New Construction Technology of a Shallow Tunnel in Boulder-Cobble Mixed Grounds

Table 1

∅25 ultimate pull-out strength of bolts.

Number	Bolt condition	Actual penetration length (m)	Ultimate pull-out strength	Causes of termination	Gripping force corrected value (kN)
3	Including drill	1.38	62.5	When loaded to 62.5 kN, it suddenly fell back to 22.1 kN and could not continue to increase	37.4
5	Including drill	1.24	74.3	Loading to 74.3 kN reduces the drop to 28 kN	47.6
7	Including drill	1.35	72.2	Loading to 72.2 kN reduces the drop to 30.2 kN	49.9
9	Including drill	1.50	82.5	Achieves a predetermined value of 100 kN	≥80.0
3	Excluding drill	1.71	92.2	Loading to 92.2 kN reduces the drop to 42.0 kN	70.1
4	Excluding drill	1.94	100	Achieves a predetermined value of 100 kN	≥80.0
5	Excluding drill	1.60	86.6	Loading to 86.6 kN reduces the drop to 38 kN	64.5
6	Excluding drill	1.78	100	Achieves a predetermined value of 100 kN	≥80.0