Bojana Dolinar

CORRELATION BETWEEN SURFACE AREA AND ATTERBERG LIMITS OF FINE-GRAINED SOILS

As the water content is increased, the consistency of a fine-grained soil changes from a semi-solid state to a plastic state and finally to a liquid state. The plastic limit (PL) is the point at which the consistency, caused by the soil water content, is transformed from a semi-solid state to a plastic state. The liquid limit (LL) is the point at which the consistency is transformed from a plastic state to a liquid state. The plastic limit and liquid limit are often collectively referred to as the Atterberg (or consistency) Limits. Although the liquid and plastic limits are easily determined, fundamental interpretations of the limits and quantitative relationships between their values and compositional factors are more complex. Previous studies examined artificially-prepared soil samples that contained monomineralic clays and a non-clay substance(quartz sand). These studies have shown that in soils without expandable clays the PL and LL water contents were mostly related to surface area and clay content. For soils that contain expandable clays, the PL and LL values are also dependent on interlayer water content. Hence, expandable clay mineral contents are needed to calculate PL and LL values. These relationships have been presented in a general analytical form. The aim of these investigations was to identify practical applications. Mineral compositions and surface areas of five randomly selected natural soil samples were used to estimate PL and LL values. The estimated values were compared to experimentally measured liquid limits (by the ‘fall-cone’ test) and plastic limit (by the ‘rolling thread’ test) values. The measured PL values ranged from 18.77 to 44.92% and the LL values from 31.19 to 82.10%. The differences between estimated and measured Atterberg Limits were 3.0–7.1% for thePL and 2.7–7.8% for the LL. Minor differences in measured and estimated Atterberg Limits were probably due to soil organic matter (1.2–2.7%).

Liquid Limit and Specific Surface of Clay Particles

In this paper a new method for determining the liquid limit of nonexpanding soils is presented. The liquid limit value primarily depends on the type and quantity of clay minerals in soils. This relationship, however, has never been presented in general analytical form that would enable a consistent determination of the influence of mineralogical properties of different soils on the liquid limit. The findings described in the article define those mineralogical properties of soils, which determine the quantity of water at the liquid limit. It was found that the water content at the liquid limit depends on the size and the quantity of clay grains in soils that contain only nonexpanding minerals. In case of expanding minerals in soils, the size and the quantity of clays determine only the quantity of intergrain water, while the total water content depends on the quantity of interlayer water also.

NLP Optimization Model as a Failure Mechanism for Geosynthetic Reinforced Slopes Subjected to Pore-Water Pressure

AbstractThe majority of slope failures are triggered by excessive rainfall and the consequent increase in pore-water pressure within the slope. This paper presents the results of a computer code that quantifies earth pressure coefficients. This code is based on limit-equilibrium analyses and is used for the internal design of geosynthetic reinforced soil structures and to identify the critical failure mechanism. The critical failure mechanism is the largest value of out-of-balance force. For this purpose, the nonlinear programing (NLP) approach was used, and a NLP optimization model, TMAX, was developed. The model was used for failure mechanisms, assuming that the failure surfaces were bilinear. The influence of pore-water pressure on the potential failure surface was analyzed. The model was developed under basic principles. Optimally, the system is best suited for structures with varying geometries, different backfill unit weights, varying types of soil shear resistance, and different pore-water pressure...

Prediction of the soil-water characteristic curve based on the specific surface area of fine-grained soils

This paper presents a new, mathematical expression for describing the soil-water characteristic curve (SWCC) over a range of water contents where fine-grained soils exhibit plastic properties. The finding that the relationship between the soil suction and the water content can be expressed in terms of the specific surface area of soils was based on experimentally determined relationships between the water content and the soil’s specific surface area, as well as between the thickness of the adsorbed water layer on the external surfaces of clay minerals and the quantity of free-pore water for the water content between the liquid and plastic limits. The double-porosity model for the pore-space geometry was considered, as well as that all the water in the clay-aggregates is adsorbed, and that the adsorption mechanism is dominated by the van der Waals forces. The validity and applicability of the proposed equation for the SWCC estimation was verified on three samples in which the SWCC was measured, as well as the specific surface area, the mineralogical and chemical compositions, the grain size distribution, and the Atterberg limits. Despite the fact that good correlations were found between the calculated parts of the SWCC and the measured, the practical applicability of the proposed equation remains problematic due to the values of Hamaker constant, which are not yet well defined for different minerals.

A new relationship between the mobile and the adsorbed water in fine-grained soils using an effective void-ratio estimation

Firmly adsorbed water on the surfaces of clay minerals and the water that fills the unconnected and dead-end pores in saturated fine-grained soils is immobile, which means that it cannot impact on the hydraulic conductivity of these soils. Therefore, only the volume of the voids occupied by mobile water is important. This volume can be expressed as the effective porosity or the effective void ratio. In the past, many methods were proposed to determine these values: however, the obtained values varied, leading to a difference in the proposed correlation with the saturated hydraulic conductivity. This article describes a process for determining the effective void ratio and has a completely different basis to so-far suggested procedures. Determining the volume of the mobile and immobile water in the saturated fine-grained soils assumes that the quantity of the mobile water and the thickness of the adsorbed water film on the external surfaces of the clay grains are equal at the same effective stress. The total quantity of adsorbed (immobile) water on the external surfaces of clay minerals in this case depends on their size and quantity in the soil’s composition. On the basis of the determined quantities of immobile and mobile water, the ineffective and effective void ratios are calculated. The results show that the interdependence between the total void ratio and the ineffective void ratio is linear, which allows for a simple calculation of the effective void ratio. However, it should be taken into consideration that this expression can only be used for soils that do not contain swelling clay minerals. The evaluation of the hydraulic conductivity of the soils using effective void ratios, determined with the proposed method, shows good agreement with the measured values.