were not indicated by the original site investigation. Accordingly, a site investigation also should attempt to foresee and provide against difficulties that may arise during construction due to ground and/or other local conditions. Indeed, investigation should not cease once construction begins. It is essential

that the prediction of ground conditions that constitute the basic design assumption is checked as construction proceeds, and designs should be modified accordingly if conditions are revealed that differ from those predicted. An investigation of a site for an engineering structure requires not only ground exploration but also sampling of all rock or soil types that may be affected significantly by the engineering project. Data relating to the groundwater conditions, the extent of weathering and the discontinuity pattern in rock masses also are very important. In some areas there are special problems that need investigating, for example, the degree of contamination of the ground or the potential for subsidence in areas of shallow abandoned mine workings. It may be necessary in some construction projects to carry out an investigation to determine whether suitable sources of sufficient material for construction purposes are available. A site investigation also may be required to help explain the failure of an engineering structure when it is suspected that the ground conditions may have been a contributary cause. In this instance, the data obtained is used in the design of any remedial works. The complexity of a site investigation depends upon the nature of the ground conditions

and the type of engineering structure concerned. More complicated ground conditions and more sensitive large engineering structures require more rigorous investigation of the ground conditions. Although a site investigation usually consists of three stages, namely, a desk study, a preliminary reconnaissance and a site exploration, there must be a degree of flexibility in the procedure, since no two sites are the same. Any investigation begins with the formulation of aims, what it needs to achieve and which

type of information is relevant to the particular project in question. Once the pertinent questions have been posed, the nature of the investigation can be defined and the process of data collection can begin. The amount of detail required depends largely on the purpose of the investigation. For instance, less detail is required for a feasibility study for a project than is required by engineers for the design and construction of that project. Various methodologies are employed in data collection. These may include the use of remote sensing imagery, aerial photography, existing literature and maps, fieldwork and mapping, subsurface exploration by boring and drilling, sample collection, geophysical surveying and in situ testing. In some instances, geochemical data, notably when water or ground is polluted or contaminated, may need to be gathered, or monitoring programmes carried out. Once the relevant data has been obtained it must be interpreted and evaluated, and then, along with the conclusions, embodied in a report, which will contain maps and/or plans. Geographical information systems (GIS) may be used to help process the data.