Permeable Pavement System: Insights on Stormwater Facility Management through a Large-Scale Laboratory Model

The applicability of green infrastructures (GI) in the urban environment is conditioned by many factors, like hydraulic properties of soils, groundwater table, the specific context in which they are to be developed and construction work and maintenance costs (Salerno et al., 2018), thus requiring technical assessment. Among other GI, permeable pavements (PPs) can be easily retrofitted into the urban environment, although they suffer clogging that reduces their efficiency over time. An unscaled model of a PP section (2 m wide and 6 m long with 1.2% slope), has been realized inside a reinforced concrete box (Lora et al., 2016) to investigate the physical processes controlling runoff vs infiltration along time and the decay of efficiency due to clogging. The surface of the upstream portion (1.85x2 m2) is impermeable to simulate washoff of sediments, while the downstream portion (4.15x2 m2) is realized with Pervious Concrete Paver Blocks (Borgo Veneto _ Micheletto® SaS). The downstream vertical side of the PP is made of permeable bricks and two gutter channels are placed crosswise to separately collect runoff and subsurface discharge. The remaining sides, as well as the bottom of the model, are impermeable. The filter package is laid on top of a 40 cm layer of native sand (silty sand with d50=0.23 mm). From the bottom to the top: a 30 cm sub-base layer (20/40 mm gravel), a 10 cm base layer (8-12 mm gravel) and a 5 cm bedding layer (3-6 mm gravel). A geotextile (200 g/m2) separates the bedding and base layers and a 4m long drainpipe (D=125 mm) was inserted in the sub-base layer in the middle of the PP section. The facility is equipped with probes on both lateral sides: 6 tensiometers (TEROS32 METER Group) in the native sand, and 4 water content reflectometers (CS616 - Campbell Scientific) in the base and sub-base layers, while 3 piezometers (ATM/N STS) will record water table behaviour. Runoff and subsurface discharge are separately conveyed to two tipping bucket rain gauges. A rainfall simulator (Lora et al., 2016) is used to generate quite uniform rainfall distribution (80 - 150 mm/h intensity). A first set of experiments is developed to assess the efficiency of a newly constructed PP and define its maximum in- infiltration capacity. Then, a second set of experiments will simulate washoff and clogging phenomena to assess the efficiency of PP over time.