الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 172 |  |  |
| | | from | 172 | | |
Abstract
With the sprea~ of urbanlzatlon,more than half of
the world’s population now Jive in cities. The sharp increase
in population and the continuous Increase in the
cost of land developed a mount I og need for new urban
plannlng,publlc utilities and traffic organization. This
directed the attention to the Importance of the under
ground space. New technologies have been developed for
construction of subway systems and uti 1 izat ion of underground
space for storage and other purposes. Construction
of ten kilometers of tunnels Eor sanitary sewer systems
was needed to keep U[J with the rapid growth of big
cities. As a result of these new developments, a numerous
number of tunnels has been planned and constructed In
almost every country through the last two decades.
Tunnels size and depth beneath the ground surface
may be related to their uses. Shallow tllnnels with
large diameters are often used for railways or roadways
under city centers. Veep tunnels and/or small diameter
tunnels are recommended Eor wastewater projects.