Sumi Siddiqua

Evaluation of the impact of pore fluid chemistry on the hydromechanical behaviour of clay-based sealing materials

The results of an experimental program undertaken to evaluate the impact of pore fluid salinity on the hydromechanical performance of light and dense backfill materials are presented. Light and dense backfills are engineered barrier materials that are being examined in the Canadian concept for storage of spent fuel in a deep geological repository. The current research investigates the impact of pore fluid chemistry on the swelling, compressibility, stiffness, and hydraulic conductivity parameters of light and dense backfills that are required as material parameters for analysis and design. In these tests, pore fluid chemistry was selected to represent groundwater within potential host units including granite and limestone rock. Results show that the performance of light backfill is significantly affected by changes in pore fluid chemistry. The swell potential of light backfill decreases with increasing salinity of the solution. The hydraulic conductivity decreases with increasing effective montmorillonite...

A review on consolidation behavior of tailings

Abstract The proper management of tailings largely depends on its consolidation behavior. Extensive works on this sector have been performed and still it plays a significant role in economic and environmental considerations of a tailings management facility. To resolve these issues, consolidation theories had been developed for one, two, and three dimensional aspects with numerical solutions for soft soils like tailings, which behave differently from natural soils. Eventually, large strain consolidation tests have experienced, at its advance level, precise determination of experimental data because non-linear behavior of compressibility and hydraulic conductivity fits to a wide range of functions. This non-unique behavior of tailings is believed to be an aftermath of the combination of flocculation, sedimentation, consolidation, segregation, deposition, freeze-thaw, and desiccation phenomena. A review of significant contributions from the researchers has been complied and composed in this paper to illustrate the growth and revolution of works on tailings consolidation behavior.

Experimental study on the performance of light and dense backfills

Numerical modeling is a cost-effective and important approach to examine the long-term performance of engineered materials. However, to identify the appropriate constitutive model for a particular material it is necessary to measure physical properties in a laboratory. Laboratory experiments provide the data from which the input parameters for the selected model can be interpreted. This paper studies the mechanical behaviour of two clay-based sealing materials — light backfill and dense backfill — recommended for use in disposal of nuclear waste in a proposed Canadian repository. Test specimens of light and dense backfills were saturated in a triaxial cell and then subjected to specified isotropic and shearing stress paths to measure consolidation and shear characteristics. The triaxial results are interpreted in a critical state context. The light backfill results suggest that it has similar stress–strain behaviour to a bentonite–sand buffer, which has a similar composition, but different preparation pro...

Prediction of soil type and standard penetration test (SPT) value in Khulna City, Bangladesh using general regression neural network

In this study, a general regression neural network (GRNN) is developed for predicting soil type and standard penetration test (SPT) N (standard penetration resistance) values based on SPT test results. It focuses on soils mainly in Khulna City, Bangladesh that comprise fine-grained alluvium deposits of mostly silt and clay with some organic content and sand. A detailed geological and geotechnical investigation of the city and its surroundings was conducted to generalize the subsoil condition of the study area based on soil type and SPT values. The investigation results showed that the city is divided into four geological units and three geotechnical zones. To develop the GRNN model, more than 2326 field SPT values (N) have been collected from 42 clusters containing 143 boreholes spread over an area of 37 km2. Two trained models were developed: initially the borehole locations were trained with the soil types and after that the borehole location-soil types were trained with the Nc values. The model prediction was compared with the borehole data and the results showed that the GRNN model predicts well compared with the actual site investigation data. Therefore, this model can be used for future planning and expansion of the city.

Preliminary Studies of Hydraulic and Mechanical Behavior of Nanoparticle-Based Light Backfill Exposed to Pore Fluid Salinity

AbstractBecause of its high swelling pressure and low hydraulic conductivity, compacted bentonite–sand is widely accepted as a barrier/backfill material used in deep geological repositories to safely contain highly toxic radioactive waste. The majority of research conducted in this field shows that the pore fluid salinity present in the repository’s environment reduces the swelling capacity and increases the hydraulic conductivity of backfill material. However, research has yet to determine how to improve the material properties of backfill under saline water conditions. In this study, two different percentages of nanoparticles derived from bentonite (1 and 2% with respect to dry weight of bentonite) were carefully mixed with a bentonite–sand mixture to prepare a nanoparticle-based light backfill. Next, the effect of different concentrations of NaCl and CaCl2 on the hydraulic and mechanical behavior of a 50∶50 bentonite–sand mixtures was examined, at a maximum dry density of 1.24  Mg/m3. The results showe...

Compressibility Behavior of Soils: A Statistical Approach

Compressibility behavior of soil is an important parameter that implies the change in volume under applied stress, on other words, it is the relationship between void ratio and effective stress. Depending on the type of soil and their origin, the compressibility behavior varies over a wide range. Researchers presented numerous void ratio-effective stress relationships consist of different sets of equations which produce a good fit with their consolidation test data. These sets of equations for different types of soils become complex for understanding its consolidation behavior using a specific model. This paper introduces a new equation, developed by statistical analysis, to represent the compressibility behavior of both natural soils and soft soils. Results obtained from the statistical analysis in terms of coefficient of determination (R2), a measurement of the goodness of fit, indicate the acceptability and validity of the proposed equation. Experimental data from literature are generated for the statistical analysis and an elaborate discussion is presented for the applicability of the proposed universal compressibility equation. Finally, this research opens the opportunity for parametric study of the coefficients of the proposed equation that may lead to develop a relationship between the compressibility and index properties of soil.

Stabilization of Tropical Peat Using Liquid Polymer

The technology of chemically improvement of soil properties is a widely accepted approach. It is also economically viable to increase the strength of soil as well as to limit water absorption, control soil erosion and soil settlement. Encountered extensively in wetlands, fibrous peat is considered as problematic organic soil because it exhibits low compressive strength. It is generally estimated that there are around 30 million hectares of tropical land covered with highly organic soil throughout the world, out of which about 3 million hectares lie in Malaysia. The present study aimed to investigate the effect of liquid polymer as a non-traditional soil additive which namely as SS299 in peat improvement. The influence of different concentration of selected additive (1%, 2%, 3%, 4% and 5%) were investigated on compressive strength improvement of unsoaked and soaked tropical peat samples by using unconfined compressive strength (UCS) tests. In addition, the morphology changes of treated samples were assess using field emission scanning electron microscopic (FESEM) tests. The results indicated that the SS299 soil additive is able to significantly increase the unconfined compression strength of selected peat.

Study of compressive loading capacities of helical piles using torque method and induced settlements

Torque is a most widely used method to estimate the load capacities of helical piles because of its simplicity and minimal costs. This research attempts to investigate the torque method by incorporating settlements and involves its comparison with bearing equations which have also been used to estimate the capacities of helical piles. The test program consisted of installation of seven helical piles including a static axial compression test to estimate the corresponding settlements. The compression test was conducted on the seventh pile which is referred to as the test pile. The load movement curve of the test pile is used to predict the settlement of each pile corresponding to the ultimate load calculated using torque method. In addition, few methods to interpret the load movement curve have been discussed. This research would pave way to yield more reliable results using torque method and could lead to the large-scale usage of helical piles.

Impact of pore fluid chemistry on the thermal conductivity of bentonite–sand mixture

Thermal conductivity is an important parameter to consider when designing clay-based barriers for use in deep geological repositories (DGR). In the DGR environment, the infiltration of local saline groundwater can potentially change the pore fluid chemistry of a barrier over its lifetime. This change in chemistry is known to alter the thermal properties of the barrier materials. In order to examine the impact of pore fluid salinity on thermal conductivity, experiments were conducted under both distilled water and saline pore fluid conditions. The material mixtures were prepared at two different dry densities using two different salt types. Furthermore, five different thermal conductivity prediction models were selected and evaluated on their performance with respect to the experimental outcomes. In general, these results indicated that an increase in the constituent pore fluid’s salt concentration leads to a decrease in the thermal conductivity of the material. Additionally, the thermal conductivity values of the materials prepared at a high dry density were greater than of those compacted at a low dry density.

Geotechnical Properties of Wood Ash-Based Composite Fine-Grained Soil

It is observed in Bangladesh that there is an extensive use of wood as a solid biomass for heat and electricity production, which led to increase in the amount of combustion residues known as ash. These ashes are discarded and dumped here and there, resulting in pollution of the environment. It could be managed by using wood ash as a stabilizer of soft clay. It is found that there is an enhancement of the engineering properties of existing soil in stabilized forms particularly unconfined compressive strength (UCS), shear strength parameters, workability, and compaction and compressibility characteristics. Therefore, laboratory tests associated with these properties were performed for some selected percentage of wood ash, for example, 0%, 5%, 7.5%, 10%, and 12.5%. Chemical investigation of wood ash depicts that it contains approximately 30% CaO, which directs it to behave like a pozzolanic material. Besides, the test result signifying that the soil could be made lighter with the increase of moisture content, strength, and reduction of compressibility due to the addition of ash content.