Study On The Earth Pressure Behind Integral Abutment With Expanded Polystyrene Under Pseudo-static Test

The earth pressure of backfill behind the abutment in integral abutment jointless bridges(IAJBs)has a great variation when the girder is easily to the load of cycling temperature.Thus,the earth pressure increases continuously with the seasonal variation of temperature.The actual earth pressure of backfill will be larger than that of the designed earth pressure a lot,and the accumulated deformation in abutment and pile will also be produced.Therefore,many scholars put forward the measures that the area behind the abutment should be installed with elastic filler,such as expandable polystyrene(EPS),in order to reduce or control the greater earth pressure behind abutment caused by the load of circulating temperature.However,the following questions are needed to be further discussed.The effect of different thicknesses of EPS on values and distributions of earth pressure behind backfill and the calculation method of earth pressure behind backfill.The main research and conclusions are as following.(1)Based on the specimens of abutment-H-shaped pile,a low-cyclic pseudo-static experiment on interaction of abutment-pile-soil with expanded polystyrenes(EPS)of IAJBs was carried out.The investigations indicate that the expanded polystyrenes(EPS)filling behind the abutment can remarkably reduce the residual deformation of the soil and also can be significantly reduced the cumulative unbalance thrust.The thrust is reduced up to 36%when the thickness of EPS is 15cm.In addition,the horizontal thrust of abutment under girder expansion can be reduced effectively when buried the EPS filler behind the abutment,and the thrust is reduced up to 31%when the thickness of EPS is 0.15H(H is the height of the abutment).The accumulative deformation of pile and abutment can be decreased with the increases of expanded polystyrenes(EPS)thickness,especially at the 0.4m below the top of the pile,where it can be reduced by 74.3%.(2)Experimental results illustrate that the constraints of the backfill on rotation angle can be reduced remarkably,and positive and negative rotation of abutment is more symmetrical by the abutment filled with the expanded polystyrenes(EPS).The influence of different EPS thicknesses on interaction between H-shaped steel pile and soil is significant.The strains and bending moments of pile,and lateral earth pressures around pile are reduced correspondingly with the increases of the EPS thickness.Compared with results of M-0(Ocm EPS),that decreases by 46%,41%and 50%respectively.(3)The tests also indicate that the earth pressure behind backfill can be reduced significantly after the abutment filled with EPS,the maximum soil pressure are decreased with the increase of EPS thickness.The maximum soil pressure behind the abutment is reduced up to 46%when the thickness of EPS is 0.1H(H is the height of the abutment).The earth pressure distribution between 0.0H and 0.2H behind abutment is "trapezoid distribution",which is along the depth on the vertical plane.However,the earth pressure distribution between 0.6H and 1.4H behind abutment is "triangular distribution",which is along the depth on the vertical plane.For soil pressure behind the abutment in the same level,which gradually decreases when the distance away from the abutment increases.The effect of EPS on earth pressure can be ignored basically,when the distance away from the abutment is over 1.4H.(4)The distribution of strains and bending moment of piles and lateral earth pressure around piles are obtained by the experiment.At the same time,the results are compared with those calculated by m method and p-y curve method.Meanwhile,the comparison between the measured values and theoretical values of earth pressure behind the abutment are conducted,and the results show that several theoretical methods are not suitable for the calculation of earth pressure behind abutment with EPS.In addition,the FEM on the interaction of abutment-pile-soil with expanded polystyrenes(EPS)in IAJBs is established by the ABAQUS software,the results of that are checked with the experimental results.Finally,based on reduction coefficient of earth pressure considering EPS,the simplified calculation method of earth pressure behind abutment with EPS is proposed.