High axial flow rates within and along tunnels, excavated for deposition of high level nuclear waste, may increase the transport capacity of potential escape routes for radionuclides that have been released to the buffer surrounding the waste canisters, or to the tunnel backfill materials, from leaking fuel canisters. High flow rates may be found if the tunnel interior has a high permeability, either initially due to the composition of the backfill material or at later times due to degradation of low permeability backfill material components. If a disturbed rock zone, a DRZ, of increased permeability was created as a result of direct damage done to the wall region during tunnel excavation, this zone may contain additional possible escape routes. Low-permeability tunnel plugs, keyed into slots cut in the rock walls, have been suggested as means of reducing axial flow rates. This paper deals with different aspects of such tunnel-plug systems. A preliminary estimate of the potential for tunnel plugs to reduce axial flow rates is made using analytical expressions. A number of numerical techniques are employed to investigate the hydraulic, mechanical and hydromechanical performance. These include μFLOW (FEM flow calculations), FLAC (finite difference mechanical calculations) and 3DEC (distinct element mechanical calculations). The mechanical calculations concern the mechanical stability in the rock surrounding the slot and permeability changes in that rock caused by stress redistribution. The results show that the effects of tunnel plugs are very significant in most cases. A discussion on the validity of the results and the applicability of the used methods is provided. 相似文献
This study covers the graphical analysis of deformation values measured in the Kızlaç T3A tunnel (Osmaniye, Turkey), which was built as a part of the Tarsus–Adana–Gaziantep Motorway Project. Excavation was performed through a sequence which was composed of sandstone–shale alternation, sandstone and dolerite dyke. Horizontal, longitudinal and settlement deformation values were optically read and recorded daily on a computer. These data were evaluated according to New Austrian Tunneling Method. Total deformation measurement, risky area determination and forecast of transitions between weak and stiff rock, stiff and weak rock were assessed as a result of deformation evaluation for tunnel stability, safety and economy.
The largest resultant deformation value (13 mm) was measured in the sandstone–shale alternation between chainage 500 and 550 m, which was highly weathered by groundwater and affected by local tectonic disturbance. The smallest deformation value was observed in a stiff dolerite dyke between 370 and 430 m, where at times the deformation values decreased to zero. In the sandstone, small resultant deformation values (2–4 mm) were also recorded. The 500–550-m interval of tunnel alignment had the highest risk for tunnel instability in the studied section but the deformation values (maximum 13 mm) were within the tolerable deformation range (10 cm). Small negative longitudinal deformation values decreasing between chainage 320 and 370 m and small positive longitudinal deformation values decreasing between 420 and 480 m indicate the sandstone–shale alternation (weak rock) and the dyke (stiff rock) and sandstone (stiff rock), and the sandstone–shale alternation with a fault gauge zone (weak rock), respectively. These longitudinal deformations needed probable to predict the lithological transitions ahead of the face, which in timely were used to determination of the tunnel support system. 相似文献
In this paper, support measures obtained with the RMR classification method were used for estimating the support capacity of wedges found in relatively shallow tunnels. This was done for the Platamon railway tunnel, in northern Greece, which is at present, under construction. According to our investigation, the safety factors, which were calculated using the above mentioned support measures, were much higher than the theoretically needed safety factor. In cases where the height of the wedges is much greater than their base and the rockmass quality is very poor, the proposed RMR support measures could be introduced. In these cases, additional techniques, which include steel ribs and shotcrete (together with rock bolts), could be used. 相似文献
Overburden soil beds situated above a fault are often deformed by propagation of bedrock thrusting from the fault during large earthquake. The deformed beds formed a triangular shear zone. This coseismic faulting often causes damage to underground tunnels located in the shear zone. The present research studies the deformation behavior of the overburden soil beds and the tunnel, the associated mechanism and the impact on the safety of tunnel linings induced by a large blind thrust slip. Based on sandbox experimental and numerical studies, it is found that results from numerical analysis are in agreement with the sandbox model tests with regard to growths of the shear zones within the soil beds, location of the tunnel in this shear zone and deformations of the tunnel. The potential major shear zone may be bent or bifurcated into two sub-shear zones owing to existence of a tunnel inside the shear zone. Furthermore, the occurrence of back-thrust faulting will threaten the safety of nearby structures. It was also identified that stiffness of the soil and the fault dip angles are among the major factors controlling the configuration of shear zones, the stresses within the soil, and the loads on tunnel linings. Based on the identified mechanisms, the strategies for hazard prevention are accordingly suggested and discussed. 相似文献