Tome Architecture and management of a geological repository - Andra

4 - General architecture of the repository in a granite mediumThe presence of unstable or permeable zones along the planned course of the shaft governs thefeasibility of this solution. This explains why the "raise-boring" technique does not generally apply toshafts requiring rock supports during the construction process.• Ramp dimensioning and descriptionThe ramp accommodates two tracks dimensioned to enable vehicle passing. A dedicated undergroundinstallation construction work ramp is a sloping drift comprising a series of straight sections dipping atabout 15% and curved sections with curvature radius of over 30 metres. The ramp has an independentventilation system.The "inverted U" geometry of the ramp section is 5-6 m high and 6-8 m wide. It has recessesapproximately every 250 metres, to park vehicles waiting to be repaired or for turning manoeuvres.Laterally, about every hundred meters refuge bays are constructed. The ramp is connected to aventilation shaft by a small drift (with a section of about 5 m 2 ) at roughly one kilometre intervals. Theramp is about 4 km long.The slope of a dedicated package transfer ramp would be limited to 10% and the length of the straightsections to about 80 metres. An escape lane is sited in the axis of the descending sections at each bend,dimensioned to absorb the potential energy of an uncontrolled vehicle. The package transfer ramp is 5-6 kilometres long.Ramp constructionRamp construction is also based on drilling and blasting (Figure 4.2.4).Detailed surveying of the volume of rock required for installing the ramp has to be carried out(boreholes, geophysics, hydro-geological tests, etc.) just as it does for shafts.This survey work serves to specify the ramp course and to refine the design of the surface trench. Thewhole ramp is lined with formed concrete. Once this trench is constructed, ramp sinking starts by fullface drilling and blasting.The trench and ramp floors comprise a concrete slab. The ramp walls are simply fitted with safetymesh bolted to the rock. Only zones that present mechanical instability or water ingress are injectedwith a cementitious grout and lined with formed concrete as required.These injections do not aim at making waterproof the rock volume to be crossed, but at maintainingfavourable conditions for continued excavation work and at limiting excavation-related disturbanceson the hydro-geological medium.Dossier 2005 Granite - ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL REPOSITORY66/228