Engineering and environmental assessment of soilbag-based slope stabilisation for sustainable landslide mitigation in mountainous area.

Changes in land use significantly impact landslide occurrence, particularly in mountainous areas in northern Thailand, where human activities such as urbanization, deforestation, and slope modifications alter natural slope angles, increasing susceptibility to landslides. To address this issue, an appropriate method using soilbags has been widely used for slope stabilisation in northern Thailand, but their effectiveness and sustainability require assessment. This research highlights the need to evaluate the stability of the soilbag-based method. In this study, a case study was conducted in northern Thailand, focusing on an area characterised by high-risk landslide potential. This research focuses on numerical evaluation the slope stability of soilbag-reinforced structures and discusses environmental sustainability. The study includes site investigations using an unmanned aerial photogrammetric survey for slope geometry evaluation and employing the microtremor survey technique for subsurface investigation. Soil and soilbag material parameters are obtained from existing literatures. Modelling incorporates hydrological data, slope geometry, subsurface conditions, and material parameters. Afterwards, the pore-water pressure results and safety factors are analysed. Finally, the sustainability of soilbags is discussed based on the Sustainable Development Goals (SDGs). The results demonstrate that soilbags effectively mitigate pore-water pressures, improve stability, and align with several SDGs objectives. This study enhances understanding of soilbags in slope stabilisation and introduces a sustainable landslide mitigation approach for landslide-prone regions.

Undrained stability of braced excavations in clay considering the nonstationary random field of undrained shear strength.

The basal heave stability of supported excavations is an essential problem in geotechnical engineering. This paper considers the probabilistic analysis of basal heave stability of supported excavations with spatially random soils by employing the random adaptive finite element limit analysis and Monte Carlo simulations to simulate all possible outcomes under parametric uncertainty. The effect of soil strength variability is investigated for various parameters, including the width and depth of the excavation ratio, strength gradient factor, and vertical correlation length. Probabilistic basal stability results have also been employed to determine the probability of design failure for a practical range of deterministic factors of safety. Considering probabilistic failure analysis, the more complete failure patterns caused by the various vertical correlation length would decrease the probability of design failure. There are different tendencies between the probability of design failure at the same safety factor with various vertical correlation lengths. These results can be of great interest to engineering practitioners in the design process of excavation problems.

Use of polypropylene fibers extracted from recycled surgical face masks in cement mortar.

The use of personal protective equipment (PPE), particularly single-use surgical face masks (FMs), has increased drastically owing to the ongoing Covid-19 pandemic. This study aimed to demonstrate the feasibility of utilizing recycled FM fibers in cement mortar. For this, FMs were used by removing the inner nose wires and ear loops and cutting them into two different sizes: 10 mm × 5 mm and 20 mm × 5 mm. The FMs were then introduced into five mixtures at 0 (control), 0.10, 0.15, 0.20, and 0.25 % by volume. The following mechanical properties of the mixtures were then tested: workability, density, porosity, water absorption, and the related strengths (compressive, direct tensile, and flexural). In addition, the microstructures of the mixtures were analyzed using a scanning electron microscope. The results revealed that introducing FM fibers, particularly an FM with a 5 mm diameter and 10 mm length, in the mortar increased both the tensile and flexural strengths. Among the various combinations of FMs studied, a mixture containing 0.15 % FMs exhibited the best performance. The findings of this research reveal that FMs can be reused as fibers to enhance the tensile and flexural strengths of cement mortar.

Mechanisms of chloride and sulfate removal from municipal-solid-waste-incineration fly ash (MSWI FA): Effect of acid-base solutions.

A general approach to managing municipal solid waste is by incineration. Unfortunately, large amounts of municipal-solid-waste-incineration fly ash (MSWI FA) is produced in the process, with their heavy metals content posing further problems to the environment. One fundamental treatment of MSWI FA heavy metals is called solidification-stabilization, where MSWI FA is solidified in cement-based materials to cap hazardous elements from being released into the environment. Mortar formed from this cement mixed with MSWI FA suffer from decreased compressive strength due to their chloride and sulfate contents. Thus, pre-treatment of MSWI FA to remove these salts before producing mortar is desirable. This study investigated treating MSWI FA with deionized water, 0.01 M and 0.1 M nitric acid, and 0.1 M and 0.25 M sodium carbonate to remove chloride and sulfate. Physical and chemical structures of treated and untreated MSWI FA was studied to understand the chloride and sulfate removal mechanisms. Treated MSWI FA was used as cement replacement in mortar, and the compressive strength was tested. Results suggest that all of the treatment solutions tested in this study can equally remove chloride (around 250,000 mg/kg), but sodium carbonate can remove sulfate at the highest extent (15,821 mg/kg). In addition, mortar with deionized-water-treated MSWI FA gave the highest compressive strength. Heavy metals leaching was tested by the Toxicity Characterization Leaching Procedure (TCLP) method, with results passing the standard.

Evaluation of Microencapsulation Techniques for MICP Bacterial Spores Applied in Self-Healing Concrete.

Concrete cracks must be repaired promptly in order to prevent structural damage and to prolong the structural life of the building (or other such construction). Biological self-healing concrete is a recent alternative technology involving the biochemical reaction of microbial induced calcium carbonate precipitation (MICP). This study determined the most appropriate technique to encapsulate spores of Bacillus sphaericus LMG 22257 with sodium alginate so as to protect the bacterial spores during the concrete mixing and hardening period. Three techniques (extrusion, spray drying and freeze drying) to encapsulate the bacterial spores with sodium alginate were evaluated. The freeze-drying process provided the highest bacterial spore survival rate (100%), while the extruded and spray-dried processes had a lower spore survival rate of 93.8% and 79.9%, respectively. To investigate the viability of microencapsulated spores after being mixed with mortar, the decomposed urea analysis was conducted. The results revealed that the freeze-dried spores also showed the highest level of urea decomposition (metabolic activity assay used as a surrogate marker of spore germination and vegetative cell viability). Thus, the self-healing performance of concrete mixed with freeze-dried spores was evaluated. The results showed that the crack healing ratio observed from the mortar specimens with freeze-dried microencapsulated spores were significantly higher than those without bacteria. This study revealed that freeze drying has a high potential as a microencapsulation technique for application to self-healing concrete technology.

The performance of vetivers (Chrysopogon zizaniodes and Chrysopogon nemoralis) on heavy metals phytoremediation: laboratory investigation.

Phytoremediation with vetiver was investigated in relation to heavy metal contaminated soil in Thailand. The work compared the performance of two species of vetiver named Songkhla 3 (Chrysopogon zizaniodes) and Prachuap Khiri Khan (Chrysopogon nemoralis) in absorbing lead, zinc, and cadmium in contaminated soils. Toxicity Characteristic Leaching Procedure (TCLP), and Allium tests were conducted to determine toxicity of treated soil. Ethylenediaminetetraacetic acid (EDTA) was also used to increase heavy metals concentration in solution in soil, which led to an increase in translocation and bioaccumulation factors. In general, results showed that concentration of heavy metals decreased in soil and increased in both the shoots and roots of vetivers during a 4-month treatment period. TCLP results indicated that the concentration of zinc and cadmium in contaminated soil was reduced over treatment time, and significantly increased after EDTA was applied. To confirm vetiver performance in phytoremediation, Allium testing showed that remained heavy metals in treated soils had no effect on nucleus aberration. Songkhla 3 and Prachuap Khiri Khan showed similar trends in their ability to remediate lead, zinc, and cadmium from contaminated soil. Both species could accumulate higher concentrations of heavy metals in their shoots and roots over time, and with EDTA application.

Leaching mechanisms of heavy metals from fly ash stabilised soils.

Fly ash is an industrial waste material that is repurposed as a soil stabiliser worldwide. In Thailand, many ground improvement projects utilise mixtures of cement and fly ash to stabilise weak soils. In this study, leaching mechanisms of arsenic, chromium, lead, and zinc from cement and fly ash stabilised soils were investigated in the laboratory. Leaching tests were performed, with different leachants and pH conditions, on cement and fly ash stabilised soils used for soil improvement in road embankment construction projects in Northern Thailand. The results suggested that chemical compounds (CaO and MgO) on fly ash surfaces can control the pH of the fly ash and soil leachant. The dissolution of chromium and zinc was found to be amphoteric and controlled by oxide minerals at a high or low pH. Arsenic leaching was found to be oxyanionic where AsO43- prevented the adsorption of arsenic onto the negatively charged fly ash surface. Different types of leachant also leached out in different amounts of heavy metals.