ssc412 topics 2015 - university of pretoria€¦ · be a long term form of renewable electricity...
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SSC412: FINAL YEAR RESEARCH PROJECT
TOPICS FOR 2015
3 November 2014
1 WATER RESOURCES
1.1 SUPERVISOR: PROF FANIE VAN VUUREN
1.1.1 MODELLING OF GAUGING STRUCTURES
Directorate Hydrological Services in the Department Water Affairs and Sanitation operates
approximately 800 gauging structures across the South Africa. These structures are designed to
measure low to medium discharges in rivers. The flow range measured cover approximately 70
percent of the runoff volume at a gauging structure. To gauge the 30% volume runoff not measured
within the gauging capacity of a structure, the rating of a structure is extended mainly by extending
the rating theoretically or by means of backwater calculations. There exists however an area of
uncertainty on the correct application of gauging structure theory when the structural gauging
capacity of a structure is exceeded. This is especially true in the case of compounded Crump
structures equipped with dividing walls designed in accordance with ISO standards. A physical model
will be used to verify the stage curves.
Students working on this should have transport to conduct the tests at the Department of Water
Affairs and Sanitation Laboratories in Pretoria West.
1.1.2 EVALUATION OF PUMP EFFICIENCY SYSTEMS
The high cost in electricity requires a relook at the efficiency of pumping systems. In the CoT water
supply area there are numerous pumping systems. These systems will be reviewed by recording the
operating time, volume transferred, friction and secondary looses in the system. From the data a
model to prioritize the systems for upgrade, extension or replacement will be set up. Each student
will at least model 3 pump stations.
Students should have transport to conduct the tests at the various pump stations in Tshwane.
1.1.3 REVIEWING THE HYDRAULIC OPERATIONAL CAPACITY OF CULVERTS IN THE COT STORM
WATER SYSTEM
The problems leading to the hydraulic failure of inlet controlled culverts are associated with the
blockage and layout at these culverts. Students will have to survey a number of structures in a
specific river reach, calculate their current and design capacities and set up a numeric model to
analyse their influence and the temporal storage which they create.
Students should have transport to conduct the tests in different water courses in Tshwane.
1.1.4 CAVITATION PREVENTION IN CONTROL VALVES
At high differential head at control valves leads to cavitation. Previous work and a patent by Prof van
Vuuren provided a solution to this problem. In collaboration with the CoT tests will be conducted at
a number of locations with the intention to verify the application and improve on the installation
and modification to control valves.
Students should have transport to conduct the tests in different water courses in Tshwane.
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1.1.5 LEAK DETECTION USING INVERSE TRANSIENTS
A pressure wave can be generated in a conduit by chancing the operating regime. The inefficiencies
like leaks in the system will result in a reflection wave which can be recorded. By assessing these
pressure waves, the location and the extent of the efficiency can be quantified.
Students should have transport to conduct the tests in different water courses in Tshwane.
1.1.6 REVIEW OF THE INFLUENCE OF THE LAYOUT OF VALVE INSTALLATION ON THE ACCURACY
OF VOLUMETRIC FLOW METERS
The installation of water meters requires that the upstream and downstream influences on the flow
should be minimised to ensure accurate measurement. Flow meters will be tested in different
installation layouts. This will provide indication on the installation requirements. The model test will
be setup in the hydraulic laboratories at the Proefplaas.
Students should have transport to conduct the tests.
1.1.7 CHANGING THE INLETS OF CULVERTS TO PREVENT SEDIMENTATION
Sedimentation is a problem in inlet controlled culverts. Experimental work was conducted in
2013/2014 and needs refinement in a larger physical model. It is also envisaged that with support
from SANRAL that some field work will have to be undertaken.
If access to CFD capabilities can be acquired numerical modelling will also be considered.
1.2 SUPERVISOR: MR M VAN DIJK
1.2.1 DEVELOPMENT AND TESTING OF SMALL HYDROPOWER GENERATION UNITS
There is a need in the country to provide electricity in remote areas. Pico hydro installations are
typically used in developing countries for energy provision to isolated communities where the
national electricity grid is not available. There are some commercial hydropower systems available
that provides power by using the pressure drop across a pressure reducing valve to run a generator.
The focus of this proposed research initiative however is the development/implementation of an
inline hydro turbine into a water distribution network.
It is proposed to develop an energy recovery solution that would enable local authorities to produce
clean, reliable, low-cost electricity from the excess energy available in their water pipelines. An inline
turbine that captures energy from fast-moving water inside of small diameter, gravity-fed pipelines
with no impact on flow or operation will be developed. Depending on head pressure, flow and pipe
diameter, the turbine installation would be capable of producing from a few Watts to almost 1 kW of
renewable, zero emissions electricity by extracting pressure head.
It is aimed to develop an inline turbine unit which can easily be installed in a pipeline to provide
energy for use on site to power various devices located within close proximity of the turbine unit e.g.
motorised pilots, sensors, telemetry, PLC, sump pumps and lighting.
Preliminary work has been done and results look very promising. Currently there are 3 types that
have been developed, which require testing, verification and further improvement. The work will be
done in Pretoria. Students should have transport to conduct the tests.
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1.2.2 BUILDING AND TESTING OF A DEMONSTRATION HYDROPOWER FACILITY ON THE
PROEFPLAAS
The Mechanical Department had redundant hydropower turbines in their laboratory. These turbines
were moved to the Proefplaas where a demonstration plant needs to be built. The turbine set-up
will need to be equipped with the necessary measuring equipment, tested and calibrated to allow
for future experimental work to be conducted using this setup.
1.2.3 SMALL-SCALE HYDROPOWER DEVELOPMENT FOR RURAL ELECTRIFICATION IN SOUTH
AFRICA
The proposed research project shall outline the possibilities of using small hydropower systems for
rural village electrification in South Africa. The aim of this research project would be to enhance the
uptake of micro-hydro technology, making local stakeholders (private sector, financial sector,
government entities, etc.) aware of the opportunities that this technology brings and the
coordinated efforts required to get this technology successful again.
The expansion of the national grid to supply rural areas is not a priority at the moment. Mini, micro
and pico-hydropower are particular types of small scale hydropower where the installed capacity is
less than 1MW. As with other small scale hydropower schemes, these schemes have the potential to
be a long term form of renewable electricity generation because projects have shorter lead times
than large-scale projects and can last for up to- 50 years.
Access to electricity serves a vital role in empowering community development by expanding
opportunities for education, fostering the growth of local businesses, and improving quality of life.
Where electricity is not available, rural areas rely on traditional fuel sources that are poor sources of
lighting, detrimental to the environment and users’ personal health. Hydropower is less expensive
and less polluting than traditional fuel sources such as kerosene or diesel.
This research project looks at ways in which mini, micro and pico-hydropower can be used in the
generation of electricity for rural applications in South Africa. Some field work will be conducted in
the district municipality of uMzinyathi and OR Tambo (KZN and EC) where sites have been identified.
1.2.4 DETERMINING THE OPERATIONAL REQUIREMENTS FOR A HYDROPOWER PLANT FOR
EFFICIENT OPERATION
An initial scoping investigation highlighted the potential hydropower generation at the inlets to
storage reservoirs. In South Africa there are 284 municipalities and several water supply utilities all
owning and operating gravity water supply distribution systems which have some type of pressure
dissipating system at the downstream end of the supply pipe. The University of Pretoria (UP)
supported by the Water Research Commission (WRC) constructed a hydropower plant at the Pierre
van Ryneveld Reservoir.
This system now needs operational rules to be set up. Optimize power generation versus ensuring
an acceptable water level in the reservoir to satisfy the varying demands. The student will be
required to record the water levels, pressure, energy generation, flow rate in and out of the
reservoir etc. and setup an operational set of rules. In short reservoir routing (mass balance) linked
to energy generation.
The student should have transport to conduct the tests at the Pierre van Ryneveld Reservoir.
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1.3 SUPERVISOR: MS I LOOTS
1.3.1 THE INFLUENCE OF CATCHMENT DEVELOPMENT ON RUNOFF
It is widely accepted that urban development results in a decrease of permeability of a catchment
and will therefore cause floods with higher and faster peaks. However, this assumption does not
take into account the possibility of retention and attenuation in the system, due to property
boundaries or the levelling of naturally sloping areas. It may be that urban flooding is severely
overestimated.
It is proposed to set up an area at the Experimental Farm where antecedent conditions, rainfall and
run-off can be measured and compared to internationally accepted calculation methods.
The student should be available to set up the experiment before the end of 2014.
1.3.2 METHODS TO ENSURE SUSTAINABLE MOUNTAIN BIKE TRAILS
Mountain bike trails runs down steep slopes and uneven terrain. These tracks create high erosion
damage potential and methods to reduce the potential scour needs to be evaluated. Students
interested in this topic should have access to courts where the proposed remedial actions could be
reviewed.
2 TRANSPORTATION
2.1 SUPERVISOR: PROF WYNAND STEYN
2.1.1 EVALUATION AND CALIBRATION OF TIME DOMAIN REFLECTROMETRY (TDR) METHOD FOR
DENSITY AND WATER CONTENT MEASUREMENT
The in situ moisture content and density of pavement materials are vital for an understanding of the
performance and life of the layer. TDR technology has been used in the agricultural area for many
years for measuring the in situ moisture content. However, it is know that material properties
(including density) affects the value. This project will evaluate the level to which TDR data are
influenced by material properties and parameters through mainly laboratory testing and field
evaluation.
2.1.2 THE EFFECTS OF MATERIAL SCALING FOR CENTRIFUGE TESTING OF PAVEMENT LAYERS
The civil centrifuge at the University of Pretoria is being used for non-traditional testing such as
pavement structure evaluations. In these tests, materials need to be scaled to enable realistic
models to be constructed. However, the effect of this scaling on various pavement material
properties is not always clear. In this project the effects of scaling of the following materials will be
evaluated:
• Bitumen viscosity and layer thickness around aggregate
• Granular material grading
• Stabilized material bonds
2.1.3 EVALUATION OF THE BEHAVIOUR OF A LAYERED PAVEMENT STRUCTURE UNDER
CENTRIFUGE MODELLING CONDITIONS
The civil centrifuge at the University of Pretoria is used to evaluate the behaviour of structures under
accelerated g-forces. Scaled pavement structures are also tested under ranges of moisture,
temperature, load and material property conditions. In this project a selection of pavement
structures will be evaluated where the pavement properties are selected to model pavement
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structures with a range of balance conditions and the performance of these structures under scaled
loading evaluated. PIV will be used and a range of sloped structures and materials with ranges of
densities and moisture contents can be included.
2.1.4 EVALUATION OF THE DEVELOPMENT OF RESIDUAL STRESSES INSIDE LABORATORY
COMPACTION MODELS
When pavement materials are compacted a horizontal stress develops. In real roads this stress acts
against the surrounding material. In laboratory tests this stress acts against the steel mould. There
are various theories regarding the effect of this horizontal stress and possible residual compaction
stresses on pavement material properties. In this project these stresses will be measured under a
range of conditions and their potential effects on standard pavement material layer properties
determined.
2.1.5 EVALUATION OF THE STRESS DISTRIBUTION BETWEEN FWD / LFWD LOADING PLATE AND
ROAD SURFACE
The FWD and LFWD are used to evaluate the condition of a pavement structure with. This project
will evaluate the actual stress distribution between the FWD / LFWD loading plates and a range of
pavement surface types to enable better modelling of these data.
2.1.6 EVALUATION OF ΕMU COILS FOR SOIL STRAIN MEASUREMENTS
εmu coils are used to measure soil strain. They have not been used for long in South African
pavements, although international experience exists regarding their use. Recently, many εmu coils
have been installed in a local pavement and the response of these εmu coils will be compared to
similar εmu coils installed under laboratory conditions to verify their responses under varying
moisture conditions and with varying soil types.
2.1.7 USE OF TELEMETRIC GYROSCOPE FOR MEASURING ROAD GEOMETRY
Telemetric unit data in vehicles typically provide data on the location (GPS), acceleration
(accelerometer) and translation (gyroscope) of the vehicle. Current studies are evaluating the use of
the acceleration data for evaluating road condition. This project will evaluate use of the gyroscope
data to offer a low-cost road geometry evaluation system. The project will require in situ
measurements of actual roads for which the geometric data are available to compare the accuracy
of the process.
2.1.8 USE OF TELEMETRIC ACCELEROMETER FOR EVALUATING DYNAMIC BRIDGE DECK JOINT
CHANGES
Bridge deck joints are used as the link between a bridge deck and the abutments. Due to diurnal
temperature changes, the effect of the joints on vehicles changes through the day. This project will
evaluate to what degree these changes can be observed using vehicle telematics accelerometer data
through measurements over a diurnal cycle on a number of bridge deck joints.
2.1.9 VEHICLE TELEMATICS ACCIDENT DATA VS SKID RESISTANCE AND LAST FEW SECONDS
PERFORMANCE OF VEHICLE
Vehicle telematics data are used to identify vehicle accidents. Some of these accidents may be
caused due to road geometry and skid resistance issues. This project will attempt to link the
telematics accident data and skid resistance measurements to develop a tool for predicting areas
where skid resistance values on the road are probably below standard.
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2.1.10 EVALUATION OF A CYCLIST RIDING QUALITY METRIC
Riding quality of roads are typically measured using a car-based roughness metric (IRI) The
difference in vehicle geometry and mass cause the IRI metric not to be applicable to cyclists. With
more cyclists using public roads, the development of a riding quality metric for bicycles can lead to a
more comprehensive and objective rating of roads for use by cyclists. This project will evaluate the
possibilities of developing such a metric.
Student must have own MTB.
2.1.11 SEASONALITY EFFECTS OF ROAD MAINTENANCE ACTIONS
Road maintenance is required to keep infrastructure in a good condition. However, seasonality
effects (natural, retail, academic, agricultural) all affect the road use conditions and should be
incorporated into a road maintenance planning model. This project will evaluate the typical
parameters that cause seasonality on road use, measure typical effects of seasonality and evaluate
the potential benefits of planning maintenance actions in line with seasonality issues on selected
pavements.
2.2 SUPERVISOR: PROF JAMES MAINA
2.2.1 SOFT GRANULAR BASE TOPS WITH THIN ASPHALT LAYERS IDENTIFIED WITH THE LIGHT OR
NORMAL FALLING WEIGHT DEFLECTOMETER
Recent premature cracking on a number of road pavements with fresh thin asphalt surfacings
identified the soft (often moist) top 50mm of a granular base layer as one of the main contributors
to the development of the premature crocodile cracking observed. The Falling Weight Deflectometer
(FWD) and Light Weight Deflectometer (LWD) are ideal non-destructive test equipment to identify
such potential problems using a benchmark method.
In this project, the student will use such benchmark methods, where deflection bowl parameters are
determined directly, in simple spreadsheet calculations, using the measured deflection bowl.
Deflection bowl parameters, such as the base layer index (BLI) and radius of curvature (RoC) are
typical parameters determined with the deflection at 0, 200 and 300mm from point of maximum
deflection. New Area parameters in this same zone around the point of maximum deflection also
show promise as analyses tools and the student will evaluate these parameters. The LWD with a
smaller diameter load and limited depth of influence offers the opportunity to develop even
different deflection bowl parameters closer to the point of maximum deflection, e.g deflection at 0,
100 and 125mm.
2.2.2 DEVELOPMENT OF GREEN MATERIALS THROUGH RECYCLING OF ASPHALT CONCRETE AND
COMPARISON OF PERFORMANCE WITH CONVENTIONAL MATERIALS
The objective of this project is to contribute to the environment by evaluating potential reuse of
road construction materials and provide technological solutions to road owners/operators for cost-
effective delivery and maintenance of transport infrastructure to address the growing demand.
In this project, the student will carry out performance tests of asphalt mixtures with different
percentages of recycled materials and compare them with asphalt mixtures produced using new
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materials. The student will make recommendations for optimum percentage of recycled asphalt to
use in road construction without affecting the quality and performance of road pavement.
2.2.3 CHARACTERIZATION OF PERFORMANCE BEHAVIOR OF ASPHALT MIXTURES PRODUCED BY
INCORPORATING MARGINAL MATERIALS
The objective of this project is to contribute to the environment by evaluating potential use of the
so-called marginal road construction materials and provide technological solutions to road
owners/operators for cost-effective delivery and maintenance of transport infrastructure to address
the growing demand. Marginal materials are materials considered not fit for use in road
construction.
In this project, the student will carry out performance tests on asphalt mixtures produced using
marginal materials as road construction materials. The results of performance tests will be
compared those for asphalt mixtures produced using new materials. The student will make
recommendations on potential use of marginal materials in the production of asphalt mixtures
without affecting the quality and performance of road pavement.
2.2.4 PERFORMANCE CHARACTERIZATION OF SELECTED UNBOUND MATERIALS BASED ON
CYCLIC SHEAR LOAD TESTING
Performance of road pavements is highly dependent on the behaviour of unbound materials under
repeated traffic loading.
The objective of this project is to develop a better understanding of the response of granular layers
to cyclic shear loading in order to be able to predict the expected performance of these materials
under traffic loading
Through laboratory testing, the student will participate in a project that is aimed at reviewing
existing and/or developing new testing protocols to be used by researchers and the industry.
2.2.5 INVESTIGATION ON INFLUENCE OF PROPORTION OF FINES ON THE COMPACTION OF
UNBOUND MATERIALS
The objective of this project is to look at aspects not previously investigated, such as the influence of
fines and particle size distribution (gradation) on the performance of a granular material to better
characterize performance of preselected unbound materials, which are used as base layers in road
pavements.
In this project the student will focus his/her work on using triaxial testing equipment to subject
samples to different stress paths during testing.
Through laboratory testing, the student will participate in a project that is aimed at reviewing
existing and/or developing new testing protocols to be used by researchers and the industry to
better characterize performance of preselected unbound materials, which are used as base layers in
road pavements.
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2.2.6 COMPARATIVE ANALYSIS OF THE STRAIN ENERGY CAPACITY, RECOVERABLE AND
IRRECOVERABLE PROPERTIES OF UNBOUND AND BOUND MATERIALS
The objective of this project is to look at inherent characteristics of unbound and bound materials in
terms of their strain energy capacity and find correlation with their performance based on
permanent deformation testing.
In this project, the student will focus his/her work on using triaxial testing equipment.
Through laboratory testing, the student will participate in a project that is aimed at developing new
testing protocols to be used by researchers and the industry to better characterize performance of
both unbound and bound materials, which are used as base layers in road pavements.
2.3 SUPERVISOR: PROF CHRISTO VENTER
2.3.1 MEASURING DRIVER AGGRESSIVENESS FOR MICRO-SIMULATION OF TRAFFIC PATTERNS
Microsimulation of traffic patterns involves the use of indicators of driver aggressiveness to
approximate drivers’ propensity to speed and to accept smaller gaps when changing lanes. Software
packages use indicators derived in other countries that have not been verified for local conditions.
The study will collect data on driver behaviour in Tshwane, derive aggressiveness distributions, and
compare these to international results to determine the appropriateness of using indicators
imported from elsewhere.
2.3.2 VARIABILITY AND RELIABILITY OF FREEWAY TRAVEL TIMES
The day-to-day reliability of travel times is an important determinant of the Level of Service of road
networks. Data obtained from the GFIP e-toll gantries allows us to measure this reliability over long
periods of time. The student will select appropriate measures of reliability and variability, quantify
them for the case of the Gauteng freeway system using gantry data, and examine trends and
patterns that emerge.
2.3.3 USE OF GPS DATA TO ESTIMATE VOLUME-DELAY FUNCTIONS FOR URBAN ROADS
Mobile GPS tracking data from commercial suppliers such as Tracker can be used to determine the
travel time or delay on specific road sections. When matched with volume counts taken during the
same period, the volume-delay relationship can be extracted across a wide range of operational
conditions. These relationships are important from traffic modeling and simulation. The student will
use GPS data from Tracker, matched with volume data from roadside counting stations, to develop
and test a method for estimating volume-delay relationships for a sample of roads.
2.3.4 APPLYING GPS TECHNOLOGIES TO UNDERSTAND WALKING PATTERNS IN
NEIGHBOURHOODS
The objective is to use GPS-derived observations of the daily walking patterns of people, coupled
with in-depth follow-up interviews, to understand the factors affecting pedestrians’ choices of
routes and times for walking. The student will apply a survey methodology developed at Tuks, to
(1) track the walking patterns of a small sample of volunteers over the course of 3 or 4 days,
using mobile GPS trackers;
(2) develop maps of individuals’ walking patterns from the GPS data;
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(3) conduct qualitative interviews with the volunteers to determine the reasons behind their
route choices; and
(4) analyse the results to determine which environmental factors have the largest impact on
people’s walking patterns.
2.3.5 CORRECTION FACTORS FOR WALKING DISTANCES MEASURED WITH GPS LOGGERS
GPS loggers are being used to track walking patterns and estimate the distances that people walk on
a daily basis. Previous studies have shown that the distances obtained from the GPS experiments
have varying accuracy, depending on speed and environmental factors. The student will derive
correction factors for correcting GPS-derived distances using experiments during which walking
patterns of volunteers are tracked, and compared to actual distances.
2.3.6 ACCESS TO BUS RAPID TRANSIT: WALK OR RIDE?
A critical design parameter for Bus Rapid Transit systems is the walking distances that people are
willing to tolerate to access a BRT bus line, before they start considering using feeder buses.
However feeder buses usually charge an extra fare, so the access mode decision comes down to a
trade-off between walk time and money. The student will analyse data already collected from actual
Rea Vaya users in Soweto to determine this trade-off, and to establish probabilistic catchment area
boundaries for BRT trunk and feeder services.
3 STRUCTURES
3.1 SUPERVISOR: PROF WALTER BURDZIK
3.1.1 BRACING OF LONG COMPRESSION WEB MEMBERS IN TIMBER TRUSSES
Long compression web members in timber trusses are often braced by nailing a board to the top of
the web to form a T. The standard size for the brace is usually a 36 mm x 111 mm Grade 5 member
that is nailed to the web with the nail spacing being 300 mm. The assumption is made that by
providing the brace, the effective length is halved. This has not been tested for veracity.
Various options, such as varying the size of the T, nail spacing and even cruciform braces are to be
investigated using standard structural software and Eurocode based equations and validated by
means of tests. Each option will entail at least 10 tests.
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73 x 36 –nails
@ 300
73 x 36 –nails
@ 150
36 x 73 36 x 73
36 x 111 36 x 111
73 x 36 –nails
@ 300 73 x 36 –nails
@ 150
36 x 73
36 x 73
36 x 73
36 x 73 36 x 73 36 x 73
36 x 73
111 x 36 –nails
@ 300
111 x 36 –nails
@ 150
111 x 36 –nails
@ 300 111 x 36 –nails
@ 150
36 x 111 36 x 111
36 x 111 36 x 111 36 x 111
50 x 36 –
nails @ 300
50 x 36 –
nails @ 150
73 x 36 –
nails @ 300
73 x 36 –
nails @ 150
73 x 36 –
nails @ 300
73 x 36 –
nails @ 150
36 x 36 both sides 36 x 36 both sides
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3.2 PROF CHRIS ROTH
3.2.1 BASEPLATES
A few small models of baseplates and holding-down bolts will be used to determine the influence
of various factors on the strength/stiffness of the connection.
3.2.2 MODELS FOR USE IN SIN 223 AND SIN 311
The student will prepare models to illustrate various structural concepts: types of supports, loads,
continuous beams, frames, grids, etc. The models must show that student understands structural
behaviour, and demonstrate it to others. For the purposes of the research project, the student will
also be required to test the models to obtain quantitative results for force, deflections, etc.
3.2.3 DISTRIBUTION OF BASIC INPUT VARIABLES IN REINFORCED CONCRETE CONSTRUCTION IN
PRETORIA
Basic input variables for reinforced concrete design include material properties of concrete and
steel, geometry of actual construction, quality control on site, etc. Although we assume fixed values
for these variables in design, in practice the values vary. This work will be to quantify the variability
in slab thickness and possibly other selected variables. Measured values must be analyzed.
3.2.4 RAIL DEFECT DISTRIBUTIONS
Defects in steel rails, such as cracks or broken welds, can cause derailments and the prediction of
defects is an important part of rail maintenance. This work will involve collecting data on rail defects
and fitting models to the defects. Parameters for defects in tangents, curves will be fitted. This
may require some interface with Transnet Freight Rail.
3.3 SUPERVISOR: PROF BEN VAN RENSBURG AND MS SARAH SKORPEN
3.3.1 LATERAL TORSIONAL BUCKLING OF CANTILEVERS
For aesthetic reasons certain prominent cantilevers are provided with limited lateral and torsional
restraint over the span. To effectively design such cantilevers an accurate estimate of the critical
buckling moment is required. Codes of practice generally suggest that an “effective length” be used
to determine the critical buckling moment. The restraint conditions at the support and tip
determines the effective lengths of laterally unsupported cantilevers.
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In this research topic the lateral torsional stability of cantilever beams, taking the length, loading and
support conditions for the adjacent span into account will be studied. Next year we want to test
typical channel sections used as purlins
3.3.2 LIGHT STEEL FRAME BUILDINGS
The advent of light steel frame building in South Africa is one of the new developments in steel
building practice. Light steel frame buildings consist of (workshop pre-assembled) structural wall
frames, floors and roof trusses, manufactured from cold-formed light gauge galvanized steel
sections. A South African code is available to guide designers. However, certain problem areas exist
which require further research and recommendations to assist designers, especially for higher and
longer span structures. Work was done in previous years on certain problem areas, but further
research and development are necessary.
The suggested projects will involve studying the literature; visiting the light steel frame building
industry to investigate the construction methods; refining the problem statement; devising a test
programme and designing the test specimens; conducting tests at the University; drawing
conclusions from the test results and making recommendations for new construction techniques
and/or suggesting improvements to the existing techniques.
3.3.3 RESISTANCE BY SHEAR WALLS AGAINST RACKING FORCES
Wall bracing is required to transfer all horizontal forces from the roof, walls and floors to the
appropriate suspended floor diaphragms and to the foundations. Various bracing options are
available. (K or cross bracing have been employed.) The objectives of the project are to develop
more effective bracing systems for the shear walls.
This year a new method of bracing for shear walls with openings was investigated
3.3.4 REDUCING THE DEFLECTION AND VIBRATION OF SUSPENDED FLOORS
Structural floors are light and transient loads could cause undesirable deflections or vibrations.
Floors generally span in one direction. Achieving two-directional action could considerably reduce
the possible deflection and vibration. Different techniques are to be investigated to achieve two-
directional action.
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3.3.5 THE BEHAVIOR OF 0.8 MM THIN G550 SHEET STEEL SCREWED CONNECTIONS
This would include the testing of single overlap screwed connections concentrically loaded in shear.
The base plates could be varied to investigate the effect of different steel thicknesses (eg. thin gauge
steel and thicker hot rolled steel).
3.3.6 DESIGN OF END PLATE CONNECTIONS IN STEEL BEAM MOMENT CONNECTIONS
Moment connections in steel structures are a significant part of the cost of the structure. The
determination of the load distribution in a moment connection is a challenge. The new “Green
Book” published by the S A Institute of Steel Construction provides resistance values for bolts in
tension, depending on the end plate thickness, the geometry of the bolt group and the positions of
stiffeners. The objective of the project is to use yield-line analysis to determine the capacity of bolts
in an end plate connection and correlate the analytical values with experimentally obtained values.
Each student on the project will investigate a different bolt arrangement.
3.4 SUPERVISOR: PROF NICK DEKKER AND MS SARAH SKORPEN
3.4.1 COMPOSITE CONCRETE AND STEEL BEAMS
Composite action between layers of different material is achieved when slip between the layers is
prevented. In conventional steel-concrete composite construction this is achieved using steel studs
which are welded to the steel beam, however there are other innovative methods of achieving a
shear connection.
This research project involves investigating the effectiveness of a herringbone type shear connector.
The student will need to conduct a literature review around composite beams and different shear
connectors used today, and then conduct experimental work to ascertain if this type of connection is
suitable for composite construction.
3.4.2 INTEGRAL BRIDGES IN SOUTH AFRICA
UP is going to be involved in the monitoring of a 90m long integral bridge. Topics relating to the
analysis of integral bridges and calibration of the instrumentation are available.
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4 BUILDING MATERIALS
4.1 SUPERVISOR: PROF ELSABE KEARSLEY
4.1.1 ASR IN HIGH STRENGTH CONCRETE
Many South African aggregates are prone to Alkali-Silica reaction but the reaction can be prevented
by limiting the alkali content in the concrete. The use of cement extenders in traditional concrete
mixtures prevents the onset of the attack. With Ultra-high strength concrete relatively high cement
contents are used and ASR could become a problem again. In this project the student will determine
the effect of very high cement contents on the reactivity of concrete.
4.1.2 DURABILITY INDEX TESTING
Durability Index Testing is currently prescribed for structures such as bridges, but the prescribed
values seems to be very high for the strength classes. Contractors are claiming that they have to
manufacture 60 MPa concrete to meet the 30 MPa durability specifications, while being paid for
delivering 30 MPa concrete. The test results seem to be influenced by cement source and
composition. In this project the student will test concrete at different ages, made with different
blended cements in different strength classes for durability. The effect of site curing will be taken
into account.
4.1.3 OPTIMUM CEMENT CONTENT
Current specifications include a minimum cement content as well as a maximum water/cement ratio
for concrete exposed to aggressive environments. With modern superplasticizers it is possible to
manufacture high strength concrete with very low water contents. Theoretically aggregate is less
permeable than cement paste, which means concrete containing less cement should be more
durable- in contradiction to the current specifications. The aim of this project would be to determine
whether there is an optimum or minimum cement content required to manufacture durable, high
strength concrete. This project could include the use of multi-variable statistical analysis.
4.1.4 DURABILITY OF CONCRETE EXPOSED TO ACID WATER
The mines currently have a problem with the concrete used to line mine infrastructure as the
chlorides and sulfates in the mine water attacks the concrete, resulting in the reinforcing rusting. In
this project the student will look at ways to minimize the ingress of chlorides and sulfates into
concrete.
4.1.5 FIBRE REINFORCED CONCRETE FOR ULTRA THIN CONTINUOUSLY REINFORCED CONCRETE
PAVEMENTS (UTCRCP)
UTCRCP is currently used in trail sections on the National Highways. These concrete layers are as thin
as 50 mm and significant volumes of reinforcing are used to ensure ductile behaviour. Relatively high
fibre contents are required for UTCRCP and different types, length and combinations of fibres should
be tested to determine the optimum fibre composition for reinforcing these thin sections.
4.1.6 UTCRCP MODELLING
The behaviour of Ultra-thin continuously reinforced concrete pavement (UTCRCP) depends on the
behaviour of supporting material. This project will look at the consequences of changing the
layerworks used in UTCRCP. Scale models will be studied.
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4.1.7 MESH FOR ULTRA THIN CONTINUOUSLY REINFORCED CONCRETE PAVEMENTS (UTCRCP)
UTCRCP is currently used in trail sections on the National Highways. These concrete layers are as thin
as 50 mm and significant volumes of reinforcing are used to ensure ductile behaviour. Relatively high
steel mesh contents are required for UTCRCP and different combinations of strand spacing should be
tested to determine the optimum mesh composition for reinforcing these thin sections. This project
will look as scale models containing different wire spacings in the length and width of the pavement.
4.1.8 EXPANSION OF MATERIALS USED IN UTCRCP
Local “buckling” of UTCRCP has taken place and on trial sections on the N12 the mesh “snapped”. At
this stage these failures seem to take place on very hot days, when the concrete is saturated after
rain. In this project the student will determine the actual expansion of concrete caused by variations
in moisture content and temperature.
4.1.9 THERMAL PROPERTIES OF FOAMED CONCRETE
Foamed concrete can be manufactured with densities as low as 300 kg/m3 and at such low densities
the concrete is known to heat up significantly as a result of the cement hydration. The concrete can
however be used to prevent heat entering or escaping from structures. In light of the new
regulations on thermal efficiency, research on the thermal properties of foamed concrete is
required.
4.1.10 FACTORS AFFECTING THE MEASURED STIFFNESS OF CONCRETE
It is known that the stiffness of concrete is not a constant and the stiffness is affected by the
strength, load-level, aggregate type and sample size and shape. In this study the student will
determine the effect of these factors on the measured stiffness. This project could include the use of
multi-variable statistical analysis.
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4.1.11 OPTIMIZING THE USE OF FLY ASH IN CONCRETE
Although fly ash has been used in concrete for decades, many questions remain un-answered such
as:
• Can pozzolanicity be predicted?
• How does the chemical composition of fly ash influence the hydration?
• How can we energetically modify fly ash and cement?
• What is the pozzolanic potential of milled bottom ash?
• Is there an optimum water/cement ratio for concrete containing ash?
• Is there an optimum ash content?
4.1.12 BLENDED CEMENTS
In this project the student will used a laboratory ball mill to manufacture cement. The effect of
gypsum content, grinding aid and blending will be determined. Heat of hydration, setting time and
strength development will be investigated.
4.1.13 RECYCLED AGGREGATE
It has been proved that 100% of the coarse aggregate in concrete can be replaced with recycled
aggregate without any significant reduction in strength. There does seem to be an increase in long
term deformation of concrete containing recycled aggregate. In this project the student will
establish whether recycled aggregate concrete can be used to manufacture pre-stressed concrete.
4.1.14 ULTRA HIGH PERFORMANCE CONCRETE
It is possible to make concrete with strength in excess of 200 MPa .By reinforcing this concrete with
high strength steel fibres a matrix with properties similar to steel can be obtained. In this project the
student will investigate the optimum composition for thin panels made from this type of composite.
4.1.15 PIV FOR MEASURING STRAIN IN FIBRE REINFORCED CONCRETE
Concrete reinforced with steel fibres has post-cracking strength and the stress-strain behaviour of
the concrete is a function of the fibre type and content. Determining the actual stress distribution in
beams is challenging and the use of cameras to determine deformation could save time and money.
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In this project students will compare the readings recorded by camera with LVDT readings to
evaluate the possibility of using PIV for strain measurement in concrete.
4.2 SUPERVISOR: DR MAXIM KOVTUN
4.2.1 ALKALI-SILICA REACTION IN ALKALI-ACTIVATED MORTARS
Alkali-silica reaction (ASR) is a big concern in South Africa. Many rocks used as aggregates in
concrete production, contain reactive silica which causes ASR. Relatively high concentrations of
alkalis are used in alkali-activated binders which can cause ASR. The aim of the project is a
comparative study of ASR in alkali-activated binders and ordinal Portland cement.
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4.2.2 INITIAL SHRINKAGE OF GEOPOLYMERS CONTAINING DIFFERENT ACTIVATORS
According to many researches, geopolymers have increased shrinkage in comparison to ordinary
Portland cement. The aim of the work is to determine shrinkage behaviour of geopolymers during
the first 24 hours of hardening.
4.2.3 INFLUENCE OF ADDITION OF THERMALLY TREATED CLAY AND ZEOLITES ON STRENGTH
AND INITIAL SHRINKAGE OF ALKALI-ACTIVATED SLAG CONCRETES
One of the main disadvantages of alkali-activated slag concrete is relatively high shrinkage. The aim
of the work is to study influence of addition of thermally treated clay and zeolites on compressive
strength and initial shrinkage of alkali-activated slag concrete.
4.2.4 BACKFILLING CONTAING ALKALI-ACTIVATED BINDER
South Africa is one of the biggest exporters of natural mineral resources. Sustainable service of
existing mines is a key element of South African economy. The aim of the project is to develop
backfilling mix containing alkali-activated binder and mine tailings.
4.2.5 DIRECT ELECTRICAL CURING OF GEOPOLYMERS
Geopolymers are sensitive to a heat treatment. Very often, it is difficult to provide any heat
treatment of concrete on construction site. From another hand, construction sites have electrical
power supply most of the times. The aim of the project is to study process of direct electrical curing
of geopolymers.
4.2.6 TERNARY GEOPOLYMER MIXES
Ternary concrete mixes containing ordinary Portland cement, fly ash and silica fume are well known.
The aim of the project is to develop ternary geopolymer mixes containing ≥50% fly ash and providing
relatively high early strength at ambient temperature.
4.2.7 INFUENCE OF AGGREGATE TYPE ON STRENGTH KINETCS OF ALKALI-ACTIVATED SLAG
CONCRETE
Alkali-activated slag concrete containing a neutral granulated blast-furnace slag and sodium
carbonate has slow strength development at ambient temperature. The aim of the study is to
investigate if different aggregate type will influence the strength kinetics.
4.2.8 ELECTRIC ARC FURNACE SLAG AS AGGREGATE IN GEOPOLYMERS
Electric arc furnace (EAF) slag is a by-product which can be utilized as aggregate in concrete. The aim
of the study is to design geopolymer concrete with EAF slag aggregate and to study its properties
comparatively to ordinary Portland cement concrete.
4.2.9 INFLUENCE OF ALKALINE SOLUTION CONCENTRATION ON PROPERTIES OF GEOPOLYMERS
Concentration of alkaline solution is a critical parameter in geopolymer technology. The aim of the
study is to show how concentration of alkaline solution influences properties of geopolymer
concrete.
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5 RAILWAY ENGINEERING
5.1 SUPERVISOR: PROF HANNES GRABE
Please note:
• All Railway Engineering research topics are linked to industry needs and are sponsored or
supported in different ways by Transnet Freight Rail and other industry partners.
• Students choosing Railway Engineering should discuss the topics with Prof. Gräbe before
submitting their choices. There are transportation, time and various other terms and
conditions that apply.
• Most of the research will be carried out on the Proefplaas on the test track and the soon to
be installed MTS testing frame.
• For the limited number of field experiments, students should have own transport and be
able to drive to site.
5.1.1 CONVENTIONAL TRACK PERFORMANCE AND CHARACTERIZATION
During November 2012, a 30 m section of railway line was constructed on the Agricultural farm
(Proefplaas), University of Pretoria. Loading on the track is provided by a specially designed bogie
with a capacity of 80 ton. A number of projects (defined or new and original) will be available to
investigate various aspects related to the performance of the conventional track structure:
1.1 PIV (Particle Image Velocimetry) methods to study and interpret track component
deformation
1.2 A numerical and field study into the linearity of track deflection under seating and
maximum loading conditions
1.3 Track Characterization using geophysical techniques (e.g. geophones or PSPA)
1.4 The determination of track and ballast stiffness and damping parameters
1.5 Evaluation of the effect of thick (100g/m2) geotextiles on track stiffness and damping
1.6 Own topic as defined by the student in consultation with the supervisor
5.1.2 TUBULAR MODULAR TRACK
Tubular Modular Track is a South African invention and a ballast-less alternative to conventional
track. TMT modules are pre-casted in a factory and then transported to site where installation takes
place. TMT has specific advantages over other track structures which include lower maintenance
cost, slower track deterioration and higher stability.
A number of topics are available which include laboratory tests on components of TMT, field tests at
an appropriate site as well as numerical analysis. Tubular Track topics include the following:
2.1 The effect of different rail pads on rail creep through TMT modules
2.2 Noise and vibration measurements near Tubular Modular Track
2.3 Lateral rail head rotation between fastenings (TMT vs. Conventional track)
2.4 Stiffness and damping characteristics of different TMT components
2.5 Quick-curing grout for small geometric corrections below TMT modules
5.1.3 GAUTRAIN
The Gautrain Rapid Rail Link railway system has since the year 2000 seen a higher than predicted
growth in ridership of both commuters between Pretoria and Johannesburg and airport passengers
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to and from OR Tambo International airport. The dedicated passenger transport nature of Gautrain
offers ideal opportunity for studies into various aspects related to track geometry and riding quality.
The following topics are available:
3.1 Correlating track geometry measurements with riding quality innovations (2 students)
3.2 Validation of the relationship between speed, wheel load, superelevation and lateral
forces in railway curves
3.3 Own topic as defined by the student in consultation with the supervisor
5.1.4 RESILIENT AND PERMANENT DEFORMATION BEHAVIOUR OF TRACK SUBSTRUCTURES
An existing research test site has been in use for several years on the Coal Line between Vryheid and
Empangeni. Instrumentation already installed includes MDDs and strain gauges. Field tests will be
carried out to model the resilient and permanent deformation behaviour of the track foundation by
using new techniques and novel instrumentation.
4.1 Characterizing seating and loaded stiffness of track ballast by using Remote Video
Monitoring
4.2 Establishing the non-linear load-deflection characteristics of a heavy haul track
formation by using MDD’s and numerical modelling
4.3 Track Characterization using geophysical techniques (e.g. geophones)
5.1.5 THE USE OF UNDER-SLEEPER PADS TO REDUCE BALLAST DEGRADATION
Under-sleepers pads (USP) are now being developed to lower the contact stress and increase the
contact area between the sleeper and the ballast. The student will carry out laboratory tests to
evaluate the design life and deterioration of USPs on railway lines, especially heavy haul.
5.1.6 NUMERICAL MODELLING OF TRACK STRUCTURES
STRAND7 is a useful finite element software package that can be used to create 3D models of track
components and track structures. The student can choose his own topic and create an FEA model to
investigate a particular aspect in the field of conventional or non-conventional track structures. Field
measurements will be carried out to calibrate the FEA model. The aim of the study will be to
enhance track design and to optimize performance. Possible topics:
6.1 Embankment settlement under a variety of axle loadings
6.2 Track transitions (e.g. tunnel, viaduct, bridge and TMT transitions to conventional track)
6.3 Slab track design for different axle loadings
6.4 Numerical modelling of seepage in railway tunnels
6 GEOTECHNICAL ENGINEERING
6.1 SUPERVISOR: PROF GERHARD HEYMANN
Soil mechanics is a young and challenging subject and many aspects of soil behaviour is still poorly
understood. During this year you were introduced to a wide range of soil mechanics topics including
seepage, consolidation theory, strength of soil as well as engineering applications such as shallow
foundations, retaining structures and slope stability. This is an open invitation for students who have
an interesting soil mechanics related question or problem that they want to investigate as a final
year project.
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6.2 SUPERVISOR: PROF EBEN RUST
6.2.1 LIQUEFACTION POTENTIAL OF TAILINGS DAMS
Tailings dams are situated at mines, which may be subject to regular seismic activity, which may lead
to liquefaction of a dam. This is a risk to the mine and this risk needs to be evaluated.
1. Empirical solution. (This is the preferred method). (It will be preferable if this student can
write a program for a computer).
2. Effective stress method. (Not for the faint of heart)
6.2.2 SOILS IDENTIFICATION VIA THE PIEZOCONE
Soils ID in tailings is problematic due to the highly layered nature of the material. Current
international practice does not cater for these conditions. Several methods exist to carry out the
identification. The student will be required to compare these methods and possibly come up with a
new method.
6.2.3 DETERMINING THE PERMEABILITY AND LIQUEFACTION OF LAYERED TAILINGS IN THE LAB
This skripsie has been an ongoing project in our labs and is currently researched by a PhD student.
Carry out your own version of this test in a hydraulic column. Additionally, demonstrate liquefaction
in the column. (Lots of instrumentation).
6.2.4 OWN SUBJECT
The student could propose a research topic in Geotechnical or Environmental engineering which will
be evaluated by the leader. Alternatively the student could carry out research in collaboration with
outside consultants under the guidance of the leader.
6.3 SUPERVISOR: PROF SW JACOBSZ
6.3.1 APPLICATIONS USING PIV
PIV stands for Particle Image Velocimetry and originated in the field of fluid dynamics. Small
particles are injected into fluid stream, high-speed photos are taken and the movement of the
particles are tracked to study the movement of the fluid. A modification of this method applicable
to certain geotechnical and structural problems was developed at the University of Cambridge
between 1999 and 2002: If photos can be taken of a soil body or structure being deformed by, for
example, the loading of a foundation, the photos can be compared with one-another to find the
displacement vectors in the soil below the foundation. From the displacement vectors the strains in
the soil can be calculated. The technique is versatile, very accurate and easy to apply. The only
instrument required is a conventional digital camera.
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Figure 1 A pile test being carried out with displacement monitoring using PIV.
Figure 1 shows a pile test being carried out using PIV to monitor movement. The technique has also
been used to measure ground settlement on, for example, a consolidating landfill site. Students are
encouraged to suggest their own monitoring project using PIV. Possible examples include studying
the movement of structures or ground and the deformation or movement of beams or other
structural elements.
6.3.2 STUDYING DOLOMITE SINKHOLES
Figure 2 below taken from the National Standard for the development of dolomitic land (SANS 1936)
suggests a method for the estimation of the maximum size of a sinkhole. The method basically
comprises the extrapolation of a funnel from bedrock to the surface at various slope angles in the
different soil layers. The method is known to give over-conservative results, resulting in costly
design solutions because of the large sinkhole size that developers have to cater for when using this
method.
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Figure 2 Determining the size of a dolomite sinkhole
Progression of dolomitic sinkholes to the surface
It is believed that an alternative way of looking at possible sinkhole size is to investigate the
maximum distance that a soil layer of a certain thickness and strength can span. In addition, in the
case of material too weak to span a cavity, recent experiments suggest that the diameter of a
sinkhole is controlled by the size of the zone in the subsoil over which support is removed, i.e. if
support is removed over a diameter of 3m wide, the diameter of the depression appearing at the
surface will also be 3m. The propagation of sinkholes to the surface in physical models can be
studied by slowly extracting water from a water-filled balloon.
1. Observe cavity propagation to the surface in soils of various strengths* under the controlled
formation of a cavity at depth. Different grades of sand at various moisture contents will be
tested in models at 1g to observe cavity propagation. At nearly all real-life sinkholes that
appear a leaking pipe can be found. Cavities in soils will be stable indefinitely until
disturbed. The disturbance can be vibration, but much more often, it is caused by leaking
services. The effects of leaking services on the stability of a cavity at depth in a soil mass will
also be investigated.
2. Assess settlement development at the surface in response to the formation of a cavity at
depth. The intention is to investigate if any warning signs of imminent collapse can be
identified by monitoring surface settlement above a potential sinkhole. Soil settlement at
the surface will be monitored with LVDTs in response to the controlled creation of a cavity at
depth. Mini-extensometers made from hypodermic needles sliding within each other will
also be used to observe subsurface settlement in addition to surface settlement.
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3. Measure horizontal and vertical strains in the soil above the cavity as it grows. Thin brass
strips will be strain gauged, provided with rough texture and buried in the sand above a
growing cavity to observe strain developing in the soil in response to the growth of the
cavity. Results can be compared to the predictions of a finite element analysis.
4. Use Particle Image Velocimetry (PIV) to track soil movement around and above the growing
cavity. PIV can be used to measure the displacement field in the entire soils mass and from
the displacements the strain distribution in the soil can be calculated. The student will be
responsible to set up a camera in front of a box with a glass window through which
photographs of the sand behind the window will be taken as the cavity grows. Existing
software is available for the image analysis.
All physical models will be carried out at 1G in the laboratory. Only models judged by the supervisor
to be of sufficient merit might be tested on the centrifuge.
*Strength of soil in the centrifuge: The soil used in the centrifuge is clean fine silica sand. The
material essentially only has frictional strength (φ’ = 37°) and zero cohesion. In order to span over a
cavity a material requires a certain amount of cohesive strength in addition to friction. Cohesive
strength is achieved by using moist sand. It is, however, not easy to vary the amount of moisture in
a given sand to change the amount of cohesion because under high acceleration in the centrifuge all
excess moisture rapidly drains, leaving the soil at a constant moisture content known as its field
capacity. The field capacity is a function of the particle size and density.
6.3.3 DETERMINING SOIL-MOISTURE CHARACTERISTIC CURVES (SMCC)
When soil is allowed to dry out from the saturated state the pore pressure in the soil will drop and
become negative, generating suctions, as the moisture content of the soil reduces and the material
desaturates. The relationship between suction pressure and the moisture content is referred to as
the soil-moisture characteristic curve or soil-water characteristic curve and is illustrated conceptually
in Figure 3. This curve forms the basis of unsaturated soil mechanics and is important in
understanding the strength of unsaturated soils because pore water suctions influence the effective
stress and therefore the strength of such soils. Measuring the soil moisture characteristic curve
requires special equipment and is expensive and time consuming.
We are working on a method to measure the SMCC using piezometers which can measure negative
pore pressures as samples dry out while they are being weighed continuously. Weighing the
samples continuously allows the moisture content to be determined through the entire drying out
process. In addition, large negative pore pressures can be measured using a technique using filter
paper described by Hamblin (1981) and Chandler (1986). Several soil types will be tested to assess
the success of the proposed method.
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Figure 3 Soil moisture characteristic curve
6.3.4 MODELLING AND MONITORING PORE PRESSURES IN A SLIMES DAM DURING
CONSTRUCTION
Work carried out using settlement columns in the Geotechnical Group has shown that consolidation
of newly placed tailings layers occur rapidly after placement and that modelling consolidation as
such does not explain why some tailings dams can be constructed at very high rates of rise. It is
believed that over-consolidation due to drying out and desiccation of tailings is responsible for much
of the strength. Very limited data is available on the changes in pore pressures (positive and
negative) during the construction of tailings dams. It is proposed to model the construction of a few
layers of a tailings dam a by placing layers of tailings slurry in container and allowing them to dry out
under lights while measuring pore pressures using tensiometers. This will provide a valuable record
of the changes in pore pressure during the construction of a tailings dam which will shed light on the
understanding of strength gain of tailings. The work will be compared to that of Chapman (2012)
who used the filter paper method to measure suctions.
6.3.5 CALIBRATING TENSIOMETERS IN THE TRIAXIAL APPARATUS
Le Roux (2013) developed tensiometers (piezometers capable of measuring negative pressures) from
the pressure sensors used in diving watches and high air-entry ceramic filters. The tensiometers
were calibrated by De Wet (2014) using an oedometer as described below:
The suction probes were placed in the centre of a clay sample which was loaded to a certain stress in
the oedometer. Consider Terzaghi’s effective stress equation below: During loading, the total stress
will increase by a certain amount which will initially be matched by the pore pressure. As the sample
consolidates, the pore pressure will dissipate and the effective stress will eventually be equal to the
applied load. When the applied load is removed, the total stress will be zero. However, the
effective stress requires time to change as consolidation occurs and will therefore not be zero after
load removal. For the equation to be in balance (i.e. the right hand side also equal to zero) a
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negative pore pressure equal to the removed total stress will be imposed. Measuring the known
negative pressure with the tensiometer will allow it to be calibrated.
σt = σ’ + u
Problems were encountered to ensure proper saturation of the tensiometers in the oedometer. It is
intended to calibrate the sensors by measuring known suctions in a range of low-permeability
materials. This will be achieved by placing a suction probe in the centre of a clay sample which will
be loaded to a certain stress in the triaxial apparatus and then unloaded rapidly as described by
Ridley and Burland (1993).
6.3.6 SOILS SPANNING OVER CAVITIES – A STRUCTURAL APPROACH
Before a sinkhole can appear at the surface, a final stable layer of soil spans over a cavity at depth.
As the cavity approaches the surface, the spanning soil layer becomes increasingly unstable until it
collapses. It is believed that the strength and geometry of the final soil layer controls the size of the
sinkhole that will eventually appear at the surface. It is desired to investigate the development of
stresses in this soils layer or arch towards failure using finite element analyses of beams, slabs and
arches spanning over cavities. It is known that the development of stress in beams of different
depths differ. Predictions from the finite element work will therefore be compared with those from
conventional Euler beam theory.
Failure of the material comprising the beams can be modelled using various failure criteria like the
Mohr-Coulomb model shown below. A modification of the failure line on the tension side is
predicted from a theory known as Griffiths theory which stems from the field of fracture mechanics,
which can also be considered. Stress states at various locations within the beam, slab or arch will be
plotted in normal stress-shear stress space and compared to the failure envelope to assess how the
structure progresses towards failure as the slab or arch becomes thinner. An opportunity exists to
investigate various material models and closed form solutions, also those used by structural
engineers, to assess how they predict failure to occur.
Figure 4 The Mohr-Coulomb failure envelope often used for modelling the failure of soil
φ
c
τ
σ’ c/2
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Figure 5 Stress development at various locations to be modelled in slabs, beams and arches.
6.3.7 THE STRENGTH OF SOILS BONDED BY SUCTIONS
Linked to the development of stresses in a soil slab or arch in a study of sinkhole formation is the
study of the strength of soils itself. Most of the soils in South Africa are unsaturated, implying that
they may possess considerable tensile strengths due to the presence of suctions. Van der Meulen
(2013) and Gaspar (2014) carried out a series of tests on silt samples bonded by suctions. It is
proposed to expand this work by creating suction-bonded soil samples and then testing them in the
laboratory by means of shear box tests, triaxial tests, uniaxial compressive tests, split cylinder tensile
strength tests and others. Work by others has indicated that Griffiths theory (mentioned above)
predicts the strength of weakly cemented sand samples very well. It is suspected that Griffiths
theory may also describe the strength of suction-bonded silts very well and this needs to be verified.
Figure 6 Samples prepared for triaxial testing held together by suctions.
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6.3.8 SETTLEMENT OF BACKFILLED OPENCAST MINES
When an opencast mine is rehabilitated, the material excavated during mining is replaced in the
excavation, shaped to create a free-draining topography, covered with a layer of topsoil and
vegetated. Over time, water infiltrates through the topsoil layer into the loose backfill material,
causing the water table to rise, resulting in settlement of the backfill known as collapse settlement.
It is often necessary to construct infrastructure over backfilled mines. This includes roads, railway
lines, pipelines, overland conveyor belts, canals, re-establishment of stream diverted to allow mining
and even the reinstatement of previously mined-out wetlands. The problem with collapse
settlement is that it is not uniform, resulting in differential settlement at the surface and damage to
infrastructure. Example: streams re-instated over previously mined areas must be lined to prevent
infiltration into the loose underlying backfill. Differential settlement can result in damage to the
liner system. How to design infrastructure to survive differential settlement is becoming a hot topic!
If we can model differential settlement in the centrifuge realistically we can use models to study the
effect of differential settlement of various structures and also ways in which damage can be
minimised.
In order to determine whether differential settlement can be modelled realistically in the centrifuge
a method to describe the differential settlement must be found. This method can then be used to
describe differential settlements from both a full-scale situation and the centrifuge data and
compared. Some work in this regard was done by Dressler (2014).
Factors controlling magnitude of collapse settlement
It is believed that the following factors control the magnitude of collapse settlement
• Initial moisture content of backfill
• Initial density of backfill
• Grading of backfill (fine to coarse, uniform to well-graded)
• Material type (carbonaceous, sandstone, shale etc)
6.3.9 EFFECT OF INITIAL DENSITY AND MOISTURE CONTENT ON COLLAPSE SETTLEMENT
The effect of density and the initial moisture content of a material are likely to have an influence on
the amount of collapse settlement that the material is likely to undergo upon inundation with water.
A range of experiments will be carried out to measure collapse settlement of materials placed at
various densities and moisture contents. The outcome will hopefully illustrate that by nominal
compaction, the problem of differential collapse settlement can be mitigated. Settlement will be
monitored through a glass window using PIV.
6.3.10 EFFECT OF PARTICLE SIZE AND SHAPE OF GRADING CURVE ON COLLAPSE SETTLEMENT
Materials comprising various uniform particle sizes will be saturated and settlements recorded
during tests to assess the effect of particle size on the magnitude of collapse settlement. Thereafter
materials comprising a range of particle sizes will be tested and results compared with the first tests
results to identify rules which can be used for prediction of collapse settlement. (Density and
moisture content to be kept constant). Settlement will be monitored through a glass window using
PIV.
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6.3.11 DESCRIBING DIFFERENTIAL SETTLEMENT
Perhaps the simplest way to describe differential settlement is to measure the average and
maximum peak-to-trough distance on the settlement profile. This does, however, not provide any
information about the spacing of the peaks and troughs or how sharp they are. More sophisticated
methods must be investigated as described below. These methods will be tested to describe
differential settlement profiles recently obtained from an active coal mine.
6.3.12 FREQUENCY – SETTLEMENT PLOTS (FAST FOURIER TRANSFORM)
This method involves a Fast Fourier Transform analysis (available in Excel) of the settlement profile,
the outcome of which is a plot showing frequency (horizontal distance between peaks and troughs
on the soil surface) vs amplitude (vertical distance between peaks and troughs on the soil surface).
The shape of the curve uniquely characterises the differential settlement pattern. Various profile
shapes will be analysed to assess the efficiency of the method. Before the settlement profile can be
described it will be normalised. One possible means of normalisation is to divide the vertical
settlement by the maximum settlement and then to characterise the settlement profile over a
horizontal length of say 100 times the maximum trough-to-peak settlement.
6.3.13 FRACTAL METHOD
A method based on fractal theory is illustrated in Figure 4. The length of the observed soil surface
profile will be measured using measuring bars of different lengths. When using a relatively long
measuring bar, the total length of the surface profile will be underestimated because the bar is too
long to measure small undulations in the surface profile. As the length of the measuring bar is
gradually reduced, the total measured length of the profile will increase up to a point when all the
small undulations have been accounted for. By measuring the surface profile length using bars of
different length and then plotting the total measured profile length against the length of the
measuring bar, a unique curve will be obtained which characterises the differential settlement
profile uniquely. Various profile shapes will be analysed to assess the efficiency of the method.
(Normalising a settlement profile.)
Figure 7 Fractal method for describing a differential settlement profile
Length of measure
Measured
surface
profile
length
Curve characterising the
pattern of differential
settlement
L2
L1 L1 L1
L2
Soil surface profile
Different length
measures
L1
L2
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6.3.14 VARIOGRAM METHOD
Variograms are found in statistics. Applying a variogram analysis to a differential settlement profile
will produce a graph plotting the vertical distance between two points on a profile as a function of
their horizontal distance apart and describes a differential settlement profile uniquely. An Excel
macro will be developed to carry out this analysis. Various profile shapes will be analysed to assess
the efficiency of the method. (Normalising a settlement profile.)
6.3.15 STRAINS IN GEOGRIDS IN CLAY LINERS
Various types of infrastructure like tailings dams and landfill sites have to be lined with impermeable
liner system usually incorporating clay layers. Should significant movement occur underneath the
liner, the clay layer may crack resulting in the liner leaking. The use of geogrids to reinforce the clay
layers is being considered to improve the ability of the clay liner to withstand movement. It is
proposed to construct clay layers on a sand layer above a trapdoor. By releasing sand from the
trapdoor the clay layer can be forced to deform downward. Water can be made to pond above the
clay liner to test the integrity of the liner. Disappearance of the liner will signify failure of the clay
layer. The best location of the geogrid within or below the clay layer will be investigate, as well as
the use of geogrids of various flexibilities.
6.3.16 AUTOMATING THE RECORDING OF TRIAXIAL TEST DATA
The Department of Civil Engineering houses the most respected triaxial test laboratory on the
continent. Options to increase the laboratory’s productivity are being considered. One such option
is the automation of the recording of triaxial tests data using suitable instrumentation and data
loggers.
Recording of loads applied to samples can be automated easily by fitting displacement transducers
in the loading rings. Pore pressures are already logged electronically and can simply be recorded.
The challenge lies in devising an electronically logged volume gauge to measure flow out of a sample
during consolidation and permeability stages of tests.
The student will work closely with Mr van Staden in the laboratory and fit the necessary
instrumentation to the loading rings, log all data electronically and develop a volume gauge. Results
will be compared to the results of tests recorded manually (the current practice) to identify any
shortcomings.
6.3.17 CALIBRATION OF SAND HOPPER
An automated sand rainer was built by the civil engineering laboratory technical staff which is use to
place sand in centrifuge models under controlled conditions. The drop height and sand flow rate can
be adjusted to control the density of sand placed. The system was calibrated for fine silica sand by
Sykes (2014) but needs to be calibrated for other grades of sand to determine how the drop height
and flow rate of sand affects the density of sand placed in a model container.
6.3.18 THE USE OF POLARISED LIGHT WITH PIV
Figure 8 shows a centrifuge test during which a model foundation was loaded and photographed
using vertically polarised light. It was discovered that the interaction between polarised light and
the mesh used for PIV resulted in interesting patterns when examining strain distributions in the
sand (see Figure 9). The cause is thought to be related to the Moire-effect, the interaction between
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overlapping grids of varying coarseness and/or orientation illustrated in Figure 10. The physical
meaning of the patterns shown in Figure 9 has to be investigated.
It is proposed to photograph a shallow rectangular dish filled with sand using polarised and normal
light and then to apply to range of known displacement in a known direction and to then investigate
the resulting patterns and compare with Moire theory. Precisely controllable movement can be
applied by placing the sand sample on a shear box. This is considered to be challenging project.
Figure 8 A foundation load test carried out in the centrifuge
Figure 9 Shear strain distribution from PIV using polarised light and normal light
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Figure 10 Illustration of the Moire-effect resulting from the overlapping of grids of different orientation.
Note: Students interested to use physical models for their research projects must note that they will
be responsible for constructing and testing the models themselves. Good hand skills are required to
work with physical models.