Execution certification of underground infiltration systems

Underground infiltration systems as test cases

We can still admire some of the buildings that are already thousands of years old. Just think of the Chinese wall, the pyramids in Egypt and the temples of ancient Greece. This indicates that all these buildings had an important function and therefore had to meet high quality standards. For example, we can still find roads that were built in Roman times. These roads had to be reliable so that armies and traders could move quickly through the Empire in order to defend their safety and wealth. Even today, well-built roads are the arteries of our economy and society. Their construction must meet high quality standards. Checking that these requirements are met requires a great deal of effort on the part of all those involved in building the infrastructure. In order to be able to respond better to this, execution certification was started in 2016.

A number of test cases of critical executions were selected by various stakeholders from the infrastructure sector. Contractors, builders, manufacturers and experts were brought around the table for these executions (something that was still permitted at the time) in an advisory board to establish together, in consensus, how a high-quality execution should take place. These rules were formalised in 'Technical Requirements' (PTV). It was also determined how the quality of this execution could be maintained. On the one hand through training and self-monitoring by the contractor and on the other hand through supervision by an independent institution. A contractor who meets these requirements receives a certificate for this specific execution.

A builder who lets a certified 'executor' carry out the works has immediately proof that he has previously demonstrated that he is able to carry out the works in a qualitative manner. In this way, the contractor can distinguish himself and knows that everyone in possession of such a certificate is assessed in the same way, which prevents unfair competition.

In executions that are difficult to repair later on, such as underground constructions, a perfect execution is certainly crucial. That is why, from the start of the execution certification, it was decided to include the installation of underground infiltration systems as one of the test cases.

Whereas in the past rainwater used to be discharged quickly into the watercourses, people have come to realise that it is better to allow this water to gradually infiltrate the soil as much as possible. Watercourses are allowed to meander, pavements have to be permeable and wadis were constructed. Water that was nevertheless collected via roofs, terraces, roads and pavements is discharged into underground systems that gradually infiltrate the water into the soil.

These underground infiltration systems are quite new and not yet sufficiently known. Moreover, these systems exist in all kinds of shapes and sizes:

• on-site built composite infiltration crates wrapped with geotextiles;
• horizontally installed permeable pipes made of porous concrete or plastic;
• infiltration system by means of concrete cellars;
• porous and bottomless concrete inspection chambers;
• infiltration chambers in porous prefabricated concrete and concealed porous concrete channels;
• vertical infiltration piles and street gullies with vertical infiltration;
• infiltration units made of prefabricated infiltration crates encased in geotextiles;
• …