A number of earth dams in Canada are founded on and constructed with glaciolacustrine clay deposits. This type of soil can have stability issues particularly in aging dams. Environmental loading such as wetting-drying and freezing-thawing produce fissures and can cause degradation in shear strength with time. This thesis provides an opportunity to assess the stability of an aging earth fill dam. The author’s research focused on a typical earth fill dam in Ontario. A comprehensive field investigation was conducted. Cone Penetration Test (CPTu) was carried out to determine the in-situ strength of the local materials. Shelby tubes with diameter of 102 mm and 76 mm were used to retrieve soil samples from the clay foundation, clay core and placed clay blanket. Structural and mineralogical components of the clay were examined by means of Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) test, respectively. A series of laboratory tests such as consolidated-undrained compression tests, direct shear tests, and 1D consolidation tests were carried out to determine the strength and the deformation parameters. Finally, seepage and stress-deformation modelling as well as slope stability analysis were performed to assess the stability of the earth fill dam. / October 2016

This research consists of scale model shake table tests to investigate the development of seismic earth pressures in soft clay. The soft clay was modeled after prototype San Francisco Bay Mud consisting of a mixture of kaolinite, bentonite, class C fly ash and water. A flexible walled testing container founded on a 1g shake table was used to house the model soil and mimic 1D site response. An array of accelerometers embedded in the model soil measure during an input earthquake motion. A scale model wall is equipped with pressure sensors to measure the seismic earth pressures over the duration of an input earthquake motion. A total of 14 time histories were run through this test set up. A single degree of freedom oscillator was added to the scale model wall and used to mimic the period of a structure. Test results show that for retaining walls with clay soils seismic earth pressures develop triangularly over the face of the wall with an amplitude of about 3.8 times the static pressures. For small building structures, the development of seismic earth pressures depends on height above the base of the wall. Although the pressure distribution is not well defined, localized peaks in pressure are observed at depths of 1/3H and 2/3H below the ground surface. Arias intensity and cumulative absolute velocity correlate linearly with the measured dynamic pressures. Differences between arias intensity and cumulative absolute velocity for each scale model configuration are not pronounced. The simplified Monnobe-Okabe method was also evaluated in this study. Although the Mononobe-Okabe method may be inappropriate for cohesive soils, a seismic coefficient of about 1/10 the PGA was back-calculated from empirically measured earth pressures. The results of this investigation provides an empirical basis to the behavior of walls in clay.

Stone column is a cost-effective ground improvement technique that is typically employed for low-rise buildings and road embankments. This technique mainly uses naturally occurring materials as its load transferring medium. However, stone columns have some constraints because of the loose interactions between their aggregates which can lead to uncontrolled settlements, especially in soft soils. As a result, their performance is usually improved by the inclusion of geosynthetics either in layers or as a confinement. However, there was a lack of studies that used a binder within the stone column aggregates with a view to limit the bulging/lateral spreading of its aggregates in such soils. In this study, the upper portion of the stone columns was replaced by different grades of unreinforced concrete. The length of the concrete, as well as the depth of the soil beneath the columns, were varied. The effects of these different variables, when the resulting column was subjected to an applied load, were investigated. The optimum configuration of the above was identified and its resulting change in performance when it was combined with a reinforced bedding layer was studied. Considering application/installation procedures on site, it was best deemed to install and test a geosynthetic-reinforced bedding layer on top of, rather than within, the stone column. It was observed that increasing the grades of concrete did not have any consistent influence on the performance of the resulting columns when there was a considerable layer of soil beneath them. The hybrid stone columns (combination of stone and concrete) performed better than the normal stone column and even to a full concrete column of the same length in several cases. Physical modelling revealed that the bulging length ranges from 2.0-2.4D (D is the diameter of the column). Test results for the optimum hybrid stone column yielded a maximum load improvement factor of 3 to 6 folds (200% to 500% increase in bearing capacity) depending on their respective configuration compared to the unreinforced soil. The improvement factor was further increased to 9.9-fold (nearly 900% increase in bearing capacity) when the optimum hybrid stone column was tested in combination with a reinforced bedding layer. The findings from this research can be used to enhance and promote the stone column ground improvement technique while still providing an economical advantage as well.

Since the development of plastics in the 1930’s, plastics have increasingly become widely used for packaging in the commercial market place. With this application being for immediate disposal, the amount of plastic waste generated presents a challenge in the disposal thereof. The risks associated with non-biodegradable products on humans and animal life, pressure on existing landfills and the increasing costs thereof have necessitated the development of alternative options for waste management over the years. Research has resulted in various forms of treatments and recycling processes adopted and implemented as environmentally and economically viable solutions. The use of this recycled material in various applications, such as soil reinforcement addresses the need for engineering solutions with a multifaceted approach which strike a balance between environment, economy and equity. This has been the driving force behind research on the use of alternative materials in engineering design. This study aimed to present an investigation into the use of recycled Linear Low-Density (LLDPE) as reinforcement in Cape Flats sand. To understand the implication of the main aim of the investigation, a review of literature on soil reinforcement theory, various forms of reinforcement material and previous studies was conducted. The selected material for testing was in the form of pellets and flakes produced during the recycling process. Triaxial tests were done on samples where the concentration of the inclusions and compaction effort was varied. The test data presented showed that both pellets and flakes affected the shear strength by plotting Mohr’s circles and the relationship between shear stress and normal stress, which revealed changes in the shear strength parameters. The friction angle was increased by 3.35% at an optimum pellet concentration of 5%. Inclusion of the flakes, however, resulted in a maximum improvement in cohesion of 295% at 0.25% concentration. A discussion on the stress- strain relationship gave an indication on the effect on the stiffness. This showed that the peak shear stress was reached at higher strains when the flakes and pellets were included, compared to the unreinforced sand. Improvements by up to 25% were recorded from the initial 6% strain at peak shear stress of unreinforced sand. In concluding the study, Slide7.0 was used to conduct a 2D finite element analysis using Bishop’s method to analyse the practical application of LLDPE flakes and pellets for slope stability. The optimum shear strength parameters were used in the model, which resulted in an improved global factor of safety meeting the minimum requirement of 1.25.

The use of geosynthetics has rapidly increased in nearly all geotechnical related fields as they allow for innovations, improved performance and cost effectiveness in projects. However, when geosynthetics are installed on sites, particularly on landfill slopes, their interface interaction against the adjacent materials becomes the critical section where shear failure is likely to occur. For this reason, their shear strength behaviour is determined in the laboratory at anticipated site conditions, mainly using a direct shear device to obtain design parameters. These laboratory tests are preferably conducted in accordance with ASTM-D5321 and ASTM-D6243 standards. The direct shear equipment, however, requires the use of an appropriate gripping system for shear to take place in the desired interface. Otherwise, tensile failure within the tested geosynthetics will be generated, resulting in obtaining design parameters which do not represent the actual field performance of the tested geosynthetics. This could lead to unsafe, cost ineffective, etc. design of projects with the respective geosynthetic materials. To date, many laboratories use a variety of gripping systems in a direct shear device to determine the shear design characteristics of geosynthetics and the preferred system remains a topic of concern. As a consequence, there is a large variability in the test results obtained, thus, difficulties in their interpretations. In this research, the effects of two commonly used gripping systems in a direct shear device, namely the nail plate (NP) and sandpaper (SP), have been investigated using a landfill case liner. This liner consisted of the three different classes of geosynthetics which are popularly installed in a landfill i.e. geotextile, geomembrane and geosynthetic clay liner. The results revealed that there exists a dissimilarity in the mobilized shear strength at geosynthetic interface when the NP is used as compared to the utilization of the SP due to the specimen engagement with the respective gripping systems. The exact difference, however, was not established as it varied depending on the interface tested. This highlighted the need to standardize the geosynthetic gripping systems in a direct shear device as it would capture these variations, increase result reproducibility and ease their interpretations.

The Mount Moorosi village is situated in the Senqu River Valley of southern Lesotho, within the Stormberg landform. The integrity and aesthetic appearance of nearly all the structures in this area are undermined by recurrent cracks. At present, no apparent institutionalised effort had been conducted to investigate the source of this problem. The crack patterns were associated with the possible volume change of the underlaying loess like soil. This soil has caused a disastrous failure to brittle civil engineering structures in various parts of the world. Its behaviour is attributed to sand and silt particles bonded by minerals, which become active upon saturation and induce hydrocollapse settlement. This study characterised the volume change properties of the underlaid deposits in Mount Moorosi. The research utilised representative samples from trial pits in the study region to perform laboratory experiments such as the Atterberg limits, wet sieving, sedimentation, free swell, x-ray diffraction, scanning electron microscope and slaking. The consolidated undrained tests and hydrocollapse potential were also determined from the GEOCOMP triaxial and Global Digital System oedometer, respectively. Results revealed that Mount Moorosi is generally underlaid by a more than 3 m thickness of low plasticity (9 to 17 %) silty-sandy loess. The material had significant warping (up to 27 mm) in linear shrinkage that illustrated potential inducement of detrimental stresses to the superimposed structures during drying. The identification and quantification of the mineralogy composition clearly evidenced the passive minerals (quartz, feldspar and mica) to be predominant (86 %), while the active phases (kaolinite, carbonates, sulfates, halides, the oxides and hydroxides of aluminum and iron) were subordinate (14 %), which substantiated potential soil settlement upon wetting. Furthermore, the micrographs depicted structures that synergistically enhanced the collapse properties of the tested deposits. These included the porous clays, silts bonded by clay and silts coated with clay, which all rendered a metastable fabric. A comparison of the stressstrain graphical plots from the consolidated undrained tests at the field and saturated moisture contents indicated a drastic reduction (up to 73 %) in deviator stress at saturated water content. This was attributed to the augmentation of the interparticle spaces, caused by a rise of up to 337 kPa in pore water pressure. Shear strength parameters obtained from Mohr’s failure envelopes were also decreased by up to 80 %. The hydrocollapse index measured from the oedometer tests ranged from 10 to 15 % at a vertical stress of 200 kPa. It indicated severe settlement problems for structures constructed on this soil. This was caused by the loss in shear strength of the soil under the saturated conditions and a high slaking mechanism that reached a maximum rating of 4. Generally, the mineralogy composition, morphology, saturated shear strength, slaking and hydrocollapse index collectively indicated the possibility of soil volume decrease. In fact, the check for serviceability limit state demonstrated a settlement that exceeded the tolerable value of 50 mm. The cracks observed on structures were, therefore, related to soil settlement. This study recommends further research on suitable ground techniques to minimise settlement, thereby improving the durability of structures. Moreover, investigations should be conducted to understand the pressure induced by warping during shrinkage.

Includes bibliographical references. / Engineers are often faced with construction of pavement structures over soft and compressible subgrade. Such conditions render the structures unable to withstand required design loads and thus are susceptible to high settlements associated with excessive distress leading to pavement damage. The use of imported quality fill to improve the load-bearing capacity of the subgrade has limited benefits, which leads to the necessity of an alternative construction approach to attain the necessary strength of the soil structure. The use of geosynthetics in soil offers a better alternative to improvement of the soil's stability. This research was conducted to determine the degree of improvement of the load-bearing capacity and reduction in settlement due to geosynthetic reinforcement of a soft clay overlain by granular material.

All modern day landfills contain a series of perforated pipes installed beneath the waste whose purpose is to collect all liquid which drains through the cell. This system is called the leachate collection system and its primary purpose is to drain any liquid toward a central location where it is pumped and then treated, discharged, or recirculated. It has been discovered that certain landfills see a buildup of precipitates within the system which leads to clogged pipes and buildup of leachate head on top of the landfill. The formation of the precipitates is linked to the chemical and biological make-up of the leachate generated within the landfill. In order to better understand this clogging process and thus be able to prevent it in future landfills, the chemical and biological characteristics of leachate as well as landfill design must be examined. It is now known that ash content within the waste will lead to greater clogging. This is due to the fact that ash contributes greater amounts of the calcium necessary for biofilm to grow within the drainage media. While one solution to this problem is the monofilling of ash residue in separate landfills, many operators still choose to combine MSW and ash. Since no law exists prohibiting the later it is the goal of this research to design a model which may be used by landfill operators to foresee clogging potential of their landfill and thus prevent it. The main objective of this study is to use a "film growth approach" to simulate clogging in Florida landfills. The change of hydraulic properties and porosities of leachate drainage materials due to calcium carbonate buildup will be predicted using Florida specific leachate composition data and leachate generation data for typical landfills operated in different micro-climates of the state. The results of this investigation will be used to examine the adequacy of the current design methodology of leachate collection systems in the state of Florida. The findings of this study will then be used to estimate the service life of LCSs in different regions of the state. The study was conducted in four stages. The first stage consisted of a literature review of previous laboratory and field tests of LCSs. It also took into account all available FDEP databases of leachate quality and quantity. The second stage aimed at modeling calcium carbonate growth within an LCS based on results obtained in the first stage. The third stage consisted of an analysis of LCS clogging results as applied to model landfills which represented typical landfills throughout the state of Florida. The performance of these model landfills and LCSs was evaluated to see what kinds of changes are noticeable in the leachate quality and quantity over the lifetime of the landfill. Clogging of drainage media was the main focus of this stage because this clogging is the biggest contributor to LCS failure. Finally the adequacy of design of LCSs in model landfills was examined and adjusted as needed based on results obtained in stages 1-3. It was also possible to estimate the service life of existing and future LCSs to make sure that no leachate ever escapes the landfill and contaminates the groundwater. / A Thesis submitted to the Department of Civil and Environmental Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester, 2014. / November 6, 2014. / Clogging, Florida, Landfill, LCS, Leachate, MSW / Includes bibliographical references. / Tarek Abichou, Professor Directing Thesis; Gang Chen, Committee Member; Clayton Clark, II, Committee Member.

Geotechnical structures such as composite liner systems in landfills consist of multiple interfaces, which include a broad range of geosynthetics in conjunction with soil, rocks and any other related materials. This results in the introduction of many interface planes into the structure, which can potentially create instability especially along the slope and ultimately result in failure. To date, many laboratories use single interface testing instead of multi-layer interface testing to determine geosynthetic shear design characteristic values that are used in the design of structures such as landfill liners. A topic of discussion remains the preferred interface testing configuration and only a few studies have substantiated and quantified the significance of varying the different interface shear testing configurations. This study, therefore, aimed to evaluate and compare the effects of the use of the two interface test configurations on the shear strength of soil/geosynthetic and geosynthetic/geosynthetic interfaces. Furthermore, it was intended to identify the test configuration that provides the most critical shear strength results, while also understanding the fundamental mechanisms responsible for the shear strength observed. In this study, three geosynthetics were used: geotextile (GTX), geomembrane (GMB) and geosynthetic clay liner (GCL), which generally constitute the critical interface components of a lining system in a modern South African landfill liner. Two soils were utilised as a part of the materials required for the investigation and they were: river sand and red clay. The laboratory tests were conducted under saturated conditions in accordance with the ASTM D5321 and ASTM D6243 standards, using a 305 mm x 305 mm large direct shear box. The tests were carried out over a range of applied normal pressures of 50, 100, 200 and 400 kPa. A constant shear rate of 1.0 mm/min was used in the interface tests that did not involve GCLs or clay specimens and therefore no excess pore pressure was anticipated at the interface. On the other hand, for all other interface tests involving either clay or GCLs samples, a shearing rate of 0.1 mm/min was utilized. The results showed that nonlinear behaviour of the shear stress versus shear displacement responses was exhibited in both the single and multi-layer interface tests, regardless of the normal stress applied. However, it was noted that with an increase in normal stress applied, the deviation in mobilized shear stress between the two test configurations increased, with single interface tests yielding higher shear stress values compared to multi-layer interface tests. In single interface tests, the high shear stresses could be related to the clamping that confined each of the test specimens during shearing to one end of the shear block. On the other hand, only the top and bottom test specimens were clamped in multi-layer interface tests, thus allowing failure to have occurred at the weakest of the available interfaces. Moreover, for single interface tests, peak strengths were generally 9% lower for the range of normal stresses considered, whereas Large Displacement (LD) strengths were generally 24 % lower for the single interface tests, compared to the peak and LD strength values for multi-layer interface tests. This was particularly observed at low normal stresses between 50 and 200 kPa, and it could probably have been caused by the rigid clamping of the geosynthetics which results in some tensile strains in the geosynthetics. In addition, it was observed in multi-layer interface tests that a transfer of shear stresses within the system could have occurred, which could have led to higher overall shear resistance of the composite. As a result, single interface tests yielded a conservative estimate of the peak and LD shear strengths for the tested interfaces compared to multi-layer interface tests. This may be attributed to higher displacement along with the critical interface in single interface tests than in multi-layer interface tests. To allow the investigator to observe the displacement, as well as the possible transfer of shear stresses within the system during the shearing of the various geosynthetics, it was recommended that real-time monitoring of the displacement mobilization should be carried out in multi-layer interface tests during shearing.

Geomembranes are often utilized as fluid barriers in geotechnical applications such as landfills. Due to their relative impermeability and chemical resistance characteristics, they are usually used alongside other geosynthetics like geotextiles in landfills to constitute base, side-slope, and cover liner systems. Uniquely, within the side-slope liner composite system, which consists of multiple geosynthetics interfaces, the geomembrane/geotextile (GMB/GTX) interface is known to have relatively low shear strength. In an effort to mitigate sliding failure occurrence at the GMB/GTX interface, asperities have been incorporated into GMB manufacturing to increase the shear characteristics. Presently, many GMB with various asperities properties is now available because of asperities proven advantage. Challengingly, only a few studies have substantiated and quantified the importance of varying asperities properties (height, density, and shape) on the GMB/GTX interface. Therefore, this study was aimed at investigating the effects of asperities variation on GMB/GTX interface shear characteristics and mechanism, as well as to identify the asperity parameters combination which optimizes the GMB/GTX interface shear strength. The GMB/GTX interface shear tests were conducted according to ASTM D5321, under saturated conditions with the “305 mm by 305 mm” direct shear box at applied normal stresses; 25 kPa to 400 kPa. In this research, the two common geotextile polymers (polypropylene and polyester) in South Africa were used at the GMB/GTX interface. Also, the geomembranes used had their asperity height varied from 0 mm to 2.02 mm, while the asperity density and shape were varied from 0 to 663 spikes per 10000 mm2 , and conical to hook-cone asperity shape, respectively. GMB/GTX interface shear results showed that with a 70 % increase in the geomembrane asperity height at constant asperity density, friction angle increased by 25 %. Also, an average increase of 25 % in the friction angle was observed as asperity density was doubled at constant asperity height. However, the friction angle was not significantly affected by changes in asperity shape from conical to “hook-cone” shape. Therefore, among identified asperities and roughness features, asperity height together with surface roughness affect the GMB/GTX interface shear parameter more dominantly. These outcomes present a better explanation of the “fibre/asperity” interaction at the GMB/GTX interface and identified asperity properties which optimised surface interaction. The optimised interaction produces efficient shear mechanism that would ultimately lead to a stable and durable landfill liner system.