Design, Testing and Emplacement of Sand-Bentonite for the ...

Design, Testing and Emplacement of
Sand-Bentonite for the construction of

a GAs-Permeable Seal Test
(GAST)

ICEM2013, 10th September 2013

S.P. Teodori, J. Rueedi, M. Reinhold, D. Manca

23.01.2014

Overview of the presentation

 Background, aims and design of the experiment
 Requirements / design criteria for a Sand/Bentonite (S/B) seal
 Testing campaign
 S/B QA / QC methods
 Major outcomes from the experiment emplacement
 Concluding remarks

Before (24.10.11)

@23.01.2014

Background

 NAGRA has proposed Opalinus Clay as possible host rock for a for a
L/ILW repository: low permeability and excellent barrier against
radionuclide transport

 Because significant amounts of gas are generated in a repository for
L/ILW, a demonstration that gas can escape without compromising
long-term safety is required

 “Engineered gas transport system" – EGTS: a seal made of
sand/bentonite mixtures with bentonite content of 20-30% which
exhibits a low permeability for water and a relatively high
permeability for gas

L/ILW repository concept Gas permeable repository seal
(Nagra, 2008) (Sand/Bentonite mixture)

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GAST: aims of the experiment

 Demonstration of the effective functioning of gas permeable seals at
realistic scale (“proof of the concept”)

 Validation and improvement of current conceptual models for the
re-saturation and gas invasion processes into S/B seals at realistic
scale

 Determination of up-scaled gas/water permeability of S/B seals (i.e.
two-phase flow parameters for large-scale models)

Experiment concept Before (24.10.11)
After (16.05.12)
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GAST experiment layout as emplaced

 Main features: 8 m seal length, 2.30 m effective height, emplaced in
28 layers of which 5 are instrumentation layers

2.30 m 3.50 m

2.00 m 8.00 m
12.00 m
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Requirements and design criteria for a S/B seal

Component Design criteria Requirements (Nagra, 2008)

S/B seal Homogeneous material properties Intrinsic permeability = 1E-18 m2
Cross-section as large as possible (Permeability = 1E-11 m/s)
Sodium bentonite MX-80 (Wyoming)

Initial knowledge Tashiro et al.,1998
 Hydraulic conductivity = f (d) S/B 70/30

S/B 90/10 S/B 80/20

 Previous projects at GTS demonstrated that it is
possible to design S/B mixtures with the desired
physical and hydraulic properties

Gas Migration Test (GMT) - RWMC

@23.01.2014

Overview of the testing campaign with S/B

Why a testing campaign?
Properties of the emplaced S/B mixture are influenced by:
(a) Mixing ratio S/B and type of mixing apparatus
(b) Water content of the S/B mixture
(c) Type and grain size distribution of the sand component
(d) Compacting method (e.g. device, layer thickness, etc)
Narrowing down process to the final emplacement for achieving the

requirements based on the design criteria

Pre-investigations
-Lab. tests (permeability and Proctor)
-Field tests (mixing, homogeneity, compaction methods and devices)

Pre-tests at GTS (1:1 scale)
-Field tests (mixing, homogeneity, compaction)
-QA methods (core cutter, Troxler)

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Pre-investigations: laboratory tests

 Permeability tests Gruaz et al., 2011

S/B 80/20: Safety margin  average target density of 1.7 g/cm3
Difficult compaction  minimum of 1.6 g/cm3

 Proctor tests (Compaction energy = 3.4 MJ/m3)

S/B mixture Maximum dry Optimum water The S/B mixtures shows
S/B [70/30] – MX80 density [g/cm3] content [-] maximum emplacement dry
S/B [80/20] – MX80 11.7 densities 1.8-2.0 g/cm3 with
S/B [80/20] – Volclay 1.94 optimum water content
10.7 varying between 10-13%
1.87
13
1.84

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Pre-investigations: field tests

How to emplace the experiment?

Component Available emplacement option Choice for construction

S/B seal Inclined compaction in layers Horizontal compaction in layers
Horizontal compaction in layers

Blocks or rings in S/B

Horizontal compaction can guarantee a homogenous compaction with respect to the
height of S/B body but not used in the headspace area due to compacting space
limitations

 Mixing and homogeneity tests

QA: samples were extracted before and after adding water to the mixture and washed
through a 0.125 mm sieve

concrete mixer truck

stationary concrete S/B 80/20
mixer drum

Bentonite content: 19.5 ± 0.5% Bentonite content: 19.2 ± 1.2%

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Pre-investigations: field tests

 Compaction tests

(a) Compaction device dimensions vs. narrow conditions

(b) Compacting speed and energy

(c) Initial layer optimal thickness For achieving the highest
(d) Multilayer compaction and stability density increase and

compacted layer thickness of
10 cm with both the backfill
rammer and the compaction
plate, it was concluded that
the initial layer thickness

should be 19 cm

Compaction plate Sheep-foot roller
(static and dynamic)

d = 1.67 g/cm3 S/B d = 1.71 ÷ 1.77 g/cm3
80/20

Backfill rammer Backfill rammer Total height up to 1.8 m
(horizontal compaction) (inclined compaction)

d = 1.81 g/cm3 d = 1.81 g/cm3

@10 23.01.2014

Overview of the testing campaign with S/B

 Why a testing campaign?
Properties of the emplaced S/B mixture are influenced by:
(a) Mixing ratio S/B and type of mixing apparatus
(b) Water content of the S/B mixture
(c) Type and grain size distribution of the sand component
(d) Compacting method (e.g. device, layer thickness, etc)
Narrowing down process to the final emplacement for achieving the

requirements based on the design criteria

Pre-investigations
-Lab. tests (permeability and Proctor)
-Field tests (mixing, homogeneity, compaction methods and devices)

Pre-tests at GTS (1:1 scale)
-Field tests (mixing, homogeneity, compaction)
-QA methods (core cutter, Troxler)

@23.01.2014

Emplacement pre-tests at Grimsel Test Site

 Aims:
(a) Verify the interactions between the selected

materials for the experiment: S/B 80/20 when
compacted above softer layers (e.g. loose
granular bentonite) and close to border zones
(e.g. wooden framework)
(b) S/B performance evaluated with different QA
methods: both on horizontal and vertical planes
with the core cutter and neutron-gamma
(Troxler) methods

10 horizontal layers compacted with a backfill rammer

@23.01.2014

Emplacement pre-tests: outcomes

 Horizontal planes

Core cutter tests Layer Number of Average dry density
specimens [g/cm3]
2 1.74 2.50 m 1.77 1.77 1.79
4 9 1.79 1.77
6 9 1.79 2.20 m B 1.81 C
8 7 1.74 Layer # 6
10 8 1.70 1.79 1.79
10 1.75
Average A

 Vertical planes (after formwork removal) Troxler probes

3 d = 1.54 g/cm3
21 d = 1.60 g/cm3

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S/B QA methods for the GAST experiment

 Aims
(a) Assure that the requirements are fulfilled
(b) Define the main parameters necessary to characterize the materials

used
(c) Provide a sound knowledge and database for future activities (e.g.

modeling, further lab studies)

QA plan for instrumentation layer

 Tests
(a) Laboratory
o Homogeneity

(a) On-site 28 layers of which 5 were instrumentation layers
o Water content
o Core cutter
o Troxler
o MBM (2D & 3D)

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Nr of samples S/B QA: outcomes from the experiment emplacement

 Homogeneity tests for S/B 80/20 (sieving tests)

257 samples
40 Average sand content: 79.5±0.54%

35
30
25
20
15
10

5
0

77.8 78 78.2 78.4 78.6 78.8 79 79.2 79.4 79.6 79.8 80 80.2 80.4 80.6 80.8 81
sand content (%)

@15 23.01.2014

S/B QA: outcomes from the experiment emplacement

 S/B water content (on-site oven drying)

 Decreasing tendency from ca. 10.8% to ca. 9.5% (average 10.3%)
 More compaction efforts and time (respect to the optimum value of

13% from the Proctor tests)

water content (-) 0.16 y = -4E-05x + 0.1079
0.14 R² = 0.1775
0.12
0.10 50 100 150 200 250 300
0.08 sample number
0.06
0.04
0.02
0.00

0

Water content of S/B material during the construction period from
November 2011 to April 2012

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S/B QA: outcomes from the experiment emplacement

 Dry densities in the S/B seal (on-site core cutter tests)

 Slight decrease of densities towards the borders of each layer (e.g. layer 23)
 Border zones are generally more complicated to be compacted where

instruments and tunnel walls were hindering easy access, particularly towards
the headspace area

2.00
L1

L2

L3

L4
1.60 L5

L6

L7

Dry density dry density (g/cm3) 1.20 L8
averaged L9
among all L10
layers: L11
L12

1.73 g/cm3 0.80 L13
L14

L15

L16

0.40 L17

L20

L21

L23

0.00 L24
1.50 L27
-1.50 -1.00 -0.50 0.00 0.50 1.00

radial direction (m) L28

@17 23.01.2014

S/B QA: outcomes from the experiment emplacement

 Dry densities in the S/B seal (Troxler probes)

 Density profiles measurements at the five instrumentation layers (vertical or or
in an angle of 45°)

 The dry densities are relatively constant over the depth of the single profiles,
with the exception of the consistently lower values closed to the surface
(boundary effect)

 The water content has a tendency to decrease with increasing depths, where
again the topmost point seems to be consistently higher than the deeper
points (boundary effect)

Averaged dry densities and water content for each instrumented layer (9-15 measurements)

1750 16

Dry density (kg/m3)1700 15
water content (wt%)165014
1600 Dry density Layer 6 13
1550 averaged among Layer 11 12 Water content averaged among
1500 Layer 16 11 all layers: 11.7 %
1450 all layers: Layer 23 10
1400 1.66 g/cm3 Layer 28 5 10 15 20 25 30
9 distance from surface (cm)
0 5 10 15 20 25 30 8
distance from surface (cm)
0

@18 23.01.2014

dry density ()g/cm3S/B QA: outcomes from the experiment emplacement

 Dry densities in the S/B seal (2D mass balance method)

 The S/B mass was tracked for each layer (total 83.419 kg)
 The surface of each layer was scanned with an on-site theodolite to obtain a

mesh with grid size of about 0.5 m and approximated to a transversal 2D
section

Dry density
averaged among
2 all layers:
1.9 1.67 g/cm3

1.8

1.7

1.6

1.5

1.4

1.3

L1
L2
L3
L4
L5
L6
Filling L5/L6
L7
L8
L9
L10
L11
L12
L13
L14
L15
L16
L17
L18i / 19i / L20
L21
L22i / L23
24
L25i / 26i / L27
L28

Layer

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S/B QA: outcomes from the experiment emplacement

 Dry densities in the S/B seal (3D mass balance method)

 3D scans were performed at each instrumentation layer (L6, L11, L16, L23
and L28) after having scanned the empty tunnel

L24-L28
L17-L23
L12-L16
L7-L11

L1-L6

Layers Average dry density [g/cm3]
L24-L28 2.06
L17-L23 1.55
L12-L16 1.62
L7-L11 1.62
1.62
L1-L6 1.65
Average

@20 23.01.2014

Conclusions

 The sand/bentonite (S/B) mixtures produced at industrial scale
proved to be homogeneous

 Water content 2-3% lower than the Proctor optimal (increase
of compaction effort)

 Emplacement densities are slightly lower towards the
border zones (e.g. formworks, tunnel walls)

Dry density Core cutter Troxler Method MBM 2D MBM 3D
Water content 1.73 (1.72) (0-30cm) Troxler 1.67 1.65
(5-30cm) 10.3 10.3
10.3 1.66
11.7 1.68
(10.3)

 Overall, independently from the QA methodology, the emplaced
average S/B dry densities showed to be within the range of
1.65-1.73 g/cm3  average intrinsic permeability < 1E-18 m2

Objective accomplished!
 The online monitoring of the GAST experiment will provide

more information about the density distributions and saturation
pattern in the S/B seal

@21 23.01.2014

Thank you very much

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www.grimsel.com

22 23.01.2014 Thanks for your kind attention