We previously published an article on how to mark a plot...
Today, at Arquitectos Barcelona – Terrats Arquitectura, we carry out the next step in the execution of any work, the excavation for the foundation. In this case it is a strip footing foundation for the sanitary floor, in a house that we are building in Begues, in the Baix Llobregat of Barcelona. We tell you how it is done:
This is a task that is normally carried out by the machinist, ie an excavation company, or by the contractor if the appropriate machinery is available. However, as architects, it is our job to supervise the entire process and ensure that the work is carried out correctly, since if the foundation is poor, numerous catastrophic pathologies can occur in the building, such as differential settlement, which in the long run it could cause, at best, unpleasant cracks of a considerable size.
For this reason, at Arquitectos Barcelona – Terrats Arquitectura, we always personally supervise each and every one of the complexities throughout the project, in numerous site visits.
So, as architects, how can we supervise this type of operation?
Here's a quick guide!
Previous information:
To begin with, we have to keep in mind that hardly any geotech is perfect. We are going to find irregularities and unforeseen events when digging and we are going to see that the "firm ground" or resistant layer will not always be at the same height. Here we explain some steps and detailed instructions on how to overcome these situations and how to act when supervising the excavation.
Execution:
1- Make sure that the land has a clean access for the excavator and that the excavation machinery can enter, sometimes this will lead to the demolition of part of the wall of the land, so it will be necessary to improvise a door for the work, since either with aluminum plates or of another type.
2- The excavator must dig vertically and with the shovel of the size of the footing or the running footing in this case, so that it remains of the corresponding width at the time of concreting.
3- Regardless of what the geotechnician says, the excavation must be carried out until finding “firm ground”, that is, the resistant substrate of the terrain, and continue approximately 20-30 cm, so that the foundation is embedded in said resistant terrain. Identifying this terrain will be fairly obvious on most terrain.
4- This substrate does not have to be all at the same level, so many times the batch of reinforced and concrete will come out larger than planned, since there will be sections where it will be necessary to go deeper to find solid ground. It will be our builders who will have to re-grow it and level it afterwards.
5- In case of finding any anomaly during the excavation, it will be necessary to evaluate how this anomaly can affect the confinement capacity and compressive strength provided by this terrain. For example, in the case of finding an old construction water tank, this construction will not exert confinement force to the strip footing, so it will have to be cleaned and the area filled with earth.
6- Once the excavation has been carried out up to 20-30 cm. Inside the solid ground, around the entire perimeter it will be necessary to check that the entire excavation is "clean", making sure that there is only solid ground below and no roots or organic elements that could affect the foundation in the future.
This excavation is ready for concrete, it will serve as formwork for the foundation, which will give way to the waiting for pillars or load-bearing walls on which we can build our floors and build our home.
Thank you very much for your time and we hope you found it useful!
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