Project Oufei is the largest individual reclamation project in Wenzhou city, China, and the main infrastructure consists of seawalls, sluices and separation dikes. These infrastructures face repeated horizontal forces from wind and waves; thus, it is essential to evaluate the lateral bearing of single pile used for sluice gates. This paper presents a case study on lateral monotonic and cyclic behaviour of bored piles in soft soils. Four instrumented piles were loaded monotonically and cyclically to assess the contribution of soil improvement by vacuum preloading with prefabricated vertical drains. The test results show that the ultimate horizontal capacities were 200 kPa and 100 kPa for piles in the treated zone and untreated zone, respectively, under monotonic loading and up to 220 kPa and 120 kPa for piles in the treated zone and untreated zone, respectively, under cyclic loading, indicating that the ultimate horizontal capacity of piles in the treated zone can meet the design requirement of 130 kPa. Moreover, soil improvement decreased the maximum bending moment of the bored piles and enhanced the pile head stiffness, and the influence depth of soil improvement is up to 10 m. This indicates that soil improvement by vacuum preloading with prefabricated vertical drains is effective and can be used for lateral loading in reclamation project.