Analysis of protection time of tunnel based on displacement theory of shotcrete and bolt support for weak surrounding rock

Based on the displacement theory of shotcrete and bolt support for weak surrounding rock and combined with Yehuling No.2 tunnel engineering,by using theoretical analysis and site monitoring,the time and space effect of the release of displacement of surrounding space near soft rock tunnel was studied and analyzed.On the basis of the study,according to surrounding rock creep curves,the reasonable supporting time was chosen.Results show that too obvious time and space effect after the soft rock tunnel excavation easily produce displacement and rock creep can cause damage to surrounding rock or retaining structure.Due to the existence of soft rock breaking properties,reasonable secondary supporting time can be worked out through site monitoring and theoretical calculation according to the displacement curve.This method is better than the past supporting time determined by experience or analogy method,related design parameter and the actual inspection data coincide very much.