Seismic Response Analysis Of Geogrid-reinforced Soil Flexible Abutment Under Two-way Seismic Action

The impact of earthquake action on the stability of abutments has always been one of the key research contents in the seismic design of bridges.Compared with gravity abutments,there are relatively few seismic studies on composite flexible abutments made of soil-reinforced materials,and most of the papers are studying the effect of horizontal seismic force on reinforced abutments,and there are few studies of horizontal and vertical seismic forces on flexible abutments.The lack of related research makes it difficult to form the seismic design code of reinforced soil flexible abutment,and the seismic design code of reinforced retaining wall is also more referenced in the construction of reinforced soil flexible abutment.In order to design more in line with the specifications of reinforced soil flexible abutments,more research reports are needed to provide reference for the formulation of seismic design specifications for reinforced soil flexible abutments.This paper mainly studies the seismic response of different overburden loads and lap lengths to reinforced soil flexible abutments under bidirectional seismic action,so as to find out the rules for reference.To this end,the theoretical research of earthquake earth pressure and the optimization results of calculation methods;the damage index,earthquake damage form and research of gravity abutment,integral abutment and reinforced soil flexible abutment under earthquake action are summarized.The finite element reinforced soil flexible abutment model was established,and the dynamic analysis module of the finite element numerical analysis software FLAC^3Dwas used to simulate and analyze the seismic response law of the reinforced soil flexible abutment under bidirectional seismic action.Seismic waves on Northridge Earthquake collected at Topanga Station in 2008 were used as input dynamic loads.The analysis angles of the earthquake response include:horizontal displacement of the abutment wall,settlement of the abutment and comparison with outside the reinforced area,acceleration ratio of the wall,changes of the horizontal earth pressure and vertical earth pressure of the soil behind the wall,Stress of the reinforced material.The main conclusions of this study are as follows:（1）Under the action of bidirectional seismic earthquake,the increase of the overlying load can reduce the expansion coefficient of the acceleration of the abutment deck,but the excessive load will cause the problem of the bearing capacity of the foundation,so an appropriate intermediate value should be selected;The load keeps the vertical earth pressure behind the deck slab stable before and after the earthquake,and the vertical earth pressure of the soil at the end of the reinforcement area will decrease.（2）The increase of the overlying load will cause the increase of the horizontal displacement of the middle and upper part of the abutment deck,attention should be paid to the structural setting of the bridge to limit the horizontal displacement of the top of the abutment;the increase of the overlying load will increase the settlement of the abutment,under the fixed lap length,the span of the bridge should not be too long to avoid problems with the stability of the abutment under two-way seismic action due to excessive load.（3）The increase of the lap length of the bridge will reduce the overall horizontal displacement of the bridge abutment,but it will also increase the horizontal earth pressure behind the panel,earth pressure exceeds design value.（4）The lap length has little effect on the vertical earth pressure before and after the earthquake at the interface between the panel and the soil,and the vertical earth pressure at the end of the reinforcement area will decrease with the increase of the lap length.（5）The geogrid effectively limits the movement of the soil under earthquake action,Under the condition that the reinforcement setting of the abutment remains unchanged,with the increase of the single-span span of the bridge and the increase of the lap length,the adjacent soil will gradually be affected,which can prevent the large horizontal displacement of the soil.