Application of pervious pavements - a laboratory scale study
The introduction of pervious pavements addresses all the principles in Water Sensitive Urban Design. A pervious pavement is a load bearing pavement structure that is permeable to water. The pervious layer sits on the top of a reservoir storage layer. Pervious pavements reduce the flood peak as well as improve the quality of stormwater at source before it is transported to receiving waters or reused productively. The water infiltrates through the pavement to a sub-base reservoir, from where it infiltrates slowly to the soil or to drains. By reducing flow rates and volumes transported to downstream receiving waters, pervious pavements decrease the size of downstream drainage infrastructure. Similarly, pervious pavements also reduce nutrients and toxicants in stormwater runoff. These pollutants if left un-trapped will contaminate the drainage system, groundwater and receiving waters.
To be accepted as a viable solution, understanding of the influence of design parameters on the infiltration rate both from the bedding and the sub base as well as strength of the pavement requires to be established. The design of a particular pavement will need to be customised for different properties of sub layer materials present in different sites. In addition, the designs will have to meet the local government stormwater discharge standards. The design of drainage systems underneath pervious pavements will need to be based on the permeability of the whole pervious system.
A new research initiative at the School of Civil and Geological Engineering at RMIT is aimed at developing an understanding of the influence of design parameters of pervious pavements on the effectiveness in maximising the efficiency of water sensitive urban design.
The objectives of the initial stage of the research project reported here were to:
● design a laboratory scale physical model of a pervious pavement based on published literature and actual practice
● investigate the infiltration rate from the pervious surface as well as from the whole pavement including the bedding and sub-base and
● obtain relationships between rainfall intensity, infiltration rate and runoff quantity based on sub-grade material
A laboratory scale pavement model was constructed at RMIT University in Melbourne Australia to develop relationships between the surface runoff and the infiltration volume from a pervious pavement with an Eco-Pavement surface (Figure 1). 2-5mm crushed gravel and 5-20mm open graded gravel were chosen as the bedding and sub-base material (Figure 2). Initial tests such as dry and wet density, crushing values, hydraulic conductivity, California Bearing Ratio tests for aggregate material were conducted before designing and constructing the pavement model. The design of the pervious pavement structure was based on recommendations of Shackel et al (2003). The test model was constructed in a 1.5*1.5m steel box which is specially set up with infiltration holes on the bottom plate. A rainfall simulator with evenly spaced 24 sprays was set up above the pervious pavement surface.
The paper presents design aspects of the pavement model, the tests carried out in designing the pavement, the experimental procedure and results obtained from rainfall simulator tests. The development of an analytical model to estimate the runoff from a pervious pavement depending on the rainfall intensity, pavement structure and sub-grade material will be presented next. Outcomes from the work reported here will be discussed and planning of the next stage of the research program will be presented.
References:
Shackel B., Ball J., and Mearing M., 2003. ‘Using Permeable Eco-paving to Achieve Improved Water Quality for Urban Pavement’. Proceedings of 7th International Conference on Concrete Block Paving, Sun City.12th -15th Oct 2003
