580 ENGINEERING GEOLOGY/Site and Ground Investigation sample, the height of the water in the standpipe falling The times at the beginning, t1, and end, t2, of the test are recorded and these, together with the two corresponding heights, h1 and h2, the crosssectional area of the standpipe, a, and cross-sectional area, A, and length, l, of specimen are substituted in the following expression to derive the coefficient of permeability, k: kẳ 2:303al log10 h1 log10 h2 ị At2 t1 ị ẵ13 Variations of permeability in rocks under stress can be obtained by using a radial percolation test A cylindrical specimen, in which an axial hole is drilled, is placed in the radial percolation cell The latter can either contain water under pressure where the axial hole is in contact with atmospheric pressure; or water can be injected under pressure into the hole (Figure 15B) The flow is radial over almost the whole height of the sample and is convergent when the water pressure is applied to the outer face of the specimen, and divergent when the water is under pressure within the axial hole Porous rocks remain more or less unaffected by pressure changes On the other hand, fissured rocks exhibit far greater permeability in divergent flow than in convergent flow Moreover, fissured rocks exhibit a continuous increase in permeability as the pressure attributable to divergent flow is increased See Also Aggregates Engineering Geology: Codes of Practice; Natural and Anthropogenic Geohazards; Problematic Rocks Further Reading Anon (1975) Methods of Sampling and Testing Mineral Aggregates, Sands and Fillers, BS 812 London: British Standards Institution Anon (1982) Standard Test Methods for Absorption and Bulk Specific Gravity of Natural Building Stone, C93 117 Philadelphia: American Society for Testing Materials Bell FG (ed.) (1992) Engineering in Rock Masses Oxford: Butterworth Heinemann Bell FG (2000) Engineering Properties of Soils and Rocks Oxford: Blackwell Science Brown ET (ed.) (1981) Rock Characterization, Testing and Monitoring Oxford: Pergamon Press Farmer IW (1983) Engineering Behaviour of Rocks, 2nd ed London: Chapman and Hall Goodman RE (1989) An Introduction to Rock Mechanics, 2nd ed New York: Wiley Hudson JA and Harrison JP (1997) Engineering Rock Mechanics: An Introduction to the Principles Oxford: Pergamon Site and Ground Investigation J R Greenwood, Nottingham Trent University, Nottingham, UK ß 2005, Elsevier Ltd All Rights Reserved Introduction and Terminology The procedure of ‘investigation’ is fundamental to any project or activity involving the ground The historical records need to be reviewed, current conditions need to be established, and the consequences of the proposed activity, works, or construction need to be carefully considered Investigation is an on-going process of establishing and reviewing the facts and processing the information to assist our future activities With respect to construction works the following definitions are used: ‘Site investigation’ is a continuous process, as the construction project develops, involving both the site under consideration and the interaction with the surrounding areas It is not confined to obtaining information on geotechnical aspects but may include hydrological, meteorological, geological, and environmental investigation ‘Ground investigation’ is more site-specific and aims to investigate ground and groundwater conditions in and around the site of a proposed development or an identified post-construction problem The term ‘site characterization’ is now also used; it stems from the environmental specialist’s study of contaminated sites but is equally applicable to any site ‘Characterization’ perhaps implies the results of ‘investigation’ This article reviews the procedures necessary for quality site investigation to be carried out and describes some of the ground investigation techniques