基于D-P条件等效的黏性土隧道开挖地层力学行为有限元分析

Finite Element Analysis of Mechanical Behavior of Cohesive Soil Tunnel Excavation Based on D-P Condition Equivalent

摘要:

基于三轴试验应力?应变结果，获取了依托工程黏性土强度参数。通过德鲁克?普拉格条件（D-P条件）等效，实现了摩尔?库伦（M-C）黏性土材料的D-P准则模拟方法。采用“间隙约束法”模拟衬砌支护时机对地层力学行为的影响。通过数值计算讨论了黏性土盾构隧道地层参数以及施工特性对地层力学行为及支护反力的影响。研究发现：黏聚力、内摩擦角以及开挖洞径对围岩塑性区半径及支护反力的影响基本呈线性关系，随黏聚力和内摩擦角的增大，塑性区半径和支护反力明显减小，内摩擦角的影响显著于黏聚力。开挖洞径由6 m增大到14 m，塑性区半径增大约210 %，支护反力增大约230 %。土侧压力系数将显著影响开挖后塑性区形状、范围以及支护反力的分布。随着支护时间的延后，塑性区逐渐增大，支护反力逐渐减小，当释放的位移超过总位移的40 %时，两者增减幅度均有明显降低。就依托工程而言，当将地层含水率控制在8 %~15 %间，当地层收敛约为总位移的20 %时，可充分发挥地层自承能力从而降低支护反力。

Abstract:

Based on the stress-strain results of triaxial test， the strength parameters of cohesive soil were obtained. A Drucker-Prager （D-P） criterion-based simulation method for Mohr-Coulomb （M-C） cohesive soil is then established according to the Drucker-Prager condition equivalence. The ‘Gap Constraint Method’ is applied to simulate the influence of the supporting time on the soil mechanical behavior. The influence of stratum parameters and construction characteristics on stratum mechanical behavior and support reaction force of shield tunnel in cohesive soil is finally discussed by using the proposed numerical calculation methods. It can be found that he radius of plastic zone and support reaction force of surrounding rock have a linear relationship with the cohesion， the internal friction angle and the tunnel diameter. The radius of the plastic zone and the supporting reaction decreased significantly with the increase of cohesion and internal friction angle， and the influence of the internal friction angle is more distinct. When the tunnel diameter increases from 6 m to 14 m， the radius of plastic zone increases by about 210 %， and the support reaction increases by about 230 %. The lateral pressure coefficient will significantly affect the shape， the range， and the distribution of the plastic zone after excavation. The plastic zone gradually increases and the support reaction force gradually decreases with the extension of support time. When the released displacement exceeds by 40 % of the total displacement， both the increase and the decrease tend to mitigate. Taking the engineering practice in this paper as an example， when the stratum moisture content is controlled between 8 % and 15 %， the stratum convergence is about 20 % of the total displacement， the stratum self-supporting ability can be fully exerted to reduce the support reaction.