Laboratory Testing of Swelling Gouge From Weakness Zone - Principle And Recent Update

摘要: Weakness zones or faults containing swelling clay represent a challenging situation in hard rock tunnelling. When excavating such zones, failures have occurred occasionally even though particular precautions been taken. Instability has encountered during tunnel excavation and sometimes also long after completion. One of the most recent cases failure, fall at Hanekleiv road southeast Norway, ten years The was fault zone where had identified, about 1.1 km from northern entrance southbound tube. Cracks detected applied shotcrete excavation. In one major weakness Finnfast subsea tunnel, monitoring carried out by Norwegian Geotechnical Institute (NGI). Strain gauges load cells were installed reinforced rib near crown springlines tunnel. mass quality estimated for two based on Q classification system. However, it is hardly possible to characterize complex conditions with an empirical Except important feature size (thickness) effects can not be fully accounted Gouge materials collected mineral composition identified X-ray diffraction analysis. Laboratory testing measuring pressure remoulded specimens, free test used quantify potential. Numerical modelling powerful tool engineering planning design, particularly when difficulties uncertainties are expected underground A three-dimensional program normally preferred complicated mechanical computation tunnelling through zones/faults. Inappropriate use two-dimensional may induce large deviation simulation results. extent illustrated numerical comparison finite element Phase2 threedimensional difference FLAC3D. instrumented provides opportunity quantitatively evaluate loading ribs. FLAC3D this modelling, pore distribution around periphery each blasting round determined using ground water flow full support (spiling bolts, shotcrete, radial face ribs) included model. zone, side sprayed concrete simulated Mohr-Coulomb spiling bots, bolts steel bars ribs various built-in structural elements according characteristics. Different pressures simulation, ranging zero 0.20 MPa interval 0.04 MPa. Though considerably increases support, all instrumentation data results show that far less than its compressive strength. found much higher close face, area more critical terms stability. It concluded caused combination gravitational collapse due very low internal friction. process likely both joints accumulation moisture behind water/frost shielding, ventilation little effect strength reduced absorption process. Swelling reduction gradually developed till suddenly took place. FLAC3D, strain softening model order simulate post failure behaviour consideration cracks Three stages states focused first stage represented detection shotcrete. considered second stage. Combined last Simulation verify collapse. pressure, analysis, limited influence while played role development instability. Based analysis cases, chart practical procedures estimation zones/faults recommended, which site investigation, laboratory integrated. Instrumentation regular inspection signs instability stability control back Further research issue recommended enrich knowledge ground.