To determine the design shear strength of seabed, the method by unconfined compressive strength with the combined use of triaxial CU test (combined method) had been proposed. The combined method was used in 4th runway project of Tokyo International Airport and in the construction project of breakwater in Sakai-Minato Port. In the 4th runway project, it was found that the quality of high plastic clay taken by fixed piston thin wall sampler or Denison type triple tube samplerr was fairy good and that the combined method was effective to avoid the underestimation of strength of low plastic clay. In the case of Sakai-Minato Port, although the breakwater had been constructed on improved ground previously, the breakwater could be constructed without any improvement, because the strength of intermediate soil was evaluated correctly by the combined method.

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Time-dependent deformation is important subject in geotechnical engineering where in long-term behavior is concerned. Time-dependent deformation is defined as development of shear- and/or volumetric deformation under a constant state of stress which can lead to long term settlement. In this paper, an experimental program is carried out to investigate the effects of stress levels on creep behavior of sandy clay soil. One-dimensional oedometer single stage and stepwise tests are carried out under single drainage condition on dried and water-saturated sandy clay soil at different stress levels, and the test results are explained using the coefficient of secondary compression (Cα) and compression index (Cc). In this study, it is assumed that the time-dependent deformation begins at the end of primary consolidation when the excess pore water pressure is completely dissipated. The experimental results indicate that at low stress level, large amount of time-dependent deformation is occurred in water saturated samples, and with increment of stress level, time-dependent deformation rate decreases, but in dry samples with increasing stress level time-dependent deformation rate increases. There is an approximately linear relation between the void ratio and the logarithm of effective axial stress, and the compression index (Cc) of the saturated sandy clay samples is higher than that of the dry sandy clay samples.

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The consolidation characteristics of soft sediment dredges from Newark bay area, New Jersey, is investigated through seepage induced consolidation test device. In this paper the seepage induced consolidation test device was constructed and used to evaluate compressibility and permeability behavior of fine, low density sediments. Conventional consolidation tests usually involve restrictive assumptions on the amount of strain, hydraulic conductivity and coefficient of consolidation which makes them impractical dealing with soft sediments at low stress levels. The soft nature of dredged material and mine tailings hinders using conventional consolidometers for testing purposes. It is difficult to test the compressibility and permeability of these types of sediments at low effective stresses. Therefore a consolidation cell, based on seepage force was constructed based on seepage induced consolidation tester (SICT) at University of Colorado at Boulder and the consolidation characteristics of soft sediments dredged from seabed is investigated. Results of this research program showed that this method of testing is applicable to the soft sediment consolidation testing and provides reliable and repeatable results.

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Determination of undrained shear strength Su and sensitivity St of soft soils and sediments are important in geotechnical design as well as in sediment management. Usually these properties are deduced from laboratory or field tests. In lab, vane shear test (VST) is commonly used in clayey soft soils. Other testing is available such as the full flow penetrometers mainly used for in situ offshore engineering and for centrifuge modeling applications. Among them, the T-bar test (TBT) is not really used in geotechnical lab at 1 g level in small layers of soft soils put in containers. This paper deals with measurement of undrained shear strength (Su) of soft clays (kaolin clay) and dam sediment under conditions of natural drying, consolidation and drainage, using two different methodologies, namely T-bar and vane shear tests. Vane shear test is a standard test for Su measurement but not applicable for obtaining a continuous profiling of Su versus depth and it provides rather discrete measurements. Hence T-bar test has been used to observe a continuous phenomenon during shearing. Many studies have been reported comparing standard vane shear and T-bar tests to ensure applicability of the latter. Two different types of soils was tested to check the repetitiveness of testing and to validate previous works performed on Su measurement of kaolin clay using T-bar tests.Besides, in order to measure remolded shear strength, the vane is rapidly rotated through several revolutions until the clay becomes remolded. Again the same procedure is followed to measure the remolded shear strength. The ratio of two shear strengths measured (i.e. peak strength and remolded strength respectively) gives the sensitivity St. In addition to this, for comparative studies of TBT and VST, the methodology involves the rotation of vane blade 90 degrees anticlockwise and then 90 degrees clockwise. Although, this method is not usually used for VST testing, it enables to compare Su measured in anticlockwise rotation with the downward movement of T-bar. Likewise, Su is measured during clockwise rotation with the upward movement of T-Bar. In order to obtain compatibility between measurements made with T-bar and vane shear tests, it is interesting to study the ratio of measurements made by both tests. So, in order to do that, the peak value of each curve from vane shear test is compared with the average value of Su measured by T-bar test along the depth of blade insertion. This practice is appropriate for comparison because Su has been assumed as uniformly distributed over the entire height of the vane. So, in order to test the suitability of the comparison, the above practice is followed for all tests in kaolin clay and dam sediments. But still, it was interesting to observe the average of the ratios measured by different numbers of tests in kaolin and dam sediments and to compare them in order to see the applicability of the tests for different types of soils. So, average values of ratio (r), r = Su (VST)/Su (TBT) are proposed. All test results are reported and discussed in the paper and conclusions are given.

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Ultra-soft clay generally has properties such as a large water content, a large void ratio, a large liquid index, companied with physical properties of a small coefficient of consolidation, a low soil strength and a small inner friction angle in quick-shearing test. Under a preload of 80 kPa, the ratio of settlement to soil height reaches 50%, much larger than that for common soft soil. When the consolidation pressure is less than 200 kPa, large changes occur in deformation and void ratio accompanied with a large consolidation rate. When the consolidation pressure exceeds 200 kPa, the rate of change for deformation and void ratio variation tends to be slow.

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The rheological behavior of clayey soil with high water content was studied by using vane shear and viscometer tests. This paper establishes correlations of rheological properties measured by these testing methods, focusing on three aspects: influence of the shape of rotational spindle, i.e., vane and cylinder, the boundary effect of the specimen container and rotational speed (shear rate). It is found that the shape of the rotational spindle and rotational speed have great influence on the rheological properties, such as yield stress and viscosity.

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In this research, the physical properties and stress paths of commercially available Malaysian kaolinite silts have been made available for laboratory testings. Properties and behavior of the kaolinite silts with varying clay contents have been studied in terms of particle size distribution, Atterberg limits and consolidated isotropic undrained (CIU) triaxial tests. Through understanding the physical and mechanical properties of the kaolinite silts, the results will form baseline data for the study of riverbank soils of Sarawak, which are dominated by similar high plasticity soft silts. Linear but inversely proportional relationships have been established between the effective angles of internal friction and the Atterberg limits. Hence, the designers may use the established equations to estimate the preliminary effective angle of internal friction if the only available data is Atterberg limits.

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