为解决长距离引调水工程中，极软岩隧洞在施工过程中出现的围岩大变形、初期支护衬砌开裂、围岩掉块垮塌、地表边坡沉降变形、施工进度缓慢等工程问题，以南水北调引江补汉工程12-1#施工支洞为例，针对其穿越极软岩（炭质页岩单轴抗压强度<5 MPa）地层时出现的围岩大变形问题，综合采用3DEC离散元数值模拟、现场监测与工程实践总结相结合的方法，系统分析极软岩隧洞开挖过程中围岩大变形的时空演化规律，并提出对应的分级控制措施。研究结果表明： 极软岩隧洞开挖后围岩前期变形大，且主要集中在上台阶开挖后的1~4 d，分台阶开挖配合临时仰拱封闭成环和竖向支撑，能够及时提供向上的拱形支撑作用，减少极软岩围岩变形量，并能将变形收敛时间缩短至12 d。提出3级控制技术： 采用108 mm管棚+42 mm小导管注浆对围岩进行超前加固； 实施“三台阶+竖向支撑+双临时仰拱”工法； 及时跟进钢拱架与喷锚支护措施。经现场实践，该控制技术可有效降低拱顶围岩沉降变形量，初期支护完成后沉降变形趋于稳定，监测后期变形量在20 mm以内。
To address the engineering challenges posed by large deformations of surrounding rock, cracking of primary support, rockfall collapse, surface settlement, and slow construction progress in long-distance water diversion tunnels through extremely soft rock formations, a case study is conducted on the Adit #12-1 of the Yangtze River-to-Hanjiang River Water Diversion Project. Focusing on carbonaceous shale strata with uniaxial compressive strength below 5 MPa, an integrated approach combining 3DEC discrete element numerical simulation, field monitoring, and engineering practice are employed to systematically analyze the spatiotemporal evolution of large deformations during tunnel excavation in extremely soft rock. The results reveal that the surrounding rock experiences significant early-stage deformation, primarily concentrated within 1 to 4 days after upper bench excavation. By implementing a three-bench excavation method with temporary invert closure and vertical struts, the deformation convergence time can be reduced to 12 days while minimizing deformation magnitude through enhanced arching effects. Based on these findings, a threestage control strategy is proposed: advance reinforcement using 108 mm pipe roofing combined with 42 mm grouted spiles; implementation of a “three-bench + vertical struts + dual temporary inverts” excavation method; and timely installation of steel ribs and shotcrete support. This approach has demonstrated excellent application results in Adit #12-1. Following the completion of primary support, settlement deformation stabilized, with subsequent monitoring measurements remaining within 20 mm.
