Differential LevelingA.Importance of Leveling1. The determination of elevations is called leveling2. Measuring relative elevations changes is a comparatively simply process 3. Precise and accurate control of relative elevations are critical to most construction projectsDifferential LevelingB. The Level1. A level consist of a highpo!ered telescope2. The level is attached to a spirit or "u""le level that #eeps the line of sight of the telescope hori$ontalDifferential Leveling3. Level Instrument%.&'Differential LevelingLevel Instrument%.('%.&&%.&1%.&2%.&3%.&%Differential LevelingC. Definitions)tarting point*elevation 1''.'' ft+Point APoint ,,) - (.32 ft ./ - 1'(.32 ft 0) - 3.1' ft1levation - 1'3.22 ftDifferential LevelingDefinitions1. Bench mark (BM)relatively permanent point of #no!n elevation0) - 3.1' ft)tarting point*elevation 1''.'' ft+Point APoint ,,) - (.32 ft ./ - 1'(.32 ft 0) - 3.1' ft1levation - 1'3.22 ftDifferential LevelingDefinitions. Backsight (B!)a sight ta#en to the level rod held at a point of #no!n elevation *either a ,M or TP+)tarting point*elevation 1''.'' ft+Point APoint ,,) - (.32 ft ./ - 1'(.32 ft 0) - 3.1' ft1levation - 1'3.22 ftDifferential LevelingDefinitions3. "eight of instrument ("I)the elevation of the line of sight of the telescope)tarting point*elevation 1''.'' ft+Point APoint ,,) - (.32 ft ./ - 1'(.32 ft 0) - 3.1' ft1levation - 1'3.22 ftDifferential LevelingDefinitions#. $oresight ($!)a sight ta#en on any point to determine its elevation)tarting point*elevation 1''.'' ft+Point APoint ,,) - (.32 ft ./ - 1'(.32 ft 0) - 3.1' ft1levation - 1'3.22 ftDifferential LevelingD. Computation of %levations%levation 1&&.&&B!1.'#Point,M11levation ,) ./ 0)BM112.(% 112.(% 1''.''1. ,) 2 1levation- ./Differential LevelingComputation of %levations%levation 1&&.&&B!1.'#$!3.11Point,M1TP11levation ,) ./ 0)T(1BM112.(% 112.(%3.11 1'3.&32. ./0) - 1levation1''.''Differential LevelingComputation of %levations%levation 1&&.&&B!1.'#$!3.11Point,M1TP11levation ,) ./ 0)T(1BM112.(% 112.(%3.11 1'3.&3B!1&.))1'.44 12'.%11''.''Differential LevelingComputation of %levations%levation 1&&.&&B!1.'#$!3.11Point,M1TP11levation ,) ./ 0)T(1BM112.(% 112.(%3.11 1'3.&3B!1&.))1'.44 12'.%1$!.*'T(

2.&( TP2115.4&1''.''Differential LevelingComputation of %levations%levation 1&&.&&B!1.'#$!3.11Point,M1TP11levation ,) ./ 0)T(1BM112.(% 112.(%3.11 1'3.&3B!1&.))1'.44 12'.%1$!.*'T(

2.&( TP2115.4&B!+.,3.52 125.&51''.''Differential LevelingComputation of %levations%levation 1&&.&&B!1.'#$!3.11Point,M1TP11levation ,) ./ 0)T(1BM112.(% 112.(%3.11 1'3.&3B!1&.))1'.44 12'.%1$!.*'T(

2.&( TP2115.4&B!+.,3.52 125.&5BM

$!3.1&,M23.1' 12%.%51''.''Differential LevelingComputation of %levations%levation 1&&.&&B!1.'#$!3.11Point,M1TP11levation ,) ./ 0)T(1BM112.(% 112.(%3.11 1'3.&3B!1&.))1'.44 12'.%1$!.*'T(

2.&( TP2115.4&B!+.,3.52 125.&5BM

$!3.1&,M23.1' 12%.%51''.''Differential LevelingComputation of %levations3. 6hange in elevation summation of the "ac#sight and the foresight then su"tract-33.# .).,,6hange in elevation - 33.# .).,, /#.#,Point,M1TP11levation ,) ./ 0)12.(% 112.(%3.11 1'3.&3 1'.44 12'.%12.&( TP2115.4& 3.52 125.&5,M23.1' 12%.%51''.''Differential Leveling%. The initial 0acksight (B!) is ta#en to a point of #no!n elevation&. The "ac#sight reading is added to the elevation of the #no!n point to compute the height of the instrument ("I)(. The level may "e moved to a temporary point called a turning point (T()5. The elevation of a point is the height of the instrument ("I) minus the foresight ($!)Differential LevelingComputation of %levations . 1roup (ro0lemPrepare a set of level notes for the survey illustrated "elo!.7hat are the elevations of points TP1 and TP28B!1.,$!#.+1T(1BMB!.33$!'.1,T(

%levation 3*'.')Differential LevelingComputation of %levations . 1roup (ro0lemB!1.,$!#.+1T(1BMB!.33$!'.1,T(

%levation 3*'.')1.25 3&5.3&%.31 3&3.'% 2.33 3&&.35(.15Point,M1TP11levation ,) ./ 0)TP23%3.2'3&(.(423.(' 11.'4 5.%4Differential Leveling%. Common Mistakes1. Misreading the rodreading 3.&% instead of 3.%&2. Moving the turning pointuse a !ell9defined TP3. 0ield note mista#es!or# !ithin your group to chec# you records%. Mista#es !ith e:tended rodma#e sure the leveling rod is fully e:tendedDifferential LevelingCommon Mistakes&. Level rod not vertical(. )ettling of leveling rod5. Leveling rod not fully e:tended or incorrect length4. Level instrument not level3. /nstrument out of adjustment1'. 1nvironment!ind and heatDifferential Leveling$. !uggestions for 1oo2 Leveling1. Anchor tripod legs firmly2. 6hec# the "u""le level "efore and after each reading3. Ta#e as little time as possi"le "et!een ,) and 0)%. Try to #eep the distance to the ,) and the 0) e;ual&. Provide the rodperson !ith a level for the rodDifferential Leveling1nd of Differential Leveling