Abstract: A series of 1-D consolidation tests were carried out for soft clay with different over pressure ratios(OPR) and different preloading durations.It was found that longer surcharge preloading duration could make the total magnitude of deformation of soft clay larger,and the more surcharge preloading duration and the larger OPR,the less magnitude of secondary compression deformation of soft clay after unloading was,compared with that under permanent pressure loading.For the purpose of finishing secondary compression deformation of soft clay early,too large OPR was not necessary.The calculated results from one construction site indicated that shorter OPR also could satisfy the demand of control settlement when surcharge preloading duration was longer.