Observational Method in

Geotechnical Engineering

Robert J. Werner, P.E.

FAILURE PLANE

Design Based on Most Probable Conditions

Identify Worse-Case Eventualities

Develop Reliable Monitoring Plan

Predict Monitoring Outcomes

Establish Action Plan (In Advance)

Monitor & Report Promptly

Modify Design / Implement Action Plan

Peck 1969 – Ninth Rankine Lecture “Advantages and Limitations of the Observational Method in Applied Soil Mechanics”

LOUISIANA SITE

Design Based on Lower-Bound Conditions

Identify Worse-Case Eventualities

Continue Monitoring Plan

Predict Monitoring Outcomes

Establish Improvement Plan

Monitor & Report

Implement Improvement Plan if Warranted

Pleistocene

Session 67

Wednesday 10:00-11:45

Room 2

Robert J. Werner, P.E.

I-20 & US-80 BRIDGES

BRIEF HISTORY

1929 RR BRIDGE SLOPE FAILURE

U.S. 80

BRIDGE

TOWER 1

PEDESTALS

FAILURE PLANE US-80 BRIDGE

NB-10

NEW INCLINOMETER BORING

IPI-10R

IPI-10R

426’ 423’ 870’ 423’ 426’

W-3 W-2 W-1 E-1 E-2 E-3

PP15 PP15’

E E EF F EFF F

SuspendedSpan

AnchorSpan

SimpleSpan

SimpleSpan

AnchorSpan

EastWest

CantileverSpans

I-20 BRIDGE MOVEMENT

SUMMARY OF I-20 PIER MOVEMENTS

(in) (arc-sec) (in) (arc-sec)

1. 1999 and 2000 Prior to 5/2001 6.00 6.50

2. 2003 Feb2/5/2003 to

2/6/20030.50 50 0.50 0

3. 2005 Aug 8/2/2005 0.75 0 0.50 50

4. 2005 Nov 11/17/2005 0.25 0 0.25 0

5. 2006 Aug - Sep8/13/2006 to

9/21/20060.50 50 0.75 75

6. 2007 Sep - Dec9/21/2009 to

12/19/20070.50 50 0.50 25

7. 2009 Sep - Dec0/28/2009 to

12/22/20090.20 25 0.00 20

8. 2010 Nov11/7/2010 to

11/22/20100.20 25 0.00 10

9. 2011 Oct10/20/2011 to

10/24/20110.25 0 0.25 25

10. 2012 June - Sep6/29/2012 to

9/21/20121.25 75 1.00 75

10.50 300 10.25 300

Summary of I-20 Bridge Pier Movements (+ direction is west)

Top of Pier E-1Top of Pier E-2

Estimated Time or Time Period

Total Movement (+/-)

1. Prior to 5/2001

GENERALIZED PROFILE

Peak Shear Strength = 5.4°

MOVEMENTS at I-8 (PIER E-2)

3/31/11 BATHYMETRY

SAA at I-8 (PIER E-2)

INCLINOMETER I-12 at PIER E-1 (2003)

I-12 Inclinometer

Reading on

March 11, 2012

El. -63’

0.25” Additional Displacement Since Last Reading in Oct. 2007 Inclinometer Displacement is About 1/3 of Measured Top of Pier E-1 Movement

Calibrate Stability & Deformation Models Based on Measured / Observed Conditions (Over the Past 84 Years)

Identify Worse-Case Eventualities

Develop Improvements That Do Not Alter Fundamental Site Behavior

Predict Monitoring Outcomes

Establish Action Plan (Warning System, Structural Modifications)

Continue Monitoring (Real-Time)

Implement Additional Improvements, if Warranted

COMPLETE SCOUR HOLE FILLING

STABILIZATION DRAINS

I-20 DRAIN

(1972)

US-80

DRAIN

(1940s)

SURFACE WATER DRAINAGE

QUIZ