1. Photos placed in horizontal position
with even amount of white space
between photos and header
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin
Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND NO. 2014-15977PE
Applying Engineered Safety Approach in
Project Planning
Proposed Project: Ground Subsidence Repair
Darren Wood

2. Outline
 Project Introduction and Objectives
 Condition Assessment
 Site Survey
 Engineering Evaluation of Causes and Impacts
 Develop Engineering Solution
 Risk Assessment and Mitigation
 Analyze Hazards Associated With Work
 Identify Methods to Control Hazards to Reduce Risk
 Develop Project Proposal
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3. Project Introduction
 Asphalt is subsiding at the south corner of the chemical
storage yard located near Building C943
 The area is adjacent to 3125 gallon capacity above-ground
liquid nitrogen tank and along MANTL perimeter wall
 Asphalt pavement has been repaired before but subsidence
continues to occur
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4. Project Objectives
 Investigate underlying
causes for the ground
subsidence
 Develop practical
engineering solution to
correct the problem
 Apply engineered-safety
principles
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Schematic Site Plan

5. Condition Assessment
 Area of approximately 11
feet by 28 feet contains a
single ground squirrel
tunnel entrance and six
subsidence holes.
 Ground squirrel tunnel
entrance next to tank pad
 Subsidence holes 1-3 feet in
length, 6-15 inches wide, and
2-8 inches deep
 Numerous ground squirrel
tunnels in surrounding field
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LN
Tank

6. Engineering Evaluation of Causes
 Likely Causes of Ground
Subsidence
 Collapsing ground squirrel
holes
 Rampant squirrel activities in
surrounding dirt field
 Decaying tree roots leaving
openings that are collapsing
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Tunnels going
Under MANTL
Perimeter wall

7. Engineering Evaluation of Impacts
 Potential Impacts of Further Deteriorating Condition
 Programmatic Impacts
 Temporary loss of mission capability dependent on liquid nitrogen
 Safety risks due to settlement of LN tank foundation
 Tripping injuries
 Tank or pipeline failure
 Struck-by/fall-upon injuries
 BLEVE (boiling-liquid expanding vapor explosion). Liquid nitrogen density
0.8g/mL, nitrogen gas density 1.25g/L (that’s an expansion ratio of 694)
 Cryogenic exposure (liquid nitrogen boils at −196°C)
 Frostbite
 Cryogenic burns
 Pulmonary edema
 Eye damage
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8. Develop Engineering Solutions
 Research bio-friendly ground squirrel control alternatives
 Interview subject matter experts in environmental and zoology fields
 Talked to Robert Holland, SNL/CA Environmental Technical Professional
 Emailed Eric Krussman, San Francisco Zoo Assistant Curator
 Internet research from pest control places, gardening groups, and
government sites
 Study engineering methods to repair subsiding area
 Talked to Anne Yang, SNL/CA Strategic Planner
 Research engineering and construction techniques for excavation and
backfill
 Recommended engineering solution
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9. Proposed Engineering Solution
Phase 1: Set barrier fence to block migration of ground squirrels
into storage yard
 Capture the existing ground squirrels
 Dig a trench around the MANTL wall and install galvanized
mesh screening to prevent ground squirrel access
 Ground squirrel burrows can go as deep as five feet in places, but a
four foot trench to install a four foot wide mesh should suffice as a
deterrent
 Entire wall not needed, only 50 foot length around problem area
 Galvanized mesh available at most hardware stores as a 4 foot wide
roll and is strong enough to keep squirrels out but won’t rust or
otherwise degrade for several years
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10. Proposed Engineering Solution
Phase 2: Repair asphalt pavement
 Remove asphalt pavement and excavate 4 feet down
 Install controlled low-strength concrete fill (flowable concrete
slurry) to fill the excavated area.
 Advantages of controlled low-strength concrete
 Adequate strength to resist settling
 Self-compacting, starts as a liquid, thoroughly filling voids and cracks
 More efficient installation than compacted gravel fill
 Cost competitive with gravel fill
 Improves worker safety by reducing possible cave-ins
 Lay down a new asphalt surface over fill
 Advantages of asphalt
 Less expensive than concrete
 Matches surrounding chemical storage yard 10

11. Analyze Hazards Associated With
Work
 Interview subject matter experts in safety
 Mike Roth SNL/CA Industrial Hygienist
 John Hostak SNL/CA Safety Engineer
 Hazard Analysis
 LN release
 Construction work could damage piping or tank, causing leakage or failure
 Ground movement
 Excavating and trenching next to LN tank and MANTL perimeter wall
could cause soil to shift into excavated area
 Could cause collapse or shifting of LN tank and/or MANTL perimeter wall
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12. Identify Methods to Control Hazards
to Reduce Risk
Risk Risk Mitigation Measures
Liquid nitrogen release Empty LN tank during asphalt
pavement repair
Tank shift or fall Provide temporary brace to LN tank
and shore up excavated area
MANTL Wall shift or collapse in work
area
Provide temporary support of MANTL
perimeter wall during trench
excavation
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13. Develop Project Plan
 Develop Project Charter
 Scope of work- proposed engineering solution
 Justification- engineering evaluation of impacts
 Risk mitigation plan- methods to control hazards
 Budget needs and optimal project schedule:
 Estimated project cost= $100,000
 Optimal schedule FY 15
 Next step: Incorporate into FY 15 Funding Request
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14. Questions?
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