I was curious to see whether all the many ideas we had developed during the last weeks were really to be suited to erect a suspension bridge of more than 70 metres – by people, who from our point of view had no idea of even the most basic principles of construction.

The necessary equipment and material Damaso and I could easily organise. What turned out to be the major problem was money. Although Zoe gave me the advice to bring enough cash, I didn’t carry the bundles necessary. Instead I counted on various forms of plastic money, hoping that at least in Lima and Tarapoto where they have countless banks, getting cash wouldn’t be a problem. The disillusion came on the very first day. Starting with the argument that my credit card isn’t one up to the statement that all my accounts are completely empty I heard everything. At the end I was able to get a little cash every day and sum up the money to the amount I needed.

Normally you reach Tres Unidos in about three hours from Tarapoto. After a two hours drive on the Peruvian version of a street you cross a river by a log-boat and then you change to a so-called „motokarro“ that brings you to the village. The truck with all the material we bought took ten hours. It had to travel further along the river side until the next bridge suitable for trucks and then go back all the way to the Tres Unidos side of the river.

Damaso and I we took the short way and already prepared the work in the village when the mayor answered our “The truck will soon be here” , with a short but strict “No, it will not”.

To our surprised we learned from him that after rainfalls the street has an impassable passage. So we hurried to help the truck driver. Only after unloading and reloading, the truck was finally able to go on with its load and bring our materials to Tres Unidos.

The impatience of the villagers concerning the start of the construction work was impressive. Even Damaso pushed for a fast beginning. Unfortunately at this time we didn’t have marked the excavation’s outline nor did we define any centre line and the ant-like way of working was superfluous.

After many explanations, convincing and with help of the wonderful sketches Roland Weber made for us I was able to make clear that we need to do some preparatory work first. So with the same passion, everybody helped measuring although nobody really seemed to understand what exactly we did.

However soon after that the practical work could begin and from the children to the aged everybody was carrying the pickaxe.

Eventually we put up the first reinforcement cage as a model for the ones to follow. The local welder, who works with venturesome equipment, produced the necessary bending tool. And the volunteers were astonished about how fast and easy it is to set up and stabilise the steel grid with diagonal braces.

Next to the horizontal measuring of the abutments I had to clarify the levelling before I could leave. Although the bridge would be more or less unsusceptible to level differences in its foundations, levelling is still an important aspect.

What I had forgotten, was the laser measurement tool I had used in January. But not so the villagers. They wanted to know where the laser is, believing that without the tool we won’t be able to go on any further. What a good idea to direct the technical concept of bridge building only to locally available and easy to use tools!

But “easy to use” is relative. I thought a 100 metres tube scale is easy to use. But although I demonstrated the use with a 2 metres piece, six of my volunteers were not able to fill the tube with water from the river – not in one and a half hour. I cannot tell why and finally we took a hopper and got the tube filled. The level marks were cut into tree trunks and my work was finished. Now I look forward to the next visit in August.

With the start of the construction phase minor changes in the technical planning arose and at the same time solutions for details were found.

After the second measuring of the ground we had to correct the bridge’s length from 64 to 72 metres. In general this hasn't any influence on the construction planning since our static calculations were adequately dimensioned and the change of length does not matter. Nevertheless it approves our decision for a revised pylon design to be right.

In the run-up to the construction phase we had already discussed that our choosen version of the pylon design might not be stable enough for the bridge’s length. But since we wanted to do without additional bracing and therefore additional joints that would have caused a need for further maintenance, we favoured the version of a braced rectangle. (see right part of the picture)  

Advice from some of our experienced engineer clients however has finally prompted us to choose another option. Now the pylons will become supported by two additional tree trunks on each side. This needs a bigger foundation but to build this shouldn’t be a problem. 

By now we also clarified one of the most important details – how to connect the wooden pylons with the foundations. Since we’d like to see the bridge to stand there for quite a while, the wood better does not get into contact with soil or the concrete. Otherwise it will rot away. So we decided to place a kind of metal shoe in between.

A t-shaped metal element will be welded in Tres Unidos, which becomes casted in concrete on four rods of reinforcement. The trunk will be slit in the middle, positioned onto the t-form and bolted with small pieces of reinforcement. This way the pylon is secured against tilting as well as it can assimilate tractive forces.

Starting the constructing phase we naturally started with the abutments and foundations. To be honest we were really surprised, what a huge amount of soil needs to be moved for that. The excavation for the abutment only has the size of a respectable swimming pool.

Keeping the size as small as possible was our main intention but since everything needs to dug out by hand, we couldn’t plan a deep excavation. The walls could have collapsed and burry the workers underneath. In addition we had to take care not to fall below the highest possible water level otherwise there would be a risk of undermining the abutments once the ground-water table rises. So the only way to substitute missing depth and earth thrust from above was to correspondently widen the excavation.

Comic-style drawings that illustrate every step of the excavation were made to ensure that everything runs smoothly. Thanks to Roland Weber from DSI München, who supported us with his fantastic painting talent.

By now we even received more photographs from Tres Unidos, showing that everything runs perfect

On the very first we want to thank LEIKRA GmbH for sponsoring the project with 1.500 EUR. With this we bought all the cables and necessary cable clamps in Lima.

A constantly updated list of costs and expenses can be found on our homepage. Who wants to support the project will find our “shopping list” there and everybody can still take a stake in.