Water Runoff Properties for Expanded Clay LWA in Green Roofs

Abstract

A lightweight aggregate (LWA) is a material that has a lower density than rock aggregates. There are many civil engineering application possibilities for LWA. A potential field of application for expanded clay LWA is as a storm water retaining layer in green roofs. In order to design reliable structures of green roofs, more knowledge about the characteristics of the material is needed. The purpose of this master thesis was to test if the software SEEP/W is an appropriate tool for simulation of water runoff from a green roof, designed with expanded clay LWA. The numerical modeling was not performed for all types of expanded clay LWA, but on crushed Leca® 4-10mm and round 10-20mm alone. To test if SEEP/W is advisable tool for simulating water flow in expanded clay LWA, a back calculation of a laboratory experiment was done. The purpose of back calculating the experiment is to calibrate a numerical model and then use it for a full scale ideal roof. Thereafter a sensitivity analysis of the SEEP/W input parameters was performed. It was possible to back calculate the laboratory experiment, meaning obtaining the same relation between water going in and water going out of the tested Leca® material. However, a lot of numerical problems occurred in the simulations. Unrealistic results were displayed, especially for Leca® 10-20mmR. In order to improve the performance of the material, and thereby obtain better water retaining characteristic, a suggestion is to increase the porosity and lower the saturated hydraulic conductivity for the expanded clay LWA materials in order to obtain a higher attenuation.