基于黏弹-塑性圆孔扩张理论压力注浆锚杆锚-土界面黏结强度计算方法

压力注浆锚杆在隧道、边坡、基坑等支护工程中应用广泛。为了预测锚杆在不同注浆压力下的锚-土界面黏结强度，将锚-土界面法向应力的发展过程分为2个计算阶段：压力注浆时锚孔扩张半径的计算和浆液硬化后界面法向应力的计算。在计算时，将锚孔扩张过程视为无限土体中的瞬时圆孔扩张问题，考虑塑性区土体服从统一强度准则，推导出压力注浆时锚孔扩张半径解答；然后，考虑土体的时变特性，引入黏弹-塑性圆孔扩张理论，采用Merchant模型推导出浆液硬化后界面法向应力随时间衰减的解答；最后，基于库仑抗剪强度公式，建立了压力注浆锚杆锚-土界面黏结强度的理论计算方法。为了验证所提计算方法的可靠性，采用自制的锚杆微元体压力注浆装置，制作了3种不同注浆压力下的锚杆试样并开展了拉拔试验。将获得的试验结果与所提理论计算结果进行对比，并结合已有的压力注浆土钉拉拔试验结果进一步验证。结果表明：提出的压力注浆锚杆锚-土界面黏结强度的理论计算方法能够准确的预测试验数据，可为工程设计提供参考。最后进行了参数分析，结果表明：锚-土界面黏结强度与注浆压力呈线性关系，注浆压力增大能有效提高锚杆的承载性能；锚-土界面黏结强度随着复合模量的增大呈现...

Method for Calculating Soil-grout Interface Bond Strength of Pressure-grouted Anchors Based on Viscoelastic-plastic Cavity Expansion Theory

Pressure-grouted anchors are widely used in tunnels, slope supports, and foundation pit reinforcements. In this study, the development process of the normal stress at the soil-grout interface was divided into two calculation stages to predict the bond strength of the soil-grout interface under different grouting pressures. The two stages are calculations for the expansion radius of the anchor hole during pressure grouting and the normal stress on the interface after slurry hardening. At the beginning of the calculations, the expansion of the anchor hole was regarded as an instantaneous cavity expansion problem in infinite soil. The solution of the anchor hole expansion radius during pressure grouting was derived, assuming that the soil in the plastic zone obeys the unified strength criterion. Next, the rheological properties of the surrounding soil were considered in the second stage of the theoretical analysis. The viscoelastic-plastic cavity expansion theory and Merchant model were introduced, and the solution of the interface normal stress attenuation with time after slurry hardening was derived. Finally, a new theoretical calculation method for the soil-grout interface bond strength of pressure-grouted anchors was developed based on the Coulomb failure criterion. The anchor specimens and soil-grout interface shear tests with three grouting pressures were performed using a specially designed device to validate the proposed calculation method. The theoretical calculation and experimental results of this study and existing pressure-grouted soil nail pull-out test results were compared. The consistency of the results demonstrates that the proposed theoretical method precisely calculates the soil-grout interface bond strength of pressure-grouted anchors. The calculation method presented in this paper provides a reference for engineering designs. Parametric analysis was conducted, and the following conclusions were drawn. The bond strength of the soil-grout interface has a linear relationship with the grouting pressure, and increasing the grouting pressure can effectively increase the bearing capacity of the anchor. The bond strength of the soil-grout interface increases nonlinearly with an increase in the composite modulus.