卸荷作用下预应力锚索锚固特性研究

Study on Anchorage Characteristics of Prestressed Anchor Cable under Unloading

在超前预应力锚固或边锚固边开挖工程中,卸荷作用影响已张拉锚索的预应力和锚固段剪应力分布。通过卸荷条件下拉力、压力集中型锚索锚固特性试验,研究卸荷带锚索的荷载传递机制、锚索锚固段剪应力分布规律和预应力发展规律。研究表明:卸荷作用对拉力集中型锚索索体表面剪应力的影响主要为内锚段起点1/3内锚段长度范围内的剪应力增大;对2种锚索注浆体表面剪应力的影响主要为剪应力分布曲线峰值增大。压力集中型锚索注浆体剪应力的峰值增大比率较拉力集中型锚索的更大。卸荷作用导致了2种锚索注浆体剪应力集中区发生塑性滑移破坏,因而2种锚索注浆体剪应力峰值点向内部小距离移动。卸荷作用导致了2种锚索预应力产生台阶式的增大,压力集中型锚索预应力的增加比率比拉力集中型锚索预应力的大。研究结果为预应力锚索的优化设计提供了一定的参考。

In the pre-stressed anchoring or edge-anchored excavation project,the unloading affects the prestress and the shear stress distribution of the anchorage section of the tensioned anchor cable.Through the anchorage characteristics experiment of tension and pressure concentrated anchor cable under unloading condition,the load transfer mechanism of unloading belt and anchor cable,the distribution law of shear stress and prestress development law of anchor cable anchorage are studied.The researches show that the effect of unloading on the surface shear stress of the concentrated anchor cable is mainly due to the increase of shear stress in the range of 1/3 of the internal anchor section at the starting point of the internal anchor section.The effect of unloading on the surface shear stress of the two types of anchored grouting bodies is mainly due to the peak value of the shear stress distribution curve.The peak increase ratio of the shear stress of the pressure-concentrated anchor cable is larger than that of the tension-concentrated anchor cable.The unloading causes plastic slippage damage in the shear stress concentration zone of the two anchor grouting bodies,so the peak points of the shear stress of the two anchor grouting bodies move to a small distance inside.The unloading causes a stepwise increase in the prestressing of the two anchor cables,and the increase ratio of the stress concentration anchor cable prestress is greater than the increase ratio of the tension concentrated anchor cable prestress.The researches provide a reference for the optimal design of the prestressed anchor cable.