Engineering Introduction

Located at South of Jinan Province, Heilongyu Tunneling of express highway circling city has a shoal buried depth. Surrounding rocks are Cambrian thin-layer limestone with developmental joint fissure. For assuring the effect of support, hollow anchor bars are used. 

The Construction of Hollow Anchor Bars

Sign the designed position on shotcrete then drill with pneumatic rock drills. After drilling and cleaning, put hollow anchor bars with backstop anchor head, set nut and stop plug in the hole. According to the depth of the hole to position the font set nut. The back set nut is pushed by propeller to expand the stop plug for a sealing effect. 

A special grouting beak is connected with the tail of hollow anchor bar. As slurry, the cement mortar is injected from bolt hole.The admixture of early strength, plasticity and expansibility should be added to make sure the slurry has early strength, fluidity,expansibility, compactibility and high bearing strength. Grouting pressure usually is 210MPa.

After grouting for 24h, hollow anchor bar has ability of anchoring primarily. Tighten the plate with blind nut so that it can cling to surrounding rocks. The tightening force of blind nut should be less than 20kN. When the angle between bolt and plate is bigger than 16°,the mortar can rapidly solidified should be filled at the back of plate then tighten the plate. When tightening, mesh reinforcement can be put between plates to enhance the effect of support.