Evaluation of cyclic displacement amplitude of integral bridge abutment on backfill soil pressure and settlements

Expansion joints and sliding bearings in conventional bridges eliminate the forces in deck cause by temperature fluctuation. There are always problems with these bridges during operation. Usually expansion joints and sliding bearings damage due to various reasons and lead to high maintenance costs. Also the seismic stability of abutments in conventional bridges is low during earthquakes and usually lead to large bumps behind abutments. The deck in an integral bridge is integrated with abutments, and expansion joints and sliding bearings eliminated. With elimination of expansion joints and sliding bearings, the associated problems with them will eliminate. But there are also problems with integral abutment bridges. In integral bridges, the expansion and contraction of deck causes many geotechnical problems in backfill soil behind abutments. In summer, when the temperature is high, the expansion of deck moves abutments toward the backfill soil. This relative displacement between abutments and backfill soil results in increasing pressure behind abutments in backfill soil. In winter when the temperature is low, the contraction of deck pulls away the abutments from backfill soil. This relative displacement results in soil settlements behind abutments and causes large bumps in surface. The cyclic moving during expansion and contraction, also leads to growing lateral earth pressure in backfill soil. The amplitude of wall displacement has a great effect on lateral soil coefficient and soil settlements. Three different magnitudes of normalized wall displacements δ/H = 0.2%, 0.6%, 1% selected during this research and evaluated. The results showed that by increasing in normalized wall displacements (δ/H) the settlement and peak lateral soil coefficient (Kpeak) of soil behind the wall meaningfully amplified. Also the results of tests in comparison with some existing manuals for integral bridges showed that the lateral soil coefficient in upper parts of the wall is underestimated by manuals.