锚固段穿越双地层拉力型锚索拉拔力学模型及应用

预应力锚索灌浆体与周围岩土体结合面的极限黏结强度是预应力锚索设计优化的基础参数，然而该参数的取值目前还严重依赖于经验，尤其对于锚固段穿越双地层的工况。此外，预应力锚索现场拉拔试验只是被用来验证初步设计方案是否满足极限承载力要求，并未与设计方案优化建立定量联系。基于对拉力型预应力锚索工作状态作出的合理化假设，建立了适用于锚固段穿越双地层的拉力型预应力锚索拉拔传力机理力学模型，即弹簧-粘片力学模型。该模型给出了锚索锚固段剪应力状态处于不同阶段时的锚固段剪应力分布函数、拉拔力上下限以及拉拔力-始端位移理论关系式。通过将弹簧-粘片力学模型与现场拉拔试验相结合，提出了一种适用于锚固段穿越双地层的预应力锚索极限黏结强度的半解析预测方法。通过与实际工程中的预应力锚索现场拉拔试验成果及三维有限差分数值分析的对比，验证了该预测方法的有效性及其在预应力锚索设计优化中的应用性。研究结果表明：采用所提出的半解析预测方法确定锚固段穿越双地层的预应力锚索极限黏结强度时，只需开展一组现场拉拔试验，从而克服了仅依靠现场拉拔试验获取双地层中极限黏结强度时需开展至少2组现场拉拔试验的缺点，可大幅节约工程造价且有效缩短了工期，具有较好的工程应用前景。

A Pullout Mechanical Model for Tension-type Ground Anchor Penetrating Two Soil Stratums and Its Application

The interfacial bond strength between the grout of ground anchor and the surrounding soil is a primary parameter for design optimization. However, determination of this parameter depends heavily on experience, especially for the case where the grouted segment penetrates two soil layers. In addition, the results of the ground anchor in-situ pullout tests are used only for verifying the designed ultimate pullout capacity, and have not been connected quantificationally to the design optimization. Based on several reasonable assumptions, this paper establishes a spring-dashpot model for modelling the load-transferring mechanism of ground anchor. This model is applicable for the case where the grouted segment penetrates two soil layers. In this model, the shear stress distribution functions along the grouted segment, the upper and lower limits of the pullout load, and the theoretical relations between pullout load and displacement are given for different stages of the shear stress development. Based on a combination of the spring-dashpot model and the in-situ pullout testing results, a semi-analytical method for estimating average interfacial bond strengths of ground anchor is proposed. The performance and applicability for design optimization of the proposed method are validated by comparing with the 3D finite difference analysis and in-situ pullout testing results. According to this study, the determination of the average interfacial bond strengths for the tension-type ground anchor penetrating two soil stratums by using the proposed method requires only one group of in-situ pullout test, which indicates that this method overcomes the deficiency of requiring at least two groups of in-situ pullout tests in the conventional prediction method. Therefore, the proposed method has the advantages of reducing the construction costs, and shortening the construction period, demonstrating the broad application prospects of this method.