Rankin

Question 1

How many trenches were used? Which systems were being replaced?

Answer 1

5 trenches for storm and sanitary pipe replacements

Question 2

what were type material types/sizes of the new pipes?

Answer 2

For Storm - 300mm to 525mm reinforced concrete pipes
For Sanitary - 150mm vitrified clay pipes

Question 3

What were the soil conditions?

Answer 3

Stiff clay and rocks

Question 4

What were the reasons for the pipe failures?

Answer 4

• Insufficient Bedding materials
• Inadequate design (design error) considerations for trench widths
• cracks in the pipes may lead to washout and bending failure in other locations

Question 5

Elaborate on the insufficient bedding material failure

Answer 5

-doesn’t provide adequate uniform support
-capacity could be increased by more than double (from 1.1 to 2.5)
-May have contributed to uneven settlement issues and bending failure
-importance of bedding not conveyed to construction team

Question 6

Elaborate on the inadequate design of the trench width

Answer 6

-If trench widths have been specified, more reliable calculations could be done
-Pipe spacing not specified
Pipes too close may have imposed unexpected load distributions on pipes below beside
Too much additional load may have led to exceeding cracking limit
-Crushing failure of pipes indicate cracking load was exceeded
-Bending failure of pipes due to unequal load distributions
-Proper construction techniques used according to experts retained by MHLP

Question 7

Cracks in the pipe may have led to washouts and bending failures in other locations - caused by????

Answer 7

-Washout failure of pipes due to crushing
-Removal of support, and increased bending in shallower areas

Question 8

What was the issue with the drawings?

Answer 8

-Pipe elevations shown
-location of pipe in trenches not clear
-trench widths not identified
-physical limitations on widths in some locations

Question 9

How does failure differ in deep pipes vs shallow pipes

Answer 9

Deep pipes - longitudinal cracks from crushing
Shallow pipes - transverse cracks from bending

Question 10

What are some solutions to avoid pipe failure?

Answer 10

-designers should clearly define the pipe installation and trench specifications on the construction drawings. If the drawings are unclear, the contractor should clarify the information with the designer
-The designer should ensure that the trench is widen enough for compaction equipment to fit into the trench.
-contractor should use jumper jack to compact trench fill
-compact in lifts

Question 11

what were some causes of the listowel collapse?

Answer 11

• lamination thicknesses were found to be nonuniform throughout their length decreasing the effectiveness of the glue bonding process
• faulty glue bonds due to improper fabricating and glue bonds
• laminated sections contained 10 laminations instead of designed 11