Urban Materials Flows

Since 1965, many attempts have been made to establish urban materials use (Wolman 1965; Aston et al. 1972; Newcombe 1977; Newcombe et al. 1978; Douglas 1983). Nevertheless, even the amount of mineral matter entering the urban fabric is difficult to establish, as facing and flooring materials, such as marbles, granites and tiles, are often imported. At the present state of knowledge, for any given country, it is usual to assume that all the bricks, aggregates and cement used come from national mineral production.

Another type of materials flow is involved with road construction and infrastructure development. Masses of earth surface material are removed in foundation excavation, trenching, making cuttings, tunnels and embankments. Statistics of these quantities are not easily obtained, but accounts of major projects in the engineering literature usually give a global figure of the amount of earth moving involved. For example, some 20MMT of material was excavated and moved during the construction of the Channel Tunnel (CIRIA 1997; Varley and Shuttleworth 1995) while the building of a 3.1km-long second runway at Manchester Airport involved the importation of over 1MMT of concrete aggregates and the excavation of 2.8 million cubic meters (Mm3) of earth (A. Jack, earthworks agent, Amex-Tarmac Joint Venture, personal communication 24 November 1997).

The construction of road surfaces will be accounted for in assessments of mining and quarrying and in quantities of construction and demolition waste and road planings (scrapings from used road surfaces) recycled into aggregates for road making. However, the building of roads and highways also requires moving substantial amounts of earth - cut and fill. Each individual section of road will of course vary in accordance with the natural topography. In the UK, for example, recent motorway projects required the movement of approximately 500000 tons per km of earth and rock and, on average, earth and overburden has to be removed to a depth of 0.75m to make way for the foundations for new urban construction and the provision of minor service roads (Douglas and Lawson 2001).

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