Intrinsic compression behaviour of an expansive clay from Western Australia is investigated using the intrinsic framework in this study. Oedometer results conform with the intrinsic concept at post-yield phase. However, there is a great impact of initial water content on the compression curves at pre-yield stage. It specifies that there is an initial structure similar to a natural clay structure which resists applied forces at this phase and it is related to the amount of initial water content at the preparation stage. Nonetheless, this interparticle bonding is demolished when vertical stress becomes greater than remoulded yield stress. The findings also show that the remoulded yield stress of a reconstituted clay decreases non-linearly with the increase of initial water content, and is remarkably affected by its clay mineralogy. The remoulded yield stress of a soil with the predominant clay of smectite is far greater than those of other clay minerals despite having the same normalised initial void ratio value ( 0 ⁄ ). Moreover, remoulded yield stress of an expansive soil with main clay mineral of smectite decreases more abruptly than for other clay minerals reported in the literature. Reconstituted compression indexes ( * , 100 * ) for clays with a considerable amount of smectite are also greater than respective values for other clay minerals.
Twenty-four direct shear tests were conducted on remolded/reconstituted specimens to study the effect of initial water content on the undrained shear strength of expansive clays. The laboratory tests illustrate that the shear behavior of the studied clayey soil is dependent on both the confining pressure and the initial water content at which the specimen was prepared. In fact, the undrained shear strength decreases with increasing initial water content. Similarly to the compression behavior, the intrinsic concept can also be used to predict the undrained shear strength of the studied soil. Additionally, the relationship between the void index, which is a normalized invariant of void ratio, and the undrained shear strength can be defined uniquely by a straight line. The experimental results also show that the normalized undrained shear strength, which is defined as the ratio of the peak undrained shear strength to the normal stress, varies with the initial water content from 0.25 to 0.50. Moreover, a decreasing trend is found for the range of pre-consolidation stress between 50 and 400 kPa.
Measurement of the compression indexes of clayey soils, particularly reconstituted clays with a high initial water content, is generally time-consuming and costly. A mitigation of these constraints could include a correlation between the compression indexes and the consistency limits of the clay soil that can be measured reliably. In this paper, the time-tested concepts of intrinsic framework and normalisation methods were used to derive a correlation between the compression indexes of reconstituted clays and the soil void ratios at consistency limits. The proposed method is based on the assumption that a unique relationship exists between consolidation pressures and consistency limits. Furthermore, the equation was simplified to estimate the compression index as a function of consistency indexes. Then, the equation was validated via comparison with a wide range of results reported in the literature regarding various types of clay. Results of this comparison suggest that there is an exclusive relationship between compression index and consistency limits for reconstituted clays.
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