How to Estimate Excavation in Earthworks for Civil Engineers

Steps in Excavation Work in Construction

Excavation is not just digging. It follows a step-by-step sequence:
1. Site Clearing – This clears around the work area and defining the excavation limits.
2. Setting Out – Surveying the surroundings and mark the boundaries.
3. Excavation to Design Depth – Calculating the depth that will be excavated based on the plan, then will start digging.
4. Soil Disposal – Excess soil is either being hauled off-site or stockpiled for reuse like backfilling.
5. Compaction – in some cases, the bottom of the excavation is compacted to improve bearing capacity.

In this lesson, we’ll learn how to calculate the depth that we need to excavate.

ISOLATED FOOTING EXCAVATION

Step 1: Determine how many footing of the same size

F1: 7 Footings
F2: 2 Footings

Step 2: Compute for the volume that will be excavated for the same footings.

$L \times W \times H$

Where:
L = Length of the footing + 2 (0.25 m)
W = Width of the footing + 2 (0.25 m)
H = Height from the bottom of the footing to the N.G.L. + (0.1 m)

Footing 1:

$L= 1500 + 2(250) = 2000$
$W = 1500 + 2(250) = 2000$
$H = 1300 + 100 = 1400$

$L \times W \times H$
$2m \times 2m \times 1.4$
$=5.6 m^3$

Footing 2:

Footing excavation earthworks construction

$L = 1200 + 2(250) = 1650$
$W = 1200 + 2(250) = 1650$
$H = 1300 + 100 (gravel bed) = 1400$

$L \times W \times H$
$1.65m \times 1.65m \times 1.4 m$
$=3.82m^3$

Step 2: Multiple the volume to the number of footing of the same lengths
$F1: 7 footings \times 5.6 m^3 = 39.2 m^3$
$F2: 2 footinga \times 3.82 m^3 = 7.64 m^3$