When constructing underground facilities in developing countries, additional problems are often encountered, beyond those common in industrialized countries. This paper presents aspects on design, rock support, construction organization and execution, based on experience from underground construction and mines in developing countries. The conclusion is that underground location of facilities is feasible and advantageous - also in developing countries.

INTRODUCTION

Use of the underground space may be an advantageous solution to many serious problems regarding environment, energy and storage in many less industrialized regions of our world. Many of these regions are situated within tropical areas, where the rock normally is more weathered than in the temperate zones. Geologica1 movements have cause faults, and partly decomposed rock is often mixed with sound zones. High influx of ground water is a common problem. These conditions demand consideration, in the design stage as well as during the construction. From experience of underground construction in such regions, often with bad rock conditions, we know that favourable rock conditions are not a must for location of facilities underground. On the other hand, a successful undertaking of underground works under such conditions demands that local and often very special conditions are carefully considered as well in the planning and the design as during the construction.

DESIGN OF UNDERGROUND STRUCTURES IN DEVELOPING COUNTRIES
Design in Weak Rock

The fact that we very often have to make the underground structures in less good rock has to be reflected in the design. The size of the caverns may have to be limited. Higher vaulting of the roofs, rounded corners, more of arch shaped walls, circular tunnels, higher demands on cautious blasting, substantial supporting work and permanent concrete lining are some factors to consider. These factors increase the costs of the projects and it is therefore important not to resort to these remedies more than necessary. It may be noted that the design of underground chambers nowadays can be well adapted to the rock quality. An example of this is, La. the newly developed method "POLYTANK", in which case the normally designed long chambers for oil storage are replaced by a system of vertical cylinders. By this method the support problems are reduced. With reference to the design of 1arge underground chambers in weak or fractured rock, I would 1ike to call attention to the importance of not making more openings or cuts than absolutely necessary in walls and roofs. Too many or inappropriate openings could cause cave in of an underground cavern. Access. Experience shows that access for construction purpose to an underground chamber is preferably established by inclined access tunnels instead of vertical shafts. The bigger the chambers, the more definite is the preference for access tunnels. Advantages connected with the use of an access tunnel compared to a shaft justify the higher construction cost of the access tunnel.

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