No abstract

In order to investigate the performance behavior of soft ground improvement using different vacuum consolidation methods (VCM) and different PVD thicknesses, four trial sections namely C1, C2, D1, and D2 were constructed. VCM without airtight membrane using cap drains and direct tubing system (VCM-DT) were used for the first two sections with PVD thickness of 3 mm and 7mm for C1 and C2, respectively. VCM with airtight membrane and band drains (VCM-MB) were applied for the last two sections for D1 and D2with PVD thickness of 3 mm and 7 mm, respectively. The soil conditions, construction procedures, instrumentation program, and monitored results of the above trial sections are presented in this paper. The results confirmed that the effective vacuum pressure in PVD mainly depends on vacuum consolidation methods and the assumption of uniform distribution of vacuum pressures along the PVD depth which can be suggested for practical design. For VCM-MB using PVD thickness of 3 mm arranged in triangular pattern of 0.9 m spacing, the degree of consolidation of more than 90% can be achieved in less than 8 months of vacuum pumping. However, for VCM-DT, further investigation is needed for preventing air leakage in vacuum system particularly for the case of thick soft clay deposits with large deformations during the preloading.

Multiproxy analyses including grain size, total organic carbon (TOC), total sulfur (TS), total nitrogen (TN), calcium carbonate (CaCO3) contents, diatom as well as sedimentary properties of the boring core KM-11 (54 m in length) collected from a brackish lake, Lake Kamo, are used to reconstruct paleoenvironment and coastal evolution of northeast coast of Sado Island in central Japan. Anoxic and normal marine sediments can be detected by TOC-TS relationship, and the origin of organic matter is inferred from the TOC/TN ratio. Geochemical characteristics of the sediments respond striking to sea-level change. In the Late Pleistocene, fluvial sediments are characterized by high TOC, very low TS and terrigenous organic matter. The overlying coastal marsh sediments are characterized by high TOC and abruptly increasing trend of TS suggesting sea water spilled into the site, and are overlain by estuarine sediments which obviously indicates the beginning of the Holocene transgression. Embayment sediments are characterized by low TOC, marine organic matter and low productivity condition indicating the rapid relative sea-level rise. The maximum Holocene transgression could be inferred between 6,500 and 5,000 yrs BP. After that fluctuations of relative sea-level are characterized by high TOC, high TS, a mixed type of marine/terrigenous organic matter and high productivity condition to be inferred marine/brackish lagoonal sediments. Diatom floral changes of the core KM-11 also support the geochemical data to interpret the paleoenvironment and evolution of the coastal deposits.

The aim of the study was to know a trend of mechanical behavior and geotechnical properties; applied for, calculating the mechanical behavior of the ground, planning the infrastructure, specially the traffic system and port, and building a rational investigated-procedure by combinations of in-situ tests, sampling and laboratory tests. Sedimentary environments of the CLM1 core at Caolanh city, Mekong River Delta (MRD) were reestablished based upon the deposit properties. Investigate the geotechnical properties and origin of the formation of them. CLM1 core site which has seven facies; each facies has presents a typical sequence of the geotechnical properties. Post-depositional processes have important role in formation of geotechnical properties.

The aim of the study is to find out the changes of geotechnical properties of the Holocene sediments that formed in the delta plain of the Mekong River. Giong Trom, Ben Tre province is chosen as a case study to investigate. Simultaneously, the changes of the geotechnical properties were compared with the sedimentary changes of the previous research results. The results of this study were applied for calculating the foundation of structures and planning the infrastructure of the area.