Flexible Pavement Design Structural Design Procedure to determine D1, D2 and D3 1. Determine the total ESAL for the design period 2. Determine the design serviceability loss (βπππΌ = ππ − ππ‘ ) 3. Determine the effective Mr for each segment AND find a1,a2,a3 4. Determine the drainage coefficient (m2 and m3) 5. Select the reliability design level (R) and overall standard deviation (So) 6. Use monograph to find Structural Number – SN 7. Determine Layer Thickness Flexible Pavement Design 1) Pavement Performance → βπππΌ = ππ − ππ‘ PSI=Present Serviceability Index (0-5, 5 is best) – quantifies pavement performance pi= Initial serviceability Index (4.2-4.5) pt=Terminal serviceability Index (2.5-3.0 for major highway), (2.0 - lower class.) 2) Traffic (ESAL) πΈππ΄πΏπ = ππ ∗ πΊππ ∗ π΄π΄π·ππ ∗ 365 ∗ ππ ∗ πΉπΈπ , πΊππ = [(1+π)π −1] π r=i/100 and is not zero, if annual growth is zero, growth factor=design period i=growth rate, n= design life (years) ESALi=equivalent accumulated 18kip (80kN) single axle load for axle category i fd=design lane factor Grn=growth factor for a given growth rate t and design period n AADTi=first year annual average daily traffic for axle category i Ni=number of axles on each vehicle category i FEi=load equivalency factor for axle category i 3) Road Soils (Subgrade), → ππ Expressed in terms of CBR (California Bearing Ratio) or R-value (Resistance and Resilient Modulus (Mr). if only CBR or R are known: πΉππ ππ ππ2 πΎπ To Determine Design ESAL: ESALi = fd ∗ Grn ∗ AADTi ∗ 365 ∗ Ni ∗ FEi , ESAL = ∑ ESALi fd=design lane factor – From Table 2 using # of Lanes – in % - as decimal Grn=growth factor – From Table 3 using design period & annual growth rate AADT = Average Daily Traffic (Given) , 365 = # of days/year, Ni=number of axles on each vehicle category i FEi=load equivalency factor for axle category I – From Table 1 – using load. Design ESAL using Truck Factors: ESALi = fd ∗ Grn ∗ AADTi ∗ 365 ∗ fi , ESAL = ∑ ESALi fi= Truck Factor for vehicles in truck category i – From Table 4 using the type of rural/urban system and vehicle type to get the truck factor. ∑ESALi π₯ 365 ππ’ππππ ππ πππ’πππ ∑(# ππ ππ₯πππ (π‘ππ’πππ ) π₯ πΏπππ πΈππ’ππ£ππππππ¦ ππππ‘ππ (πΏπΈπΉ))π₯ 365 = ππ’ππππ ππ πππ’πππ Overall Truck Factor = →Traffic Factor is the same as truck factor but considering all vehicles and not just trucks → 365 is to convert to ESAL/year → ESAL refers to the damage on the road and it is not linear because different loads have different load distributions. →The effect of the passenger cars and the motorists is negligible for the damage of the road compared to trucks, which means they can be ignored. → ππ = 1500 πΆπ΅π (ππππ πππππππ π ππππ , πΆπ΅π ≤ 10) → ππ = 220 πΆπ΅π (ππππ πππππππ π ππππ , πΆπ΅π ≤ 10) ππ ππ ( 2 ) = 1000 + 555 ∗ (π − π£πππ’π)πππ π ≤ 20 ππ πΎπ ππ ( 2 ) = 145 + 80.4 ∗ (π − π£πππ’π)πππ π ≤ 20 π 4) Materials of Construction → π3 , π2 , π1 Quality of materials of pavement layers is determined using: π3 (π π’ππππ π), π2 (πππ π), π3 (π π’πππππ) ππ = π1 π·1 + π2 π·2 π2 + π3 π·3 π3 - get π3 – subbase - from chart using CBR or Mr or R or Triaxial - get π2 – base course - from chart using CBR or Mr or R or Triaxial - get π1 – surface course – from Graph using elastic or resilient modulus πΉππ ∑ESALi =∑(# ππ ππ₯πππ (π‘ππ’πππ ) π₯ πΏπππ πΈππ’ππ£ππππππ¦ ππππ‘ππ (πΏπΈπΉ)) →Find LEF’s from Table with single, Tandem, and tridem axles. π2 ∑π’π 5) Environment → π’π = π Temperature and rainfall are the two main environmental factors used to evaluate pavement performance in AASHTO. Mr is determined using the above formula and Table 19.6, n is the number of Mr’s used. The formula represents average. 6) Drainage → π2 πππ π3 Effect of drainage calculated for base (π2 ) and subbase (π3 ) – π2 = π3 π’ππππ π π ππππππππ →Use drainage quality and % time of saturation to get m2 and m3 The mi factors are based on both the percentage of time during which the pavement structure will be nearly saturated and on the quality of drainage, which is dependent on the time it takes to drain the base layer to 50 percent of saturation. 7) Reliability (R) Reliability design level (R) is introduced to account for uncertainties in the traffic and performance predictions. Determine Reliability from table. Overall standard deviation (So) is 0.4-0.5 (flexible pavement) and 0.3-0.4 (Rigid pavement). Next, SN could be determined by using the monograph. 1. Draw a line joining the reliability level and the overall standard deviation So, and extend this line to intersect the first TL line at point A. 2. Draw a line joining point A to the desired ESAL of , and extend this line to intersect the second TL line at point B. 3. Draw a line joining point B and resilient modulus (Mr) of the roadbed soil, and extend this line to intersect the design serviceability loss chart at point C. 4. Draw a horizontal line from point C to intersect the design serviceability loss (PSI) curve at point D. 5. Draw a vertical line to intersect the design SN, and read this value Pavement is made of of 4 layers: From top to bottom: subsurface course(a1), base(a2), sub-base(a3), subgrade To get SN at first – use π΄π of subgrade layer, then, → ππ π ππ ππ π‘βπ πππ π, π·ππ‘ππππππ ππ1 (ππππππππβ) ππ1 = π1 π·1 πππ‘ π·1 , Round D → D∗ → ππ1∗ = π1 π·1∗ πβπππ ππππππ’π π£πππ’π ππ π·1 π’π πππ πππππ , ππππ π·1∗ → π’π π ππ ππ π‘βπ π π’ππππ π. π·ππ‘ππππππ ππ2 (ππππππππβ) ππ2 = π1 π·1∗ + π2 π·2 π2 , πππ‘ π·2 πβπππ ππππππ’π π£πππ’π ππ π·2 π’π πππ πππππ, ππππ π·2∗ → π’π π ππ ππ π‘βπ π π’ππππππ. π·ππ‘ππππππ ππ3 (ππππππππβ) ππ3 = π1 π·1∗ + π2 π·2∗ π2 + π3 π·3∗ π3 , πππ‘ π·3 πβπππ ππππππ’π π£πππ’π ππ π·3 π’π πππ πππππ, ππππ π·3∗ OR since ππ3 = SN from step 6, then just find D3 simply. Note: Always round up 1 or 2 inches for the diameter Equations of Motion π£ = ππ‘ + π£0 , π·π = Dilemma Zone (π£ 2 − π£02 ) = π(π₯ − π₯0 ), 2 π£02 − π£ 2 , π· = ππππππππ πππ π‘ππππ. 2π(π ± πΊ) π 1 π₯ = ππ‘ 2 + π£0 π‘ + π₯0 2 π2 = π£02 π£02 π£0 π€+π , π₯π = π£0 πΏ2 + ∗ , ππππ = πΏ2 + ∗ + 2(π₯ − π£0 πΏ2 ) 2π2 2π2 π£0 2π₯ π1 = (π−πΏ 2 1) + 2(π€+πΏ−π£0 π) (π−πΏ)2 , τπππ = δ2 + v0 2a∗2 + w+L v0 Vertical Curve Crest πΏπππ = 2π − 200(√β1 +√β2 ) |π΄| 2 (π ≥ πΏ), πΏπππ = |π΄|π 2 200(√β1 +√β2 ) 2 (π ≤ πΏ), π΄ = |πΊ2 − πΊ1 | [πππ π€ππ ππ %]. ππ ππππ πΏπππ → π ππππ, πππ·, π < πΏ ππ π πΏ, πΏπππ (ππ‘) πΏ πΏ πΏ ππ π πππ£π π£πππ‘ππππ ππ’ππ£π → π΄, πΎ ππππ π‘ππππ, πΏ = πΎπ΄, ππ‘π. π΅ππΆ = ππ‘π. πππΌ − , ππ‘π. πΈππΆ = ππ‘π. πππΌ + , πΈπππ£. π΅ππΆ = πΈπππ£. πππΌ + π1 , 2 2 2 πΏ πΏπΊ1 2 πΊ1 −πΊ2 πΈπππ£. πΈππΆ = πΈπππ£. πππΌ + π2 , [ πβππβ = , πβππβ = πΏπΊ12 200(πΊ1 −πΊ2 ) ] πππ ππ πππ πΆπ, ππππ = [πππΆπππ + ( πΊ1 100 π₯ 2 ) π₯] + π¦, π¦ = 4πΈ ( ) , πΈ = πΏ π΄πΏ 800 Vertical Curve Sag Same steps as Vertical Curve Crest except πΏπππ is found differently. πΏπππ = 2π − CHAPTER 3 – Traffic Stream Flow Models π = ππππ€, π = ππππ ππ‘π¦, π£, π’ = π ππππ, β = π‘πππ βππππ€ππ¦, π = π ππππππ 1⁄2 (π£ 2 − π£02 ) = π(π₯ − π₯0 ) (π = πππππππππ‘πππ, π£ = π ππππ, π₯ = πππ ππ‘πππ) 2 π₯π = π£ ⁄2π (ππ = πππππππππ‘πππ ππππππ) π 2 π₯π = π£ ∗ πΏ + π£ ⁄2π (ππ = πππππππππ‘πππ ππππππ€) π π₯π = π + π₯1 − ππΏ − π₯0 , 2 (π = ππ’ππππ ππ ππππ , πΏ = πππππ‘β ππ πππ) 2 200(β+ππ‘πππ½) π΄ (π > πΏ), πΏπππ = π΄π 2 200(β+ππ‘πππ½) (π < πΏ), Horizontal Curve 5729.6 1719 β π (ππ‘) = , π (π) = , , π = π π‘ππ ( ), π·π π·π 2 πΏ= π βπ 180 = 100β D ,, β β β πΏπΆ = 2π π ππ ( ) , π = π (1 − πππ ( )) , πΈ = π (sec ( ) − 1) , 2 2 2 π = π£ ∗ πΏ + π£ ⁄2π − π£ ⁄2π + ππΏ + π₯0 π π Stopping Sight Distance π = 1⁄π = β ∗ π’ , π£02 − π£ 2 π£02 − π£ 2 (β ππ βππππ€ππ¦(π ), β ππ ππππ π‘. π ππππππ, π ππ βππππ€ππ¦(π), π’ ππ ππππ π ππππ) (π’πβπππ), (πππ€πβπππ) π· = π· = 1 π π β = ⁄π 2π(π + πΊ) 2π(π − πΊ) 1 ππππ ππππ πππππ: π’π = ⁄π ∗ ∑π£π π = 0.6 πππ¦, 0.3 π€ππ‘ π·π = πππ πΌ, πΊ = π‘πππΌ 1 π· πππ· = π£ ∗ πΏ + π·π , πΏ = π ππππ‘πππ π‘πππ πππππ ππππ πππππ; π’π = 1⁄1 1 π‘ππ£π = ∗ ∑ π π£π ∑ Curvilinear Motion π π£π π = π’ ∗ π (π = ππππ€, π’ = ππππ π ππππ, π = πππππππ‘πππ‘πππ) π£2 π + ππ = (1 − ππ π), π = π‘πππ½, πππ = 0 πππ π‘π¦πππππ βππβπ€ππ¦ 1 π’2 π’2 ππ πππππππ πΉπππ€: π = = 1⁄(π’πΏ + − + ππΏ + π₯0 ) π 2ππ 2π ππ π’ π =π’∗π = = π ∗ π’(π) Regime Decelerating of leading Decelerating of following ⁄(π’πΏ + π’2 − π’2 + ππΏ + π₯ ) 0 A ∞ dn 2ππ 2π ππ B de dn ππ‘ππ‘ππππππ¦ πππ πππ£ππ πππ πππ£πππ ππβππππ; π π0⁄ C ∞ de = π (π0 ππ # π£πβπππππ , π ππ ππππ€, π ππ π‘πππ ) D Dec of leading = Dec of following ππ πππ πππ£ππ πππ£ππ , π‘ππππππ π π‘πππππ; π = ⁄πΏ , ππ = πππ E No Braking ( π ππ πππππππ‘πππ‘πππ ππ = #πππ π ππ, πΏ = πππππ‘β, π = π ππππ, π = π‘πππ) πππ πππ£ππ πππ£π π€ππ‘β π π‘ππππ; ππππ π‘π€π ππ’ππ πππ πππ‘β π£ππππππππ π£πππ¦πππ π πππππ . 2πππ′ π Passing Sight Distance π = π0 − ππ = ππ − πππ (ππ ππ # ππ£πππ‘πππππ, ππ ππ #πππ π ππ) ππ‘ 2π π⁄ = π − ππ, ππ€⁄ = π − ππ , ππ⁄ = π − ππ , π = (ππ€ + ππ )⁄ π1 = 1.47π‘ [π£ − π + ( 1 )] , π2 = 1.47ππ‘2 , π4 = 2 , π3 ππ πππ£ππ. π€ π 2 3 π ππ€ ππ (ππ€ + ππ ) ππ€ π πΏ Lateral Displacement πππππ ππππ πππππ; =π− ( ) ππ€ π’ ππ€ πππ πππππ ππ πππ πππππππππ‘, π ππ πππππ. , ππ π£π πΏ ππ€ ππ€ π ππ πππππ‘β π‘π πππ πππππ. , = 2 2 ( ) ππ’πππ‘ππ‘π¦; = π‘ππ£π = πππ£π = ππ€ − , ππ€ − πππ£π = ππ‘ π +π π’ π π π£ ππ π ππππ (ππ€ ππ π‘πππ π‘πππ£ππ ππππππ‘πππ, ππ€ ππ πππ’ππ‘ ππ’ππππ ππ’π, π ππ ππππ€) Super-elevation Design (−ππ€ ); πππ£π > ππ€ (πππ π‘ πππ π‘ππ π‘βππ ππ£πππππ) (+ππ€ ); πππ£π < ππ€ (πππ π‘ π πππ€ππ π‘βππ ππ£πππππ) π£2 π + π = ππ€ = 0 (πππ π‘ ππ ππ£πππππ) π ππ πΏ π’= (ππ£πππππ π π‘ππππ π ππππ) πππ£π πβππππ€ππ£ππ : ππ − ππ π’π π€ = ( ) ππ − ππ (ππ ππ ππππ€ πππ, ππ ππ ππππ€ π π‘πππ‘, ππ ππ ππππ. πππ, ππ ππ ππππ. π π‘πππ‘) (+)π’π π€ ππ ππ ππππππ‘πππ ππ π π‘ππππ ππππ€, (−)π’π π€ ππ π’ππ π‘ππππ ππππππ‘πππ, π’π π€ = 0 ππ π π‘ππ‘ππππππ¦ Level of Service (Freeway) Step 1: Compute FFS → πΉπΉπ = π΅πΉπΉπ − ππΏπ − ππΏπΆ − ππ − ππΌπ· , FFS = Free Flow Speed, BFFS = base free-flow speed, 110 km/h (urban), 120 km/h (rural) Adjustments: fLW=Lane Width , fLC=right shoulder Lateral Clearance, fN=Number of Lanes ( rural freeway - fN = 0) , fID=Interchange density Step 2: Compute vp→ π£π = π ππ»πΉ∗π∗ππ ∗ππ»π , ππ»π = 1 1+ππ (πΈπ −1)+ππ (πΈπ −1) vp=15 min passenger car equivalent flow rate (pc/h/ln), PHF=Peak hour factor, ππ»πΉ = π»ππ’πππ¦ π£πππ’ππ 4∗ππππ 15 min π£πππ’ππ (Typically b/w 0.8 & 0.95) V = πππ₯ 15 min ππππ€ πππ‘π PHF V=hourly peak vehicle volume in one direction (veh/h), N=Number of travel lanes in one direction, fp=Driver population factor (0.85-1.0, use 1 for commuter traffic) fHV=Heavy vehicle adjustment factor PT=% of trucks (in decimal), PR=% of recreation vehicles (in decimal), ET=Truck adjustment Factor, ER=Recreation vehicle adjustment Factor ET and ER depend on type of terrain (Level, Rolling, Mountainous) For upgrades, ET and ER also depend on upgrade (%)and length(km), For Downgrades, ET depends on downgrade%) and length, but ER is treated as a level terrain Step 3: Average passing car speed (S) Use ππ and FFS Curve in Curve to find average passenger car speed (S) OR Use: For 90 < FFS ≤ 120 km/h and (3100 – 15FFS) < vp ≤ (1800 + 5FFS) π£π +15πΉπΉπ−3100 2.6 1 π = πΉπΉπ − [28 (23πΉπΉπ − 1800) ( 20πΉπΉπ−1300 ) π£π π ] Vp = flow rate (pc/km/ln), S = average passenger-car speed (km/h) Step 5: Compute LOS using Table or Graph for Freeway * compare the calculated D with the density range in Table 1 – Freeway – LOS + When comparing – Choose lower LOS at all times ! ** the only difference between upgrade and downgrade is the ππ»π factor – The effect of heavy trucks is more severe in the upgrade section which means that LOS of Upgrade will be less than LOS of Downgrade. Find Capacity - Use LOS E and find Vp in PC/hr/lane using FFS limits in table V PHF∗N∗fp ∗fHV → vp ∗ π ∗ ππ ∗ ππ»π = V PHF V Then, Hourly Volume = ∗ ππ»πΉ PHF Find Number of Lanes – Using the LOS and the FFS – determine the vp and then use π= V vp ∗PHF ∗ππ ∗ππ»π , V PHF & No passing Zone π 1 ,π = , ππ»πΉ ∗ ππΊ ∗ ππ»π π»π 1 + ππ (πΈπ − 1) + ππ (πΈπ − 1) π»ππ’πππ¦ π£πππ’ππ ππ»πΉ = 4 ∗ ππππ 15 min π£πππ’ππ vp=Passenger car equivalent flow rate for peak 15min period, V=hourly volume (vph), fHV=adjustment factor for heavy vehicles, fG=grade adjustment for level or rolling terrain PT and PR = Decimal partition of trucks (buses) and RV’s in traffic, ET and ER = Passenger car equivalent π£π = To calculate ππ → Estimate vp using PHF, use π£π = π ππ»πΉ calculated value of Then, calculate BPTSF & fd/np AND find PTSF and get LOS from table , D=Density (pc/Km/ln) Find max 15 min flow rate - vp = ππππΉ = π΅ππππΉ + ππ/ππ , π΅ππππΉ = 100(1 − π −0.000879ππ ), PTSF=Percent spent following for both directions (%), BPTSF=Base percent time spent following for both directions (%), fd/np=adjustment in PTSF (%), - found from table using vp & Directional Split vp to estimate fG, ET and ER which will provide value of vp close to vp initially calculated. and check that new vp and old vp are in the same range. If yes, Continue, If not, use new vp and find new fG & fHV, and so on. For 90 < FFS ≤ 120 km/h and vp ≤ (3100 - 15FFS) → π = πΉπΉπ Step 4: Compute the density (D) π·= Level of Service (Two Lane) Capacity of two-lane highways is 1,700 pc/hr for each direction and will normally not exceed 3,200 pc/hr for both directions for long section of the highway Class I two-lane highways – LOS depends on % time spent following(PTSF) in platoons & Average travel speed (ATS). Then Compare, take lower LOS Class II two-lane highways - LOS depends only on the % time spent following (PTSF) Step 1: Compute PTSF→ = πππ₯ 15 min ππππ€ πππ‘π – and use vp & FFS in Graph to see whether Number of Lanes meets the required LOS →A freeway is a divided highway with full access control and two or more lanes in each direction. → An LOS is a performance measure of a highway at traffic volume less than capacity →LOS A - Free-flow operation βͺ Vehicles are completely free to manoeuvre βͺ Effects of incidents or point breaks are easily absorbed - Density (D) ≤ 7 pc/km/ln →LOS B - Free-flow operation βͺ Ability to maneuver is only slightly restricted βͺ Effects of minor incidents still easily absorbed - Density (D) ≤ 11 pc/km/ln →LOS C - Speeds at or near FFS βͺ Freedom to maneuver is noticeably restricted βͺ Queues may form behind any significant blockage. - Density (D) ≤ 16 pc/km/ln →LOS D - Speeds decline slightly with increasing flows βͺ Density increases more quickly βͺ Freedom to maneuver is more noticeably limited βͺ Minor incidents create queuing Density (D) ≤ 22 pc/km/ln →LOS E - Operation near or at capacity βͺ No useable gaps, and little room to manoeuvre βͺ Any disruption causes queuing Density (D) ≤ 28 pc/km/ln →LOS F - Breakdown in flow βͺ Queues form behind breakdown points βͺ Demand > capacity - Number of cars arriving at a point > the number discharged Step 2: Compute ATS π΄ππ = πΉπΉπ − 0.0125π£π − πππ , ATS=Average travel speed for both directions of travel combined (mi/h), fnp=adjustment for the percentage of no passing zones πΉπΉπ = π΅πΉπΉπ − ππΏπ − ππ΄ (ππ π‘ππππ‘π) FFS=Free flow speed (Km/h). fLS=Adjustment for lane and shoulder width fA=Adjustment for number of access points per mile ππ ππ πΉπΉπ = ππΉπ + 0.0125 ∗ (πππππ ππππ π’ππππππ‘ ππ‘ > 200 ), ππ»π β SFM=Mean Speed of traffic measured in the field (mi/h), Vf = observed flow rate for period when field data was obtained (veh/h) fHV = heavy-vehicle adjustment factor π 1 π£π = , π = , ππ»πΉ ∗ ππΊ ∗ ππ»π π»π 1 + ππ (πΈπ − 1) + ππ (πΈπ − 1) fG=grade adjustment for level or rolling terrain fG & fHV are dependant on vp, therefore, π£π = π ππ»πΉ , then determine fG & fHV, and check that new vp and old vp are in the same range. If yes, Continue, If not, use new vp and find new fG & fHV, and so on. Then, find fnp and calculate ATS and get LOS from table. Step 3: Compute LOS for Class I and Class II 1) First comparing vp with the two-way capacity of 3,200 pc/h 2) If vp is greater than capacity, the LOS is F 3) Also, if the demand flow rate in either direction (vp times directional split) is > 1700 pc/h, the LOS is F Class I uses both ATS and PTSF , Class II uses only PTSF Chapter 1 – Introduction →A transportation system may be defined as consisting of the fixed facilities, the flow entities, and the control system that permit people and goods to overcome the friction of geographical space efficiently in order to participate in a timely manner in some desired activity. →Transportation system classification: Land, Air, Water, Pipelines. Chapter 2 – Roadway Design →Braking Distance is affected by the original speed of the vehicle, the type of brake system in use, and the coefficient of friction between its tires and the road surface. → Banking or super-elevation – components of vehicle’s weight increase the resistance to the sliding tendency → Stopping distance = Braking distance + Time for perception-reaction x speed → Freeways βͺ Uninterrupted traffic flow βͺ Full control of access (access to and exit from these facilities are permitted only at controlled locations such as entrance and exit ramps) → Highways βͺ Uninterrupted traffic flow βͺ Partial control of access (access or exit may have permitted directly from or to abutting property or via a limited number of at-grade intersection) → Arterial roads: high-capacity urban roads. The primary function of an arterial road is to deliver traffic from collector roads to freeways. → Super-elevation design βͺ Normal crown: typical cross section on a tangent section (no super-elevation) βͺ Remove crown (Reverse crown): a super-elevated cross section which is sloped across the entire traveled way in the same direction and at a rate equal to the typical cross slope on tangent section (e.g. 2%) βͺTangent runout: change from a normal crown section to a point where the adverse cross slope of the outside lane is removed (i.e. the outside lane is level) βͺSuper-elevation runoff: change in cross slope from the end of tangent runout to a section that is fully super-elevated. Chapter 3 – Traffic Stream Flow Models →Traffic Flow Elements →• Flow (q) • Density/Concentration (k) • Speed (v, u) • Time Headway (h) • Space Headway or Spacing (S) → Free-flow condition: very low concentration and very high speed (speed ↑, spacing ↑, concentration ↓) → Free-flow speed, uf: maximum speed at zero concentration (when concentration approaches zero) →Concentration (k): ratio of the number of vehicles appearing on the photograph to the length of the roadway segment. →Time headway (h): difference between the time when the front of a vehicle arrives at a point on the highway and the time the front of the next vehicle arrives at the same point →h = (constant spacing) / (constant speed of operation) → h = 1/ q ** →Space headway (S): difference in position between the front of a vehicle and the front of the next vehicle Chapter 5 – Pavement Design - Part 1: Pavement materials & Types: Asphalt ο· Strong cement, readily adhesive, highly waterproof, and durable (Asphalt Institute) ο· Asphalt concrete ο· Flexible pavement: maintains intimate contact with and distributes loads to the subgrade and depends on aggregate interlock, particle friction, and cohesion for stability Portland cement ο· Rigid pavement ο· More advantages compared to asphalt pavement in terms of strength requirement ο· Distribution of loads to the subgrade, Portland-cement concrete slab of relatively high bending resistance Pavement Design Traffic load (Most important – thickness of pavement), Soils, Environment, Reliability Subgrade Soil Classification Resilient Modulus – Mechanical Behavior - measure of material stiffness Granular base/subbase layers: elastoplastic behavior. Designed to simulate the behavior of soils and granular materials when subjected to traffic loading within a pavement system. Similar to modulus of elasticity. Depends on Density, Gradation, fine contents, and moisture content, At low levels of moisture content: increase in the resilient modulus due to suction. At high levels of moisture content: reduction in the resilient modulus due to pore pressure. California Bearing Ratio - Relative strength of a soil with respect to crushed rock. Penetration test for evaluation of the mechanical strength of natural ground, subgrades and basecourses. Determination of the load deformation curve of the soil in the laboratory using the standard CBR testing equipment. Chapter 5 – Pavement Design - Part 2: Flexible Pavement Design Layers(bottom to top): 1. Subgrade, 2. Subbase Course, 3. Base Course, 4. Surface Course. Subgrade: natural materials, foundation of the pavement structure, certain strength properties Subbase: • A layer of granular materials that is located between the subgrade and base course • Quality of materials is superior to that of the subgrade but inferior to that of the base course • Can be omitted if the quality of the subgrade material meets the requirements of the subbase • Specifications are in terms of plasticity, gradation, and strength • Main functions: • Reduces the stresses applied on the subgrade • Serves in water drainage • Protects the base course against volume changes of the subgrade Granular base: • Usually granular materials such as crushed stone, crushed or uncrushed gravel or slag, and sand • Strict specifications for plasticity, gradation, and strength • Can be stabilized using Portland cement, asphalt, or lime when a higher strength is required or when the available materials do not meet the specifications • Main functions: • Acts as a foundation to the surface course • Distributes the stresses on the subbase into a large area • Protects the surface course against volume changes that may take place in the subgrade Surface: The surface course is the upper course of the road pavement consists of: a mixture of mineral aggregates and asphalt. Main functions: • Transmits the wheel loads to the underlying layers within acceptable limits. • Resists abrasive forces due to traffic. • Provides skid-resistant driving surface. • Preventing the penetration of surface water into the underlying layers and withstands high tire pressures. • The thickness of the surface layer can vary from 3 in. to more than 6 in., depending on the expected traffic on the pavement. Asphalt: Natural substance that has some amazing physical properties βͺ Adhesive, elastic, able to stretch, bend and flex without breaking (cohesive) βͺ Waterproofing βͺ At air temperatures, very thick liquid (highly viscous) βͺ When heated, it becomes thinner and easier to use Properties of Asphalt Materials: Consistency βͺ Vary from solid to liquid βͺ Consistency of asphalt + associated temperature β Aging and temperature sustainability βͺ When exposed to environmental elements: deterioration, loose plasticity and become brittle βͺ This natural deterioration of the asphalt material is known as weathering. βͺ Durability: resistance of the asphalt material to weathering. Asphalt Mixtures: Asphalt cement + coarse aggregate + fine aggregate + other materials βͺ Hot-mix, hot-laid/hot-mix, cold-laid/cold-mix, cold-laid βͺ Resist deformation from imposed traffic loads, be skid resistant even when wet, and not be affected easily by weathering forces βͺ Hot-mix, hot-laid asphalt mixture is produced by properly blending asphalt cement, coarse aggregate, fine aggregate, and filler (dust) at temperatures ranging from about 80 C to 160 C. βͺ Hot-mix, hot-laid asphalt mixture normally is used for high type pavement construction Asphalt Mixtures: hot-mix, cold-laid βͺ Manufactured hot and then shipped and laid immediately or stockpiled for used at a future date βͺ Small jobs βͺ Patching high-type pavement (asphalt concrete surfaced) Asphalt Mixtures: cold-mix, cold laid βͺ Emulsified asphalts and low-viscosity cutback asphalts are used to produce cold-mix asphalt mixtures. βͺ Immediately after production or stockpiled for use later General Principles of Flexible Pavement Design βͺ Multilayered elastic system • Objective: is to determine the minimum thickness of pavement layers that is enough • To Avoid overloading or overstressing the subgrade • Avoid overloading or overstressing any one or more of the pavement layers • Maintain good serviceability performance along the pavement design life Pavement structure required on top of a specific layer is expressed in terms of a Structural number (SN) which is an index number which may be converted to thickness of various flexible pavement layers through the use of layer coefficients