boehm-foundation solutions for new tanks

8/17/2019 Boehm-Foundation Solutions for New Tanks

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www.HaywardBaker.com

Foundation Solutions for New TanksNISTM – 6 th Annual International Aboveground Storage Tank Conference and

Trade Show – September 19, 2013

http://www.nistm.org/index.html


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Presentation Outline

• Some Definitions to set the stage• Design Considerations for Supporting Tanks• Ground Improvement Tank Support Methods

– Stone Columns – Soil Mixing – Wick Drains – Other Improvement

• Conclusions


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• Conclusions


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Above Ground Storage Tanks are not built on thebest sites, so they offer foundation challenges

• Soft Compressible Soils – The load is always there – Differential Settlements offer maintenance challenges – Edge stability can lead to catastrophic consequences

• Mixed bearing soils and placed fills• Foundations available

– –

– – Im prov ed Groun d


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Soft soil beneath the tank can consolidatewith time rendering the tank useless


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Lack of sufficient edge stability can create floorplate failure or buckling of shell


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What types of Ground Improvement methods aretank friendly?

• Stone Columns – Vibro Piers – Aggregate Piers – Geo Piers

• Wick Drains – Vertical Drains (PVDs) – Need surcharge + time – Using the tank for surcharge is risky

• Displacement Piles – CMCs, DeWall Piles, CSCs

•Rigid Inclusions

• Deep Dynamic Compaction• Soil Mixing – Wet and Dry Methods


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Why does Ground Improvement make sense forTanks?

• Offers faster site turnover• Predictable long term performance• Higher Tank Capaci t ies

• Controllable settlements• Usually less expensive than traditional methods• Flexible Designs

• Very good history in the USA as a widely acceptedpractice


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Arrangement of Treatment

• Typically in a square patternunder the floor of the tank

• Replacement ratios from 10to 50%

• Placement of elementsdirectly beneath the shell

• Typically settlement criteriacontrols design


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The Load Transfer Platform Must ProvideUniform Support of the Load from the Tank

• Uses a semi rigid transferplatform

• Designed to limit dishingbetween GI elements

• Crushed rock isfantastic…but sand willdo

• Layers of geogrid toincrease efficiency


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• Conclusions


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Design soil parameters used in the GroundImprovement solution for support of the tank

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Stability check is crucial to the success of thetank foundation project

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Stresses under the tank as well as overlappingstresses from other tanks must be checked


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Numerical model setup to analyze the long termperformance of the Soil Mix support system

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• Conclusions


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Vibro-Replacement or Stone Columns:reinforce the ground with aggregate

Performed in-situ up to 120 feet deep

Effective above and below the water table

Performed using wet top-feed method or drybottom-feed method

Commonly used for seismic responseimprovement

Vibro Systems

Vibrocompaction

Vibro-Replacement StoneColumns

VibroPiers / Aggregate Piers1

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3


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Typical Boring and design from the tank side ofthe project

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• Stone Columnsdesigned to carry 2/3load from tank

• Treatment depths just

into the dense sand• Maximum center

settlement – 4 inches

• Maximum perimetersettlement – 3 inches

• Satisfies all criteria


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Hydrotest Data from Stone Column Supportedtanks…the settlement has been designed


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• Conclusions


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Dry Soil mixing methods are utilized in wettersofter soils or where REM is a problem

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Dry binder materials arepneumatically injected into thesoil during the dry mixingprocess

Bottom up method of soilmixing

There must be adequate soilmoisture for the binders tofully hydrate often limitingdesign strengths


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Dry or Wet Mixing can be used to treat 100%of the soil to form blocks

Dust

Control

BinderShuttle

24-TonTanker

GeofabricSurcharge (2-

ft)

20 ft20 ft


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Dry Soil Mixing at Port Everglades to supporttanks in organic soils


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The Project was contracted as design-build andmet the following criteria

• Design Strength – Allowable bearing capacity of 3,750 lbs/ft 2 for thein-situ soil mass

• Settlement – Planar tilting not to exceed 8 inches (100-ft

diameter), 10 inches (125-ft diameter) across thediameter of the tank

– Center-to-edge dishing not to exceed 5 inches(100-ft diameter), 6 inches (125-ft diameter)

– Out of Plane Differential not to exceed 3/8 inch inan arc length of 30 feet


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Dry mass mixing is working in block cellarrangement working from platform


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Following Mass mixing, the tank foundation canbe completed using ring beams

All tanksconstructed on

shallowfoundations

Foundation

elementsconstructed to

bear directly onsoil mix / or

compacted fill

bearing on soilmix

No relievingplatform is

required


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Following the work and after the tank is built thehydrotest is monitored from start to finish

k h d l d


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Supporting tanks with Deep Mixed Columns andMass Mixing can provide an economical solution

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C i f h S il i h fi


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Construction of the Soilcrete Mat is the first stepin the process

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Mass Mix Cap is thefirst element to beinstalled. Designthickness of 10 feet.

C l i ll d h h h il


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Columns are installed through the soilcrete matto complete the foundation system

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Columns installed in a singlepass depth of 75 feet

Th h k b i d h


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The three new tanks being constructed over thenew structural support system using Soil Mixing

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M i i h T k f ll h i h d i


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Monitoring the Tank to full height duringhydrotest

Final HydrotestHeight of 46’- 3”RingwallSettlement wellwithin APItolerances as wellas floor settlement


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Lots of Happy Tanks!

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– Stone Columns

– Soil Mixing – Wick Drains – Other Improvement

• Conclusions


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Wick Drains – The General Idea

Without Drains

Clay

Bedrock

With Drains

Bedrock

How are wick drains installed and how do they


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How are wick drains installed and how do theywork?

• The Drains can beinstalled to depthsgreater than 100 ft.

• Very fast installationspeeds

• The water has to go

somewhere on site!• Needs surcharge


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– Stone Columns

– Soil Mixing – Wick Drains – Other Improvement

• Conclusions


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Dynamic Compaction for Chemical Storage

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Ground Modification for Asphalt Storage Tanks

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Conclusions

GI Method Soft Soils,Compressible Soils,

Organic Soils

Mixed Soils orUndocumented

Fills

Liquefiable Soils orClean Sands

Sandy Soils

Wick Drains Excellent-Requires Preload-May require stagedloading

Good-May require extrameasures to install-Requires Preload-May require stagedloading

N/A N/A

Earthquake Drains N/A N/A Good N/A

Stone Columns orAggregate Piers

Good-Sufficient settlementreduction may not beachievable

Very Good Excellent Excellent

Rigid Inclusions Very Good Very Good N/A Good

Soil Mixing - Columns Excellent Very Good Excellent Excellent

Soil Mixing - Mass Excellent Good to N/A-Depending on soil type

Excellent Good

h k


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Thank You!! Questions?

Dennis W. Boehm [email protected] Baker www.haywardbaker.com

509 North Sam Houston Parkway/Houston, Texas

281-668-1870

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