Page 52 - Pipeline Rules of Thumb Handbook

Construction 39

DITCHING

How many cubic yards of excavation in a mile of ditch?

.
Multiply the width in inches by the depth in inches by 1.36; 12 ¥ 30 1 36 = 490 cubic yards per mile.
¥
the answer is cubic yards per mile.
1
The rule is correct within about / 5 of 1 percent; actually
the errors in depth and width are much greater than this. To
Example. How many cubic yards of excavation in a mile get the cubic yards per 1,000 feet, as in computing rock ditch-
of 12-inch ditch 30-inch deep? ing, use 0.257 instead of 1.36.

Shrinkage and expansion of excavated and compacted soil

Ever notice how the spoil from a ditch occupies a greater Volume of undisturbed clay soil:
volume than the ditch itself? There’s a reason. Excavate sand
and it expands about 10 percent. Ordinary soil expands about 35 ¥ 50 17 5 cu ft per lineal foot of ditch.
.
.
.
=
25 percent and clay expands about 40 percent.
Here’s a summary of the bulk you can expect from Volume of the spoil will be 143 percent of the undisturbed
excavated soil: volume.
Type soil Undisturbed Excavated Compacted
¥
.
.
Volume of spoil = 143 175 = 25 + cu ft per lineal foot.
Sand . . . . . . . . . . . . 1.00 . . . . . . . . 1.11 . . . . . . . . 0.95
Ordinary earth . . . . . 1.00 . . . . . . . . 1.25. . . . . . . . 0.90 Through mechanical compaction this volume can be
Clay . . . . . . . . . . . . . 1.00 . . . . . . . . 1.43. . . . . . . . 0.90 reduced to 15.75cuft.
Example. Find the volume of loose spoil from a pipeline
ditch 42 inches wide, 60 inches deep. The excavation is
through clay.

Ditching and trenching: labor/equipment considerations

In determining the labor crew and equipment spread for 8. When blasting, use extreme caution and protection.
ditching and trenching operations, the following should be 9. Clean up blasted rock to prevent damage to coated pipe.
given consideration should they apply to the particular
project:
Nominal Minimum Normal Minimum
1. Ditching or trenching for buried pipelines should be in Pipe Size Width Coverage
accordance with the following table of minimum width Inches Inches Inches
and coverage for all soil formations.
4 22 30
2. In rock, cut ditches at least six (6) inches wider. 6 26 30
3. If dirt-filled benches are used, ditch should be excavated 8 26 30
10 26 30
deeper to obtain proper coverage.
12 30 30
4. Trench should be excavated to greater depth when 14 32 30
required for proper installation of the pipe where the 16 36 30
18 38 30
topography of the country warrants same.
20 40 30
5. Repair any damage to and maintain existing natural or 24 44 30
other drainage facilities. 30 50 30
36 52 36
6. Do not open ditch too far in advance of pipelay crew.
42 58 36
7. Obtain permits for blasting.