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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 RepairDarren Wood

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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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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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Project Objectives

Investigate underlying causes for the ground subsidence

Develop practical engineering solution to correct the problem

Apply engineered-safety principles

Schematic Site Plan

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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

LNTank

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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

Tunnels goingUnder MANTLPerimeter wall

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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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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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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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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

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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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Identify Methods to Control Hazards to Reduce Risk

Risk Risk Mitigation MeasuresLiquid nitrogen release Empty LN tank during asphalt

pavement repairTank shift or fall Provide temporary brace to LN tank

and shore up excavated areaMANTL Wall shift or collapse in work area

Provide temporary support of MANTL perimeter wall during trench excavation

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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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Questions?