Abstract:
Bangladesh is a densely populated country with a 32% coastal area. Many coastal regions of Bangladesh have very soft to soft soil with poor geotechnical properties such as very low bearing capacity, high compressibility, great susceptibility to volumetric change, and a very long time of consolidation. Soft soils are categorized as problematic soils, and Geotechnical Engineers have always struggled with Construction on soft soils. In order to use soft soils for engineering applications, it is necessary to treat them first. Construction on problematic soils is possible by applying suitable ground improvement techniques.
High Vacuum Densification Method (HVDM) is an innovative ground improvement technique to treat saturated soft soil in a cost-effective and time-efficient manner. It is based on the combination of the two processes of Vacuum Consolidation and Dynamic Compaction to improve saturated soft cohesive soil. In the HVDM technique, the vacuum helps to generate negative pore pressure, and dynamic compaction helps to generate positive pore pressure in the soil. The negative and positive pore pressure in the soil creates a lateral pressure gradient, and this pressure gradient helps to accelerate the consolidation process.
In this research, an experimental investigation of HVDM was carried out in a physical model. In this model, all associated arrangements of field execution of HVDM were simulated. The experiment was carried out on the collected sample after numerous trials on the physical model. Also, the pore pressure and settlement were measured during the investigation and compared with field results. After the successful execution of the HVDM experiment in the physical model, undisturbed samples were collected by Core Cutter Method for conducting consolidation, Direct shear, Triaxial CD, and UCS test. Also, remolded samples were made at the same density and moisture content to compare with HVDM-treated samples.
After the successful execution of HVDM, it was found that 94 % compaction was achieved in the physical model. The UCS test shows that the HVDM-treated sample achieved 37 % greater unconfined compressive strength than the remolded sample. Also, the Triaxial CD test shows that HVDM treated samples have 38 % greater deviator stress and 66 % greater cohesion than the remolded sample. Comparing Consolidation, Triaxial CD, Direct shear, and UCS test results of HVDM treated with remolded samples, it is seen that the HVDM treated samples were stiffer and achieved greater strength than remolded samples. The visual evidence, settlement, and pore pressure curve of the HVDM experiment are proof of rapid consolidation, maximum density, and a remarkable change in the stiffness of HVDM-treated soil.
Finally, it can be concluded that the HVDM is a cost and time-effective ground improvement method. The desired stiffness can be achieved within a short time run of HVDM.
