Geotechnical reinforcement work for foundation of extending an existing residential building

University essay from KTH/Jord- och bergmekanik

Abstract: The last hundreds of years there has been a land elevation that causes an increased distance between the groundwater level and the buildings founded on wooden piles. When wooden piles are exposed to air, rot fungus occurs which causes the pile to lose its bearing capacity. With the critical problem of housing shortage, the demand can be met if an innovative solution is created by extending a superstructure on top of an existing building within the city center of Stockholm. The purpose of this thesis is to investigate whether it is profitable to extend an existing building with a superstructure when reinforcing an existing foundation. By an extensive literature survey, a model is created and exposed to several analyzes containing both analytical and numerical calculations. Based on the acquired knowledge, the model reflects the most common building built within the city center of Stockholm, that was founded on wooden piles, where the geological conditions consist of clay. A new foundation has been designed consisting of drilled end-bearing steel piles. For the two pile dimensions of RD220/12.5 and RD170/10, the possible load transfer methods of full niches, ground beam with half a niche, yoke beams and slab with half a niche are analyzed, respectively. These methods were combined differently to obtain the possible combinations performed in this building, that in turn, gives the difference in the amount of work and costs. An intended superstructure consisting of four storeys in wood is then applied on the existing building to once again, obtain the differences in amount of work and costs. Comparing these two cases, the profitability is determined. The study shows for the larger pile that the superstructure entails no difference in the required amount of piles and therefore, no difference in the total cost compared to the existing building. However, for the smaller pile, the superstructure entails a small increase in the required amount of piles and the cost. The study resulted that the larger pile provides the cheapest geotechnical reinforcement work, regardless if the superstructure is applied or not, compared to the smaller pile. The thesis show that it is profitable to extend an existing building when the existing foundation is strengthened, due to the great revenue of the superstructure, which entails that the profitability is a fact.

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