OpenUCT :: Browsing by Subject "Geotechnical Engineering"

Browsing by Subject "Geotechnical Engineering"

Now showing 1 - 12 of 12

Open Access
A Comparative Study on Shear Strength Testing of Single and Multi-layer Interfaces using Large Direct Shear Apparatus
(2021) Muluti, Shade; Kalumba, Denis; Sobhee-Beetul, Laxmee
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.
Open Access
A laboratory investigation on the shear strength characteristics of soil reinforced with recycled linear low-density polyethylene
(2018) Nolutshungu, Lita; Kalumba, Denis
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.
Open Access
A study on ground improvement using a combination of stone and concrete columns
(2018) Pudaruth, Yogendra; Kalumba, Denis; Sobhee-Beetul, Laxmee
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.
Open Access
An Investigation into the Effects of Asperities on Geomembrane/Geotextile Interface Shear Characteristics
(2020) Adeleke,Daniel; Kalumba, Denis; Nolutshungu, Lita; Oriokot, Johnny
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.
Open Access
An investigation into the volume change characteristics of loess like soil in Mount Moorosi Village in Lesotho
(2019) Damane, Monica; Kalumba, Denis; Sobhee-Beetul, Laxmee
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.
Open Access
An Investigation of the Effects of Specimen Gripping Systems on Shear Stress at the Geosynthetic/Geosynthetic Interface in Landfill Applications
(2019) Sikwanda, Charles; Kalumba, Denis; Nolutshungu, Lita
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.
Open Access
Evaluation of the electrical density gauge for in-situ moisture and density determination
(2015) Lekea, Angella; Kalumba, Denis; Chebet, Faridah
Densification of soil during construction of earth structures is achieved through the process of compaction by application of mechanical energy to obtain the required engineering properties of the soil for a particular project such as hydraulic conductivity, soil strength and compressibility. These properties are dependent on attainment of high compaction densities normally achieved at specific moisture contents for a given compactive effort. The optimum moisture content and maximum dry density for a particular soil is determined by means of Proctor tests in the laboratory. A relative compaction index is then used to correlate the laboratory values with the field compaction values obtained using in-situ tests. The Sand Cone (SC) and Nuclear Density Gauge (NDG) are the common field tests used to the dry density and moisture content of the soil for purposes of quality control of the compaction process. The sand cone is a laborious test that involves excavation of part of the compacted layer and requires a 24-hour waiting period to obtain the moisture content of the soil through the laboratory oven method. The NDG on the other hand is less laborious, however it uses a radioactive source that is a potential health hazard and therefore requires strict handling, storage and maintenance of the equipment to maintain safety standards. The Electrical Density Gauge (EDG) is an alternative in-situ test that is quicker, safer and easier to maintain since it uses electric current to measure the compaction characteristics of the soil. The objective of the study was to determine the repeatability, accuracy and applicability of the EDG on South African soils by comparing its measurements for dry density and moisture content in the laboratory and in the field to the results from the sand cone and oven method. In the laboratory, a clean sand and a clayey sand were tested at the optimum moisture content and at ± 3% of the optimum moisture content. The soils were compacted to 200 mm using the RT74 rammer and the compaction values first tested using the EDG then followed by the sand cone test at the centre of the EDG test spot. The moisture content of the excavated sample from the sand cone test was determined using the oven method. For the field tests, the compaction characteristics of a sandy gravel and three uniformly graded sands were tested in-situ using the EDG followed by the sand cone test. Overall, the EDG measurements were repeatable based on test-retest comparison of the paired measurements. EDG results for moisture content were consistent with the values obtained from the laboratory oven method especially in the uniformly graded sands. However, the density measurements differed from the results of the sand cone test, which was considered the reference test for determination of field soil density. It is recommended that the EDG calibration relationship for bulk density be revised in order to improve the accuracy of the density measurements.
Open Access
Experimental study of shear behaviour of high density polyethylene reinforced sand under triaxial compression
(2017) Wanyama, Paul; Kalumba, Denis; Chebet, Faridah
Soil reinforcement is an ancient technique which involves the addition of tensile elements like plastics in the soil to increase its engineering properties like shear strength, settlement, cohesion and bearing capacity. In consideration of this, a series of triaxial tests were undertaken to investigate the reinforcing effect of High-Density Polyethylene (HDPE) plastic material in Cape Flats sand, predominant in the Western Cape region of South Africa. Plastic strips of various lengths were randomly included to the soil at different concentrations to form a homogenous soil-plastic composite specimen prepared at varying compactive effort. Using a split mould, cylindrical specimens of 50 mm diameter and 100 mm height were prepared using the dry tamping technique. The test specimens were compacted to achieve target average dry densities of the composite sample. The plastic strip reinforcement parameters comprised of 7.5 mm to 30 mm lengths, and concentrations of 0.1 % to 0.3 % by weight of dry sand. Triaxial compression tests were performed using confining pressures of 50 kPa, 100 kPa, 200 kPa, 300 kPa and 400 kPa at a shear rate of 0.075 %/min, and to a maximum strain of 10 %. Laboratory results favourably suggest that there is an improvement in the soil shear strength properties due to these inclusions. The friction angle increased up to a peak value on varying plastic strip length and concentration, beyond which further addition of plastic material led to a reduction in the friction angle. The greatest friction angle was reported at plastic strip length and content of 15 mm and 0.2 % respectively. Additionally, the results indicate that a higher compactive effort leads to a greater increase in friction angle of the soil. The existence of a critical confining stress was observed from triaxial test results on soil-plastic composites. This threshold limit was influenced significantly by the plastic inclusions, and the range of confining stresses. Consequently, a bilinear failure envelope was reported in reinforced samples while unreinforced specimens realised a linear relationship. The Mohr-Coulomb failure line above the critical confining pressure almost paralleled the unreinforced linear relationship. An embankment model was developed using Slide Modeler software and the factor of safety of slope was analysed with unreinforced and reinforced backfill subjected to static and dynamic loading. It was observed that the safety factor increased due to polyethylene strip inclusions. Therefore, the proposed technique will find potential practical applicability in low-cost embankment or road construction.
Open Access
Geotechnical engineering design of a tunnel support system - a case study of Karuma (600MW) hydropower project
(2017) Ongodia, Joan Evelyn; Kalumba, Denis
Tunnels have been built since 2180 B.C., through the stone age. They became popular worldwide since the eighteenth century, as transportation, military, mining, conveyance, storage and flood control structures. Due to the increasing world population, urbanization and industrialization, the construction of underground tunnel structures are preferred as they limit interferences with existing surface uses of the land and water bodies. Although underground tunnels are a common flexible construction alternative, they are high hazard risk structures. The risks are mostly related to ground conditions. Tunnels buried at depth disturb in-situ conditions, cause ground instability and ultimately failure. Widespread tunnel failures, though not publicly advertised because of their adverse implications, have claimed human lives, cleared cities, cost 100 million United States dollars' worth in financial losses and year-long project delays. As such, stability of the structures is crucial to prevent the catastrophes thereby reducing societal outcries. Permanency of underground structures is ensured by provision of adequate resistance to any impeding failure of the ground surrounding deep underground excavations. The effectiveness of the ground-support interaction depends on geology, material properties, geotechnical parameters, loads of the surrounding ground mass and mechanism of the interaction. Using actual project information, the factors influencing stability, structural resistance as well as methods to select the required support are explored in this dissertation. The study used typical geological data of an underground tunnel component of Karuma, a proposed 600MW hydropower project in Uganda. It doubles as the largest hydropower project and first underground construction, to date. The project is located along the River Nile in a sensitive ecosystem neighboring both a major national park and the Great Rift Valley system in East Africa. The instability problem at Karuma was assessed using scientific and universal tunneling practice. Typical site data formed input for the geotechnical engineering design of the tunnel support based on analytical, observational and empirical methods. The study demonstrated that all methods were independent and dissimilar for the same geotechnical engineering challenge of the underground structure. The most comprehensive method was the one based on geotechnical engineering principles and rock mechanics theory. The outcomes of the different approaches in this study were unique functions of their underlying scientific philosophies. The study proposes that in designing adequate support systems to resist forces causing failure of underground tunnels, excavations buried in the ground should encompass several methods. The most conservative design should be chosen to ensure permanency.
Open Access
Investigating the feasibility of implementing microbially induced calcite precipitation to stabilize sand, clay and gold tailings
(2022) Hyde, Rhonda; Nolutshungu, Lita; Randall, Dyllon
Microbially Induced Calcite Precipitation (MICP) is an emerging bio-mediated technology which has been successfully applied in soil improvement research. MICP uses the enzyme urease produced from bacteria to breakdown urea into carbonate ions. These carbonate ions combine with free calcium ions to form calcium carbonate, which acts as a bio-cement. MICP presents a unique, sustainable soil improvement solution to the pressing issues resulting from tailings impoundment failures. It has shown potential through increasing shear strength and decreasing porosity in soils. However, MICP applications in soil improvement outside erosion mitigation in granular soils remain limited. This is similar to the limited use of injection treatment, in comparison to the more prevalent spraying and surface percolation in MICP applications. This research focused on the efficacy of the developed injection procedure for administering the MICP treatment to increase shear strength and decrease porosity in sand, clay and gold tailings at greater depths and evaluating its feasibility. By determining the efficacy and significance of the treatment in improving the geotechnical characteristics of the soil samples, the methodology can be evaluated for its application as a soil improvement technique. Results showed successful cementation of the particles of the soils tested with an increase in cohesion of 7.7% and 23.1% for clay, and tailings respectively and an infinite increase in the apparent cohesion of sand from 0 to 20kPa. The response to MICP treatment in terms of the angle of internal friction were inconclusive, where a decrease was observed across the board. This was attributed to complex stress-strain behaviour as well as the particle morphology. A decrease in porosity of approximately 26% in clay and 8% in tailings was observed, whilst sand had an increase of approximately 3%. The increase in porosity in sand was identified as a result of the erosion of the coarse uncemented particles during treatment. The results emphasised the greater success of MICP treatment in more granular soils, with sand achieving the greatest improvement with regard to the apparent cohesion and particle density. Characteristically, the particle sizes of the gold tailings fell between the fine clay and the coarse sand which was reflected in the response of the gold tailings to treatment. Overall, sand had the greatest increase in shear strength, followed by the gold tailings and lastly the clay. The gold tailings contained a higher percentage of fines than the sand, illustrating the limitation of MICP applications in fine grained soils. However, the predominant coarse fraction allowed for an overall increase in the shear strength parameters in the gold tailings. An evaluation of the feasibility shows that the methods provide a scalable soil improvement technique in stabilisation applications in contrast to existing MICP surface treatments in sands. In clays and tailings however, interactions of heavy metals with the microbial community as well as the particle size limit the efficacy of MICP. In conclusion, MICP is found to be a feasible soil improvement technique in stabilising gold tailings with the consideration of the impact of heavy metals and the particle size on the efficacy of the treatment.
Open Access
Investigation of hydro-mechanical particle flow through horizontal orifices
(2018) Qiu, Zhenghui; Kalumba, Denis; Lai Sang, Johnny
In the modern world, as the global population continues to rise, the need for and recovery of natural resources is becoming ever more relevant. Identifying optimisation solutions for the recovery of granular resources has progressed into one of the most dominant development areas in the mining and processing industries. Two relevant examples from these sectors include the offshore extraction of materials from the ocean floor via hydraulic transport and the processing of mineral particulates through chutes, and hoppers. A common feature of recovery employed in such areas is the rate at which these materials pass through an orifice. The orifice is the interface between the implemented collection or transport system and the targeted material source. Extensive research has been done on the gravitational passing of particles through an orifice, where in contrast, limited knowledge exists on alternative driving factors of flow. The movement of particles induced both mechanically and hydraulically formed the basis of this dissertation in which selected granular materials were experimentally characterised. Specifically, the following were studied: the effect of orifice and particle size, changes in system velocity and the effects of suction. The system encompassed a scaled down model of a real-life application. An experimental and numerical analysis approach was undertaken, where the calibration of the simulated model was dependent on the former. A total of 327 experimental tests were conducted on the flow ability of high sphericity (±95% roundness) glass beads. A numerical model based on the physical parameters was calibrated to further assist in the overall analysis of the system. The model was of a discrete element method (DEM) type. Empirically, it was found that the Beverloo law, an expression used to describe the discharge of particles through a hopper, had many aspects that were dimensionally suited for the study. Through certain boundary assumptions made in the study, the law was in agreement with the stated outputs. The ratio (R) between the orifice (Dₒ) and particle diameter (dₚ) had a significant influence on the entrainment rate, where there existed a region (R > 4) of limiting flow. Changes in the system velocity, were found to have a negligible effect on the overall recovery but a direct relationship with the rate at which the material was collected. The introduction of suction improved the recovery of materials greatly, increasing the mass flow rate by more than 300%. The in-depth analysis on a multitude of orifice configurations, considerably extended the understanding of the behaviour of particles passing through an opening, particularly spherical particles under fluid or mechanical driven flow. Results indicated that there was a lot of potential for improving the optimisation of granular flow. Optimisation in this sense was defined as maximising the recovery (%) or collection rate (kg/s) of the system. Boundary conditions and design guidelines were offered to address this issue. Areas where further research could advance this understanding were highlighted.
Open Access
Reinforcement of pavement subgrade using granular fill and a geosynthetic layer
(2014) Oriokot, Johnson Johnny Onapito; Kalumba, Denis
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.

Browsing by Subject "Geotechnical Engineering"

Results Per Page

Sort Options