山区复杂地形条件下土工合成材料加筋土边坡失稳机理与稳定性分析方法研究

Geosynthetic soil reinforcement is widely used for the slope engineering in the mountainous terrain of the highway, railway and airport. However, the topographic effects due to the rugged mountainous terrain may affect the stability of the reinforced steep slopes and even result in failures and landslides. Traditional stability analyses of the reinforced slopes neglected the decrease of the reinforcement by the excessive overlap and the significant three-dimensional (3D) effects. For this reason, a newly developed pullout testing device is proposed using a transparent soil and Digital Image Correlation measurement technique, to explore the mechanism of soil-geogrid interaction in the overlapped reinforcement. The pullout tests are conducted using polypropylene uniaxial and biaxial geogrids under different angles and spaces of the overlapped reinforcement. Using discrete element method simulates the tests to investigate the meso-mechanism of the interaction. A modelling of the soil-geogrid interaction strength is presented from the experimental results. Based on the geometric features of the 3D slopes, a method is established to analyze the stability of a reinforced slope with a turning corner or curve and to investigate its 3D effect. Finally, the presented modelling of the soil-geogrid interaction strength is included into the stability analysis of 3D reinforced slopes. The method is developed for assessment and design of the reinforced steep slopes in the mountainous terrain. Through study on a historical case, the presented method can be verified and used for design in practice.

土工合成材料加筋土技术由于其经济性和生态性被用于山区公路、铁路和机场建设的高大边坡工程中，然而山区复杂地形环境不利于加筋边坡稳定性控制，产生破坏及滑坡灾害。已有的加筋边坡稳定性分析忽略了山区地形引起的不利因素，尤其是格栅重叠铺设的加筋效果降低和山区边坡显著的空间特性。为此，本项目运用透明土与数字图像技术结合的方式研制可细观测量的拉拔试验设备，开展不同重叠铺设方式下单向和双向格栅拉拔试验，结合离散元数值模拟从宏细观层面揭示重叠铺设下格栅筋土界面特性的影响机理，建立重叠铺设下格栅筋土界面摩擦强度模型。考虑山区地形引起的边坡外形几何空间特点，建立转角和弯曲外形的加筋边坡稳定性三维分析方法，揭示三维外形对加筋边坡稳定性的影响规律。最终将格栅重叠铺设下的筋土界面强度模型融入到加筋边坡稳定性三维分析方法中，建立山区加筋边坡三维稳定性评价方法和设计理论，结合工程失稳和设计案例对该方法进行验证和应用。

土工格栅作为一种加筋材料被广泛应用于边坡工程中，然而加筋作用机理和稳定性分析方法却滞后于工程实际，影响了加筋技术在山区重大边坡工程中的应用。本项目针对山区加筋土边坡建设遇到的筋材重叠铺设和空间效应问题，通过开展拉拔试验研究探明了土工格栅重叠铺设对土工格栅筋土界面摩擦特性的影响规律及其作用机理，基于稳定性理论建立了三维加筋土边坡稳定性分析与设计方法，揭示了三维效应对加筋土边坡稳定性的影响规律。研究结果表明：格栅重叠铺设对筋土界面摩擦强度有一定的提升作用，随着重叠铺设间距增大这种增强效果逐渐减弱，相对双向格栅而言单向格栅的筋土界面强度受重叠铺设引起的增强作用更为显著，这是由于重叠铺设对土颗粒的嵌固有明显增强作用；通过建立考虑筋材拔出破坏的加筋边坡筋材内力计算方法，筋材长度直接影响了筋材抗拔强度分布，随着筋材长度的减小，中下部筋材拉力增大，工程中可能需要考虑将更高极限抗拉强度的筋材铺设在边坡下部；基于三维边坡稳定理论建立了外凸转角和弯曲加筋边坡三维稳定性分析方法，实现了三维转角和弯曲边坡所需加筋强度和长度的计算，空间效应会增加滑裂面深度，致使设计所需的加筋长度增加；考虑山谷边界作用建立了对称V形山谷加筋边坡的三维稳定性分析方法，加筋边坡所需最大加筋力随谷坡张角减小而减小，场地空间效应更加突出，加筋边坡最危险破坏面滑出点垂直高度随谷坡张角减小而增大，最危险破坏面的滑出点约为1/3坡高。本项目的研究成果不仅具有很好的工程应用价值，而且深化了筋土界面作用机制的认识，填补了加筋土技术应用于山区边坡安全设计的理论空白。