Chapter 5 6 Flashcards
Surfaces
provide support forvehicles traveling on transportation facilities
Guideways
in addition toproviding support, also provide lateral guidance
- Surface Courses\n* Base Course\n* Subbase\n* Geotextiles
COMPONENTS
Surface courses
usually consist ofasphalt or Portland cement concrete
Base courses
consist of aggregatessuch as gravel and crushed rock
Subbases
may consist of eitherunstabilized compacted aggregate or stabilized materials
geotextiles
used to add strength,control moisture, and prevent the movement of fine materials into drainagelayers
Asphalt
The pavement isconsidered to be flexible
plasticdeformation
The failuremechanism of asphalt
Concrete
The pavement isconsidered to be rigid
Fatigue
The failuremechanism of concrete
Traffic loads \n\nEffects of environmental conditions \n\nEvaluation of the load–bearing capacity of the subgrade material \n\nAvailability of materials
DesignConsideration
Computerized optimization program \n\nMechanistic methods based on stress–strain calculations \n\nEmpirical methods
DesignMethods
Pumping
a failure mechanismwhere fine materials in a saturated base form a slurry with the water in thebase. As wheel loads pass over the pavement, some of this slurry is forced outthrough cracks in the surface of the pavement
AASHTO RIGID PAVEMENT DESIGNMETHOD
the most common design method for Portlandcement pavement for highways; it relates soilconditions, traffic characteristics and pavement design characteristics to a performance index value expected at theend of the pavement’s design life
PORTLAND CEMENT ASSOCIATIONMETHOD
it is an iterative method, inwhich it is assumed that the pavement fails in fatigue after a certain number of significant deflections
- Alligator Cracking\n* Block Cracking\n* Transverse Cracking\n* Longitudinal Cracking\n* Raveling\n* Drip Track Raveling\n* Bleeding or Flushing
Pavement Failure
v ALLIGATORCRACKING
a series of interconnected or interlaced crackscaused by fatigue failure of the asphalt concrete surface under repeatedtraffic loading.
v BLOCKCRACKING
cracks forming largeinterconnected polygons, usually with sharp corners or angles. These cracks aregenerally caused by hardening and shrinkage of the asphalt and/or reflectioncracking from underlying layers such as cement–treated base
v TRANSVERSECRACKING
cracks approximately at rightangles to the pavement centerline. These may be caused by shrinkage ordifferential thermal stress of the asphalt concrete or may be by reflectivecracks.
v LONGITUDINALCRACKING
cracks approximately parallelto the pavement centerline. These are caused by poorly constructed constructionjoints and shrinkage of the asphalt concrete surface: they may also bereflective cracks
v RAVELING
wearing away of the pavementsurface caused by the dislodging of aggregate particles and binder. This isusually a result of insufficient asphalt binder in the mix or stripping ofasphalt from particles of aggregate.
v DRIPTRACK RAVELING
progressive disintegration ofthe surface between the wheel paths caused by dripping of gasoline or oil fromvehicles
v BLEEDINGOR FLUSHING
the exuding of bitumen onto thepavement surface, causing a reduction in skid resistance. ;generallycaused by excessive amounts of asphalt in the mix and/or low air voids content.It occurs in asphalt fills the voids in the mix during hot weather and thenexudes out onto the surface of the pavement.
ü Bituminous seal coat \n\nü Asphalt concrete overlays \n\nü Recycling of asphalt concrete pavement
Maintenance andrehabilitation for asphalt concrete pavement
v FAULTING \n\nv SETTLEMENT \n\nv BLOWUPS \n\nv JOINTOR CRACK SPALLING \n\nv SURFACEATTRITION OR SURFACE ABRASSION \n\nv SURFACEPOLISH
Types of pavement distress affecting Portland cement concrete pavements
v FAULTING
elevation differences betweenadjacent slabs at transverse joints. usually the result of pumping,and is a major source of Portland concrete pavement failure.
v SETTLEMENT
local sagging in the pavementcaused by differential settlement, consolidation, or movement of the underlyingearth mass.
v BLOWUPS
localized upward buckling andshattering of the slabs at transverse joints or cracks. It can occur whentransverse joints are filled with incompressible solid materials. They areespecially common where pavement is sanded in winter to counteract icy conditionsand in areas subject to large temperature changes.
v JOINTOR CRACK SPALLING
the breakdown ordisintegrations of slab edges at joints or cracks, usually resulting in theloss of sound concrete and the progressive widening of the joint or crack.
v SURFACEATTRITION OR SURFACE ABRASSION
abnormal surface wear, usuallyresulting from poor–quality surface mortar or coarse aggregate.
v SURFACEPOLISH
lossof the original surface texture due to traffic action
ü Installation of edge drains \n\nü Grinding of the slabs \n\nü Replacement of badly cracked or deteriorated slab \n\nü Asphalt concrete overlays \n\nü Grooving to reduce hydroplaning \n\nUseof special thin concrete surface treatment
Maintenance andrehabilitation actions for Portland cement concrete pavements
- Subgrade\n* Ballast\n* Ties\n* Rails\n* Spikes\n* Jointbar\n* Gage Bars\n* Rail Anchors
TRACK STRUCTURES
v AREMA
technical and specification writing arm of theAssociation of American Railroad; its standards are used throughout North America,including Canada and Mexico
v Rail Section
A description ofthe weight and profile of the rail. The rail section is usually stamped on theweb of rail. The first two or three numbers tell the weight per 3’ (one yard)section of rail.
5/8” beneath the top surface of the rail
Distance between two running rails
56–1/2” or 4’ 8–1/2”.
Standard Gage
GageSide
The area betweenthe two running rails.
v Field Side(of the Track)
The area on the“out sides” of each of the running rails
v Ballast
crushedaggregate (frequently stone) that is used within a track.
v Compromise Bars
aspecial type of Splice Bar that connects one piece of rail that is of one railsection to another piece of rail of a different rail section.
v Cross Tie
astandard railroad tie. Cross ties are either 6” x 8” or 7” x 9”. Length variesfrom 8 to 8–1/2’.
v Joint BarsCast
steel bars that connect one piece of rail to the next. Joint bars are punchedwith holes to match the end drilling on a rail.
v Rail
Thesteel beams on which the railcar wheels travel. eitherbolted together at the joints using joint bars or it is continuously welded. A full length of bolted * is usually 33’ or 39’.
v Relay
“Used”track material.
v Spike
The“nail” that holds a rail to a tie.
v Sub ballast
crushedaggregate (frequently stone) that is installed before track constructionbegins. ;provides a foundation and drainage for the track structure.
v Switch Tie
atie that is longer than the standard 8– 1/2’ cross tie and is used through aturnout from the switch points and continuing beyond the frog. They aregenerally 7” x 9” and vary in length from 9’ to 17’.
v Tie Plate
thesteel plate that is installed between the tie and the rail and is pre–punchedfor track spikes. ;prevent the rail from cutting into the tieand will distribute the load that is on the rail across a larger area of thetie.
single shouldered
have one ridgeagainst which the rail is spiked
double shouldered
they have two ridges into which the base of the rail must fit and be spiked against.
v Tie Plug
Asoft wood filler that is used to fill the hole where a track spike is removedbefore the tie is respiked.
v Track Ballast
crushedaggregate (frequently stone) that is used under and between the ties of a track.
v Track Bolt
Abolt with a button head and oval neck and a threaded nut designed to fastentogether rails and splice bars and other rail joint fastenings
- Bumping Post\n* Derail\n* Wheel Stops
Track Accessories
v Bumping Post
atriangular steel structure at the end of a track that prevents a railcar frommoving beyond the end of the track by making contact with the railcar coupler.
v Derail
adevice installed on a track to intentionally derail a car for safety purposes.(e.g. to prevent a car on an industry side track from rolling out onto themainline.)
v Wheel Stops
smallerdevices that are attached on a track to prevent a railcar from moving beyondthe wheel stops by making contact with the railcar wheels..
v Compromise Joint
thepoint where two rails that are different rail sections connect with CompromiseBars.
v Crossing Diamond
steelcasting that allows two tracks to intersect and cross each other.
v Flangeways
thegap between the running rail and anything installed along the gage side of arail.
v Surfacing
newtrack and turnouts are constructed directly on the subgrade and then buried instone. After this, they are raised out of the stone to the final elevation bytamping stone under the ties. The excess stone is contoured or removed and therails are aligned to remove any kinks.
Ties
–areused to maintain gage and to transmit wheel loads from the rails to theballast.
Center–BoundTrack–
A condition where repeated loads will further compact the ballast under theends of the ties, leaving them supported only at their centers.
· StoneBlocks \n\n· HardWood \n\n· Concrete \n\n· Steel \n\n· HybridPlastics
Composition of Ties
Creosote
– acomponent used to treat hardwood ties that makes last for at least 30 – 40years before needing replaced.
· Length– 8 to 9 feet
Length of Tie
· Width– 7 inches
Width of Tie
· Height– 8 to 9 inches
Height of Tie
· Distancebetween face of ties – 10 inches
Distance between ties
Rails
– Apermanent track composed of a line of parallel metal rails fixed to sleepers,for transport of passengers and goods in the trains.
Distancebetween two rails –1.435 meters (standard)
Distance between rails
Commonlength of rails – 39feet (standard)
Common length of rails
RailWeights in common use – 42kg/m to 75 kg/m
Rail weights
- Track Resurfacing\n* Tamper
Track Maintenance
TrackResurfacing –
acombination into a single operation of restoration of horizontal and verticalalignment, replacement of worn or defective ties or rails, and cleaning orrestoration of ballast.
Tamper–
amachine used in track maintenance.
Noise
is unwanted sound judged to beunpleasant, loud or disruptive to hearing.
includes control of noise at the source, location and designof facilities, construction of noise barriers, insulation of receptors andnoise mitigation for airports
Mitigationof noise impacts
decibel (dB)
is used to measure sound level
A–weighted soundlevel scale
the scale most often encountered in analysis of transportation–relatednoise. This scale correlates well with human response, and is available as abuilt in feature on most sound meters
Reduce noise at the source\nLocation and orientation of runways to route arrivals and departures\nInsulation Receptors\nOperational restrictions\nInstallation of noise barrier
Airport Noise Mitigation
- Reduce noise at the source –
focused onjet engine design. it include the primary jet andmachinery noise. The introduction of fan jet engines resulted in majorreduction in primary jet noise since the fan exhaust. Machinery noise has beenreduced by acoustical lining of theinlet and ducts. As as result engine noise has been reduced by about 15 Dbsince the introduction of commercial jet aircraft.
- Location and orientation of runways toroute arrivals and departures
– this is assessed by constructing maps forecastingnoise level contours around the proposed runways and approach paths.
- Insulationreceptors –
for residential areas FAR requires that were day–nightaverage noise level (Ldn) exceeds 65 dBA, it should beinstalled to reduce interior noise levels to 45 dBA or less. It include insulation of roof and walls, blocking the air paths such ascracks around doors, installation of storm doors and storm windows andinstallation of acoustical doors and windows.
- Operationalrestrictions
– include modifications to flight paths and flight profiles,especially on takeoff, and curfews or others on late nightoperation.
- Installationof noise barriers \n
– Noise barriers have been used to shieldreceptors from noise from ground operations including takeoff runs.
Use of Mufflers\n Use of Quiet Pavement\n* Use of Noise Dampers on wheels and use of rail facing\n* Installation of noise barriers
Measures tocontrol highway and railway noise:
Noise barriers
commonly consist of earth berms or walls constructed of wood, metal orconcrete. In addition transparent and translucent plastic have been used. Bermsand walls are sometimes combined.
Fresnel diffraction/Barrier Attenuation
Primary noise attenuation mechanism
N is equal to two multiplied to the quotient of eight and lambda
Fresnel Number
Clean water act\nEndangered species act
Federal laws related to mitigation of habitat encroachment
· tidalmud flats· saltwatermarshes · freshwatermarshes · swampsbogs
Wetlands include habitats such as
- Particulates\n* Metals such as lead, copper and zinc\n* Hydrocarbon, nutrients and bacteria
Runofffrom paved areas often contains a variety of contaminants:
- Spilled Fuel2. Pavement Wear3. AtmosphericDust4. Wear of Tireand Vehicle Parts5. Fecal Matter
Theultimate sources of these contaminants include:
WaterQuality
governed by EPA (Environmental ProtectionAgency) regulations issued under the Clean Water Act. Section 405 of the CleanWater Act of 1987 contains language directly related to stormwater management
Flood Control Policy
is generally a matter of local concern, and is usually governedby local ordinances. In addition, transportation agencies may be subject tolitigation if damage results from intensified discharges or upstream floodingdue to backwater.
Water Quantity
for flood control the recurrence interval for the design storm is normally 10 years or more.
Water Quality
are designed to detain the “first flush” of the storm, whichcontains most of the contaminants
- Detention basins\n* Infiltration trenches\n* Porous pavements\n* Vegetative Filter Strips\n* Grassed swales\n* Wetlands
Facilitiescommonly used for stormwater management include the following:
- Settling2. Chemical Decay3. BiologicalUptake4. Adsorption5. VariousPhysical, chemical, and biological processes
Methods inRemoving Pollutants
- Concerns aboutimpact on groundwater.2. Whereinfiltration is used.3. Concerns aboutthe impact on wetlands.
Constraints on StormwaterManagement Systems include:
Hazardous wastes and contaminated soils
often present in the right–of–way of transportationfacilities
Transportation agencies
are often responsible for remediation of these hazards, eventhough they may result from the actions of previous landowners.
- Petroleum\n* Asbestos\n* Lead
Types of Hazardous waste
- Service Station2. Various industrial uses
The main sources of hazardouswaste and soil contamination are:
Service stations,
for instances, are usually located alongside major highway;whenever existing highway are widened, it is likely to be necessary to acquireservice station sites.
Soilcontamination
is when hazardous substances are mixed into thenatural soil then the soil becomes contaminated making the soil not usable foranything and it can harm many things
- Agriculturalwaste2. Humanwaste3. Industrialwaste4. Mercury5. Lead6. Pesticidesand Herbicides7. PetroleumhydrocarbonRoadsalts
SOil Contaminants
- Landfilling2. Containment3. Treatment
REMEDIATION OPTIONS BY SPECIALIZEDENGINEERING FIRMS:
Landfill
– carefully designed structure built into or on top of the groundin which trash is isolated from the surrounding environment (groundwater, air,rain). This isolation is accomplished with a bottom liner and daily covering ofsoil.
CONTAINMENT
This involves sealing off hazardous waste orcontaminated soil by means of capping, grout curtains, slurry walls, or sheetpiles, or encapsulation in concrete vaults or bridge abutments
Incineration
A waste treatment technology, which includes thecombustion of waste for recovering enery; coupled with high temperature waste treatmentsare recognized as thermal treatments
Solidification/Stabilization
is a treatmenttechnology for contaminated soils, either for cleanup/remediation alone or aspart of a brownfield redevelopment.
Aeration/Land Farming
soils are spread and volatile petroleum productsare allowed to evaporate; in land farming, it is combined with aprocess of fertilization and cultivation in which microbes break down thepetroleum.
Traffic congestion
exists wherever demand exceed the capacity
Trends in accident rates
trends
Organizational
Agencies involved in transportation safety
Equality of access
Provide adequate access to the transportation system for all types of people
Poor, elderly and physically handicapped
3 groups seen underserved\n
technical\nlegal\npolitical elements
process of developing a transportation system
AASHTO, ASTM, Civil Aviation board
Design Standard
bid documents, plans, specifications, estimates
design documents
includes the designof geometric cross sections, horizontal lignment, vertical alignment, intersections and various design details
Geometric design for transportation facilities
Vertical alignment
documented by a profile
Profile
agraph which has elevation as its vertical axis and distance, measured stations along the centerline or other reference line of the facility as its horizontal axis
Horizontal alignment
horizontal tangents, circular curves an dpossibly transition curves without transition curves
Superelevation
Used to counteract the centripetal acceleration produced as a vehicle rounds a curve
Earthwork quantities
usually expressed as volumes, in metric units.
Mass diagram
Calculation of optimum haul strategies and earthwork costs is done by meads of using this diagram
mass diagram
a graph of cumulative volume of earthwork versus distance in stations from the beginning of the job, in which cut is considered to be positive and fill negative.
