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on the existing wall. This ensured that the wall did not

fail due to imposed loads during the construction phase.

As a precaution all crane-based activities were situated

over 10 m from the quay wall.

To install the foundation piles the specification ad-

vised the use of impact hammers instead of vibratory

hammers, as the latter are known to have the potential

to induce vibration into the surrounding ground due to

their high frequency.

This vibration could liquefy the soil in a localised area

around the toe of the existing wall, which would reduce

the shear properties of the sub soil, most likely causing

the toe of the existing sheet pile wall to rotate, inducing

a serious failure.

To carry out the piling operation, the contractors

used two BSP hydraulic impact hammers. First a CG240,

with a 16 t dropweight, suspended from a Kobelco 180

t crawler crane and mounted on a 40 m x 15 m floating

barge, drove the 27 t king piles. Then a suspended CX85

with a 7 t dropweight was used to drive the sheet piles

and form the combination wall.

Prior to installing the piles, BSP carried out an im-

portant modification to the CG240 hammer. This in-

volved having legs fitted rather than a pile sleeve which

reduced the overall weight and also enabled the ham-

mer to drive the king piles while avoiding any clash with

the pile template which had to be kept in place until

driving was complete.

Geotechnical investigations allowed the SSA JV to

size the correct hammers for the project. During pile

driving the soil conditions along the quay wall were no

problem for the BSP hammers. Pile-driving durations in

excess of two hours previously encountered on Berth

12 were substantially reduced through the use of these

more powerful and reliable impact hammers.

Steel piles used for the combination wall included

double I section HZ 1180M piles (king piles) to form the

structural elements, and AZ 18-700 sheet piles acting

as filler sections amounted to some 10,550 tonnes. A

seven-bay pile guide frame was used to ensure the piles

were kept within their vertical and horizontal alignment

tolerances without twisting.

Because of logistical difficulties and space restrictions

the 27 m long king piles were located on a designated

area within the harbour complex where they were pro-

filed with a curved cutting edge to aid installation. The

402 anchor piles 33m long underwent additional prepa-

rations for the HP grout system.

Design consultant Railway and Civil Engineering

Consultants (RCE), the design consultant for project

manager Transnet Capital Projects, proposed that the

Müller Verpress Pile (MV-Pile or HP) system was em-

ployed for anchoring the combination wall, as an alter-

native to the traditional dead-man anchor solution. This

is the first time the system has been used on a construc-

tion project in South Africa.

The system makes use of H-section bearing piles

supplied with thickened flanges. The piles are usually

driven at 45 degrees to the combination wall through

the centre of the king pile to which it is later pinned.

While the pile is being driven to level, grout is pumped

out near the toe of the pile at 10 bar. The grout acts as

lubricant during driving, and once set, it bonds to the

steel pile and the surrounding substrate, increasing the

frictional resistance of the anchor as well as protecting

it from the adverse effects of corrosion.

The success of HP piling was measured through the

results of the test piles, which passed the stringent test-

ing and specification requirements set forth in the

contract and was an important aspect of the project that

the Stefanutti Stocks Axsys JV prides itself on accom-

plishing successfully.

BSP Foundations International

We thank Eswee Kruger, site planner on the Maydon Wharf project,

for his photographs, and Tim Milner, consultant Bid Manager for

Stefanutti Stocks Marine for the use of his photographs and the text

in this article.

Contractors World International

Contractors World International Vol 7 No 4

14