Frans van der Merwe

Keller Geotechnics

The Milnerton Beach node, an important recreational and tourism destination, is situated on the west coast of Cape Town. This stretch of coastline is one of Cape Town’s greatest ‘hotspots’ in terms of risk and vulnerability to coastal erosion and effect of storm surges and reduced resilience as beaches and dune systems are less able to recover from...

The stability of over-steep road embankments often worsens with time. In many cases the slope deterioration can be ascribed to continual downslope creep of a surficial layer of soil that has been affected by infiltration of rainfall. Such infiltration reduces the suction in the surficial layer interacting with the environment. With every season the...

Since 2016, more than five kilometres of microtunnel-bored-and-jacked sewer pipes have been laid in Cape Town. The use of trenchless technologies is favoured where the excavation depth exceeds 4m as conventional shoring and dewatering often become unfeasible. Also, where pipes are being laid within developed urban areas between existing services, w...

The stability of soil embankment slopes is an important aspect of infrastructure works, as many crucial roads, buildings and runways are ultimately supported by them. As changing climate patterns affect slope stability, the infrastructure in turn is put at risk. Increasingly, studies are being undertaken worldwide to investigate the effect of harsh...

The objective of this chapter is to provide guidance to designers in obtaining sufficient geotechnical subsurface information for the design and successful implementation of the works. The City’s minimum geotechnical investigation requirements, that should be carried out prior and during construction, are stipulated in this chapter. Sufficient geot...

Part 3 of this series will address issues such as the use of stressed self-drilling hollow bar grouted anchors, anchor and soil nail corrosion considerations, the use of non-prestressed soil nails in embedded piled walls, seismic loading, limit on crack widths in concrete pile sections, and typical failures or disputes that have arisen in South Afr...

The second part of this article will discuss beam-on-elastic (BOE) analysis methods, appropriate constitutive models, reduced passive resistance due to 3D effects, interface friction, reliability-based design, estimation of displacements, and the structural design of shotcrete infill panels. A comprehensive questionnaire was developed and forwarded...

Using SPT-N results to derived Hardening Soil HS Soil Model Parameter

Eurocode 7 (EN1997-1), will be adopted in South Africa as the geotechnical design code, replacing working stress design, with limit state design. EN1997-1 design approach 1(DA1) is the preferred approach in South Africa with a special National Annex for South African practice. DA1, Combination 1 and 2 applies partial factors on characteristic shear...

This article forms part of a series of articles on segmental retaining walls (SRWs), following on Mind the Gap – towards the elimination of open assembly configuration in segmental retaining walls and The Proof is in the Pulling which appeared respectively in the April 2018 and April 2019 editions of Civil Engineering. This article discusses the im...

FRP has been used in mining and tunnelling for many years and is now being used in soil nails and tieback ground anchor applications due to the durability concerns associated with conventional steel reinforcement. No guidelines could be found that assist the designer of soil-nailed retaining structures in the use of FRP bars. This article therefore...

A comprehensive questionnaire was developed to gauge the current design practices followed for deep excavation design in South Africa. This forms part of the compilation of the revised SAICE Lateral Support in Surface Excavation (LSSE) Code of Practice incorporating limit state design in accordance with EN1997 (Eurocode 7 – Basis for Geotechnical D...

The design and modelling of foundations cross two civil engineering disciplines, namely structural and geotechnical engineering. The structural engineer goes into great detail when sizing foundations to ensure effective load transfer from the superstructure to the underlying geoma- terials. This is usually accomplished by deriving the load and mome...

In many practical problems, the hydrologic and stress-strain behaviour of natural or engineered systems comprises soil that is strongly influenced by the presence, absence, or changes of interfacial interactions that govern unsaturated principles. The traditional saturated soil mechanics approach often fails to satisfactorily describe or predict th...

This paper will discuss 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 60 m. A signific...

The design of multi-anchored tieback soldier pile wall basements in Sandton is typically based on either empirical methods or two-dimensional finite element modelling, ignoring the effects of matric suction in unsaturated residual granites. The designer, however, often relies on previous experience in a similar subsurface profile rather than establ...

This article is a follow-up to the article that appeared in the April 2018 issue of Civil Engineering under the title “Mind the Gap – towards the elimination of open assembly configuration in segmental retaining walls”. This article identifies objectives for further study and clarifies issues with the open-block assembly based on connection strengt...

It is well known that soils cannot be excavated vertically without some cohesion being present in the soil mass. Soil-nailed walls require the excavation to proceed in unsupported vertical lifts before the application of a stiff shotcrete-and-mesh facing, and therefore require cohesion (Figure 1). This cohesion can be present due to one of two shea...

The fi rst phase of the upgrade of the N2 Freeway Section 26 has seen 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 45 m deep piles that required subcontractor Keller- Franki to import a massive Bauer BG28 rig for the project. The project al...

Towards the elimination of open assembly configuration in segmental retaining walls

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 Sou...

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 deformat...

The use of Mechanically Stabilised Earth (MSE) Walls were opted for at the Mount Edgecombe Interchange as a result of economic considerations and horizontal space constraints. Unconsolidated founding conditions as well as the mere extent of the MSE Walls called for ground improvement of the walls' foundations as well as several design reviews of bo...

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 indica...

The Franschhoek Pass (R45) is one of South Africa’s iconic mountain passes, serving as a gateway to the Overberg. The year 2013 saw numerous cases of slope instability along the route due to unseasonably high rainfall. In response, SMEC South Africa (Pty) Ltd was tasked by the Western Cape Department of Transport and Public Works with repairing dam...

The Tensar TW1 System was developed as an alternative to traditional retaining wall options and has been used extensively in Europe and elsewhere internationally. The system has very recently been introduced into the South African market through Kaytech Engineered Fabrics. This article discusses the use of the system on a major road upgrade contrac...

Screwed-in-Casing Augered Piles (SICAP) are a commonly used foundation type for bridges around the world. This pile type is predominantly favoured on bridges which carry significant loads under strict settlement criteria; SICAP provides higher confidence in the construction methodology and also allows for good quality assurance tests subsequently a...

is article discusses the increased use and applicability of the Continuous Surface Wave (CSW) test by using three recently completed projects as examples – a major bridge over the Jukskei River in Gauteng, extensions to the engineering building at Stellenbosch University, and the rehabilitation of a dolomite subsidence on the R21 freeway. Th ese ex...