Study On Reasonable Permeability Of Pervious Liner In Free Flow Tunnel

With developing and scale increasing of the tunnel projects, more and more scholarspaid attention to the thought of permeable liner. By using a analytical model of seepage ofcircular deep tunnel and the basic theory about groundwater seepage analysis, the circulardeep tunnel seepage analytic solutions were obtained. While establishing a mechanical modelof circular tunnel, and using Mohr-Coulomb criterion, the deep circular tunnel elastoplasticstress and displacement solutions were deduced with considering body force of seepage.Based on circular deep tunnel seepage analytic solutions and plastic stress displacementsolutions, a influence different liner and surrounding rock permeability ratios and differentliner thicknesses exerted upon groundwater seepage, body force of seepage, tunnel leakage,plastic zone, stress, radial displacement of rock and liner was analyzed and studied. Thisresearch work content and the main conclusions were as follows.(1)An analytical model of circular deep tunnel seepage was established and itsseepage analytical solutions were obtained as well. The effect of different liner andsurrounding rock permeability ratios and different liner thicknesses on groundwater seepagefield, the head of outer edge of liner, body force of seepage, tunnel leakage was explored.Case results showed that when liner was impermeable, the external water head of liner washuge. When liner was permeable, the water head rapidly decreased from outside to inside, andwith the liner permeability coefficient increased, the decrease magnitude increased. The bodyforce of seepage within the liner decreased rapidly, mutated on the junction of liner andsurrounding rock, flattened in surrounding rock. Tunnel leakage increased rapidly as the ratiosof permeability coefficient of liner and surrounding rock were less than1, but when the ratiowas greater than15, underground seepage, body force of seepage and tunnel leakage were nolonger changed dramatically. The liner thicknesses had no influence on seepage field withinthe liner, but only within surrounding rock as the liner permeability was constant. Comparedwith the thickness of the liner, the liner permeability had a greater influence on undergroundseepage.Liner thicknesses had no significant effect on body force of seepage. When the linerpermeability less than the surrounding rock permeability, the greater lining thickness was, thetunnel leakage decreased more obvious. On the contrary, liner thickness has no significantinfluence on the tunnel leakage. （2）The elastoplastic stress and displacement solutions of deep circular tunnel werededuced with considering body force of seepage, case results showed that when the liner wasimpermeable, it existed a large plastic zone in tunnel, tensile stress existed in liner, the radialdisplacement was large. The plastic radius changed smaller, liner and surrounding rock werein compression, hoop stresses increased gradually within the liner, mutated on the junction ofthe lining and surrounding rock,increased fast within the surrounding rock, decreased slowlyafter reaching a peak, radial displacement become smaller when the liner was permeable. Butthe plastic radius, radial stresses, hoop stresses and radial displacements keep stable when theratios of permeability of liner and surrounding rock were greater than15. When the linerpermeability was less than rock permeability, the increasing of liner thicknesses had noobvious effect on reducing plastic zone, on the contrary, the plastic radius keep constant whileliner thickness increased. Liner thickness had a greater impact on the hoop stress on thejunction of liner and surrounding rock, but had no influence on radial stresses, hoop stressesand radial displacements within the scope of the liner and the surrounding rock in the freeflow tunnel.(3)The reasonable ratio of permeability coefficient of liner and surrounding rockin circular free flow tunnel was15permeable liner was determined by the specification oftunnel leakage, the principle of minimum plastic zone，the principle of playing compressionperformance of rock and liner, the principle of minimum radial displacement, theoreticallyachievement of permeable liner was discussed as well.