Numerical Analysis Of Geosynthetic-reinforced Soil Integral Abutment Subjected To Seismic Loads

The bearings and expansion joints in conventional simply supported bridges should be repaired and replaced regularly. This can greatly increases the life cycle cost of bridges. Simply supported girder bridges suffered the most severe damage during earthquakes. Integral bridges have no bearings or joints between the decks and abutments and thus can significantly reduce maintenance requirements and costs over a bridge’s service life. The superstructures and abutments are rigidly connected in integral bridges. This allows for remarkably increased redundancy and continuity, which are expected to have much higher seismic stability. There was a lack of research on the seismic behavior of full-height integral abutments. There is no common design code for the calculation of seismic pressure of integral abutment. Since large earth pressure and settlement will occur in the backfill behind the integral abutment, some researchers come up with a new type of bridge, geosynthetic-reinforced soil integral abutment bridge, to solve this problem. This paper developed a dynamic constitutive model using the FLAC, which can consider some of soil properties under cyclic loading. Numerical analysis of the seismic response of a full height integral abutment bridge was carried out using the FLAC. A parametric study was also investigated of the bridge. Then this paper carried out the numerical analysis of the seismic response of the geosynthetic-reinforced soil integral abutment bridge. Its dynamic response mechanism was discussed. In addition, a parametric study was also investigated of the GRS integral bridge. The results are presented below:(1) A dynamic constitutive model, which can consider some properties of soil under cyclic loading, such non-linear behavior and hysteresis behavior, was developed using the fish language in FLAC. The model was validated using a soil column under different loading conditions. The model was used in the numerical analysis of the influence of deep excavation on the ground seismic response.(2) The seismic response of a full height integral abutment bridge was carried out using the FLAC. The results show that the integration between the superstructure and the abutment would affect the dynamic response of the abutment significantly. The commonly used M-O method when calculating the seismic earth pressure behind the abutment gives a much smaller total horizontal earth pressure and a lower action position, which is unsafe. The parametric study of the abutment showed that the horizontal earth pressure, abutment bending moment and horizontal displacement will increase as the inertia force of the bridge deck increases, which is caused by the increase of peak acceleration and the increase of the bridge span. When the abutment height increases, the abutment’s deformation mode will change from rotation to bending. The horizontal earth pressure distribution will be more uniform and the maximum value will be much smaller when putting a compressible layer behind the abutment. However, larger abutment bending moment will occur instead.(3) The seismic response of geosynthetic-reinforced soil integral bridge together with other three different kind of abutment was carried out using the FLAC. The results show that the seismic stability of conventional simply supported bridge, GRS conventional bridge, integral bridge and GRS integral bridge increases in turn. Compared with 1 meter thick integral abutment, 0.4 meter thick GRS integral abutment has smaller bending moment and needs less steel, as well as the same natural frequency and displacement. GRS will be more effective when the abutment is thinner or the abutment is higher.(4) The parametric study of the GRS integral bridge abutment showed that GRS means smaller bending moment and displacement when the abutment is higher. The Yang’s modulus and length of the reinforced material has some effect on GRS integral bridge abutment’s seismic performance. However, when they reach some magnitude, there will be no effect. The vertical spacing of the reinforced material almost has no effect on GRS integral bridge abutment’s seismic response.(5) An optimization design was investigated to solve the mutation in the settlement of the backfill behind the abutment. The results show that the problem could be solved if the reinforced material is properly distributed, which means the reinforced material is longer in the upper part of the backfill and shorter in the lower part.