Plane Surveying Levelling

Transcription

1 Deprtment of Civil Engineering, UC Introduction: Levelling is mens y which surveyors cn determine the elevtion of points, using other known points s references. Levelling is perhps the most sic of surveying opertions nd forms n importnt fundmentl prt of lmost every surveying project. Equipment: Levelling is crried out y the use of: Spirit Level, often clled n Engineer s Level, nd level rod. he level rod resemles lrge fold-up ruler ut is not ccurtely referred to s such. sics of Levelling: In levelling, the surveyor looks ck (S) to point of known elevtion to determine the elevtion of his or her instrument (EI). he surveyor then looks forwrd () to point of unknown elevtion nd determines the elevtion of tht point using the elevtion of his or her instrument (EI) nd the vlue on the level rod red through the level s telescope. S EI = M Point Once the elevtion of point is determined, tht point cn e used for determining the elevtions of other points. In this wy, the surveyor my lep-frog forwrd, eventully determining the elevtions of points tht re imprcticl from the initil loction, nd developing greter ccurcy y mens of closed trverse. Pge 1 of 8

2 Deprtment of Civil Engineering, UC Smple Levelling rverse: S SII SIII S IS M S IS SI IP 64 S EI = S EI = S EI = M P P M SI SII SIII Pge 2 of 8

3 Deprtment of Civil Engineering, UC Smple rverse Dt: SION S ELEV. INS. IS ELEV. LENGH CORR. EL. M SI to M SI to P SII to P SII to IP from peg test SII to P SIII to P SIII to M Surveyors ccumulte levelling dt in specific fshion. his formt ensures tht ll the relevnt dt is preserved nd none is lost. Clcultions re performed s you go, mking mistkes esier to detect. his is importnt in levelling since turning point my not e mrked to revisit in cse of error. Smple Correction Clcultions: Σ(.S. F.S.) = = m his is the closure error. djust on sis of shot lengths. Σ shot lengths = 168 m (exclude IS s from this) M to P1 = 63 m correction (63/168) = M to P2 = correction (124/168) = M to M = correction (168/168) = Pge 3 of 8

4 Deprtment of Civil Engineering, UC ccurcy in Levelling: In levelling, we wnt to determine the difference in elevtion etween nd. However, Spirit Level my not e perfectly ligned tht is, the telescope my not e ligned correctly with the level plne descried y the level ule. e error ngle, thet error ngle, thet e d d Definitions: d d = length of shot to = length of shot to = ctul reding t = ctul reding t e e = error component t due to telescope mislignme nt = error component t due to telescope mislignme nt = reding t seen through telescope = reding t seen through telescope = e = d e tnθ nd nd = e = d e tnθ = = [ d tnθ ] [ d tnθ ] ( ) + ( d d ) tnθ therefore : = only if [ tnθ = 0] nd/or [ d d ] = 0 Pge 4 of 8

5 Deprtment of Civil Engineering, UC Levelling the Peg est: Setup 1: Equl shot lengths to nd. (ie: d=d) herefore: (-) is ccurte d d ' ' Setup 2: Unequl shot lengths to nd. herefore: ( - ) is not ccurte d' d' = ( ' ' ) + ( d d ) ' ' tnθ tnθ = ( ) ( ' ' ) ( d d ) ' ' θ = tn 1 ( ) ( ' ' ) ( d d ) ' ' Peg est results re reported in degrees nd s slopes. useful wy to express peg test results is in the units of mm (high/low) per m length of shot. hese results re used to determine how creful you must e lncing s nd S s, s well s to correct intermedite shots. (IS s) Pge 5 of 8

6 Deprtment of Civil Engineering, UC Definitions: Here re definitions for some commonly used terms relted to levelling nd sic surveying: erm Definition Plum or Verticl Line the line t ny point on the erth s surfce which follows the grvity vector down towrds the centre of the erth Level Surfce surfce tht is everywhere perpendiculr to verticl lines Horizontl Surfce plne perpendiculr to verticl line nd perpendiculr to level surfce Elevtion the verticl distnce ove or elow given reference level surfce Difference in Elevtion of two he verticl distnce etween the two level surfces contining the points two points Dtum n ssigned or ssumed reference level surfce enchmrk permnent or semi-permnent physicl loction of known or ssigned elevtion Levelling surveying opertion crried out to determine the elevtion of points or to find the difference in elevtion of points Spirit Level/Engineer s Level surveying instrument used to crry out levelling ckshot (S) sighting with level ck to point of known elevtion Foreshot () sighting with level to determine the elevtion of point urning Point point t which you hve estlised n elevtion with nd on which you will susequently tke S Intermedite Shot foreshot to point t which you wnt to know the elevtion ut which will not e used s turning point Peg est Surveying opertion crried out to determine if the levelling ule nd telescope line-of-sight re prllel Elevtion of Instrument (EI) Elevtion of the telescope cross-hirs lncing shots ttempt when doing levelling survey to keep the lengths of nd S t ny given instrument setup s close s possile. Closure Error Difference in elevtion determined from the levelling survey nd the known elevtion of enchmrk. Pge 6 of 8

7 Deprtment of Civil Engineering, UC LEVELLING FIELD EXERCISE Instructions: Ech 4 or 5 person prty will split up into 2 su-prties for this exercise. Ech su-prty of 2 or 3 people will e required to: 1. Determine the length of your pce nd report it. Find how mny degrees of rc re represented y ech grdtion on the level ule. Report in smllest units. 2. Perform peg test to check your instrument. Note the error, nd if it is lrge (> 0.5 mm per 1 m), e creful tht you lnce S's nd 's. DON' DJUS. Ech person in the group should record the results of the peg test in their own field ook. Report the error s cm s/20m s, mm/m, degrees high or low, frction of degrees, nd s degree s, minutes, seconds. 3. Perform level circuits, one y ech memer of the group. Ech circuit must e closed, nd the elevtion of the monuments shown on tht circuit must e determined. Determine the elevtion of individul steps of the designted stircse. 4. Determine the grde of the est sidewlk on Min Mll in the re of your trverse. Reporting: Ech individul's field ook should contin the results of the peg test. Ech should lso contin the field notes, error nd djustment clcultions for tht person s level circuit. During the exercise, once dt from t lest two monuments hs een collected nd recorded in your field ook, you must hve one of the s initil it. his is criticl. Field ooks without initils re not cceptle. rief reminder plese do not record your dt nywhere else except into your fieldook. Equipment Required for ech 2-person su-prty: 1 Engineer s Level 1 level rod. Evlution: Required Elements: Your pce length nd ule degrees Peg est: mesurements, digrm, clcultions, explntion rverse: dt tle, pln digrm with ll informtion, error clcultions, lncing Pge 7 of 8

8 Deprtment of Civil Engineering, UC Chem Eng stirs (& elev of ll stirs) EL = M6 - Klink Stone Rusty Hut M5 - mnhole cover 1. M7 - top of ike rck & ottom of wlking ridge M4 - mnhole cover M5 - mnhole cover Chem Eng stirs M6 - Klink Stone N M4 - mnhole cover ottom of wlking ridge Min Mll M1 - mnhole cover (y stem vents) M7 - top of ike rck CEME 2. M1 - mnhole cover M2 - top of stirs M3 - top of stirs M7 - top of ike rck & ottom of wlking ridge M3 - top of stirs M2 - top of stirs (& elev of ll stirs) Pge 8 of 8