Construction World January 2015

CONSTRUCTION WORLD

JANUARY

2015

PROJECT PROFILE

Both structures included abutments at

either end with three sets of intermediate

piers between. The south overpass was

cast as a continuous deck in three stages

along its length, whilst the north overpass

was cast in four stages split transversely into

individual spans.

Environmental impact

consideration

Where possible existing road materials were

recycled for re-use in the project. On the N9

and the N1, the base course layer was milled,

supplemented with crushed material and

stabilized with cement to form a new sub-base

layer. New pavement layer materials were

sourced from six local borrow pits and one

commercial source in Colesberg. The borrow

pits have been satisfactorily rehabilitated in

terms of environmental management plans

which were in place prior to the commence-

ment of the project.

The interchange precinct now contains

many features which enhance aesthetics and

address environmental issues. The fill and

cut slopes of the roadworks and the areas

affected by construction were rehabilitated

with the use of imported topsoil and hydros-

eeding. The seed composition was identified

by a specialist from the University of Free

State who determined the vegetation types

classification as Upper Eastern Karoo.

The site was also assessed by environ-

mental, heritage, paleontological and botan-

ical specialists prior and during construction.

Health and safety

Following the recommendations of an expert

appointed to minimise noise levels, the inter-

change precinct was further enhanced by the

construction of earth berms to reduce audial

impacts, particularly of heavy vehicles, on

residents adjacent to the roads. In addition

flood protection berms were designed and

constructed in the interchange area to control

storm water runoff, which in the recent past

had flooded the Engen access road and prop-

erty and the entrance road to Colesberg.

The project was built under trafficked

conditions and this was achieved by accom-

modating two-way traffic initially using one

way stop-go passing lanes, and later using

a two way bypass through some sacrificial

widening. This latter innovation enabled road

users to experience less inconvenience by not

having to stop and wait for oncoming traffic to

pass through the deviation.

In the case of the N1 upgrade and the

construction of the N1/N9 interchange, the N1

north and south carriageways were deviated

so that the interchange could be built without

disruption to traffic flow on the route.

The N9 and the N1/N9 interchange

precincts were maintained during the

construction period by the contractor to

ensure that the road surface was in a satisfac-

tory condition from a safety aspect while new

construction continued simultaneously.

Cost and quality

The project was completed within the

approved amended budget and the amended

time. Basil Read, in joint venture with

Newport Construction, commenced construc-

tion in March 2011 and the contract was

completed in April 2014 at a combined value

of just over R400-million for the interchange

and the N9 rehabilitation.

The N1/N9 interchange portion of the

works was delayed by three months due to

administrative issues relating to access to

the Colesberg Engen 1-Stop, which is situated

right in the heart of the planned interchange.

As a result the project was phased

so that the N9 portion of the works com-

menced as originally planned, with the N1/N9

interchange

portion

the

works

commencing three months later targeting and

achieving a simultaneous completion date.

This project was governed by rigid quality

control standards, which resulted in quality

acceptance testing for all road and concrete

materials. During this process more than

8 000 quality tests were carried out on the

road layers and pavement structure and more

than 7 000 quality tests were carried out on all

the concrete structures.

Risk management

Risks that were successfully managed and

overcome included the following:

The comprehensive stakeholder consul-

tation process resulted in a three month

delay in the interchange construction but was

resolved to the satisfaction of all concerned.

While the N9 rehabilitation started on

time, it was soon discovered that the roadbed

adjacent to the route was saturated due to

exceptionally high rainfall experienced in the

area. The saturated in-situ materials were

unable to drain due to impervious underlying

layers and had to be removed and replaced

with suitable rock fill from various sources

such as widened cuttings and blasting from

borrow pits. Ultimately 40 000 m

of rock fill,

which required urgent sourcing and procure-

ment, was placed to enable the project to

proceed. This resulted in the programme

being extended by almost six months.

Hard rock materials such as crushed stone

base course, surfacing aggregate, crusher

dust and concrete stone were to be supplied

from a separately operated source about

45 km south of Colesberg. However the

dolerite stone from this source failed the

durability requirements and the contractor

proposed an alternative in Colesberg. This

alternative source was tested and approved,

with significant cost savings due to its prox-

imity to the site. Had this alternative not been

successful, the probable resultant delays may

have had a significant negative cost impact on

the outcome of the project.

Preparing the deck formwork north overpass.

Low perspective of south overpass.