基于非线性能量耗散理论的盾构斜井/隧道掘进面稳定性研究

Collapse hazard is a sudden major disaster frequently occurred during the shield construction of inclined wells and tunnels, and the instability of heading faces is the main cause of this disaster. This project improves the traditional testing equipment for heading faces, where a self-developed displacement-controlled model test device is employed and the advanced three-dimensional particle image velocimetry is incorporated. The deformation and failure characteristics of surrounding rock are emphatically studied, and the spatial-temporal evolution rule as well as the failure characteristics of heading faces is obtained. On that basis, a three-dimensional failure mechanism of heading faces is constructed. By virtue of the tangential technique, the nonlinear failure criterion is introduced into the upper bound theorem of limit analysis. The nonlinear energy dissipation mechanism during collapse procedure is analyzed and corresponding equation of energy dissipation at limit state is established. The calculation method for nonlinear energy dissipation is proposed and the limit collapse pressure together with the optimal failure surface is determined. The index system for stability of heading faces is constructed. The rate of nonlinear energy dissipation with respect to each index is discussed and the criterion for heading face collapse is established on the basis of energy conservation law. Collapse mechanism of heading faces is revealed and preventive methods are put forward, which can provide a theoretical basis for the stability assessment of heading faces during the shield construction of inclined wells and tunnels.

坍塌灾害，是盾构斜井/隧道中常见的重大突发性灾害，掘进面失稳是造成坍塌灾害的主要原因。本项目改进传统测试设备，采用自主研发的位移控制式掘进面坍塌模型试验装置，结合先进的三维颗粒图像测速技术，以围岩变形和破坏特性为研究重点，获取掘进面渐进破坏时空演化规律与极限状态下临界破坏特征，构建掘进面的三维坍塌模型。利用切线技术将非线性破坏准则引入到极限分析上限理论中，分析坍塌过程中掘进面的非线性能量耗散机制，建立极限破坏状态下掘进面的非线性能量耗散方程，提出非线性能量耗散计算方法，确定掘进面的极限坍塌压力和最危险破坏面。构建掘进面稳定性的评价指标体系，研究坍塌过程中各项指标的非线性能量耗散率，基于能量守恒定律建立掘进面的失稳破坏判别准则，阐明掘进面的失稳破坏机理，提出掘进面坍塌灾害的防治方法，为解决盾构斜井/隧道掘进面的稳定性问题提供理论依据。

目前，在盾构法的施工过程中，保障掘进面的稳定性是一个重难点。本项目基于线性、非线性能量耗散理论分别建立了浅埋和深埋条件下盾构隧道(斜井)掘进面的二维、三维坍塌与挤出破坏能量耗散机制，根据虚功率原理推导了掘进面围岩压力解析解。考虑岩土体物理力学指标及工程参数的离散性，构建了盾构隧道(斜井)掘进面稳定性的评价指标体系，建立了浅埋和深埋条件下掘进面的失稳破坏判别准则，阐述了掘进面的失稳破坏机理，提出了掘进面坍塌灾害的防治方法。基于线性、非线性破坏准则，在孔隙水、地震力等外在因素作用下，采用能量耗散理论研究了浅埋和深埋条件下盾构隧道(斜井)掘进面的稳定性与安全性问题。研究表明，非线性破坏准则参数、孔隙水压力系数、地震力系数、土体非均质性以及各向异性等均对围岩压力以及潜在破坏面产生较大的影响。随着孔隙水压力系数增大，围岩压力增大，破坏面向洞内靠近，破坏高度减小，破坏范围减小；随着地下水位线高度增加，围岩压力急剧增加，破坏面向外拓展。随着水平和竖直地震力增大，坍塌压力增大，挤出压力减小。土体非均质参数增大时，围岩压力线性减小；各向异性系数增大时，围岩压力增大。考虑到岩土体参数的离散性，地下水位线高度、孔隙水压力、水平或竖直地震力增大时，失效概率显著增大。将研究成果应用于长沙地铁中，现场实测范围6500~14500kN正好在本项目计算方法所得到的理论值范围4667~26056kN之内，计算结果较好的吻合性充分验证了本项目方法的正确性与适用性，同时也反应出现场盾构掘进时总推力大小的合理性与经济性。本项目研究成果适用于采矿工程、地铁工程等领域，为盾构法施工提供合理的掘进参数，可保障盾构“连续、快速、稳定”的掘进姿态，提高盾构机的施工效率，预防重大的突发性塌方灾害，具有重要的科研价值和工程意义。