INTERNAL PRESSURE DECREASING METHOD ON TUNNEL EXPERIMENT AND SUITABLE PATTERN FOR TUNNEL ROCK BOLT.

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Up to this time rock-bolt pattern test has been experimented by external pressure method. In that method, tunnel was set in bedrock unstressed, and external pressure is added around bedrock. In actual, tunnel is excavated in bedrock earth-pressured. Now more realizing, we adopt internal pressure decreasing method. After setting the internal pressure generate instrument, external pressure is added and internal pressure occurs in reaction. Excavation is simulated by decreasing this pressure. The tunnel experiment equipment is plane strain type, and its size is 1.4×1.4×0.3m and the model tunnel diameter is 40 cm. In these experiment , friction between model bedrock and tunnel test equipment injures stress transmission and internal pressure at tunnel wall don't occur as expected. So we use Teflon seat and liquid paraffin between them to cut friction, but some mount of friction remain and internal pressure become smaller than external. So we must add some mount of internal pressure actively by oil units. We did followings.(1) Development of the internal pressure generate instrument (φ=40 cm, depth=30 cm).(2) Experimental study of the friction coefficient using Teflon seat and liquid paraffin between model bedrock and tunnel experiment equipment and theoretical study of the control method for internal pressure at tunnel wall considering friction.(3) Establishment of internal pressure decreasing method on tunnel experiment.(4) Comparing experiments with several rock-bolt patterns (aluminum-bar φ=4 mm, length=6,12,24 cm) in the condition total rock-bolt length of each pattern is equal, and non bolt pattern.(5) Short rock-bolt is more effective than long one from the results of experiments on lateral presser coefficient k=1.0.