| One of the main challenges that geotechnical engineers and contractors encounter is the In-situ improvement of soft cohesive soils. The importance of doing this improvement fast and economically clarifies in countries with large population and, consequently, large request of infrastructures, such as China, India, and other developing countries in Asia. The traditional techniques to improve soft cohesive soils are: (a) prefabricated vertical drains (PVDs) and fill preloading, (b) vacuum consolidation together with PVDs, (c) stone columns, (d) thermal treatment, (e) chemical mixing, (f) electro-osmosis, and (g) deep dynamic compaction. Although all of the above-mentioned techniques are available in field of soil improvement, but PVDs in combination with fill surcharge preloading method appears to be the most common used technique. Recently, the vacuum consolidation with surcharge preloading looks interesting for expediting consolidation and reducing consolidation time. In large projects like land reclamation of the dredged materials, port facility constructions, airport runways, soft soil improvement area could be considerably large, resulting in the limitation on the availability of surcharge material for fill preloading. Hence, development of more economic ways to treat soft cohesive soils in large projects, where preloading fill could not be economically found, is of interest.;In the past, the application of vacuum either alone or in combination with static surcharge loading has been utilized to facilitate consolidation in saturated cohesive soils. Though the dynamic compaction technique was introduced by Menard (1975) as a feasible technique for use in saturated cohesive soils, due to possible rubber soil phenomenon it has not been widely used to improve soft cohesive soils. Fast development of infrastructures in China leads to an innovative soft cohesive soil treatment technique in 2000, rapidly applied in advancing countries in Asia. The core of the above-mentioned treatment method has been termed as "High Vacuum Densification Method" (HVDM). This technique combines two well-known soil improvement methods consisting of vacuum consolidation and deep dynamic compaction and makes an intelligent yet efficient soft soil treatment method suitable for large areas within a relatively short time period.;The work presented throughout this research is concerned with developing a numerical modeling of HVDM in saturated/partially saturated cohesive soil using FLAC 3D with Cap-Yield and Modified Cam-Clay constitutive models with coupling fluid and mechanical together in order to achieve a better understanding of the behavior of cohesive soils under dynamic compaction and vacuum consolidation. An extensive FD parametric study conducted to investigate the influence of soil properties, operational parameters of DC, and negative vacuum pressure amplitude on the soil responses like: generation of EPWP, change of mean effective stress and surface settlement. Finally a step by step design methodology for HVDM in saturated and partially saturated cohesive soils will be presented. |
