Architecture and management of a geological repository - Andra

7 – The shafts and the drifts7.5.1.1 The shaft construction methodsFor the construction of large diameter shafts, the conventional method consists of sinking the shaftsfrom the surface by blasting the rock with explosives or drilling the rock with a roadheader andinstalling as the sinking operation progresses the ground support and the liner of the shaft. Thismethod is well adapted to the planned usable diameters between 6.50 m and 11.50 m.Fully mechanised sinking methods have been developed in the mining industry. The “shaft drilling″method consists of drilling shafts with a kind of vertical tunnel drilling machine equipped with cuttingwheels. In the “raise boring” method, a ″pilot hole″ approximately 30 cm in diameter is drilled fromthe surface down to a pre-existing drift. From the drift, a boring tool is raised in the drilled section upto the surface. These technologies offer the advantage of not requiring personnel in the shafts duringthe sinking operations, but the disadvantage of not allowing the ground support and liner of the shaftto be progressively installed during the sinking operations. Moreover, in the current state oftechnology, these methods are not applicable to the diameters considered.7.5.1.2 The main phases in the construction of a shaft by a conventional methodIn order to construct a shaft, a foreshaft is sunk a few tens of metres into the ground and then the shaftsinking equipment is installed. Then the main sinking operations take place. After the sinkingoperations are completed, the shaft equipment is installed and then the final machinery.• ForeshaftForeshaft construction details can vary according to the exact location of the shafts and thecharacteristics of the ground close to the surface. According to the consistency of the surface ground,the first few metres can be excavated with a dredger. The foreshaft is sunk a few tens of metres bysuccessive sinking phases with drilling and blasting and ground support by rockbolts and grillage (andshotcrete, if necessary). As soon as there is no longer any risk of damaging it with blasting, areinforced concrete slab is poured to serve as a base for the construction of the shaft.• Shaft sinking equipmentThe shaft sinking equipment is generally made up of two sub-assemblies : on the one hand, themovable equipment circulating in the shaft and, on the other hand, the fixed equipment located on thesurface.The movable equipment consists of a movable planking and a platform from which the work in theshaft is performed. The planking and platform are suspended on cables and are progressively loweredas the worksites progress.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM305/495