采用长距离水平冻结暗挖法的浅埋大断面地铁隧道施工技术

Construction Technique for the Shallow-Buried Subway Tunnel with Large-Section by Long-Distance Horizontal Ground Freezing Method and Undermining Method

通过人工冻土试验、有限元数值分析和大型物理模型试验,研究浅埋大断面地铁隧道采用长距离水平冻结暗挖法的施工技术。通过现场土的人工冻土试验,得到土体冻结的物理力学指标。有限元数值分析结果表明,随着冻结壁厚度的增加,冻结壁的强度和稳定性增加。大型物理模型试验结果表明,冻胀和融沉量都随着冻结壁厚度的增加而明显增大;当冻结壁厚度为4.5 m时,预测实际工程地表冻胀和融沉量均已超过允许值。根据上述研究结果,进行了冻结施工方案的设计和优化。在施工过程中,改进超长距离水平冻结管连接方式,采用跟管钻进新技术,确保了冻结孔的成孔质量;采取设置卸压孔、加大盐水流量和融沉跟踪注浆等技术措施,有效地控制了地面的冻胀和融沉,确保了工程顺利地完成。

Based on the artificially frozen soil test, finite element numerical simulation and large-scale physical model test, the construction technology of long-distance horizontal ground freezing method and undermining method adopted for the construction of shallow-buried subway tunnel with large-section was studied. The physical and mechanical indexes of the frozen soil were obtained after the artificially frozen soil test on the in-situ undisturbed soil sample. The finite element numerical analysis results indicate that the strength and the stability of the frozen wall are improved along with the increase of the frozen wall thickness. The results of the large-scale physical model test show that both the frost heaving and the tha- wing settlement increase obviously with the thickness of the frozen wall. It is predicted that when the thickness of the frozen wall is 4. 5 m, the surface frost heaving and the thawing settlement both have exceeded the allowable values in the practical engineering. The design and optimization of the freezing construction scheme were conducted according to the above research results. During the construction process, the connection mode was improved for the long-distance horizontal freezing pipe, and the new technology of drilling with simultaneous casing was adopted to ensure the completion quality of the freezing holes. The surface frost heaving and thawing settlement were effectively controlled by several technical measures, such as applying pressure relief vents, increasing brine flow, tracing and grouting the thawing settlement, which ensured the successful completion of the engineering.