Physical model experiment of external water pressure in lining surrounding rock of a deep tunnel with cross faults
[Objective]To elucidate the action mechanisms of external water pressure on the composite system of surrounding rock,grouting ring,and tunnel lining under complex geological conditions,a large-scale high external water pressure physical model experimental system suitable for deep-buried tunnels was developed.[Methods]The typical tunnel sections of the Songlin Tunnel TSLT-005 and TSLT-006 cross faults in the Kunming section of the Central Yunnan Water Diversion Project were selected as the research objects.The research encompassed physical model experiments on the external water pressure impacting the tunnel lining in deep-buried environments crossed by faults.The study aimed to determine the pressure variation laws across different tunnel depths,groundwater levels,and drainage conditions,proposing a range of recommended values for external water pressure reduction coefficients applicable under various operational scenarios.[Results]The findings indicated that tunnel depth and groundwater level substantially impact the external water pressure exerted on tunnel linings.An increase in tunnel depth enhanced the geostress effects,which,in turn,decreased both the porosity and permeability of the surrounding rock and grouting circle.This reduction effectively diminished the potential energy of groundwater seepage,thereby lowering the overall external water pressure on the lining.Conversely,rising groundwater levels increased the full-ring external water pressure on the lining,with high water pressure dispersing finer particles within the rock mass and fostering the development of more extensive seepage channels.This reduction also resulted in a higher rate of infiltration pressure increase correlated with rising groundwater levels.Furthermore,incorporating drainage holes into the lining substantially lowered the external water pressure affecting the upper shoulder areas of the tunnel.However,the presence of cross faults within the surrounding rock of the tunnel can mitigate the effectiveness of this pressure reduction,especially at the lining sections influenced by faults.The presence of cross faults had a significant impact on the water pressure outside the lining.Under high water table conditions,the influence range on the surrounding rock lining structure must be considered.Regarding specific recommendations,for tunnels at 600 m depth,the external water pressure reduction coefficient was approximately 92％of that at 200 m depth when undrained and approximately 85％when drained.In scenarios with cross faults,the external water pressure reduction coefficient at the most disadvantageous point of the lining without drainage should be no less than 0.95.With drainage,this coefficient can be more leniently adjusted to 0.82.Finally,the finite element numerical simulation method was used to verify the physical model test results of water pressure outside the lining,and the error was approximately 9.3％under the undrained lining condition and 7.8％under the drained lining condition,which indicated that the physical model experimental results were reasonable and feasible.[Conclusions]This research results provide crucial scientific guidance for designing,constructing,and safely managing deep-buried tunnel projects in regions with abundant water resources.
Central Yunnan Water Diversion Project tunnelphysical model experimentalhigh external water pressurefault rupture zone
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