Field performance of Fully Grouted piezometers - Sisgeo · Field performance of Fully Grouted piezometers Lucia Simeoni , Fabio De Polo, Giovanni Caloni, ... etop etop t top

FMGM2011 – L. Simeoni, F. De Polo, G. Caloni & G. Pezzetti - [email protected]

Field performance of Fully Grouted

piezometers

Lucia Simeoni*, Fabio De Polo**, Giovanni Caloni***, Giorgio Pezzetti****

* University of Trento, Italy

** Autonomous Province of Bolzano, Italy

*** SisGeo s.r.l., Italy

**** Field s.r.l., Italy

FMGM2011 – L. Simeoni, F. De Polo, G. Caloni & G. Pezzetti - [email protected] 2

Past experiences

McKenna (1995):

Field tests with pneumatic piezometers

Upper piezometers

Lower piezometers

Small reading differences of about 2 kPa

Periodical measurements -> Question: “What is the response time”?


Past experiences

Mikkelsen & Green (2003):

Laboratory tests with vibrating wire piezometers

Response time of a couple of minutes

One grout and geometry -> Question: “What the response time depends on?”

Chamber

Piezometer


Questions

1. How can we evaluate the response time?

2. Is it acceptable for a real time

assessment of the stability of river

embankments?


Testing program

1. Laboratory testing for analysing the

response time

2. Field testing for verifying the acceptability


Laboratory

porewater pressure

control/measurement

cell pressure control

porewater pressure

measurement

soil

specimenO-ring sealimpermeabile flexible

membrane

porous stone

Measured pressure

Imposed pressure

Grout:

water+cement+bentonite

2.5 - 1 - 0.3

Size:

D = 7 cm

H = 2, 4 o 8 cm

Resistive transducer


Laboratory

Test

name

Pressure

changeS2-01 S4-01 S8-01 S2-02 S4-02 S8-02 S4-03 S8-03

From

[kPa]

To

[kPa]

A 20 100 x x x x x x x

B 100 200 x x x x x x x x

C 200 300 x x x x x x x x

D 300 500 x x x x x x x x

E 500 300 x x x x x x x x

EA 300 310 x x

EB 310 330 x x

EC 330 360 x x

ED 360 410 x x

EE 410 480 x x

EF 480 410 x x

EG 410 360 x x

EH 360 330 x x

EI 330 310 x x

EL 310 300 x x

F 300 200 x x x x x x x x

G 200 100 x x x x x x x x

H 100 20 x x x x x x

I 20 30 x x x x x x

L 30 50 x x x x x x

M 50 80 x x x x x x

N 80 130 x x x x x x

O 130 200 x x x x x x

P 200 130 x x x x x x

Q 130 80 x x x x x x

R 80 50 x x x x x x

S 50 30 x x x x x x

T 30 20 x x x x x x

Sample S2-01 S4-01 S8-01 S2-02 S4-02 S8-02 S4-03 S8-03

Height

[cm] 2 4 8 2 4 8 4 8

Treming

group 1 1 1 2 2 2 3 3

Cruring time

[days] 43 30 37 43 36 38 50 48

141 pore water pressure

increments/decrements

8 samples “tremied” and left curing

under deaired water


Laboratory

0 2 4 6 8 10 12 14 16Time (min)

80

100

120

140

160

180

200

Wat

er p

ress

ure

(k

Pa)

S8-01 test BImposed Bottom pressure

Measured Top pressure

0 2 4 6 8 10 12 14 16Time (min)

80

100

120

140

160

180

200

Wat

er p

ress

ure

(k

Pa)

S8-01 test GMeasured Top pressure

Imposed Bottom pressure

increment decrement

150 kPa

150 k

Pa

Step 1: flushing

600 kPa

600 k

Pa

20 kPa

Step 2: cell pressure increment

600 kPa

600 k

Pa

Step 3: pore water pressure change

Measured

Imposed


Laboratory

0,

,

, 1etop

tetop

ttopu

uU Degree of excess water pressure

95.0:95,95 ttopUt

The response time t95 would not rely on the pore water pressure

Response time

1. water and soil incompressible;

2. Darcy’s law holds;

3. equalization volume approximately linear with the change in

water pressure (by b [L2])

gAk

Hbt 395

kg [L/T] H [L]

A [L2]

Definitions:

Assumptions:

Response time:


Laboratory

t95 decreases with increasing uaverage

0 50 100 150 200 250 300 350 400 450u average (kPa)

0

1

2

3

4

5

6

7

8

t 95 (

min

)

2 cm, uw

4 cm, uw

8 cm, uw

2 cm, dw

4 cm, dw

8 cm, dw

H = 8 cm

H = 4 cm

H = 2 cm

t95 < 8 min


Laboratory

(ua-uw)

J

Js

J

r

Drying(dw)

Wetting(uw)

s* JsJr J

k/ks

t

u

z

u

u

kee

e

w

g

2

2

J

0,

,

, 1etop

tetop

ttopu

uU

Degree of excess water pressure “Terzaghi’s equation”

95.095, ttopU

0 50 100 150 200 250 300 350 400 450u average (kPa)

0

1

2

3

4

5

6

7

8

t 95 (

min

)

2 cm, uw

4 cm, uw

8 cm, uw

2 cm, dw

4 cm, dw

8 cm, dw

H = 8 cm

H = 4 cm

H = 2 cm

•t95 depends on u

•Incompressibility

and saturation are

nolonger valid

•kg, J vary with u

•kg, J/u

constant for a

given range of u


Laboratory

uaverage = 20 ÷ 500 kPa cv = 2 ÷ 90 cm2/min

e

w

g

v

Δu

Δγ

kc

J

coefficient of “consolidation”

cv estimation by best-fitting

v

2

95c

H1t

0 50 100 150 200 250 300 350 400 450u average (kPa)

0

10

20

30

40

50

60

70

80

90

c v (

cm2/m

in)

2 cm, uw

4 cm, uw

8 cm, uw

2 cm, dw

4 cm, dw

8 cm, dw

H = 8 cm

H = 4 cm

H = 2 cm

0.001 0.01 0.1 1t/H2 (min/cm2)

0

0.2

0.4

0.6

0.8

1

Uto

p

S8-03 test Bmeasured

computed


Field

Fully grouted piezometers would make the installation faster and easier.

About 140 km of the Adige River (Bozen, Italy) flows between embankments.

More than 100 piezometers and open standpipes have been used to monitor their stability.


Field

Field test: right-side embankment of the Adige River @ Egna (Bozen, Italy)

Fully grouted piezometer

Conventionally installed piezometer


dataloggerFully-grouted

FGPTraditional

TP

aa

b

b

Water table

on 14.03.11Bentonite

seal

Fine gravel

pack

Cement-clay

grout

a

b

Unit AEmbankment

Unit C1Upper fluvio-lacustrine deposit

Unit C2Lower fluvio-lacustrine deposit

Adige River

Sandy silt

Silty sand

with gravel

kh=10-4 m/s

kh=10-5 m/s

Gravel with

silty sand

15

Field

217.09 m a.s.l. 217.09 m a.s.l.

209.52

204.97

210.49

204.09

4 m

Soil profile Geometry

a: upper piezometers “not recoverable”

b: lower piezometers “recoverable”


a

b

Unit AEmbankment

Unit C1Upper fluvio-lacustrine deposit

Unit C2Lower fluvio-lacustrine deposit

Adige River

Sandy silt

Silty sand

with gravel

kh=10-4 m/s

kh=10-5 m/s

Gravel with

silty sand

16

Field

Grain size distribution

0.001 0.01 0.1 1 10 100

d (mm)

0

20

40

60

80

100

fractio

n f

ine

r %

TP2 (C1-211.2)

TP3 (C1-210.6)

TP5 (C1-208.7)

TP7 (C2-204.9)

FGP1 (C1-209.6)

FGP2 (C2-204.6)

0.002 0.006 0.02 0.06 0.2 0.6 2 6 20 60 200

Clay Silt

Fine Medium Coarse Fine Medium Coarse Fine Medium Coarse

Sand Gravel Cobble

217.09 m a.s.l.

Soil profile

C1 C2


dataloggerFully-grouted

FGPTraditional

TP

aa

b

b

Water table

on 14.03.11Bentonite

seal

Fine gravel

pack

Cement-clay

grout

17

Field

217.09 m a.s.l.

209.52

204.97

210.49

204.09

4 m

Materials Geometry

Fully grouted Piezometer

Grout:

water 2.5

cement 1

clay 0.45

Traditional Piezometer

Gravel pack:

fine gravel 2-6 mm (1.25 m height)

Bentonite seal:

bentonite pellets


Field

a: Upper piezometers “not recoverable” (type Sisgeo P235S1)

• resistive transducer, absolute;

• filter: ceramic, diameter 15 mm e pore size 0.25 mm;

• FS: 100 kPa.


Field

a: Upper piezometers “not recoverable” (type Sisgeo P235S1)

The filter screwed underwater Transducer fastened upside-down


Field

b: Lower peizometers “recoverable” (type Sisgeo P252C)

• resistive transducer, absolute;

• filter: sinterized, pore size 40 mm;

• conical tip fitted with o-ring;

• FS: 200 kPa;

• Casagrande filter 200 mm (P101);

• blind pipe1.5”.


Field

FGP: installation (March 2011)

a

b

1

Instrumentation insertion

standpipe

Casagrande filter

Transducer a

b

2

Grouting bottom-up

a

b

3

Drill casing retrieving

Drill casing


Field

Hydraulic conductivity

Material kv o kh (m/s) test

Grout Kv/kh 10-10Laboratory/field, falling head;

Sandy silt C1 kh 10-5field, falling head

Silty sand with gravel C2 kh 10-4field, falling head

k grout << k soil


Field

Hydraulic conductivity

Material kv o kh (m/s) test

Grout Kv/kh 10-10Laboratory/field, falling head;

1.0E-11

1.0E-10

1.0E-09

1.0E-08

1.0E-07

0 5 10 15 20 25

kv [m

/s]

days

215.80

215.90

216.00

216.10

216.20

216.30

216.40

216.50

00:00:00

00:03:25

00:06:50

00:10:15

00:13:40

00:17:05

00:20:30

00:23:55

00:27:20

00:30:45

00:34:10

00:37:35

00:41:00

00:44:25

00:47:50

00:51:15

00:54:40

00:58:05

01:01:30

01:04:55

01:08:20

01:11:45

01:15:10

01:18:35

01:22:00

01:25:25

01:28:50

01:32:15

01:35:40

01:39:05

01:42:30

01:45:55

01:49:20

01:52:45

01:56:10

01:59:35

02:03:00

h [m]

t [h.mm.ss]

Laboratory: 1.3x10-10 m/s after 15 days Field: 4.0x10-10 m/s

2 h

35 c

m


Field

Measurements: May 19 to May 31, 2011

a: upper piezometers

“not recoverable”

b: lower piezometers

“recoverable”

19/5/11 21/5/11 23/5/11 25/5/11 27/5/11 29/5/11 31/5/11data (dd/m/yy)

211

212

213

214

215

216

217

H (

m)

Upper piezometers

FGPa (209.5 m)

TPa (210.0-211.3 m)

Adige River

19/5/11 21/5/11 23/5/11 25/5/11 27/5/11 29/5/11 31/5/11data (dd/m/yy)

211

212

213

214

215

216

217

H (

m)

Lower piezometers

FGPb (205.0 m)

TPb (204.0 m)

Adige River

water extraction river rise

Coherent

with downward

seepage

Not coherent

with downward

seepage


10/6/11 17/6/11 24/6/11 1/7/11 8/7/11data (dd/m/yy)

-0.6

-0.4

-0.2

0

0.2

0.4

H

(m

) Differences

FGPa-TPa

FGPb-TPb

25

Field

Measurements: June 10 to July 11, 2011

Hydraulic heads

Differences

river rises Coherent with downward seepage

10/6/11 17/6/11 24/6/11 1/7/11 8/7/11data (dd/m/yy)

212

213

214

215

216

217

H (

m)

FGPa (209.5 m)

TPa (210.0-211.3 m)

FGPb (205.0 m)

TPb (204.0 m)

Adige River


Conclusions 1/2

Very good conformance of fully grouted piezometers in terms of response time

(some minutes, depending on the drainage path);

Response time could be calculated with cv=2÷90 cm2/min. It depends on

stiffness, hydraulic conductivity, degree of saturation;

In the field, small differences in hydraulic head were calculated between fully

grouted and traditional piezometers;

Differences should be due to different response times and/or gravel pack

height;

Response time of fully grouted piezometers resulted acceptable to monitor the

stability of river embankments


Conclusions 2/2

Fully grouted method provides an easier and faster installation, more precise

control of transducer depths.

The use of “standpipe + Casagrande filter” allows the use of a transducer with

large pore sinterised filter, making easier its saturation.

With the “standpipe + Casagrande filter” the transducer may be retrieved.

Fully grouted piezometers must be avoided when the average value of pore

water pressure in an interval depth is needed.


Thank

you!

Documents

Field performance of Fully Grouted piezometers - Sisgeo · Field performance of Fully Grouted piezometers Lucia Simeoni *, Fabio De Polo**, Giovanni Caloni***, ... etop etop t top

Field performance of Fully Grouted piezometers - Sisgeo · Field performance of Fully Grouted piezometers Lucia Simeoni , Fabio De Polo, Giovanni Caloni, ... etop etop t top