Shahid Azam

Expansive characteristics of gypsiferous/anhydritic soil formations

Abstract Geology and climatic and environmental conditions have led to the formation of expansive soils in the Eastern Province of Saudi Arabia. Calcium sulphate, which commonly occurs in such soils, is well known for phase transformation and dissolution. Phase changes from gypsum to anhydrite and vice versa, and dissolution of these phases, add to the potential hazards of local expansive soils. This paper discusses the behaviour of the expansive soil formations of eastern Saudi Arabia containing gypsum and anhydrite.

Large Strain Settling Behavior of Polymer-Amended Laterite Slurries

Knowledge of the settling properties of polymer-amended slurries is pivotal for improving throughput and yield during metal extraction and for developing tailings streams with superior geotechnical properties. This paper focuses on the large strain settling behavior of laterite slurries. The investigated slurry exhibited two settling regimes—sedimentation occurred up to e=em=8 and consolidation started at e=es=6.5. Bipower law functions best described the entire process in the form of e-σ′ and k-e relationships. Polymer addition generally improved slurry compressibility and hydraulic conductivity. The settling behavior of polymer-amended slurries was governed by large interfloc voids during sedimentation and by small intrafloc pores during consolidation. The combined effect of polymer parameters was effectively captured by the term polymer characteristic coefficient. Fit parameters for the e-σ′ and k-e relationships were directly proportional to Cp. Both the settling rate and amount varied extensively dur...

EFFECTS OF CALCIUM SULFATE ON SWELLING POTENTIAL OF AN EXPANSIVE CLAY

Due to a reversible hydration-dehydration reaction, calcium sulfate undergoes phase transformations between a hydrated phase, gypsum, and a dehydrated phase, anhydrite. Due to the harsh climatic and environmental conditions in eastern Saudi Arabia, such phase changes add to the potential swelling hazards of local expansive clays. The adsorption of water by expansive soils and the hydration of anhydrite to gypsum create swelling pressure and are the sources of much damage to foundations throughout the world. This paper attempts to assess the swelling caused by the interaction of calcium sulfate phases, especially gypsum and anhydrite, with expansive clay. This assessment was primarily based on studying the geotechnical, mineralogical, and volume change characteristics of calcium sulfate-bearing soils. X-ray and thermal analyses were used to estimate the type and amount of minerals present during phase transformation of calcium sulfate. The swelling potential was determined using an improved version of the simple odometer and constant-volume tests. The conventional odometer is the device normally used in these tests. However, the size of soil samples, the complete confinement, and the rigidity of the conventional odometer impose serious limitations on the application of the laboratory results to actual field problems. Therefore, the authors investigated the use of a large-scale odometer with different mold sizes and shapes on the swelling potential of some mixtures of expansive clay and calcium sulfate phases. In addition, the soil fabric of these mixtures was investigated using scanning electron microscopy to explain the volume change behavior. The results of this investigation indicated that the swelling potential of clay-calcium sulfate mixtures decreased as the percentage of calcium sulfate was increased, and this reduction was more pronounced when gypsum was used. Swelling pressure was observed to be the highest in the conventional odometer and lowest in the large-scale square odometer mold.

Geotechnical Characterization and Sedimentation Behavior of Laterite Slurries

Laterites are the main source of economic metals such as nickel and cobalt. In many parts of the globe, these metals are extracted using the pressure acid leach operation. An efficient rate of sedimentation and a high solids content of the material are two prerequisites for this process. To understand the geotechnical behavior of laterite slurries under ambient process conditions, a comprehensive laboratory characterization and sedmentation protocol was developed. Results indicate that due to changes in material characteristics, sedimentation behavior of laterite slurries is improved during the metal extraction process. The rate and concentration of sedimentation are directly related for this class of materials.

Volume Change Behavior of a Fissured Expansive Clay Containing Anhydrous Calcium Sulfate

Expansive clays in eastern Saudi Arabia are generally fissured and contain high quantities of anhydrous calcium sulfate. Similar to clay minerals, this secondary mineral causes swelling when hydrated and forms gypsum that, in turn, dehydrates and transfers back to anhydrite during compression. The main objective of this paper was to understand the volume change behavior of a local expansive clay containing 50 percent anhydrous calcium sulfate. Swelling and consolidation tests were conducted on undisturbed field samples according to the constant volume method. A conventional oedometer sample was used to determine the maximum possible volume change. Likewise, a large-scale oedometer sample was used to capture the influence of fissuring on volume change. The large-scale sample was thoroughly instrumented to determine both the vertical and the lateral swelling pressure. Results indicated a two-fold increase in swelling pressure of the desiccated clay when corrections were applied to account for sample disturbance. The corrected vertical swelling pressure of the clay was 320 kPa for the conventional sample and 245 kPa for the large-scale sample. The lateral swelling pressure was 40 percent of the vertical swelling pressure and the swelling index was one-third of the compression index for the investigated soil.

An Intelligent Expert Systems' Approach to Layout Decision Analysis and Design under Uncertainty

This chapter describes an intelligent soft computing based approach to layout decision analysis and design. The solution methodology involves the use of heuristics, metaheuristics, human intuition as well as soft computing tools like artificial neural networks, fuzzy logic, and expert systems. The research framework and prototype contribute to the field of intelligent decision making in layout analysis and design by enabling explicit representation of experts’ knowledge, formal modeling of fuzzy user preferences, and swift generation/manipulation of superior layout alternatives to facilitate the cognitive, ergonomic, and economic efficiency of layout designers.

Large-strain consolidation modeling of mine waste tailings

BackgroundSustainable management of mine waste tailings during operation, closure, and reclamation requires a clear understanding of modeling the large-strain consolidation behaviour of these loose and toxic slurries. A state-of-the-art was presented focusing on process phenomenology and coordinate systems for tailings dewatering thereby devising a simple constitutive equation with a small number of input parameters. A one-dimensional self-weight consolidation model for quiescent conditions was developed using the finite element method. Test data on oil sand fine tailings were used for model training and predictions were made for an upper bound and a lower bound of various tailings types using a 1 m high hypothetical column.ResultsResults indicated that hydraulic conductivity along with specific gravity dictated pore water pressure dissipation and effective stress development with respect to both time and depth. Likewise, volume compressibility and initial solids was found to govern the void ratio reduction and solids content increase with respect to both time and depth.ConclusionsThe developed model requires a small numbers of input parameters and is capable of capturing the behaviour of a wide range of tailings. Depending on field conditions, the model can predict multiple filling conditions and various types of drainage systems in tailings containment facilities by incorporating appropriate boundary conditions.

Compressive Strength of Compacted Clay-Sand Mixes

The use of sand to improve the strength of natural clays provides a viable alternative for civil infrastructure construction involving earthwork. The main objective of this note was to investigate the compressive strength of compacted clay-sand mixes. A natural clay of high plasticity was mixed with 20% and 40% sand (SP) and their compaction and strength properties were determined. Results indicated that the investigated materials exhibited a brittle behaviour on the dry side of optimum and a ductile behaviour on the wet side of optimum. For each material, the compressive strength increased with an increase in density following a power law function. Conversely, the compressive strength increased with decreasing water content of the material following a similar function. Finally, the compressive strength decreased with an increase in sand content because of increased material heterogeneity and loss of sand grains from the sides during shearing.

Geotechnical performance of a uranium tailings containment facility at Key Lake, Saskatchewan

The main objective of this paper was to investigate the geotechnical performance of uranium tailings in the Deilmann Tailings Management Facility (DTMF) at Key Lake, Saskatchewan, Canada. Laboratory analyses of core samples indicated that the high water content (100–250%) at the tailings surface gradually decreases with depth and reaches around 60–80% at the DTMF bottom. The corresponding solids content values were found to be 30 ± 5% at the surface and 60 ± 5% at the bottom. The grain size data correlated well with both the water content and the solids content profiles, that is, an increase in fines content or an increase in coarse content was associated with an increase in water content (decrease in solids content) and vice versa. The investigated tailings generally exhibited segregation within a narrow range of +2 to −2%, when scaled with respect to the average solids content over a vertical profile. A fines water ratio of around 50 ± 5% was found to be associated with negligible segregation. The effective stress was found to be up to 600 kPa at the DTMF bottom. At low effective stress (around 5 kPa), void ratio ranged from 3.0 to 5.0, while at high effective stress (around 600 kPa) the range of void ratios was generally between 0.5 and 1.0.

Swell–shrink–consolidation behavior of compacted expansive clays

Abstract The main objective of this study was to develop a clear understanding of the volume change properties of compacted expansive clays. An expansive clay (Gs = 2⋅74 and material finer than 0⋅002 mm = 60%) with a significant water adsorption capacity (wl = 77% and wp = 27%) was used. The maximum dry density was found to be 1⋅45 g cm−3 at the optimum water content of 26% which is close to wp. The soil water characteristics curve exhibited two air entry values for all of the index properties: a lower value (10 kPa for gravimetric water content (w), volumetric water content (θ), and degree of saturation (S)) corresponding to drainage through inter-aggregate pores followed by a higher value (100 kPa for w and θ but 6000 kPa for S) associated with seepage through the soil matrix. The shrinkage path during progressive drying of the investigated expansive clay exhibited an S-shaped curve with three distinct portions: an initial low structural shrinkage (S = 100% to S = 85%) followed by a sharp decline during normal shrinkage (S = 85% to S = 75%) and then by a low decrease during residual shrinkage (S = 75% to S = 0). The swelling potential and swelling pressure curves were also S-shaped with the following swelling stages: slow initial swelling because of the low unsaturated hydraulic conductivity; rapid primary swelling due to an established wetting front; and low secondary swelling owing to near saturation conditions. The swelling potential measured 10% and the corrected swelling pressure was found to be 290 kPa. Likewise, the compression index and the swell index were found to be 0⋅17 and 0⋅09, respectively. The predicted heave for a 1 m thick clay was found to range between 70 mm and 90 mm.