3. Read the text carefully and do the tasks that follow:

Gradual technological improvements in the 17-th and 18-th centuries increased commercial travel, improved vehicles and the breeding of better horses. Rural roads became impassable in wet weather. These factors created an increasing demand for better roads.

Up to this time roads similar to the Roman roads were built. However, owing to a scarcity of a suitable material and the high cost of labour, the amount of stone material used was progressively reduced and the work was carried out less thoroughly. Research was carried out to find out more rational methods of using stone for pavement construction which would reduce both the amount of labour and the cost. And in the last half of the 18-th century the farthers of modern road building and road maintenance appeared in France and Britain.

Tresaquet. In France in 1764, Pierre Tresaquet, became an engineer of bridges and roads in Limoges. He developed an entirely new type of relatively light road surface, based on theory that the underlying natural formation should support the load.

His standard cross-section, 18 feet wide, consisted of an eight-inch-thick course of uniform stones laid edgewise on the natural formation and covered by a two-inch layer of broken stone. The second layer was topped with one-inch layer of smaller broken stone. In order to maintain surface level Tresaquest's pavement was placed in an excavated trench — a technique that made drainage a difficult problem.

Figure 2

McAdam. The greatest advance came from John McAdam, born in 1756 in Scotland. He reached major heights in his road-building career after 1804 when he was appointed general surveyor for Bristol. The roads leading to Bristol were in poor condition. There he showed that traffic could be supported by a relatively thin layer of small, single-sized pieces of broken stone placed and compacted on a well-drained natural formation and covered by an impermeable surface of smaller stones.

Mc Adam is famous for the surface he developed for roads. This kind of surface, called macadam, is still used today. Mc Adam also stressed the importance of proper drainage to keep roads on a solid foundation. Drainage was essential to the success of Mc Adam’s method and he required the pavement to be elevated above the surrounding surface. The structural layer of broken stone was eight inches thick and used stone of two or three inches maximum size laid in layers and compacted by traffic. The top layer was 2 inches thick, using three-quarter-inch stone to fill surface voids between the large stones. Continuous maintenance was essential.

Russian engineers were the first ones to construct granular surfacing laid on sand base which are now widely used in other countries. The use of a sand base permitted the cost of construction to be reduced and the removal of water from the subgrade to be facilitated. It helped to increase subgrade stability.

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