This study investigates the strength performance and microstructural changes of a sandy gypseous soil improved with fly ash-based geopolymer, for shallow and deep applications. Different proportions of geopolymer were added to a natural gypseous soil having a gypsum content of 30% to 40% with different water contents. The fly ash was activated using sodium hydroxide with molar concentrations 8 and 12 molar and sodium silicate. The ratios of the fly ash to the activator were 1 and 2. Specimens were cured for different ages at 30°C. To simulate the field conditions, a number of specimens were immersed in a salt-saturated solution. Materials performance was evaluated at the macro level by performing unconfined compression test and at micro level by performing scanning electron microscopy test. The study showed that an increase in the molar concentration of sodium hydroxide and of the binder ratio improved material’s strength particularly at lower water contents of the soil. Increasing the binder content to about 30% improved the strength by enhancing the bonding between the soil particles. On the other hand, immersing the samples in the salt solution led, in most cases, to breakdown of the geopolymer network, as confirmed by the SEM images. It was concluded that the fly ash geopolymer-soil mixtures under investigation can provide as high as 8 MPa uniaxial strength under no sulfate attack. However, under sulfate attack condition, this strength can decrease to as low as 0.5 MPa. Even under the worst case, the later strength can be just enough to support shallow foundations rested on a saturated gypseous soil.
ABSTRACT:The gypseous soils are distributed in many regions in Iraq and other countries. Therefore, it is necessary to study the behavior of such soils due to the large damages that affects the structures founded and constructed in or on it.This research is concerned with studying the effect of leaching soil process on the stability of an embankment erected on foundation gypseous soil. The finite element method is adopted in this research. The analyses carried out using a nonlinear, increment, and stress-dependent finite element computer program. The hyperbolic stress-strain parameters used in the finite element analyses are estimated by the data collected from triaxial compression tests of some researchers. The analysis of the embankment problem carried out, shows that the leaching process for foundation gypseous soil increases the displacements and deformations of the embankment and its foundation. Finally, this research necessitate the success using of the finite element method in design and analyses of the important structures and buildings erected on gypseous soils that may expose to the effect of leaching process. This means that there is possibility to predicate the behavior of structure by a powerful means to establish the suitable solutions for any problems that may be occurred as a result of the present gypseous soil.
Collapse of gypseous soils may cause excessive settlement and serious damage to engineering structures. Various improvement approaches, such as mechanical techniques and chemical additions, have been used to reduce the collapsibility of these soils. The odometer test has traditionally been used to assess the collapsibility of the improved gypseous soils; however, because the small size of test specimens, this method may not adequately reflect field conditions. In this research, a laboratory model test of 600 x 600 x 600 mm with a model footing of 100 x 100 mm was developed to measure the collapse characteristics of a gypseous soil. The top layer underneath the footing was improved by compaction, cement kiln dust (CKD), geogrid, and a combination between CKD and geogrid. The top layer was improved at two values of thickness of 50 and 100 mm. The results obtained from this study indicate that the values collapsibility settlement reduction factor for compacted soil and the soil treated with CKD were 75 and 82%, 89% receptively. These values increased up to 95 % when a combination of CKD and geogrid was applied. As discussed herein, the aforementioned treatment methods can effectively be used to improve the collapsibility of gypseous soils.
ABSTRACT A study of the effect of cutback MC-60 on the permeability and compressibility characteristics of sandy gypseous soil is presented. Series of laboratory tests are carried out including classification, compaction, and conventional oedometer tests as well as a new test named compressibility- permeability leaching test. Test results shows that the superlative enhancement in compressibility and permeability and thereby in collapsibility occurred with 7% additive.
The gypseous soils are distributed in many locations in Iraq. The Engineering properties of such soil will be changed when it is wetted and it leads to failure which causes danger on the structures built on. This reason needs to study its properties and to find the way to treat it. In this study, natural properties of soil prepared from Samarra-Salah al deen governorate were studied. The gypsum content of soil is about 32%. To improve this soil, many trials were carried out on the soil by additive of Portland cement and calcium chloride. For the importance of the compressibility of the soil, the effect of the additives were studied and it is found that addition of 3% of cement or 5% of calcium chloride will improve the soil compressibility.
A BSTRACT: Leaching effects on permeability and compressibility characteristics of undisturbed sandy gypseous soil were investigated in this study. Time, stress level, strain, leachate condition and flow velocity were considered. The loading, leaching and permeability measurements were carried out utilizing the constant head pereameter with special modifications. Test results show that salt leaching and thereby leaching strain is a time dependent process. Also as leaching strain continued coefficient of permeability decreases.
Abstract. In this research, Artificial Neural Networks (ANNs) will be used in an attempt to predict collapse potential of gypseous soils. Two models are built one for collapse potential obtained by single oedemeter test and the other is for collapse potential obtained by double oedemeter test. A database of laboratory measurements for collapse potential is used. Six parameters are considered to have the most significant impact on the magnitude of collapse potential and are being used as an input to the models. These include the Gypsum content, Initial void ratio, Total unit weight, Initial water content, Dry unit weight, Soaking pressure. The output model will be the corresponding collapse potential. Multi-layer perceptron trainings using back propagation algorithm are used in this work. A number of issues in relation to ANN construction such as the effect of ANN geometry and internal parameters on the performance of ANN models are investigated. Information on the relative importance of the factors affecting the collapse potential are presented and practical equations for prediction of collapse potential from single oedemeter test and double oedemeter test in gypseous soils are developed. It was found that ANNs have the ability to predict the collapse potential from single oedemeter test and double oedemeter test in gypseous soil samples with a good degree of accuracy. The ANN models developed to study the impact of the internal network parameters on model performance indicate that ANN performance is sensitive to the number of hidden layer nodes, momentum terms, learning rate, and transfer functions. The sensitivity analysis indicated that for the models the results indicate that the initial void ratio and gypsum content have the most significant affect on the predicted the collapse potential.Keywords. Artificial Neural Networks, collapse potential, gypseous soils