Design Construction and Perfromance of Stone Column - 07 Dawson

7/24/2019 Design Construction and Perfromance of Stone Column - 07 Dawson

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CASE HISTORY:

Design, Construction, and Performanceof Stone Column Ground Improvementbeneath an MSE Wall

Karen Dawson, P.E. & Sean Shin, Ph.D, P.E., CH2M HILL, Bellevue, WA, USA

Suthan Pooranampillai, Ph.D., AMEC E&I, Edmonton, AB, Canada

Dominic Parmantier, P.E., Condon Johnson & Associates, Inc., Kent, WA, USA

37thAnnual Conference on Deep Foundations

Houston, TX October 16-19, 2012

Presentation Overview

Description

Project

Subsurface Conditions

Design Considerations andMethods

Construction

Layout

Equipment

Quality

Observations

Conclusions


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Project Location

Subsurface Conditions

ML with occasional layers of MH,

CL, SM, and OL. Some gravel in

lower interbeds

Properties

PI = generally 0 to 15,

occasionally >20

Zones with organics (LOI up to 7%)

Cc = 0.14

c = 1.6 ft2/day

C = 0.005

pH = 4.5 and 5.9

Resistivity = 225 to 8200 -cm

Liquefiable under design 0.27 g

PGA


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Roadway Features

New bridge abutment and approach embankment up to 50high

Walls ~700 long required because of space limitations

Time available for preloading

Need for Ground Improvement

Liquefiable soils

Maintain global stability during seismic event

Secondary benefit - Limit consolidation settlement of wall


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Global Stability Cases

1. Static long-term

2. Static construction (included preload)

3. Start of shaking

4. During shaking

5. Post shaking

Design Steps

1. Defined allowable post-earthquake deformations

< 6 at bridge abutment

< 12 wall away from abutment

2. Determined yield accelerations that would result in allowable

deformations (Bray and Travasarou, 2007)

3. Determine composite strength from global stability analyses


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Design Steps Continued

4. Determine AR to provide composite strength

Used = 40 degrees for stone

Used equations by Priebe (1995) to develop composite

Increased stiffness from columns resulted in reduction in CSR

(Baez and Martin, 1993; Priebe, 1998) so that native soil

between columns was no longer liquefiable.

5. Use ground improvement factor (Priebe, 1995) to estimate

primary consolidation

Final Design

AR = 15%

10 month preload with 20% surcharge (additional criteria forpavement: limit secondary compression to 2 in 15 years)

Instrumentation for settlement verification


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Construction Contract Requirements

AR = 15%

Minimum column diameter = 30

qt > 110 tsf or N60 > 24 for clean or already dense layers

Yield plots to verify stone volume

Additional explorations to define bearing layer

Test sections Verify diameter and volume of stone in layered stratigraphy

Verify equipment response indicates bearing layer reached

Verify continuous stone by sonic coring

Means and Methods

Bearing LayerVerification

14 CPT

6 SPT

Total counting

owners

explorations ~

1 per 1,700 SF


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Means and Methods

Layout Triangular with 8 spacing and 3.25 diameter columns

Triangular with 11 spacing and 3.5 diameter through

existing embankment

D-54

D-56

E-55

F-54

F-56

O-169

O-171

P-170

R-169

R-171

TestArea1TestArea2

AREAA

AREAB

AREAC

CSWALL

RVWALL

8ft 8

ft

Means and Methods

Equipment Manitowoc 4000 and 4100

crawler cranes

Dry bottom feed electric

probe (V23) 11.7 x 13.8,

2.4 tons, 34 tons dynamic

force


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Means and Methods

After first test section, predrilled most holes (SR-60) 16 kelly

Means and Methods

Automated Data Acquisition System


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Data Acquisition System Printout

High amperage at tip

Observations

Vibrations: Mostly < 0.5 ips

Peak vector sum = 1.1 ips

with probe working 7 from

gas main.


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Observations

Fines migration intocore was variable

Clean core

Relatively clean core

Dirty core

Observations

Fines migration continued Correlation with

stratigraphy? Not that we

could tell.

Revised technique to

improve stone percentage

(e.g. shorter pulls, more

care in fully inserting probe

between pulls, changed air

pressure)


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Observations

Fines migration continued

Backcalculated c ignoring drainage to stone column

matches lab testing values and typical values in literature.

Laboratory average

cz = 1.6 ft2/day

Backcalc no radial drainage

cz = 1.5 to 2.0 ft2/day

Backcalc with drainage cr~ 0.5 ft

2/day

cz ~ 0.05 ft2/day

Conclusions

1. Abundance of subsurface explorations is important for

planning and pay, especially in layered stratigraphy (1 per

2,000 SF+)

2. Automated data acquisition system is and excellent tool for

quality control, especially in silty soils with AR-based

performance

3. Rapid drainage through stone columns should not be

assumed.


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Items for Improvement?

Methods for verifying insitu strength of stone column inAR-based design.

Questions?

Documents

Design Construction and Perfromance of Stone Column - 07 Dawson