Abstract In order to study the support effect of self-drilling hollow anchor bolt in sandy pebble stratum, a drilling test and pullout test were conducted based on a tunnel in sandy pebble stratum of Tibet. The tests show that the average drilling depth of ?25 anchor bolt is 1.50 m which is 42.7% of the designed length, torsion failure or idling occurs when it reaches the limit depth and drilling can′ t go further; the average drilling depth of ?51 bolt without drill bit is 1.15 m which is 38.3% of the designed length, and continuous drilling can′ t be fulfilled; the average drilling depth of ?25 anchor bolt increases by 23.1% when the drill bit is removed and the average drilling depth of ?51 bolt increases by 95.2% when the drill bit is removed; the average pullout force of ?25 bolt is close to the designed value of 50 kN, but the anchoring effect doesn′ t work. 4 optimization measures for construction support were determined based on the test results of anchor bolts, specifically systematic bolts is eliminated to reduce disturbance of sur? rounding rock; the drill bit is removed and the anchor bolt is drilled directly; the group number of feet-lock bolt is increased from 1 to 2 to ensure total support length; the ?25 advanced anchor bolt with a length of 1.8 m is selected instead of the ?51 anchor bolt with a length of 2.5 m. The monitoring data show that convergence deformation of the tunnel increases slightly after scheme adjustment while the crown settlement decreases obviously, the tunnel construction speed increases significantly and the safety is quite improved.
Abstract：
In order to study the support effect of self-drilling hollow anchor bolt in sandy pebble stratum, a drilling test and pullout test were conducted based on a tunnel in sandy pebble stratum of Tibet. The tests show that the average drilling depth of ?25 anchor bolt is 1.50 m which is 42.7% of the designed length, torsion failure or idling occurs when it reaches the limit depth and drilling can′ t go further; the average drilling depth of ?51 bolt without drill bit is 1.15 m which is 38.3% of the designed length, and continuous drilling can′ t be fulfilled; the average drilling depth of ?25 anchor bolt increases by 23.1% when the drill bit is removed and the average drilling depth of ?51 bolt increases by 95.2% when the drill bit is removed; the average pullout force of ?25 bolt is close to the designed value of 50 kN, but the anchoring effect doesn′ t work. 4 optimization measures for construction support were determined based on the test results of anchor bolts, specifically systematic bolts is eliminated to reduce disturbance of sur? rounding rock; the drill bit is removed and the anchor bolt is drilled directly; the group number of feet-lock bolt is increased from 1 to 2 to ensure total support length; the ?25 advanced anchor bolt with a length of 1.8 m is selected instead of the ?51 anchor bolt with a length of 2.5 m. The monitoring data show that convergence deformation of the tunnel increases slightly after scheme adjustment while the crown settlement decreases obviously, the tunnel construction speed increases significantly and the safety is quite improved.
CAO Xiaoyong1 FENG Zhihua1,
3 SHI Yanwen2 SONG Feiting2 LAI Jinxing2
.Field Test and Analysis of Mechanical Behaviors of the Self-drilling Hollow Grouting Anchor Bolt for the Tunnel in Sandy Pebble Stratum[J] MODERN TUNNELLING TECHNOLOGY, 2019,V56(3): 125-132
2019, Vol. 56 