\section {Large Cavities and Vessels}

\subsection{introduction} (L. Mosca)
\begin{enumerate} 

\item  remind the list of the present candidate sites for future projects of Very Large ("Megaton scale") Laboratories :

Japan :
HYperKamioka site 

North America :
Cascades-Icicle Creek, WA/USA (Greenfield escarpment site \& nearby railroad 
                                                         tunnel)
Henderson Mine, Empire, CO/USA (Operating molybdenum mine since mid 1970s)
Homestake Mine, Lead, SD/USA (Former operating gold mine)
Kimballton Mine, Giles Co., VA/USA (Limestone mine \& adjacent subsurface)
San Jacinto, CA/USA (Greenfield escarpment site)
Soudan Mine, Soudan, MN/USA (Operating lab at former iron mine, expansion into 
                                                         adjacent Subsurface)
SNOLAB, Sudbury, Ontario/CANADA (Operating lab in operating nickel mine)
WIPP, Carlsbad, NM/USA (Operating lab in operating low-level waste facility)

Europe :
Fréjus road tunnel (connecting France with Italy)
Poland site

\item  shows the Volume (m3) vs Depth (mwe) distribution for some of these candidate sites compared to the already existing laboratories.

\item  Emphasizes that the challenge is now to find out the best site(s) with :
      - relatively large depth
      - very large volume (megaton scale)
      -  well adapted access configurations and infrastructures
      -  favourable environmental conditions (geographic, scientific, logistic, etc.)
      - convenient position (long baseline) with respect to accelerator(s)

    and, last not least, to be able to excavate and stabilize such cavities of unprecedented size
\end{enumerate}

\subsection{Large cavities in USA,Japan and Europe}  

The laboratoire souterrain de modane has been presented by its director (G.Gerbier)
as an introduction  also in view of the visit of this deep underground laboratory  planned in the afternoon.

 The three following talks concerned the projects of large cavities excavations respectively in North-America, in Japan and in Europe. 	

\begin{enumerate}


\item {\bf "Large excavations in the USA"} prepared by Lee Petersen (Minneapolis), was in fact presented by Chang Kee Jung (Stony Brook), due to the impossibility for Lee Petersen to attend this conference.
This talk starts with a brief review of the North-American sites presently submitted to the DUSEL (Deep Underground Science and Engineering Laboratory ) for selection (see the list  above), then the site characteristics important for large excavations are discussed, with the following considerations and consequences.
\begin{figure}[htbp]
\begin{center}
\epsfig{figure=./figures/petersen.epsf,height=7.cm}
\caption{DUSEL candidats sites }
\label{DUSEL}
\end{center}
\end{figure}
The rock "material" can be strong, stiff or brittle and the rock "mass" behavior is controlled by discontinuities. As a consequence the rock mass strength can range from 1/2 to 1/10 of rock material strength. Discontinuities give rock masses scale effects depending if the rock is "massive" (excavation dimensions smaller than discontinuity spacing), or "jointed" or "blocky" (excavation dimensions larger than discontinuity spacing), or even heavily jointed (excavation dimensions much larger than discontinuity spacing).The rock Engineering is concerned with the "rock stresses" in situ, where the "vertical stress" is essentially controlled by the weight of overlying rock, while the "horizontal stress" is controlled by tectonic forces (builds stresses) and creep (relaxes stresses). 
At depth, ?vert. Å ?horiz.  unless there are active tectonic forces.
On the basis of all these elements, the following consequences have been derived, concerning:
- the depth (shielding capacity) : all sites appear adequate
- the rock type (rock chemistry) : all sites appear adequate, but salt at WIPP may be 
                                                       problematic (due to creep \& solubility)
- the rock quality (in situ stress) : all sites are potentially suitable, but none are guaranteed 
                                                  feasible 
- the access (rock removal) : all sites are potentially suitable, but horizontal access is 
                                                beneficial
and emphasis has been put on the most important of these characteristics : the rock type for which creep and solubility are the principal issues; the rock quality which commonly influences costs by a factor of 2 to 4, and which could make a site unfeasible, and finally the access, especially for rock removal, which can influence costs significantly, and which is very site dependent.
Then the requirements of rock engineering for large cavern construction have been stressed :
a) find a site with excellent rock type and quality
b) characterize the rock mass : this is the "job one"
c) avoid tectonic zones and characterize the in situ stresses
d) select size, shape and orientation of the cavity, in order to minimize the rock support, the stress concentrations, etc.

Finally, the following remarks concluded the talk :
Is a megadetector feasible?    If qualified, yes
What are the qualifications?
- the rock conditions and depth : the best location at the best site, and not too deep
- enlightened funding agencies : to understand and manage the risks and the cost 
  uncertainties
- the site factors : the rock removal, which needs competing demands for resources
- the contractor : to be chosen on cost and qualifications criteria





\item {\bf "Study on the Excavation of the Hyper-KAMIOKANDE Cavern at Kamioka Mine (Mitsui Mining \& Smelting Co., Ltd. (MITSUI KINZOKU)) in Japan"} by Tetsuo NAKAGAWA (Tokyo). 
    
The summary on this "Ongoing Investigation and Feasibility Study" at the end of the talk looks very well adapted to fit in this "white-paper", so it is inserted here (nearly) as it is :

*Site Selection : TOCHIBORA Mine, at a depth (overburn) of about 500m (cavern in between 480m and 550m) is the most appropriate location with very competent rock condition.

\begin{figure}[htbp]
\begin{center}
\epsfig{figure=./figures/nakagawa.epsf,height=8.cm}
\caption{site proposed for HyperK}
\label{HyK}
\end{center}
\end{figure}

Cavern Design: Two 250m Long Parallel Tunnels with Modified Egg Shaped Section of 2,076m2 are capable of being safely excavated and stabilized.
Stress Concentration at the Cavern Ends should be relieved by Rounding the Edge to form "Slanted Ellipsoid" (for example Protruded Length of 9.04m )  
*Cavern Layout : Two Parallel Tunnels as above should be Located properly with 80m Ð100m Spacing and 50m-100m Offset to avoid the Deteriorated Zone of Surrounding Faults such as "Namari", "Anko", "240?-ME" Faults.
In Determining the Direction of the Tunnel-Axis (for example 42 ?N from E ), Asymmetry of the Real In-Situ Initial Stress Conditions must be seriously considered. Further Investigations and Rock Engineering Studies are needed, and especially Measurements of In-Situ Initial Rock Stresses are indispensable, including Direct Exploration Drilling \& Geo-survey Tunneling at the TOCHIBORA MineÕs Candidate Site.

Themes of our Major Concerns : 
    On Further Engineering Study of Rock-Mechanics \& Construction
  
*Excavation Method Ð Bench Stoping or Modified Sublevel Stoping Method

*Effective Rock Support System and Monitored, Informed Excavation System should be Designed and Harmonized with Construction Design \& Procedures in Well Organized Manners.

*Main Haulage Tunnel Design  Speedy \& Convenient Routes should be Proposed.

*Treatment method of the Excavated Waste Rock should be considered.
 - Disposal in the existing Waste Tailing Dam, we think negotiation with the Authorities of Mine Safety Laws is necessary.
 - Reuse as Construction Materials, Crushed Gravel Rocks, Sands, Mixing Material in Concrete Products etc. could be possible.

*Clean Water Resource \& Supply at TOCHIBORA Mine should be precisely Planned and Estimated

*The Hyper-K Cavern Construction Scheduling \& 
  Precise Cost Estimation need to be pushed forward.




\item {\bf "Large excavations in Europe".}(M.Lévy)

He considered as candidate site the Fréjus mountain crossed by a road-tunnel connecting France (Modane) to Italy (Bardonecchia). He stressed the fact that the quality (parameters) of the rock is well known there due to the systematic investigations (measurements) that have been performed during the excavation of the road tunnel. He reminded that a second tunnel (called "safety Tunnel"), close and parallel to the present road tunnel, should be realized in the next few years, while the final value of its diameter (about 6m or about 9m) is still a matter of discussion between the French and the Italian side.   
	
The above-mentioned measurements allow to select three regions where the rock is of good quality (essentially where the "convergence" parameter is minimal) : the best of these regions is in the middle of the Tunnel, with an overburn of about 1750 m of rock, and the other two are at about 3km respectively from each entrance (France and Italy), with an overburn of about 1750 m of rock.
	A preliminary study of feasibility is just started for an excavation of a total volume of about one million cubic meters, in two different positions : in the mentioned central region (near to the present LSM Laboratory), and in one of the other two pre-selected regions (the one on the French side). This preliminary study is considering two different geometries : the "tunnel shape" and the "shaft shape" and is supposed to give, in addition to the feasibility characteristics and conditions, also an indication of the possible method(s) of excavation with a row estimate of cost and time of realisation. The most sensitive dimension being the width (the so-called "span" by the specialists) of the cavities, this preliminary study will a priori investigate width values up to 60m in the case of the "tunnel shape" and of 75m in the case of the "shaft shape".

\begin{figure}[htbp]
\begin{center}
\epsfig{figure=./figures/trelsm.epsf,height=7.cm}
\caption{possible scenario for the installation of a Megaton detector in the
Fréjus Tunnel}
\label{tre}
\end{center}
\end{figure}

\item Finally Pierre Duffaut, engineer of the "école des mines" and expert in geology (ancient President of the CFMR "Comité Français de Mécanique des Roches") gave the last talk of this session on a subject "transversal" with respect to the various possible sites, with the title : {\bf"Engineering of large and deep rock caverns for physics research"}
 
He started by giving several exemples of large caverns, both natural and man-made,  in France and worldwide and discussing the shape of their section and practice of their support.
Then he presented a recent French textbook on Rock Mechanics, "Manuel de mécanique des roches " in two volumes : vol. 1 : Fundamentals (2000) and vol. 2 : Applications	(2004), a collective work of the French Committee on Rock Mechanics, coordinated by himself. The section 3 of the 2nd volume : "Mechanics of underground works" and especially the chapter 20 therein : " Caverns " is particularly relevant to the main purpose of this session.
	In this context he insisted on the importance of geology in geotechnique : " all underground works are embedded in geology. Inside the ground, we are like surgeons in a man body, where the anatomy correspond to the materials and structures inside the ground, and the physiology to all what is moving, water, heat, stress, surface and where morphology may give useful clues ".
"We have to accept the ground as it comes; it is the same with weather, along the Norwegian proverb :"no bad weather, only poor clothes", which gives in our case : "no bad ground, only poor engineering".


	Then Pierre Duffaut remind us with the "theory of the hole and the stress control" fig. \ref{fig:hole} and in this context he develops its main message, concerning a method to significantly reduce the constaints in the rock, as explained in the following few transparencies :														
\begin{figure}[htbp]
\begin{center}
\epsfig{figure=./figures/utopie.epsf,height=7.cm}
\caption{Reinforcement before excavation}
\label{fig:utopie}
\end{center}
\end{figure}

\begin{figure}[htbp]
\begin{center}
\epsfig{figure=./figures/duffaut.epsf,height=7.cm}
\caption{The theory of the hole inside a highly stressed medium \& stress control}
\label{fig:hole}
\end{center}
\end{figure}
\end{enumerate}

And finally {\bf"Some conclusions for a billion litres (megaton) chamber"}
\begin{itemize}
\item - multiple caverns would call for very wide spacing
\item - horizontal caverns are very sensitive to rock \& stress anisotropy (one direction only 
   permitted) 
\item - many experts suppose that granite-like rocks are the best ones .
but deformation of schistose rocks, such as Fréjus rocks, could assist destressing before  excavation a megaton cavern at Fréjus is an impressive challenge and I would like to help you to master it.
\end{itemize}
