The resilience and performance of quay walls during devastating events such as tsunamis and earthquake are critical for coastal infrastructure. Conventional design standards mostly address vertical or inclined quay walls, neglecting the potential benefits of more complex geometry, such as bilinear backface. This study presents a seismic design and stability analysis of quay walls with a bilinear backface under the combined action of tsunamis and earthquake. The study findings reveal a significant reduction in safety factors in terms of sliding and overturning when quay walls are simultaneously exposed to tsunami and earthquake forces. The study also proposes a bilinear wall geometry, considering key factors such as tsunami wave height, water depth, submergence height, excess pore pressure ratio, and wall inclination. This study aims to enhance the design and construction of quay walls with a bilinear backface, thereby improving the safety of coastal structures and communities against these rare but devastating events.

Historic quay walls in many Dutch cities are supported by an array of vertical timber piles which run through soft soil deposits and rest on a sand layer, providing end-bearing support. As these structures experience horizontal loads, the foundation piles are loaded in bending. This is the dominant loading case of pile foundations of dams, lock heads, and sometimes bridge abutments as well. To accurately model and evaluate the timber pile foundations, a proper estimate of their bending properties is essential. Therefore the mechanical properties of existing spruce foundation piles, retrieved from a historic quay wall (1905) at Overamstel in Amsterdam, Netherlands, were studied. Six piles were subjected to a four-point bending experiment. The outer fiber stress was kept constant between the point loads, leading to a failure at the weakest cross section. Measurements of the curvature and force distribution were taken along the pile length during loading. In addition, biological decay in the outer layer of the timber piles, also referred to as the soft shell, was identified with microdrillings. Internal strains were measured successfully by gluing fiber-optic wires inside the soft shell of the timber piles. The experiments indicated significant variations in modulus of elasticity and modulus of rupture across the tested population, but indicated a strong correlation. Modulus of elasticity averaged 16.5 GPa with a variation coefficient of 0.30, whereas the modulus of rupture averaged 23.2 N/mm2 with a variation coefficient of 0.26. Bacterial deterioration was found to be independent of both the outer pile diameter and the location along the timber pile. The soft shell had an average thickness of 21 mm, but it did not contribute significantly to the structural strength of the piles. This study could present a template for assessing the remaining service life not only of historic quay walls but also of other timber pile foundations under bending loads.

The seismic performance of a caisson structure under two types of models with a saturated sandy foundation (CSS) and an expanded polystyrene (EPS) composite soil foundation (CES) are studied using shaking table tests. The macro phenomena of the two different foundation models are described and analyzed. The effects of the replacement of EPS composite soil on seismic-induced liquefaction of backfill and the dynamic performance of a caisson structure are evaluated in detail. The results show that the excess pore water pressure generation in the CES is significantly slower than that in the CSS during the shaking. The dynamic earth pressure acting on the caisson has a triangular shape. The response of horizontal acceleration, displacement, settlement, and rotation angle of the caisson in the CES is smaller than that in the CSS, which means the caisson in the CES has a better seismic performance. Furthermore, the out-of-phase phenomenon between dynamic earth thrust and inertial force in the CES is more obvious than that in the CSS, which is beneficial to reduce the lateral force and improve the stability of the caisson structure.