Well experienced Construction Professional Steve Keightley - Smith shares a site incident that taught him a good lesson on being an effective Site Agent.
In 1994 we had a good civil engineering job
at the then Western Deep Levels 3 Shaft near Carletonville. Anglo American had
checked the gold grade of the waste rock dump at No. 3 shaft and found that it
averaged 3-4 grams /ton which was very high considering the dump was on the
surface and all they needed to do was process the rock. They did not have
sufficient milling capacity on the mine, so they decided to build a new milling
plant. The job consisted of 2 large mill foundations, 2 x 10 m dia silos 30 m
high, 2 x 50 m diameter thickeners, mill building, conveyors, transfer towers,
control rooms, substations, various tank foundations, pipe rack foundations, roads,
and paving.
It was my first job that involved sliding
and we had a very experienced in-house sliding division. Two 30 m high 10 m
diameter silos was easy work for a team that had built numerous grain silo
complexes that were usually +- 10 silos +-40 m high with concrete coned roofs,
and had also worked on the Sasol 2 & 3 chimneys +- 200 m high. The silos
also had railway line rails, lining on the interiors of the silos to prevent
the rock from the conveyors wearing away the insides of the concrete silos. We
were working for Anglo American who had a huge amount of experience on building
mine infrastructure from all the work they had done on the Free State gold
mines. Western Deep Levels was also one of Anglos top gold mines and no
expenses was spared to ensure this was a word class job. Anglo had learnt from
experience to build their plants to a high standard to ensure they lasted.
The silos had 300 mm wide walls and
recessed pockets at the top to support steel beams that held up the roof and
supported the conveyors that fed the silos. The recessed pockets had 25 mm
steel plates with fish tail lugs cast into the bottom of the pockets to weld
the steel beams to.
We had a Liebherr 45/45 luffing jib tower
crane on rails so we could move it between the 2 silos. Concrete was mixed by a
400 R diesel mixer with timber bulkheads to separate the aggregates and a
cement store that stored the bags of cement. Concrete was volume batched with a
team of laborer’s using wheelbarrows feeding the mixer with aggregate and
cement. (Which was normal in those days)
The sliding team and concrete team worked
12 hours a day per shift 24 hours a day until the slide was finished.
Both slides went well. The shutter was stripped
plus the access tower which had access stairs.
We continued with the construction of the
rest of the plant. M&R Mechanicals were appointed as the structural &
mechanical contractor. They arrived on site, did their establishment, and
started getting deliveries of steel. One of the first activities was to
pre-assemble the steel platform that sat on top of the silos. They had a 100-ton
American lattice boom crane on wheels that they used to assemble the platform
and then the big day arrived for them to lift it on top of the silo. This was their
first big lift and the whole project & site team was there to watch their
first big moment.
All went well with the lift but when they
tried to lower the platform into the recessed pockets at the top of the silo the
steel did not go deep enough into the silo and the beams stuck out the top of
the silo. There was great consternation, drawings were quickly pulled out,
measurements were taken, people were sent up in a bosuns chair to check and
check again.
We then got the bad news, the recesses in
the top of the silo with the 25 mm steel plate with +-400 mm long fish tail
lugs were cast too high up on the silo. They sent me up in the bosuns chair to
check myself and I confirmed that the plates were cast in at the wrong level
and the recesses were not deep enough.
The silos had sat for +- 3 months before
the mechanical had arrived on site, and once the slide had been stripped and
the access tower stripped, and the tower cranes stripped there was no way to
get to the top of the silos, and no one had thought to double check them. We
were too busy focusing on other areas of the plant and trying to keep to the
program.
Now the challenges started. We had to find
a team, as this was extra work, not in the allowable, build up access towers to
each of the 4 big pockets and 2 smaller pockets on each silo, make work
platforms 30 m up in the sky, break out the concrete, remove the steel plates
with the fish tail lugs, set the right levels and grout in the steel plates
& lugs with non- shrink grout.
The concrete had been standing for 3
months, so it was rock hard, it was a difficult job with heavy compressed air
breakers and there was limited space for more than 2 people on the platform. I
had to go up and check the progress and to check each pocket before they were cast,
and it was not fun climbing up the scaffold to each pocket. There were no
access stairs, so we climbed up the scaffold to the rest platforms every +- 6 m.
The M&R Lattice boom crane operator was
real shit, and it cost us a case of beer every time he helped us to lift a
jackhammer or to lift the heavy steel plates or grout. It cost us plenty of
cases of beer.
We were under big pressure with Anglo as
M&R were charging standing time for their silo team and the crane even
though they were using them on other jobs.
I got so tired of climbing up each
individual scaffold tower that I would climb up one, and then for the first
time straddle the top of the silo and inch my way across to the next pocket.
This was very slow and as I got used to being up there, I would just walk along
the 300 mm wide wall 30 m up in the sky. Safet was not such a big issue in
those days.
We eventually finished the work, double
checked it, and told the project team that we were finished. They sent their
people up in the bosuns chair and confirmed it was correct and M&R
Mechanicals could carry on with their work. We stripped our scaffold towers and
carried on with the rest of the work.
It cost us quite a lot of money for the
standing time costs M&R Mechanicals had incurred and the clients QS`s were
very quick to deduct the money in out next payment certificate. We were unable
to claim it back from our sliding division as they were an inhouse division and
we had only picked up the problem 3 months after they had finished work.
So, the moral of the story is – Check,
Check and Check Again. As the site agent for the job, you are responsible for
the job, the whole job. Don’t leave it up to others to check unless you trust
them. You are the responsible person on the site and accountable for the site,
and until the maintenance period is over, you have completed any remedial works,
and received your final retention it’s your baby.
Steve Keightley - Smith is a Construction Professional with over 40 years of Civil Engineering, Building and associated Construction experience on Major Mining, Water Treatment, Railway, Industrial and Building Projects in Southern Africa.
Steve has held senior management positions at Concor, Trencon and Basil Read. Was involved in a number of Joint Venture contracts with other major civils contractors. He also has experience in cross border construction activities in Zimbabwe, DRC, Mozambique, and Botswana and investigations in Namibia, Angola, Zambia and Uganda.
He has also spent time on Grootegeluk coal mine, Medupi and Kusile power stations and the coal mines supplying the power stations.
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