ARQ GEOTECH (PTY) LTD

COMPANY PROFILE

ARQ GEOTECH (PTY) LTD SUBSIDIARY OF ARQ CONSULTING ENGINEERS (PTY) LTD Capability Statement – Geotechnical

Geotechnics is one of ARQ’s key areas of specialisation. ARQ Geotech is active in a wide range of

geotechnical fields both within the borders of South Africa and internationally, providing professional

engineering services to a wide range of clients in the private and public sector.

We undertake and oversee geotechnical investigations which range from basic to highly advanced – each,

tailor made for site conditions, proposed land use and our clients need. We specialise in various forms of

analyses and designs including Slope Stability & Seepage, Lateral Support, Piled and Shallow Foundation

Design, Ground Improvement, and more; both within South Africa and internationally.

While hand-calculations and simple spreadsheet models are used to develop judgment in respect of

geotechnical problems, our sophisticated analytical methods and software allow us to design ambitious

and innovative geotechnical systems ensuring that our client receives the optimization allowed by the

latest technological developments. Design-compliance field measurement is regularly applied to complete

the investigation-analysis-design loop, or simply for the purpose of quality assurance, while the

requirements of OHS and environmental legislation are rigorously observed to ensure safety and minimum

disturbance to the environment.

Innovative and cost-saving solutions, coupled with detailed attention to each client’s specific needs, have

established us as one of the preferred Geotechnical firms in the industry.

A BIT ABOUT OURSELVES

OUR CAPABILITIES

Thomas O’Brien Yokazi Mkalali

Pr. Eng. BSc Geology

Coert van Dyk Hannes Taljaard Katy O’Brien Werner Britz

B. Eng. Hons B. Eng. Civil B. Eng. Hons. B. Eng. Civil

Brendon Blok Paul le Roux

B. Eng. Civil B. Eng. Hons.

Steve Mandumba Madaleen Booysen

Pr. Sci. Nat. BSc Geology

Directors

Geotechnical

Engineers

Engineering

Geologists

Drafting

THE GEOTECHNICAL “A-TEAM”

PILING AND LATERAL SUPPORT DESIGN SERVICES

ARQ Geotech works closely with Terra Strata Construction and is responsible for undertaking tender

design, detailed design, input during construction as well approval of quality and monitoring

documentation from construction works.

Piling projects typically entail the installation of

foundation piles for various structures including

multi-storey buildings, bridges, silos, cranes,

warehouses, reservoirs etc. Pile types employed

include self-drilling anchor (SDA) micropiles,

percussion bored micropiles, large diameter ODEX

piles, auger piles (open hole, underslurry and cased)

and continuous flight auger (CFA) piles.

Lateral support projects typically entail providing

support to retain soil and/or rock in excavations for

various purpose including road cuttings, basement

excavations, large foundation excavations, bridge

widenings, bulk earthworks platforms, pits, box cuts,

highwalls etc. Lateral support systems employed

include passive systems utilizing soil nails and rock

bolts with a reinforced shotcrete facing, cantilevered

pile walls as well as active systems utilizing multiple

rows of post-tensioned ground anchors often installed in conjunction with a pile wall (secant or soldier pile

wall). Temporary as well as permanent lateral support solutions are provided depending on the project

specific needs.

PROJECTS OF INTEREST

TASEZ DEVELOPMENT PHASE 1A

ARQ Geotech (Pty) Ltd was requested by Zutari

(Pty) Ltd to provide geotechnical services for the

bulk earthworks design of the site as well as for

foundation recommendations for various proposed

structures (retaining walls, buildings). The

geotechnical services consisted of geotechnical

investigations, evaluations, and inspections in

Watloo, Pretoria.

An initial geotechnical investigation was completed

by ARQ in 2019 providing a preliminary insight into

the geology and geotechnical conditions on site. The

outcome of this report was used as an input in the

preliminary design of the bulk earthworks by Zutari. Between 2020 and 2021, ARQ conducted a desktop

study and evaluation to support Zutari’s design by providing typical foundation recommendations.

Furthermore, two new additional geotechnical investigations were conducted by ARQ to provide detailed

geotechnical information to support the design bulk earthworks and foundation designs for various

structures.

Lastly, ARQ conducted regular site visits/inspections to support construction and provide valuable

geotechnical inputs.

Some geotechnical constraints dealt with in the project consisted of:

• Complex geology with numerous diabase intrusions into the Silverton Shale. This resulted in highly

variable geological conditions at different areas of the site,

• The abundant shale rock on site proved inadequate for use in engineered fill due to lower classification

(G9-G8) than the required G7 fill. Large quantities of import material were required as well as a

selectively used shale rock fill material,

• Abundant shallow perched groundwater occurring, generally in the norther part of the site. Various

temporary and permanent groundwater drainage solutions were proposed to facilitate construction

and protect the structures.

waves which are emitted by a

source, and propagate through the

subsurface. MASW was selected

over seismic refraction as it is more

apt at providing accurate readings of

possible soft zones overlain by

denser/stiffer zones and is also not

affected by the water table.

WATERKLOOF MARINA – UNCONTROLLED FILL IMPROVEMENT AND RISK

MITIGATION

Central Developments constructed a large residential development (including multi-level structures) on a

site in Monument Park situated partially on a historic clay quarry backfilled in places with uncontrolled

brick and other rubble. The brick fill is up to 20m thick in places and highly variable in composition. This

naturally posed a risk to structures founded upon it and required investigation and settlement mitigation

measures. ARQ was tasked with, amongst others, the geotechnical investigation of uncontrolled fills,

characterisation of materials and assistance in derivation of appropriate measures to afford safe

construction of structures on this material (as removal and replacement was not economically viable).

After extensive investigations, Dynamic compaction (DC) was conducted on the north western platform of

the development to improve fill density and uniformity. See Figure 1 depicting the platform after primary

DC.

The efficacy of the DC was then evaluated through the following mechanisms to quantify risk and to serve

as input to appropriate foundation design for residential structures:

• Analysis of DC trial penetration data

• Test pits (post DC)

• Geophysical testing (multi-channel analysis of surface waves – MASW), and

• Before and after ground surface survey to assess effect of densification

Amongst the other investigative measures set out above, multi-channel analysis of surface waves (MASW)

geophysical testing was conducted as the primary mechanism to assess the quality and efficacy of DC, and

investigate the fill for anomalies or voiding. The MASW method entails measurement of velocity of shear

This testing had the added benefit of providing information to depths beyond the brick fill and establishing

probable insitu shale rock level. Tests were conducted on five (5) traverses, almost 100m in length. Refer

to Figure 2 below for a typical MASW profile and to Figure 3 for “before DC and after DC” test pit wall

comparison showing densification effects.

North-western platform after primary DC

Typical MAWS profile in brick rubble after DC

MASW testing indicated no major low-density (soft) zones, though variable subsurface conditions were

still present as expected. The results of the investigation were used to quantify likely long-term settlements

and differential settlements and were used as input into the design of appropriately stiffened reinforced

concrete rafts for founding of structures.

The structures have subsequently been constructed and are preforming satisfactorily.

FAR WEST GOLD RECOVERIES REGIONAL TAILINGS FACILITY

In the interests of re-mining and consolidating tailings on the West Rand for environmental and economic

benefits, the concept of the Far West Gold Recoveries (FWGR) Regional Tailings Facility (RTF) was

developed. The conceptual design of the RTF presents a 4th Generation upstream on-wall cyclone ring dyke

dam with a pumped decant and expected Rate of Rise (RoR) of 4-6m per year.

If the RTF is implemented as designed, it should be possible over the next 3 to 4 decades, to re-move and

re-locate virtually every existing gold tailings dam on the Far West Rand to the RTF – a total of 1,3Bt,

thereby generating beneficial economic activity for the period and substantially reducing the current

impact footprint.

The final RTF will have an ovoid footprint covering 960Ha, a top surface area of 550Ha, a height

of 135m and side slopes of 1:4.

Before and after DC view of test pit side

wall

FWGR

RTF

Geotechnical profiles and material parameters were obtained for the foundation through geotechnical

investigations at the site of the proposed RTF. Tailings material parameters were derived via lab and insitu

testing conducted on tailings at the Brakpan TSF – which is deemed representative of the proposed RTF.

Limit Equilibrium, 2D and 3D Finite

Element modelling was undertaken to

examine the stability of the proposed

facility under predefined Mohr Coulomb

strength conditions, as well as by

employing the NorSand constitutive

model.

Stability was found to be satisfactory for

drained and peak-undrained conditions,

but marginal when residual undrained

conditions are assumed. A 2D and more

detailed 3D dynamic analysis, where

representative seismic time histories were developed and simulated indicate that meaningful liquefaction

is not expected for a 1 in 5 000-year seismic event.

BRAKPAN TAILINGS STORAGEACILITY STABILITY REVIEW

The Brakpan Tailings Storage Facility (TSF)

has been operational since 1985, with a

footprint of 800Ha, perimeter of 11km and

maximum height of about 100m, it holds

approximately 496 million cubic metres of

tailings material.

An investigation into the Brakpan TSF was

conducted by a team of professionals aiming to

investigate and validate various stability

aspects, not only for Brakpan TSF itself, but

upstream cyclone facilities in South Africa in

general. The evaluation involved a site

investigation comprising insitu testing

including CPTu, seismic cone and pressure

meter testing. Samples were collected during this investigation and submitted for laboratory testing, which

included conventional triaxial testing as well as critical state triaxial testing. All available information,

including current and historic aerial surveys, piezometric data, findings of previous and the current

geotechnical investigations, was interrogated to simulate conditions of the facility as accurately as possible.

In addition to this, a probabilistic seismic hazard assessment was conducted and used to develop

representative time history events for analysis.

A stability assessment was conducted in 2D and 3D, utilising Limit Equilibrium and Finite Element software

packages. The commonly used Mohr Coulomb material model as well as the more complex critical state

NorSand constitutive model were utilised to assess the stability of the facility and potential for liquefaction.

For the latter, various triggering methods were considered, including the effects of seismic occurrences.

For this, 3D models of the facility were submitted to dynamic seismic loading and stresses, strains and

displacements assess throughout the event.

ARQ Geotech was responsible for supervision and monitoring of the geotechnical investigation,

interpretation of insitu and laboratory test results and derivation of geotechnical profiles and material

parameters for analysis.

With this completed, ARQ conducted Limit Equilibrium, 2D and 3D Finite Element modelling and analysis

to examine the stability of the facility under predefined Mohr

Coulomb strength conditions, as well as by employing the

NorSand constitutive model. Staged construction simulation

of the facility allowed for stresses to be ‘built in’ to the

models and the potential for static liquefaction assessed.

Furthermore, dynamic analyses were conducted to simulate

seismic time histories, allow to assessment of potential to

cyclic liquefaction.

ABEL ERASMUS PASS

A small portion of the embankment on the R36 (provincial road), between Ohrigstad and Hoedspruit in the

Limpopo Province, South Africa, failed circa 2013. Photographs of the failure is provided in the figures

below.

Model of a portion of the facility

Analysis results, showing failure mode for the Western portion of the facility under peak undrained conditions.

ARQ conducted various site inspections and investigations to determine the possible cause of failure. ARQ

was subsequently appointed to conduct slope stability (using finite element methods) and hydrology

analyses in order to provide remedial solutions. These analyses were focussed on improving the site

drainage characteristic and reinstating the failed embankment and roadway.

Improving site drainage would comprise constructing various channels, stone pitching, gabions and

improved inlet and outlet structures at the existing culverts to control runoff water. The failed slope was

stabilised by installing 21 No. vertical and 21 No. raked (at 45° from vertical into the embankment) self-

drilling anchor piles. Re-instatement of the embankment comprises G7 material reinforced with a 50kN bi-

axial strength geogrid every 5th layer. This provides additional stiffness against movements in the direction

perpendicular to the roadway in which the

failure took place previously.

The figure overleaf depicts the model of the

slope used in the finite element analysis with the

self-drilling anchor piles and geogrids installed.

Implementation of this design commenced in

March 2017 with the completion date set at

November 2017.

ARQ’s site supervision team consists of a

professional structural engineer as the resident

engineer (RE) and a geotechnical engineer as

assistant to the RE. The technical team to the

project comprises Mr Alan Parrock with over 40 years’ experience in geotechnical engineering, as well as

the director of ARQ’s Structural division and director of ARQ’s Geotechnical division.

KHUMA SPORTS COMPLEX

Geotechnical investigation and dolomite stability

evaluation for the sports complex. The development

comprises a hall, pavilion, sport field and a parking lot.

ARQ conducted a geotechnical investigation consisting of

a gravity survey, seven (7) test pits and four (4)

percussion boreholes. The test pits were excavated to a

maximum of 3.2m within the in-situ material and the

percussion boreholes were drilled at least 6 m into

competent dolomite bedrock.

Soil samples were collected and delivered to Pretoria for

laboratory tests.

The field and laboratory results were analysed at the office to

determine the potential presence of problem soils (heaving,

collapsible, erodible, dispersive…), the excavatability of the

material, its suitability for use in various engineered layerworks

and fills and its adequacy as foundation material. Furthermore a dolomite stability assessment was

conducted and the Inherent Hazard Class of the site was allocated.

A report was submitted to the client provide inputs on some key geotechnical aspects of the site as listed

above and a foundation recommendation was provided

VOSLOORUS LICENSE DEPARTMENT DRIVE-THROUGH

Geotechnical investigation and dolomite stability evaluation for the license department drive-through

station. The development will include a new single storey concrete building.

ARQ conducted a geotechnical investigation consisting of a gravity survey, four (4) test pits and five (5)

percussion boreholes. The test pits were excavated to a maximum of 3.0m within the in-situ material and

the percussion boreholes were drilled at least 6 m into competent dolomite bedrock.

Soil samples were collected and delivered to Pretoria for laboratory tests.

The field and laboratory results were analysed at the office to determine the potential presence of problem

soils (heaving, collapsible, erodible, dispersive…), the excavatability of the material, its suitability for use

in various engineered layerworks and fills and its adequacy as foundation material. Furthermore a

dolomite stability assessment was conducted and the Inherent Hazard Class of the site was allocated.

A report was submitted to the client provide inputs on some key geotechnical aspects of the site as listed

above and a foundation recommendation was provided.

EXCELSIOR MASTS FOUNDATIONS

ARQ was requested, by Goldwind (Pty) Ltd, to conduct a geotechnical evaluation of the probable cause of

the movement observed on several of the intermediate monopole towers on the Vryheid-Excelsior

overhead distribution line for the Excelsior Wind Farm.

Furthermore, ARQ was to witness the proposed remedial work and provide input as to the integrity of the

foundation material at each tower during the remedial works.

Movement at the base of mast 48. Assessment of foundation conditions for remedial works

Additionally, ARQ assisted Goldwind in confirming the condition of the fills at the straining towers.

Prior to removal of backfill material from around the monopoles, DCP tests and limited Troxler tests (for

straining towers) were conducted on the backfill material, and the material was sampled in places for

laboratory tests to investigate its adequacy and compliance to design specifications.

After removal of backfill material a visual inspection and further DCP testing was done into the in-situ

material in the base of the excavation to verify the integrity of the founding material. The field and

laboratory results were analysed and presented in a report to the client. The report also detailed the issues

encountered at specific towers/masts that needed additional attention during remedial works.

RAMADIEPA DAM

As part of an expansion project, the Ramadiepa Dam was selected for an upgrade that would consist in an

increase in height and possible of the footprint as well.

The geotechnical investigation at Ramadiepa Dam was aimed at determining the geotechnical properties

of the construction materials used for the embankment dam. The investigation looked at the materials on

the embankment slopes as well as in the dam’s clay core.

Additionally, the investigation was conducted to obtain properties of the discontinuities of the rock mass

at the floor of the Dam’s spillway. The works conducted consisted of the following:

a) 8 Test pits on the dam,

b) 2 Rotary core boreholes, and

c) Dam foundation’s discontinuity mapping.

The test pits were excavated to a maximum of 3m within the in-situ material and boreholes were drilled to

7m. Soil and rock samples were collected and sent to a SANAS accredited laboratory tests. The discontinuity

mapping consisted of multiple joint line surveys

attempting to identify and record geotechnical

properties of the joints and the rock. Discontinuities

were represented in terms of their dip and dip direction

and illustrated by means of a stereographic projection.

The field and laboratory results were analysed and

presented in a report with limited interpretation. A

report was submitted to the client provide inputs on

some key geotechnical aspects of the site as described

above.

SEK – KIPOI MINE EXPANSION

Geotechnical investigation for various structures forming part of

the Stage 2 expansion of the mine. The expansion includes the

assessment of the stability of a soil retaining structure (gabion

wall) as well as the construction of the following new structures:

a) Crushing and scrubbing circuits and ancillaries,

b) Copper cobalt Axillary Plant (CCAP), and

c) Water Treatment Plant.

ARQ conducted a geotechnical investigation consisting of six test

pits and 12 Dynamic Cone Penetrometer (DCP) tests. The test pits

were excavated to a

maximum of 5m within

the in-situ material and

DCP tests were conducted

on surface as well as at

some depth within the

test pits. Soil samples were collected and shipped to South Africa

for laboratory tests. Furthermore, a visual assessment of the

gabion wall conducted, and feedback of the slightly bulging wall

sent to the client. However, no further geotechnical analysis was

conducted for the wall. The field and laboratory results were

analysed at the office to determine the potential presence of

problem soils (heaving, collapsible, erodible, dispersive…), the

excavatability of the material, its suitability for use in various

engineered layerworks and fills and its adequacy as foundation

material. A report was submitted to the client provide inputs on

some key geotechnical aspects of the site as listed above and a

foundation recommendation was provided.

TELKOM HIGHVELD AND ERASMIA

ARQ Geotech (Pty) Ltd was appointed by Mr Chris du Plooy of Bidvest Facility Management, hence forth

known as the Client, to conduct a dolomite stability investigation for an existing Telkom Tower located at

Highveld exchange. The investigation comprised of a deep sub-surface investigation, in the form of

percussion boreholes, constituting a dolomite stability investigation.

Six (6) percussion boreholes were drilled by Hennie Erwee drilling contractors on site as close to the tower

as practically possible given the existing services on the site. The boreholes were also placed in areas of

suspected subsidence or where gravity lows were measured. The boreholes were drilled until 6m of

competent bedrock was encountered. This equated to depths varying between 10m to 37m. Chip samples

collected during the drilling process were profiled at ARQ’s offices by an ARQ geologist according to current

standards (Brink and Bruin, 2002).

The dolomite stability investigation provided information in terms of:

• Materials occurring at depth on the site,

• Potential low-density zones and voids, and

• Water table.

This information was used in the dolomite stability assessment to provide a dolomite site classification of

IHC 6 to 8. According to the SANS 1936-1 the DAD is D4, based on the IHC classifications. The area is

currently used for “commercial and miscellaneous non-residential development category C3 (Tower of

55m, >3 storeys)”. This will necessitate that the development will have to comply with D4 precautionary

measures as outlined in SANS 1936-3. ARQ recommended a foundation solution/ remedial measures to

stabilise the communication tower and span the required 15m loss of support

BOOYSENDAL CENTRAL – CHANGE HOUSE & MANAGEMENT OFFICE

Northam Platinum’s Booysendal Mine

is situated about 50km North West of

Mashishing (formerly Lydenburg) on

the border of the Mpumalanga and

Limpopo Province.

ARQ Geotech was appointed in 2015

by DRA Global, the mine’s main EPCM

contractor, as Geotechnical Consultant

for the expansion project.

The mine extracts platinum and other

platinum group minerals from

deposits in the eastern limb of the

Bushveld Igneous Complex (BIC). Northam plans to increase its current production through construction

of several large infrastructure components at its new “Central Mine” complex.

As part of the infrastructure required on the platform at the Central Box-cut a state-of-the-art change

house, boasting a solar driven heating system that can produce hot water for over 2 000 people, and an

office building controlling underground activities remotely, are presently under construction.

ARQ’s initial geotechnical investigation on the platform in the area earmarked for the Change House and

Office Building comprised test pits. The investigation identified that the ground conditions below the

footprint of these buildings (single and double storey structures) was of concern – consisting of rock

fragments in a granular matrix which was described as loose in places. The platform fill layer varied in

thickness from 0 to 3m thick. This layer could be susceptible to movement resulting from the re-

arrangement of particles into denser formation, which would be triggered by the additional load imposed

by the structures and an increase in moisture content.

The risk was addressed via in-situ treatment of the platform material utilising Rapid Impact Compaction

(RIC). RIC if a form of dynamic compaction which entails densification of substrate through energy

imparted by a mass of 9-12ton falling through a distance of 1-1.5m at a rate of approximately 40-60 blows

per minute. Energy is imparted to the fill material through the machine’s foot/pad, which is moved over

the full extent of the site in a grid arrangement – typically 3-3.5m centre/centre with “one in the middle”.

RIC was determined as the best-fit for the specific site as

the method possesses sufficient energy to achieve the

required “depth of influence” while minimising vibrations

which may otherwise detrimentally affect existing

structures and services.

ARQ undertook an RIC design and recommended

compaction imprints on a grid spacing of 3.2m “with one in

the middle”. A maximum of 35 blows per pad with the 9-

ton hammer were recommended, with blow count being

stopped short of this maximum figure should penetration

of the foot into the fill slow to an acceptance criterion.

After the completion of RIC in-situ treatment, quality assurance was undertaken via Continuous Surface

Wave (CSW) testing. CSW testing is a geophysical method which is used to calculate the in-situ stiffness of

soil or rock through measuring the propagation velocity of Raleigh waves (one of two types of surface

waves) through the media. The stiffness of the fill post-RIC was then utilised to calculate likely total and

differential settlements of the structures.

ARQ undertook close supervision of the foundation excavations to ensure that any residual variability

observed is addressed on its own merit. The supervision consisted of visual assessments as well as a review

of Dynamic Cone Penetration (DCP) and Troxler density data.

Through the application of a well suited in-situ ground improvement method, and appropriate quality

assurance methods, the founding of the Office Block and Change house was allowed to proceed with

appropriately reduced risk.

BOOYSENDAL CENTRAL BOX-CULVERT

Northam Platinum’s Booysendal Mine is situated

about 50km north west of Mashishing (formerly

Lydenburg) on the border of the Mpumalanga and

Limpopo Provinces. ARQ Geotech was appointed in

2015 by DRA Global, the mine’s main EPCM

contractor, as Geotechnical Consultant for the

expansion project.

The mine extracts platinum and other platinum group

minerals from deposits in the eastern limb of the

Bushveld Igneous Complex (BIC). Northam plans to

increase its current production through construction

of several large infrastructure components at its new “Central Mine” complex. Several box-cuts in the valley

surrounding the Groot-Dwars River will serve as portals, bringing ore to surface. The Booysendal Central

Box-cut is the first of these structures. ARQ Geotech oversaw the geotechnical investigation on the

proposed footprint area for the box-cut and together with DRA’s engineers set the base level of the box-cut

such that the portals would be situated in competent rock – facilitating stability of portal entries. With the

overall box-cut geometry set, ARQ Geotech proceeded to develop a 3D geotechnical model of the materials,

and derived strength and stiffness parameters.

Conceptual design resulted in selection of a 70˚ highwall, stabilised in terms of global stability with soil

nails and rock bolts up to 9.5m in length. Local stability and durability of the highwall excavation face was

achieved by the application of a steel mesh reinforced, sprayed concrete facing. Detailed design was

undertaken using advanced finite element analysis (FEA) of representative cross sections, backed up by

simpler software and hand calculation methods, and vetted by years of experience.

Construction of the box-cut commenced in mid-

2016 with ARQ Geotech providing part time site

supervision to endure that the design was

implemented correctly, and that quality was up to

standard. The box-cut highwall stabilization was

completed in late-2017 and culminated in a high

wall standing proud at a height of 31m. Materials

excavated were utilised to construct a large

platform which will accommodate a wide range of

associated surface infrastructure.

Seven decline portals were driven into the

competent rock exposed at the base of the

highwall. Portals were developed “on reef” from word-go, thus aiding in the cost-efficacy of the

operation. To date the highwall lateral support is performing as predicted and is effectively retaining the

mountainside and allowing safe entry to the reef below.

SANI PASS – UPGRADING OF MAIN ROAD P318 FROM TROUTBACK TO SANI TOP PHASE The project involves the upgrade of the Sani Pass (P318)

Main Road. The scope of works was divided into 2 contracts,

namely a structures and roads contract, which were

awarded to Chris Africa Civils and Leomat Construction

respectively. Chris Africa were responsible for the

construction of 7 cast insitu box culverts, one incorporated

in a large valley fill cladded with Terramesh baskets and

one bridge. Leomat are responsible for mass earthworks,

construction of ancillary drainage (v-drains etc.), installation of precast concrete pipe culverts,

construction of lateral support structures in the forms of concrete retaining walls, Terramesh and gabions

walls and shotcrete and soil nail walls.

PORT LOUIS RING ROAD – POST FAILURE STABILISATION FOR A MECHANICALLY STABILISED EARTH WALL

The Ring Road Phase 1 project in Mauritius was

constructed during from 2010–2013, and

comprises a 4.9km long dual carriageway. Early

2014, cracks appeared on the northbound

carriageway, followed by the collapse of a 15m

high MESW portion of the fill (Figure 1).

Observations pointed to a textbook slope failure

with “slip at the lip” and “bulge at the toe”,

indicating that deep seated movement occurred.

ARQ was appointed to conduct a geotechnical

investigation to identify the mechanisms of

failure, to design remedial measures and to

supervise the implementation of the remedial

measures.

The investigation comprised rotary core drilling (triple tube to maximize core recovery and minimize

sample disturbance) with SPTs, undisturbed sampling and subsequent laboratory testing including

numerous triaxial tests.

Using results from the investigation ARQ conducted Finite Element Analyses (FEA) to identify the failure

mechanism and to design the remedial measures. A deep seated failure mechanism was identified (Figure

2). Remedial measures were designed which comprised inter alia a vertical secant piled wall supported by

7-strand, 3-level, high strength ground anchors, coupled with a geosynthetic reinforced fill section behind

the reconstructed MSE wall (Figure 3).

Figure 2 Figure 3

Figure 1

Remedial work to the Port Louis Ring Road was completed mid-2017 (Figure 4) after the resolution of

several design and construction challenges. At the end of

the day all challenges were overcome and the road was

reinstated to its original state by implementing state of

the art geotechnical solutions.

NWAMITWA DAM

The proposed Nwamitwa Dam is located at the confluence of the

Groot Letaba and Nwanedzi Rivers, some 40 km east of Tzaneen,

Limpopo Province, South Africa. The dam will increase the

assurance of yield and enhance the water resources of the Groot

Letaba River in serving the needs of the Mopani District of eastern

Limpopo Province.

The dam indicates a maximum height of 43 m above river elevation

and will comprise the following components:

• A central concrete section of 350 m length and a maximum

height above lowest foundation of 43.5 m,

• Zoned earthfill embankments on the left and right flanks, 1

200m and 1 900m in length respectively, with a maximum

height of 24 m,

• An outlet works with a dry well and a maximum discharge capacity of 18 m3/s,

• A spillway with a maximum discharge capacity of approximately 6800 m3/s,

• The interface between the embankments and the central concrete spillway is created with wrap-

around embankments.

The underlying geology in the area of The Nwamitwa Dam is Mesoaechean granitoid gneisses, specifically

the Groot Letaba Gneiss (previously Goudplaats Gneiss), which has been intruded by younger diabase

dykes. ARQ Consulting Engineers was sub-contracted to undertake the tender geotechnical investigations

and to prepare the tender design for the new Nwamitwa Dam. ARQ’s Geotechnical department was

responsible for co-ordinating and conducting the geotechnical investigation for the dam footprint and

sourcing applicable material for the construction of the dam as well as the access roads.

This investigation comprised of:

• Desk study of available geological information,

• Field mapping,

• Dynamic Cone Penetrometer (DCP) and Dynamic Probe Super Heavy (DPSH) testing,

Figure 4

• Geophysical surveys,

• Additional rotary core drilling (incorporating

Standard Penetration Testing),

• Test pitting,

• Water pressure (Lugeon) testing and measurement of

the water table,

• Laboratory testing, and

• Seismic hazard assessment.

Data gained from this investigation was then used to

design the various dam components. The Geotechnical

department worked in tandem with the Dams & Hydro

department to develop the earth embankment of the dam.

RocScience’s RS2 finite element software was utilised to

ensure the embankment exhibited adequate margins of

safety while producing a cost-effective and practical

configuration.

RAISING OF THE TZANEEN DAM

The raising of the Tzaneen Dam is being implemented by the

Department of Water and Sanitation (DWS) in tandem with

the construction of the new Nwamitwa Dam. This forms part

of the Groot Letaba River Water Development Project aimed

at increasing the assurance of yield of the Groot Letaba River

in serving the needs of the Mopani District of eastern

Limpopo Province. ARQ Consulting Engineers was sub-

contracted to undertake the tender geotechnical

investigations and to prepare the tender design for the

Tzaneen Dam raising.

The proposed raising will add an additional 3 m to the spillway and approximately 1.5 m to the

embankment non-overspill crest. The latter is likely to be undertaken by means of engineered fill and thus

compatibility with the existing clay core must be assured.

The geotechnical investigation, conducted by ARQ’s Geotechnical Department, comprised:

• Rotary core drilling with Standard Penetration Tests (SPTs) on the existing embankment,

• Continuous SPT testing on the upstream slope of the earth embankment,

• Test pit investigation in the surrounding area for suitable construction material, and

• Comprehensive laboratory testing (including foundation indicators, moisture-density tests, triaxial

testing and permeability testing).

This was done with the aim of confirming

conditions within the existing embankment as

well as sourcing material suitable for

construction of the raising.

Using information gathered from the above

investigation, the Geotechnical department then

worked in conjunction with ARQ’s Dams &

Hydros department to develop a safe

configuration for the raised embankment

structure. The stability of the current

embankment was also evaluated. Design configurations were assessed using hand calculations, limit

equilibrium and finite element methods.

RocScience’s RS2 software was used for the finite element stability evaluation of the existing structure

embankment as well as the raising. Representative cross sections of the embankment were selected and

analysed under plane strain conditions. The use of this software ensured that acceptable strains and

stresses were calculated within the embankment and raising. It was also confirmed that factors of safety

adhering to current standards and norms were achieved.

BOOYSENDAL CENTRAL DEVELOPMENT

Northam Platinum’s Booysendal Mine is situated near the town of Burgersfort in the Limpopo Province,

South Africa. As part of the mine’s recent endeavours to extend its mining activities into the Steelpoort

Valley, a new area was earmarked for the development of its Central Complex.

The Central Complex Development boasts a 30 m high, 140 m wide box-cut high wall at the foot of the

mountain in which seven portals, each 10 m wide, will be constructed to provide access to the sought-after

UG2 and Merensky platinum reefs. ARQ was responsible for the stability of the high wall and a lateral

support design was conducted based on data from a combination of 39 vertical and inclined rotary-core-

drilled boreholes. These boreholes were positioned strategically to intercept the main joints in the rock

mass, as well as important zones of weathering that will potentially influence the stability of both the high

wall (outside face) and the seven portals, the livelihood of the whole operation. The locality of the boreholes

is indicated on the pictures below.The lateral support design for the high wall, comprising two benches,

was conducted using advanced finite element computer software to provide a life-of-mine solution. It

comprises multiple rows of Threadbar 500 soil nails and a steel-mesh-reinforced shotcrete layer. Various

cross-sections of the high wall were utilised in the design to provide a cost- effective soil nail layout.

The diagram below indicates a model of one of the cross-sections used for design purposes.

Designs were conducted for both serviceability (SLS) and ultimate limit state (ULS) load conditions. The

development also comprises a wide variety of supporting surface infrastructure on terraces which includes

a 4 000 ton raw ore silo, 8 Ml water reservoir, a crusher plant, a pollution control dam, a 140 person change

house and smaller structures like offices and boardrooms. ARQ was also responsible for the investigation

and design of the foundations for these structures.

The remote Central Complex is situated some 7 km from the current functioning Booysendal North

plant and will be connected via an access road traversing the mountainous terrain. The optimised

route alignment includes eight cuttings up to 10.5 m high and 250 m long. The photographs below

depict only two of these cuttings under construction

Further developments as part of the Booysendal Central Complex include a rope-conveyor system that will

transport raw ore material from the 4 000 ton silo at Booysendal Central to a newly acquired processing

plant some 4 km across the valley and the Groot Dwars River. This state-of-the-art system will comprise 12

pylons up to 60 m high and will dramatically increase the raw ore processing capacity of the new

development. ARQ was responsible for the foundation investigation and design recommendations of these

structures, focussing on deep clay strata beneath the foundations coupled with high horizontal structural

forces and accompanying moments.

RESIDENTUAL DEVELOPMENT – PRETORIA EAST

ARQ was appointed as geotechnical specialists in assessing and overcoming various challenges faced on

the site of a large residential development in Pretoria. The two main areas of focus were:

Slope Stability

The development is located on the site of an old

quarry, where a 40 m high cutting face exists. Before

housing units can be constructed on top of the quarry

high wall, the stability required assessment, in this

case, improvement via the installation of piles. The

piles interrupt the potential failure plane and thus

stabilise the slope allowing construction of

residential units in close proximity to the face. The

design was undertaken using RocScience’s RS2 finite

element analysis software and checked using various

other methods. Ultimately, 30 m long, 750mm

diameter reinforced concrete piles spaced at 5 m c/c

were utilised to bring the probability of failure and

reliability index within allowable limits.

Dynamic Compaction

Large areas of the site were historically backfilled with

reject brick rubble, ash and other uncontrolled materials.

ARQ was appointed to investigate these fill locations and to

derive a means to allow construction of housing units in the

affected areas. After an extensive investigation, including

percussion drilling, Continuous Surface Wave (CSW)

testing, test pits and in-situ density testing, Rapid Impact

Compaction (RIC) was determined to be the most effective

means of densification. ARQ undertook an RIC compaction

design using purpose programed spreadsheets and

supplied the client with an RIC specification which could be

used for tender. With these measures implemented, the

problematic fill areas of the site could be used for

construction.

PORT LOUIS RING ROAD SLOP STABILISATION

A section of the Port Louis Ring Road (PLRR) from chainage 3 520 to 3 450, comprising a Reinforced Earth

structure of some 15 m in height, collapsed circa March 2014. Investigative drilling under the control of

ARQ of RSA was undertaken and supervised by an ARQ geotechnical engineer. The ARQ engineer logged

the core and undisturbed samples were retrieved ensuring that their integrity was maintained. These were

carefully packed in wooden boxes and sent via airfreight to the SANS accredited Geostrada Laboratory in

Pretoria, South Africa. There they were extruded, with little or no disturbance and tested under SCU

conditions. Some samples were sent to the accredited Geolab and tested under SCD conditions such that

Poisson’s ratio for the material was derived. Meticulous analysis of the test results was undertaken in

generating effective stress Mohr Coulomb and Duncan Chang hyperbolic parameters.

The situation, after removal of some of the failed area, was modelled by extracting sections from the

surveyed data within the Autocad CAD computer package and these were input to the RocScience’s RS2

version 8/9 finite element software. Remedial measures in the form of a vertical secant piled wall (1.08 m

φ), supported by 7-strand, 3-level, high strength ground anchors, coupled with a geosynthetically

reinforced fill section behind the reconstructed RE wall, were incrementally modelled by the software in

up to 16 stages, mirroring actual construction practice.

Strength Reduction Factor (SRF) values in both the

serviceability (SLS) and ultimate limit state (ULS)

condition for each section were determined as

satisfying internationally accepted norms. These

values, coupled with very high reliability predictions

and numerous redundancy paths via the chosen layout,

indicated an extremely robust solution.

The secant pile wall comprising 93 piles and the ground

anchors comprising 128 anchors with a total of 4 000 linear metres have been installed. Monitoring of the

wall movement is done on a weekly basis and the system is performing very well. Backfilling at the anchors

and the road embankment on top is currently in progress and will be completed within the next two

months. Graphics below depict a) failed road b) finite element model used in analysis and c) the secant pile

wall and ground anchors prior to backfilling.

WWW.ARQ.CO.ZA

Physical Address: 6 Daventry Street, Lynnwood Manor, 0081, Pretoria, South Africa

Postal Address: PO Box 76379, Lynnwood Ridge, 0040, Pretoria, South Africa

Office: +27 (12) 348 6668

Fax: +27 (12) 348 6669

Email: arq@arq.co.za