deep mixing columns - 03 sabatini

7/24/2019 Deep Mixing Columns - 03 Sabatini

1/11

EVALUATIONOFDEFECTSINDEEPMIXING

METHOD

COLUMNS

USED

FOR

STRUCTURAL

FOUNDATIONSUPPORT

Paul

Sabatini

October

17,

2012

Geosyntec

Consultants

Oak

Brook,

IL

ProjectOverview

Some 6,000, 23m long DMM elementswere installed to support 124 LNG processtrain mats

During early phases of construction, coringrevealed clay inclusions and unmixed zones

Owner requested analyses andassessments to confirm a fit

for

purpose

foundation system


2/11

Project

Overview

(Cont.) We reviewed available DMM core data

Contractors QA/QC coring program should

be increased

Site activities and investigations proposed

to provide reliable physical data

Contractor declined to implement our

investigative proposals

DMMCoreReview


3/11

As

Built

DMM

Elements

SummaryofCoreEvaluation

Summarized results of 182 cores using

Contractor field observations of full

diameter poor quality core (PQC)

Information used to define defect scenarios

for 3D numerical modeling

Design Defect Length = 1 m

Worst Case Defect length = 2m


4/11

Numerical

Modeling 3D finite element analyses of DMM columns

(with defects) and foundation mats

Use Zone 5 foundation with lowest DMMreplacement ratio (i.e., on the order of 0.35)because drag loads would be largest

Drag loads from longterm settlements in theUnit II clays

Seventeen (17) cases without downdrag and

five additional cases with downdrag

AnalysisModel


5/11

Loaded

Areas

of

Mats

Checkerboard(CB)EntireMat A50Partial

A load of 50 kPa is applied over the shaded areas.

The self-weight of the mat, 18 kPa, is applied over the remainderarea of the mat.

HorizontalDistribution

of

Defect

Regions

RegionA RegionCRegionB

RegionD RegionFRegionE


6/11

HorizontalDistributionofDefectRegions(Cont.)

RegionAModified RegionBModified2RegionBModified1

RegionFModified RegionCBOutRegionCBIn

VerticalDistribution

of

DMM

Column

Defects

2mDefectDistribution 1mDefectDistribution

0.5 m DefectUnit I

Layer

Unit II

Layer

Unit IIIA-1

Layer

+2.23 m LAT+2.73 m LAT

-0.5 m LAT0 m LAT

-6 m LAT-5 m LAT

0.5 m Defect

1.0 m Defect

Bottom of Mat

Unit I

Layer

Unit II

Layer

Unit IIIA-1

Layer

-0.5 m LAT0 m LAT

-5.5 m LAT-5 m LAT

0.5 m Defect

0.5 m Defect

Bottom of Mat


7/11

Results

for

Perfect

DMM

Case

Soil LayersSettlement

(mm)

Layer

Thickness

(m)

Unit I 1.1 3.98

Unit II 6.7 3

Unit IIIA-1 10.4 11

Unit IIIB-1 3.2 7

Unit IIIB-2 4.3 12

Unit V 4.3 6

Unit VI 3.5 36

Sum 33.4 78.98

ResultsforA50Case

MaxSettlement=36.3mm

Min.S22=2130kPa

Max.S22=1950kPa


8/11

Results

for

B50

Case

MaxSettlement=43.9mm

Min.S22=3210kPa

Max.S22=2970kPa

EffectsofDefects

Case Settlement

(mm)

MatStress

(%

of

Design

Allowable)

MatStress

(%

of

Ultimate)

Perfect 33.4 85 52

A50 36.3 104 64

B50 43.9 157 96

B50 Modified1 34.6 82 51

B50 Modified2 36.0 83 51

Pressure=50kPa

DefectLength=2m


9/11

Summary

Defects

Only Even for perfect DMM elements, 85

percent of the allowable design stressesare mobilized

Partial defects on the edges or in interiorDMM island elements are not critical andresult in computed stresses very similar tothose where no defects exist

Defects are critical if they are continuous

across multiple DMM elements

Downdrag,Non

Uniform

Loading

and

DMMElementswithDefects

Address effects of downdrag settlements onmat supported by perfect DMM elements andthose with defects

Downdrag settlements result from secondarycompression settlements of the Unit II clays

Analyses are conducted for a 3m thick and 6mthick Unit II clay layer

Nonuniform (i.e., checkerboard) loading also

considered


10/11

CriticalDowndrag Scenario

UnitILayer

UnitIILayer

0.5mLAT0mLAT

5.5mLAT5mLAT

0.5mDefect

0.5mDefect

BottomofMat

UnitIIIA1Layer

8Defects

2Defects

15cm

0cm

UnitII

5cm

DistributionofDMMColumnDefects,DefectRegionsandLoadingArea

SecondaryCompressionSettlements oftheUnitIIsoillayer

EffectsofDefectsandDowndragDefectAssessment Downdrag Assessment

C as e Se tt le me nt

(mm)

MatStress

(%ofDesign

Allowable)

MatStress

(%of

Ultimate)

Downdrag

Settlement

(cm)

Settlement

(mm)

MatStress

(%ofDesign

Allowable)

MatStress

(%of

Ultimate)

Perfect 33.4 85 52 10/5 49.4 104 64

A50Modified

1m

34.1 84 52 10/5 50.7 103 64

CBPerfect 32.6 104 64 15/5 51.1 122 75

CBInside

Modified1m

33.8 119 73 15/5 52.9 141 87


11/11

Summary Downdrag settlements result in significant

increases in DMM and mat stresses

For Case A50Modified1m, computed mat stressesare very similar to those for the Perfect case

Even with nonuniform loading, continuous defectsup to 1m long, and the largest postulateddowndrag settlements, computed mat stresses forCase CBInsideModified1m are less than theequivalent ultimate concrete stress for the mat

ProjectSpecific

Conclusions

on

FoundationFitnessforPurpose

Foundation mats with three (3) interior DMM islandelements or more are fitfor purpose

Mats with only one interior DMM island element are mostprone to adverse performance if defects exist in thatelement

The assumption of defects (or completely unmixed zones)occurring at specific elevations and which penetrate acrossthe entire width of a DMM element is conservative

Most of the dead load for each mat has been applied andmeasured total settlements range from less than 2 mm to10 mm.

deep mixing columns - 03 sabatini

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