Numerical parametric study on behavior of bearing reinforcement earth walls with different backfill material properties

This paper presents a numerical parametric study on behavior of bearing reinforcement earth (BRE) walls with different backfill properties using the finite-element method software PLAXIS 2D. The primary objective of this study was to improve the understanding of bearing stress, settlement, lateral earth pressure, and horizontal wall movement of BRE walls with different backfill materials. The second objective of this study was to evaluate the effects of various soil–structure interactions, foundations, and stiffness of reinforcements on horizontal wall deformations. The backfill materials consisted of four types of soil, which were mixtures of silty clay and sand at different fine contents of 2, 20, 40, and 80% by dry weight. The model parameters for the numerical simulation were obtained from the conventional laboratory tests and back-calculated from the laboratory pullout tests of the bearing reinforcement. The geotextile elements were used to model the bearing reinforcements by converting the contribution of friction and bearing resistances to the equivalent friction resistance, which was represented by the soil–bearing reinforcement interaction ratio, Rinter. The values of Rinter decreased following a polynomial function as an increase of fine content in the ranges of 0.65–0.38 and 0.75–0.40 for the numbers of transverse members, n = 2 and 3, respectively. The simulated bearing stress in the reinforced zone decreased from the front to the back of the wall because the BRE wall behaved as a rigid body built on the relatively firm foundation retaining the unreinforced backfill. The foundation settlement decreased from the facing of the wall to the unreinforced zone for all backfill properties due to the slight rotation of the wall. The relationship between the maximum horizontal wall movement and the fine content can be expressed by a polynomial function. The maximum horizontal wall movement significantly increased as the fine content increased. The excessive movement was realized when the fine content was greater than 45%. The increase of the fine content moved the location of the maximum wall movement higher up from the mid to the top of the wall. A numerical parametric study was conducted to investigate the soil–structure interaction, foundation, and stiffness of reinforcement. These parameters affected the horizontal wall deformation, which is especially important for serviceability of BRE walls. The knowledge gained from this study provides a preliminary guideline in predicting the behavior of BRE walls and may be used to investigate other BRE walls with different wall heights and features of bearing reinforcements

Utilising novel green binders in ground improvement applications

Special attention is being paid currently to geopolymers as novel binders in ground improvement applications. The use of industrial by-products such as fly ash (FA) and slag (S) in the synthesis of geopolymers makes these alternatives to traditional binders, such as Portland cement, sustainable binders with low-carbon footprint. Geopolymers have been studied and used in a variety of applications, such as concrete or ceramic manufacturing, with controllable conditions of production environment. There are however limited knowledge on the use of geopolymers, as stabilising binders, in ground improvement projects and lack of certainties as to how these new binders would behave in the field where varying factors such as water table or temperature could affect the strength development. This study evaluates the reliability of using a FA and S based geopolymer to stabilise a soft marine clay. The strength development and the mineralogy of the mixtures were studied. The combined FA+S contents were 10, 20 and 30%, and mixtures were prepared at water contents of 0.75, 1.0 and 1.25 liquid limit (LL). Samples were cured for 28 days at temperatures of 10, 25 and 40°C. Strength development was significantly increased by adding the FA+S content, particularly at 20% and higher. Moreover, when the water content was increased from 0.75 to 1.0 LL, strength development was enhanced, followed by a decrease at water content of 1.25 LL. Furthermore, by increasing the curing temperature, higher strengths were achieved and the strength development was accelerated. The results indicated that green geopolymeric binders could be used as reliable binders in ground improvement applications

Practical approach to predict the shear strength of fibre-reinforced clay

yesCarpet waste fibres have a higher volume to weight ratios and once discarded into landfills, these fibres occupy a larger volume than other materials of similar weight. This research evaluates the efficiency of two types of carpet waste fibre as sustainable soil reinforcing materials to improve the shear strength of clay. A series of consolidated undrained (CU) triaxial compression tests were carried out to study the shear strength of reinforced clays with 1%, to 5% carpet waste fibres. The results indicated that carpet waste fibres improve the effective shear stress ratio and deviator stress of the host soil significantly. Addition of 1%, 3% and 5% carpet fibres could improve the effective stress ratio of the unreinforced soil by 17.6%, 53.5% and 70.6%, respectively at an initial effective consolidation stress of 200 kPa. In this study, a nonlinear regression model was developed based on a modified form of the hyperbolic model to predict the relationship between effective shear stress ratio, deviator stress and axial strain of fibre-reinforced soil samples with various fibre contents when subjected to various initial effective consolidation stresses. The proposed model was validated using the published experimental data, with predictions using this model found to be in excellent agreement