Roads and Airfields

Memorize the following words:

excavation - земляные работы anchor - крепление

fill -насыпь drill - бурить

wind - изгибаться scrape - скрести

paving - устройство защитного покрытия

silt - глинистый заполнитель

sheepsfoot roller - кулачковый каток

compaction - искусственное уплотнение грунта

subgrade - подошва, основание

subbase - основание сооружения

I. Read the text and make up its outline.

From Asia Minor to Spain, from Central Europe to North Africa, the great achievement of the Romans was to build some 50,000 miles of roads for the consolidation of their Empire and the governing of its peoples. From Canada to Mexico, from the Atlantic to the Pacific, the people of the United States have built over 3,600,000 miles of roads for the opening up of their country and for its full development as an industrial nation.

An English poet once sang of the time when "the rolling English drunkard made the rolling English road." In those days, roads swung around hills and obstacles and switchbacked up hill and down dale. They had a charm of their own, but they have become unsuited to the fast and heavy road traffic that has arisen since.

The fast highways of the world today have relatively flat gradients; they dispense entirely with bends, and such curves as they have are very gradual. Many penetrate hills and mountains, cross valleys and ravines; and a great deal of excavation and fin are necessary if they are to be kept reasonably straight and not too steep. Fortunately, modern methods of mechanical excavation both in "dirt" (or "muck") and in rock are fast and economical, so that nowadays the location engineer can plan with confidence routes involving large quantities of excavation.

Though many mountain roads are planned to climb steeply and wind sharply to avoid the enormous amount of excavation that would otherwise be required, a surface route sometimes becomes virtually impossible. Then the only thing to do is to tunnel through the mountains, or span the cliffs.

Excavation is the job of moving soil and rock. There are many different kinds of soil to be shifted, and vastly differing conditions of site and climate in which this work must be carried out. There are obvious differences between scraping sand in an arid desert and draglining mud and silt in a marsh; between blasting hard granite from the side of an icebound mountain and ripping the softer shales and sandstones in a summer valley; between struggling with wet sticky clay and moving waterlogged gravel. But knowledge of the machines and techniques required to deal with such variety is not enough. The civil engineer must also turn to geology and to the new science of soil mechanics. There is no one way of handling excavation problems: each project must be dealt with on its merits.

Roads and airfields are used for very different purposes, but to the civil engineer there are no important technical differences. The general excavation and paving procedures are similar, and the differences are largely in the dimensions.

The pavement of a four-lane concrete road is usually about 50 feet wide and rarely more than 10 inches thick. A heavy bomber runway may be two or three times as thick, and up to 12,000 feet long and 300 feet wide. The main difference is that an airfield must be made level over an area considerably wider than its runways; and to provide modern aircraft with safe approaches, excavation may be-considerable at the ends of the runways. So far as possible, then, airfield sites are chosen on level ground. But what do you do when there are mountains close by and all available land is occupied?

The planning of the Kai Tak Airport in Hong Kong was complicated and largely determined by the mountainous topography of the area. The Hong Kong district is very crowded and there is very little flat land. The engineers therefore adopted the ingenious idea of building the main runway in the sea! One approach is from the southeast and is a straight-instrument run from the sea through the Lei Mun Gap between Hong Kong Island and the mainland. To avoid the inland mountains, the other approach is over the sea and along the coast from the west, and involves a 40-degree turn followed by a 3000-foot straight run to the touchdown threshold. This unique approach was thoroughly tested before it was finally adopted. The runway is built as a promontory 8500 feet long and 800 feet wide, jutting out into the bay. To make this artificial promontory, some 10 million cubic yards of sand were dredged from the sea bottom and pumped between massive protective walls of rock rising 50 feet from the seabed. A further 3 million cubic yards of decomposed granite were dug out of the hills on the mainland and dumped on the upper portion of the promontory.