Jamal Alsharef

Potential of Using Nanocarbons to Stabilize Weak Soils

Soil stabilization, using a variety of stabilizers, is a common method used by engineers and designers to enhance the properties of soil. The use of nanomaterials for soil stabilization is one of the most active research areas that also encompass a number of disciplines, including civil engineering and construction materials. Soils improved by nanomaterials could provide a novel, smart, and eco- and environment-friendly construction material for sustainability. In this case, carbon nanomaterials (CNMs) have become candidates for numerous applications in civil engineering. The main objective of this paper is to explore improvements in the physical properties of UKM residual soil using small amounts (0.05, 0.075, 0.1, and 0.2%) of nanocarbons, that is, carbon nanotube (multiwall carbon nanotube (MWCNTs)) and carbon nanofibers (CNFs). The parameters investigated in this study include Atterberg’s limits, optimum water content, maximum dry density, specific gravity, pH, and hydraulic conductivity. Nanocarbons increased the pH values from 3.93 to 4.16. Furthermore, the hydraulic conductivity values of the stabilized fine-grained soil samples containing MWCNTs decreased from  m/s to  m/s and, in the reinforcement sample by CNFs, the hydraulic conductivity value decreased to  m/s. Small amount of nanocarbons (MWCNTs and CNFs) decreased the optimum moisture content, increased maximum dry density, reduced the plasticity index, and also had a significant effect on its hydraulic conductivity.

Comparison between unit cell and plane strain models of stone column ground improvement

This article presents a comparative study of the behaviour of clayey soil reinforcements using stone column ground improvement by means of numerical analyses. Two-dimensional finite element analyses with commercially available software, PLAXIS, were performed on end-bearing stone columns using 15-noded triangular elements to investigate the impact of the modelling type on the stress concentration ratio and failure mechanism of an improved foundation system. Consolidation analyses were conducted throughout the study using Mohr-Coulomb’s criterion. The computed values of the stress concentration ratios were compared for different key parameters, including the diameters of stone columns, c/c spacing of columns, friction angle of stone column material, and undrained cohesion of soft soil. The major conclusions of this study were that the stone column in the unit cell model shared between 2.5 to 3.14 times more loads than the surrounding soil, whilst in the plane strain model it shared between 1.7 to 2.9 times more loads. The use of plane strain approach to model the stone column gave a more comprehensive representation of the stress distribution and load transfer between the soil and columns, in addition to being a better method than the unit cell concept to evaluate the failure mode in this system.

Performance of soil stabilized with carbon nanomaterials

The use of nanomaterials to stabilize soil is a developing research area in geotechnical engineering. In this study, the use of carbon nanotube was compared to carbon nanofiber for possible applications in soil stabilization. Fundamental properties such as Atterberg’s limits and compaction characteristics were first explored. Then the hydraulic conductivities of the soil-nanomaterial reinforcement were determined. The maximum amounts of the nanomaterial used is 0.2 % by dry weight of the soil. Both nanomaterials increased the specific gravity, dry densities and pH values slightly. Furthermore, the hydraulic conductivity decreases for samples with carbon nanotube and greater decrease was obtained for samples with carbon nanofiber. These results indicated that small amounts of nanomaterials used can provide measurable changes in the soil behavior. Thus, the nanomaterials used in this study can be further considered as potential soil stabilization materials.

Simulation of Stone Column Ground Improvement (Comparison between Axisymmetric and Plane Strain)

Most of the numerical studies on stone columns are based on the unit cell concept. However, the impact of interactions between adjacent columns and between the columns and the surrounding soil has not been investigated thoroughly. In this study, the finite element software, PLAXIS-2D-V8.2, was used to simulate a stone column as a unit cell and as a plane strain model in order to specify the difference between the performances of each model. The key factors that were investigated included the diameter and c/c spacing of the stone columns, friction angle of the stone column material and undrained cohesion of the soft soil. The emphasis of this parametric study was on the settlement improvement factor and excess pore water pressure, since these are critical to the design of stone columns. The main findings of this study were that in the plane strain model, the settlement improvement factor ranged between 2.2 and 3.2, which means that the settlement was improved more than twice. Meanwhile, in the unit cell concept, the settlement improvement factor did not exceed 1.53. The results of the settlement improvement were compared with the theoretical solutions that are commonly used for studies into the behaviour of stone columns. The unit cell model showed a lower peak value of excess pore water pressure than the plane strain model.

Influence of carbon nanofibers on the shear strength and comparing cohesion of direct shear test and AFM

The stabilization and enhancement of the engineering properties of fine and coarse grained soil has heavily relied on reinforcement and admixture materials. This study discusses the effect of the additive of Carbon nanofibers (CNF) on the characteristics of soils in terms of shear strength. The content of CNF was changed within the range of 0.05 to 0.2% by total dry weight of the reinforced samples. In achieving the objective of minimizing the number of experimental runs and thus conserve material, time as well as overall cost, the Box–Behnken approach was chosen as the method for statistical prediction. The scanning electron microscopy (SEM) and Atomic force microscopy (AFM) has been utilized in studying features of CNF in stabilized soil samples and force at the origin of the cohesion (c) of soil. Test results reveal that the increases peak and residual shear strength of the reinforcement soil samples were increased with an increase in the CNF content. The pre-eminence of ionic correlation forces in the cohesion of soil was confirmed by the force (cohesion) measurements by (AFM). The statistical prediction’s relatively high correlation coefficients justified the results.

Evaluation of permanent deformation and durability of epoxidized natural rubber modified asphalt mix

The road distresses have caused too much in maintenance cost. However, better understandings of the behaviours and properties of asphalt, couples with greater development in technology, have allowed paving technologists to examine the benefits of introducing additives and modifiers. As a result, modifiers such as polymers are the most popular modifiers used to improve the performance of asphalt mix. This study was conducted to investigate the use of epoxidized natural rubber (ENR) to be mixed with asphalt mix. Tests were conducted to investigate the performance characteristics of ENR-asphalt mixes, where the mixes were prepared according to the wet process. Mechanical testing on the ENR-asphalt mixes have demonstrated that the asphalt mix permanent deformation performance at high temperature was found to be improved compared to the base mixes. However, the durability studies have indicated that ENR-asphalt mixes are slightly susceptible with the presence of moisture. The durability of the ENR-asphalt mixes were found to be enhanced in term of permanent deformation at high and intermediate temperatures compared to the base asphalt mixes. As conclusion, asphalt pavement performance can be enhanced by using ENR as modifier to face the major road distresses.

Influence of Nanolime and Curing Period on Unconfined Compressive Strength of Soil

This paper presents the improvement of the unconfined compressive strength (UCS) of soil by mixing different percentages of nanolime and 5% lime with soil. The UCS of treated soil increased significantly over curing time with increasing percentage of nanolime. The optimum results were reached at only 0.5% nanolime admixtures which were much higher than 5% lime admixture. This may be due to higher ability of nanolime to flocculate and agglomerate the soil particles compared with the lime. In addition, the lime could fill only the micropores while nanolime could fill the micro- and nanopores as well. The strength gain is inversely proportional to the remolded moisture content and curing period. However, when the content of nanolime used is larger than 0.5%, nanolime particles are not uniformly dispersed. Therefore, a weak area in the form of voids is created, consequently the homogeneous hydrated microstructure cannot be formed, and finally the strength will decrease.