The effect of microbial calcite precipitation on the retention properties of unsaturated fine-grained soils: discussion of the governing factors

In recent years, biogeotechnology has been introduced as a novel and environmentally friendly technique for soil improvement. The need to address global warming and the adverse environmental effects of the chemical additives have led to the emergence and development of the techniques which use calcite producing microorganisms in order to improve soil mechanical properties. While the effects of microbial induced calcite precipitation (MICP) on the hydraulics and mechanics of saturated coarse-grained soils have been well examined and studied, there is not yet much information on the effects these microorganisms would have on the unsaturated soil mechanical behaviour. The first step, in this regard, is to understand the effect of the processes involved in the MICP on the soil retention properties. Soil water suction is a key factor controlling soil hydraulic and mechanical behaviour. In this study, the influence of MICP on the soil total suction in an unsaturated fine-grained soil sample has been explored using filter paper experiment. The results of this study revealed that by increasing the amount of bacterial solution, the soil saturation-total suction curves are significantly affected. The soil water retention changes are attributed to the change in double layer thickness as well as the precipitation of calcite crystals

Thermo-mechanical behaviour of a compacted swelling clay

Compacted unsaturated swelling clay is often considered as a possible buffer material for deep nuclear waste disposal. An isotropic cell permitting simultaneous control of suction, temperature and pressure was used to study the thermo-mechanical behaviour of this clay. Tests were performed at total suctions ranging from 9 to 110 MPa, temperature from 25 to 80 degrees C, isotropic pressure from 0.1 to 60 MPa. It was observed that heating at constant suction and pressure induces either swelling or contraction. The results from compression tests at constant suction and temperature evidenced that at lower suction, the yield pressure was lower, the elastic compressibility parameter and the plastic compressibility parameter were higher. On the other hand, at a similar suction, the yield pressure was slightly influenced by the temperature; and the compressibility parameters were insensitive to temperature changes. The thermal hardening phenomenon was equally evidenced by following a thermo-mechanical path of loading-heating-cooling-reloading

The effect of microbial calcite precipitation on the retention properties of unsaturated fine-grained soils: discussion of the governing factors

In recent years, biogeotechnology has been introduced as a novel and environmentally friendly technique for soil improvement. The need to address global warming and the adverse environmental effects of the chemical additives have led to the emergence and development of the techniques which use calcite producing microorganisms in order to improve soil mechanical properties. While the effects of microbial induced calcite precipitation (MICP) on the hydraulics and mechanics of saturated coarse-grained soils have been well examined and studied, there is not yet much information on the effects these microorganisms would have on the unsaturated soil mechanical behaviour. The first step, in this regard, is to understand the effect of the processes involved in the MICP on the soil retention properties. Soil water suction is a key factor controlling soil hydraulic and mechanical behaviour. In this study, the influence of MICP on the soil total suction in an unsaturated fine-grained soil sample has been explored using filter paper experiment. The results of this study revealed that by increasing the amount of bacterial solution, the soil saturation-total suction curves are significantly affected. The soil water retention changes are attributed to the change in double layer thickness as well as the precipitation of calcite crystals

Mixed-valence properties of a dinuclear ruthenium complex bridged by bis(phenylcyanamido)tetrazine

The novel bridging ligand 3,6-bis(phenylcyanamido)-1,2,4,5-tetrazine (tdpcH2) and its dinuclear complex [{Ru(ttpy)(bpy)}2(μ-tdpc)][PF6]2 were prepared and characterized by elemental analysis and 1H NMR spectroscopy. Cyclic voltammetry and vis-NIR and IR spectroelectrochemistry of [{Ru(ttpy)(bpy)}2(μ-td

Effects of Biological Stabilization on the Water Retention Properties of Unsaturated Soils

The soil water retention curve (SWRC) is one of the most fundamental characteristics of unsaturated soils. Because unsaturated soils are subjected to a range of natural processes and engineered treatments, a thorough understanding is needed of how their retention properties change when exposed to each separate treatment. In recent years, several biological treatment methods, such as microbial-induced calcite precipitation (MICP), have been introduced as environmentally friendly techniques. This study investigates the effect of biological treatment by means of Bacillus sphaericus on the SWRC of both coarse-grained and fine-grained soil samples. Pore fluid pH, X-ray diffraction, and scanning electron microscopy tests are used to better delineate the mechanisms affecting biologically induced alterations of SWRCs. Results showed that higher bacterial concentrations produced higher air-entry values in coarse-grained soils. However, the fine-grained samples showed an initial increase followed by a decrease in the air-entry value when the bacterial concentration increased. Changes in the soil porous structure and double-layer thickness are thought to be main reasons causing the different behavior of fine-grained soils

Effects of Biological Stabilization on the Water Retention Properties of Unsaturated Soils

The soil water retention curve (SWRC) is one of the most fundamental characteristics of unsaturated soils. Because unsaturated soils are subjected to a range of natural processes and engineered treatments, a thorough understanding is needed of how their retention properties change when exposed to each separate treatment. In recent years, several biological treatment methods, such as microbial-induced calcite precipitation (MICP), have been introduced as environmentally friendly techniques. This study investigates the effect of biological treatment by means of Bacillus sphaericus on the SWRC of both coarse-grained and fine-grained soil samples. Pore fluid pH, X-ray diffraction, and scanning electron microscopy tests are used to better delineate the mechanisms affecting biologically induced alterations of SWRCs. Results showed that higher bacterial concentrations produced higher air-entry values in coarse-grained soils. However, the fine-grained samples showed an initial increase followed by a decrease in the air-entry value when the bacterial concentration increased. Changes in the soil porous structure and double-layer thickness are thought to be main reasons causing the different behavior of fine-grained soils

Body composition and basal metabolic rate in systemic lupus erythematosus patients

Aim of the work: Descriptions of the body composition parameters and metabolism in systemic lupus erythematosus (SLE) patients are limited. The aim of the present work was to assess the body composition factors and basal metabolic rate (BMR) in Iranian SLE patients and to study its relation to disease activity. Patients and methods: Seventy-four female SLE patients and 76 matched controls were included in the present study. The body mass index (BMI), body fat (BF), visceral fat (VF), body muscle (BM) and basal metabolic rate (BMR) were measured using BIA (bioelectrical impedance analysis). The international physical activity questionnaire (IPAQ) was used to assess physical activity. SLE disease activity index (SLEDAI) was assessed for all the patients. Results: The mean age of the patients was 38.5 ± 10.1 years with a median disease duration of 7.5 years. The median SLEDAI was 4. Body composition factors (BMI, BF, VF, and BM) were not significantly different between the patients and their controls. The BMR in SLE patients was significantly lower (1328.4 ± 154.6 kcal/day) than the controls (1400.4 ± 200.4 kcal/day) (p = 0.01). No differences have been found in body composition parameters and BMR between the SLE patients with high and low SLEDAI or daily corticosteroid dose. There was no significant correlation between the SLEDAI and any of the studied parameters except for a negative association with age (r = −0.3, p = 0.03). Conclusion: SLE women have a significantly lower BMR compared to their controls. No significant differences have been observed regarding BMI, BF, BM and VF between the groups