Field performance of Fully Grouted piezometers · FMGM2011 –L. Simeoni, F. De Polo, G. Caloni &...
Transcript of Field performance of Fully Grouted piezometers · FMGM2011 –L. Simeoni, F. De Polo, G. Caloni &...
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”?
FMGM2011 – L. Simeoni, F. De Polo, G. Caloni & G. Pezzetti - [email protected] 3
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
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Questions
1. How can we evaluate the response time?
2. Is it acceptable for a real time
assessment of the stability of river
embankments?
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Testing program
1. Laboratory testing for analysing the
response time
2. Field testing for verifying the acceptability
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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
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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
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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
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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:
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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
FMGM2011 – L. Simeoni, F. De Polo, G. Caloni & G. Pezzetti - [email protected] 11
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
FMGM2011 – L. Simeoni, F. De Polo, G. Caloni & G. Pezzetti - [email protected] 12
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
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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.
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Field
Field test: right-side embankment of the Adige River @ Egna (Bozen, Italy)
Fully grouted piezometer
Conventionally installed piezometer
FMGM2011 – L. Simeoni, F. De Polo, G. Caloni & G. Pezzetti - [email protected]
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”
FMGM2011 – L. Simeoni, F. De Polo, G. Caloni & G. Pezzetti - [email protected]
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
FMGM2011 – L. Simeoni, F. De Polo, G. Caloni & G. Pezzetti - [email protected]
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
FMGM2011 – L. Simeoni, F. De Polo, G. Caloni & G. Pezzetti - [email protected] 18
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.
FMGM2011 – L. Simeoni, F. De Polo, G. Caloni & G. Pezzetti - [email protected] 19
Field
a: Upper piezometers “not recoverable” (type Sisgeo P235S1)
The filter screwed underwater Transducer fastened upside-down
FMGM2011 – L. Simeoni, F. De Polo, G. Caloni & G. Pezzetti - [email protected] 20
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”.
FMGM2011 – L. Simeoni, F. De Polo, G. Caloni & G. Pezzetti - [email protected] 21
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
FMGM2011 – L. Simeoni, F. De Polo, G. Caloni & G. Pezzetti - [email protected] 22
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
FMGM2011 – L. Simeoni, F. De Polo, G. Caloni & G. Pezzetti - [email protected] 23
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
FMGM2011 – L. Simeoni, F. De Polo, G. Caloni & G. Pezzetti - [email protected] 24
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
FMGM2011 – L. Simeoni, F. De Polo, G. Caloni & G. Pezzetti - [email protected]
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
FMGM2011 – L. Simeoni, F. De Polo, G. Caloni & G. Pezzetti - [email protected] 26
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
FMGM2011 – L. Simeoni, F. De Polo, G. Caloni & G. Pezzetti - [email protected] 27
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.