Trench Encasements, Backfill, and Compaction

Question 1

Trench load design for all types of pipe is based on stable bedding and firm foundations.

Answer 1

True

Question 2

Asphalt and concrete overlays will crack and pose future problems if the base of the trench is not stable.

Answer 2

True

Question 3

Full concrete encasement should be three inches on the top, bottom, and sides of the conduits.

Answer 3

True

Question 4

Conduit is subject to temperature rise as the concrete cures. The temperature rise may cause the conduit to expand slightly and this should be compensated for by pouring the concrete from the center of the run, thereby allowing the free end to expand.

Answer 4

True

Question 5

What are the three types of concrete?

Answer 5

Normal
High early strength
Sulfate-resisting

Question 6

High early strength Portland cement should be used for all concrete construction when it is necessary to remove forms and open structures to traffic after the concrete has been placed.

Answer 6

True

Question 7

What is the most common reason for cable failure in direct buried cable?

Answer 7

stones pressing against the cable

Question 8

Backfill should be free of large stones (three inches in any dimension or larger should not be permitted), nor should frozen or muddy soil, organic material, clods, trash, or any object that may cause a void to form in the backfill be allowed.

Answer 8

True

Question 9

To avoid damage to conduits, mechanical tampers should not be used until conduit configurations have been covered with at least 12 inches of hand-tamped backfill.

Answer 9

True

Question 10

Backfilling and tamping alongside conduits should be performed in two-inch thick layers until level with the top of the conduit or duct configurations

Answer 10

True

Question 11

Trenches should be compacted to

Answer 11

90%
Top 6” compacted to 95%

Question 12

Class ? concrete is normally used for conduit base or top protection.

Answer 12

2A

Question 13

Class 2 concrete is normally used for trench encasement and should have a compressive strength at ? seven days after the pour.

Answer 13

2,000 psi

Question 14

The type of Portland cement that may be used during low temperatures is ? .

Answer 14

high early strength

Question 15

Rebar is never used to reinforce an encasement because it will interfere with the electromagnetic field around the cables.

Answer 15

False

Question 16

Because the weight of soil and the possibility of collapsing conduits, backfill should not be allowed to “freefall” more than ? as the trench is being filled.

Answer 16

2’

Question 17

If no mechanical equipment is available to compact the soil in a trench, water compaction is a quick and easy way to ensure the soil is properly compacted.

Answer 17

False

Question 18

Dozers and loaders should not be used to compact the soil unless the conduit or encasements have ? or more of soil cover.

Answer 18

5’

Question 19

When it is necessary to work the concrete between and around closely spaced units, the concrete that is normally used for encasements is Class ? .

Answer 19

2B

Question 20

Sulfate-resisting Portland cement can withstand exposure to severe ? conditions in the soil.

Answer 20

Alkali