03 Shuttle

Draft Subject To Revision 3/7/2012

1

Compaction Grouting Consensus GuideShort Course

Compaction Grouting DesignDr. Dawn Shuttle, PE

Objectives of the Design Module

1.Become familiar with standard CGdesign.

2.Know what can be densified, and why.

3.Understand why slower injection isbetter…..

4.Understand the limitations of standardanalysis of compaction grouting.


2

Slides 5 to 8 have been relocated to‘advances’

Start with the conceptual model ….Soil Behavior 101

Loose soil contracting during shear….


3

Soil Behavior 101

Dense soil expanding during shear….

BUT we don’t want the soil to expand

Soil Behavior 101

-5-4-3-2-1012345

volu

met

ric s

train

: %

contraction

expansion

0

200

400

600

0 5 10 15axial strain: %

devi

ator

stre

ss, q

: kPa

Loose

-5-4-3-2-1012345

volu

met

ric s

train

: %

contraction

expansion

0

200

400

600

800

1000

0 5 10 15axial strain: %

devi

ator

stre

ss, q

: kP

a

Dense

Easy tocompactiongrout Impossible to

compactiongrout


4

0.500

0.600

0.700

0.800

0.900

10 100 1000 10000

Mean effective stress, p' (kPa)

Void

ratio

, e

emax

CSL

G667

G665G662

G681G682

G685

cee

Erksak

Loose

Dense

Relationship between Dr and SoilDescription

RelativeDensity (%)

DescriptiveTerm

Approximate

0 – 15 Very loose +0.1

15 – 35 Loose 0.0

35 – 65 Medium Dense -0.05

65 – 85 Dense -0.1

85 – 100 Very Dense -0.3

minmax

max

eeeeDr

0 3

3 10

10 18

18 30

>30


5

Density matters

• CG only works for‘looser’ soils

• Generally > 0.05• If soil is ‘dense’ CG canactually make looser….

• If in doubt, considersome shear box (ortriaxial) testing

• Or consider CPT testing-5-4-3-2-1012345

volu

met

ric s

train

: %

contraction

expansion

0

200

400

600

0 5 10 15 20 25 30 35 40axial strain: %

devi

ator

stre

ss, q

: kPa

Dense

What about the increase of meaneffective stress?

By far the most “bang for your buck” from shearing

mean stress increase

shearing


6

Drained vs. Undrained

Drained loading

Undrained loading +consolidation

Modified from Kovacevic et al., 2000

contraction

Drained or Undrained ?

ALWAYS DRAINED !


7

Practically Injection Rate

• Typical injection rate is on the order of2ft3/min. ( 57 litres/min)

• Slower rates may be needed for sensitiveapplications.

• Higher rates may be used under certainconditions (but likely needs advancedmonitoring and/or analysis).

CG Mechanics – Injection Rate• However, grouting at high injection ratesmay be harder to control.

• High injection ratesmay produce undrainedbehavior.

– Densification is reduced significantly.

– Injection pressure is greatly increased.

• Rule of thumb, 8 psi/min; 1 to 2 ft3/min.55 kPa; 28 to 57 litres/min


8

CG Mechanics – Injection Rate• Injection rates should be slow enough toallow pore pressure dissipation consistentwith the surrounding soils’ permeabilityrate. => successful compaction

• Unbalanced injection rates can producehydraulic fracturing.

• Hydrofracture formation can preclude thecontrolled intergranular shearing necessaryto successful densification.

Soils types suitable for CG

• Need the grout to displace the grout, notpermeate into the soil’s pore space

• Need pore pressures to dissipate….

GRAVEL USUALLY NOT SUITABLE

But low mobility grout is good for filling voids

CLAYS NOT SUITABLE, SILTS ????


9

Pressure at depth

• The pressure that matters is the pressure atgrout injection – not at surface

• Measuring this will be covered in detail in“Field Advances”

• Simpler (although less accurate) approach isthe offset approach

gaugepressure

length

Atmosphericpressure

Pressure drop down groutpipe = pressure drop / length


10

Design – questions before we start

• Is the soil suitable ? (density, type)

• Layering ?

• Nearby structures or topography changes ?

Design considerations

• Layering ?

from Byle (2000)


11

Design considerations

• Nearby structures ?

• Topography change ?

Building foundations

Utilities

Slope

Cliff

Effect of confinementvery loose


12

Effect of confinementloose

With confinement = +0.05

Very Loose Silty Sand

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0 0.25 0.5 0.75 1 1.25 1.5

Radial Distance from Grouthole (m)

Initial Void Ratio1 ft3 ( 0.03 m3)2 ft3 (0.06 m3)3 ft3 (0.09 m3)4 ft3 (0.11 m3)5 ft3 (0.14 m3)7 ft3 (0.20 m3)


13

with confinement = -0.10

Medium Dense Silty Sand

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0 0.25 0.5 0.75 1 1.25 1.5

Radial Distance from Grouthole (m)

Initial Void Ratio1 ft3 ( 0.03 m3)2 ft3 (0.06 m3)3 ft3 (0.09 m3)4 ft3 (0.11 m3)5 ft3 (0.14 m3)7 ft3 (0.20 m3)

CG Mechanics – Confinement• Soil densification more effective if confinedby stiffer soil zones, either above or adjacentto the expanding grout mass.

• Enables development of higher localstresses, forcing particles closer togetherduring shear.

• Importance of drilling/injecting in sequenceon a grid pattern.


14

Grout quantity estimate

• To reliably estimate grout quantities you needreliable in situ soil properties– Sadly, there really is no way round this– Will the soil dilate or contract ?– Density– Layering

• Need a good low mobility grout• Control of injection• Slow injection• Remember some ‘leakage’

10 m

8 m

Plan

Layer 1: Dense sand

Layer 2: Fill

5 m d = 1360 kg/m3

Layer 3: Rock

Soil Profile

Proposed Building


15

Example ‘grout volume estimate’calculation

• Current density (kg/m3) = 1360

• Target density (kg/m3) = 1700

• Required reduction in volume (%) 20 %mass of soil remains constant

Mass = Volume * Density

Convenient to assume initial volume = 1

1 * 1360 = Final Vol * 1700

Final Vol = 0.80

1 – 0.8 = 0.2

Example ‘grout volume estimate’calculation

• Volume of soil to be grouted (m2) = 5*(8+10) * (10+10) = 1800

• Volume of grout to be injected (m2) = 0.2 * 1800 = 360

• Volume per metre depth (m2) = 360 / 5 = 72

• Spacing = 2.5 m (usually about 2 – 3.5 m)

• Number of holes 18 /2.5 * 20/2.5 72

• Grout per hole per m depth (m3) = 360/(5*72) = 1.(radius = 0.56 m)


16

Layout of the holes

row

row

row

row

row

Typical spacing 6 12 ft (1.8 – 3.6m)

Confine


17

Fill in

Remember the columns will move…

so need to “round up” volumes


18

Controlling Grout Injection(and the things to watch…)

• Pressure limit at a given injection rate– The injection rate matters !

• Volume of grout limit– This is usually quoted per stage

• Monitor movements– Buildings, utilities, etc

• Maximum lift at surface– Raising the ground surface has little effect on thein situ soil density (i.e. avoid!!)

Points for the contract

• Remember you’re paying to have the soilmade denser – NOT to pump grout.

• So either– Specify the final soil density and how this densitywill be confirmed, or

– Specify RATE as well as volume and limitingpressure for refusal


19

Points to take away

• Compaction grouting works by shearing thesoil to very high strains

• Loose soils densify during shearing (but densesoils can loosen)

• Undrained soils don’t change volume duringshearing (so CG won’t work)

• Compaction grouting is not difficult to design,but does need a good knowledge of the soiland the site

Thank you for your kind attention

The Presenters for the Compaction Grouting Consensus Guide Short Course, their employers, affiliates,successors, and anyone acting under their authority disclaim any and all liability for any personal injury, propertydamage, financial loss, or other damages of any nature whatsoever, including without limitation any direct,indirect, special, exemplary, or consequential damages, resulting from any person’s use of, or reliance on any andall materials presented at the aforesaid short course, which is presented for information purposes only.

03 Shuttle

Documents

Transcript of 03 Shuttle