Field tests on large deformation control method for surrounding rock of deep tunnel in fault zone with high geostress
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摘要: 针对新莲隧道大埋深、高地应力、大变形凸显的实际情况,开展单层支护、双层支护、刚性强支、超前导洞+扩挖方案下支护受力及变形控制方法现场试验研究。结果表明：①原设计方案1支护偏弱不足以抵抗围岩形变压力,平导支护应力超过设计应力值率达100%,正洞支护侵限严重,换拱率100%；②“让抗结合”的双层支护方案2,下台阶与仰拱同步施作,不利于下部围岩应力释放,仰拱隆起开裂,边墙换拱率84%；变更下台阶与仰拱分段施作后,仰拱应力缓慢释放,大变形得以控制；③采用“刚性强支”理念的方案3,增设了“H175型钢+大拱脚靴套+锁脚锚杆套管”,提升了拱架整体刚度,最大收敛变形速率减小42.4%、月开挖进尺达90 m；④采取“超前导洞+扩挖”的方案4,实现了应力分阶段缓释,大变形得到有效控制,但纤维混凝土的应用及超前导洞支护的拆除增加了成本和工序。建议跨断裂破碎带段采用经济合理、工序简便、支护调整灵活的方案3进行施工,方案4可作为更大围岩变形的预备方案。同时拱顶预留变形量可近似按边墙预留变形量的1/2留设。Abstract: In view of the actual situation of large buried depth, high crustal stress and large deformation of Xinlian tunnel, field tests on support force and deformation control methods are carried out with single-layer support, double-layer support, rigid strong support, advanced pilot tunnel + expansion scheme. The results show that: (1) The original design scheme No.1 is not strong enough to resist the deformation pressure of surrounding rock. The stress ratio of flat guide support exceeds the design stress value by 100%, the invading limit of support is serious, and the arch replacement rate is 100%. (2) The double-layer support scheme No.2 of combining resistance with resistance is adopted. The synchronous operation of lower bench and inverted arch simplifies the operation sequence, but it is not conducive to stress release. The inverted arch is uplift crack and the rate of changing arch of side wall is 84%. When the lower bench and the inverted arch are sectioned and operated, the stress in the inverted arch is slowly released, and the large deformation is controlled. (3) Scheme No. 3 of rigid strong support by 'H175 steel+large arch boot sleeve+lock foot anchor sleeve’ is adopted, the overall rigidity of the arch is improved, the maximum convergence deformation rate is reduced by 42.4%, and the excavation per month can reach more than 90 m. (4) Scheme No. 4 of 'leading tunnel + enlarging excavation’ is adopted to realize the stress release by stages, and the large deformation is effectively controlled. However, the application of fiber-reinforced concrete and the demolition of leading tunnel support increase the cost and process. Scheme No.3 is recommended of for its economical rationality, simple construction procedure, and flexible support adjustment. Scheme No.4 can be as a preparation scheme for larger deformation of surrounding rock. At the same time, the reserved deformation of vault can be approximately 1/2 of the reserved deformation of side wall.
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图 6 双层支护方案围岩变形与时间关系
Figure 6. Relationship between deformation and time of surrounding rock under double-layer support
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图 8 超前导洞方案围岩变形与时间关系
Figure 8. Relationship between deformation and time of surrounding rock conder advanced pilot
表 1 地质构造情况
Table 1 Conditions of geological structure
名称 主要特征 对工程影响评价 大脑包正断层 断层与线位相交,交角约65°。为一倾NE正断层,倾角为65°,断层带宽约100 m,断层NE盘出露地层C2-3灰岩夹页岩；NW盘岩层为∈1c砂岩夹页岩。断层带岩体较破碎,灰岩多呈角砾状及砂土状,页岩层间褶曲较发育,层理变化较大。 断层带岩体较破碎,完整性较差,对隧道影响大。 小箐断层 断层与线位相交,交角约76°。断层走向N6°E,倾向、倾角不明,断层带宽约50~80 m,断层两盘岩层均为∈1c砂岩夹页岩。断层带岩体较破碎,页岩层间褶曲较发育,层理变化较大。 断层带岩体较破碎,完整性较差,对隧道影响大。 脚步哨逆断层 断层与线位相交,交角84°。为一倾NE逆断层,倾角60°。倾向南东,断层NE为∈1c灰岩夹页岩；NW盘岩层为T2白云岩及P2β玄武岩,岩体完整性差,地表多呈碎屑状。 断层带岩性较杂,风化差异大,富水性好,对隧道影响大。 
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表 2 支护受力监测结果
Table 2 Monitoring results of support forces
断面里程 钢支撑内力/MPa 喷混凝土应力/MPa 围岩压力/MPa 设计值 实测值 最值位置 设计值 实测值 最值位置 实测值 最值位置 PDK723+330 188/-260 98.2/-392.6 仰拱内侧/右拱脚内侧 2.0/-24.2 2.0/-24.2 右拱脚内侧/右边墙外侧 0.839 右边墙 PDK723+340 188/-260 410.7/-419.3 右拱腰内外两侧 2.0/-24.2 -/-46.4 右拱腰外测 0.837 左边墙 PDK723+350 188/-260 219.6/-415.0 左拱脚内侧/左拱脚外侧 2.0/-24.2 27.0/-27.0 左拱脚内侧/右边墙外侧 1.087 左边墙 PDK723+360 188/-260 -/-312.4 右拱腰内侧 2.0/-24.2 9.2/-36.0 右拱脚外侧/右边墙内侧 0.827 右边墙 PDK723+370 188/-260 -/-301.6 左拱脚外侧 2.0/-24.2 -/-19.4 左边墙外侧 0.819 左边墙 PDK723+380 188/-260 -/-259.3 拱顶外侧 2.0/-24.2 8.4/-26.3 右拱腰内侧/右拱腰内侧 0.982 右拱腰
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表 3 试验工况
Table 3 Test schemes
工况 试验方案 试验段落 1 原单层设计支护方案：预留30 cm变形量、全环I20b钢拱架、纵向Φ25钢筋连接。 DK724+010—DK724+040 2 让抗结合的双层支护方案：下台阶与仰拱一次性开挖或分阶段开挖（预留30 cm+15 cm变形量,格栅柔性支护与型钢拱架刚性支护并用）。 DK724+040—DK724+120 3 刚性强支方案：单层支护+拱架加强+扩大拱脚及靴套+优化锁脚锚杆套管（预留60 cm变形量、全环H175钢拱架、纵向I14型钢连接、Φ76锁脚锚杆套管）。 DK724+120—DK724+180 4 超前导洞+扩挖方案：超前导洞同平导设计、正洞预留30 cm变形量,全环I25b钢拱架、拱墙C30喷射纤维混凝土、纵向I14型钢连接。 DK724+180—DK724+230
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表 4 刚性强支支护参数
Table 4 Parameters of rigid strong support
项目 支护参数 初期支护 预留变形量 60 cm 喷混凝土 全环喷33 cm厚的C30混凝土、拱墙采用纤维混凝土 超前支护 Φ42小导管预注浆、长4.5 m、环向间距40 cm、每环38根 系统锚杆 拱部ΦG32自进式锚杆、长6 m；边墙Φ22砂浆锚杆、长6 m、间距0.8×0.8 m 锁脚锚杆 ΦG32自进式锚杆、长6 m、8根 钢架 全环H175型钢、间距0.5 m 钢筋网 Φ8双层钢筋网、间距10 cm×10 cm 纵向连接 I14型钢钢架、间距1.0 m 其他措施 拱腰及边墙钢架接头处设置4排Φ60深孔注浆钢花管、纵向间距0.6 m、每根长8 m；浅孔注浆管、注浆孔间距1.2 m(环)×0.6 m(纵) 二次衬砌 C35钢筋混凝土、钢筋环向采用Φ25@20 cm,纵向采用Φ14@20 cm,箍筋采用Φ10@20 cm,拱墙厚60 cm,仰拱厚70 cm
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表 5 正洞扩挖支护参数
Table 5 Parameters of expansion excavation of tunnel
项目 支护参数 初期支护 预留变形量 30 cm 喷混凝土 全环喷33cm厚C30混凝土,拱墙采用纤维混凝土 超前支护 Φ42小导管预注浆、长4.5 m、环向间距40 cm、每环38根 系统锚杆 拱部ΦG32自进式锚杆、长6 m；边墙Φ22砂浆锚杆、长6 m、间距0.8×0.8 m 锁脚锚杆 ΦG32自进式锚杆、长6 m、8根 钢架 全环I25b型钢、间距0.5 m 钢筋网 Φ8双层钢筋网、间距10 cm×10 cm 纵向连接 I14型钢钢架、间距1.0 m 其他措施 拱腰及边墙钢架接头处设置4排Φ60深孔注浆钢花管、纵向间距0.6 m、每根长8 m；浅孔注浆管、注浆孔间距1.2 m(环)×0.6 m(纵) 二次衬砌 C35钢筋混凝土、钢筋环向采用Φ25@20 cm,纵向采用Φ14@20 cm,箍筋采用Φ10@20 cm,拱墙厚60 cm,仰拱厚70 cm
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表 6 试验方案对比分析
Table 6 Comparative analysis of test schemes
试验方案 工况 里程 预留变形量/cm 长度/m 换拱率/% 日变形速率最值/(cm·d-1) 最大累计变形量/cm 最大拱顶沉降/cm 月开挖进尺/m 1 原单层设计支护方案 DK724+010—DK724+040 30 30 100 4.2 69.5 34.6 15 2 双层支护方案(下台阶与仰拱同步施作) DK724+040—DK724+080 30+15 40 84 3.8 49.5 18.9 20 双层支护方案(下台阶与仰拱分阶段施作) DK724+080—DK724+120 30+15 40 0 3.4 44.5 17.8 40 3 刚性强支方案 DK724+120—DK724+180 60 60 0 3.2 54.3 26.2 90 4 超前导洞+扩挖 DK724+180—DK724+230 40+30 50 0 2.8 28.4 14.3 60 注： 试验方案4变形数值为扩挖主洞的围岩变形值。
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