Experimental Study On The Under-reamed Anchoring Mechanism In The Soil

With the development of the construction area depth and breadth recently, unfavorable situations appear frequently, such as poor geological conditions, difficult to operate, high risk and so on. Ordinary bolt has been unable to meet the requirements of anchorage, while under-reamed anchors have the advantages of large anchoring force, simple manufacturing process and easy installation, which can solve these engineering problems effectively. The under-reamed anchor is still in the initial stage of exploration in China. Although the types of under-reamed anchors, the development of reaming tools and the construction of under-reamed anchors have been a useful attempt, the understanding of the anchoring mechanism and the force characteristics of the under-reamed anchor is not clear enough and lacks the necessary experimental analysis.In this paper, considering the mechanical properties of the soil and the stress characteristics of the anchor in the soil, the semi-cylindrical test box and the anchor model are designed. The digital speckle technique is used to obtain the corresponding displacement field and strain field, and the numerical simulation is carried out with ANSYS. The stress characteristics and anchoring mechanism of the under-reamed anchor are analyzed. There are the following conclusions:(1) Using visual experimental method, combined with digital speckle correlation technology for indoor experiments. The distribution,development and evolution characteristics of the X and Y displacements of the anchored soils are consistent with the numerical simulation results,which indicates that the experimental device and the experimental method are feasible.(2) Under the same loading condition, the existence of the enlarged end makes the anchoring force of the under-reamed anchor significantly improved. With the increase of the diameter, the load-displacement curve of the experimental load-displacement curve increases slightly in the reinforcement stage. The load capacity of the rough anchor is significantly enhanced compared to the smooth anchor, and the specimen has a greater displacement before the damage, which is great for the safety monitoring and forecasting of the engineering support.(3) The displacement curve of the soil in the radial section of the specimen with variable diameter shows a significant nonlinearity with the experiment. The larger the displacement, the higher the fitting degree of the curve and the logarithmic curve. The anchoring force of the reaming anchor is mainly composed of three parts: the side friction resistance of the expanded and non-expanding sections and the anchoring force provided by the variable diameter section, which mainly depends on the physical and mechanical properties of the soil.(4) The numerical simulation results show that the simulated load-displacement curve has the same trend as the curve obtained by the experiment. The X-direction displacement of the anchor soil mainly occurs on both sides of the variable-diameter section, and the Y-direction displacement is mainly generated above the variable-diameter section,which is consistent with the experimental results. With the increase of the load, the Y-direction displacement occurs in the soil at the end of the enlarged end due to its ideal elastic-plastic in a certain range of, and the phenomenon of layered fracture occurs in indoor test due to the soil reached the limit state.