negative skin friction aaron budge minnesota state university

8/13/2019 Negative Skin Friction Aaron Budge Minnesota State University

1/46

Negative Skin Friction

Aaron S. Budge, Ph.D., P.E.Minnesota State University, Mankato


2/46

A QUICK ITEM OF INTEREST

Mn/DOT-funded survey to State DOTs

41 out of 50 States eventually responded(with some prodding!)

One of several questions How much do

states use driven piles, vs. drilled shafts, vs.shallow foundations for transportation

applications?

Of the first 35 respondents, the following

results were obtained


3/46


4/46

RESULTS OF THE STATE DOT SETUP

SURVEY2 For transportation applications in your state, which of the

following best describes the use of Drilled Shafts:

0 0% Our agency never uses Drilled Shafts for

transportation applications

2 6% Our agency rarely uses Drilled Shafts for


20 57% Our agency occasionally uses Drilled Shafts for


13 37% Our agency often uses Drilled Shafts fortransportation applications

0 0% Our agency almost exclusively uses Drilled

Shafts for transportation applications


5/46

RESULTS OF THE STATE DOT SETUP

SURVEY3 For transportation applications in your state, which of the

following best describes the use of Shallow Foundations:

0 0% Our agency never uses Shallow Foundations for


8 23% Our agency rarely uses Shallow Foundations for


12 34% Our agency occasionally uses Shallow

Foundations for transportation applications

15 43% Our agency often uses Shallow Foundations fortransportation applications

0 0% Our agency almost exclusively uses Shallow

Foundations for transportation applications


6/46

FUNDAMENTAL QUESTION #1:

WHAT IS NEGATIVE SKIN FRICTION(a.k.a. DOWNDRAG or DRAGLOAD)?

Downward load at pile topresisted by upward (pos.)

skin friction in soil layers and

end bearing at the pile toe- USUALLY --..

But, what if the soil moves

DOWNWARD with respect tothe pile???


7/46



In what situations might this phenomenon occur?1 Embankment fill placed after pile driving?

(WHY?)

2 Site dewatering subsequent to pile driving?3 Soil liquefaction due to seismic activity or

other vibration?

4 - Other cases?


8/46




9/46




10/46

As an example:Maple Grove, MN

New Interchange

Soil Profile at site =>

Predicted 3-5 inches

of settlement.Piles driven prior

to fill placement.

PROBLEMS?

(Stay tuned!)


11/46



Should we estimate negative skinfriction using the same relationships

and calculations as we use for

positive skin friction (Nordlund,Tomlinson, etc.)?

Neutral plane and other approachesare available to identify where

negative friction stops and positive

friction begins.


12/46



With respect to Load and ResistanceFactor Design (LRFD), how should

dragload be appropriately dealt with?

Reduced pile capacity!

Dead Load?

Live Load?Which load factor is appropriate?


13/46


HOW MUCH DOWNDRAG LOAD EXISTS?

Mn/DOT has funded several studies

to quantify the magnitude ofdowndrag experienced. Several

sites have been monitored where

settlement of the foundationmaterial with respect to the piling

was anticipated (i.e., fill placed near

piles AFTER pile driving.)

HOW CAN WE MEASURE Rs1?


14/46

HOW TO MEASURE DOWNDRAG LOAD

VIBRATING WIRE GAGES

FIBER OPTIC or RUGGEDIZED RESISTANCE GAGES

Do you install gages before or after driving?


15/46

INSTRUMENTATION OF A BRIDGE

(GAGES INSTALLED BEFORE DRIVING)


16/46


(GAGES INSTALLED AFTER DRIVING)


17/46


(GAGES INSTALLED AFTER DRIVING)


18/46


WHAT ARE THESE?


19/46

OPTIONS AVAILABLE TO REDUCE

NEGATIVE SKIN FRICTION?

BITUMEN COATING

PLASTIC COATING TEFLON COATING

PILE SLEEVES


20/46

Instrumented

Sleeved PileInstrumented

Unsleeved Pile


MAPLE GROVE, MN


21/46


MAPLE GROVE, MN

ShapeAccelArray (SAA)


22/46


MAPLE GROVE, MNShapeAccelArray (SAA)


23/46


MAPLE GROVE, MN

Gage A-48


24/46

DATA COLLECTED FIRST 50 DAYS


25/46

STRAIN DATA COLLECTED 11 MONTHS

0

50

100

150

200

250

300

0 50

100

150

200

250

300

350

Elapsed Time (days)

RawMicrostrain

.


26/46

A CLOSER LOOK AT TEMPERATURE

With the apparent creep during periods ofminimal construction activity, the thermal

strain effects were of interest Basic idea if the temperature changes in the

soil/pile such that the pile wants to change

length but cannot (due to friction forces of thesoil), thermal induced strains will bemeasured by the gages that should NOT be

included in the downdrag/pile load response.


27/46

TEMP DATA COLLECTED 11 MONTHS

0

5

10

15

20

25

30

050

100

150

200

250

300

350

Elapsed Time (days)

Temperatu

reReading(Celsius).


28/46

A CLOSER LOOK AT TEMPERATURE

-20

-15

-10

-5

0

5

10

-15.0 -10.0 -5.0 0.0 5.0

Delta Temp (deg F)

Delta

Strain(micros

train).

A-01 A-11 A-21 A-31 A-41 A-48

A-50A A-50B A-55A A-55B


29/46

CORRECTED DATA 11 MONTHS

0

50

100

150

200

250

300

0 50

100

150

200

250

300

350

Elapsed Time (days)

Microstrain

.

Raw Microstrain Temperature Corrected Microstrain


30/46

CORRECTED DATA 11 MONTHS


31/46

ESTIMATED VS. MEASURED


32/46

LOAD PROFILES

0

10

20

30

40

50

60

70

0 50 100 150 200 250 300

Depthfrom

PileCap

(ft)

.

Measured Total Load

Pile A Data -Unsleeved

8/1/2009 9/1/2009 10/1/2009 12/1/2009 1/1/2010 2/1/2010 3/1/2010 4/1/2010

5/1/2010 6/1/2010 7/1/2010 8/1/2010 9/1/2010 10/1/2010 11/1/2010 11/30/2010

"Original grade" at approx. 12 ft from

Pile Cap


33/46

LOAD PROFILES

0

10

20

30

40

50

60

70

0 50 100 150 200 250 300

Depthfrom

PileCap(ft)

.

Measured Total Load

Pile B Data -Sleeved

8/1/2009 9/1/2009 10/1/2009 12/1/2009 1/1/2010 2/1/2010 3/1/2010 4/1/2010

5/1/2010 6/1/2010 7/1/2010 8/1/2010 9/1/2010 10/1/2010 11/1/2010 11/30/2010

"Original grade" at approx. 12 ft fromPile Cap


34/46

LOAD PROFILE REGIONS

0 50 100 150 200 250 3000

10

20

30

40

50

60

70

0 50 100 150 200 250 300

UnsleevedSleeved


35/46

Region 2

0 50 100 150 200 250 3000

10

20

30

40

50

60

70

0 50 100 150 200 250 300

UnsleevedSleeved



36/46

Region 3

0 50 100 150 200 250 3000

10

20

30

40

50

60

70

0 50 100 150 200 250 300

UnsleevedSleeved



37/46


CROSSTOWN COMMONS EXPANSION


38/46




39/46




40/46


50


41/46

-400

-350

-300

-250

-200

-150

-100

-50

0

50

4/2/2008

6/1/2008

7/31/2008

9/29/2008

11/28/2008

1/27/2009

3/28/2009

5/27/2009

7/26/2009

9/24/2009

11/23/2009

1/22/2010

Time Stamp

ChangeinStrain(microstr

ain).

Gage C12 Load Gage C8 Load Gage C6 Load Gage C1 Load


42/46

CONCLUSIONS

At both sites, downdrag was measurable; at

Maple Grove observed pile strains began to

increase immediately when embankment fill wasplaced over compressible soils, prior to the

application of any structural loads.

At Crosstown, increases in strain continued forweeks after wall construction was completed,

corresponding to continued consolidation of

foundation soils.


43/46

CONCLUSIONS

The strain and deflection data suggest that

additional strain, and therefore loading, is

intimately linked with the soil consolidationbehavior and construction and placement of the

bridge components.

Temperature effects were observed to addcomplexity to strain gage data evaluation,

although a period of steady-state load and

variable temperatures offered a method todevelop a correction factor.


44/46

CONCLUSIONS

Pile strains were observed to decrease only with

the removal of the temporary soil surcharges;

added loads always appeared to result incorresponding increases in pile strain.

Vibrating wire strain gages and SAA deflection

monitoring systems were shown to be effectivesensors for the long term performance monitoring

of downdrag impacts.


45/46

CONCLUSIONS

Mn/DOT continues to move forward with similar

monitoring projects (currently one underway with

Steele County and a second underway withWashington County) to improve understanding

with respect to the magnitude of negative skin

friction with the intent of developing a betterdesign strategy in the future.


46/46

Questions???

[email protected]

negative skin friction aaron budge minnesota state university

Documents