Basements execution in existing buildings

The consolidated areas of cities, as they stand today, are the result of an urban design concept which dates back to the days before cars existed or when they were still a novelty. Many of these areas have, in the meantime, became extremely important both from a residential and commercial standpoint, heightening their appeal because of their proximity to the decision-making centres and workplaces of an increasing percentage of the population. We have therefore seen these areas becoming progressively revitalised, while their land value has increased significantly.

Car parking, however, remains a problem. Today Portugal is one of the countries of Europe which makes the greatest use of individual transport and this is very much reflected in the daily lives of city dwellers. Street-level parking options were irredeemably exhausted a long time ago. Of course nowadays the most prestigious consolidated areas are dotted with underground car parks, but they are inconvenient to use on a day-to-day basis and their capacity is limited.

In an effort to contribute towards solving this problem, Stap – a company specialising in the structural rehabilitation of existing constructions - and JetSJ – which has vast experience in the field of designing special foundations and underpinning – have developed a virtually non-invasive methodology which enables basements to be executed in existing buildings without disrupting their use.

The proposed methodology is the result of adapting the "Up&Down" system to the characteristics of our building stock. This method has a proven track record in works of this nature in several large cities in the United States and Europe.

The first step is generally to gather information on the building to be enhanced, the block of which it forms a part, the characteristics of the subsoil and other relevant data. Based on this information, a preliminary study is drawn up, including a technical and economic feasibility assessment of the intervention. Once the intervention has been given the green light in agreement with the Client, a more thorough structural assessment of the building is performed, the final design drawn up and the necessary licences obtained (see flow chart).

The execution itself is preceded by a careful inspection of the neighbouring buildings. A series of micropiles is then executed aimed at transferring the weight of the building to a deeper layer of soil, endowed with an adequate load capacity and located below the last basement to be executed. The existing foundation is then underpinned using a series of reinforced concrete beams supported by the micropiles. At the same time, the top beam for the peripheral containment is executed, also supported by the micropiles.

The peripheral containment is then executed using appropriately shored up panels and pins. The next stage consists of executing the new permanent foundations, taking full advantage of the micropiles already executed.

Finally, the remaining slab panels are executed for the new basement (see examples in the computer graphics).

Executing basements in existing buildings in the most prestigious areas of cities using unobtrusive methods is an excellent alternative to street-level parking or using public car parks, thereby avoiding the inherent inconveniences.

JetSJ performs studies, consultations, designs, supervision, training and assistance for Geotechnics and Special Foundations, and its mission is to fulfil its Clients' expectations, working as a partnership, helping to make the best technical and economic decisions.

The level of qualification, experience and degree of motivation of the company's technical team has enabled innovative geotechnical solutions to be developed, using the most advanced tools and technologies. These aspects have a direct impact on the safety, quality, durability and economics of the construction works devised.

More information at www.jetsj.pt.