Abstract: In airport engineering projects, there are strict requirements for the post construction settlement and post construction differential settlement in runways. The prefabricated vertical drainage method with surcharge preloading is often applied for the treatment of large soft soil areas. The spacing of the vertical drains as well as the surcharge ratio are the direct factors that affecting the quality and effect of the soft soil improvement. In the current design code for the soil improvement, the recommended vertical spacing varies between 0.7m and 2.1m with no clear theoretical recommendations on the applied surcharge ratio. Therefore, the quality and effect of soft improvement could not be guaranteed without careful engineering evaluation. In this paper, the Zouma Lake soil improvement was studied throughout the theoretical analysis and the model tests to illustrate the influence of spacing of the vertical drains and the surcharge ratio on the consolidation settlement. Based on the field settlement monitoring data, the influence effect of both factors on the soft soil consolidation was compared and analyzed, with indices of the predicted final settlement and the degree of soft soil consolidations.

Key words: soft soils, drainage and consolidations, surcharge method, post construction settlement, zouma lake project