DEM Simulation of the Load Transfer Mechanism of a GRPS Embankment with a Fixed Geogrid Technique

As a new technique, a fixed geogrid in a geogrid-reinforced and pile-supported (GRPS) embankments has been used to reduce the total and differential settlement. To investigate the load transfer mechanism of the fixed geogrid technique of a GRPS embankment, three discrete element method (DEM) models of pile-supported embankments were established, including an unreinforced embankment, a geogrid reinforced embankment, and a fixed geogrid reinforced embankment. The efficacy of the pile, the evolution law of the contact force chain and the axial force of the reinforcement, and the microscopic load-bearing structure of the soil were investigated. Numerical simulation results showed that the embankment self-weight and surcharge load were transferred to the pile through the soil arching and tensile membrane effect. The settlement could be effectively reduced via the addition of the reinforcement, and the fixed geogrid technique was more conducive to improving the load-bearing ratio of the pile than the traditional reinforcement technique. Compared with the traditional technique of a GRPS embankment, the fixed geogrid technique had a better effect on reducing the total and differential settlement. With the increase in the surcharge load and the settlement of the soft subsoil, the reinforcement transferred a greater load to the pile. The results also showed that the stress of the embankment fill was concentrated at the pile top in all three models. The GRPS embankment with a fixed geogrid technique had a lower soil stress concentration than the other two cases. The contact force chain and stress in the embankment also showed that the reformation of the microscopic load-bearing system of the embankment fill was the internal mechanism that caused the development of the soil arching and the redistribution of stress. Furthermore, the evolution of the fabric parameters in the arching area could reflect the evolution of the soil arching structure. In the fixed geogrid case, the proportion of the load transferred to the pile from the soil arching effect was reduced, and the vertical load transferred to the pile top by the tensile membrane effect accounted for 22–28% in this study. Under the combined effect of the tensile membrane and the soil arching, the efficacy of the pile could increase by 10%.

Load transfer mechanism of a load distributive compression anchor installed in weathered rock layer

The demand for a load distributive compression anchor (LDCA) in construction sites has been increasing, owing to its high bearing capacity and removable steel strand. As an LDCA comprises multiple anchor bodies and unbonded steel strands, the load applied to the strand generates a distributive compressive stress in the grout, preventing high concentration of grout–ground shear stress. Unlike in the conventional anchors, in an LDCA, independent load transfer of each anchor body induces interference effect between adjacent anchor bodies. Therefore, for an efficient design of an LDCA, it is necessary to investigate the load transfer mechanism considering the effect of multiple anchor bodies. In this study, a series of anchor pull-out field tests were conducted for LDCAs consisting of single, double, and triple anchor bodies spaced by 1, 2, and 3 m for all cases. According to the test results, the LDCA showed a stiffer load–displacement behavior with an increase in the number and spacing of the anchor body. The multiple anchor bodies of the LDCA generated an overlapping of the grout axial load and induced its rapid dissipation, increasing the grout–ground shear stress. This interference effect was more clearly observed with a decrease in the anchor body spacing.