Determination of characteristic values for marine clay
Recently, limit state design (LSD) in geotechnical engineering has been developed through LRFD in North America and Eurocode 7 in Europe. LRFD is an approach that estimates resistance by design model and that multiplies resistance factor by calculated resistance to reflect the uncertainty of materials and design models. Whereas, Eurocode 7 employs the partial resistance factor applied directly to each variable in resistance equation that individual soil properties such as cohesion and angle of internal friction are applied. Current methods of estimating characteristic value were discussed with the marine clay of Korea within the framework of characteristic value which has globally argued during the processing of development of Eurocode 7 for geotechnical design. Estimation of characteristic value, an issue of this dispute, affects not only determination of design value applied directly to design of geotechnical structures, but also economic feasibility and stability following results of design. In this paper, the characteristic values for main marine clay were calculated and compared with using some methods proposed. As a result, it was appeared that most of the computed values were close to mean value and less conservative in the order of Student/Ovesen, Schneider and EN 1990. In case of EN 1990 approach, however, it was inappropriate to assess geotechnical design value being calculated less than zero with statistical variability. Also, it was found that current methods have trend of estimating more conservative characteristic values when larger in ground variability.
Determination of characteristic soil values by statistical methods
According to new European standard, EC 7, characteristic values are the fundamental input data for geotechnical verifications using the concept of partial safety factors. Characteristic values have to be determined for impacts as well as for soil properties. Although, European standard, EC 7, and German supplementary rules, specified in DIN 1054, give a consistent definition of characteristic values of a soil property, first experiences with the concept of partial safety factors have shown some problems with the interpretation of these definitions. Besides, the geotechnical expert has significant discretion in the determination of characteristic soil values and this influences the results of geotechnical verifications. If results of field- and laboratory tests are available in an adequate sample size, statistical methods are an effective tool to determine characteris- tic soil values in a verifiable way and to get best possible information from realized site investigations. The following paper points out simple statistical methods and gives recommendations for their practical application. All procedures are demonstrated with the help of examples.
Silica in Soils1
Publisher Summary Silica in free and combined forms is a dominant component of the solid material of many soils, and dissolved silica is commonly a major solute of soil solutions. Breakdown of primary silicates, translocation of silica in solution, and deposition of secondary silica-containing substances are involved in the development of soils. Ions essential for the growth of plants are released to the soil solution as silicates weather, and these ions may be held against leaching at exchange sites on other silicates. Silica is absorbed in appreciable quantities by some plants and is returned to the surface of the soil as the plants decay. The nature and transformations of silica and silicates in soil are, thus, fundamental to an understanding of many aspects of soil and plant sciences.