Hanène Souli

Effect of lime on some physical parameters of a natural expansive clay from Algeria

Over the last three decades, highly plastic soils have been one of the major sources of problems in roads, railways and buildings in Algeria. In these cases, soil treatment is essential to improve the engineering properties of these materials. The aim of this article was to study the effect of added lime on the physical properties of soil. Experiments were performed on a local natural clayey soil in order to investigate the influence of lime on consistency limits, total specific surface, compaction characteristics, swelling potential and swelling pressure. In addition, mercury intrusion porosimetry tests were carried out to determine the pore size distribution of the untreated and treated samples. The results show that the liquid limit decreases, the plastic limit increases and the total specific surface area decreases with the percentage of added lime. Compaction characteristics are affected by the addition of lime, the optimum water content increasing and the maximum dry unit weight decreasing in the presence of a high amount of lime. This stabilisation method leads to significant reductions in the swelling of the studied soil, exceeding 60%. The treatment with a high percentage of lime significantly reduces the average pore diameter of the treated clay.

Determination of the maximum diameter of free fines to assess the internal stability of coarse granular materials

In granular soils, suffusion may occur only if three conditions are met: (i) the hydraulic gradient is high enough; (ii) the fine particles are not blocked by the constrictions of the larger ones; and (iii) the fine particles are free to move, i.e. they are not prevented to move by a steric condition. The aim of the paper is to determine the maximum diameter of the particles for the third condition, which are called the “free fines”. Three methods are examined: (i) the direct measurement of the bulk volume of binary mixtures of fine and coarse grains, (ii) the method proposed by Ghafghazi and Azhari in 2012 and (iii) a new method based on the calculation of the fine content for which the fines fill the voids between the coarse grains. Some methods, proved difficult to apply in practice, whereas the new method appeared consistent with the available experimental results. In particular, the method permitted to predict the results of flow tests carried out on binary mixtures of glass balls as well as gap-graded granular materials or materials with continuous grain size distributions.

Analysis of the internal stability of coarse granular materials according to various criteria

Flow tests under high hydraulic gradients were carried out to estimate the internal stability of various granular materials with grains ranging from .08 to 16 mm. Twenty grain size distributions were tested, either continuous or discontinuous (gap-graded). After the tests, the materials were separated into three layers and the grain size distribution of each layer was measured. The soils were classified as stable if the maximum difference between the passing percentages of the upper and lower layer did not exceed 5% and as unstable otherwise. The experimental data were compared with the results given by some internal stability criteria which are obased on very different approaches. The same method was applied to about 40 soils from the literature. It was found that the simple criterion of Kézdi, which consists in separating the soils into ‘coarse’ and ‘fine’ fractions at different values of the diameter and applying Terzaghi filter rule to the two fractions, led to global agreement with the experimental data, whereas the two other criteria gave unsatisfactory results. However, a few differences were noted between Kézdi classification and the results of the tests, showing the need for further research, especially in one case (over 65) where the soil was classified as stable and proved unstable.

Durability of Bioclogging Treatment of Soils

A study of the clogging of two soils, a sand with grains ranging from 0.4 to 4 mm, and a gravel with grains ranging from 1 to 10 mm, was carried out by feeding the bacteria initially present in the soils. The focus of this research is to study the durability of bioclogging. The results showed that clogging occurred quickly after the injection of nutrients. The soils were subjected to gradient increases and a critical hydraulic gradient i(crit) (corresponding to the gradient for which unclogging occurred and an increase in the flow of water was observed) was determined. It is equal to 0.8 for the sand and to 0.06 for the gravel. The durability of bioclogged soils was also studied by performing 10 to 30 hydraulic gradient cycles between the initial value and i(crit)/2. For the sand, the permeability increase after the cycles was very low. In contrast, in the gravel, unclogging occurred very quickly, highlighting the influence of grain size and materials grading

Using an Improved Jet-Erosion Test to Study the Influence of Soil Parameters on the Erosion of a Silty Soil

AbstractA new jet-erosion test device has been developed to measure the erosion volume of soils under laboratory conditions. This device allows the determination of a complete erosion profile in ad...

Relationships between the internal erosion parameters and the mechanical properties of granular materials

Abstract Granular soil in construction of earth works can be solicited by hydrodynamic and mechanical forces. Fine particles constituting these soils may be eroded by the flow leading to a modification of their mechanical behaviour. Classically, the susceptibility of granular soils to internal erosion is assessed by internal stability criteria. In this paper, numerical modelling using discrete elements method is performed to study the mechanical behaviour of eroded soils on triaxial paths. Soils samples were generated according to known particle size distribution and void ratio. Triaxial test have been simulated on samples with the same initial void ratio and same confining stress. Relation has been established between soil mechanical behaviour and its internal stability. Finally, taking into account the relationship between the internal erosion parameters and the mechanical properties of granular materials, a new approach to assess the soil stability has been presented.