Architecture and management of a geological repository - Andra

10.3.12.1 Shaft observation systemThe equipment used in the shafts are divided into eight sections, located in different horizons of thegeological environment (cf. Figure 10.3.20). Their vertical distribution depends on the presence ofdirect pendulums integrated into a duct in the lining, in order to monitor the overall dimensionalstability of the shaft. The experience feedback relating to their use in dams and confinementenclosures suggests that the height of each pendulum should be limited to between approximately60 and 80 metres.In this way, all the sections (exceptfor the section at the bottom of theshaft) are spaced out atapproximately 80 metres. Threesections are proposed for theinstrumentation in argilite: one at thebottom of the shaft, one at therepository horizon and another at thetop of the Callovo-Oxfordianformation. Three sections aredistributed in the upper and midOxfordian limestones. One sectionallows monitoring in the Barroislimestones and another in theKimmerigian marl layer (located atapproximately –100 metres forexample).Each section allows detailedmonitoring of the shaft lining and thenear-field. Four radial directionmonitoring units seem to besufficient to detect any asymmetry inmechanical evolution, as shown inFigure 10.3.21. The monitoringequipment installed in each unitresembles the equipment describedfor B cells (see section 10.3.7) andfor the drifts (see section 10.3.11)with the exception of deeper radialbore-holes and the presence of themeasurement table for a pendulum inone of the units.The details of a monitoring unit,including the measurement tableoperating the vertical pendulumrelating to the corresponding section,is illustrated in Figure 10.3.22.Figure 10.3.20 Distribution of the instrumented sections andthe pendulums in a shaftIt makes it possible to monitor themechanical strength and the dimensional stability of the structure and the mechanical and hydraulicevolutions of the near-field. It should be noted that the pendulum measurement table enables themeasurement of relative displacement of the lining in three direction, for a height corresponding tothat of the pendulum (separating two instrumented sections). The pendulum chain on a generator lineenables the displacements to be cumulated in the three directions and allows calculation of the overalldeformation over the whole depth of the shaft.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM416/495