Experimental Study on Settlement of Backfill in Integral Bridge Abutments Induced by Seasonal Temperature Changes

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To reduce construction cost, minimize long-term maintenance of girder beams, and prevent water infiltration-induced erosion problems at expansion joints, integral bridge abutments have been increasingly used in the practice. This type of abutments is subjected to passive earth pressures when bridge girders expand at high temperatures. When the bridge girders contract at low temperatures, backfill materials tend to move downward, inducing settlement of the backfill and creating “the bump at the end of the bridge” problem. This problem becomes progressively worse over time. Some research has investigated the mechanisms associated with this problem; however, more research is needed to further understand these mechanisms, especially under controlled conditions. This paper presents four physical model tests conducted to investigate the mechanisms and effects of seasonal temperature changes on the movements at the bottom of the abutment and the settlement on the backfill. In these tests, concrete blocks were tied together using three thread rods to simulate the abutment, while the Kansas River sand was used as the backfill material and compacted in lifts. A manual jack was used to control cyclic movements of the abutment to simulate the seasonal temperature changes. The movements of the abutment and the settlement on the backfill were monitored during each test. The experimental results showed that the influences of the abutment movement on the settlement of the backfill decreased with the distance from the back of the abutment but increased with the number of cycles. When the abutment toe was allowed to have more movement during cyclic movement, a triangular sliding wedge more likely formed, thus causing a settlement trough on the backfill. The magnitude of the horizontal displacement and the number of movement cycles of the abutment could affect the formation of a slip surface between an active sliding wedge and a stable soil. Larger abutment displacement required fewer number of movement cycles for the slip surface to occur, and the formation of the slip surface changed the settlement profile.