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

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. FLAC^3D 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.