laguna at fréjus laguna/laguna-lbno general meeting march 3 th -5 th , 2011, cern

LAGUNA at Fréjus

LAGUNA/LAGUNA-LBNO General Meeting

March 3th-5th, 2011, CERN

Eng. Francesco Amberg

>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)

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

(LSM)G3

New safety tunnel

LSM Underground Laboratory Modane

Cross connection

Safety tunnel

(currently under construction, expected conclusion 2014)

Location of new detector near existing infrastructure

LSM(1982)

Safety tunnel(2009 – under construction)

Road tunnel(1974 – 1978)

New detector(example with MEMPHYS)

Geology

Trias Series Calcareous schists

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

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

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

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)

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°

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)

Earthquake hazard potential in EU

FrejusLow hazard

Type of detector to receive

Volume of excavation:

•GLACIER: 160'000 m3

•LENA: 111'000 m3

•MEMPHYS: 838'000 m3 (3 caverns)

LAGUNA – Largest man-made excavation

10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.00.00

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

Span [m]

Singular cases

Empirical designs methods not reliable (no

experience)

Basic principles – Displacements

• Radial displacement (δr) ~ Excavation radius (R)• Plastic radius (Rpl) ~ Excavation radius (R)

Road tunnel : R=6.1 m , δr=10

Memphys : R=33.5 m

δr=55 cm

Basic principles – Effect of gravity

• Wedge pressure (p) ~ Excavation radius (R)

• Bolt length ~ Excavation radius (R)

Support per m2 ~ R2 (also for lining)

Road tunnel : R=6.1 m , lining d=50

Memphys : R=33.5 m

lining d=2.7 m

Analysis of wedge stability

Analysis of displacements - 3D model (FLAC)

Displacements – Short term

Failure zone – Short term

GLACIER – Final lining

• Thickness: 1.5 m (roof and vertical wall)

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

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

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.

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

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).

Thermal interaction with rock (MEMPHYS)

Solution with the insulation Solution without the insulation

ROCK: T = 30°C

WATER: T = 13°CHEAT ENERGY TRANSFER (Q)

GLACIER

MEMPHYS

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

TOTAL 30.0 M€

Cost per m3 (142'000 m3): ~210 €/ m3

MEMPHYS

TOTAL 166.7 M€

Cost per m3 (911'000 m3): ~180 €/ m3

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.

LAGUNA-LBNO at Frejus – Option 1

Same volume as MEMPHYS option with 3 tanks butcost reduction of 11.5 M€ for excavation and support

LAGUNA-LBNO at Frejus – Option 2

Excavation and support of additional LENA costs only 23 M€

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).

THANK YOU FOR YOUR ATTENTION

Graphic layout

laguna at fréjus laguna/laguna-lbno general meeting march 3 th -5 th , 2011, cern

frjus general meeting

rock mass ok

middle of frjus road

kpashort term

kpamedium term

powerpoint laguna

external lsm

francesco amberg laguna

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