Download - DETERMINING SLOPE
3-1Determining Slope
NOTES
OBJECTIVES
The purpose of this chapter is to:
•Measureslope.•Calculatepercentslope.•Understandthedifferentlocationsthatslopemaybemeasuredfrom.
Slope
Whatisslope?
Slopeisthechangeinelevation,measuredin consistentunits,fromonepointtoanother.
Whywouldslopebeafactorinevaluatingasiteforanonlotsewagedisposalsystem?
3DETERMININGSLOPE
Revised5/12
3-2 Determining Slope
NOTES
How To Measure Slope
Slopemustbemeasuredperpendiculartothecontoursoftheland.Contoursarelinesofequalelevation.
Therearetwowaystomeasureslope:
1) Bytakingfieldmeasurementsanddividing theverticaldistancebythehorizontal
distance(rise÷run),andthenmultiplyingby100forpercentslope.
2) Bymeasuringtheanglewithaninstrument.
3-3Determining Slope
NOTES
1) VERTICAL AND HORIZONTAL DISTANCES
Slopecanbecalculatedbyusingtheriseoverrunmethodofdividingtheverticaldistancebythehorizontaldistance.Multiplytheansweryougetby100togetpercentslope.
verticaldistance÷horizontaldistance=slope
RISE
RUN
3-4 Determining Slope
NOTES
SAMPLE PROBLEM
Solveforthepercentslope.Roundtothenearestwholepercent.
Verticaldistanceis6feet8inchesandhorizontal distanceis38feet.Percentslope=________
EXERCISE 3-1
Solveforthepercentslope.Roundtothenearestwholepercent.
1)Verticaldistanceis5feetandhorizontaldistanceis57feet.Percentslope=_______
2)Verticaldistanceis3feet5inchesandhorizontal distanceis56feet.Percentslope=_______
3)Verticaldistanceis5feet4inchesandhorizontal distanceis48feet7inches.Percentslope= .
3-5Determining Slope
NOTES
2) MEASURING THE ANGLE
Slopecanalsobedeterminedbymeasuringtheangle.Withthismethod,horizontalandverticaldistancesarenotneeded.Aninstrumentisusedinstead.
angle
3-6 Determining Slope
NOTES
Instruments to Determine Slope
LOCK LEVEL
TOOLS:
1)Reeltapemeasureof100feetor greater
2)Measuringrodorpockettapemeasure
3)Screwdriver,chainingpin,orlargespike
PROCEDURE:
Measure the Run
1)Pushthescrewdriver,chainingpin,orlargespikeintothegroundthroughthehookonthezeroendofthereeltapemeasureatpointA.
2)MeasurethedistancebetweenpointsAandB;thiswillgiveyoutherun(horizontaldistance).Thisdistanceshouldbetheapproximatewidthoftheabsorptionareaforanin-groundsystemorthedistancefromtoeofbermtotoeofbermforanel-evatedsystem.
3)Toaccuratelymeasuretherun,thereeltapemustbepulledlevelasshowninthedrawingabove.
Rise(verticaldistance)(measuringrod)
Run(horizontaldistance)(reeltape)
PointBPoint
A
3-7Determining Slope
NOTES
Measure the Rise
4)StandingatpointB,lineupthelevelingbubbleonthecrosshairinthelocklevel.SlidethelocklevelupordownthemeasuringroduntilthecrosshairislineduponpointA.
5)Oncethispositionisachieved,readthenumberonthemeasuringrod.Thisistherise(verticaldistance).
Calculate the Percent Slope
6)Calculatethepercentslopebydividingthe verticaldistancebythehorizontaldistanceandmultiplyby100forpercentslope.
RiseRun
× 100=percentslope
3-8 Determining Slope
NOTES
ABNEY LEVEL
TheangleismeasureddirectlywithanAbneylevel.
TOOL: Atargetatthesameverticaldistanceabovegradeasyoureyeheight.Forexample,ameasuringrodortapearoundanobjectsuchasatreeorstake.
PROCEDURE:
1)SetupyourtargetatpointA.
2)MeasurethedistancebetweenpointsAandB;thiswillgiveyoutherun(horizontaldistance).Thisdistanceshouldbetheapproximatewidthoftheabsorptionareaforanin-groundsystemorthedistancefromtoeofbermtotoeofbermforanelevatedsystem.
3)StandingatB,lookthroughtheeyepieceoftheAbneylevelandsightthetargetatpointA.SlopemaybemeasuredupordownhillwithanAbneylevel.
4)Lineupthecrosshaironthetarget,andturnthethumbscrewontheAbneyleveluntilthebubblelinesupwiththecrosshair.
5)Readthepercentslopedirectlyoffthedial indicator.
Equalheight
B-Eyeheight
A-Targetateyeheight
Angle
3-9Determining Slope
NOTES
CLINOMETER
TheClinometer,liketheAbneylevel,worksonthesameprincipleofmeasuringtheangledirectly.
TOOL:Atargetatthesameverticaldistanceabovegradeasyoureyeheight.Forexample,ameasuringrodortapearoundanobjectsuchasatreeorstake.
PROCEDURE:
1)SetupyourtargetatpointA.
2)MeasurethedistancebetweenpointsAandB;thiswillgiveyoutherun(horizontaldistance).Thisdistanceshouldbetheapproximatewidthoftheabsorptionareaforanin-groundsystemorthedistancefromtoeofbermtotoeofbermforanelevatedsystem.
3)Standingattheotherendofslope(B),lookthroughtheeyepieceoftheClinometerwithoneeye,andlookatthetargetwiththeothereye.BotheyesmustbeopenfortheClinometertowork.Sight(eitherupslopeordownslope)atthetargetatpointA.
4)Whilelookingintotheeyepiece,lineupthecrosshairwiththetargetandreadthepercentslopedirectlyfromthescaleintheclinometer.
Equalheight
B-Eyeheight
A-Targetateyeheight
Angle
3-10 Determining Slope
NOTES
LASER LEVEL/BUILDER’S LEVEL/TRANSIT
Thelaserlevelmeasurestheexactelevationchange.Theverticalandhorizontaldistancesareusedtocalculateslope.
Warning:Neverlookdirectlyintothelaserlightasdoingsocouldcausepermanenteyedamageorblindness.
TOOLS:
1)Measuringrodwithtarget (purchaseaspartofpackagewithlaser)
2)Reeltapemeasureof100feetorgreater
ACB
3-11Determining Slope
NOTES
PROCEDURE:
1)Setupthelaserlevelatalocationclosetotheproposedabsorptionarea,whereyouhave
unobstructedsighttopointsAandB.
2)Pullthetapemeasurelevel,asyouwouldwith thelocklevel,tomeasuretherun(horizontal distance)betweenAandB.Thisdistance betweenAandBwouldbethewidthofthe absorptionarea.
3)Walktothehighestverticalpointofthe absorptionarea(A).Holdtherodexactly vertical,orplumb,atA,andmovethesightingtargetupordownontheroduntilthelaser
beamstrikesthetargetatA,creatinganaudiblesound.Recordtheelevationmeasured.
4)Walktothelowestpartoftheabsorptionarea(B).Holdtherodexactlyvertical,orplumb,atB,
andmovethesightingtargetupordownontheroduntilthelaserbeamstrikesthetargetatB,creatinganaudiblesound.Recordtheelevationmeasured.
5)SubtracttheelevationmeasuredatAfromtheelevationmeasuredatB.Thedifferencebetweenthesetwoelevationsistherise(verticaldis-tance).
6)Tocalculatepercentslope,dividetherise(verti-caldistance)bytherun(horizontaldistance)andmultiplyby100.
3-12 Determining Slope
NOTES
Example: Atthetopoftheslope(A),youread6feetonthemeasuringrod.Atthebottomoftheslope(B),youread12feetonthemeasuringrod.Yourhorizontaldistanceis75feet.
Whatisthepercentslope?
Greatestverticalreference–smallestverticalreference=verticaldistance
Verticaldistance÷horizontaldistance=slope
Slope×100=percentslope
6ft.
75ft.
12ft.
A
B
3-13Determining Slope
NOTES
CALIBRATE THE SLOPE-MEASURING INSTRUMENT
•Periodicallycheckyourslope-measuringinstru-menttoensurethatitismeasuringslopeaccu-rately.
•Checkthemanufacturer’sinstructionsonhowtocalibratetheinstrument.
•Setupaknownslopesomewhere,suchasyourhomeoroffice,tofrequentlychecktheaccuracyofyourinstrument.
3-14 Determining Slope
NOTES
Locations To Measure Slope From
KEY TERMS
The____________________________ispartoftheonlotsewagedisposalsystem.Itistheaggregate-filledareawheretheeffluentseepsintothesoil.
Inasandmound,the_______________ofthe_____________istheedgeofthesoilmaterialthatisplacedaroundthesand.Thebermholdsthematerialinplace.
3-15Determining Slope
NOTES
1) IN-GROUND SYSTEM
Foranin-groundsystem,slopeismeasuredfromextremityofaggregateontheupslopesidetotheextremityofaggregateonthedownslopeside.
PROPOSED IN-GROUND SYSTEM
3-16 Determining Slope
NOTES
2) ELEVATED SYSTEM
Foranelevatedsystem,slopeismeasuredfromextremityofthebermontheupslopesidetoextremityofthebermonthedownslopeside.Thesteepertheslope,usuallythelargertheberm.
PROPOSED ELEVATED SYSTEM –
Gradual Slope
PROPOSED ELEVATED SYSTEM –
Steep Slope
3-17Determining Slope
NOTES
3) MEASURE THE STEEPEST SLOPE
Iftheslopevaries,differs,orchangesoveralargeportionoftheareabeingmeasured,thenthesteep-est,ormaximum,slopemustbeused.
Inthediagrambelow,16percentistheslopeusedbecauseitisthesteepest,ormaximum,slopeintheareabeingconsidered.
Maximum Slope
25percentisthemaximumslopeforasitetobeap-provedforanonlotsewagedisposalsystem.Whentheslopeisclose,accuracyisveryimportant.Makesuretheslopeiscorrectlymeasuredduringthesesituations.
Formoreinformation,youcanconsultpageI-A-2oftheslopesectionofthefieldmanualthatlistsspe-cificsloperequirementsforconventionalsystems.