ABSTRACT
In this lecture, four underground opening structures in rocks that require preservation are discussed.
The 3000-year-old water storage system was discovered underneath the archeological site of Tel Beer Sheva in southern Israel. The system was excavated to allow water storage for the inhabitants of the city for times of war when it would not be possible to go out of the walls of the city to obtain water from the nearby stream. A water tunnel was excavated connecting the stream in the outskirts of the city to the underground system that was filled with water during the rainy seasons. The ancient engineers were very wise in their utilization of the rock mass structure for efficient excavation; the system is comprised of several small chambers, the walls of which are aligned with the direction of the principal vertical joint sets (Fig. 1). The rock mass consists of horizontally layered and vertically jointed chalks, with bedding and joint spacing in the order of tens of centimeters only. This intensely “blocky” rock mass structure therefore poses a great challenge for safe creation of underground space, and, indeed, the ancient engineers have experienced a major collapse of a roof segment at the time of construction due to an attempt to create excessively large spans. They erected a massive support pillar, made of local materials from the nearby stream, mainly rounded blocks made of limestone, which successfully arrested any further collapse. The system, even with its precarious rock mass structure, has been standing unsupported since then, until it was discovered by modern archeologists. The engineering geology aspects of this case have been discussed by Hatzor and Benary (1998).
