**Abstract**

Regarding the impact of construction processes on the environment, the reduction of CO2 has an important role. The production of materials e.g. reinforced concrete, and the construction of structures consume large amounts of energy, which leads to a large emission of CO2. The target is the reduction of the amount of construction material used and of the energy consumed for construction. For this, the structures have to be optimized regarding the geometry considering the requirements of the stability, serviceability, and durability. Also, foundation systems of high-rise buildings can be optimized regarding CO2 emission. For the optimization, three parts have to be considered. The first part is the detection of the real load-deformation behavior of a foundation element. This can be reached by large-scale load tests in situ. The second part is to use the hybrid foundation system Combined Pile-Raft Foundation (CPRF), which combines the bearing capacities of the raft and of the piles. The third part is the realistic prediction of the load-deformation behavior of the foundation. For this three-dimensional, nonlinear calculations using the Finite-Element-Method (FEM) are necessary. The contribution explains the three parts and shows the application in engineering praxis, including case studies.

**Keywords:** CO2 reduction, load test, Combined Pile-Raft Foundation, high-rise building, sustainability
