Calibration of Design Methods for Slope Stabilization and Earth Retention

J. Erik Loehr

Civil and Environmental EngineeringUniversity of Missouri - Columbia

General Design Approach

RaxialR

Reinforcing Member

Potential Sliding Surface

transverseR

Motivation

Design methods appear conservative Have performance data, but it’s

underutilized Would like to make prudent use of

performance data to improve design methods

“Calibration” of Design Method

Objective is design method that predicts F=1.0 when deformations becomes “just unacceptable”

F

1.00.0

Initial Performance Function

Calibrated Function

limit

Required Data

Deformations as function of time Inclinometers Surface surveys

Piezometric levels as function of time

Soil/Rock properties

Loads/moments in members not required, but helpful

I435-Wornall Road Site

June 2001

I435-Wornall Road “As-Built”

Stiff to very stiff clay

Hard Formation

Soft to medium clay3 rows driven perpendicular (8-ft)

11 rows driven vertical (8-ft)

1 row driven vertical (5-ft)

2 rows driven vertical (3.5-ft)

N

I435-Wornall Site Instrumentation

I-1I-2

I-3I-4IM-1

IM-2

IM-3

IM-4P-1,2

P-3,4

Legend:Piezometers

Instrumented Members

Inclinometers

N

Approx. Slide Extent

Crest

Toe

I435-Wornall Site: Piezometric Levels0

2

4

6

8

10

N D J F M A M J J A S O N D J F M A M J J A

Date

Dept

h of

Wat

er F

rom

Gro

und

Surfa

ce (f

t)

P-1P-2P-3P-4

2001 2002 2003

P1P2

P4P3

I435 Site Piezometric LevelsUpper Stratum

Middle Stratum

Lower Stratum April 11, 2002

Upper Stratum

Middle Stratum

Lower Stratum May 13, 2002

Upper Stratum

Middle Stratum

Lower Stratum

July 12, 2002

Theoretical Factors of Safety

4/11/02

5/13/02

6/10/02

7/12/02

8/22/02

1.0

1.1

1.2

1.3

1.4

1.5

M A M J J A S O N D JDate

Fact

or o

f Saf

ety

Uncalibrated Method

Unreinforced

F calculated using measuredpore pressure conditions

I435-Wornall Road Performance

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

N D J F M A M J J A S O N D J F M A M J J ADate

Cum

ulat

ive D

ispla

cem

ent (

in)

I-1

I-2

I-3

I-4

2001 2002 2003

Stage 1 Stage 2 Stage 3

Field Performance Function

1.0

1.1

1.2

1.3

1.4

1.5

0.0 0.5 1.0 1.5 2.0 2.5 3.0Cumulative Lateral Displacement (in)

Fact

or o

f Saf

ety

Measured Performance

Extrapolated Performance

Inferred Performance

Field Performance Functions

1.0

1.1

1.2

1.3

1.4

1.5

0.0 0.5 1.0 1.5 2.0 2.5 3.0Cumulative Lateral Displacement (in)

Fact

or o

f Saf

ety

Measured Performance

Extrapolated Performance

Calibrated Performance

Inferred Performance

Theoretical Factors of Safety

5/13

/02

4/11

/02

6/10

/02

7/12

/02

8/22

/02

1.0

1.1

1.2

1.3

1.4

1.5

M A M J J A S O N D JDate

Fact

or o

f Saf

ety

Calibrated Method

Uncalibrated Method

Unreinforced

F calculated using measuredpore pressure conditions

Conclusions

Approach at least produces method that is consistent with observed field behavior

Non-uniqueness in approach can be addressed by performing additional calibrations

Limited to application for similar techniques

Prudent basis for incrementally improving design over time

Large-scale modeling

Acknowledgements

Project Sponsors Missouri Department of Transportation,

project RI98-007 National Science Foundation, project

CMS0093164 Recycled Materials Resource Center, UNH Epoch Composite Products, Lamar, MO The Judy Company, Kansas City, MO

John Bowders and Hani Salim, MU Faculty

Tom Fennessey, MoDOT MU Graduate students

Calibration based on I435-Wornall Site

0

1

2

3

4

5

6

7

8

9

10

0 200 400 600 800 1000 1200 1400 1600Limit Soil Pressure (psf)

Dep

th (f

t)

f ' = 27°c ' = 56.5 psfg = 125 pcfu =0

Shaded region indicates range suggested by calibrations for I-435 Wornall Road site