Research Into The Effect Of Ground Gully On Stability Of Weak Surrounding Rock In Large-span Shallow Tunnel

Due to the complexity of geological conditions on the large-span tunnel withweak surrounding rock, the stability of surrounding rock is seriously influenced by thegeological factors during the excavation. As one kind of special landscape for hills,gullies bring on some uncertainty to the safety of tunnel construction. For shallowburied tunnels with large span, the excavation process and support structures are bothhighly required under such special landscape. Unsuitable process may cause someserious troubles, such as collapse and slump at tunnel heading. All of these troubles notonly damage the supporting structures and affect the progress of construction, but alsothreat the safety builders. Thus the effect of gully on stability of surrounding rockshould be paid more attention during the construction, and the mechanism of sucheffects should be investigated in detail.The engineering background of this paper is Qixiaying tunnel which is located onJing-Xin highway project. According to the previous geological survey, the surroundingrock is classified as Level V. Based on the monitoring data from Qixiaying tunnel, therelationship between gully and crown settlement, pressure of surrounding rock, andinternal stress of initial steel support is investigated under the two steps excavationmethods with primary support. According to the large span shallow tunnel of weak rockwith the primary support, the effect of different gully form on surrounding rock stabilityis researched through the compare of rock displacement and stress, initial support stressand change of plastic zone on numerical model. The surrounding rock stress,displacement and initial support stress and plastic zone change under the unsymmetricalloadings shallow tunnel with gully is compare with without gully, which get the effect of gully on the rock stability. Therefore, the surrounding rock stress, displacement andstress of initial support and plastic zone change on the unsymmetrical loadings shallowtunnel under gully with reinforcement is compare with without reinforcement,reinforcement effect is analyzed. Finally, the monitoring and simulation results arecomparatively analyzed through the crown settlement and surrounding rock pressure oftunnel section under gully to verify the rationality of the model and to bring certainguiding significance for the future similar tunnel engineering construction.