Strength behavior and microstructural characteristics of tropical laterite soil treated with sodium silicate-based liquid stabilizer

Although the effects of nontraditional stabilizers on the geotechnical properties of tropical soils has been the issue of investigation in recent years, the micro-structural characteristics of nontraditional soil additives and in particular selected additive (TX-85) have not been fully studied. Nontraditional soil stabilization additives are widely used for stabilizing marginal materials. These additives are low-cost alternatives to traditional construction materials and have different compositions. They also differ from one another while interacting with soil. In line with that, it was the objective of this research to investigate the strength properties and physicochemical mechanisms related to tropical laterite soil mixed with the liquid stabilizer TX-85. Macro-structure study, i.e., compaction, and unconfined compression strength test were used to assess the engineering and shear properties of the stabilized laterite soil. In addition, the possible mechanisms that contributed to the stabilization process were discussed using various spectroscopic and microscopic techniques such as X-ray diffractometry (XRD), energy-dispersive X-ray spectrometry, scanning electron microscopy, and Fourier transform infrared spectroscopy. From engineering point of view, the results indicated that the strength of TX-85 stabilized laterite soil improved significantly. The degree of improvement was approximately four times stronger than natural soil after a 7-day curing period. The XRD showed no crystalline products (gel form). Moreover, weathering effects were obvious in TX-85 treated samples in most of clay minerals’ peak intensities. These effects were reduced especially for kaolinite mineral inside the soil with curing time.     

Physicochemical behavior of tropical laterite soil stabilized with non-traditional additive

Non-traditional soil stabilizers are widely used for treating weak materials. These additives are cost- and time-effective alternatives to more traditional materials such as lime and cement. It has been well established that the treatment of natural soil with chemical additives will gradually affect the size, shape, and arrangement of soil particles. Furthermore, the degree of improvement is dependent on the quantity and the pattern of new products formed on and around the soil particles. In this paper, unconfined compressive strength (UCS) test was performed as an index of soil improvement on mix designs treated with calcium-based powder stabilizer (SH-85). The time-dependent changes in shear strength parameter and compressibility behavior of treated soil were also studied using standard direct shear and one-dimensional consolidation tests. In order to better understand the shape and surface area of treated particles, FESEM, N₂-BET, and particle size distribution analysis were performed on soil-stabilizer matrix. From engineering standpoint, the UCS results showed that the degree of improvement for SH-85-stabilized laterite soil was roughly five times stronger than the untreated soil at the early stages of curing (7-day period). Also, a significant increase in the compressibility resistance of treated samples with curing time was observed. Based on the results, less porous and denser soil fabric was seen on the surface of clay particles. FESEM images of the treated mix designs showed the formation of white lumps in the soil fabric with the cementitious gel filling the pores in the soil structure.     

Plastic deformation of orthoenstatite and the ortho- to high-pressure clinoenstatite transition: a metadynamics simulation study

Atomic-scale mechanisms of plastic deformation in orthoenstatite, MgSiO₃ are studied by computer simulation methods. The combined use of metadynamics and molecular dynamics allows a direct observation of the structural changes during the creation of stacking faults in the (100) plane. A sequence of slip deformations in two different (100) planes at P = 15 GPa and T = 1,000 K reveals a probable transformation mechanism for the ortho- to high-pressure clinopyroxene transition. Each of the observed slips consists of at least four partial deformations crossing high-energy intermediate structures. In agreement with experimental studies, both (100)[010] and (100)[001] slip systems are activated in the deformation process. The observation of a dominant (100)[001] single slip system in pyroxenes may be related to the fact that high-energy intermediate dislocations with (100)[010] component are not stable on geological or experimental timescales.     

Bearing capacity of soft soil model treated with end-bearing bottom ash columns

Granular column technique is a soil improvement method used to increase the bearing capacity of a soft soil area by replacing the soil with a group of granular column materials. The by-product utilisation is a worldwide interest for sustainable infrastructure development. Bottom ash, which is a combustion deposit derived from coal burning, is a potential by-product that could be used alternatively to sand or aggregate as a green granular column material. This research is to study the potential use of the bottom ash column-improved soft clay by conducting a series of small-scale physical modelling test. The bearing capacity behaviour and failure mode of soft clay improved with end-bearing group of bottom ash columns with and without geotextile encasement are investigated. The bearing capacity of soft clay is significantly enhanced by the inclusion of bottom ash columns; that is, 239% of bearing capacity improvement is observed with only 13% of improvement area. The bulging of the bottom ash column is transferred to buckling failure with higher bearing capacity when the bottom ash column is encased by geotextile. The outcome of this research leads to the usage of bottom ash by-product as a granular column material in sustainable soil improvement technique.