压力分散型锚索锚固段受力特性试验分析

Field test and mechanical analysis of anchorage segment of pressure-dispersion anchors

压力分散型锚索锚固段注浆体与围岩的黏结应力是荷载传递研究的核心问题,目前直接测试界面黏结力存在一定的难度。针对压力分散型锚索注浆体的轴对称应力条件,在现场试验中通过自制的应变砖测点直接测得靠近孔壁的注浆体切向剪应力,以反映界面黏结力分布,同时进行了钢绞线握裹力测试。分析了轴向应变与切向剪应力的分布规律,探讨了轴向压缩量对荷载传递的特性的影响。采用FLAC3D进行数值模拟,对锚固段注浆体轴力的不均匀性、注浆体切向剪应力与注浆体与围岩接触面剪应力分布的联系与差别等进行探讨。确定了现场试验和数值计算条件的压力分散型锚索有效长度为2 m左右,并建议将锚固段设计长度改为3 m。

The bond stress between grout body and surrounding rock is the key problem in the load transfer mechanism of pressure-dispersion anchors.At present,it is also difficult to get the bond stress directly.It is mostly obtained by subtracting pressure stress values along the axes,which are calculated by axial pressure strain value from strain gages.By this method,the error is large because the pressure stain is not uniform in the section and the radial strain is not taken into account.Due to the axially symmetric stress condition of the grout body of anchorage section,self-made strain bricks are fixed into the right places of the grout body.The bricks are used to measure the shear stain near wall of the hole so as to reflect the characteristics of the bond stress on the interface.The grip between gout and steel strand is also tested by use of another 5 m-long cable for calculating prestress loss.The influences of axial compression and radial swelling are analyzed,and the distribution rules of axial strain,radial strain and tangential shear stress are discussed.FLAC3D is used to simulate pressure-dispersion anchors in the field test.The uniformity of axial stress in grout section,and the relationship and differences between tangential shear stress and bond stress of grout body are discussed.Finally,the distribution characters of axial stain and shearing stress are achieved.The effective length of anchorage section is confirmed to be 2 m,and the design length of anchoring section with change from 5 m to 3 m is put forward.