NATURAL PROCESSES AS JUSTIFICATION FACTORS FOR DECISIONS ON PORT HYDRAULIC STRUCTURES

Abstract

The effects of sea waves and currents on harbour hydraulic structures are analysed from published open source data and the characteristics of scour from waves, including tsunami waves, are considered. Local bottom scour threatening the general stability of gravity-type engineering structures can arise under the effect of storm waves and currents, jets from ship propulsion devices and tsunami waves near hydraulic engineering structures. The types of scour mechanisms from sea waves have been investigated, i.e., local, general, and overtopping scour. There is a lack of sufficient measurement data for general scour to verify the calculation methods. Generally, general scour does not damage a structure, although it can contribute to its destruction by other types of scour when they overlap. Therefore, existing studies mainly focus on the analysis of local scour. The relationship between local scour and ground liquefaction and their influence on the stability of marine hydraulic structures is established. Failure mechanisms of hydraulic structures due to erosion by tsunami waves are analyzed: leeward and seaward toe scour, crown armour failure, parapet wall failure, sliding failure. The tsunami wave scour enhancement parameter is given, which is the fraction by which the pore pressure gradient reduces the frictional forces resisting scour. Significant ground instability occurs when the scour amplification parameter Λ exceeds a value of 0.5 (Λ ≥ 0.5). The parameter Λ can be used to assess areas where instantaneous liquefaction may be responsible for scour and sediment movement and to further recalculate erosion depths obtained without considering liquefaction. Liquefaction from a tsunami wave may penetrate up to 28% of the maximum erosion depth due to shear forces. The liquefaction phenomenon may occur due to a sudden drop in the water level in the area of return flow concentration. Consequently, the liquefaction phenomenon must be considered in the stability and erosion analysis around the structure.