Many researches for design of the system rock-bolt tunnelling method (S.R.T.M) have been carried out by experimental and analytical methods in Railway Technical Re-Search Institute, JNR.
In order to clarity the reinforcing effect of rock bolts, the strength test was performed by assuming the block model reinforced with rock bolts as a part of the Side wall of the actual tunnel as shown in Figure 1.
The size of the model was 20 cm width, 25 cm in depth and 30 cm in height. It was assumed that two surfaces perpendicular to the axis of the surfaces under Plain strain condition.
(Figure in full paper)
Screwed brass poles of 3 mm in diameter were used for the bolts. Three different intervals between bolts used for the test were 30 mm, 40 mm and 50 mm and existance of the bearing plate was also one of the test conditions considered.
The loading condition was the strain control method (0.2 mm/min up to the maximum loading and thereon 1 mm/min).
Low strength mortar was used as test bedrock.
Photo 1 shows the test conditions where both side surfaces are confined by the two steel plates of 12 mm in thickness, connected tightly by 4 steel poles (22 mm in diameter) allowing no relative displace to each other. Teflon sheet was inserted on contact surfaces between the test apparatus and the test material in order to minimize the friction.
(Figure in full paper)
Various types of tests conducted are tabulated in Table 1. 13 × 13 mm plates were used for bearing plates.
(Table in full paper)
The Load-Displacement (Vertical) curves are shown in Figure 2 for each test case. The curves shown an yield condition at 5 to 8 tons. Clear relationship was not observed between yield load and test materials.
It is only after the yield condition that the significant difference on the results are observed by the use of bolts, by the number of bolts installed and by the use of bearing plates.
When rock bolts are not installed, failure occurs immediately after the yield. While rock bolts are installed, the load continues to increase although the rate of increase of loading becomes small. A maximum load and displacement to failure with rock bolts are 29 times and 3 8 times larger respectively than what would be expected without rock bolts. The area surrounded by the load vs. displacement curve and the axis of abscissa, which represents the amount of energy required to a failure and can be the parameter of toughness, increased by a factor of several ten times.
(Figure in full paper)
When bearing plates are not attached to rock bolts, the entire free surface of the bedrock is heaved and the bolts shows a behavior of creeping into the test bedrock. Surface bedrock becomes extremely exfoliated near the failure condition, but the breakage of rock bolts are not observed.
