AllyCAD Showcase

'Mining A Connection'


Jeffares and Green,
Johannesberg

"When you get on site, always expect the unexpected, because what's in or under the ground is not on the drawing." Lukas Edwards spends a lot of time on site making sure that the unexpected is dealt with properly and professionally.

"It's not the plan that is important, it's the planning," said his namesake, but no relation, Graeme Edwards. "Today, the design has to be a rolling one, adapted as unknown circumstances come to light; a sort of 'design as you go' plan."

"The necessity for a project to have a professional engineer as the RE today cannot be stressed enough," says Philip Zulch, a project manager alongside Lukas at Jeffares and Green. "There are simply no substitutes for training and experience. The demands on a Resident Engineer today in terms of safety and accountability are enormous. For instance, if a worker from a sub-contractor is injured or killed, the sub-contractor, the RE and client are all accountable, and what's more, criminal charges can be laid against all three."

Just before Christmas 2004, Philip and Lukas completed a 600m dual carriage way called Stoneridge Drive. They took over the project once the design and tenders had all been completed. "We started at the construction phase. This in itself is a major challenge, as we had no knowledge of what had transpired before our involvement. So we have had to face issues that were dealt with, but due to time constraints during the design phase, were not followed through," says Philip. "Project management was a major component of this project."

The two roundabouts and the 4m-bulk excavation posed no great challenges. "Our biggest challenges came from two existing pressure Rand Water pipelines lying in the road that needed to be relocated in the road reserve. The excavation of the pipes went down as far as 6m. The whole project was pinpointed around the relocation of these water pipelines. Once these pipes were moved, we could get on with the road project," says Philip.

"As soon as the pipes have been moved, they need to be butted and welded before you can do the pressure tests. This is where our problems started. We were refused permission to cut the water because the company Nestlé has a huge R2.5bn factory downstream that uses water for its cooling system."

"We had originally made arrangements to cut the high pressure feed over a weekend. The day before the cut, Edenvale Water told us that Nestlé couldn't be without water for even a single hour. Fortunately Edenvale Water has bypass systems between their high and low pressure systems. We designed a bypass system that bypassed their bypass system, so no-one was ever without water - we felt almost triumphant at the end," says Lukas with a proud smile. "I find that Civil Designer is excellent design software, especially for water and sewer applications, while AllyCAD provides the right tools for a top-class presentation.”

The sewer line was designed to start at a depth of about 1.5m, running through an existing culvert, and then tying up to an existing manhole. On the plan this posed no problem; on site this was a different picture altogether. "On the other side of the culvert, we found that the culvert had been sealed and a massive retaining wall had been built. Our connection was beyond that wall, which we couldn't just break down."

"We knew the sewer connection point was there somewhere, but exactly where it was, we couldn't be sure," says Lukas. "To
  get there, we had to break through the existing culvert floor - 600mm of concrete with 3 layers of reinforcing - and then tunnel in the general direction towards the tie-up point for about 10m under the retaining wall."

The work was done by hand; men working with machines in a confined space. "The time spent in the tunnel had to be short, due to noise and dust, as well as the poor light and air quality. When we started the tunnel was already 80m into the culvert, so conditions for tunnelling were not good at all," says Lukas.

Stoneridge Drive was part of the services for Phase A of Greenstone Park. A shopping centre with cinemas that go 12m below natural ground form part of the development, and the sewer lines were part of the service Lukas and Philip had to supply. "We ended up doing a sewerage connection point at a depth of 6m, where it was planned to be 1.5m."

"For this short section of 122m of pipes we had to use shoring, doing the work in sections. What should have taken two weeks to complete stretched to two months. On a job like this, the liaison between all the different parties - the project management side - is basically the biggest challenge. In the final phase of this contract we needed to lay our walkways, but the electrical contractor was laying his cables."

On this job three major water tie-ins were needed. Both Joburg Water and Edenvale Water were involved. "To co-ordinate those guys, to get them on site to shut off their valves is very difficult. These tie-ins were really difficult; 600mm cement asbestos pipes married to steel. That means that you have an oval pipe on the outside and a round pipe inserted in the centre. The time constraint was the killer here."

"The 16 megalitre reservoir had a 2-day capacity. For the 2 months we were on site, we checked it every day and it was full. On the day they came to cut the supply, it was only half-full; no-one knows why. So now we had half the time. Then on the day, Edenvale Water couldn't get the pressure down. Two days later they found that there was one valve in the system that should've been closed but was open, so we were delayed by 2 days," says Lukas.

Existing services lying under the ground are becoming an increasing problem. "During the design phase the drawings are sent to the authorities with a request for them to mark all the existing services, and how they want them protected, etc. The tender is done according to this information. But when you get on site, it seldom matches the supplied information," says Philip.

"We have had a situation where an electricity cable was accidentally ripped up. We contacted everyone, but no one came forward. Finally three weeks later, some one said, 'hey, that's our cable.' It's scary that that can happen. On the Stoneridge Drive job, we have an item on our bill of R100 000 for services that no one knows about. We know something is going to happen, so we have to allow for it."

World War 2 General and former US President Dwight D Eisenhower understood the value of 'rolling plans.' "In preparing for battle I always found that plans are useless, but planning is indispensable," he said. Lukas Edwards and Philip Zulch know this only too well.


 
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