The development of urban underground space is a critical way to alleviate the lack of urban resources, and improve environmental conditions as well as residents' quality of life, which has important practical significance. As the most densely populated and economically developed areas, coastal cities face many challenges in underground space development owing to their unique environmental geological conditions. This study examined the current situation of underground space development, academic research, technology application, evaluation methods, planning, and legislation in coastal cities in China. On this basis, it analyzed the future development trends, and presented reasonable suggestions for the critical scientific and technical problems faced by the development of underground space in coastal cities. The key suggestions are as follows: it is necessary to define and clarify the critical geological issues, distributions, and hazards that affect underground space development and major engineering construction in coastal cities; the land‐sea integrated detection technology for sea crossing bridges and submarine tunnels needs to be studied; in evaluating the suitability of underground space in coastal cities, the land and sea area evaluation factors should be integrated; and the evaluation system of land‐sea integration needs to be established.

Background: With the increased frequency of extreme weather, landslides induced by extremely heavy rainfall pose a major threat to human lives and property safety. In July 2020, a landslide occurred in the strongly weathered Laoshan Scenic Spot in Qingdao, China, and a short period of heavy rainfall was the main factor inducing the landslide. Method: Based on the similarity criterion, three groups of laboratory model tests under different extreme rainfall conditions were conducted using a large landslide model test box. The rainfall infiltration responses under different rainfall intensities, deformation processes, and failure modes of the slope were analyzed. The inducing mechanism and rainfall disaster process of granite landslides induced by extreme rainfall in strongly weathered areas were summarized. Result: The results showed that (1) a completely weathered granite landslide induced by rainfall had four stages, i.e., infiltration erosion, surface deformation, damage deepening, and overall instability, and the landslide was characterized by "sheet slip". (2) With greater rainfall intensities, the rainfall infiltration rate was higher, the changes in soil pressure, pore water pressure, water content, and matrix suction were faster, and the hysteresis effect was weaker. (3) A certain spatial distribution pattern was observed between slope deformation/damage and rainfall infiltration, and the research results could provide references for landslide warning and treatment in strongly weathered granite areas.

Rainfall is the main factor inducing landslides. Clarifying rainfall-induced landslides’ mechanisms and establishing adequate warning and prevention measures are crucial for regional disaster prevention and sustainable development. The weathering degree of fully weathered granite slopes is high, and the engineering mechanics property is poor, so it is easy to lose stability under extreme rainfall conditions. In this paper, the Fanling fully weathered granite landslide in Laoshan Scenic Spot in eastern China is taken as the research object, and the fluid–solid coupling landslide numerical model is established using ABAQUS 2022. The numerical simulation is carried out under five different rainfall intensity and time conditions, and the seepage field response, deformation response, and stability of the slope are analyzed. The research results indicate that (1) the fully weathered granite landslide in Fanling is a thrust-type landslide, and the response of horizontal deformation is greater than that of vertical deformation. (2) Compared with a long-term small rainstorm, a short-term heavy rainstorm is more harmful, and the slope is more prone to instability and damage. (3) The established unstable and under-stable rainfall warning curves for fully weathered granite landslides can provide a reference for the warning and prevention of similar regional landslides.