Study On Stability Of Precast Box Invert Structure Of Highway Tunnel Under Earthquake

Prefabrication is the main trend of underground engineering lining structure development.The prefabrication of highway tunnel invert structure has the advantages of fast construction speed,high quality of finished products,low labor cost and low environmental impact,and has broad application prospects.With the rapid development of Chinese economy,more and more highway tunnels are constructed in earthquakeprone areas.When earthquake occurs,the lining structure is prone to crack,fall blocks and other damages.It is of great theoretical and engineering value to study the seismic performance of the prefabricated invert structures of highway tunnels.Based on a highway tunnel project in Gansu Province,a new precast invert structure of box type is proposed to study the stability of the tunnel structure under earthquake.The seismic dynamic response laws of precast invert structures in highway tunnels under different seismic acceleration,buried depth,precast invert design parameters and surrounding rock conditions were analyzed,and effective anti-vibration measures were proposed.The main research results are as follows:(1)Through the investigation and statistical analysis of the tunnel earthquake damage,the tunnel lining is mainly presented with cracking,concrete spaling,falling blocks,subgrade bottom bulge,large area collapse of the arch and other failure forms.The main influencing factors of the earthquake damage include earthquake magnitude,epicenter distance and focal depth,formation lithology and poor geological conditions,tunnel lining depth and tunnel structure.(2)The mechanical deformation characteristics of cast-in-place invert tunnel and precast invert tunnel are compared and analyzed.Under the action of earthquake,the whole highway tunnel takes on axial stretching deformation,the upper edge of the precast invert takes on uplift deformation and horizontal stretching deformation,and the side wall of the tunnel takes on horizontal compression deformation.The displacement of precast invert tunnel is smaller than that of cast-in-place invert tunnel,and the maximum principal stress peak of precast invert tunnel is larger than that of precast invert tunnel,and precast invert tunnel has better seismic performance.(3)The influence of different invert blocks and different invert thickness on the displacement,stress and plastic zone of highway tunnel lining structure under earthquake was obtained.The results show that the vertical displacement peaks of inverts are in the order of one invert < three inverts < seven inverts < five inverts.Increasing the thickness of the upper edge can significantly improve the seismic performance of the tunnel.It is recommended to adopt a precast invert structure with an upper edge thickness of 30 cm and a lower edge thickness of 35 cm.(4)The influence laws of different peak acceleration of ground motion,different tunnel depth and different surrounding rock conditions on the displacement,stress and plastic zone of highway tunnel lining structure under the action of earthquake are obtained.The results show that the vertical displacement of invert and the peak dynamic acceleration basically meet the linear growth relationship.With the increase of the peak value of ground motion acceleration,the maximum principal stress peak value of tunnel lining increases gradually,and the plastic failure becomes more and more serious.The vertical displacement peak of 150 m buried tunnel is the smallest,and the invert uplift of 50 m buried tunnel is the most serious.The invert uplift in grade Ⅴ surrounding rock is serious,and the seismic performance of the invert in grade Ⅳ surrounding rock is greatly improved.(5)The best measures for vibration resistance and absorption of the precast invert of the box type in highway tunnel are obtained.The results show that 4m grouting thickness and 20 cm damping layer can achieve the best reinforcement effect.The final value of vertical displacement and maximum principal stress of invert are reduced by about 67%.There are 71 pictures,17 tables and 83 references in this thesis.