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 arc 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. © 2022 Xi'an Highway University. All rights reserved.