Characterization Of Swelling Stress And Soil Moisture Deficiency Relationship For Expansive Unsaturated Soils

DissertationExpansive soils vary in volume, in relation to water content. Volume changes when wetting (swelling) and drying (shrinkage). Lightweight structures in construction are the most vulnerable structures experiencing severe defects when built on these soils. In South Africa, expansive soils are the most problematic which impose challenges to civil engineers. The prediction of the swelling stress has been a concern to the construction industry for a long time. The swelling stress is generally ignored in engineering practice. Nonetheless, the swelling stress can develop significant uplift forces detrimental to the stability of foundations. Considering the swelling stress in foundation design in expansive soils enhance the durability, the service life, and reduce the cost of assessment and repair works to be undertaken in the future. Mathematical models are offered as an alternative to direct oedometer testing. Mathematical models are a useful tool to assess swelling stress. The aim of this study was to characterize the relationship between the swelling stress, the soil suction, and other soil parameters. Moreover, develop mathematical models to predict the swelling stress of field compacted expansive soils. Laboratory tests have been performed such as particle size distribution, Atterberg limits, linear shrinkage, specific gravity, free swell ratio, X-ray diffraction, soil suction measurement, modified Proctor compaction test, and zero-swell test (ZST). Multiple regression analysis was performed using software NCSS11 to analyze the data obtained from the experiments. The relationships between the swelling stress and other soil parameters were established. It was observed that, at the optimum moisture content (OMC), the swelling stress values are within the range of 48.88 kPa to 261.81 kPa, and the matric suction values are within the range of 222.843 kPa to 1,778.27 kPa. The swelling stress values on the dry side of the OMC are higher than values on the wet side. In addition, compaction at the OMC can reduce the swelling stress by 15%. Furthermore, the geotechnical index properties, the swelling parameters, affect the swelling stress of compacted expansive soils. Nevertheless, there is a key impact of the type of clay mineral on swelling stress. Six predictive mathematical models were developed. These models were validated using soil samples collected from various areas across the province of Free State (Petrusburg, Bloemfontein, Winburg, Welkom, and Bethlehem). Lastly, good correlations between predicted values and values obtained from experimental works confirm the reliability of the multiple regression analysis. The data points are very close to the line 1:1. Furthermore, the graphical analysis shows that the correlation of the values obtained from the models developed in this study are more precise than the values obtained from other models. Therefore, the predictive models developed in this research work are capable to estimate the swelling stress with acceptable accuracy

Assessment of theMineral Composition of Heaving Soils Using Geotechnical Properties

ArticleThe behaviour of heaving soils is generally governed by the matric suction. Nonetheless, the mineralogical characteristics influence the geotechnical behaviour. X-ray diffraction is a common technique used to determine the mineral composition. This equipment is costly and the process time-consuming. The objective of this research is to develop predictive mathematical models to determine the predominant minerals in heaving soils. Soil samples are collected from identified areas across Free State province by digging at 50 cm depth from the ground surface. Geotechnical lab studies such as particle size distribution, Atterberg limits, specific gravity, free swell ratio, free swell index, linear shrinkage, and X-ray diffraction are performed to evaluate soil properties. A stepwise analysis is conducted to determine the response of each type of mineral to soil properties, and select the best subsets. Moreover, the influence of soil minerals on soil properties is achieved by investigating the correlation between the relevant soil properties and each mineral. Multivariate regression is performed utilizing MINITAB 18 program to develop mathematical predictive models. These equations are assessed base on correlation coefficient, probability value (P-value), and standard residual pattern analysis. The predominant minerals can be assessed with acceptable accuracy utilizing the proposed semi-empirical models

Evaluation of the Unsaturated Shear Strength Parameters of Compacted, Heaving Soil Using Geotechnical Properties

Abstract The shear strength is a fundamental property of soil material under structural loads. The determination of shear strength properties of unsaturated soils is challenging and time-consuming. Geotechnical predictive models can be utilized to assess the unsaturated shear strength of heaving soil. This study attempts to propose predictive models to evaluate the unsaturated shear strength parameters of compacted heaving soil. These parameters include the angle of internal friction associated with the net normal stress (ϕ'), angle indicating the rate of increase in shear strength with respect to a change in matric suction (ϕb), and effective cohesion (c'). The geotechnical properties of soils were assessed through laboratory tests such as particle size distribution, consistency limits, specific gravity, modified Proctor compaction test, swelling test, suction test, and advanced triaxial testing. Multivariate analysis was conducted using NCSS 12 software to design the models. The validation of models includes the determination coefficient, probability value, comparing experimental values with predicted values, and comparing the developed models with other model found in recent literature. The models engineered in this study can estimate the unsaturated shear strength parameters of compacted heaving soil with acceptable precision