Collapse, roof fall, ground subsidence and other engineering disasters happen often in bias and close spacing tunnels. In the related design specifications, constructing methods, supporting parameters and constructing steps must be designed specially. With the help of FLAC3D, circular excavation with different steps and with bias rate P of 1.16, 1.25 and 1.5 were simulated, construction mechanics and results of rock’s settlement were analyzed as well. Results show that when a tunnel with bias rate of 1.16, 1.25 and 1.5, rock pillars minimum spacing between the two closing tunnel is correspond to 18 m, 24 m and 30 m. While the bias pressure was great in the right side wall on the right tunnel, a wide range of plastic zone is produced, the stability of sidewall was influenced in which should be reinforced support. Finally, taking into account the actual terrain conditions, rock pillars in the middle distance was designed with 18 m, monitoring results show that the spacing design is reasonable, stability of surrounding rock met the requirements, the reliability of numerical simulation results were verified.%偏压隧道易发生塌方、冒顶、地表塌陷等工程灾害,在小净距偏压隧道的相关设计规范中,要求对其施工方法、支护参数以及施工顺序进行特殊设计.用FLAC3D对小净距偏压隧道在不同施工间距下循环开挖过程进行了模拟,对偏压率P分别为1.16、1.25和1.5时的不同间距,以及不同偏压率时的施工力学效应和围岩沉降进行了研究.结果表明：当隧道偏压率分别为1.5、1.25和1.16时,2隧道中间岩柱最小合理间距分别为30、24和18 m；偏压过大时,围岩大范围塑性区集中于右洞右边墙侧,需加强对右边墙的支护.考虑偏压浅埋隧道的实际地形情况,设计中间岩柱间距为18 m,监测数据结果显示18 m的间距设计是合理的,满足围岩稳定性要求,验证了数值模拟研究结果的可靠性.
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