Numerical Analysis of the Impact Response of a Lattice-Shaped Diaphragm Wall Bridge Foundation Under Local Scour Using a Rigid Steel Impactor

Local scour reduces the lateral restraint provided by surrounding soil and may amplify the impact-induced response of bridge foundations. This study investigates the response of a lattice-shaped diaphragm wall (LSDW) foundation–soil system under predefined local-scour conditions using a three-dimensional explicit finite element model and a nominally rigid steel impactor. A 1:30 reduced-scale configuration was analyzed at impact velocities of 2, 3, and 4 m/s and scour depths of 0, 200, 300, and 400 mm. Increasing impact velocity generally increased wall displacement, velocity, and elastic principal-stress demand, whereas deeper scour reduced the remaining embedment and the restraint provided by the surrounding soil. Relative to the corresponding unscoured conditions, the normalized peak wall-top displacement ratios were 1.28–1.38, 2.01–3.66, and 3.28–5.45 for scour depths of 200, 300, and 400 mm, respectively. The velocity distribution showed an increasingly pronounced rotational contribution as the remaining embedment decreased. Case 9 produced the largest overall response, with a peak wall-top displacement of 398.7 mm and a peak wall-top velocity of 5.2 m/s. Because direct physical validation was unavailable, the results should be interpreted as comparative model-scale trends rather than validated prototype predictions.