Ⅴ级围岩-断层条件下修正地震系数法对铁路隧道适用范围研究

Study on Applicability of Modified Seismic Coefficient Method to Railway Tunnels under Condition of GradeⅤSurrounding Rock and Fault

合理的抗震计算方法是隧道结构合理设计的基础。长期以来,隧道结构的抗震设计多采用地震系数法,但当隧道埋深较大时,此方法具有明显的缺陷。按照地震系数法计算时作用在隧道上的水平惯性力随埋深的增加而增加,与实际震害统计不完全相符。采用反应位移法及动力时程法对地震系数法的上覆地层高度进行修正,获取不同内净空最大跨度隧道结构上覆地层的等效高度。进而将修正后的结果与跨断层振动台模型试验进行对比,研究修正地震系数法在跨断层铁路隧道中的适用性。结果表明:对于隧道内净空最大跨度B,当B≤8 m、8 m<B≤12 m及B>12 m时,上覆地层等效高度分别为5.0B、4.1B、1.7B,且等效高度不受地震加速度峰值影响。振动台模型试验显示,当B=6.4 m时,加速度峰值越大,断层破碎带对邻近衬砌内力影响越明显。对于0.15g、0.3g峰值加速度工况,当分别远离断层面距离2.66B、5.63B后,修正后的地震系数法结果可以较好的包络住振动台模型试验的衬砌内力极值,为地震系数法有效的适用范围。所得结论对提升地震系数法在铁路隧道抗震设防设计方面的应用具有一定价值。

Reasonable seismic calculation method is the basis of rational design of tunnel structure.For a long time,the seismic coefficient method has been used in the seismic design of tunnel structures.However,when the tunnel is buried deep,this method has obvious defects.When calculated according to the seismic coefficient method,the horizontal inertial force acting on the tunnel increases with the increase of the buried depth,which is not completely consistent with the actual seismic damage statistics.In this paper,the response displacement method and dynamic time history method were used to modify the overlying stratum height of seismic coefficient method,and to obtain the equivalent height of the overlying stratum of the tunnel structure with the maximum span of different internal clearance.The modified results were compared with the cross-fault shaking table model test to study the applicability of the modified seismic coefficient method in the cross-fault railway tunnel.The results show that the equivalent heights of the overlying strata are 5.0B,4.1B and 1.7B respectively for the maximum span B of the tunnel clearance when B is equal or less than 8 m,8 m<B<12 m and B>12 m,and the equivalent heights are not affected by the peak seismic acceleration.The shaking table model test shows that when B=6.4 m,the greater the peak acceleration,the more obvious the influence of fault fracture zone on the internal force of adjacent lining.For 0.15g and 0.3g peak acceleration conditions,when the distance from fault plane is 2.66B and 5.63B respectively,the modified seismic coefficient method can better envelop the maximum internal force of the lining in the shaking table model test,which is an effective application scope of the seismic coefficient method.The conclusions obtained in this paper are valuable for the application of the lifting seismic coefficient method in the seismic fortification design of railway tunnels.