Basics of a Good Rural Road!

Transcription

1 Basics of a Good Rural Road! WTA Convention -- October 27, 2015! By Steve Pudloski! Transportation Information Center thanks its partners for their support and assistance

2 Three sessions this morning! 8:30!Characteristics of!!!!a Well Built Road!!!9:30!Break!!9:45!Traffic Safety and!!!!!traffic Engineering!!10:45 Break!!11:00!Road Maintenance!!!!and Operations!!Noon Lunch!

3 Session 1: Characteristics of a Well Built Road! WTA Convention! on October 27, 2015! Transportation Information Center thanks its partners for their support and assistance

4 Session 1: Topics Basics of a Good Road 10 pieces of advice Basic Road Geometry State Standards + Pavement Structure Thickness = strength Soils Basics Soil types and strength Drainage Basics Drainage System Details

5 1. BulleDn #19 Basics of a Good Road 1. Get water away from the road 2. Build on a firm foundadon 3. Use the best materials 4. Compact all layers 5. Design for traffic loads and volumes 6. Design for maintenance 7. Pave only when ready 8. Build form the botom up 9. Protect your investment 10. Keep good records

6 2. Basic Road Geometry Urban pavements have curbs and guters to direct drainage to catch basins and buried storm sewers. Rural pavements are uncurbed and drainage is provided by roadside ditches or swales (shallow ditches).

7 Rural Cross- secdon

8 Cross- secdon Design Factors Traffic speed Traffic volume Vehicle mix (cars, trucks, buses, bikes) Land use (traffic & parking generators) Conflicts (turns, parking, merging) Terrain (sight distance, slope) Pedestrian & bicycles (schools, parks)

9 Cross- secdon Design Elements Road width and lane width Shoulder width and material Longitudinal slope of the road Ditch width, depth, and slope Roadside clear zone Horizontal and VerDcal curve radius Crown and super- elevadon at curves Sight curves, intersecdons, drives

10 Infrastructure fundamentals cross- secdon 66 ROW (49.5 min) Roadway (surface and shoulder) Resurface/RecondiDon 22 to 30 Reconstruct 26 to 36 Shoulder and ditch, shown in red From Chapter Trans and ExisDng Town Road Improvement Standards

11 Wisconsin State Law Town Road Standards 82.50, 82.18, and Trans From Trans Table'A'E'Reconstruction'from'Trans' Traffic'Volume Roadway'Width'in'Feet Design' Class Current'ADT Design' Speed'MPH Traveled' Way Shoulder Roadway T1 Under' T2 250'E' T3 Over' Table'A'E'Resurfacing'and'Reconditioning'from'Trans' Traffic'Volume Roadway'Width'in'Feet Design' Class Current'ADT Design' Speed'MPH Traveled' Way Shoulder Roadway TR1 Under'250 E TR2 250'E' TR3 401E TR4 Over'

12 From Trans 204

13 From Trans 204

14 From Trans 204

15 3. Pavement Structure How do pavements carry loads Types of pavement structures Traffic loading Pavement thickness design method

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17 DeflecDon causes deterioradon

18 Repeated deflecdon causes fadgue cracking cracking of the pavement from the botom up due to repeated deflecdon of the pavement fadgue cracking occurs as damage accumulates over muldple deflecdon cycles Graphic Source: Methodology And Calibration Of Fatigue Transfer Functions For Mechanistic-empirical Flexible Pavement Design By Angela L. Priest David H. Timm NCAT Report December 2006

19 Types of Pavement Structures Rigid Pavement: A pavement structure whose surface and principal load bearing component is a portland cement concrete slab of reladvely high bending resistance. Flexible Pavement: A pavement structure which maintains indmate contact with and distributes loads to the subgrade and depends upon it for strength and aggregate interlock, pardcle fricdon, and cohesion for stability.

20 How Pavements Carry Loads 6500 lbs 6500 lbs pressure < 0.3 psi pressure 3 psi Concrete s Rigidness spreads the load over a large area and keeps pressures on the subgrade low.

21 Soil Types Excellent to Good Soils (High Support) Retains substandal amount of support capacity when wet. Clean and sharp sand and gravel that are well graded, i.e., good distribudon of pardcle sizes and low voids. Minimally affected by frost. Medium Soils (Medium Support) Retains moderate amount of firmness when wet. Loams, silty sands and sand & gravel with some clay and fine silt. Some frost heaving. Poor Soils (Poor Support) Becomes son and plasdc when wet. High clay and silt content. Organic soils are also poor.

22 Soil Capacity to Bear Loads Field sample that is tested in the lab with the test at saturated condidons CBR is the California Bearing RaDo Crushed Limestone CBR = 100 Good Soil CBR = 17 Medium Soil CBR = 9 Poor Soil CBR = 3 New Measure is Resilient Modulus

23 Distress caused by heavy loads Wheel Load Hot-mix asphalt Base Subbase Natural soil

24 Pavement Thickness Design Adequate pavement thickness design is the result of a thorough soil survey coupled with a mathemadcal evaluadon of such factors as vehicle volume and composidon, subgrade soil support, and the strengths of materials used in the pavement structure. Evolving Design Methodology Empirical CombinaDon MechanisDc (Road Test) (MEPDG)

25 Empirical Method of Thickness Design Calculate traffic factor for design year Project the number and mix of vehicles One 80,000# truck equals the loading (damage) of 7,000 to 10,000 cars AASHTO : 18,000# per axle or 18kips Equivalent Single Axle Loads (ESALS) Empirical formula to calculate traffic factor which will be used with soil and pavement strengths to set thickness

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27 TF IBR Structural Number Structural Number (Dt) is an abstract number related to the strength required of the total pavement structure and is the sum of the strength of each pavement layer. It is calculated by multiplying the thickness of the layer by the strength coefficient of the layer. Dt = a1d1 + a2d2 + a3d3 a1, a2, a3 are coefficients of Strength of the surface, base, and subbase materials. D1, D2, D3 are the thickness in inches of the surface, base, and subbase materials

28 4. Natural Soils Basics Mixture of mineral and organic mater with voids that are filled with water and/or air Soils can vary greatly from spot to spot and from layer to layer Load bearing strength of any given soil will vary with water content but not all soils lose the same strength when wet There is an opdmum water content at which a soil is most dense and carries the greatest load that can be determined by lab tests

29 Important Soil CharacterisDcs Size of the pardcles DistribuDon of sizes (called gradadon) Moisture content Wear - - abrasion resistance Hardness - - strength in compression Fractured number, irregularity and sharpness of faces Freeze / thaw soundness Deleterious materials (deteriorate)

30 How Size & Distribution are Measured Stack of nesting sieves with the biggest openings at the top and a pan at the bottom Pour the stone in the top, washed, shake the stack, weigh each sieve, determine percent passing each sieve

31 Typical Sizes of Sieves 75 mm (3 in) 50 mm ( 2 in ) 37.5 mm (1 1/2 in) 31.5 mm (1 1/4 in) 12.5 mm (1/2 in) 25 mm (1 in) 12.5 mm (1/2 in) 9.5 mm (3/8 in) 4.75 mm (#4) 0.2 mm (#10) mm (# 40) mm (#200) 19 mm (3/4in)

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33 Gravel vs. Stone Gravel is a natural occurring material produced by fricdon during the wind, water erosion process Rounded material Needs to be crushed for some uses Stone usually means Crushed Stone that has been mined then crushed to various sizes to create angular pieces with sharp edges Most projects use materials that are locally available to reduce transport costs

34 Why Use Well Graded Stone Smaller pardcles fill up spaces between the larger rock to reduce air voids in the mix, thereby increasing aggregate interlock and strengthening the structure at the OpDmum Water Content Stone Particles

35 Improving Soils under Pavements Chemical treatments Lime Coal Fly Ash Portland cement Requires lab tests and filed tests Purposes Soil drying Soil property modificadons StabilizaDon, increase long term strength

36 Improving Soils under Pavements GeosyntheDcs SeparaDon, StabilizaDon Reinforcement Types GeotexDles Woven Non- Woven Geogrid Geocels

37 Some Pavement Design Examples

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40 Source: ESALS

41 More Weight More DeflecDon More Damage 18,000 lb. single axle 24,000 lb. single axle 10,000 lb. 18,000 lb. 18,000 lb. 10,000 lb. 24,000 lb. 24,000 lb. 2.1 Damage Units 6.1 Damage Units 34,000 lb. tandem axle 12,000 lb. 34,000 lb. 34,000 lb. 2.4 Damage Units

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43 Rural pavements Crown (2% slope from center to edge) Shoulder (3% slope across shoulder) Ditch (3 to 1 slope to ditch botom) Ditch botom at least 1 below pavement Rural pavements Ditch longitudinal grade at least 1% Steep ditches require flow controls to reduce erosion and scour Road (driveway) crossings by culvert pipe designed for drainage area

44 Rural Cross- secdon Ditch must be below the road base.

45 Drainage: Soils, Water, Pavements Subsurface Drainage System In areas that have high ground water or in soils that are slow draining or are subject to capillary acdon An system of pipes (underdrains) that have small openings along the pipe and are surrounded by well draining soil or stone to allow water to enter the pipe and be conveyed to a ditch or storm sewer

46 Subdrain & filtradon edge drain

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