Abstract: The soft soils of a lakeside road is improved by vacuum preloading. The improvement effect is verified by the vane shear tests and static penetration tests. The in-situ test results indicate that the shear strength value after improvement is obviously promoted. Based on the relevant theory and empirical formula, a procedure for deducing the over-consolidation ratio and the effective consolidation stress from shear strength is proposed. The distribution of the effective consolidation stress with depth is in accordance with the decrease of the pore water pressure with depth.