Construction World March 2016

CONSTRUCTION WORLD

MARCH

2016

Murray & Roberts

Infrastructure, a

division of Murray &

Roberts Construction,

reports that the

construction of the 35

wind turbine bases at

the Noupoort Wind

Farm as well as the

ancillary civil works has

been completed.

his 35 wind turbine farm is

located in the Umsobomvu

District some 10 km east of

Noupoort on the top of the

mountain range of the same

name. Once completed this wind farm, which

will be operated by Mainstream, will feed

80 MW capacity back into the national grid via

a 132 kV overhead power line.

The contract is being undertaken by

Murray & Roberts Infrastructure in a consor-

tium with CONCO. Murray & Roberts Infra-

structure’s scope of work includes all wind

turbine generator foundations and adjoin-

ing hard stands, 32 km of gravel access

roads, the maintenance of a section of the

existing N9 and the maintenance of 10 km

of the Oorlogspoort District road. The

company is also responsible for 33 km of

cable trenching for the electrical cable reticu-

lation which connects the wind turbines

to the on-site substation.

CONCO is responsible for the electrical

component of the balance of plant works

including the engineering, procurement

and construction of the medium voltage

collector system, substation and overhead

line connection. The 2.3 MW wind turbines

will be supplied and installed by Siemens

Wind Power.

The wind farm, which is spread over a

4 000 hectare area, will accommodate 35

wind turbine generators and is divided into

four circuits namely A, B, C and D with eight

turbines on circuit B and nine turbines on the

remaining three.

Stephan Venter, project manager for

Murray & Roberts Infrastructure, says the

PROJECT PROFILE

location has had extreme inclement weather

including unseasonable rainfall as well as

snowfall on the mountain top. This had an

impact on the contract which started in

February 2015 but Venter says that through

sound management and attention to

logistical and engineering best practice the

company stayed on programme for this

16 month contract.

Foundation construction

Construction of the 35 wind turbine gener-

ator foundations started in February 2015

with the foundations being excavated to

suitable founding conditions, cleaned and

then blinding placed. Blinding is 10 MPa to

level the ground in the excavation. Once the

blinding is cured sufficiently, the hold-

ing-down bolts are installed to the specified

levels, and this is followed by rebar installa-

tion and foundation shuttering.

Each turbine base has a diameter of

19 metres comprising 45,8 ton of reinforced

steel and 369 m

of 30 MPa concrete. The

plinth requires 23 m

of 60 MPa concrete

and once cast, backfilling is done. A total of

1 600 t of reinforcing steel will be used.

“The process was the same for all the

foundations and these were completed in two

stages; firstly the conical sections followed

three days later by the plinth sections,” Venter

explains. All elements were cast in-situ,

utilising Murray & Roberts Infrastructure’s

on-site concrete batch plant

Trenching for cable ducts

Each of the bases has 30 cable ducts going

through it and this facilitates the connection

of the turbine to the pad mount transformer

(PT); from the PT it goes directly to the

substation. This required 33 km of trenching

for the cable reticulation and this was done

using a Tesmec rock wheel machine and

chain trencher. The trench width is between

350 mm and 1 metre wide depending on the

reticulation connection.

CONCO is responsible for the cable instal-

lation placing another layer of bedding over

the cables with Murray & Roberts Infrastruc-

ture backfilling up to ground level. Following

compaction, the top soil is replaced, the area

fertilised and seeded with an indigenous

grass mix.

Hard stands

Each wind turbine generator has a hard

stand adjacent to its final position. The hard

stand facilitates the erection of the wind

turbines, each of which has a tower that is

100 metres high.

NOUPOORT WIND FARM

progressing well

Erection of the bolt pack after blinding has been

poured at Platform 24 at Noupoort Wind Farm.

Bolt pack erection after pouring blinding on one of

the wind turbine bases at Noupoort Wind Farm.

Steel reinforcement in progress on a base at

Noupoort Wind Farm.