Bridge building in Rwanda: How engineers provided a lifeline for one rural community
29 January 2019
Awaiting the official opening of the Gatare bridge in Rwanda, which EuropEngineers and Bridges 2 Prosperity (B2P) collaborated on in July 2018.
The Gatare bridge project began in July 2018 when EuropEngineers, in collaboration with Bridges to Prosperity, decided to send an industry team to build a footbridge for villagers in an isolated, rural community in Rwanda.
The 10-strong project team was drawn from EuropEngineers companies, namely, Basler & Hoffman, BuroHappold, Setec, Pondio Ingenieros, Salfo & Associates SA and ROD.
Our task was to travel to Nyarugenge municipality in the Kigali province and build a 37m suspended bridge over the Yanza River, which floods 90 to 180 days of the year, cutting off local access to critical resources.
The purpose of the new bridge is to provide the Gasiza and Rubonobono communities with safe passage across the river and year-round access to the local market, health clinic and primary school.
Arriving in Rwanda
Following several weeks of planning and preparation, our project team arrived in Nyarugenge on Sunday, November 3.
Our goal was to complete the bridge by Friday, November 16, so we wasted no time in hiring two 4X4s at the airport before setting off to buy provisions at the local market.
After a short stop at the bridge site, we made our way to the place we would call ‘home’ for the next 12 days. Our accommodation was basic, but we were luckier than most in that we had beds and electricity, but unfortunately no running water.
The project kick-off
Work on site began on Monday, November 4. As team construction lead, I was responsible for developing the daily work plan and overseeing the activities of both the industry team and the local community staff working on the construction site.
Communication was one of the first challenges we faced. Many of the locals had very little English, if any, while only three of our own team spoke English as their first language.
Thankfully, with some help from the B2P staff on the ground, the two teams integrated well, and the local volunteers participated fully in every phase of the construction.
This was very important because the locals will have responsibility for the operation and maintenance of the bridge going forward, and familiarity with the bridge components and the process behind their construction will make this task much easier.
Dealing with the unexpected
During our first morning on site, we discovered that the bridge design had changed while we were en route to Rwanda and that the appropriate bridge cables would not arrive onsite until that afternoon.
We also realised that, due to the height of the abutment, we could not set up the level within the boundaries of the site. Instead, it had to be set up on a road adjacent to the site so we could view the centre of the span and the abutment, where the desired cable sag was marked.
The cables had to be pulled manually with a winch at one end to achieve the desired cable sags at mid-span. To facilitate the release of the winch, the cable sag had to be set above the desired level so that when the cable sagged from the release of the winch, the cable wouldn’t sit below the desired level. This took several attempts before it was achieved.
Work gets under way in earnest
By the end of our second day on site, the cables had been set and the deck cross beam preparation was well under way. This allowed us to start to grout and tar the cables in the dead end abutment (the side opposite where the cables had been pulled from) and start the backfilling.
The backfilling was a manual process and involved physically lifting all the big and small stones on site and placing them in the abutment.
The next step involved mixing the concrete for the dead end abutment approach slab in an area of the site affectionately known as ‘the pit’. In one afternoon alone, we succeeded in mixing and placing almost five-and-a-half metres of concrete, in temperatures in excess of 30 degrees.
The concrete delivery system was very primitive. It consisted of filling a plastic watering can, which we had spilt to form two trays, with concrete and then delivering it to the desired location on the abutment.
A sightseeing weekend
By the end of our first week on site, and in spite of the intense heat and rudimentary equipment, we had made more progress than originally anticipated.
We decided to take the weekend off, so we headed to Lake Kivu in southwest Rwanda to relax and reacquaint ourselves with running water. It was just the recharge we needed for our second week on site.
On our way back to Kigali, we stopped by the Dian Fossey Gorilla Fund International centre in northwest Rwanda, where we learned about the efforts to protect the country’s mountain gorillas from threats to their survival.
The last week
At the start of our second week, we completed the deck, and with the dead load sag level confirmed on the cables, the grouting/backfilling/concreting of the live end began.
Every able-bodied person on site jumped back into ‘the pit’, and the process was completed within one-and-a-half days – no mean feat considering the searing heat and thunderstorms passing overhead.
By Wednesday, the bridge was complete, and the fencing on both the approach ramps and the site clearance was finished.
We celebrated with a game of soccer with the local team, before hosting a BBQ on site for everybody who had worked on the project with us.
The official opening
The bridge was officially opened at 10.30am on Friday, November 16, in front of a crowd of more than 400 people, including TV camera crews.
Notwithstanding the large group of local politicians present, the opening ceremony itself was very different to any I had attended before. A DJ began spinning the decks and an MC worked the crowd from 9am that morning, and two separate time slots within the proceedings were allocated to dance and celebration. And, you just knew the craic was good when the bodyguard of one of the dignitaries, who was dressed in full military fatigues, started dancing with everybody else.
Making a difference
As with so many projects, once we arrived on site, our team became so focused on delivering the bridge that, at times, we lost sight of just how much a project like this can mean to the local community.
This was brought sharply back into focus for us during the opening ceremony when one of the community leaders described how, during the rainy season every year, several children are swept away at the crossing. He also shared a harrowing story of a woman in labour who, in trying to cross the swollen river to get to the local hospital, was forced back by the water.
When you hear stories like these, it really makes you appreciate the positive impact our work in building the new bridge will have on the local community. Hitting a deadline or a project milestone can suddenly feel quite unimportant when compared with making a real and positive difference to people’s daily lives.
Our team is extremely proud of the small part we played in improving the lives of the people in this small Rwandan village, and we are very grateful to have been given the opportunity to do so.
The bridge is a 37m span suspended (stress ribbon) bridge. It consists of 2 No. handrail cables and 2 No. deck cables.
The deck was formed with 38 No. cross beams, located at 1m centres, made with a combination of steel and timber and placed on top of the walkway cables.
The walking surface consists of a series of 2m-long timber planks, placed five abreast, laid on top of the cross beams. The cross beams were connected firstly to the cables by 10mm dia. reinforcing bars acting as stringers, and secondly, to the walkway cables by manually bending the stringer around both the cable and the cross beams.
For the handrail cable connection, the stringer was manually looped around the handrail cable. A wire mesh was then attached to the handrail cable and deck to ‘fill the gap’ between the cables.
The cables were anchored in both abutments by passing them through a concrete anchor beam and clamping the cable against itself with a series of drops forge anchors.
When our team arrived to site, the abutment walls and tiers had been built, so once the cable sag was set, the abutments were backfilled with stones of varying sizes and layers of mortar.
Finally, fence posts were installed, and a 100mm deep approach slab was formed over the entire top surface of the abutment.
Author: Andrew O’Connell, senior engineer Roughan & O’Donovan. A chartered engineer, his most recent projects include the detailed design of the Royal Canal Premium Cycle Route Phase 2, the Enniscorthy Flood Defence Scheme – Bridgeworks and the Athy Distributor Road. He is a member of the executive committee of Engineers Without Borders Ireland.http://www.engineersjournal.ie/2019/01/29/bridge-building-in-rwanda-how-engineers-provided-a-lifeline-for-one-rural-community/http://www.engineersjournal.ie/wp-content/uploads/2019/01/a-aaaaarw3-1024x512.jpghttp://www.engineersjournal.ie/wp-content/uploads/2019/01/a-aaaaarw3-300x300.jpgCivilAfrica,bridges,Roughan and O'Donovan