Case Study: Mount Edgecombe Interchange –investigation, design and construction of a complex geotechnical project

Pequenino,F.P. Van der Merwe,F.H. Purchase,C. Warren-Codrington,C.J.. 2019. ARC

This paper discusses key observations and lessons learnt from the geotechnical investigation, design and construction for the four level Mt Edgecombe Interchange. The interchange is the largest and most complex yet to be constructed in South Africa and is situated on a weak succession of coastal sands and clays to depths of over 60m. A significant feature of the project was the geotechnical works. It is considered important to bring to the fore projects where the benefits of having adequate investigations, robust codes or client specifications, and meaningful roles for geotechnical engineers, contributed to its ultimate success.

Stability of the temporary excavation between Soldier Piles in Unsaturated Residual Granites in Sandton CBD

F. H. van der Merwe and J.H. Engelbrecht . 2019. ARC

The design of multi-anchored tieback soldier pile walls in Sandton is typically based on either empirical methods or two-dimensional finite element modelling, ignoring the effects of matric suction in un-saturated residual granites. The designer, however, often relies on previous experience in a similar subsurface profile rather than established theory, to assess the ability of the soil to arch between soldier piles. Using expe-rience rather than a sound theoretical basis for design could potentially be problematic. Excavations typically proceed in intervals between 1.5m and 2.5m before a reinforced shotcrete liner is applied.

Lugeon Tests at Partial Saturation: Experimental and Empirical Contributions

B. R. Jones, J.L van Rooy and M.A Dippenaar. 2018. Rock mechanics and Rock Engineering

Implications of improved understanding of variably saturated flow are numerous, especially given the complexity, heterogeneity, and anisotropy of the intermediate fractured vadose zone. One such an implication is the quantification of water movement for engineering purposes, as flow-through unsaturated discontinuities cannot be quantified through commonly applied saturated approaches.

Verifying the ground treatment as proposed by the Secondary Permeability Index during dam foundation grouting

B. R Jones, J.L van Rooy and D.J Mouton. 2018. Bulletin of Engineering Geology and the Environment

The Secondary Permeability Index (SPI) is a permeability-based rock mass classification, which when complemented with the degree of jointing can be employed as an approximation to the ground treatment design. However, when the grout mix and success of the grout operation are known, a back-analysis can be conducted to infer the degree of jointing. The aim of this paper is to back-analyse and verify the ground treatment as proposed by the SPI from water pressure tests conducted in primary production grout boreholes, at the De Hoop Dam in South Africa. 

Partially to fully saturated flow through smooth, clean, open fractures: qualitative experimental studies

B. R Jones, L.B Brouwers and M.A Dippenaar. 2018. Hydrogeology Journal

Fractures are both rough and irregular but can be expressed by a simple model concept of two smooth parallel plates and the associated cubic law governing discharge through saturated fractures. However, in natural conditions and in the intermediate vadose zone, these assumptions are likely violated. This paper presents a qualitative experimental study investigating the cubic law under variable saturation in initially dry free-draining discrete fractures

The problem with MSE walls

F. H. van der Merwe, C. Warren-Codrington and F. Pequenino. 2017. SAICE

Mechanically Stabilised Earth (MSE) walls have a growing application in place of conventional retaining systems for varying reasons, most notably economy and constructability. However, there have recently been a number of failures or instances of poor performance of these systems throughout the southern African region. An evaluation of these indicates that there are two fundamental causes for poor performance. Th e fi rst relates to the nature in which MSE structures are planned, designed and constructed. Th e second relates to the need for the geotechnical designer to develop a clear understanding of the subsurface conditions, together with a need for routine verifi cations of the ground conditions, design, construction and materials during the process of construction. 

Dynamic Replacement Stone Columns

F. H. van der Merwe and C. Purchase. 2017. Proceedings of the 9th YGE Conference SAICE

Dynamic replacement penetration tests, with both the Dynamic Compaction (DC) and Rapid Impact Compaction (RIC) methods, have been carried out on three sites in South Africa on variable ground profiles. Quality assurance is normally done by means of plate load tests on selected stone columns and a limit is typically placed on the acceptable deformation modulus, for the Engineer to approve works. The results from the penetration tests are presented, with a comparison of the achieved deformation moduli. A method is developed, based on impact engineering formulation, taking into consideration drop height and pounder weight and shape to predict the deformation modulus that would be achieved for a certain penetration depth.  

Can One Use The Dynamic Cone Penetrometer To Predict The Allowable Bearing Pressure?

K. A Mogotsi, F.H van der Merwe. September 2017. Proceedings of the 9th YGE Conference SAICE

It is a common question asked by the structural engineer to the geotechnical engineer whether one can determine allowable bearing pressure from a set of Dynamic Cone Penetrometer (DCP) results. This often comes as a shock to the geotechnical engineer as the DCP test wouldn’t be applicable in most applications. The DCP was originally designed in South Africa by Kleyn (1975) and was originally intended to be used for pavement applications as an indicator test.

On the Influence of Varying Aperture on Flow Mechanisms in an Initially Dry Vertical Smooth Parallel Fracture Under Free-Draining Conditions

K. P. Segole and J.L. Van Rooy. September 2017. Proceedings of the 9th YGE Conference SAICE.

It is essential to understand the properties and behaviour of rock mass, mainly in a hydrogeological context as well as various geotechnical applications. However, most of these processes occur as bulk fluid flow in the unsaturated zone and single fracture flow becomes imperative in understanding these processes, including, the identification of fluid flow mechanisms.

Assessing geotechnical centrifuge modelling in addressing variably saturated flow in soil and fractured rock

B. R. Jones, L.B Brouwers, W.D van Tonder and M.A Dippenaar. 2017. Environmental Science and Pollution Research

The vadose zone typically comprises soil underlain by fractured rock. Often, surface water and groundwater parameters are readily available, but variably saturated flow through soil and rock are oversimplified or estimated as input for hydrological models. In this paper, a series of geotechnical centrifuge experiments are conducted to contribute to the knowledge gaps in: (i) variably saturated flow and dispersion in soil and (ii) variably saturated flow in discrete vertical and horizontal fractures.

A qualitative model study on the effect of geosynthetic foundation reinforcement in sand overlying very soft clay

B. R. Jones, S.W Jacobsz and J.L van Rooy. 2016. Journal of South African Institute of Civil Engineering, vol 58 (2)

A centrifuge model study was carried out investigating the effects of the inclusion of geogrid reinforcement in a sand layer constructed over a thin, very soft clay layer to facilitate the construction of warehouse floors supporting product stockpiles. The use of geogrid reinforcement allowed larger surcharge loads to be applied for a given amount of settlement by allowing load to be spread over the footprint area of the geogrid due to the tension membrane effect and its associated benefits.

N2 Upgrade - Taming the uMdloti

Pequenino,F.P. and van der Merwe, F.H. April 2016. SAICE Civil Engineering.

The first phase of the upgrade of the N2 Freeway Section 26 saw extensive geotechnical works. A feature of this phase of the project included the widening of the dual uMdloti River viaducts. The viaducts are founded on 45m deep piles that required subcontractor KellerFranki to import a massive Bauer BG28 rig for the project. The project also included over 2km of fabric reinforced Mechanically Stabilised Earth Walls and 2km of cut retaining walls. This article discusses some of the more interesting facets of the geotechnical components of the project.

Geotechnical Characterisation and Stability Assessment of Two Pitwall Slopes at a Large Aggregate Quarry, Durban, South Africa

A.J Greet, B. R. Jones and E.D.C Hingston. 2015. Engineering Geology for Society and territory-Volume 2

Two unique pitwall slopes have been identified as major zones of potential slope instability at Coedmore Quarry. The first pitwall is a highly jointed rock slope known as a bullnose, whilst the second is a rehabilitated slope comprising cohesionless waste rock material resting at the angle of repose on the mined out pit slope benches. Consideration was given to all the internal and external aspects governing the stability of each slope, including geotechnical properties of the materials, ground induced acceleration due to blasting and the presence of groundwater from rainfall infiltration.

Stabilising Technology (Tensar TW1) Introduced to South Africa

Naidoo,S. Pequenino,F.P. and van der Merwe, F.H. April 2015. SAICE Civil Engineering and Sep 2015. Construction World

Article discusses the use of an innovative Mechanically Stabilised Earth (MSE) wall system on the Balito Drive road upgrade project in Durban, KwaZulu-Natal. This was one of the first and largest applications of this technology in South Africa to date. The system comprises the specifically designed TW1 block, combined with high-density polyethylene (HDPE) grid mats - known as Tensar uniaxial georgics - that are attached by a special connector into the blocks and extended horizontally to secure and reinforce the fill, thereby turning the whole structure into a monolithic mass.

Testing of Screwed-In-Casing Augered Piles using the Osterberg Load cell at the Mt Edgecombe Interchange

van der Merwe,F.H and Pequenino,F.P. Sept 2014. Proceedings of the 8th YGE Confrence SAICE.

Technical paper discusses the design and design verification of Screwed-in-Casing Augered Piles (SICAP) for the Mt Edgecombe Interchange at Umhlanga, Durban. In oder to optimism the pile foundation design and verify design assumptions and expected pile behaviour, full-scale pile load tests were undertaken on three test piles using the Osterberg load cell (O-cell). In addition to confirming the ultimate design parameters the results of the load test provided valuable insight to the load settlement performance exhibited by these piles and enabled the design to be adjusted accordingly.

Some practical applications of CSW testing in South Africa

Pequenino,F.P. and van der Merwe,F.H. April 2013. SAICE Civil Engineering

Article discusses the increased use and applicability of the Continuous Surface Wave Test by example from three recently completed projects; a major bridge over the Jukskei River, a 4 storey library at Stellenbosch University, and the rehabilitation of a dolomite subsidence on the R21 Freeway.  The examples show how the test is useful in supplementing information on ground conditions, in deriving design parameters where no other test method is possible, and as a tool used for quality assurance purposes on a major construction project.

Geotechnical investgations for upgrades to N2 from Mt Edgecombe to Tongaat Toll Plaza

Pequenino,F.P. and Van Haute, S.C. 2011. Proceedings of the 7th YGE Confrence SAICE.

Technical paper discusses the geotechnical investigation and design of various aspects relating to some of the geotechnical constraints encountered for the upgrade and widening of the N2 freeway between Mt Edgecombe and the Tongaat Toll Plaza including: Settlement and consolidation of approach fills to the uMdloti Dual Viaducts, Pile foundations to Umhlanga River Bridges and uMdloti Viaducts and Lateral support to various cuttings and structures along the route.

Deterministic stability analyses of a rehabilitated pit wall slope at Coedmore Quarry, Durban

K. Naidoo, B. R Jones, E.D.C Hingston. 2011. Proceedings of the 12th ISRM International Congress on Rock Mechanics, 12th ISRM Congress, Taylor & francis, London.

Coedmore Quarry's on-going rehabilitation programme involved the tipping of waste rock over final highwall's. However, this was stopped as it was a concern that it might prove to be a geotechnical hazard. The stability analysis was based on kinematic observation that failure would occur as a translational slip of cohesionless waste rock material. 

Construction starts on geotechnically challenging N17 Nasweto freeway link for 2010 World Cup

Pequenino,F.P. April 2008. SAICE Civil Engineering.

This article discusses some of the numerous geotechnical challenges presented along a relatively short freeway link constructed to provide much needed access from the N1 to Soweto and the Soccer City and Orlando Stadiums for the 2010 World Cup. Besides several large bridges over challenging geological terrain, there are deep cuts through existing tailings deposits, shallow undermining and a significant portion of the route constructed over and utilising existing tailings. 

Mamelodi sewer tunnel under construction

Varndell,P. and Pequenino,F.P. April 2006. SAICE Civil Engineering

Article discusses the investigation and design of a 3m diameter, 760m tunnel through the Magaliesberg in Pretoria. Extensive core drilling (holes up to 120m deep) and laboratory testing was carried out to investigate the geotechnical conditions and rock mass characteristics for the tunnel design. This project demonstrated the true value that a detailed geotechnical investigation can add to a project; reducing numerous variables that such a tunnelling project would encounter. These parameters were utilised in the tunnel design, inlcuding geological delinitation and rock mass characterisation.

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