Text 2. Foundations of Pisa Leaning Tower

Match the following words and translations.

Why does the Leaning Tower of Pisa lean? The answer is that its foundations were not soundly laid. From earliest times, architects and engineers have been aware of the problems involved in laying a building’s foundations; but they have not always realized to what extent the earth can be pressed down by the weight of a building. Too little allowance has sometimes been made for the possibility of a heavy structure’s sinking unevenly. (Though the Leaning Tower is 14ft out of the perpendicular, it has never toppled. As the building began to lean over, the builders altered the design of the upper stories to balance it. At the same time as one side of it sank into the ground, the earth beneath was compressed until it became dense enough to prevent further movement.)

If the earth is stable, laying the foundations of small buildings possess few problems. But in a tall modern structure the load may be very heavy indeed; and the foundation engineer has an extremely important job to do. To begin with, he must have a thorough understanding of soil mechanics, which entails a scientific study of the ground to see what load it can bear without dangerous movement.

Trial pits are dug, or holes are bored, in order to collect undisturbed samples of earth from various depths. By examining these, the engineer can forecast the probable shifts in the earth during and after building, according to the sort of foundation he designs. Thus he comes to the most important decision of all in the building’s construction: He decides whether the earth is of the type that can best support each column on a separate solid block, or whether he must aim at lightness and, as it were, ‘float’ the building on hollow foundations.

If firm ground has been found only at great depth, the foundation engineer may use piles. These are solid shafts made either by driving reinforced, precast concrete deep into the ground, or by boring holes in the earth and pouring in the concrete. Each pile supports its load in one, or both, of two ways. It may serve as a column with its foot driven into solid earth or rock or it may stand firm because friction along its sides ‘grips’ the column and prevents it from sinking.

But when it is a question of floating a building, the foundations take the form of a vast, hollow concrete box. It is divided into chambers that will house heating and ventilating plants as well as provide garage and storage space for the building.

Luckiest of all are those foundation engineers whose buildings stand on hard rock like granite or ironstone. For them neither piles nor flotation need be used.