highway design - techniques for proper planning and execution

Continues Improvement Is Better Than Delayed Perfection

- Mark Twain

Improvements in planning and Execution

of new road

By Tanaji . M . Gunjate

Need For Improvement

• To have a Reliable Infrastructure.• To have a Green Infrastructure.• To have a Smart And Safe Infrastructure.• To have a Human Infrastructure.

Reliable Infrastructure

• Lifetime engineering• Fast, hindrance-free maintenance• Balancing demand and capacity• Asset management tools

• Saving natural resources• Emission Control

Green Infrastructure

• Safe design• Smart design• Smart communication• Smart monitoring

Smart and Safe Infrastructure

• Public security• Multi-functional use• Human design

Human Infrastructure

Road Planning Process

• Highway Location Survey.• Highway Alignment Survey• Highway Traffic Survey• Highway Geotechnical Investigation Survey

engineering Survey

• Map study•  Reconnaissance• Preliminary surveys•  Final location and detailed surveys

Highway Location Survey

• Setting out alignment on ground. • Taking cross-sections to full right of way at fixed

interval.

Highway Alignment Survey

• Classified traffic in terms of Car, Two Wheeler, Three wheeler, Trucks, MAV, Bus, Mini bus, LCV, Cycle, Animal driven vehicles, cart, etc. are counted 24/7 on project highway and Average daily traffic is calculated.

• Traffic varies on road by season, month, week, week-days, hours.

• Seasonal variation factor is use to convert ADT to AADT.

Highway Traffic Survey

• Trail pits / Bore Holes are taken at fixed interval on projected road.

• Soil samples are tested to know the engineering properties of soil.

(a) Gradation (b) Atterber’s limit (c) Free swelling Index (d) CBR

Highway Geotechnical Survey

• DGPS ( Differential Global Positioning System).• Total Station.• Video Graphic Vehicle count .• Ground Penitrating Radar

Modern Techniques OF Survey

Element of Highway Design.

Design Vehicle• Design vehicles are selected motor vehicles with the weight, dimensions, and operating characteristics used to establish highway design controls for accommodating vehicles of designated classes.

• For purposes of geometric design, each design vehicle has larger physical dimensions and a larger minimum turning radius than most vehicles in its class.

Classification of Design Vehicle As per IRC-3-1983

Maximum Dimensions of Road Vehicles As per IRC-3-1983

Dimension of vehicle

Details Maximum Dimension (m)

(Excluding front and rear bumper)

• Width All Vehicles. 2.50• Height (a) Single-Decked vehicle for normal

application .3.80

(b) Double-decked Vehicle . 4.75• Length (a) Single-unit truck with two or more axles.

(type 2,3)11.00

(b) Single-unit bus with two or more axles. (type 2,3)

12.00

(c) Semi- Trailer tractor combinations (type 2-s1, 2-s2, 3-s1, 3-s2)

16.00

(d) Tractor and Trailer combinations (type 2-2, 3-2, 2-3, 3-3)

18.00

Choice of Design Vehicle• The choice of design vehicle is influenced by the

functional classification of a roadway, and by the proportions of the various types and sizes of vehicles expected to use the facility.

• On rural facilities, to accommodate truck traffic, one of the semitrailer combination trucks should be considered in design.

• In urban areas that are highly built-up, intersections may be designed to provide fully for passenger vehicles but require the larger vehicles to swing wide upon turning

• The vehicle which occurs with considerable frequency is often selected as the design vehicle.

• The largest of all the several design vehicles are usually accommodated in the design of freeways, subject to state laws on permitted vehicles.

AASHTO Turning Templates

AutoTURN Sample

Design Speed • The speed with which vehicles travel on the road is seldom the maximum speed the vehicle is capable.

• Choice of design speed depends on the function of the road as also terrain conditions. Terrain is classified by the general slope of the country across the highway alignment.

S. NO. Terrain classificationPer cent cross slope of the

country1 Plain 00-10

2 Rolling 10-25

3 Mountainous 25-60

4 Steep <60

Design Speed SR.NO.

Road Classificatio

n

Design Speed (in KMPH)Plain Terrain Rolling Terrain Mountainous

TerrainSteep Terrain

Ruling Design Speed

Minimum

Design Speed

Ruling Design Speed

Minimum

Design Speed

Ruling Design Speed

Minimum

Design Speed

Ruling Design Speed

Minimum

Design Speed

1 National And State Highway

100 80 80 65 50 40 40 30

2 Major District Road

80 65 65 50 40 30 30 20

3 Other District Road

65 50 50 40 30 25 25 20

4 Village Road 50 40 40 35 25 20 25 20

Tangents & Curves

Tangent

Curve

Tangent to Circular Curve

Tangent to Spiral Curve toCircular Curve

Layout of a Simple Horizontal CurveR = Radius of Circular CurvePC = Point of Curvature (or BC = Beginning of Curve )PT = = Point of Tangency (or EC= End of Curve )PI = Point of IntersectionT = Tangent Length

(T = PI – BC = EC - PI)L = Length of Curvature

(L = EC – BC)M = Middle OrdinateE = External DistanceC = Chord LengthΔ = Deflection Angle

Circular Curve Components

Properties of Circular CurvesDegree of Curvature• Traditionally, the “steepness” of the curvature is

defined by either the radius (R) or the degree of curvature (D)

• Degree of curvature = angle subtended by an arc of length 100 feet

R = 5730 / D

(Degree of curvature is not used with metric units

because D is defined in terms of feet.)

Properties of Circular CurvesLength of Curve• For a given external angle (Δ), the length of curve (L)

is directly related to the radius (R)L = (RΔπ) / 180

= RΔ / 57.3 R = Radius of Circular Curve L = Length of Curvature Δ = Deflection Angle• In other words, the longer the curve, the larger the radius

of curvature

Properties of Circular Curves

Other Formulas…

Tangent: T = R tan(Δ/2)

Chord: C = 2R sin(Δ/2)

Mid Ordinate: M = R – R cos(Δ/2)

External Distance: E = R sec(Δ/2) - R

Circular Curve Geometry

Circular Curve With Transition

• The amount by which the outer edge of a curve on a road or railway is banked above the inner edge.

Superelevation

SuperelevationRoad Plan ViewRoad Section View

CL2%2%

Road Plan ViewRoad Section View

CL2%1.5%

Superelevation

Road Plan ViewRoad Section View

CL2%1%

Superelevation

SuperelevationRoad Plan ViewRoad Section View

CL2%0.5%

SuperelevationRoad Plan ViewRoad Section View

CL2%-0.0%

SuperelevationRoad Plan ViewRoad Section View

CL2%-0.5%

SuperelevationRoad Plan ViewRoad Section View

CL2%-1%

-1.5%

SuperelevationRoad Plan ViewRoad Section View

CL2%2%

SuperelevationRoad Plan ViewRoad Section View

2%-2%CL

SuperelevationRoad Plan ViewRoad Section View

3%-3%CL

SuperelevationRoad Plan ViewRoad Section View

4%-4%CL

SuperelevationRoad Plan ViewRoad Section View

3%-3%CL

SuperelevationRoad Plan ViewRoad Section View

2%-2%CL

SuperelevationRoad Plan ViewRoad Section View

2%CL

-1.5%

SuperelevationRoad Plan ViewRoad Section View

2%CL

-1%

SuperelevationRoad Plan ViewRoad Section View

2%CL

-0.5%

SuperelevationRoad Plan ViewRoad Section View

2%CL

-0.0%

SuperelevationRoad Plan ViewRoad Section View

2%CL

0.5%

SuperelevationRoad Plan ViewRoad Section View

2%CL

1%

Road Plan ViewRoad Section View

2%CL

1.5%

Superelevation

SuperelevationRoad Plan ViewRoad Section View

2%CL

2%

• Transition curves are provided in between a straight road and the Curve of a design radius. So the radius of a transition curve varies from infinity to the design radius or vice verse.  The length of the transition curve must fulfill some requirements. It is designed to fulfill the following three conditions:

Calculation of Length of Transition Curve

(a) Rate of change of centri-fugal Acceleration(C):As per IRC recommendations,   Here, C= allowable rate of change of centrifugal acceleration ()Ls= Length of the transition curve.

(b) Rate of introduction of Designed super-elevation:If pavement is rotated about center line,  then

=>

If pavement is rotated about inner edge, then

=>  where, Ls= Length of transition curve              B= width of the pavement

(c) By Empirical Formula given by IRC(Indian Roads congress):         It should not be less than             (i) For plain and ruling terrain:                (ii) For mountainous and steep terrain:

Find out the greatest length of the transition curve by the above three criteria and use to construct the transition curve.

Where R = Radius in meter V = Speed of vehicle in kmph e = Rate of superelevation f = Design value of lateral friction coefficient = 0.15• e Superelevation is provided 75%of design speed Maximum superelevation 7% for plain and rolling terrain and 10% for hilly and steep terrain

Minimum Radius OF Curve And Maximum Superelevation Required

• Mechanical widening

• Psychological widening • Extra widening +

Widening of Payment on Horizontal Curve

• Grade Compensation = .• Subjected to maximum value of .• IRC recommends compensation is not necessary for

gradient flatter than 4%.

Grade Compensation

∝

Crest Curve

Sag Curve

G1G2 G3

Vertical Alignment - Overview

Parabolic Curves

Radius Parabola

y ax2 bx c

Horizontal Curve Vertical Curve

Properties of Vertical CurvesBVC

EVC

L

G2

G1

Change in grade: A = G2 - G1 where G is expressed as % (positive /, negative \)

For a crest curve, A is negative.For a sag curve, A is positive.

L/2L/2

PI

Design of Vertical Curves

Design of Vertical Curves

• Determine the minimum length (or minimum K) for a given design speed.

– Sufficient sight distance– Driver comfort– Appearance

Crest Vertical Curve• If sight distance requirements are satisfied then safety,

comfort, and appearance will not be a problem.

h1 = height of driver’s eyes, in ft.

h2 = height of object, in ft.

• When L > SSD- • When L <SSD -

Design of Vertical Curves

Sag Vertical Curve• Stopping sight distance not an issue. What are the

criteria?– Headlight sight distance– Rider comfort– Drainage– Appearance

• When L > SSD -

• When L < SSD -

Design of Vertical Curves

• MX Road • Civil 3d

Softwares Used For Road Design

Pavement Design

Mechanistic Method of Pavement Design

• Temperature Stresses– Due to the temperature differential between the topand bottom of the slab, curling stresses (similar tobending stresses) are induced at the bottom or top ofthe slab• Frictional stresses– Due to the contraction of slab due to shrinkage or dueto drop in temperature tensile stresses are induced atthe middle portion of the slab• Wheel Load Stresses– CC slab is subjected to flexural stresses due to thewheel loads

Stresses in Rigid Pavements

Where,E = Modulus of Elasticity of concrete, MPah = thickness of slab, mμ = Poisson’s ratiok = modulus of subgrade reaction, MN/m3

Radius of Relative Stiffness

Temperature Differentials Recommended by IRC

–𝑆𝑓=𝛾𝑐𝐿 𝑓 𝑎

2

Stresses Due to Friction

Spacing of Contraction Joints• The contraction joints are spaced to limit the tensile

stress induced in the slab to the value that can be born by the slab during curing period

• Spacing is found out by taking the allowable tensilestress as 80 kPa during curing period of concrete

• For = 80 kPa, = 24 kN/m3 and = 1.5L = 4.52 mTherefore, the spacing of contraction joints is kept as 4.5 m.

Contraction Joint SpacingSpecified by IRC

Slab Thickness(cm)

Maximum Contractionjoint spacing (m)

15 4.520 4.525 4.530 5.035 5.0

A Fully Developed Crackat a Contraction Joint

IRC Recommendations on Wheel Load Stresses

• The loads causing failure of pavements are mostlyapplied by single and tandem axles, stress must bedetermined for the condition shown in chart’s given byPicket &Ray for stress computation in the interior as wellas edge region• Using fundamental concept of Westergaard and Picket&Ray’s pioneering work a computer program IITRIGIDdeveloped at IIT, Kharagpur was used for edge loadcondition

• As per IRC 58-2011 stresses in Rigid pavement by wheel load analyzed for following condition.

• (a) Bottom up Cracking -By traffic 10.00 AM to 4.00 PM• (b) Top Down Cracking -By traffic 00.00 Am to 6.00 AM

IRC Recommendations on Wheel Load Stresses

• Fixed traffic– Design is governed by single wheel load – Load repetitions is not considered as a variable – Multiple wheels are converted into single wheel – Heaviest wheel load anticipated is used in design• Variable traffic and variable vehicle (Spectrum of Axles Approach)– Both vehicle and traffic are considered independently. i.e., treat all axlesseparately and use spectrum of axles in the design

Analysis of Traffic Loading for Pavement Design

Fixed vehicle– Design is governed by the number of repetitions of standard vehicle or axle load, usually 80 kN single axle load – Repetitions of non-standard axles are converted into equivalent repetitions of standard axle using equivalent axle load factors– The cumulative number of repetitions of standard axle during the design life is termed as Equivalent Single Wheel Load (ESAL) and is the single traffic parameter for design purpose.

Analysis of Traffic Loading for Pavement Design

• Equivalent Single Axle Load is the equivalent repetitions of standard axle during the design life of the pavement.

• IRC terms this ESAL as cumulative number of standard axles during the design life.• The number of repetitions of different types of axles are converted into equivalent repetitions of standard axle by using Equivalent Axle Load Factors (EALF).

Equivalent Single Axle Load

• Approximate EALF can be worked out using the fourth power rule

Single Axle Single wheel Load EALF = (Axle Load in KN/65)^4• Single Axle Dual wheel Load EALF = (Axle Load in

KN/80)^4 Tandem Axle Load EALF = (Axle load in KN/148)^4However, as the EALF depends on axle load as wheel as the pavement configuration, the exact EALF can be worked out only by using distress models

Fourth Power Rule

• Instead of converting each axle pass into equivalent standard axle passes, It will be convenient to convert one truck pass into equivalent standard axle passes.

• The factor that converts the number of trucks into equivalent standard axle repetitions is termed as vehicle damage factor or truck factor• Therefore, Vehicle damage factor is the number of standard axles per truck

Vehicle Damage Factor (VDF)

• It is worked out by finding the directional distribution and lane distribution factors

• Directional Distribution Factor (D)– The ADT of trucks is the sum of daily truck traffic volume in both directions• – D factor is the proportion of ADT of trucks occurring in

the maximum direction• – The D factor normally varies between 0.5 to 0.6

Traffic on Design Lane

• Lane Distribution Factor (L)– Is the proportion of truck traffic occurring on the design lane– Lane Distribution Factor depends on- Number of lanes- Traffic volume• Daily Truck Traffic on Design Lane = (ADT of Trucks) × (D) × (L)

Traffic on Design Lane

Undivided Roads (Single Carriageway)No. of Traffic Lanes in Two

DirectionsPercentage of Trucks in Design

Lane (D×L)1 1002 753 40

Divided Roads (Dual Carriageway)No. of Traffic Lanes in each

DirectionPercentage of Trucks in Design

Lane (L)1 1002 753 604 40

Factors Suggested by IRC

• ESAL = (ADT of Trucks) × (365) × (D) × (L) ×(VDF) × GF• GF = r = Growth rate in decimaln = Design life in years

Computation of ESAL

• Distress models relate the structural responses to various types of distresses

• These are equations relating the allowable number of repetitions of standard axle to the appropriate pavement response as per the failure criteria adopted

Distress Model

Fatigue Cracking and Rutting

Fatigue Cracking Model• N

• **

• =

Nf = No. of cumulative standard axles t produce 20% cracked surface area

t = Tensile strain at the bottom of Bituminous Concrete layerE = Elastic Modulus of Bituminous Surface (MPa)k1, k2 = Laboratory calibrated parametersk3 = Transfer parameter

Rutting Failure Model

• *

NR = No. of Repetitions to Rutting failurec = Vertical subgrade straink4, k5 = Calibrated parameters

Damage Ratio• Allowable number of repetitions (Ni) are computed

separately for each axle type I applying the distress model

• Expected number of repetitions (ni) of each axle type i are obtained from traffic cum axle load survey• Damage Ratio (DR), which is the ratio between the expected repetitions and allowable repetitions, is worked out for each axle type• The cumulative DR of all axles should be less than 1

Definition of CBRCalifornia bearing ratio is defined as the ratio (expressed as percentage) between the load sustained by the soil sample at a specified penetration of a standard plunger (50 mm diameter) and the load sustained by the standard crushed stones at the same penetration.

• This consists of causing a plunger of 50 mm diameter to penetrate a soil sample at the rate of 1.25 mm/min.• The force (load) required to cause the penetration is plotted against measured penetration.• The loads at 2.5 mm and 5 mm penetration are recorded.• This load corresponding to 2.5 mm or 5 mm penetration is expressed as a percentage of standard load sustained by the crushed aggregates at the same penetration to obtain CBR value.

Basic Test

• The load – penetration curve may show initial concavity due to the following reasons: – The top layer of the sample might have become too soft due to soaking in water – The surface of the plunger or the surface of the sample might not be horizontal

Initial Concavity

• Draw a tangent to the load-penetration curve where it changes concavity to convexity• The point of intersection of this tangent line with the x-axis is taken as the new origin• Shift the origin to this point (new origin) and correct all the penetration values

Correction

CBR(per cent)

Maximum variationin CBR value

55-10

11-3131 and above

Permissible Variation in CBR Values

• The average CBR values corresponding to 2.5 mm and 5 mm penetration values should be worked out• If the average CBR at 2.5 mm penetration is more than that at 5 mm penetration, then the design CBR is the average CBR at 2.5 mm penetration• If the CBR at 5mm penetration is more than that at 2.5 mm penetration, then the test should be repeated. Even after the repetition, if CBR at 5mm is more than CBR at 2.5 mm, CBR at 5 mm could be adopted as the design CBR.

Design CBR

Modulus of Subgrade Reaction

Strains under Repeated Loads

The resilient modulus MR is the elastic modulus based on the recoverable strain under repeated loads, and is defined as

= deviator stress = recoverable elastic strain

Resilient Modulus

Loading Pattern

SubgradeE (MPa) = 10 CBR if CBR<5% and= 17.6 for CBR > 5%Granular subbase and base

= Composite modulus of sub-base and base(MPa)= Modulus of subgrade (MPa)= Thickness of granular layers (mm)

Relation Between CBR and E

Modulus Values for BituminousMaterials

Proctor Compaction Test for Maximum Dry Density

What Is Compaction?

• Compaction is the process of increasing the bulk density of a soil or aggregate by driving out air.

• For any soil, at a given compactive effort, the density obtained depends on the moisture content.

• For any soil, an “optimum water content” exists at which it will achieve it’s maximum density.

1. To increase strength and stability2. To decrease permeability3. To enhance resistance to erosion4. Decrease compressibility under load and minimize

settlement

Soils are compacted for the following reasons

• Sheepsfoot• Padfoot• Vibratory Roller• Grid Roller

Common Equipment

• The peak dry unit weight is called the "maximum dry density”.

• The Optimum Water Content, wopt, is the water content at the soil’s maximum dry density.

Definition: Maximum Dry Density

• Proctor Compaction Test determines the optimum water content and maximum dry density of for a soil.

• A required range for moisture is often specified by the engineer:• Ie, 3% below and 2% above optimum.

• For example, if optimum water content is 16%, the acceptable range would be from 13% to 18%.

• Percent compaction is also specified:• Meaning “required percentage of max dry density”

% Compaction = ρdry field /ρdry max

Achieving Maximum Compaction In The Field

Dry Density Curve: Proctor Test

• Sand Replacement• Core Cutter test.• Nuclear Densometer

How Do We Determine Actual Field Density?

Modified vs Standard Proctor TestParticular Modified

ProctorStandard Proctor

IS 2720(VIII) 2720(VII)Hammer Mass 4.8 Kg 2.6 Kg

Free Fall 45 cm 31 cmNumber Of

Layers5 no. 3 no.

Number Of Blows

25 25

Work Done In Joules

270 joules 60.45 joules

Compaction Efforts

4.46 times than Standard Proctor

22% of Modified Proctor

Construction & Quality Control of Flexible Pavements

Bituminous construction are classified into four categories • Interface Treatments • Thin Bituminous surface Courses • Bituminous Surface Courses • Bituminous Binder Courses

BITUMINOUS PAVEMENT CONSTRUCTION

• Prime Coat• Tack Coat• Crack Prevention Courses SAM and SAMI

INTERFACE TREATMENTS

Purpose Of Priming:• To plug the capillary voids• To coat and bond loose materials on the surface• To harden or toughen the surface• To promote adhesion between granular and the bituminous layer Choice of Primer• The primer shall be bitumen emulsion, complying with IS 8887 of a type and grade as specified (SS-1)• The use of medium curing cutback as per IS 217 shall be restricted only for sites at sub-zero temperatures or for emergency applications

INTERFACE TREATMENTS

REQUIREMENT FOR PRIMING MATERIAL

Purpose of Tack Coat:• To ensure a bond between the new construction and

the old surfaceMaterial for Tack Coat:• The primer shall be bitumen emulsion, complying with

IS 8887 of a type and grade as specified (RS-1)Use of Cutback:• It should be restricted for sites at subzero temperatures

or for emergency applications

TACK COAT

RECOMMENDED QUANTITIES OF MATERIAL FOR TACK COAT

WRONG PRACTICE OF TACK COAT

INSUFFICIENT TACK COAT

MECHANICAL PRESSURE SPRAYER FOR PRIME/TACK COAT

MECHANICAL PRESSURE Hand SPRAYER FOR PRIME/TACK COAT

20-30% more quantity of tack coat for milled surface

Properly Done Tack Coat

Thin Bituminous Surface Courses

Quantities of materials required for 10 m2 (20 mm)

OPEN GRADED PREMIX SURFACE

A. Liquid Seal Coat: comprising of a layer of binder followed by a cover of stone chipping Stone chips shall be of 6.7mm size defined as 100 per cent passing through 11.2 mm sieve and retained on 2.36 mm sieve. The quantity used for spreading shall be 0.09 cubic meter per 10 square meter area.B. Premixed Seal Coat: a thin application of fine aggregates premixed with bituminous binder The quantity of bitumen shall be 9.8 kg and 6.8 kg per 10 m2 area for type A and type B seal coat respectively

SEAL COAT

• Close-graded premix carpet is a fairly open graded mix

• It is an alternative to the open graded premix carpet and a seal coat

• It may be constructed in one operation

CLOSELY GRADED PREMIX CARPET/MIXED SEAL SURFACING

AGGREGATE GRADATION FOR MSS

POOR CONSTRUCTION OF MSS

POOR CONSTRUCTION OF MSS

• The total quantity of aggregates used shall be 0.27 cum per 10 m2 area

• The quantity of binder shall be 22.0 kg and 19.0 kg for 10m2 area for Type A and Type B surfacing respectively

QUANTITY OF AGGREGATES AND BITUMEN

BITUMINOUS SURFACE COURSES

BUILT-UP SPRAY GROUT• Preparation of Base to the Required Camber and Shape

• Application of Primer• Application of Tack Coat• Spreading and Rolling First Layer of Coarse Aggregates (0.5 cu.m/10 sq.m)

• Application of Binder - First Spray (15 kg/10 sq.m)

BUILT-UP SPRAY GROUT• Spreading and Rolling of Coarse Aggregates for the Second Layer.

• Application of Binder - Second Spray (15 kg/10 sq.m).

• Application of Key Aggregates (0.13 cu.m/10 sq.m).

• Roll and Apply Additional key aggregates, if required.

• Cover with a Seal Coat before opening to Traffic.

COMPACTION OF BITUMINOUS MIXES

• Lack of adequate compaction in field leads to reduced pavement life

• Inadequate compaction of hot mix leads to early oxidation, raveling, cracking and disintegration before its life expectancy is achieved

• 1% excess voids results in approximately about 10% reduction in life

COMPACTION OF MIXES• Lack of attention to the air voids requirement of compacted dense graded bituminous mixes is the most common cause of poor pavement performance

• Laboratory compaction produces more density, hence 95-98% of laboratory density or 92% of theoretical density is preferred in the field

Factors Affecting Compaction

Compaction Sequence• SCREEDThe screed is the first device used to compact the mat and may be operated in the vibratory mode. Approximately 75 to 85 percent of Theoretical Maximum Density (TMD) will be obtained when the mix passes out from under the screed.

Schematic of a Paver

Screed Components

Compaction Sequence• ROLLERS• Generally a series of two or three rollers is used.

Contractors can control roller compaction by varying things such as the types of rollers used, the number of roller used, roller speed, the number of roller passes over a given area of the mat, the location at which each roller works, and the pattern that each roller uses to compact the mat.

• Approximately 92 to 95 percent TMD will be obtained when all rollers are finished compacting the mat.

Steel Wheel andPneumatic Tyre Rollers

Compaction SequenceTypical roller position used in compaction are:– Breakdown Roller The first roller behind the screed. It generally effects the most density gain of any roller in the sequence. Breakdown rollers can be of any type but are most often vibratory steel wheel.– Intermediate Roller Used behind the breakdown roller if additional compaction is needed. Pneumatic tire rollers are sometimes used as intermediate rollers because they provide a different type of compaction (kneading action) than a breakdown steel wheel vibratory roller, which can help further compact the mat or at the very least, rearrange the aggregate within the mat to make it receptive to further compaction.

Compaction Sequence– Finish Roller The last roller in the sequence. It is used to provide a smooth mat surface. Although the finish roller does apply compactive effort, by the time it comes in contact with the mat, the mat may have cooled below cessation temperature. Static steel wheel rollers are almost always used as finishing rollers because they can produce the smoothest surface of any roller type

Breakdown and Intermediate RollersLined up for Effective Compaction

Steel Wheel Roller Giving the Finish

Density – Air Voids Measurementby Extracting Cores

Nuclear Density Gauge

SEGREGATION IN MIX

PROPER LOADING

GOOD PAVEMENT SURFACE

TEMPERATURE

HIGHWAY MAINTAINANCE

Highway Maintenance Definitions

• Maintenance: Is the routine work performed to keep a pavement, under normal conditions of traffic and normal forces of nature, as nearly as possible in its as constructed condition.

• Maintenance: The function of preserving, repairing, and restoring a highway and keeping it in condition for safe, convenient, and economical use

Highway Maintenance• It includes both physical maintenance activities such as

sealing, patching, and so forth and traffic service activities including painting pavement markings.

• Rehabilitation: restoring or betterment of roadway such as resurfacing.

Why Maintenance is Necessary• All Pavements require maintenance.• Stresses producing minor effects are constantly

working in all pavements.• Stresses are:

• Change in temperature and moisture; • Traffic; • Small movements in underlying or adjacent earth.

• Distresses are visible evidence of pavement wear (i.e. they are the end result of the wear process which begins when construction ends).

• Water lines and other utilities are major area of pavement maintenance.

Pavement Condition Life Cycle

Functional Overlay

Reconstruction

Lifecycle Of Pavement

Importance & Challenge of Highway Maintenance

Importance:• Protect investments made in highways.• Economic & safety of public road system.Challenges:

• increased roads (additional mileage of travel), • vehicle sizes, and traffic.• Traveling public expect higher level of maintenance.• Size of maintenance budget.

Maintenance Management• Purpose: to capture information about maintenance

activities performed & resources expanded.• Maintenance management systems do not manage

programs, reduce cost or improve performance, rather they provide maintenance engineers with the information and analytical tools needed to allow them to do so.

Maintenance Management• Elements of maintenance management programs:

• Development of an annual work program (defining activities, quantities, establish performance standards, road inventory & inspection, estimate size of the work program).

• Budgeting & allocating resources (labor, equipment, Materials).

• Work authorization & control (various administration levels).• Scheduling (balance of workload throughout the year).• Performance evaluation (work progress & productivity).• Fiscal control (monitor status of expenditures yearly).

Maintenance Operations• Road surfaces• Shoulders & approaches.• Roadsides• Bridges, & drainage structures.• Traffic controls & safety devices.

Maintenance of Road Surfaces Cont.

• Bituminous surfaces• Failures due to: weathering, failure of base or subgrade due to

material quality or compaction or improper drainage.• Repairs:

• Patching• Paint patching• Scarifying• Resealing.• Non skid surface treatment

Maintenance of Shoulders & Approaches

• Well graded gravel shoulder : blading to proper slope and filling ruts or worn out materials.

• Turf shoulders: filling holes & ruts, blading, seeding, mow & clean shoulders (weed control).

• Approaches: include public side roads, private driveways, ramps, & turnouts.

• Approach maintenance is similar to shoulder maintenance + extra efforts to maintain potholes, ruts, and other types of deterioration

Maintenance of Roadsides• Roadside: include area between traveled surface & the limit of

the right-of-way (medians, roadside parks, right-of-way fences, picnic tables, ..etc.

• Vegetation management & control (include mowing, weed eradication & control, seeding, planting vegetation, & care of trees & shrubs).

• Mowing is done to provide sight distance, improve drainage, reduce fire hazards, & improve appearance of the roadway.

• Seeding & planting vegetation are important for prevention of erosion.

• Maintenance of rest areas.• Litter control.

Maintenance of Bridges, & Drainage Structures

• Bridges: Maintenance is needed to minimize deterioration or repair damage caused by accidents, floods, or other unforeseen events.

• Steel bridges: cleaned & painted to prevent erosion.• Concrete bridge decks deterioration: Corrosion of

reinforcement bars due to penetration of water & deicing salts or chemicals.

• Bridge decks with minor deterioration: patch with special concrete.

• Bridge decks with major deterioration: Overlay or remove & construct

Maintenance of Drainage Structures & Safety Devices

• Drainage structures• Should be kept in good working conditions.• Surface drainage, ditches, & culverts

• Safety devices:Guardrails, barriers, impact attenuators, pedestrian overpasses

& underpasses, fence to restrict access of pedestrians & animals.

• Safety devices should be frequently & systematically inspected & repaired

Pavement Rehabilitation• Proper maintenance extend pavement life.• However, best-maintained pavements will deteriorate

with time and will need rehabilitation.• Conventional rehabilitation:

• Reconstruct with all new material• Patch & overlay with new wearing surface.

Design of Overlay forFlexible Pavement

Types of Overlays• Asphalt overlay over asphalt pavements• Asphalt overlays on CC pavements• CC overlays on asphalt pavements• CC overlays on CC pavements

Steps in Design of OverlaysMeasurement and estimation of the strength of the

existing pavementDesign life of overlaid pavementEstimation of the traffic to be carried by the overlaid

pavementDetermination of the thickness and the type of overlay

Effective Thickness MethodBasic concept• Thickness of overlay is the difference between the

thickness required for a new pavement and the effective thickness of the existing pavement

Where,thickness of overlay thickness of new pavement = effective thickness of existing pavement

Effective Thickness MethodAll thicknesses of new and existing materials must be

converted into an equivalent thickness of AC

= thickness of layer i = conversion factor for layer i

Asphalt Institute Conversion Factors

Deflection Approach• The structural strength of pavement is assessed by

measuring surface deflections under a standard axle load

• Larger pavement deflections imply weaker pavement and subgrade

• The overlay must be thick enough to reduce the deflection to a tolerable amount

• Rebound deflections are measured with the help of a Benkelman Beam

Deflection Approach

Deflection Approach

Specifications for Measurement• Condition survey and deflection data are used to

establish sections of uniform performance• At least 10 deflection measurements should be made

for each section per lane subject to a minimum of 20 measurements per km.

• If the highest or the lowest deflection values for the section differ from the mean by more than one-third of the mean, then extra deflection measurement should be made at 25 m on either side of point where high or low values are observed.

Pavement Condition Survey• Visual inspection of the road stretch and grouping into sub-stretches

• Assessment of pavement cracking – type & percentage cracked area

• Rut depth measurements• Observations on other types of pavement deterioration

Loading and other standards• axle load of 8170 kg / load of 4085 kg on dual wheels• tyre pressure, p = 5.6 kg / cm2• standard pavement temperature = 35o C• highest subgrade moisture content soon after

monsoon -Some precautions during rebound deflection Observations• very low or zero values• variation of individual values, not more than one third

of mean value

Actual Survey

Other Measurements and Data• Measurement of pavement temperature (at one hour intervals)

• Measurement of field moisture content of subgrade soil

• Typical subgrade soil samples for lab. Tests (soil classification)

• Other data to be collected - annual rain fall - traffic data : classified volume of vehicles of gross load over 3 t, growth rate, axle load data / VDF values

Analysis of Data• Leg correction, if any, at each point of deflection

observation:• - If (i ~ f) is less than 0.025 mm (2.5 div.), = 0.02 (D0 ~ f)• - If (i ~ f) is more than 0.025 mm (2.5 div.), = [ 0.02 (0 ~ f) +

0.0582(Di – Df) ]• Mean deflection, • Characteristic Deflection, = ( + 2 ) for important roads to

cover• - 97.7 % deflection values, or c = ( + ) for low traffic roads, to cover 84.1 % deflection values Application of temperature correction factor @ 0.01 mm per variation from the standard temperature of 35 or 0.01 (~35)

Corrections for DeflectionsTemperature Correction• Stiffness of the Bituminous layers get affected due to

which deflections vary• Standard temperature is 35• Correction for temperature variation on deflection

values measured at pavement temperature other than 35 should be 0.01mm for each degree change from the standard temperature.

Corrections for DeflectionsCorrection for Seasonal Variation• Deflection depends upon the change in the climate• Worst climate (after monsoon)-considered for design• Depends on subgrade soil and moisture content• Correction for seasonal variation depends on type of soil

subgrade (sandy/gravelly or Clayey with PI<15 or Clayey with PI>15), field moisture content, average annual rain fall (<1300 mm or >1300 mm)

Seasonal Correction Factor (clayey subgrade, PI>15, rainfall>1300)

Computation of Design Traffic• The design traffic is considered in terms of the• cumulative number of standard axles ,

• = The cumulative number of Standard Axles to be catered for in the design

• = Initial Traffic in the year of completion of construction on design lane

• = Annual growth rate of commercial vehicles• = Design life in years• = Vehicle Damage Factor

Design of Overlay (IRC)• Design curves relating characteristic pavement

deflection to the cumulative number of standard axles are to be used.

• The Deflection of the pavement after the corrections i.e., Characteristic Deflection is to be used for the design purposes.

• The design traffic in terms of cumulative standard number of axles is to be used

Overlay Thickness Design Curves (IRC)

Design of Overlay (IRC)• The thickness obtained from the curves is in terms of

Bituminous Macadam construction.• If other compositions are to be laid then -1 cm of Bituminous Macadam = 1.5 cm of WBM/Wet Mix Macadam/BUSG -1 cm of Bituminous Macadam = 0.7 cm of DBM/AC/SDBC

THANK YOU

Any Questions