Ground Improvement Why? Which? When? Ray Franz, PE, D.GE, Vice - - PowerPoint PPT Presentation

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Ground Improvement Why? Which? When? Ray Franz, PE, D.GE, Vice - - PowerPoint PPT Presentation

Nov 03, 2022 42 likes •398 views

Ground Improvement Why? Which? When? Ray Franz, PE, D.GE, Vice President 1 haywardbaker.com Outline of Presentation Address Topics of Interest solicited from you by Mr. Merklin Introduce project conditions leading to consideration of

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Ground Improvement

Why? Which? When?

Ray Franz, PE, D.GE, Vice President

haywardbaker.com

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Address Topics of Interest solicited from you by Mr. Merklin

  • Introduce project conditions leading to consideration of Ground

Improvement (Why?)

  • Summarize currently available improvement techniques (Which?)
  • Discuss applicability of techniques to subsurface conditions (When?)
  • More detail to be provided on Aggregate Columns and Rigid Inclusions by Mr. Griffin and Mr. Simonton
  • Review important geotechnical information
  • Discuss framework for specifications

Outline of Presentation

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Ground improvement technologies are geotechnical construction methods used to modify and improve poor and marginal soil and rock conditions to meet project requirements. [FHWA NHI-04-001] Ground modification is defined as the alteration of site foundation conditions

  • r project earth structures to provide better performance under design

and/or operational loading conditions [FHWA-NHI-16-027 / FHWA GEC 013]

Why use Ground Improvement?

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  • If “conventional” construction methods will not provide the required

performance.

  • If “conventional” construction methods are not cost-effective.
  • Ground improvement may ADD VALUE

Why use Ground Improvement?

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  • What is included when we define Required Performance?

− Adequate safety against or low probability of instability or strength failure − Serviceable deformations

  • Settlement
  • Lateral movements

− Adequate resistance to extreme or natural hazard loading conditions − Constructable

Why use Ground Improvement?

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  • How do we assess Cost-Effectiveness?

− Acceptable initial construction cost − Acceptable construction schedule − Predictable and acceptable life-cycle costs

  • Operating and monitoring
  • Maintenance, repair and replacement

Why use Ground Improvement?

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  • Each of your states has multiple physiographic regions with distinct surficial

geology and the associated challenges.

  • Not every state includes all of these issues, but several of these subsurface

conditions are prevalent across the Midwest:

  • Loose, granular soils
  • Compressible and low-strength, fine-grained soils
  • Organic materials
  • Karstic formations
  • Abandoned mine lands

Why use Ground Improvement?

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  • Performance Concerns are

−Excessive Settlement −Liquefaction Potential

  • How to modify / improve / alter?

−Densification

Loose, Granular Soils

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Densification techniques apply energy to rearrange particles -- decreasing void space, increasing grain to grain contact

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Densification Techniques

Vibro Compaction Dynamic Compaction

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But, what if there are fines in the soil matrix?

The realignment of the sand grains and, therefore, proper densification generally cannot be achieved when the granular soil contains more than 12 to 15 percent silt OR more than 2 percent clay.

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Compressible and Low-strength Soils

  • Performance Concerns are

−Bearing Capacity Failure −Global Instability −Slope Instability −Excessive Settlement −Differential Settlement −Creep / Long-term Settlement

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Compressible and Low-strength Soils

  • How to modify / improve / alter?

−Remove and Replace (Soil “Correction” MN) −Accelerate consolidation −Reinforce

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Compressible and Low-strength Soils

Remove and Replace − Usually, 20 ft. or less in depth

  • Controlled by equipment, available area (safe slopes), depth to

groundwater − How to determine the limits of work?

  • To what extent will conditions influence performance?
  • Probably no further
  • Use probing
  • Calibrated probe (can be relatively simple tools)
  • Cone Penetration Testing
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Compressible and Low-strength Soils

Accelerate Consolidation (and strength gain ±) −Pre-fabricated Vertical (wick) Drains

  • With pre-load / surcharge
  • Staged construction

−Without other measures, structures must be able to accommodate/tolerate magnitude of deformations

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Compressible and Low-strength Soils

Accelerate Consolidation (and strength gain) −One question was related to estimation of strength gain

  • Ladd’s SHANSEP model (Stress History and Normalized Soil

Engineering Properties) can be used

  • Requires “undisturbed” samples, oedometer and triaxial testing
  • Requires accurate field measurements of induced/residual pore

pressures to compute effective stress with time

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Compressible and Low-strength Soils

Reinforce −More to follow by subsequent speakers … −Generally,

  • Creating stiff elements below grade
  • Attract stresses to reduce deformation of compressible

soils

  • Transfer portion of applied stress to more competent

strata

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Compressible and Low-strength Soils

Reinforcement by: − Aggregate-based (granular) elements

  • Requires confinement by / support from surrounding ground
  • Unsuitable for strata that are too soft or susceptible to

degradation or decomposition − Cemented or confined elements

  • Better suited to very soft and organic deposits
  • Could include Rigid Inclusions and Soil Mixed elements
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The reinforcing concept…

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Forms of Reinforcement

  • From Han, Principles and Practice of Ground Improvement, Wiley, 2015
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  • FHWA-NHI-16-027 / FHWA GEC 013 / NHI Course No. 132034

Ground Modification Methods Reference Manual – Vol. I, April 2017

  • FHWA-NHI-16-028 / FHWA GEC 013 / NHI Course No. 132034

Ground Modification Methods Reference Manual – Vol. II, April 2017

  • https://geotechtools.org

Developed for the second Strategic Highway Research Program Project Number R02 (SHRP 2 R02) Geotechnical Solutions for Soil Improvement, Rapid Embankment Construction, and Stabilization of the Pavement Working Platform + http://www.trb.org/SHRP2

Options and Selection: Suggested References

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  • Which data are most valuable?
  • In what format do specialist contractors prefer to see the data?

− All of it!

  • Not really kidding…
  • You must have enough to really understand the expected poor

performance to engineer the improved behavior

Geotechnical Information

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  • Complete geotechnical report
  • Not just logs and test result tables
  • Scaled profiles are good
  • Existing and planned grades
  • Existing and planned utilities [below grade and above grade/overhead]
  • Groundwater regime and planned surface drainage features
  • Information regarding site history, reported past activities
  • Known contamination
  • Planned construction sequence

Information to be provided in contract documents

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  • GeoConstructability – An Owner’s Guide to Obtaining Essential

Geotechnical Information for Construction, Report of the Geotechnical Constructability Task Force, Geo-Institute of ASCE, American Society of Civil Engineers, 2011. [especially Appendices Nos. 1 and 7]

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  • “Discussion of how to write specifications (method based, performance based,

etc.) while avoiding proprietary aspects…” Contracting Framework = Design – Bid – Build

Preparing Specifications and Plans

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  • Avoid the use of “method” specifications
  • Unlikely to accommodate available tools and approaches offered by the

various specialist contractors

  • May preclude certain methods that might otherwise provide desired

performance more economically

  • Performance is the ultimate goal

Preparing Specifications and Plans

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  • Guidance for Drafting Specifications for Ground Improvement

Deep Foundations Magazine, April 2016

Do’s and Don’ts: Suggested References

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  • Regardless of Design-Bid-Build or Design-Build,
  • Understand the performance requirements for the new construction
  • Communicate them clearly, and completely, in the contract documents
  • Anticipate natural variability and appropriate means of compensation
  • Unit price by “area” units is unlikely to fairly share risk

Performance Expectations and Requirements

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  • Specify, not only the required behavior, but also the acceptable

design/analysis methods to be used by the specialist Ground Improvement engineer

  • Define review and acceptance responsibilities among the parties

Performance Expectations and Requirements

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  • Provide clarity
  • For the specialist engineer and construction team
  • For the reviewer(s)
  • For the Owner

The recurring expectation…

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  • Evaluate project setting and risks
  • Have the end in mind
  • Don’t forget the fundamental soil mechanics

When considering Ground Improvement …

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