erf 962 Kingsburgh Massive Gabion Retaining Wall

Project Background

East Rand Junction (ERJ) has been investing in the area including this R40m site development.
As part of a planned development of Kingsburgh Commercial and Industrial Park site (an area of approx. 65 000m²) that would be for:

factories,
office buildings .

Site comprises upper and lower level platform areas, with internal access roads, pedestrian access and connecting walkways to the proposed buildings.

On 17 June 2017 a slope failure took place on Section number 8 situated next to the conservation area. Slope had been constructed at 1: 1 with a height of 32m from the toe. The filled slope composed predominantly of instu fill. First attempts toward stabilisation called for reducing the driving forces by flattening the slope to 3: 1. Although stability analyses based on the assumption that the water table was at the ground surface predicted a safe condition, the regraded slope remained stable only until the following big storm of October 2017, when a second much larger slide occurred. It was obvious that a close relation existed between rainfall intensity and slope movement. Also, calculations in stability studies indicated that the average soil shear strength was much lower than originally assumed.

Reduce Driving Forces and Restrain Landslide Mass

Since the driving forces were essentially gravitational because of the weight of the soil and water and the fact that stability of soil slopes is a limiting equilibrium problem in which the external forces acting on a soil mass are at least balanced, the design to stabilise the slope had to address ways to ensure proper safety from the forces tending to cause movements. Analysis had to be performed for anticipated loadings as well as structural capability to restrain landslide mass.

15 000

tons of earth works.

6 700

Litres of
Diesel

867

2 by 1 by 1
Gabion Baskets

3 500

Gabion Rocks

5 000

Geotextile

Geo-Tech

Exposed ground after excavations did offer solid base for a loading bearing. Dson Industries Syncline Geotechnical Engineering Pty (Ltd) to conduct a Geotechnical Investigation for the “Proposed Gabion Retaining Wall at Kingsburgh Industrial Park (Uitsig Road, Astra Park), eThekwini Municipality”.

Foundations for Lateral Support System
Due to the presence of potentially collapsible sandy fill soils and underlying potentially compressible alluvial clays at anticipated founding level, it was
recommended that some ground improvement be carried out prior to foundations of the retaining wall (as per below):

Excavate subsoils to a depth of at least 1.5 metres below proposed founding level e.g. if founding level is 0.5 metres then excavation level should be 2.0metres below EGL.
Compact base of excavation to minimum 95% Modified AASHTO dry density.
Backfill the excavation over the plan area of the excavation to the proposed foundation level using imported G5 material. The total thickness of
compacted backfill below the foundation should be at least 1500mm.
The G5 material should be compacted to 97% Modified AASHTO dry density.
Material will need to be placed in 200mm loose layers.
Consideration can be given to stabilising the material with cement (3-4%).
Construct foundation on engineered fill as per Structural Engineer’s details.
Recommended ongoing testing be carried out during the ground improvement period to ensure that compactions are achieved.

Gabion Structure Applied Engineering Solution.

ERJ were keen to explore a gabion retaining wall solution for the
project. Dson Industries were initially approached by developer Len Brown of East Rand Junction to facilitate an effective, practical solution to address the slope mass instability difference in levels throughout the site.

In the early stages of the project planning phase, there were a number
of meetings , both on-site and at the client’s offices. This was an important part of the planning approval process.

Meetings between the companies and the architects prior to construction, resulted in Dson Industries being asked to design, supply and install a 6m high Mass Gravity Gabion Retaining Wall and a mass gravity reinforced earthworks slope retaining system.

Dson Industries were contacted in October 2017 to consult on the Project. It was a further 10 months before we were able to commence works (whilst the main site contractors completed the initial construction phases).The intervening period was certainly useful in terms of project planning and ongoing consultation

GeoTech

The intervening period was certainly useful in terms of project planning and ongoing consultation

Excavate subsoils to a depth of at least 2.0metres below EGL.
Compact base of excavation to minimum 95% Modified AASHTO dry density.
Backfill the excavation over the plan area of the excavation to the proposed foundation level using imported G5 material. The total thickness of compacted backfill below the foundation should be at least 1500mm.
The G5 material should be compacted to 97% Modified AASHTO dry density.
Material placed in 200mm loose layers.

THE CHALLENGE

Site Conditions presented considerable complications for material handling and safe working conditions. Bulk materials would be offloaded at top level platform and the Gabion structure being constructed located 30m below. Two driveways were cut across the steep banks to facilitate material conveying.

Services Provided By Dson Industries

Design engineer consultations
• Production of as-built drawings
• Supply of Galvanised Gabion baskets in line with the design and
supply to site
• Technical and engineering support
• Supply and installation of geotextile membrane
• Drain Pipes
• Mass gravity gabion retaining wall installation including hand-placed facing stones

PROJECT BUILD COMPONENTS, SUPPLIED BY

20 ton excavator
75mm × 75mm welded mesh gabions (4mm/3mm wire diameter, galfan coated)
Dedicated and experienced team of gabion wall construction personnel
Excavator, compressor, plate compactor, pneumatic and hand tools
Foundation stone (6F5)
Gritstone (6G) rock fill material
Granular (G5) backfill material
Post sockets, integrated into gabion units, for later fencing by others
All fixing accessories including lacing wire
Non-woven, needle-punched geotextile membrane

THE PROJECT:	Section 8 Development Works
APPLICATION:	Mass Gravity Retaining Wall
LOCATION:	ERF 962 Kingsburgh
DATE:	July 2018
CLIENT:	East Rand Junction (ERJ) Len Brown
ARCHITECT:	Architectural Concepts Barry Liggins.
GEOTECHNICAL ENGINEER	Syncline Geotechnical Engineering (Pty) Ltd
Pr. STRUCTURAL ENGINEER	Mani Govender

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