Study on the bearing mechanism of tunnel-type anchorage based on laboratory model test

To have some insight into the bearing mechanism of tunnel-type anchorage and figure out the mechanical response law of anchor plug and surrounding rock under engineering load, the tunnel-type anchorage laboratory model test scaled 1:100 is carried out. In this model test, the actual loading path and mechanic characteristic are simulated with the effective simulation of all transmission components such as saddles, cable strands, steels, anchor plug and surrounding rock and so on. Then the change law of interfacial additional stress between the anchor plug and rock, deformation response of surrounding rock are analyzed to study the temporal and spatial mechanism. And the possible failure mode is also predicted by analyzing the migration rule of the peak displacement point of deep rock mass. Main conclusions are draw as follows. (1) In the total loading process, the interfacial additional stress between the anchor plug and rock performs firstly as no response(under 0 to 5 times design loads) then increase elastically (5 to 13 times design loads) and grow quickly (13 to 19 times design loads) and sharp decrease at last(21 to 23 times design loads). (2) The anchor plug squeezes the burial surrounding rock layer-by layer from back parts to front parts in the total loading process and mobilizes the surrounding rock to bear together under the engineering load from the near to the distant. (3) Under 5 times design loads, the displacements of anchor plug and surrounding rock are negligible and then they will increase linear at low speed if the engineering load is between 5 to 13 times design loads. But the displacements growth will accelerate and the displacement of anchor plug will be greater than the displacement of surrounding rock when the engineering load reaches 13 to 21 times design load. Finally the anchor plug will be pulled out because of the serious damage of surrounding rock under 23 times design load. Last but not least, the cracks occur after at the displacements accelerated growth stage. The range of reticular fracture zone is 50 centimeters above the vault of anchor plug, 35 centimeters below the bottom of anchor plug, 35 centimeters within the left wall and 35 centimeters within the right wall of anchor plug. And the failure mode of tunnel-type anchorage is un-symmetrical trumpet-shape speculated by the fracture zone and displacement distribution law of deep-seated rock. © 2019, Science Press. All right reserved.