Axis Translation and Negative Water Column Techniques for Suction Control

Negative water column and axis translation techniques are conventionally used experimental techniques for obtaining data to interpret the engineering behavior of unsaturated soils. The negative or the hanging water column technique is used as a suction control method in the low suction range (i.e., 0–30 kPa). The axis translation technique is used in the suction range 0 to 500 kPa or higher. This technique is particularly useful for testing specimens with suction values greater than 100 kPa avoiding problems associated with cavitation. While the axis-translation technique has been commonly used, the limitations associated with this technique related to air diffusion, water volume change and evaporation are not discussed in greater detail in the literature. This paper highlights some of the key aspects related to the negative water column and axis translation technique that are of interest both to the researchers and practicing engineers.     

Some remarks on the coefficient of earth pressure at rest in compacted sandy gravel

In compacted coarse-grained materials, the stress state is largely influenced by the compaction procedure and by the characteristics of the single grains (mineralogy, shape). In this work, two compacted sandy gravels with the same grading but different grain properties have been tested in a large soft oedometer to highlight this influence. In the first part of the paper, the effect of oedometric ring deformability on the stress state is quantified in the framework of elastoplasticity. It is then shown that, for the adopted apparatus and for the tests carried out, the error in the measurement of the coefficient of earth pressure at rest K ₀ caused by ring deformability is very small. The two tested materials, compacted by wet tamping, behave differently because of their different grain properties, showing, respectively, small and large grain breakage. In primary loading, the more crushable material has values of K ₀ that compare well with Jaky’s (J Soc Hungarian Archit Eng 355–358, 1944) equation at any stress level and for every tested soil density. For the material with stronger grains, only very loose specimens that have undergone little or no compaction have a similar behaviour, while the denser specimens show the typical behaviour of overconsolidated soils, with values of K ₀ initially larger than that suggested by Jaky (J Soc Hungarian Archit Eng 355–358, 1944) for normally consolidated soils, tending to it only at the largest applied stress values. By considering the complex combined effect of tamping and grain crushing on the stress state and on the overconsolidation ratio of the soil at the end of compaction, these experimental evidences have been qualitatively explained.     

Chemo-mechanical behaviour of lightweight cemented soils

Acta Geotechnica - In this paper, a multi-scale analysis of the effect of foam on chemo-mineralogical and microstructural features of the soil–cement–water system is presented....