laguna at fréjus laguna/laguna-lbno general meeting march 3 th -5 th , 2011, cern
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LAGUNA at Fréjus LAGUNA/LAGUNA-LBNO General Meeting March 3 th -5 th , 2011, CERN Eng. Francesco Amberg. Current situation – General plan view. LSM Underground Laboratory Modane. Road tunnel (1974-78). Railway tunnel (1857-70). Longitudinl section. > 1700 m rock overburden. - PowerPoint PPT PresentationTRANSCRIPT
LAGUNA at Fréjus
LAGUNA/LAGUNA-LBNO General Meeting
March 3th-5th, 2011, CERN
Eng. Francesco Amberg
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>1700 mrock overburden
(LSM)G3
LSM Underground Laboratory Modane
Railway tunnel (1857-70)
Current situation – General plan view
Longitudinl section
6,2 km12.8 km
6,6 km
Road tunnel (1974-78)
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External LSM building
Current situation - LSM underground laboratory Modane
km 6.0 km 7.0
6,2 km6,6 km
A cavity of about 3500 m3 in the middle of Fréjus Road Tunnel in french territory
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(LSM)G3
New safety tunnel
LSM Underground Laboratory Modane
Cross connection
Safety tunnel
(currently under construction, expected conclusion 2014)
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Location of new detector near existing infrastructure
LSM(1982)
Safety tunnel(2009 – under construction)
Road tunnel(1974 – 1978)
New detector(example with MEMPHYS)
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Geology
Trias Series Calcareous schists
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Assessment of rock mass properties - Usual situation (a priori)
Laboratory tests
Intact rock propertiesModulus of elasticityE=50 GPaPoisson’s ratio n=0.2Density r=2.7 t/m3
Compressive strengthsci=100 MPa
Properties of discontinuitiesFriction angle j=35/23°Cohesion c=150/15 kPaNumber ? Orientation ?
Empirical methods
Rock mass
properties
highly uncertain
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Assessment of rock mass properties – Situation at Frejus (a posteriori)
In situ large scale testsModulus of elasticity Edin=15 GPaCompressive strength sci=15/4 MPa
Others propertiesWater inflowRock mass temperature
Back analysi
s
Rock mass
properties
Intensive analysis of tunnel behaviour during
construction (and well documented)
Excavation of road tunnelConvergence monitoringExtension of failure zone around tunnelDiscontinuities (number, orientation, quality)
Advantage of Frejus
Reduction of
uncertainties
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Back analysis of road tunnel (time-dependent behaviour)
Definition of time dependent parameters:
• Short term: from tunnel behaviour 35 m behind the face (5 days)
rock support provided only by systematic bolting(convergence 6-9 cm)
• Medium term: from convergence before casting of final lining at a
distance of round 500 m behind the face (70 days)(convergence 14-18 cm)
• Long term: from pressure acting on lining after 25 years(radial pressure 25-50 t/m2)
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Geotechnical parameters of rock mass
• Unit weight 27 kN/m3
• Elastic modulus 15 GPa
• Poisson’s ratio 0.2
• Friction angle 35/40° (lower/mean value)
• Peak cohesion 3000 kPa
• Residual cohesion 2000 kPa (short term) 500-750 kPa (medium term)
200-300 kPa (long term)
• Plastic strain 0.5 % (for reach residual cohesion)
• Dilation angle 3°
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Main characteristics of calc-schists
• Time-dependent behaviour of rock mass (displacements)
• Tendency to wedge instability on roof
• Anisotropy of rock mass properties (effect of schistosity)
• Reduction of rock mass strength after failure
• No water circulation in the rock mass (OK for cavern stability
and thermal losses during reservoir operation)
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Earthquake hazard potential in EU
FrejusLow hazard
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Type of detector to receive
Volume of excavation:
•GLACIER: 160'000 m3
•LENA: 111'000 m3
•MEMPHYS: 838'000 m3 (3 caverns)
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LAGUNA – Largest man-made excavation
10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.00.00
0.50
1.00
1.50
2.00
2.50
3.00
Lim
it o
f ex
peri
ence
Caverns for physics exper-imentsCaverns for stor-age of natural gasCavern hall for public use
Span [m]
Dep
th [
km]
Singular cases
Empirical designs methods not reliable (no
experience)
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Basic principles – Displacements
• Radial displacement (δr) ~ Excavation radius (R)• Plastic radius (Rpl) ~ Excavation radius (R)
R
Rpl
δr
Road tunnel : R=6.1 m , δr=10
cm
Memphys : R=33.5 m
δr=55 cm
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Basic principles – Effect of gravity
• Wedge pressure (p) ~ Excavation radius (R)
• Bolt length ~ Excavation radius (R)
Support per m2 ~ R2 (also for lining)
R
p
Road tunnel : R=6.1 m , lining d=50
cm
Memphys : R=33.5 m
lining d=2.7 m
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Analysis of wedge stability
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Analysis of displacements - 3D model (FLAC)
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Displacements – Short term
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Failure zone – Short term
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GLACIER – Final lining
• Thickness: 1.5 m (roof and vertical wall)
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LENA – Final lining
•Thickness: 0.7 m
(roof and vertical wall)
• In vertical walls to be installed
proceeding bottom-up
• Thickness of the lower part (20 m)
increased to 1.2 m
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MEMPHYS – Final lining•Thickness: 1.5 m (roof and vertical wall), 2.3 m in the lower part (15 m)
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Geomechanical feasibility
•GLACIER, LENA and MEMPHYS option are feasible at Fréjus site. The overall stability of the cavern is assured. A support is however
required for wedge stability.
•The geomechanical feasibility remains valid also by a small change of the size of the excavation, both in the diameter and height of the cavern.
•The geomechanical conditions at Frejus are well known and further investigations are basically not required. The safety tunnel under construction will provide further information.
•The support system proposed guarantees the long term stability and the absence of significant time dependent displacement of the cavity.
•The support system proposed has sufficient reserve to ensure the stability of the cavern in case of earthquake.
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Mechanical interaction with rock (MEMPHYS)
FREE TANK TANK IN CONTACT WITH ROCK
TOP THICKNESS 1.0 cm 1.0 cm
BOTTOM THICKNESS 15.7 cm 1.0 cm
STEELMASS 11‘170 kg 3‘970 kg
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Steel tank in contact with rock mass
• The rock loads are supported by the concrete lining and will not be
transferred on the steel tank.
• The water from the rock mass can cause an external load on the imperious tank (even if apparently the rock is dry). To avoid this type of load, it is necessary to design an external drainage system.
• The earthquake is not a problem for the steel tank, if there is not an
active fault crossing the cavern (atypical situation).
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Thermal interaction with rock (MEMPHYS)
Solution with the insulation Solution without the insulation
ROCK: T = 30°C
WATER: T = 13°CHEAT ENERGY TRANSFER (Q)
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GLACIER
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LENA
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MEMPHYS
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GLACIER
Sec. Item Cost1 Main detector 33.4 M€
2 Access galleries 6.3 M€
3 Auxiliary caverns 0.9 M€
4 Site infrastructures 20.3 M€
5 Engineering, safety costs 6.1 M€
TOTAL 66.8 M€
Cost per m3 (315'000 m3): ~210 €/ m3
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LENA
Sec. Item Cost1 Main detector 12.0 M€
2 Access galleries 5.3 M€
3 Auxiliary caverns 0.9 M€
4 Site infrastructures 9.1 M€
5 Engineering, safety costs 2.7 M€
TOTAL 30.0 M€
Cost per m3 (142'000 m3): ~210 €/ m3
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MEMPHYS
Sec. Item Cost1 Main detector 90.4 M€
2 Access galleries 9.5 M€
3 Auxiliary caverns 1.1 M€
4 Site infrastructures 50.5 M€
5 Engineering, safety costs 15.2 M€
TOTAL 166.7 M€
Cost per m3 (911'000 m3): ~180 €/ m3
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Technical feasibility – Tank construction
• Unit cost reaches 180 – 210 €/ m3; Fréjus safety tunnel: 310 €/ m3.
• The solution with tank placed in contact with the rock mass is feasible at Fréjus site for LENA and MEMPHYS option. For GLACIER option an independent tank is preferable.
• The solution with tank placed in contact with the rock mass can save the amount of steel needed (7‘200 kg for MEMPHYS option, 3‘600 kg for LENA option).
• Both the solution with the insulation and without insulation are feasible at Fréjus site.
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LAGUNA-LBNO at Frejus – Option 1
Same volume as MEMPHYS option with 3 tanks butcost reduction of 11.5 M€ for excavation and support
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LAGUNA-LBNO at Frejus – Option 2
Excavation and support of additional LENA costs only 23 M€
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General conclusions for Frejus
• The Frejus site allows to host all the detectors options proposed within LAGUNA, i.e. GLACIER, LENA and MEMPHYS.
• The rock mass behavior was deeply investigated (during highway tunnel and now safety tunnel) allowing to minimize the uncertainties and the risks related to the realization of further underground cavities.
• The excellent quality of the rock, with the appropriate amount of plasticity, allows the excavation of very large cavities at a depth of 4800 m w.e., which is the deepest in Europe (for an underground laboratory).
• The Fréjus safety tunnel, presently under construction, provides an optimal and completely safe access to the site during both construction and operation (whole life-time, e.g. 50 years).
• The Frejus rescue team, permanently in service, ensure the highest safety support both in the tunnel and in the laboratory.
• The accessibility of the Frejus site is excellent (by road or train from many international cities as Torino, Chambery, Lyon, Genève, Milano, Paris).
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THANK YOU FOR YOUR ATTENTION
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Graphic layout
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Graphic layout