Geotechnical Advances and Challenges over the Past 50 years

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www.ara.com© 2019 Applied Research Associates, Inc. ARA Proprietary

INNOVATIVE SOLUTIONS TO COMPLEX PROBLEMS

Geotechnical Advances and Challenges over the Past 50 years

Jerry A. DiMaggio, PE, D.GE

Senior Principal Engineer-Associate

Applied Research Associates, Inc.


© 2019 Applied Research Associates, Inc. ARA ProprietaryDate: November 12, 2020

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Geotechnical Advances and Challenges over the past 50 years

Key Messages

- Why this topic?

- 1970 to 2020 Recommended Processes and Procedures

- 2020 Challenges (Save the BEST for LAST!)

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Geotechnical Advances and Challenges over the Past 50 Years

Why this topic?

- It is important to know where we have been, where we are presently and where we are headed.

- A LOT has changed in 50 years mostly good BUT some not.

- Geotechnical science and engineering is critical and provides a significant contribution to Infrastructure, Mankind and the Earth.

- Poor processes and practices significantly affect the quality of life, economic well being and safety.

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Geotechnical Features

A. Shallow Foundations (spread footings and mats)B. Deep Foundations (drilled shafts, driven piles,

auger-cast and micropiles)C. Earth Retaining Structures (permanent and temporary)

D. Engineered soil fills and cutsE. Engineered rock cuts and fillsF. PavementsG. Drainage elements

Guidance provided in this presentation is based on my highway and rail experience but is applicable to all infrastructure facilities (buildings, energy, transportation, etc.)

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Example of CHANGES Deep Foundation Practice 1970 - 2020

● Load demand, performance requirements/ constraints have increased significantly. Foundation designs have become more complex and become more “optimized”.

● Pile material strengths and sizes (L and D) have increased significantly.

● Frequency, types and importance of load and integrity tests have increased significantly.

● Load Resistance Factor Design platform “requires” a close relationship between the design and construction disciplines (reliability based design).

● Construction equipment, specifications and plan details have become very complex. Project financing and delivery methods have changed.

CONSTRUCTION IS MORE IMPORTANT AND CRITICAL MUST TO SUCCESS

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Overall Objective

Failure Overly Conservative Design

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Rock Characteristics

• Strength• Regional geomaterials,

qu = 50-1500 psi

N160 (or N60)> 50

• Hard rock, qu > 1500 psi

• Rock mass properties

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AASHTO LRFD Bridge Design Specs. Section 10.4 Soil and Rock Properties

4.1 Informational Needs

4.2 Subsurface Exploration

4.3 Laboratory Tests

4.4 Insitu Tests

4.5 Geophysical Tests

4.6 Selection of Design and Construction Parameters

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Standard Penetration Test

6 blows for 6”6 blows for 6”6 blows for 6”6 blows for 6”6 blows for 6”6 blows for 6”

SPT Resistance(N-value) =6 + 6 = 12

140 lb Hammer dropping 30”

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Typical Values’f = 25o - 45o

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Correlation: SPT N160 to Drained Friction Angle

AASHTO Table 10.4.6.2.4-1

N160

Drained FrictionAngle

< 4 25 – 30

4 27 – 32

10 30 – 35

30 35 – 40

50 38 – 43



Other In-situ Exploration Tests

SPT CPT DMT PMT VST

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Selection of Soil Shear Strength

• Rate of construction loading to soil conductivity

• Effect of Applied Load Direction on measured shear strength

• Effects of expected levels of deformation on the structure

• Influence of Construction Sequence

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EVALUATION OF SOIL SHEAR STRENGTH

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• SPT• CPT • Pressuremeter• Dilatometer • Field Vane Shear

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Measured or interpreted parameter value Coefficient of Variation, V

(%)

Unit weight, 3 to 7 %

Buoyant unit weight, b 0 to 10 %

Effective stress friction angle, 2 to 13 %

Undrained shear strength, su 13 to 40 %

Undrained strength ratio (su/po) 5 to 15 %

Compression index, Cc 10 to 37 %

Preconsolidation pressure, pc 10 to 35 %

Hydraulic conductivity of saturated clay, k 68 to 90 %

Hydraulic conductivity of partially-saturated clay, k 130 to 240 %

Coefficient of consolidation, cv 33 to 68 %

Standard penetration blow count, N 15 to 45 %

Electric cone penetration test, qc 5 to 15 %

Mechanical cone penetration test, qc 15 to 37 %

Vane shear test undrained strength, suVST 10 to 20 %

15Duncan (2000), FHWA (2006)



Link between Site Characterization and Risk

Improved Site Characterization reduces risks in design, construction, and performance by:

o Reducing likelihood of encountering a differing site condition (dispute) during design and construction

o Increasing reliability of estimated geomaterial properties

o Decreasing uncertainty of subsurface conditions during construction

o Increasing the confidence in understanding the role and variability of groundwater

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Pile Types

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iiQi ≤ Rr = Rn

i =

i =

Qi =

Rr =

=

Rn =

Load modifier (eta)Load factor (gamma)Force effectFactored resistanceResistance factor (phi)Nominal resistance

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Available Nominal Resistance Verification Methods

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Static Load TestDynamic Measurements Wave Equation Analysis

Static Analysis

Where:

= nominal driving resistance (kips).

= developed hammer energy (ft-lbs) in the form

of ram weight, W, (lbs) times stroke height, h

(ft).

= pile penetration resistance (blows/inch).

1.75 log 10 100

Dynamic Formula



Pile Testing Methods

Analysis MethodResistance Factor

()(AASHTO 2014)

Est. Measure

Capacity

Stress

Energy

Capacity

Stress

Energy

Dynamic formula 0.10 (EOD) or 0.40 (EOD) X

Wave equation 0.50 (w field confirmation of hammer) X X X

Dynamic testing* 0.65 (2%) or 0.75 (100%) (0.5 uplift) X X X

Static load test** 0.75 to 0.80(wo/w dynamic) (0.6 UPLIFT)

X

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* Dynamic Test requires signal matching**Static Test requires one test pile per site

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Advances in Computer Analysis and Application Tools

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FLAC: FS=0.98

FD

LE



Service Limit State Checks

Global Stability Vertical, Horizontal Rotational

Deformations

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Extreme Event Loading: Seismic, Ice, Vehicle, Vessel, Scour, Blast



Geotechnical Assets and Asset Management (performance in post construction and long-term)

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Drilled Shafts

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Large Diameter Open Ended Pipe

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We have the learned the meaningof the word “drivability”

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Bi-directional O-cell Test

-1

-0.5

0

0.5

1

1.5

2

0 1000 2000 3000 4000 5000

Load, kips

Move

men

t, inch

es

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Statnamic Load Tests

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1-28.jpg

Geosynthetics

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Functions of Ground Improvement

• Increase bearing capacity

• Increase density

• Control deformations

• Accelerate consolidation

• Decrease imposed loads

• Provide lateral stability

• Increase resistance to liquefaction

• Transfer embankment loads to more competent soil layers

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GEOTECH TOOLSwww.GeoTechTools.org

• Main product: Web based information and guidance system• Within the system, for each of @ 60 technologies:

– Technology Fact Sheets– Photographs– Design Procedures– Quality Control/Quality Assurance Procedures– Cost Estimating– Specifications– Bibliography– Case Histories

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What aboutEarth Retaining Structures?

A structure used to hold back earth and maintain a difference in the elevation of the ground surface. Often called:

– Retaining Wall or

– Earth Retaining System

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Groundwater Measurements

• Groundwater level and pore water pressure measurements are extremely important for geotechnical analysis

• Sources of Informationo Existing wells

o Open borings

o Observation wells

o Piezometers

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Geotechnical Reports

• Field Investigation Logs

• Geotechnical Data Reports

• Geotechnical Design Reports

• Geotechnical Baseline Reports

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CURRENT Challenges: Better to Consider as GREAT OPPORTUNITES

• Poor understanding of tolerable deformations

• Mainstream application of soil/ structure interaction

• Marginal quality of construction and quality assurance

• Quality/use of lab and field subsurface information

• Definition of recommended soil/ rock parameters

• Demonstrating value added service to clients

• Communications oral and written

• OTHERS? Certainly there are many.

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• Contracting methods used by state agencies are:

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Q & A

Jerry A. [email protected]

Documents

Geotechnical Advances and Challenges over the Past 50 years