Abstract: The geometrical shape effects on the anchorage systems and their mechanical characteristics in weak soils are the controversial issues to be resolved in the anchored structure field. In the full scale field experiments, the 30 m deep under-reamed anchorages with 4.44 diameter ratio of large fixed section to borehole section are investigated; the loading–displacement curves of under-reamed anchorages demonstrated the monotonic rising in common along with increasing displacement. The anchorage test results in weak soil layers show that their excellent mechanical properties and the good ductility as well, namely, the under-reamed ground anchorage can keep higher bearing capacity when it has a larger displacement. Based on the analysis of loading–displacement curves including elastic and plastic deformation, and bearing capacity comparison of measured data and calculated value, it is found that the strain–hardening characteristics peculiar to the bearing and deformation behavior of the deep under-reamed anchorage with capsule, and also the control value of anchorage displacement. Experimental research results can provide the significant instruction for the application of new anchorage system with capsule in Ningbo area.

Key words: capsule, under-reamed anchorage, mechanical property, experimental research, construction method