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Chapter 3 Measuring Excavation and Sitework

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Measuring Sitework and Excavation Work Generally Measuring sitework and excavation work is different from measuring most of the other work of a construction project because drawings show very little detail about sitework or excavation. Information about what is currently to be found at the site has to be determined on a site visit. Soil reports may be available for larger projects. Excavation and backfill are measured by bank measure. This leaves quantities unchanged, ignoring swell and compaction factors. The estimator needs to be aware of OSHA safety requirements for excavations.

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Calculating Volumes of Excavation and Backfill for Trenches Trenches are measured using the following formula: –Volume of trench = centerline length x average width x average depth Example: volume of excavation for Figure 3.1: Average depth of wall = (5.0’ + 7.0’) / 2 = 6.0’ Average width of wall: –Width of footing3.0’ –Add for work space 2.0’ (2 x 1’-0”) –Add for cutback 6.0’ (2 x ½ depth) 11.0’ –Volume of trench: = 100’ x 11.0’ x 6’ = 6600 cu. ft. = 244 CY

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Backfill Example Backfill for Figure 3.1: –Backfill volume = excavation volume – footing volume – wall volume = 6600 – (100.0 x 3.0 x 2.0) – (100.0 x 1.0 x 4.0) –(Note that only the portion of the wall that is in the trench is deducted, so the height of wall in the trench is the average trench depth minus 2’-0” for the footing: 6’- 0” – 2’-0” is 4’-0”) = 6600 – 600 – 400 = 5600 cubic feet = 5600 / 27 cubic yards –Backfill volume = 207.4 cubic yards

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Basement Volumes (1 of 2) Basement volume = average length x average width x average depth –Example: Figure 3.2 Basement Excavation Average depth = (5.83’ + 4.17’ + 3.33’ + 4.67’) / 4 = 4.5’ Average length: Building length: 40.0’ Add for work space 2.0’ ( 2 x 1’-0”) Add for cutback 4.5’ (2 x ½ depth of excavation) Total Length = 46.5’

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Basement Volumes (2 of 2) Average width of excavation: Width of building: 28.0’ Add for work space 2.0’ ( 2 x 1’-0”) Add for cutback 4.5’ (2 x ½ depth of excavation) Total Width = 34.5’ Volume of Trench: = 46.5’ x 34.5’ x 4.5, = 7219 cu. ft. = 267.4 CY

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Grid Method of Calculating Cut and Fill Quantities (1 of 2) Calculation by the "grid method" requires a survey of the site showing the elevation of the existing grade at each intersection point on a grid. The elevation of the required new grade is also plotted at each intersection point and from these two elevations the depth of cut or fill is obtained.

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Grid Method of Calculating Cut and Fill Quantities (2 of 2) Cut volumes are calculated separately from fill volumes: –Multiply depth of cut (or fill) at an intersection point by the area “covered” by this point. –Add together all of the individual cut volumes (or fill volumes).

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Rules of Measurement for Excavation and Backfill These are some of the rules of measurement: –Excavations, backfill, and fill material shall be measured in cubic yards “bank measure.” –If different types of material will be encountered in the excavations, each type of material shall be described and measured separately. –Different types of excavations and backfill material shall be classified and measured separately. –An item of disposal of surplus soil shall be measured when there is excess excavated material. (Alternatively, the price of disposal of surplus excavated materials can be included with the excavation price.)

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Takeoff Exercise Takeoff the excavation, backfill, and service trench work for the house example shown on Figure 3.5 drawings. –See Figures 3.6A and 3.6B.

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