风积沙地层大跨公路隧道施工过程力学行为分析

采用三维数值模拟和现场监测的手段,对风积沙地层大跨公路隧道超前支护效果、工法参数优化、围岩压力释放和沉降发展规律进行分析。通过计算结果与监测数据的对比分析,得出了风积沙地层隧道开挖过程中围岩压力的变化形态、二次衬砌施作时机和最终形变荷载大小以及沉降发展等规律。分析结果表明：旋喷桩超前支护将掌子面潜在失稳区域控制在旋喷壳下部掌子面前方D/2范围（D为单洞开挖跨度14m）;三台阶法施工台阶长度宜取（1/3～1/2）D;二次衬砌落后下台阶掌子面的距离宜取D/2;二次衬砌分担荷载较大,分担比例约为50%。

Mechanical Behavior in the Construction of Large Span Highway Tunnel in Aeolian Sand Strata

The effect of advanced support,parameters optimization of construction method,rules of surrounding rock pressure release and settlement development were analyzed via three-dimensional numerical simulation and in-situ monitoring to study mechanical behavior in the construction of large span highway tunnel in aeolian sand strata.Surrounding rock pressure changing shape,timing of secondary lining construction,ultimate deformation load and settlement development rules during tunnel excavation in aeolian sand strata were figured out by contrastive analysis of numerical values and field monitoring values.The results show that advanced support with chemical churning pile limits potential instability area of tunnel working face to D/2 under the shell of piles(D is the excavation span of tunnel,D=14 m).Three-bench method of construction should take the bench length of(1/3-1/2)D,the distance of secondary lining behind the working face of the bottom step should be D/2.The secondary lining bears about 50% of external pressure.