Sediment Capture in Pervious Concrete Pavement tsystems: Effects on Hydrological Performance and Suspended Solids

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1 Concrete Sustainability Conference April 14 th 2010, Tempe, AZ Sediment Capture in Pervious Concrete Pavement tsystems: Effects on Hydrological l Performance and Suspended Solids Discharge Luis A. Mata, Ph.D. Assistant Professor Lawrence Technological University Michael Leming, Ph.D. Associate Professor North Carolina State University 2010 Concrete Sustainability Conference 1 National Ready Mixed Concrete Association

2 AGENDA 1 Background Effects of Sedimentation 2 Sediments Types and quantities 3 Exfiltrometer Test Description and Test Results 4 Design Parameters Exfiltration Rate Storage Capacity 07 May Concrete Sustainability Conference 2 National Ready Mixed Concrete Association

3 Sediment Capture Controls on quantity and quality 1 By design or performance After construction has been completed and the site is permanently stabilized, reduce the average annual total suspended solid (TSS) loadings by 80 percent an 80 percent TSS reduction is to be determined on an average annual basis Reduce the post-development loadings of TSS so that average annual TSS loadings are no greater than predevelopment loadings EPA (2009) 07 May Concrete Sustainability Conference 3 National Ready Mixed Concrete Association

4 Background Hydrological Conventional pavement Roofs Pervious Concrete Pavement System parking lot Adjacent vegetated area 07 May Concrete Sustainability Conference 4 National Ready Mixed Concrete Association

5 Sediment Transport in PCPS Basic Transport and Settling Mechanism Stoke s Law v =2.81d 2 s Filtering Mechanism v s : settling velocity of the particle (fps) d: diameter of the particle (mm) 1 Filtering by Pervious Concrete 2 Filtering by Geotextile Fabric 07 May Concrete Sustainability Conference 5 National Ready Mixed Concrete Association

6 Filtering by Pervious Concrete Pervious concrete captures stormwater and runoff with sand sediments from adjacent sites Sand sediments will deposit on top of the pavement Pervious Concrete Aggregate Base Underlying soil: sand Infiltration: 1in./hr Permeability not likely to be affected Exfiltration not likely to be affected by sediments 07 May Concrete Sustainability Conference 6 National Ready Mixed Concrete Association

7 Filtering by Geotextile Pervious concrete captures stormwater and runoff with clayey silt sediments Clayey silt sediments will most likely deposit at the bottom of the aggregate base Pervious Concrete Aggregate Base Non-compacted layer of sediments Filter Fabric Underlying soil: clayey silt Permeability not likely to be affected Exfiltration not likely to be affected by clayey silt sediments Storage capacity may be affected Compacted soil Infiltration: 0.1in./hr Concrete Sustainability Conference 7 National Ready Mixed Concrete Association

8 Filtering Pervious concrete captures stormwater and runoff with clayey silty sand sediments Most of sandy sediments will deposit on top of the pavement Clayey silt sediments will deposit at the bottom of the aggregate base Pervious Concrete Aggregate Base Filter Fabric Underlying soil: clayey silt Non-compacted layer of sediments Infiltration rate: 0.1 in./hr Infiltration rate: 0.5 in./hr Permeability may be affected Exfiltration may be affected by clayey silt sediments Storage capacity may be affected Concrete Sustainability Conference 8 National Ready Mixed Concrete Association

9 Background Sediment Deposition Sediments Sediments Uniform sediments 07 May Concrete Sustainability Conference 9 National Ready Mixed Concrete Association

10 Effects of Sdi Sedimentationi General Analytical Procedures 1 Design the PCPS in accordance with the analysis described in EB Determine the general composition of the sediment 3 Estimate the quantities of sediments anticipated over the service life of the PCPS 4 Evaluate Performance of the PCPS at the end of the design life, including the effects of sedimentation 07 May Concrete Sustainability Conference 10 National Ready Mixed Concrete Association

11 Sediments Types and Quantities 1 Design of the PCPS 2 Composition of the Sediment Sediment from Vegetated Surfaces Sediment from Pavements and Building Surfaces 3 Quantities of Sediment Deposits 4 Evaluate Performance of the PCPS 07 May Concrete Sustainability Conference 11 National Ready Mixed Concrete Association

12 Quantities Sediments 1 Universal Soil Loss Equation (USLE) E = A R K LS C P E = annual soil loss (tons/yr) A = area (acres) R = rainfall-runoff erosivity [(ft tons in)/(ac hr yr)] K = soil erodibility (tons/ac) LS = a dimensionless factor based on L=flow length (ft), and slope (%) C = surface cover (dimensionless), and P = erosion control practice (dimensionless, equal to 1 for PCPS) 2 Sediment from paved areas (Driscoll et al., 1999) 07 May Concrete Sustainability Conference 12 National Ready Mixed Concrete Association

13 Sediments Depth and Effects on Exfiltration Rate 1 Sediment Density Effects Sediment depth Exfiltration ti Through h Sediment 2 Quantities of Sediment Deposits 3 Evaluate Performance of the PCPS 07 May Concrete Sustainability Conference 13 National Ready Mixed Concrete Association

14 Exfiltrometer Test 1 Sample of soil 2 Separate finer particles (<#200) 3 Estimate sediment load per base layer area of PCPS 7 4 Mix correspondent load with water (Approx. 2% by weight) rubber 5 Add water with sediments sleeve PVC pipe to the exfiltrometer 6 Air dry for a min. of 24 hr. 7 Exfiltration rate of sediments is determined by falling head permeability techniques Permeameter 4 diameter 8 Sediment layer Filter fabric 07 May Concrete Sustainability Conference 14 National Ready Mixed Concrete Association

15 Estimates of Exfiltration Rate Exfiltrometer X r = 4.747S b X r : exfiltration rate (cm/h) S b : base layer sediment load (kg/m 2 ) 1 Exfiltrometer can be used with a range different sediment loads to improve the accuracy of the estimate 2 Provide a simple method of evaluating the resulting effects on exfiltration rate of the PCPS and on the loss of storage capacity Concrete Sustainability Conference 15 National Ready Mixed Concrete Association

16 Exfiltrometer Estimates of Equivalent Base Depth D eq,40 =0.0887S b D eq,40 : equivalent depth of a 40% porosity base occupy by sediment (cm) S b : base layer sediment load (kg/m 2 ) 1 Exfiltrometer can be used with a range different sediment loads to improve the accuracy of the estimate 2 Provide a simple method of evaluating the resulting effects on exfiltration rate of the PCPS and on the loss of storage capacity Concrete Sustainability Conference 16 National Ready Mixed Concrete Association

17 Design Parameters Exfiltration Rate 4 X r = Sb X r : exfiltration rate in cm/h S 2 b : base layer sediment load (kg/m ) Storage Capacity D eq,40 = 0.09S b D eq,40 : equivalent depth of base lost to sedimentation (cm) S b : base layer sediment load (kg/m 2 ) Concrete Sustainability Conference 17 National Ready Mixed Concrete Association

18 Effects of 1 Contribute Sdi Sedimentation to simultaneously i controlling the quantity runoff and limiting the TSS discharged into receiving waters 2 A PCPS designed to capture the entire 2 year storm will capture virtually all of the TSS in the mean design storm 3 Reduce TSS discharged into receiving waters by reducing erosion downstream of the site 4 Capture sediment can affect the hydrological performance of the PCPS in some applications 07 May Concrete Sustainability Conference 18 National Ready Mixed Concrete Association

19 Thank You 07 May Concrete Sustainability Conference 19 National Ready Mixed Concrete Association