21 research outputs found
Guidelines for sinkhole and subsidence rehabilitation based on generic geological models of a dolomite environment on the East Rand, South Africa
A sound understanding of the various factors influencing and associated with the formation of sinkholes
or subsidences on dolomite land is essential for the selection of appropriate rehabilitation methods. The
investigation and rehabilitation of numerous sinkholes and subsidences located on dolomite in the East
Rand of South Africa, created an opportunity to develop a broad based understanding of different karst
environments, their susceptibility to sinkhole and subsidence formation and best practice rehabilitation
methods. This paper is based on the guidelines developed whereby the geological model of the sinkhole
or subsidence is used to recommend an appropriate rehabilitation method. Nine typical geological
models with recommended rehabilitation methods are presented in this paper.http://www.elsevier.com/locate/jafrearsci2017-05-31hb2016Geolog
On the cubic law and variably saturated flow through discrete open rough-walled discontinuities
Fracture flow is fairly well documented with the widespread
application of, for instance, the cubic law and assumed smooth parallel plate model.
Geometrical intricacies such as aperture, roughness and infill do however significantly
influence the validity of the cubic law with even its application to smooth parallel
systems being contestable. Rock mechanical discontinuity surveys provide valuable
information regarding the discontinuity geometry that can likely contribute to the
evaluation of flow through individual fractures with variable properties. The hydraulic
aperture is available for the transmission of flow, while normal and shear stresses alter
discontinuity properties over time. In this, numerous advances have been made to
better accommodate deviations of natural discontinuity geometry to that of smooth
parallel plates and at partial saturation. The paper addresses these advances and details
conditions under which the cubic law, even in local form, fails to adequately estimate the
hydraulic properties. The role of roughness in open discontinuities is addressed in
particular, as contact areas and high amplitude roughness cause most extensive
deviation from the cubic law. Aperture of open fractures still governs hydraulic
properties, but inertial forces control flow in very rough fractures, in which instances
the applicability of the cubic law should be revisited. Open questions are finally posed,assessment of which will contribute significantly to the understanding of flow through
individual discontinuities as well as fracture networks.The Water Research Commission of South
Africa (www.wrc.org.za) for funding of project K5/2052 [68] on Multidisciplinary Vadose
Zone Hydrology, as well as project K5/2326 on Quantification of Unsaturated Flow in the
Fractured Intermediate Vadose Zone by means of Geotechnical Centrifuge (to be published
by the WRC in 2016).http://www.elsevier.com/locate/ijrmms2017-11-30hb2016Geolog
Review of engineering, hydrogeological and vadose zone hydrological aspects of the Lanseria Gneiss, Goudplaats-Hout River Gneiss and Nelspruit Suite Granite (South Africa)
Please read abstract in the article.Water Research Commission of South Africa (WRC) project K5/2052 on Multi-disciplinary Vadose Zone Hydrologyhttp://www.elsevier.com/locate/jafrearscihb201
Hazard of sinkhole formation in the Centurion CBD using the simplified method of Scenario Supposition
A large part of the land south of Pretoria is underlain by dolomite from the Chuniespoort Group
of the Transvaal Supergroup. In South Africa, dolomite rock has a notorious reputation for the
formation of sinkholes and subsidences. Thousands of people reside and work in the Centurion
area, where numerous sinkholes have occurred, causing damage and in some instances loss
of property and even lives. Centurion has rapidly densified over the last 40 years, with an
increase not only in the number of people, but also in the density of waterborne services. This
paper proposes draft guidelines for the allocation of an Inherent Hazard Class for percussion
boreholes, referred to as the ‘Simplified Method of Scenario Supposition’. This method was then
used to classify the Centurion CBD and surrounding [email protected]://www.journals.co.za/ej/ejour_civileng.htmlam201
The influence of the geological origin on soil volume change through collapse settlement
Partially saturated soils are often dense with a high bearing capacity and will subsequently only suffer
small amounts of compression under normal foundation loads. However, when wetted under load many
such soils undergo a marked and sudden increase in settlement, the phenomenon that is known as collapse
settlement.
It was originally assumed that the collapse phenomenon is largely restricted to loose aeolian deposits,
with the result that most of the research and work dealt almost exclusively with such deposits. However,
the collapse phenomenon has since been identified in a number of different transported soils as well as
residual soils, most notably the residual granitic soils associated with the Basement Complex of South
Africa.
Recent studies suggest that the geological origin of the material plays an important role in the collapse
mechanism of the particular material. This paper highlights the differences between the collapse process
in transported and residual soils by focusing on the geological origin of the material.http://www.elsevier.com/locate/jafrearscihb201
Review of engineering, hydrogeological and vadose zone hydrological aspects of the Lanseria Gneiss, Goudplaats-Hout River Gneiss and Nelspruit Suite Granite (South Africa)
Please read abstract in the article.Water Research Commission of South Africa (WRC) project K5/2052 on Multi-disciplinary Vadose Zone Hydrologyhttp://www.elsevier.com/locate/jafrearscihb201
Mechanical and hydraulic properties of residual dolomite and wad
The properties of residual dolomite, sometimes termed wad, are variable and uncertain. It represents the insoluble
residue after dissolution of dolomite and is commonly found in the Neoarchaean Malmani Subgroup of the
Chuniespoort Group (South Africa). This study comprised triaxial tests, crumb tests, X-Ray diffraction and fluorescence
spectroscopy, foundation indicators, stereo-microscope imagery and permeability testing of the represented formations
outcropping in the northeastern portions of South Africa. Results concur that residual dolomite is not typically
dispersive, has low density that can be below that of water, mostly grades in the silt fraction, has high plasticity
indices with low to high liquid limits, and has hydraulic conductivities in the order of 1x10-6 m/s. This new knowledge
database contributes to our understanding of the flow through these systems and to how ingress scenario subsidences
and sinkholes can possibly occur.The South African Water Research Commissionhttp://www.gssa.org.zapm2020Geolog
Revised test protocols for the identification of dispersive soils
Dispersive soils are prevalent in many areas of South Africa, and the presence of these
soils has always posed a problem on road construction sites. The use of dispersive soils in
roadway embankments and structures can lead to serious engineering problems if the soils
are not accurately identified before use and appropriate mitigation measures taken. The
current identification methods include the pinhole, double hydrometer, crumb and chemical
tests, which are commonly used in combination to obtain the most reliable outcome.
These laboratory tests, however, have not always been entirely consistent, whether used
in combination or individually, and it is possible that the reason lies in the actual testing
procedures. This paper discusses the observations made during a detailed investigation into
the current methods used for testing and identification of dispersive soils. The test methods
were thoroughly analysed and shortcomings identified. The differences resulting from different
test techniques are examined and solutions to overcome the problems proposed. The paper
concentrates mainly on the modification of the physical tests. The recommended solutions and
process of identification are also proposed.http://www.journals.co.za/ej/ejour_civileng.htmlam201
Field tests for the identification of silts
DATA AVAILABILITY : Data will be published in Duan Swart’s PhD thesis, articles published from the work, and the final report published by the
Water Research Commission (www.wrc.org.za).Accurately identifying soil texture and understanding soil behaviour in terms of plasticity is a crucial initial step in properly
characterizing a site, which in turn facilitates appropriate sampling and scheduling of laboratory tests. Soil identification
techniques in literature are effective at assessing pure clays and silt–clay mixtures. This paper presents a comparative study
between field tests, soil plasticity classifications, Atterberg limits, mineralogical and chemical data, SEM imagery, and
stereographical microscopy. Natural residual soils comprising varying quantities of clays, silts, and sands were used and
subjected to the same field and laboratory protocols. The findings of this study demonstrate that a series of field tests can
effectively characterize and classify soils ranging from coarse soils to fine soils exhibiting non- to highly plastic indices with
particle sizes less than 2.00 mm. By employing a single list of field tests that only necessitate water and commonly available
stationery materials on-site, the researchers have presented a valuable tool for on-site determination of soil texture and inference
of the Unified Soil Classification System (USCS). This approach streamlines the process and provides professionals
with an efficient means of assessing soil properties and determining problem soils at an early stage of the investigation and
during construction of high fills.Open access funding provided by University of Pretoria.https://www.springer.com/journal/10064am2024GeologySDG-12:Responsible consumption and productio
Revised test protocols for the identification of dispersive soils
Dispersive soils are prevalent in many areas of South Africa, and the presence of these
soils has always posed a problem on road construction sites. The use of dispersive soils in
roadway embankments and structures can lead to serious engineering problems if the soils
are not accurately identified before use and appropriate mitigation measures taken. The
current identification methods include the pinhole, double hydrometer, crumb and chemical
tests, which are commonly used in combination to obtain the most reliable outcome.
These laboratory tests, however, have not always been entirely consistent, whether used
in combination or individually, and it is possible that the reason lies in the actual testing
procedures. This paper discusses the observations made during a detailed investigation into
the current methods used for testing and identification of dispersive soils. The test methods
were thoroughly analysed and shortcomings identified. The differences resulting from different
test techniques are examined and solutions to overcome the problems proposed. The paper
concentrates mainly on the modification of the physical tests. The recommended solutions and
process of identification are also proposed.http://www.journals.co.za/ej/ejour_civileng.htmlam201