Amin Soltani

A sulphonated oil for stabilisation of expansive soils

ABSTRACT The efficiency of a commercially manufactured sulphonated oil (SO) agent in treating a highly expansive soil was investigated through an extensive experimental program. A total of six SO to water mass concentrations, i.e. 0.25, 0.5, 0.75, 1, 1.25 and 2.5%, were examined. The test program included swell–load oedometer, unconfined compressive strength and cyclic wetting and drying tests. SO-stabilisation amended the soil’s mechanical behaviour through improvements achieved in swelling and strength characteristics. The reduction in swelling potential and swelling pressure was dependent on SO concentration, while the effect of curing time was found to be insignificant. A similar dependency was concluded for the unconfined compressive strength and stiffness of the stabilised soil. Both dependencies suggested an SO concentration of 1.25% capable of yielding an optimal stabilisation scheme. Results of the cyclic wetting and drying tests indicated that the beneficiary effects of SO-stabilisation at optimum concentration, particularly in ameliorating the adverse effects of swell–shrink-related volume changes and to some extent increasing the strength, are strongly preserved under the influence of alternate wetting and drying.

Discussion of “Compressibility Behavior of Soils: A Statistical Approach” by Syed Iftekhar Ahmed and Sumi Siddiqua [Geotechnical and Geological Engineering, doi: 10.1007/s10706-016-9996-7]

Ahmed and Siddiqua (2016) introduced a new regression-based relationship in the form of a three-parameter Weibull function, herein referred to as the 3P-W model, for modeling the compressibility behavior (i.e. the void ratio-effective stress relationship) of soils. In this discussion, important drawbacks associated with the newly proposed 3P-W model were outlined. In addition, an attempt was made to extend the practicality of the proposed model by introducing a simple analytical solution to derive regression-based equations for determining the compressibility curve variables (i.e. the recompression index, pre-consolidation pressure and compression index). The proposed analytical concept is primarily intended to replace the current conventional graphical method by providing consistent-error free results. The proposed equations in this discussion accompanied by the original 3P-W model construct a unique regression aided-analytical framework which can be employed for advance numerical simulations.

Swell–Shrink–Consolidation Behavior of Rubber–Reinforced Expansive Soils

This study examines the effects of two types of recycled tire rubber of fine and coarse categories on the swell-shrink-consolidation behavior of a highly expansive soil mixture. Each of the two rubber choices were incorporated into the soil at four different content levels (i.e., rubber to dry soil mass ratio) of 5, 10, 20, and 30 %. The experimental program consisted of consistency limits, compaction, swell consolidation, swell-shrink, and unconfined compression tests. Improvement in the swell-shrink-consolidation capacity was in favor of higher rubber contents; however, when excessively included, it raised strength concerns. The swell-shrink-consolidation properties were also rubber size-dependent, meaning that the rubber of coarser sizes often outperformed finer rubber. In terms of strength, however, the two rubber types promoted similar results with marginal differences. The results of the unconfined compression tests were cross checked with the swell-shrink-consolidation properties to arrive at the optimum stabilization scenarios. A maximum rubber inclusion of 10 %, preferably the rubber of coarser category, proved to satisfy the stabilization objectives (i.e., decrease in the swell-shrink-consolidation capacity as well as maintain or improve the strength) and thus was deemed as the optimum choice. Where context changes and the strength and stiffness are not a primary concern, higher rubber inclusions of up to 20 % may also be considered acceptable.

A Note on Determination of the Preconsolidation Pressure

The preconsolidation pressure, σ′y, is commonly interpreted by means of empirical observations (or graphical constructions) with respect to e–logσ′ stress patterns (e = void ratio, and σ′ = effective stress) exhibited in the conventional oedometer test. As with any empirical/graphical procedure, the resulting estimations are associated with subjective variability and thus yield inconsistent results among individuals. Recently, the mathematical translational technique was implemented by the authors, thereby promoting a subjective-free computational framework, denoted as the 3PRH framework, for interpretation of σ′y with respect to four common graphical constructions (i.e., three semi-log and one bi-log construction), covering a variety of geometrical complexity. In this article, the 3PRH framework was first revisited in a more practical sense. The framework was then implemented to a compiled database of 34 consolidation tests to arrive at reliable correlations/comparisons between the four graphical constructions. Finally, the settlement dependency on σ′y (or type of graphical construction) was statistically examined to recommend measures for reliable settlement analyses.

A simplified method for determination of the soil–water characteristic curve variables

Abstract The air-entry value and residual state suction are two critical variables obtained from the soil–water characteristic curve (SWCC). An accurate determination of these variables is essential for the prediction of unsaturated soil properties. Currently, these variables are obtained by a conventional graphical method, which is implemented to the fitted SWCC. The graphical method is associated with subjective uncertainty, leading to inconsistent results. This study presents a new method to determine the air-entry value and residual state suction. Explicit equations are established with respect to four common van Genuchten (vG) SWCC model classes. The relationships between the air-entry value and fitting parameters are analysed using a compiled database of varying soil textural classes. The proposed equations outperform the graphical method by avoiding subjective judgements. Finally, ANOVA and sensitivity analyses are conducted to compare the advantages of the existing model classes in determination of the air-entry value.

A Framework for Interpretation of the Compressibility Behavior of Soils

This paper aims at the development of a regression-aided analytical framework for modeling and analyzing the compressibility behavior of over-consolidated soils. A three-parameter rectangular hyperbola function (3P-RH) was proposed for describing the void ratio-effective stress relationship. Validation of the 3P-RH was carried out by a compiled database gathered from the literature. Simple analytical solutions were then proposed for determining the compressibility curve variables including the compression (C-c) and recompression (C-r) indices and the preconsolidation pressure (P-c), which are intended to replace the current subjective graphical method by providing consistent results. Equations for the preconsolidation pressure were derived in accordance with four common graphical constructions covering various levels of geometrical complexity (slightly to highly subjective). A probabilistic comparison among the graphical constructions was then carried out. Furthermore, a sensitivity analysis with respect to the proposed preconsolidation pressure functions was considered to evaluate the influence of the 3P-RH fitting parameters (alpha and beta) on the preconsolidation pressure value. The proposed 3P-RH compressibility model accompanied by the suggested analytical solutions for solving the compressibility curve variables construct a unique framework for modeling the compressibility behavior of soils with an acceptable degree of accuracy and, more importantly, by a simple objective approach.