Suitability of Engineering-Geological Environment on the Basis of Its Permeability Coefficient: Four Case Studies of Fine-Grained Soils.

Marian Marschalko,Jolanta Dąbrowska,Dominik Niemiec,David Neuman,Zofia Zięba,Jakub Mońka

doi:10.3390/ma14216411

Abstract

The aim of the article is to compare two classifications systems of engineering-geological environment sustainability in terms of its permeability evaluated on the basis of permeability coefficient. The first evaluated classification assumes a permeable environment to be a positive characteristic in the engineering-geological assessment, while the other considers an impermeable environment as favourable. The four fine-grained soil materials were selected, as they had very similar, almost identical grains-size distribution, but different microstructure characterized by grains sphericity, angularity, and roughness. At the same time, the influence of changes in the density of soil materials (density index 10%, 30%, 60%, 90%) was analysed. Permeability coefficient was determined using six methods (empirical formulae, laboratory and microscopic analysis). The laboratory method falling head test (FHT) was taken as a reference test that reflected the actual water flow through the soil. It was found that with an increase in grain angularity and roughness (and a decrease in sphericity), the permeability coefficient was decreasing and this trend culminated along with gradual compaction. Moreover, the research shows that unsuitable methods may classify soil materials into wrong engineering-geological permeability classes, which may have negative consequences during engineering-geological or geotechnical assessment and cause subsequent problems in foundation engineering.

Highlights

An important factor in engineering geology is the permeability of the geological environment [1,2,3,4,5,6,7] which subsequently influences a number of boundary conditions in foundation engineering
The results show that grain sphericity, angularity, and roughness in fine-grained soils are very important parameters of foundation soils affecting the permeability expressed by permeability coefficient
The difference in the permeability coefficient between the most spherical grains of glass microbeads was four-fold in comparison with the most angular and roughest fly ash

Summary

Introduction

An important factor in engineering geology is the permeability of the geological environment [1,2,3,4,5,6,7] which subsequently influences a number of boundary conditions in foundation engineering. There are many methods of determining the permeability coefficient, but they may be generally divided into in-situ tests (i.e., pumping and borehole permeability tests), laboratory tests (i.e., constant water head test, falling water head test, capillary permeability test), empirical and predictive methods. Each of these groups has its advantages and disadvantages. Empirical formulae, which are widely used, are based mainly on the grain-size of soils and their use, easy and quick, is subject to significant errors Often these formulae, based only on grain-size diameters, do not take into account the relationship between porosity, compaction, specific surface area and permeability coefficient [17,18,19,20,21,22]

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Conclusion