A state-of-the-art review on loess tunnels

China's loess distribution area covers 640,000 km², accounting for about 6.6% of its land area and about 4.9% of the world's total loess distribution area. By the end of 2024, 838 highway loess tunnels with a length of 917 km and 470 railway loess tunnels with a length of 520 km had been built in China. With accumulated construction experience, China's loess tunnel construction technology has been significantly developed. There is an urgent need to systematically summarize and sort out the latest achievements and research results in the field of loess tunnels, and to form a set of strong theoretical system and effective technical support, so as to guide the design and construction of loess tunnels for high-quality projects, serve the strategy of strengthening China's transportation, expand the field of overseas engineering, and enhance the international competitiveness. The Journal of Traffic and Transportation Engineering (English Edition) invites more than 20 experts and scholars in the field of tunnel engineering to analyze the current situation and trend based on the engineering characteristics of loess, loess tunnel design theories and methods, loess tunnel construction methods and technologies, disease perception and prevention measures in loess tunnel operation and maintenance, and typical loess tunnel engineering cases and other topics. Overall, this review paper is able to provide references and insights for researchers and engineers in the field of loess tunnel engineering.