Analysis of local collapse cavity of loess tunnel caused by systematic bolts

• 1、School of Civil Engineering and Mechanics, Lanzhou University,LanZhou 730000
• 2、NingXia Highway and Bridge Corporation, NingXia, YinChuan 750000

Abstract：For the local phenomenon of cavity collapse after setting systematic bolts in Zhao Jiashan loess tunnel on construction, site monitoring record is applied. Based on the monitoring data, the rule of cavity collapse was summarized and the causes of formation are analyzed. The monitoring results show that the effect to the depth and volume of cavity collapse are obvious after setting systematic bolt, and it influence 30~60 degrees more than 60~90 parts on the arch waist. After comprehensive analysis, conclusion are as follows: When the loess tunnel is excavated, the stress concentration will occur in the local area, the construction of the systematic bolts will promote the release of stress, and the local failure of the loess tunnel will appear; The construction of the systematic bolts causes the construction disturbance to the plastic zone after the excavation, which reduced self stabilization of original rock and the phenomenon of local cavity collapse occurs; The comprehensive effect of the systematic bolts and the weak structural plane has important influence on the local collapse; If the local collapse cavity phenomenon is not timely treatment, the further development is to be local collapse in the loess tunnel.

Keywords： tunnel engineering loess systematic bolts cavity collapse reason analysis