The reasons to store sand in in-rock bunkers are described. A case history on the planning and excavation of the Malmi sand bunkers is presented. A complete state of stress-measurement was carried out and the whole structure was analyzed with a finite-element method. The results of these investigations verified assumptions based on previous experiences. The construction was carried out by me ns of long-hole drilling from above simultaneously with tunnelling from below.
Sanding is a well-known and widely used method of improving trafficability and traffic safety on snowy and icy roads. Under heavy traffic sand tends to fly up from the road surface and that's why salt is mixed with the sand. The salt solution forms a membrane around the sand grain. This membrane melts a hole in the ice and snow and the sand grain will stay on the road. However, when much salt is used, it causes increased corrosion in cars. In order to make sanding as efficient as possible, the sand used must be non-frozen and readily available. The sanding must be done within a short period after a snowfall, or when the roads are wet and the temperature below 0°C. The need for speed is the main reason for storing the sand near the place where it is needed.' Sand can be stored in various ways:
in sheds and
in special bunkers built for this purpose.
The special bunkers are built on or under the surface. In bunkers built on the surface the sand must be warmed up to keep it non-frozen. This, of course, involves the use of energy and is not economical. The underground bunkers are mostly blasted out of rock. Some typical bunker shapes are shown in Fig. 1. In these in-rock bunkers the sand does not freeze. Furthermore, filling and discharging is easy, thanks to gravitation. Since they are constructed under the surface, the bunkers can be large enough to fulfill regional sand requirements for a long time, although they can be refilled in the middle of winter, if necessary. By using underground space for stores, valuable areas are saved for houses and parks. Only slight changes, i.e. the roads to and from the bunkers, can be seen after construction.
In Helsinki there are some 900 km of roads which need sanding in winter. To satisfy the increasing demand for sand it has been necessary to store sand in several places in the city area. The main stores are in-rock bunkers, from which the sand is distributed.