Emöke Imre

Closed-form functions for the soil water-retention curve of sand fractions and sand mixtures

Four closed-form water-retention curve functions were validated using the previously measured water retention curve of 4 sand fractions and their 6 two-component mixtures. Out of the models of Gardner (1958), Fredlund - Xing (1994) and the simplified and non-simplified models of Van Genuchten (1980), the non-simplified model of Van Genuchten model fitted with the smallest error to the tested soils.

The Grading Entropy-based Criteria for Structural Stability of Granular Materials and Filters

This paper deals with three grading entropy-based rules that describe different soil structure stability phenomena: an internal stability rule, a filtering rule and a segregation rule. These rules are elaborated on the basis of a large amount of laboratory testing and from existing knowledge in the field. Use is made of the theory of grading entropy to derive parameters which incorporate all of the information of the grading curve into a pair of entropy-based parameters that allow soils with common behaviours to be grouped into domains on an entropy diagram. Applications of the derived entropy-based rules are presented by examining the reason of a dam failure, by testing against the existing filter rules from the literature, and by giving some examples for the design of non-segregating grading curves (discrete particle size distributions by dry weight). A physical basis for the internal stability rule is established, wherein the higher values of base

Some Comments on the Entropy-Based Criteria for Piping

This paper is an extension of previous work which characterises soil behaviours using the grading entropy diagram. The present work looks at the piping process in granular soils, by considering some new data from flood-protection dikes. The piping process is divided into three parts here: particle movement at the micro scale to segregate free water; sand boil development (which is the initiation of the pipe), and pipe growth. In the first part of the process, which occurs during the rising flood, the increase in shear stress along the dike base may cause segregation of water into micro pipes if the subsoil in the dike base is relatively loose. This occurs at the maximum dike base shear stress level (ratio of shear stress and strength) zone which is close to the toe. In the second part of the process, the shear strain increment causes a sudden, asymmetric slide and cracking of the dike leading to the localized excess pore pressure, liquefaction and the formation of a sand boil. In the third part of the process, the soil erosion initiated through the sand boil continues, and the pipe grows. The piping in the Hungarian dikes often occurs in a two-layer system; where the base layer is coarser with higher permeability and the cover layer is finer with lower permeability. The new data presented here show that the soils ejected from the sand boils are generally silty sands and sands, which are prone to both erosion (on the basis of the entropy criterion) and liquefaction. They originate from the cover layer which is basically identical to the soil used in the Dutch backward erosion experiments.

Case Studies and Benchmark Examples for the Use of Grading Entropy in Geotechnics

The grading entropy concept can be adapted to the field of geotechnics, to establish criteria for phenomena such as particle packing, particle migration and filtering, through a quantified expression of the order/disorder in the grain size distribution, in terms of two entropy-based parameters. In this paper, the grading entropy theory is applied in some geotechnical case studies, which serve as benchmark examples to illustrate its application to the characterisation of piping, softening and dispersive soils, and to filtering problems in the context of a leachate collection system for a landfill site. Further, since unstable cohesive (dispersive) soils are generally improved by lime, the effect of lime addition is also considered, on the basis of some measurements and a further application of the grading entropy concept, which allows evolutions in the entropy of a soil to be considered as its grading is modified. The examples described support the hypothesis that the potential for soil erosion and particle migration can be reliably identified using grading entropy parameters derived from grading curve data, and applied through an established soil structure stability criteria and a filtering rule. It is shown that lime modification is not necessarily helpful in stabilizing against particle migration.

Modified Grading Curve – SWCC Relations

In the ongoing research a topological interpolation method was elaborated over the N -1 dimensional space of the grading curves – represented by a N -1 dimensional simplex - using c N 2 data. The surface is selected on the basis of the grading entropy concept and the interpolated function is extended to the whole simplex by the grading entropy map. In this paper the method is further developed. The extended method is illustrated using the examples of the dry density and the parameters of the van Genuchten soil water retention function.

On the Effect of Soil Modification with Lime Using Grading Entropy

Agglomeration may take place in the presence of a cementing agent like lime. If the failure of an agglomerated body is caused by the failure of bonds then the processes are symmetric. This study shows that the effect of lime modification on the grading curve evolution in the non-normalised grading entropy diagram is basically opposite to the effect of the usual particle breakage. Both can be related to the “entropy principle” through the grading entropy concept. In the normalised grading entropy diagram the grading curve evolution path is the same except that discontinuity occurs upon the change in the fraction number. The entropy coordinate A can be used as a stability measure (i.e. in the sense that the stability increasing with A). The discontinuous change in A results in a more stable structure for breakage and less stable structure if lime is added to a small plasticity soils. In case of very high clay content the discontinuity at lime modification was stabilized.