地铁隧道邻近地裂缝带的地震响应

Seismic response of metro tunnel oriented parallel to ground fissures

采用数值模拟方法,在不同震级人工地震波作用下,研究了具有近距离平行地裂缝的地铁隧道的加速度、位移和内力特征,计算了地裂缝的影响区域、围岩动土压力变化规律和隧道与围岩接触动土压力变化规律。研究结果表明:在地表距隧道水平距离约25~50m范围内加速度响应存在一个附加放大区域;当输入地震动强度较小时(50年超越概率为63%),地铁隧道拱顶和拱底处相对水平位移都较小(约为0.39mm),但随着输入地震动强度的增大(50年超越概率为2%),拱顶和拱底的相对水平位移均逐渐增大,最终增大至1.53mm;在地震动作用下,隧道结构的左、右拱肩和拱脚处的轴力都较大,其中右拱脚处的轴力最大,为1 926kN;隧道结构的左、右拱腰处的弯矩和剪力都较大,其中最大弯矩与最大剪力在右拱腰处,分别为78.54kN·m与1 830kN;随着地震动强度的增大,隧道结构的内力逐渐增强;地裂缝附近的动土压力较大,并向两侧逐渐减小;在中震作用下隧道拱顶处,地裂缝上盘影响宽度为25m,下盘影响宽度为20m,在拱底处,地裂缝上盘影响宽度为26m,下盘影响宽度为22m;在大震作用下,地裂缝上、下盘影响宽度较中震时增大约35%;地裂缝附近的隧道拱顶和拱底的动土压力变化规律与无地裂缝时基本一致,但隧道结构附近的动土压力较大,其最大值为138kPa;在地震动作用下,隧道结构拱腰处的接触动土压力增量较大,右拱腰处即靠近地裂缝一侧最大,增量为45.27%,拱顶次之,增量为13.41%,拱底最小,增量为6.86%。

Under the different magnitudes’ synthetic earthquake waves,the acceleration,displacement and internal force were studied by the numerical simulation method for the metro tunnel oriented parallel to ground fissures in short distance,and the influence area of the ground fissures,dynamic earth pressure variation law of the surrounding rock and contacting dynamicearth pressure variation law between the tunnel and surrounding rock were calculated.Analysis result shows that there is an additional magnification area of the acceleration response within a horizontal distance of 25-50 mfrom the ground surface to the tunnel.When the magnitude of the synthetic earthquake wave is smaller（the 50-year exceedance probability is 63%）,the relatively horizontal displacements at the top and bottom of the tunnel are smaller（about 0.39 mm）,but increase with the increasing earthquake magnitude.The largest displacement is 1.53 mm when the 50-year exceedance probability is 2%.Under the earthquake,the axial forces at the right and left shoulders and foot are larger,and the largest force is 1 926 kN at the right arch foot.The moments and shear forces are larger at the right and left arch waists,and the largest moment and shear force are at the right arch waist and 78.54 kN·m and 1 830 kN,respectively.The internal force increases with the increasing earthquake magnitude.The dynamic earth pressure near the fissure is large and gradually decreases to both sides.Under the earthquake,at the top of the tunnel,the influenced widths of the hanging wall and foot wall are 25 and 20 m,respectively.At the bottom of the tunnel,the influenced widths of the hanging wall and foot wall are 26 and22 m,respectively.The influence widths of the hanging wall and foot wall of ground fissure increase by about 35% under the large earthquake compared with the moderate earthquake.The dynamic earth pressure variation laws at the top and bottom of the tunnel are similar with and without the fissures,the pressures close to the tunnel are larger,and the largest pressure is138 kPa.The contacting dynamic earth pressure increment is larger at the arch waist of the tunnel under the earthquake,the maximum increment is 45.27%at the right arch waist（close to the ground fissure）,the second increment is 13.41% at the top,and the minimum increment is6.86%at the bottom.