受地形条件及周边环境制约，中国西部地区的双洞线隧道设计间距往往较小，因此常使用连拱或小近距隧道这一特殊结构形式进行隧道设计。然而，中国西部地区地震烈度高，地震频发，而双洞间的中岩墙更易受到强震，尤其是近场地震作用的扰动，导致局部围岩塑性变形，从而影响隧道的安全。鉴于此，为研究近场地震动作用下小近距隧道围岩塑性区分布，选取合理近场地震动，考虑不同隧道近距及围岩条件建立了三维有限元数值计算模型，揭示了小近距隧道动力响应特性及围岩塑性区分布规律；基于此，通过对中岩墙的注浆加固，验证了加固措施对小近距隧道围岩塑性区的抗震有效性。研究结果表明：受近场地震动作用影响，小近距隧道中靠近中岩墙隧道拱脚部位加速度响应较为显著。横向地震激励时，右线隧道的左侧拱肩部位及右侧拱脚位置最大主应力值较为显著，而同一时刻下拱腰部位及隧道仰拱位置的最小主应力较其他位置大。强震作用下小近距隧道的围岩塑性区受岩体等级影响较大。当隧道间距为0.50倍的隧道跨度时，Ⅳ级和Ⅴ级围岩中塑性区发展最为严重，出现了中岩墙附近隧道拱腰部位的围岩塑性区贯通现象。以围岩塑性区为判别指标，中岩墙注浆加固对小近距隧道的抗震性能有利。研究结果可为高烈度地震区小近距隧道的抗震安全提供研究参考。

Restricted by topographic conditions and surrounding environment, the design spacing of double-hole tunnels in western China is often close. Therefore, the special structural form of multi-arch or small close tunnels is often used in the tunnel design. However, in the western region of China, high-intensity seismic zones are widely distributed, and the middle rock wall between the close tunnels is more susceptible under the strong earthquakes, especially the near-field ground motions, which results in large plastic deformation of local surrounding rock, and the safety operation of the tunnel was affected. Therefore, in order to study the distribution of plastic zone of surrounding rock of small close-distance tunnel under near-fault ground motion, reasonable near-fault ground motions were selected, and 3D finite element numerical models considering different tunnel close-distance and surrounding rock conditions were established. The dynamic response characteristics of small close-distance tunnel and the distribution law of plastic zone of surrounding rock were revealed. Thus, through the grouting reinforcement of the middle rock wall, the seismic effectiveness of the reinforcement measures on the plastic zone was verified. The results show that the acceleration response of the arch foot near the middle rock wall tunnel is more significant under the influence of near-field ground motion. Under transverse seismic excitation, the maximum principal stress value of the left spandrel and the right arch foot of the right line tunnel are more significant, while the minimum principal stress of the side walls and the inverted arch of the tunnel is larger. The plastic zone of surrounding rock of small-close-distance tunnel under strong earthquake is greatly affected by rock mass grade. When the tunnel spacing is 0.50 times of the tunnel span, the development of plastic zone in grade Ⅳ and grade Ⅴ surrounding rock is the most serious, and the phenomenon of plastic zone penetration of surrounding rock at the haunch of tunnel near the middle rock wall appears. Taking the plastic zone of surrounding rock as the discriminant index, the grouting reinforcement of middle rock wall is beneficial to the seismic performance of small close distance tunnel. The research results can provide a reference for the seismic safety of small close-distance tunnels in high-intensity earthquake areas.