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Gladding, McBeana division of PABCO Building Products, LLC.
Anatomy of a Pipeline Failure
Anatomy of a Pipeline Failure
Who are the Players?Owner - CityDesign EngineerGeotechnical Engineer Pipe SupplierManhole SupplierContractorConstruction Project Manager
Construction InspectorConstruction Manager
Different Geotechnical firm who provided Construction Backfill/Earthwork Observation/Testing
Pipeline
2,450 linear feet of 27-inch Vitrified Clay Pipe2,700 linear feet of 30-inch Vitrified Clay Pipe
12,550 linear feet of 42-inch Vitrified Clay Pipe13 to 20 feet of cover23 Manholes spaced at 800 feet (typ), cast in place (including 2 junction structures)
Contract Values
$1,785,320 Purchase of Vitrified Clay Pipe$2,575,120 Construction Contract$4,360,440 Total
$1,274,100 Manhole Repair Contract46% of original construction contract
Project SpecificationsVitrified Clay Pipe Specified and prepurchased by the City12-inches of crushed stone under the pipe barrelFull Geotextile EncasementCast-in-place Manholes Acceptance testing witnessed
History
Pipeline installed during summer of 2001December 2001, entire pipeline tested and accepted by construction management teamFebruary 2002, City found pipeline full of water.
Also discovered some manholes leakingThen found several cracked pipe sections
What Now??
MeetingsMeetingsLets repair the problem
Pipeline Repairs
April/May 2002, City started repairs.During this process found a number of other issues.City asked contractor to fully evaluate pipeline condition:June 2002 the contractor reported finding:
34 individual pipe sections leaking (1% of pipe segments installed)No Manhole issues
Oh No – Now what??
More repairs than anticipated
What are our choices??
DesignMaterialsConstruction
Lets look at…
Design &Materials
Fugro West Report – July 2002Observations – based on three repairs
Trench width exceeded design parametersNo (crushed stone) gap observed under the bell (bell hole) Less than the specified 12-inches of bedding One bell observed placed directly on native materialBedding material (crushed stone) not consolidated to a “non-yielding condition” as per specificationsNo evidence of erosion of trench walls or bottom observed.
Fugro West Report – July 2002Pipe Test
Four sections of 42-inch diameter pipe removed from the job site and testedAll exceeded specificationsOne tested to failure
18% over specification
Fugro West Report – July 2002Design Review
Reviewed design method, reviewed design & reviewed: earthquake ground motions; groundwater effects; hydrostatic forces and buoyancy; expansive soils; other loadsFound the calculated design safety factor for the 42-inch pipe was 1.53 to 1.80Found the actual safety factor at location of pipe failure was 2.09
Fugro West Report – July 2002Conclusions
“ The design approach employed a standard widely used method where reasonable to conservative design parameters were used”The pipe failures occurred in various locations including areas where the computed factors of safety were in excess of 1.5. For those conditions, small incremental loads alone should not have caused pipes to crack.”
Fugro West Report – July 2002Conclusions continued pg 2
“ The most likely primary causes of, or primary contributors to, distress to the pipe segments are:
The pipe segment bell was placed on the bedding or on the native soil without being “dug out”, and thus carried load that the barrel of the pipe was supposed to carry.The crushed stone pipe bedding was not compacted sufficiently to provide the full design load factor….Trench width was greater than specified in some locations, causing the load on the pipe to be greater than anticipated.”
Options
Now that both the design and materials are validated, lets look at:Construction
A firm was hired to perform a condition assessment of the entire pipeline.
Their findings are:
Condition Assessment - Pipeline
Longitudinal Cracks33 observed
Chips (1-inch or greater)107 observed
Joint spacing (3/4 to 1 1/3-inch)158 observed
Contractor repairs312 observedExamples;
18”L x 3”W x 1”D9”L x 1 ½”W x 1 ½”D
Condition Assessment - Manholes
Defects located on every manhole
No small matter
Let the games beginLawyers hiredPipe experts hired Forensic evaluations performed$$$$
Project forensic photosPipe line repairsManhole barrel jointsManhole – pipe connectionsUnauthorized repairs to manhole – pipe connectionsGrouting of flowline in first barrel section
Pipeline forensic photosPipe line repairsMost repairs associated with manholes
Pipeline forensic photosPipe joint leaksFound to be improper installation
Manhole barrel jointsThe manhole
joints were exposed and examined.
Manhole Joint issuesTwo different joint types used on job site, both in the same manhole.
Manhole Joint issuesRamneck improperly installed
Manhole Joint issuesManhole base installed upside down
Manhole – Pipe ConnectionsBoots improperly installedUnauthorized repairs
Manhole – Pipe ConnectionsBoots improperly installed
Manhole – Pipe ConnectionsUnauthorized repairs
Manhole Improper grouting of first flow channel
PVC liner not installed properlyNo consolidation of concrete
Pipeline issues identifiedCracks
Overload TypeNo bell hole
JointsBedding material found inside joint
Manhole issues identifiedManhole joint issues:
PVC liner improperly installed and leakingTwo different (barrel) joint types used on same manhole.Ramneck improperly installedManhole base installed upside down
Manhole – pipe connectionsBoots improperly installedUnauthorized repairs performed
Manhole flowline improperly grouted
ConclusionsDesign
ConservativePipe
Materials exceeded all specificationsConstruction
Manholes improperly installedPipe improperly installed
Construction inspection/testingImproper certification of pipe & manhole acceptance test results
Lessons LearnedVerify experience of consultantsProvide independent verification of critical items
Pipeline air testManhole vacuum test
Listen to warnings from team members
Any suggested design change?Yes – manhole connections
Use a VCP Bell and grout in place instead of the rubber boot
differential settlementASTM Standards, hydrostatic capabilities
“BLESSED ARE THE TROUBLE MAKERS,
FOR THEY SHALL PREVENT LETHERGY.”
Amster HowardJune 2008
Any questions?