simple soil structure interaction in innovative foundation design.pdf

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Simple Soil Structure Interaction Concepts in Innovative Foundation Design Presented To: ASCE/SAME Engineering Conference Presented By: Clyde N. Baker Jr., P.E., S.E. STS Consultants Ltd.

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Page 1: Simple Soil Structure Interaction in innovative foundation design.pdf

Simple Soil Structure Interaction Concepts in Innovative Foundation Design

Presented To: ASCE/SAME Engineering Conference

Presented By: Clyde N. Baker Jr., P.E., S.E.

STS Consultants Ltd.

Page 2: Simple Soil Structure Interaction in innovative foundation design.pdf

Introduction

� Purpose of Talk – To share some experiences and insights gained over a 50

year career on a subject hopefully of interest to both geotechnical and structural engineers.

� Method – Use well documented case histories to illustrate points.

Page 3: Simple Soil Structure Interaction in innovative foundation design.pdf

Key Points to Illustrate or Discuss

� Things are not always what they seem.

� Type of testing and amount can greatly influence predictions.

� Local geological knowledge and relevant case history experience more important than uncorrelated testing no matter how sophisticated.

� Simple tests and concepts correlated with relevant experience can result in predictions closer to reality than more elaborate testing and analysis not well correlated.

� We learn from experience but how close to the edge should we get? Take small steps. Make change gradually.

Page 4: Simple Soil Structure Interaction in innovative foundation design.pdf

Four Simple Concepts

� Use dense soil layer over soft clay as a mat to spread out loads to permit footing design instead of a mat foundation.

� Use deep basement excavation stress relief effects in ways to maximize site building capacity.

� Use of piles as settlement reducers rather than as required structural elements for building support.

� Use of variable length piles under mat to minimize differential settlement.

Page 5: Simple Soil Structure Interaction in innovative foundation design.pdf

Normal Consolidation vs. Preconsolidation

� Normal Consolidation Test - preconsolidation value often inaccurate.

� Thus settlement prediction based on test preconsolidation value is often inaccurate but usually conservative.

� Pressuremeter creep pressure quite similar to preconsolidation pressure in preconsolidated cohesive deposits.

Page 6: Simple Soil Structure Interaction in innovative foundation design.pdf

Project Name:Dunbar Builders

Depth:

25 – 27.5

Water Content:28.8%

LL: 30.1

PL: 16.1

Soil Classification:

Silty Clay, Trace Sand and

Gravel, Gray (CL)

Page 7: Simple Soil Structure Interaction in innovative foundation design.pdf

Project Name:Dunbar Builders

Depth: 25 – 27.5

Water Content:28.5%

LL: 33.4PL: 16.1

Soil Classification:Silty Clay, Trace Sand and Gravel,

Gray (CL)

Page 8: Simple Soil Structure Interaction in innovative foundation design.pdf

Project Name:Dunbar Builders

Depth: 30 – 32.5

Water Content:21.0%

LL: 28.4PL: 15.1

Soil Classification:Silty Clay, Trace Sand and Gravel,

Gray (CL)

Page 9: Simple Soil Structure Interaction in innovative foundation design.pdf
Page 10: Simple Soil Structure Interaction in innovative foundation design.pdf

Modified Mat Foundation Design on Soft Clay

Concept – Use dense sand layer over soft clay as a mat to spread out loads to

permit footing design instead of mat foundation.

– Monitor pore pressure buildup and shear displacement in soft clay during 26-story construction to see that shear strength not exceeded.

Site Investigation and Lab Testing Program Soil Profile

– Possible foundation solutions – Bearing capacity and settlement analysis– Structural design concepts– Instrumentation Program – Settlement Measurements – Conclusions

Page 11: Simple Soil Structure Interaction in innovative foundation design.pdf

Soil Profile and Properties

Page 12: Simple Soil Structure Interaction in innovative foundation design.pdf

Settlement Analysis

Assumptions: Boussinesq stress spread through dense sand layer (conservative)

– Average net stress increase beneath mat = 2000 psf

– Clay Layer: Top 8’ Normally Consolidated, Lower Clay Preconsolidated

– Average t90 = 12-16 minutes

Calculated Settlement:

• 4” at center of mat• 2-1/2” at edge of mat• 90% occurring in 9 to 12 months

Page 13: Simple Soil Structure Interaction in innovative foundation design.pdf

Summary of the Stresses Beneath the Center of the Building at a Depth of 5 Feet into the Soft Clay

Page 14: Simple Soil Structure Interaction in innovative foundation design.pdf

Inclinometer Readings

Page 15: Simple Soil Structure Interaction in innovative foundation design.pdf

Piezometer Readings

Page 16: Simple Soil Structure Interaction in innovative foundation design.pdf

Settlement Data

Page 17: Simple Soil Structure Interaction in innovative foundation design.pdf

Conclusions:� By utilizing the high bearing capacity of the dense sand layer overlying

the soft clay, a relatively thin and economical modified mat foundation design proved feasible at this site

� Construction of a building that developed theoretically induced shear stresses in the underlying soft clay soils, which exceeded the initial shear strength of the soft clay soil, was successfully accomplished by monitoring the performance of the structure and the critical soft clay. Construction loading occurred at a rate which permitted pore pressure dissipation and resultant shear strength buildup to occur fast enough so that excessive shear strains did not occur.

� Apparent pore pressure dissipation in the soft clay deposit at the site occurred more rapidly than was predicted by one-dimensional laboratory consolidation tests.

� Settlement of the structure has been less than anticipated, possibly due to insufficient recognition of overconsolidation effects.

Page 18: Simple Soil Structure Interaction in innovative foundation design.pdf

Dearborn Center

� Concept

– Use deep basement excavation stress relief in combination with new basement mat over existing caisson foundations to maximize number of additional floors possible at site.

– Building load is distributed between new mat and existing caissons based on relative stiffness predicted by pressuremeter testing.

Page 19: Simple Soil Structure Interaction in innovative foundation design.pdf

Site Investigation

� Soil

Borings and lab testing

In-situ pressuremeter testing

� Existing Foundations

Coring

Pressuremeter testing below caissons

Page 20: Simple Soil Structure Interaction in innovative foundation design.pdf

Pressuremeter Set-Up

Page 21: Simple Soil Structure Interaction in innovative foundation design.pdf

Pressuremeter Reduction

-100

0

100

200

300

400

500

600

700

800

900

0 10 20 30 40

Pressure in TSF

Inje

cted

Vo

lum

e in

CC

-10

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40

Pressure in TSF

Cre

ep in

CC

VolumeCreep

Po PlPf

E+

Pressuremeter Data Reduction (BX)

Ed

STS Consultants, Ltd.

PSEUDO-ELASTIC ZONE

PLASTIC ZONE

Ed = Deformation Modulus

Eo = Rebound Modulus

E+ = Recompression Modulus

Pf = Creep Limit

Pl = Limit Pressure

α = Ed/E+

Page 22: Simple Soil Structure Interaction in innovative foundation design.pdf

Rules with Pressuremeter

Dead Load Pressure

+ Long-term Real Live Load+ Effective Overburden Pressure

Must be less than Creep Pressure

Page 23: Simple Soil Structure Interaction in innovative foundation design.pdf

Rules with Pressuremeter (cont.)

Allowable Bearing Pressure

Where K varies from 0.8 to 1.8 depending on depth to diameter ratio and material type

Pl = Limit PressurePo = Beginning of Psuedo Elastic RangeF.S. = Factor of Safety

( )..SF

PPK ol −≤

Page 24: Simple Soil Structure Interaction in innovative foundation design.pdf

Dearborn Center Pressuremeter Profile

Page 25: Simple Soil Structure Interaction in innovative foundation design.pdf

Dearborn Soil Profile

Page 26: Simple Soil Structure Interaction in innovative foundation design.pdf

Geotechnical Analysis

� Settlement Prediction

– Existing Caissons

– New Mat

Page 27: Simple Soil Structure Interaction in innovative foundation design.pdf

Dearborn Center Deflection and Spring Calculations

Page 28: Simple Soil Structure Interaction in innovative foundation design.pdf

Dearborn Center Deflection and Spring Calculations (cont.)

Page 29: Simple Soil Structure Interaction in innovative foundation design.pdf

Dearborn Center Deflection and Spring Calculations (cont.)

Page 30: Simple Soil Structure Interaction in innovative foundation design.pdf

Dearborn Center Deflection and Spring Calculations (cont.)

Page 31: Simple Soil Structure Interaction in innovative foundation design.pdf

Dearborn Center Deflection and Spring Calculations (cont.)

Page 32: Simple Soil Structure Interaction in innovative foundation design.pdf

Dearborn Center Foundation Plan

Page 33: Simple Soil Structure Interaction in innovative foundation design.pdf

Structural

� Local distribution through shear walls � 3-dimensional SAP model used to determine

overall behavior using geotechnical developed springs.

Page 34: Simple Soil Structure Interaction in innovative foundation design.pdf

Observed Settlement

� Full structure dead load in place

� Live load not in yet

� Estimated 70% of total design load. So predicted settlement would be about 0.7 inches or about to ¾ inches

� Measured settlement varied from:� 0” on the North wall reported to be on rock caissons to

� ½” on the West wall� ” on the South wall and interior mat

� Possible likely settlement based allowing for surveyaccuracy is ” to ¾”

85

81

85

Page 35: Simple Soil Structure Interaction in innovative foundation design.pdf

South Side Office Building

� Use of straight shaft piers as settlement reducers in combined footing design over Chicago soft clay.

� Predict settlement of 12-story building on mat or strip footings on medium dense sand layer over soft clay with and without supplementary pile or pier settlement reducers

� Monitor load distribution between footing and piers and settlement during and after construction

Concept:

Page 36: Simple Soil Structure Interaction in innovative foundation design.pdf
Page 37: Simple Soil Structure Interaction in innovative foundation design.pdf
Page 38: Simple Soil Structure Interaction in innovative foundation design.pdf

Strain Gage Readings and Measured Settlement of Column B-6

-1000

-800

-600

-400

-200

0

200

3-Oct-94 3-Apr-95 3-Oct-95 2-Apr-96 2-Oct-96 2-Apr-97 2-Oct-97 2-Apr-98 2-Oct-98

Date

- = C

ompr

essi

on M

icro

stra

ins

+ =

Ten

sion

-10.0

-8.0

-6.0

-4.0

-2.0

0.0

2.0

Sett

lem

ent (

Inch

es)

Black - 1

Gray-1

Average

Settlement

Page 39: Simple Soil Structure Interaction in innovative foundation design.pdf

Strain Gage Readings and Measured Settlement of Caisson B-6

-500

-400

-300

-200

-100

0

100

200

3-Oct-

94

3-Apr-9

5

3-Oct-

95

2-Apr-9

6

2-Oct-

96

2-Apr-9

7

2-Oct-

97

2-Apr

-98

2-Oct-

98

Date

- =

Com

pres

sion

Mic

rost

rain

s +

= T

ensi

on

-5.0

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

Set

tlem

ent (

Inch

es)

Gage 8745Gage 8746AverageSettlement

Page 40: Simple Soil Structure Interaction in innovative foundation design.pdf

Strain Gage Readings and Measured Settlement of Column C-2

-1000

-800

-600

-400

-200

0

200

3-Oct-94 3-Apr-95 3-Oct-95 2-Apr-96 2-Oct-96 2-Apr-97 2-Oct-97 2-Apr-98 2-Oct-98

Date

- = C

ompr

essi

on M

icro

stra

ins

+ =

Ten

sion

-10.0

-8.0

-6.0

-4.0

-2.0

0.0

2.0

Sett

lem

ent (

Inch

es)

Black - 2

Gray-2

Average

Settlement

Page 41: Simple Soil Structure Interaction in innovative foundation design.pdf

Strain Gage Readings and Measured Settlement of Caisson C-2

-200

-150

-100

-50

0

50

100

150

200

3-Oct-94 3-Apr-95 3-Oct-95 2-Apr-96 2-Oct-96 2-Apr-97 2-Oct-97 2-Apr-98 2-Oct-98

Date

- = C

ompr

essi

on M

icro

stra

ins

+ =

Ten

sion

-2.00

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

2.00

Sett

lem

ent (

Inch

es)

Gage 8747

Gage 8748

Average

Settlement

Page 42: Simple Soil Structure Interaction in innovative foundation design.pdf

0.9481377

(59%)

2327C-2

1.25761496

(75%)

1978B-6

Settlement (inches)

Shaft Base Pressure

(ksf)

Shaft Load (kips)

Column Load (kips)

Column Number

Measured Column/Caisson Load Distributions as of April 14, 1998

Page 43: Simple Soil Structure Interaction in innovative foundation design.pdf

Conclusion:

Innovative cost effective solutions to foundation design problems are sometimes possible using combinations or mixtures of foundation elements provided that ground deformation and response to structure loading can be reasonably predicted within allowable tolerances.

Page 44: Simple Soil Structure Interaction in innovative foundation design.pdf

Petronas Towers

� Worlds tallest building (1482’)

� Worlds deepest high rise foundations up to 430’

� Worlds deepest ground improvement up to 530’

Page 45: Simple Soil Structure Interaction in innovative foundation design.pdf

Tower Foundation Profile

Page 46: Simple Soil Structure Interaction in innovative foundation design.pdf

Concept:

� Predict settlement based on modulus values based on bored pile load testing and extensive in-situ pressuremeter testing

� Use simple equivalent footing approach as well as more complete finite element computer programs to predict settlement

� Monitor settlement and load distribution in piles and on mat during and after construction

Use of variable length piles under mat to minimize critical differential settlement of worlds tallest building – Petronas Towers.

Page 47: Simple Soil Structure Interaction in innovative foundation design.pdf

Standard Penetration Resistance Profile

Page 48: Simple Soil Structure Interaction in innovative foundation design.pdf

535MPa190MPa223MPa226MPa176MPa391.8MPa186.9MPaAvg.

27312525271517# of Tests

383.3495590.3496851931479Max.

68.347.857.7325522.327.5ER Min.

149MPa64.1MPa101.8MPa109.8MPa67.9MPa133.9MPa37.6MPaAvg.

27312626271518# of Tests

470157199.422268330999Max.

11.7MPa18.3MPa38.5MPa17.8MPa32MPa10MP19.3MPaEd Min.

T2-54T2-26T1-54T1-24T1-10B23B14Boring

Pressuremeter Test Results

Overall Weighted Ed Avg. = 94.3

ER Avg. = 267

Page 49: Simple Soil Structure Interaction in innovative foundation design.pdf
Page 50: Simple Soil Structure Interaction in innovative foundation design.pdf
Page 51: Simple Soil Structure Interaction in innovative foundation design.pdf

Settlement Analysis Using Equivalent Footing Method

dEE =1

dEE =2

dEE ×= 205,4,3

MPaE

E

EEE

E

B

B

B

1359420

19485.0

1941

2.3

185.0

112.3

5,4,321

+=

+=

kPaq 130,1=

kPaq 610=

Av 60m piles

Pressuremeter Data

MpaE

MpaE

Av

Avd

267

3.94

=

=+

35.0== +E

Edα , Use 0.4

Settlement Calculation – Menard Empirical Method

1

3

020 5.43

33.1

E

Rq

R

RqR

Es

BMenard

λαλα

+���

����

×=

1, 32 =λλ for a circle

cmR 300 =

945.42

500,761.04.0

30

500,730610.0

1353

33.14.0

×

××+�

���

�×××

=Menards

mmcmcmsMenard 1.2716.255.0 =+=

Settlement Calculation – Elastic Theory

mms

E

qBs

Elastic

Elastic

59000,250

000,75100,692.035.0

10

=×××=

=µµ

Page 52: Simple Soil Structure Interaction in innovative foundation design.pdf

Elastic Compression of Shaft Down to Equivalent Footing Level

mm

kPaEm

kNkN

E

L

conc

conc

4.14000,000,27

000,40727,9

000,000,27

727,98.22.182

000,680,22

=×=∆

=××

=

=∆

σ

σ

Total Predicted Settlement By Menard Empirical Method

mmmmmmS

sS Menard

5.414.141.27 =+=∆+= �

By Elastic Theory

mmmmmmS

sS Elastic

4.734.1459 =+=∆+= �

Settlement Analysis Using Equivalent Footing Method

Page 53: Simple Soil Structure Interaction in innovative foundation design.pdf

Settlement Maps and Rock Contour Plan – Tower 1

Page 54: Simple Soil Structure Interaction in innovative foundation design.pdf

Settlement Maps and Rock Contour Plan – Tower 2

Page 55: Simple Soil Structure Interaction in innovative foundation design.pdf

Layout Plan of Instrumented Barrettes

Page 56: Simple Soil Structure Interaction in innovative foundation design.pdf

0.0m0.5m (Lev. A)

7.5m (Lev. B)

15.0m (Lev. C)

22.0m (Lev. D)

30.0m (Lev. E)

37.5m (Lev. F)

41.25m (Lev. G)

Load (kN)

Thousands

Dep

th b

elo

w c

ut-

off

leve

l

Met

ers

LOAD DISTRIBUTION CURVECOMPUTED FROM SGs MEASUREMENT

-5 5 15 25 35

0

10

20

30

40

50

Page 57: Simple Soil Structure Interaction in innovative foundation design.pdf

0.0m

0.5m (Lev. A)

9.5m (Lev. B)

12.5m (Lev. C)

27.5m (Lev. D)

36.5m (Lev. E)

45.5m (Lev. F)

54.25m (Lev. G)

Load (kN) - Thousands

Dep

th b

elo

w c

ut-

off

leve

l

Met

ers

LOAD DISTRIBUTION CURVECOMPUTED FROM SGs MEASUREMENT

-5 5 15 25 35 450

20

40

60

Page 58: Simple Soil Structure Interaction in innovative foundation design.pdf

Pressure in PSI(1 PSI = 6.9 kPa)

To

wer

Bu

ildin

g L

oad

in M

N

RELATION OF AVERAGE MAT PRESSURE CELL READINGS AND BUILDING LOAD

Page 59: Simple Soil Structure Interaction in innovative foundation design.pdf

Settlement of Tower 1 ColumnsS

ettle

men

t –m

.m.

Page 60: Simple Soil Structure Interaction in innovative foundation design.pdf

Petronas Towers: Conclusions and Lessons Learned

� In-situ testing with empirical correlations works well enough for engineering purposes .

� Menard Empirical procedures yield better settlement predictions compared to elastic theory using test pressuremeter modulus values as the Young’s modulus for the soil and geologic conditions reported herein.

� Simple hand calculations for settlement and bearing capacity can be as reliable as sophisticated computer solutions.

� Innovative cost effective foundation solutions are often possible with close interaction of geotechnical and structural engineer and cooperation of experienced contractor.

Page 61: Simple Soil Structure Interaction in innovative foundation design.pdf

References � C.N. Baker, Jr. and T.P. Wiesinger, “Modified Mat

Foundation Design Over Soft Clay”, ASTM Special Technical Publication 584

� C.N.Baker, Jr., T.D. Bushell, Rob Diebold, “Dearborn Center: A Unique Soil Structure Interaction Design”, Fifth International Conference on Case Histories, N.Y., N.Y., April, 2004.

� C.N. Baker, Jr., T.A. Kiefer, Kolbjorn Saether, “Use of Straight Shaft Piers as Settlement Reducers in Combined Footing Design Over Soft Clay”, Fifth International Conference on Case Histories, N.Y., N.Y., April, 2004.

� C.N. Baker, et. Al., Foundation Design and Performance of the World’s Tallest Building, Petronas Towers,” Fourth International Conference on Case Histories, St. Louis, March 1998.

Page 62: Simple Soil Structure Interaction in innovative foundation design.pdf

Questions???