LAUSR

Abstract Increased traffic volume in China has made it necessary to increase road capacities by widening embankments. Some of these widened embankments are located in thick soft ground that requires extra improvement beforehand. This paper presents a case study using the combined vacuum and surcharge preloading method to improve the thick soft clay foundation for an embankment widening project in Lianyungang, China. The soil improvement procedure used the combined vacuum (approximately 85 kPa) and surcharge (4.8 m in height) preloading method, the instrumentation scheme was first described and field monitoring (including the longitudinal crack along the current embankment) was also performed. After the combined vacuum and surcharge preloading, the ground settled more than 1.4 m, the average consolidation degree was more than 90%, and the cone and sleeve resistance of the soft clays increased by approximately 2–10 times. The water content, void ratio, and compression coefficient were significantly reduced while density, compression modulus, and cohesion increased substantially. These findings can be used to guide the design of the combined preloading method of the embankment widening project along the east coast of China.