Stormwater boxes - aspects on verification, simulation and installation

Stormwater boxes aspects on verification, simulation and installation In the VINNOVA financed project “Grey-green system solutions for sustainable cities” a holistic approach is applied related to the challenges following as consequences of urbanization and expected climate changes. Solutions taking into account the interaction between green surfaces and grey surfaces are studied. The growing population in the cities leads to more dense cities with a larger share of grey surfaces and in combination with an expected increase of rainfalls due to climate changes call for solutions on how to handle the stormwater. In the present report, one solution in urban areas to reduce the probability of flooding and the peak flows in the municipal stormwater networks is studied from a mechanical performance view. The solution consists of building underground detention vaults of stormwater boxes. There are also aspects on heat and comfort in urban areas that are treated in the project, but not in the present report. A general discussion concerning the standardization work and also the installation of the stormwater boxes are given. As part of the mechanical verification of the boxes experiments in laboratory and simulations of loaded boxes are carried out. It is seen by comparison of present results and previously reported results, that the vertical load bearing capacity of the investigated stormwater box is decreased by small obliquities. Here, the obliquity is caused by simultaneously applying a shearing force and a vertical compressive force on the stormwater box. In an underground application the obliquity can be caused during installation or movement of the soil surrounding the vault. It is also concluded that creep of the material, even though it is not especially studied in the present report, is essential for the long term load bearing capacity. It has been shown that Finite element simulations reproduce the real behaviour in mechanical tests performed of the stormwater boxes up to a certain load level. The part of the behaviour where load levels are approaching collapsing is not caught well by the simulations. Refinements for future studies are proposed in terms of experiments for gaining better material data and also of usage of more advanced material models. The general applicability of the method is demonstrated by analysing a loaded structure with 12 stormwater boxes vertically stacked in three layers in a brick-wall-like arrangement. The method opens for studying loaded underground installations.