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ABTECN4: Specs Writing & Construction Estimate
Construction Estimate
LESSON 2: Estimating Excavation
Estimating excavation works is considered one of the most challenging items in construction estimate. This is due
to the large number of variables that need to be considered, which requires cautious judgment and experience on
the part of the estimator. The estimator must take into account several factors to determine the size of excavation
and best method to do such. This includes the type of soil, drainage, water level, access of men & machines to the
work area, the materials to be moved to and from the site, among many others
There are two (2) types of excavation works. One is called the building excavation, while the other is site
excavation. Building excavation is the one required for building foundation while site excavation is one required for
grading (shaping the ground outside the building), roads, and paving. There are many components that appear on
the take-off for excavation. This includes the following:
1. Building Excavation
a. Bulk excavation for basements
b. Footing excavation
c. Pit excavation
d. Backfill
e. Vapor barrier
f. Sheeting & shoring
g. Dewatering
2. Site Excavation
a. Clearing & grubbing
b. Stripping and stockpile topsoil
c. Site cut & fill
d. Fine grading & compact
This estimate lesson, however, shall focus only on bulk excavation for basement & footings, site hauling and
clearing. Thus, the primary consideration to take into account in this item estimate is the soil type and property. This
is so as such affects its stability and slope during and after excavation. Hard and compact soil can be firm and
stable there wouldn't be the need to use metal or wood forms for shoring. For softer soils, however, there need to
have the proper slope of excavation to prevent the soil from possibly caving in and causing accidents to workers on
the excavation site.
Ordinary, dry earth would have a slope (rise over run) of 1 : 2.8 to 1 : 1 or an angle of repose of 20 to 40°, while
gravel would normally be sloped at 1:1 or 45°. It should be noted that greater slope is, the more materials there are
to be removed. Another factor affecting excavation and its cost is expansion of soil. Soil expands 10% to 25% more
than its original volume. On the other hand, soil shrinks to an average of 10% when compacted, such as for
backfilling operation. Light soils, like sand, take a 20 - 35° slope with the horizontal when dry, and up to 40° when
wet while hard soils can be almost vertical in slope. The table below shows the corresponding slope for the different
material type.
Table 2.01: Data Information on Various Soil Types
Approximate Slope
(a / b)
Angle of Repose*
(c, Degrees)
Ave. Weight
3
(Kg per m )
Sand, dry
1.00 : 2.80 to 1.00 : 1.40
20 to 35
1 604.00
Sand, moist
1.00 : 1.75 to 1.00 : 1.00
30 to 45
1 684.20
Sand, wet
1.00 : 2.80 to 1.00 : 1.20
20 to 40
1 844.60
Earth, ordinary, dry
1.00 : 2.80 to 1.00 : 1.00
20 to 45
1 444.00
Earth, ordinary, moist
1.00 : 2.10 to 1.00 : 1.00
25 to 45
1 444.00
Earth, ordinary, wet
1.00 : 2.10 to 1.00 : 1.75
25 to 30
1 764.40
Gravel
1.00 : 1.75 to 1.00 : 0.90
30 to 48
1 884.70
Gravel, sand, and clay
1.00 : 1.80 to 1.00 : 1.30
20 to 37
1 724.30
Type of Material
* Angle of Repose - the maximum angle with the horizontal at which a mass of material, as in a cut or embankment, will lie
without sliding
National University
COLLEGE OF ARCHITECTURE
ABTECN4: Specs Writing & Construction Estimate
I.
Building Excavation
The estimate for building excavation starts off with first identifying the total substructure or foundation boundary,
area, and volume to be excavated. This is followed by determining how far beyond the building foundations the
excavation will take place to provide sufficient distance between the toe of the slope of excavation and the
foundation walls for carpenters to work on in order to erect forms for the building foundation like walls, footings,
etc. Most commonly, said distance should not be less than 0.90m (3 ft.), nor more than 1.80m (6 ft.).
Meanwhile, if excavation is large or deep enough, a ramp may be required so that the excavating equipment
and trucks can go in and out of the excavated area.
Sample Problem No.1:
Figure 01: Building Excavation Plan
Figure 02: Building Excavation Elevation
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COLLEGE OF ARCHITECTURE
ABTECN4: Specs Writing & Construction Estimate
Given:
1. Building Area:
LxW
10.00 x 7.00m
2. Worker Space:
1.00m all around
3. Depth of Excavation:
1.50m
4. Slope of Excavation:
1 : 1 (1.50m : 1.50m)
Solution:
Step 1: Obtain the length (LT) and width (WT) of top of excavation
LT = Building Length + Space for Workers (2 sides) + Excavation Slope (2 sides)
LT = 10.00m + (1.00m x 2) + (1.50m x 2)
LT = 15.00m
WT = Building Width + Space for Workers (2 sides) + Excavation Slope (2 sides)
WT = 7.00 + (1.00m x 2) + (1.50m x 2)
WT = 12.00m
Step 2: Obtain the length (LT) and width (WT) of bottom of excavation
LB = Building Length + Space for Workers (2 sides)
LB = 10.00m + (1.00m x 2)
LB = 12.00m
WB = Building Width + Space for Workers (2 sides)
WB = 7.00 + (1.00m x 2)
WB = 9.00m
Step 3: Compute for the average length (LA) and width (WA) of excavation
LA = (LT + LB) / 2
LA = (15.00 + 12.00) / 2
LA = 13.50m
WA = (WT + WB) / 2
WA = (12.00 + 9.00) / 2
WA = 10.50m
Step 4: Compute for the total area of excavation (TABE).
TABE = LA x WA
TABE = 13.50 x 10.50
2
TABE = 141.75m
Step 5: Compute for the average volume of excavation (TVBE)
TVBE = AAVE x Depth of Excavation
TVBE = 141.75 x 1.50
3
TVBE = 212.625m
3
Answer: Total volume of building excavation (TVBE) is 212.625 m .
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II. Footings
Excavation for continuous wall footings or interior column footings are calculated in the same manner as for
building general excavation. However, if the soil conditions permit, excavation can be to the neat concrete lines
and the soil used as the form area. Excavation can be either by machine or hand, with firm soils being cut into
the exact concrete line and thus save concrete forms.
Sample Problem No.2:
An activity hall 10.00m x 15.00m is to be built with the foundation plan as illustrated below. Compute for the
required excavation works on wall and column footings.
A. Column Footing
1. Referring to Table 2.2 below, multiply the length of footing by its width and depth to get the volume of
excavation of each footing in cubic meters.
2. Add all the individually computed volumes of excavation for each column footing to get the total
volumes of excavation for column footings (TVCF).
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Table 2.02: Column Footing (CF) Data
CF
fL
fW
fD
Excavation Volume
(CF)
CF1
1.80m
1.80m
0.60m
1.944
CF2
1.20m
1.20m
0.60m
0.864
CF3
1.20m
1.20m
0.60m
0.864
CF4
1.80m
1.80m
0.60m
1.944
CF5
1.80m
1.80m
0.60m
1.944
CF6
1.20m
1.20m
0.60m
0.864
CF7
1.20m
1.20m
0.60m
0.864
CF8
1.80m
1.80m
0.60m
1.944
Total Excavation Volume for CF(TEVCF)
Note:
11.232m3
Use at least three (3) to four (4) decimal places in computation for most accuracy.
B. Wall Footing
1. Compute for the excavation volume of the given wall footings. Multiply its length by its width and its
3
depth to get the value in cubic meters (m ).
2. Add all the individually computed volumes of excavation for each wall footing to get the
volumes of excavation for wall footings (TVWF).
total
Table 2.03: Wall Footing (WF) Data
WF
fL
fW
fD
Excavation
Volume (WF)
WF1
4.60m
0.60m
0.60m
1.656
WF2
4.20m
0.60m
0.60m
1.512
WF3
4.60m
0.60m
0.60m
1.656
WF4
8.80m
0.60m
0.60m
3.168
WF5
4.60m
0.60m
0.60m
1.656
WF6
4.20m
0.60m
0.60m
1.512
WF7
4.60m
0.60m
0.60m
1.656
WF8
8.80m
0.60m
0.60m
3.168
Total Excavation Volume for WF (TEVWF)
15.984m3
C. Total Excavation Volume of Footing (TEVF) for Column & Wall Footing
TEVF = TEVCF + TEVWF
TEVF = 11.232 + 15.984
3
TEVF = 27.216m
III. Backfill
Sample Problem No. 1
Step 1: Compute for the total volume of building foundation (TVBF).
TVBF = L x W x Depth
TVBF = 10.00 x 7.00 x 1.50
3
TVBF = 105m
Step 2: Compute for backfill volume (VBACK) by deducting building foundation (VBF) from the total volume
of building excavation (VAVE).
VBACK = TVBE - TVBF
VBACK = 212.625 - 105
3
VBACK = 107.625m
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Sample Problem No. 2
Step 1: Compute for the volume of the given column footings. Multiply the length and width of a given
column footings by its thickness, and add it to the column volume, with height measured from the
top base of the footing to the natural grade line level.
Step 2: Compute the total volume of column footings by adding up all individually computed volumes of
column footings, or multiplying a given volume of column footing by its total number if such are the
same type of columns.
Step 3: Compute for the total volumes of wall footings using a similar pattern / procedure in computing the
total volume of column footings. For this, add the volume of CHB walls laid below grade level.
Step 4: Compute for the total volume of backfill works. Add the total volume of column and wall footings.
Minus said computed value from the total volume of excavation for footing (TEVF).
cH = Footing Depth (fD) - Footing Thickness (fT)
cH = 0.60m - 0.250m
cH = 0.350m
Table 2.04: Total Volume of Column Footing (TVCF)
CF
fL
fW
fT
Footing
Volume
(fV)
cL
cW
cH*
Column
Volume
(cV)
CF1
1.80m
1.80m
0.250m
0.810
0.60m
0.60m
0.35
0.126
CF2
1.20m
1.20m
0.250m
0.360
0.40m
0.40m
0.35
0.056
CF3
1.20m
1.20m
0.250m
0.360
0.40m
0.40m
0.35
0.056
CF4
1.80m
1.80m
0.250m
0.810
0.60m
0.60m
0.35
0.126
CF5
1.80m
1.80m
0.250m
0.810
0.60m
0.60m
0.35
0.126
CF6
1.20m
1.20m
0.250m
0.360
0.40m
0.40m
0.35
0.056
CF7
1.20m
1.20m
0.250m
0.360
0.40m
0.40m
0.35
0.056
CF8
1.80m
1.80m
0.250m
0.810
0.60m
0.60m
0.35
0.126
Total fV
4.680m3
Total cV
0.728m3
Total Volume of Column Footing (TVCF) = fV + cV
= 4.680 + 0.728
= 5.408m3
Table 2.05: Total Volume of Wall Footing (TVWF)
Wall Footing Volume (wfV)
Foundation Wall Volume (fwV)
WF
wfL
wfW
wfT
wfV (m3)
FW
fwL
fwT
fwD
fwV (m3)
WF1
4.60m
0.60m
0.200m
0.552
W1
4.60m
0.15
0.35
0.2415
WF2
4.20m
0.60m
0.200m
0.504
W2
4.20m
0.15
0.35
0.2205
WF3
4.60m
0.60m
0.200m
0.552
W3
4.60m
0.15
0.35
0.2415
WF4
8.80m
0.60m
0.200m
1.056
W4
8.80m
0.15
0.35
0.4620
WF5
4.60m
0.60m
0.200m
0.552
W5
4.60m
0.15
0.35
0.2415
WF6
4.20m
0.60m
0.200m
0.504
W6
4.20m
0.15
0.35
0.2205
WF7
4.60m
0.60m
0.200m
0.552
W7
4.60m
0.15
0.35
0.2415
WF8
8.80m
0.60m
0.200m
1.056
W8
8.80m
0.15
0.35
0.4620
Total wfV
5.328
Total fwV
2.331
Total Volume of Footing (TFV) = TVCF + TVWF
Total Volume of Footing (TFV) = cV + fV + wfV + fwV
= 4.680 + 0.728 + 5.328 + 2.331
TFV = 13.067m3
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Step 5: Compute for the total backfill volume (TBV). Minus total volume of footing (TVF) from the total
excavation volume of footing (TEVF).
Total Backfill Volume (TBV) = TEVF - TVF
= 27.216 - 13.067
TBV = 14.149m3
IV. Manpower
Table 2.06: Productivity Ratio Table
Productivity Ratio
Man-Hour / Unit
Unit
Manual Excavation (Structural)
6.00
Man-hour / m3
Machine Excavation (Structural)
0.50
Man-hour / m3
Backfill (Manual)
5.00
Man-hour / m3
Backfill (Machine)
2.00
Man-hour / m3
Hauling of Soil (Manual)
1.00
Man-hour / m3
Disposal of Soil (Manual)
1.69
Man-hour / m3
Gravel Fill
2.07
Man-hour / m3
A. Excavation
3
1. Multiply the total volume of excavation works (in m ) by the production rate for such works. Presume
the use of manual excavation.
Sample Problem No. 1:
Manpower for Excavation = TVBE x Manual Excavation Rate
3
3
Manpower for Excavation = 212.625 m x 6.00 Man-hour / m
Manpower for Excavation = 1,275.75 Man-hours
Sample Problem No. 2:
Manpower for Excavation = TEVF x Manual Excavation Rate
3
3
Manpower for Excavation = 27.216 m x 6.00 Man-hour / m
Manpower for Excavation = 163.296 Man-hours
B. Backfill
3
1. Multiply the total volume of backfill works (in m ) by the production rate for such works. Presume the
use of manual excavation.
Sample Problem No. 1:
Manpower for Backfill = VBACK x Manual Backfill Rate
3
3
Manpower for Backfill = 107.625 m x 5.00 Man-hour / m
Manpower for Backfill = 538.125 Man-hours
Sample Problem No. 2:
Manpower for Backfill = TBV x Manual Backfill Rate
3
3
Manpower for Backfill = 14.149 m x 5.00 Man-hour / m
Manpower for Backfill = 70.745 Man-hours
C. Hauling
1. Except for excavations works which will involve cut & fill, the volume of soil to be hauled or removed
from site is equivalent to the volume of building foundation and footings. Multiply the total volume of
building foundation and footing by the production rate of such works to obtain total manpower.
Sample Problem No. 1:
Manpower for Hauling = TVBF x Manual Hauling Rate
3
3
Manpower for Backfill = 105.00 m x 1.00 Man-hour / m
Manpower for Backfill = 105 Man-hours
Sample Problem No. 2:
Manpower for Hauling = TVF x Manual Hauling Rate
3
3
Manpower for Backfill = 13.067 m x 1.00 Man-hour / m
Manpower for Backfill = 13.067 Man-hours
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D. Disposal
1. Except for excavations works which will involve cut & fill, the volume of soil to be hauled or removed
from site is equivalent to the volume of building foundation and footings. Multiply the total volume of
building foundation and footing by the production rate of such works to obtain total manpower.
Sample Problem No. 1:
Manpower for Disposal = TVBF x Manual Disposal Rate
3
3
Manpower for Disposal = 105.00 m x 1.69 Man-hour / m
Manpower for Disposal = 177.45 Man-hours
Sample Problem No. 2:
Manpower for Disposal = TVF x Manual Disposal Rate
3
3
Manpower for Disposal = 13.067 m x 1.69 Man-hour / m
Manpower for Disposal = 22.083 Man-hours
V. References:
http://www.umich.edu/~cee431/Download/EstExmpl/EstExmpl_Excavation_TakeOff.pdf
https://civilblog.org/2015/11/20/how-to-compute-volume-of-excavation-work-on-site/
https://theconstructor.org/practical-guide/rate-analysis-of-excavation-in-earthwork/9617/
https://philconprices.com/2018/09/philippine-manpower-and-equipment-productivity-ratio/
https://www.youtube.com/watch?v=86BFvJdcUIY
https://www.youtube.com/watch?v=oVW6LuYd6A8
https://www.youtube.com/watch?v=fuUp0NUxg9g