Large-scale rising bubbles exist in some extreme marine engineering fields, such as the exploitation of combustible ice and submarine volcanism. The violent splitting and coalescence process of large-scale rising bubbles with internal pressure comparable to ambient pressure differs greatly from that of the normal small-scale bubbles and high-pressure bubbles. In this paper, the complex splitting and coalescence characteristics of large-scale rising bubbles are studied with a multi-phase smoothed particle hydrodynamics approach. The effects of the arrangement of bubbles, initial centroid distance, and the ratios of bubble radii on the bubble splitting and coalescence characteristics are investigated. The results show that the arrangement of the bubbles dictates whether or not the two bubbles coalesce and influences the coalescence mode of the bubbles further. When two large-scale bubbles are arranged horizontally, the initial spacing of bubbles has minimal influence on the coalescence features, and they always bounce off each other. When the bubbles are not placed horizontally, the bubbles can coalesce in two modes: direct-absorption coalescence and penetrating reverse-absorption coalescence. When arranged vertically, the initial centroid distance affects the coalescence extent of bubbles, and when the vertical distance exceeds five times the bubble radius, the two bubbles do not interact with each other. When the leading bubble is too large relative to the trailing bubble, the large ratios of bubble radii play negative roles in the coalescence of bubbles.
