Design of Roadway Drainage Systems Using Geocomposite Drainage Layers by Barry R. Christopher, Ph.D., P.E.

PAVEMENT DESIGN TRAFFIC LIFE-CYCLE COST ANALYSIS FAILURE CRITERIA MINIMUM THICKNESS, etc. ENVIRONMENT STRUCTURAL MODEL MATERIALS CONSTRUCTION COSTS RIDEABILITY STRUCTURAL DESIGN

OPTIMUM INVESTMENT LEVEL RELIABILITY (pavement condition) PRESENT WORTH OPTIMUM 100 %50 % TOTAL COST FUTURE INVESTMENT Maint., Rehab., User, etc. INITIAL COST

CONSIDERATIONS IN PAVEMENT DESIGN   Continuous & Rapid Deterioration with Time   Repeated & Dynamic Loading   Different Load Magnitudes & Configurations   Traffic Distribution and Growth   Change Materials Properties & Characteristics  Drainage   Contamination of Road Materials

FAILURE CRITERIA IN PAVEMENTS   RUTTING   FATIGUE CRACKING   THERMAL CRACKING   REFLECTION CRACKING   CONTAMINATION   DRAINAGE/ MOISTURE

MECHANISTIC-EMPIRICAL FRAMEWORK IN THE 2002 PAVEMENT DESIGN GUIDE.

  Temperature   Precipitation   Humidity   Depth to Water Table   Frost Susceptibility   Capillary rise Potential ENVIRONMENTAL / CLIMATIC FACTORS FACTORS

Water in the Pavement Structure Primary Cause of Distress

Standing water in a pavement indicates low permeability and poor drainage

Tire Subgrade DRAINAGE

LOADED FLEXIBLE PAVEMENT Deflection of Aggregate Base Free Water Wedge Hydrostatic Pressure Deflection of Subgrade Direction of Travel

Under traffic loading, water and base material squirting up through joint in PCC pavement

Loaded PCC Pavement Free Water Hydrostatic Pressure or Water Jet Direction of Traffic Water is Violently Displaced Carrying Suspended Fines

JOINT DETERIORATION

Water in Pavements Summary Stripping in HMA Loss of Subgrade Support Reduction of Granular Layer Stiffness Erosion of Cement-Treated Base Layers Reduction in the Pavement Service Life If Base Is Saturated for Sometime Debond between Layers

Three important components for a good pavement design Drainage Drainage Drainage

AASHTO Drainage Definitions Quality of Drainage Excellent Good Fair Poor Very Poor Water Removed Within* 2 Hours 1 Day 1 Week 1 Month Water will not Drain AASHTO Guide for Design of Pavement Structures, 1993 *Based on time to drain

Crushed Outlet Clogged Outlet

Time To Drain  For two lane road - Lane width = 24 ft, Slope = 0.01 Base k time to drainQuality OGB 1000 ft/day 2 hrs to drainExcellent DGAB 1 ft/day1 weekFair DGAB w/ fines 0.1 ft/day1 monthPoor Reality no drainsdoes not drainVery Poor

Geocomposite Drain Requirements   Sufficient stiffness to support traffic without significant deformation under dynamic loading   Inflow capacity > infiltration from adjacent layers   Sufficient transmissivity to rapidly drain the pavement section and prevent saturation of the base   Sufficient air voids within geo-composite to provide a capillary break

Drainage Geocomposite - Important Properties   Transmissivity = 4500 ft 2 /day (0.005 m 2 /sec)   Estimated Discharge: 30 ft 3 /day /ft   Creep Resistance under high Loads   Long-term Resistance to Compression   Stability Traffic Loads = Univ. of Illinois Study   Effective Porosity = 0.7   Geotextile Filtration Requirements

l l Design guidance for a new alternative drainage method   Horizontal geocomposite drainage layer tied directly and continuously into an edge drain system.   RoaDrain™ by the Tenax Corporation)   Current AASHTO and Corps of Engineers pavement design codes l l Application   Used directly to replace drainable aggregate layers in rigid or flexible pavement systems, or   Enhance the drainage of dense graded aggregate layers often used in flexible and rigid pavement systems. Design Manual for Roadway Geocomposite Underdrain Systems: SCOPE

Factors Affecting The Design   Pavement slopes   Aggregate gradation   Porosity and effective porosity   Layer saturation   Permeability

Pavement Slopes SxSx SRSR S W LRLR () SSS Rx = LRLR W S SXSX =        TanA S SXSX () =      

Pavement Slopes  Surface and subsurface slopes  Always positive S R  Recommended slopes:  0.02 m/m (normal conditions)  m/m (high rainfall)  Surface and subsurface slopes  Always positive S R  Recommended slopes:  0.02 m/m (normal conditions)  m/m (high rainfall)

t=T x m x 24 Time-to-Drain Calculation m-factor (days) Time factor Time to drain (hrs)

Time to drain t = T x m x 24 t = T x m x 24 where, t = time to drain in hours T = Time Factor T = Time Factor m = “m” factor m = “m” factor S l = L R S r /H

How to Estimate Time to Drain (t)   Input:   S and S x   W, H, k,  d, G sb, WL (for permeable base)   Interim Output:   S R, L R, S 1 {S 1 = (L R x S R )/H}   T for a desirable degree of drainage (U)   N and N e   N = [1- {  d / (9.81 x G sb )}]   N e = N x WL   “m” factor: m = (N e x L R 2 ) / (k x H)   Output: t = T x m x 24 Transmissivit y

Time-to-Drain Sensitivity   Factors affecting time-to-drain:   Effective porosity   Coefficient of permeability   Resultant slope   Resultant length   Permeable base thickness

Coefficient of Permeability, m/day Time to Drain, hrs Effect of k L R = 7.6 m H = 0.15 m U = 50% S R = 0.02 m/m

Effect of S R Resultant Slope, m/m Time to Drain, hrs L R = 7.6 m H = 0.15 m U = 50% N e = 0.25 k = 915 m/day

Effect of L R Resultant Length, m Time to Drain, hrs S R = 0.02 m/m H = 0.15 m U = 50% N e = 0.25 k = 915 m/day

Permeable Base Thickness, mm Time to Drain, hrs S R = 0.02 m/m U = 50% N e = 0.25 m/m k = 915 m/day L R = 7.6 m Effect of Thickness

Slope Factor (S 1 ) Time Factor (T 50 ) T for U = 50% Drained

RoaDrain TM Time to Drain  Case B - Beneath Pavement  Time to Drain < 10 min  Case A - Beneath Subbase  for 15 in subbase with k = 1 ft/day  Time to drain ~ 3 hours

Wisconsin DOT, Highway 60

GPR Survey

Conclusions  The RoaDrain TM geocomposite drainage layer is an effective alternative for pavement drainage.  Calculations based on time-to drain approach indicate:  adequate infiltration rates to handle significant storm events.  < 10 min. to drain the geocomposite layer.  < 2 hours hours to drain the road even when placed beneath moderately permeable dense graded aggregate base.  i.e. excellent drainage based on AASHTO 1998 criteria.  Five case studies in progress with 3 monitored study showing:  Excellent to good drainage following major storm events.  Geocomposite drains in subgrade found most effective, especially during spring thaw.  Geocomposite drains facilitated construction and may have improved roadway section stiffness.  FEM study shows good potential for Strain Energy Absorption

QUESTIONS ?