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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%。
By means of three-dimensional numerical simulation and on-site monitoring, the effects of advanced support, optimization of working parameters, pressure release of surrounding rock and settlement development of large-span highway tunnel in the area of wind-blown sand are analyzed. Through the comparison between the calculated results and the monitoring data, the variation of surrounding rock pressure, the timing of the secondary lining construction, the ultimate deformation load and the settlement and development of the tunnel during excavation of the aeolian sand are obtained. The analysis results show that the prestressed support of jet grouting pile can control the potential instability zone of the dagger face in the D / 2 range in front of the lower part of the spinneret (D is the single-hole excavation span of 14m). The construction step length of the three steps method should take (1/3 ~ 1/2) D; the distance between the secondary lining and the lower step face should be D / 2; the secondary lining should share a larger load, sharing about 50%.