Latest rock grouting technologies under sea water in Nordic countries and Japan
Masakuni TSUJI, Civil Engineering Technology division, Shimizu Corporation*;
Mitsunobu OKIHARA, Civil Engineering Technology division, Shimizu Corporation;
Hitoshi NAKASHIMA, Research Institute of Technology, Shimizu Corporation;
Toshinori SATO, Horonobe Underground Research Center, JAEA;
Kazuhei AOYAGI, Horonobe Underground Research Center, JAEA.
* Contact address: No. 16-1, Kyobashi 2-chome, Chuo-ku, Tokyo 104-8370, JAPANKey words; rock grouting, colloidal silica grout, silica sol, activated silica colloid, coastal region, sea water,geological disposal, Nordic countries
Abstract
In Japan, the coastal region is discussed to be a more suitable for the geological disposal in the council heldby ANRE. However, the engineering technology has not been fully studied to apply the repository to this region.
Regarding the engineering technology, the rock grouting has been recently studied as one of the most significanttechnologies. Although the cement has not been reported to be affected by saline water, the latest grouting
material called colloidal silica grout (CSG or silica sol in Sweden), which has become a mandatory material toseal narrow rock fractures in great depth, is known to be sensitive to salinity. It is a durable liquid grout with agelling property by mixing a salt accelerator. Its mechanism affected by sea water is unclear and its grouting
methodology in such condition is not yet established either.
Therefore, a research project on grouting under sea water was established, as a part of the public offeredproject by ANRE, in order to enhance existing rock grouting technology for disposal tunnels under sea water.
During this project, we studied on the latest grouting technologies for geological disposal in Nordic countries
and Japan by article survey and a workshop held in Finland in January 2017.
As a result, it was found that the approaches for countermeasures in grouting under sea water were different
between Japan, Sweden and Finland, which are based respectively on mixing method, design method, andcontrolling method. It seems that the best solution against this problem is in the near future to establish a hybrid
and optimal grouting methodology under sea water by combining each country’s developed technology. As for
the Japanese project, it was discovered significant to develop a generic mixing method under sea water.
1. Introduction
In Japan, the coastal region is discussed to be amore suitable for the geological disposal (see, Fig. 1)
in the aspect of transportation, in the council held byAgency for Natural Resources and Energy (ANRE),
Ministry of Economy, Trade and Industry (METI).
However, the engineering technology for the disposal
or safety assessment has not been fully studied for thepurpose of applying the repository to this region.
With regard to the engineering technology, therock grouting for the geological disposal has been
recently studied as one of the most significant
engineering technologies. The latest grouting material“colloidal silica”, which is composed of activatedsilica colloid, came to be an essential candidate toconsiderably reduce water ingress into the tunnels inthe deep underground. Although the cement grout has
not been reported to be affected by saline water, thisrather new material is known to be sensitive tosalintiy due to its gelling property by the salt
accelerator. The mechanism of its affection by sea
water is unclear and the grouting methodology insuch condition is not yet established either.

Therefore, a research project on “characterisationof colloidal silica grout under sea water” wasestablished, as a part of the public offered project byANRE, METI to enhance the existing rock grouting
technology for disposal tunnels in Japan.

Fig.1: Schematic view of feasible region of the geologicalrepository [1]. The geographical region varies from inner
to coastal region and the yellow parts indicate the ideal
candidates for the geological disposal.

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan2. Colloidal silica, a fruitful grout for repository
Rock grouting is one of the best construction
methods to reduce water ingress into the tunnels indeep underground during the excavation. In cases oftunnels for the geological repository, it had been
assumed to be hard to seal the rock mass only by theexisting rock grouting method. This is due tonarrower rock fractures must be sealed under higher
water pressure in deeper underground of repository
tunnels than of ordinary tunnels. It is also necessary
to consider the effect of the grout component on theengineered and the natural barriers, which means thata low alkaline grout is favourable.
Therefore, it has been studied and developed tosophisticate the existing rock grouting technologies.
Firstly, it was performed in Sweden and Finland (e.g.,[2] [3]), and then in Japan for a last decade (e.g., [4]).
During the development of such technologies in eachcountry, a durable liquid-type colloidal silica grout(CSG or called “silica sol” in Sweden) has become
one of most fruitful candidates for the future disposalsites (e.g., [5] or [6]) owing to its property with low
pH and the capability of sealing narrow rock fracturesthat cement cannot penetrate. Therefore, it has apotential to reduce more water inflow than a cementgrout. The main component is the liquid of
amorphous particles of SiO2 with diameters of 10-20
nm. When the main liquid is mixed with an inorganic

salt of a hardening accelerator, the silica particles
start to aggregate to form a durable gel, see Fig. 2.
Fig. 3 shows a summary of R&D and applicationon the CSG between Japan, Sweden and Finland [7].
This material was originally invented in Japan morethan 20 years ago, mainly for the stabilization of soils
as permanent structures in civil engineering. It has
now been applied for more than 1200 sites for suchground improvement purpose in Japan [8].

a) Main liquid (SiO2)c) After mixture before gellingd) Hardened homo-gel
Fig. 2: Photos of the durable liquid-type colloidal silica
grout (CSG) in Japan.

JAPANGround improvement■Needs for durability on Chemical grouting••••R&D started for long-term durable water glassmaterial (1982).
Invention of “Activated colloidal silica” andsuperfine hybrid silica (1992)
Definition of “Permanent Grouting” (1997).
Awarded Technical Development by the Japanese
Geotechnical Society (2002).

••••

Nordic countries
Rock grouting■Needs for rock sealing material toachieve severe inflow requirement aimed
for deep geological repository••

Growing market for permanent improvement•• Applied for more than 1200 sites (as of 2015).

•Rock grouting■Needs for sealing material to achieve inflow
requirement aimed for deep geologicalrepository
R&D started for colloidal silica grouting regarding
characterization and application (2007).
Experiment at the 300m depth of MIU (2010).
Laboratory tests and supplementary application to
the 160m depth of Kurashiki LPG storage (2013).
Post-grouting campaign at the 500m depth of MIU(2014).
Note that all written years are based on publishedarticles or rough estimatied by the publishied yearb) Hardening accelerator•R&D started for grouting Silica sol for rockgrouting (2003).
Grouting design methodology of silica sol wasproposed for fractured rock based on theory ofgrout penetration (2007).
Applied to Äspö HRL (No.1), and trial for somenormal tunnels (2008).
Studay and Trial for some road or raliway
tunnels (2010).
Applied to ONKALO (No.2), around (2011).

： SWEDEN, it is called ”silica sol”

No.2

No.1 Äspö HRL
No.2 ONKALO

No.1

FINLAND, it is called”Colloidal silica grout”

Fig. 3: Summary of R&D and application on colloidal silica grout (CSG) between Japan, Sweden, and Finland, referredfrom [7] (in Japanese) and translated to English by authors. It is remarkable that the CSG was firstly invented in Japan andapplied for the rock grouting in Nordic countries and then “reimported” to Japan as for rock grouting in this field.

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, JapanAs for a grouting material for hard rock, theEuropean CSG was firstly studied in Sweden byChalmers University of Technology (e.g., [9] or [10]).
The rock grouting theory and strategy with thismaterial has been developed and applied to somerecent projects in Sweden (e.g., [5]) and the guide togrouting with the CSG was published by BeFo, RockEngineering Research Foundation in Sweden [11].
Around the same time, JAEA started studying on
this grout as a new and fruitful material for grouting
tunnels in hard rock (e.g., [6]). For the first time inJapan in great depth, the CSG was applied to an
in-situ post-grouting test at 300m depth of Mizunami
Underground Research Laboratory (MIU) [12]. Then,it was carried out that comparison study on applying
the material between this test and a Swedish project[13]. Based on these experiences, the CSG wereapplied to the post- grouting campaigns at 500m
depth of MIU with catching up Swedish design
philosophy [14] , [15].

3.2. ONKALO, Finland
In Nordic countries, especially in ONKALO inFinland, a low-pH cement grout combined with theCSG was applied to seal the tunnels in great depth,
and it was firstly applied with an excavation at“demonstration tunnel 2” at 420m depth, see Fig. 5and Fig 6. It was reported that the ground water in
ONKALO contains a lot of calcium ion in solution
and the problem in the execution was that this grout
reacts aggressively with this calcium ion [17].
Therefore, grouting methods such as “waterinjection” were invented in ONKALO [19]. By thismethod, a fresh water is injected before the grouting
and thus the groundwater environment is expected tobe unsalted. In addition, fine inclusions in the rockfractures are expected to be flushed out, which makes
a positive effect to the better penetration.

3. Applications on the CSG under saline water
During the project shown in the introduction, wehave investigated the articles regarding latest
grouting technologies and especially for CSG, in the
aspect of its application under the sea or salty groundwater, among Nordic countries and Japan. Here,some of the significant findings are shown as follows.
3.1. Kurashiki National LPG Stockpiling Base, JapanThe CSG has been practically and supplementary
applied to the construction of the Kurashiki National
LPG Stockpiling Base in Japan [16]. The site is
located in the coastal region with saline groundwater.
It was applied to seal the fine fractures in order tocontrol the pressure drop of groundwater and torestrict the ingress of water. Before its application, it
was meticulously tested to obtain its basic properties
and to find the mixtures applicable to the site. Fig. 4shows an example of “turbidity check test”. Thegrout was slowly poured into the locally collected
groundwater and checked if the grout turns white atonce or not. This silica grout, which is weakly
alkaline, was controlled to be less sensitive to sea salt
by adjusting its pH between neutral or weakly acidic.
This was performed by adding an acidic pH adjuster.

Fig. 5: ONKALO and the demonstration tunnel 2 (red),
where the grouting by the CSG was carried out [17].

Fig. 6: A photo of the demonstration tunnel 2 from Posiva
Oy’s website [18]. It shows a dry condition in the tunnel.

3.3. Äspö HRL, Sweden
In Sweden, a low-pH cement grout combined with
the CSG was applied to TASS-tunnel at 450m depthof Äspö HRL see Fig. 7 [5]. Although it was notpointed out about the affection by the groundwatersuch as saline condition, the more concern was toestablish a robust methodology of grouting design inthe high ground water pressure of 3.5 MPa or toensure its durability.
Therefore, related grouting experiments on the“silica sol”, which is how this gelling grout is calledin Sweden, is still ongoing in Sweden (e.g. [20]).

a) No turbidity, applicableb) Turbidity, not applicable
Fig. 4: Turbidity check tests on sea water. It was performed
during the grouting works at the Kurashiki LPG.

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan4. Grouting workshop in Finland
During this project, we held a “workshop oncolloidal silica grouting in sea water, Helsinki” inFinland on 26th January 2017, see Fig. 9. The purpose
was to exchange information on latest grouting
technologies related to geological disposal andespecially on the technology of the CSG under seawater, with experts in related fields.

Fig. 7: Äspö HRL and the TASS-tunnel, where the grouting
by the CSG was carried out [5].

3.4. Submarine tunnel (by Norwegians), Hong Kong
Norwegians excavated a submarine tunnel called
HATS2A under Victoria Harbour in Hong Kong at
150m depth, see Fig. 8 [21]. Remarkably, theyapplied a microfine cement combined with the CSG
to their grouting works in order to attain severe
requirement of water ingress into the tunnel. As aresult, they succeeded in considerably reducing thewater ingress. For example, a fault zone that theingress expected to be 9200 litres/min per 100m
turned out to be 1.0 litres/min, which means areduction of 99.99%.
It was not pointed out about any problems of thisgrout affected by sea water in this project.
Fig. 9: “Workshop on colloidal silica grouting in sea water,
Helsinki” was held on 26th January 2017.

Fig. 8: HATS2A tunnel shown in the above and the appliedmaterials shown in the bottom [21].

The participants were affiliated with Posiva,
Saanio & Riekkola, B+Tech, ROCKPLAN, Chalmers
University of Technology, Tyréns, JAEA, andShimizu Corporation.
During the discussion, a research coordinator in
Posiva insisted that Posiva had moved into a phase of
the construction of the actual disposal facility andthus Posiva is strictly limiting the ingress of water inthe whole underground facility in order to reduce therisk of a rise in fossil water level. Moreover, it wasturned out that both the CSG and low-pH cement had
become essential materials for Posiva due to theprerequisite to keep the rock mass in deep
underground as low alkaline as possible.
We could also obtain the knowledge from Finnish
consultants that how they studied on the gellingproblems of this material under sea water or calcium
rich ground water, and understood how and why they
invented the “water injection” method.

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, JapanOn the other hand, from a Swedish expert, it waspointed out that the methods to solve this gelling
phenomenon by experiences at construction sites,such as the water injection method were not optimaland better to be avoided. He stressed that the grouting
methodology should have been more economical
based on more theoretical and experimental
approaches.
Regarding the Japanese countermeasure ofadjusting the pH of the CSG to lower alkaline, it has
been applied to the Kurashiki National LPG
stockpiling project as shown above and we werecommented as this method might be one of the best
approaches against the salty ground water so far. We
were advised that it must be needed to sophisticate
this mixing method and to confirm the effect on thegrout penetration affected by sea water in the rockfractures both by experimental approaches. Moreover,
we were advised that the difference in the constituentof sea water must have been focused.

5. Conclusion
Based on the article survey and what we knew
from the grouting workshop, we sorted out in eachcountry the ideal direction toward the development of
the grouting methodology in the CSG under sea waterwith an approach to the solution, as follows.
➢ Japan: Developing and establishing a mixing
method of the CSG using the pH adjuster isnecessary. The approach to the solution should bebased on the experience in the Kurashiki LPGstockpiling project.
➢ Sweden: Developing more reliable grouting
design and ensuring the durability for the CSG isnecessary. The approach to the solution should bebased on theories and experiments.
➢ Finland: Developing more economic controlling
methods for the CSG at site is necessary. The
approach to the solution should be based on theactual grouting works.
As a result, it was found that the approaches forcountermeasures in grouting the CSG under sea water
were different between Japan, Sweden and Finland.
In Japan, it is based on mixing method, in Sweden on
design method, and in Finland on controlling method.
Therefore, it seems that the best solution against thisproblem is in the near future to establish a hybrid andoptimal grouting methodology under sea water by
combining each country’s developed grouting
technology.
This should be performed by periodically sharing
the latest information in each country regarding thisfield.

As for this Japanese project, it was discovered
significant to develop a generic mixing method for
the CSG under saline water by referring to a previous
experience in the Kurashiki LPG stockpiling projectin Japan. We have recently started laboratory tests toestablish this method under sea water.

Acknowledgements
The investigations reported in this paper wereconducted as a part of the public offered project, acommission investigation of geological disposal
technology (Development of enhancing the disposal
system in the coastal region) under the contract with
Agency for Natural Resources and Energy, Ministryof Economy, Trade and Industry.
The authors gratefully thank to Dr. Funehag J.
belongs to Chalmers University of Technology andTyréns for the collaboration and lots of advice related
to our work, to Mr. Saarikivi H., Mr. Ikonen A., Mr.
Carroll O F., and the other members from Saanio &Riekkola for the collaboration and helping us to haverealized the grouting workshop in Finland.

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6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan