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Simplify Piezometer Installations, Lower Costs Simplify Piezometer Installations, Lower Costs and Get Better results withand Get Better results with

Fully Grouted PiezometersFully Grouted Piezometers

P. Erik Mikkelsen, P.E.Consulting EngineerGeoMetron Inc PSBellevue, WA, USA

Univ. of Florida Short Course, March 19, 2007

Open Standpipe PiezometerOpen Standpipe PiezometerObviously low material costs, but …...– Time consuming recording– Time-lag potential– Minimal and un-timely observations

Installation sensitivity/problems– time consuming backfill procedures– complicated backfill– risk of incomplete backfill

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VW Piezometer SensorsVW Piezometer SensorsAdvantages– instant reading, not influenced by observer– can be fully grouted– best suited for automated readings– calibration not influenced by lead length– high zero stability (minimal drift for decades)

Disadvantages– vulnerable to over-voltage, need protection– calibration factors, barometric influence– can be damaged by over-pressure

(After Slope Indicator)

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Fully grouted piezometerFully grouted piezometer

Why grout? …Eliminates complexityWhy does it work? …It is like saturated clay!Works like piezo sensor pushed into clayMix design? …Design based on cement content.Grout properties (new research results)

Mandrel pushedMandrel pushed--in VWP in soft clayin VWP in soft clay

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Casagrande missed the point that pressure sensors are different!

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Darcy’s Law for FlowDarcy’s Law for Flow

Grout Type Characteristics k (cm/sec) SourceNeat cement w/c = 0.53, γ = 112 pcf 10-7 Baroid

Bentonite chips hydrated 10-8 BaroidBentonite slurry 6 % solids 10-5 BaroidBentonite slurry 20 % solids 10-8 Baroid

Cement-bentonite water/solids = 4 to 1 10-6 Vaughan, 1969Cement-bentonite w : c : b = 4 : 1 : 1 5 x 10-8 Vaughan, 1973

Table 2. Permeability of some grouts

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CementCement--Bentonite GroutBentonite GroutMix ratio by weight - 2.5 water : 1 cem : 0.37 bent + or – according to consistencyMix water and cement first Add bentonite slowly, high agitation, make grout creamy, yet pumpable (Marsh # 50-60 sec)Density - 80 pcf Water Content - >100 % Modulus - about 10,000 psi30- day QU strength - 50 to 100 psiPermeability – k = 1.0E-06 cm/sec.

0

20

40

60

80

100

120

0 2 4 6 8 10 12 14

Water-Cement Ratio by Weight

Unc

onfin

ed C

ompr

essi

ve S

treng

th in

psi Marsland, 1973

Slope Indicator, 1982

Dunnicliff, 1980

Anderson, 1984 Minnitti, 1980

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VWP in Grout, 200mm thickness, 288 days curing

0

5

10

15

20

25

30

35

40

0.00 5.00 10.00 15.00 20.00

Lapsed Time in Minutes

Pres

sure

Hea

d in

Fee

t

PiezometerChamber

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VWP in Grout, Response Time vs. Curing in Days200mm grout thickness

01234

0 50 100 150 200

Curing Time in Days

Tim

e in

Min

utes

50%90%95%100%

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Normalized Cement-Bentonite Grout Properties(Marsh Number = 50 to 60 sec.)After Barr Engineering 3/9/05

0

0.5

1

1.5

2

2.5

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0

Water-Cement Ratio - w/c

Nor

mal

ized

Val

ue o

f Den

sity

, Voi

d R

atio

&

Stre

ngth

0

20

40

60

80

100

Nor

mal

ized

Val

ue o

f Per

mea

bilit

y - k

Density(pcf) = 83.8 xVoid Ratio = 4 xUCC strength = 240 xk (cm/sec) = 1.0E-7 x

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Fully grouted multiFully grouted multi--level VWPslevel VWPs

Barometric Pressure and Rainfall, Oregon Coast

950

960

970

980

990

1000

1010

1020

1030

10/1/990:00

10/31/9912:00

12/1/990:00

12/31/9912:00

1/31/000:00

3/1/0012:00

4/1/00 0:00

1999 / 2000

mill

ibar

s or

cm

of H

2O

0

0.6

1.2

1.8

2.4

3

3.6

4.2

4.8R

ainf

all p

er 1

2 ho

urs,

In

ches

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VWP - Altitude Correction

0.00

2.00

4.00

6.00

8.00

10.00

12.00

0 2000 4000 6000 8000 10000 12000

Altitude - Feet

Cor

rect

ion

- Fee

t

0.00

1.00

2.00

3.00

4.00

5.00

6.00C

orre

ctio

n - P

SI

feet of H2OPSI

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Fully Grouted Piezometer ProjectFully Grouted Piezometer Project

Raw data for fully grouted VWPRaw data for fully grouted VWP

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PROFILE 2: Pore Pressure Elevations Grnd. Elev. Assumed = 20 m

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

22.0

24.0

26.0

28.0

30.0

32.0

1-May-01 1-Jul-01 31-Aug-01 31-Oct-01 31-Dec-01 2-Mar-02

Pie

zom

etric

Ele

vatio

n, m

eter

s

#9, elev. 18.1 m#8, elev. 18 m#10, elev. 12 m#12, elev. 10.5 m#11, elev. 9 m#13, elev. 8 mEmb. Elevation

#9 #8

#10#12

#11#13

PROFILE 1: Pore Pressure Elevations,Grnd. Elev. Assumed = 20 m

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

22.0

24.0

26.0

28.0

30.0

32.0

1-May-01 1-Jul-01 31-Aug-01 31-Oct-01 31-Dec-01 2-Mar-02

Pie

zom

etri

c El

evat

ion,

met

ers

#1, elev. 18.3 m#3, elev. 11.5 m#2, elev. 11 m#5, elev. 11 m#7, elev. 10 m#6, elev. 6.5#4, elev. 5 mEmb. Elevation#4

#6

#7

#5 #2#3

#1

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CC--B grout: 55 gal. paddle mixerB grout: 55 gal. paddle mixer

400400--m deep Mm deep M--L VWP installationL VWP installation

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ConclusionsConclusionsCement-bentonite grout works!Simpler and faster installationLess chance of failed installationWorks as a high air-entry filterIt always starts out fully saturatedEliminates risk of bentonite “activity”Applicable to both boreholes and embankments