LAGUNA at Fréjus LAGUNA/LAGUNA-LBNO General Meeting March 3 th -5 th, 2011, CERN Eng. Francesco...

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 km

12.8 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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1Location 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 SeriesCalcareous schists

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1Assessment of rock mass properties - Usual situation (a

priori)

Laboratory tests

Intact rock properties

Modulus of elasticityE=50 GPa

Poisson’s ratio n=0.2

Density r=2.7 t/m3

Compressive strengthsci=100 MPa

Properties of discontinuities

Friction angle j=35/23°

Cohesion c=150/15 kPa

Number ? Orientation ?

Empirical methods

Rock mass

properties

highly uncertain

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1Assessment of rock mass properties – Situation at Frejus (a

posteriori)

In situ large scale tests

Modulus of elasticity Edin=15 GPa

Compressive strength sci=15/4 MPa

Others properties

Water inflow

Rock mass temperature

Back analysi

s

Rock mass

properties

Intensive analysis of tunnel behaviour during

construction (and well documented)

Excavation of road tunnel

Convergence monitoring

Extension of failure zone around tunnel

Discontinuities (number, orientation, quality)

Advantage of Frejus

Reduction of

uncertainties

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1Back 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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1Geotechnical 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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1Main 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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1Earthquake hazard potential in EU

FrejusLow hazard

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1Type 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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1LAGUNA – 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 experi

ence

Caverns for physics exper-imentsCaverns for stor-age of natural gasCavern hall for public use

Span [m]

Depth

[km

]

Singular cases

Empirical designs methods not reliable (no

experience)

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1Basic 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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1Basic 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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1Analysis of wedge stability

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1Analysis of displacements - 3D model (FLAC)

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1Displacements – Short term

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1Failure zone – Short term

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1GLACIER – Final lining

• Thickness: 1.5 m (roof and vertical wall)

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1LENA – 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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1MEMPHYS – Final lining

•Thickness: 1.5 m (roof and vertical wall), 2.3 m in the lower part (15 m)

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1Geomechanical 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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1Mechanical interaction with rock (MEMPHYS)

FREE TANKTANK 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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1Steel 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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1Thermal 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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1GLACIER

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1LENA

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1MEMPHYS

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1GLACIER

Sec. Item Cost

1 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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1LENA

Sec. Item Cost






TOTAL 30.0 M€

Cost per m3 (142'000 m3): ~210 €/ m3

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1MEMPHYS

Sec. Item Cost






TOTAL 166.7 M€

Cost per m3 (911'000 m3): ~180 €/ m3

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1Technical 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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1LAGUNA-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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1LAGUNA-LBNO at Frejus – Option 2

Excavation and support of additional LENA costs only 23 M€

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1General 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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1Graphic layout

LAGUNA at Fréjus LAGUNA/LAGUNA-LBNO General Meeting March 3 th -5 th, 2011, CERN Eng. Francesco...

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