Groundwater in the Perthus tunnel: feedback after excavation

Transcription

1 FIST Geoitalia 2009, Rimini, 9 11 September Symposium: Groundwater: towards a sustainable use, Antonio Dematteis 1, Riccardo Torri 1, Guido Venturini 1, Bertrand Chereau 2, Michel Ducrot 2, George Tura 3 1: SEA Consulting srl, Italia 2: Eiffage Construction, France 3: TP Ferro Concesionaria SA, España after the end A4 The thematic Perthus session: pass Hydrogeological impacts of tunnels

2 High speed and high capacity railway between Perpignan and Figueres

3 The Tunnel: Perthus Tunnel is 8,4 km long, with two tubes of 10m diameter, 30m distant one of the other Half way of the Perthus tunnel is the Les Cluses exploratory tunnel, 450 m long Two soil treatment tunnels of 6m diameter and 80m and 170m length respectively were excavated from the end of the Les Cluses exploratory tunnel The Constructor: JV ACS-DRAGADOS EIFFAGE presented their offer in September 2003, the works begun in February 2004, the time was 60 months. SEA Consulting assisted the JV for geological activities all this time. The excavation method and timing: Two Tunnel Boring Machines (Tramuntana and Mistral) excavated the two tubes in 29 month Tramuntana: 28/6/ /11/2007 Mistral: 30/9/2005-1/10/2007

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5 () Mg SO4+Cl+NO Ca Na+K 100 Ca+Mg CO3+HCO3 Cl+NO Eau non minérale Autre eau minérale Eau "type" Boulou Dupuit equation for linear groundwater flow was used to estimate the theoretical drawdown around the tunnel (radius of influence) : TtR1.= t The possible perturbation zone has been forecasted 1500m around the tunnel, only on the right side of the Rome river, especially in fault zones SO4 0 Ordinance by the Prefect (Loi sur l Eau): 1. Census of water points 2. Water sampling 3. Chemical and isotopic analysis 4. Drawdown risk analysis 5. Definition of monitoring network 6. Monitoring Hydro-geochemical studies showed different quality of waters classified in three categories: normal, mineral and thermal waters (days) t T=10-6S1 Rayon d'influence R(t) T=10-3 T=10-4 T=10-5 (m)

6 Thermal springs Le Boulou 5 thermal springs (Colette, Janette, Le Boulou, Clementine, St. Martin) 2,4 km westward the Tunnel Low discharge (1-10 l/min) Free CO 2 (Colette and Janette) Surface temperature at the springs: C Estimated deep temperature: C Estimated deepness of reservoir: 2,5 km ph acid (6,1-6,5), High TDIC ( mg HCO3 /L) High PCO 2 (0,9 1,1 bar, over-saturation)

7 Surface and ground water census (135 water points) France Spain Tunnel Type Springs Mineral spring Well Catchment Reservoir Fountain Stream River La Rome n

8 Tunnel drainage system Drainage of groundwater Drainage of tunnel polluted water (in case of accident) Drainage of groundwater

9 Drainage of groundwater into the tunnel excavation Pumping systems excavation: 1) Evacuation of groundwater inflow 2 pipelines, 220 mm diameter 4 pumps of 80 m 3 /hs at each excavation front (2 in use, 2 for backup). maximum inflow recorded punctually into the tunnel excavation: 3-4 l/s total groundwater discharge after 1,5 years from the end of the excavation: 2 l/s 2) Adduction of cold waters to the excavation front for cooling the TBM 2 pipelines, 220 mm diameter Total water discharge inflow (sum of punctual inflow) (l/s) 3,0 2,5 2,0 1,5 1,0 0,5 Mistral Tramuntana 0,0 lug-05 ott-05 gen-06 apr-06 ago-06 nov-06 feb-07 giu-07 set-07

10 Observation BH Observation BH Crossing Les Cluses fault zone Horizontal permeability 4E-06 m/s Lower vertical permeability Drawdown (m) 1.E+00 Pumping well (72 hs, 1 l/s) Drained zone SC313 - Méthode Theis Groundwater in pressure Groundwater in pressure SC6 s [m] 1.E-01 1.E-02 Courbe observée Courbe simulée Courbe simulée - late 1.E t [min] Time (min)

11 Drainage excavation and ground injection for water proofing Crossing the Les Cluses Fault zone TBM excavation (Tramuntana 10/1/07; Mistral 1/2/07) 1/01/07 SH1 - Suivi en continu Injections ( m 3 cement+bentonite+water, Feb-May 2007) 17/02/07 Cote du niveau d'eau Température /05/06 26/05/06 20/06/06 15/07/06 09/08/06 03/09/06 28/09/06 23/10/06 17/11/06 12/12/06 06/01/07 31/01/07 25/02/07 22/03/07 16/04/07 11/05/07 05/06/07 30/06/07 25/07/07 19/08/07 13/09/07 08/10/07 02/11/07 27/11/07 22/12/07 16/01/08 10/02/08 06/03/08 31/03/08 25/04/08 20/05/08 14/06/08 09/07/08 03/08/08 28/08/08 22/09/08 17/10/08 11/11/08 06/12/08 31/12/08 25/01/09 19/02/09 16/03/09 10/04/09 05/05/09 30/05/09 24/06/09 19/07/09 [mngf] [ C] 19/06/07 Drawdown 26 m Temperature Water table Temps

12 Drainage excavation and ground injection for water proofing Crossing the Creu del Signal Fault zone TBM excavation SC305 - Suivi en continu Injections Temperature /05/06 26/05/06 20/06/06 15/07/06 09/08/06 03/09/06 28/09/06 23/10/06 17/11/06 12/12/06 06/01/07 31/01/07 25/02/07 22/03/07 16/04/07 11/05/07 05/06/07 30/06/07 25/07/07 19/08/07 13/09/07 08/10/07 02/11/07 27/11/07 22/12/07 16/01/08 10/02/08 06/03/08 31/03/08 25/04/08 20/05/08 14/06/08 09/07/08 03/08/08 28/08/08 22/09/08 17/10/08 11/11/08 06/12/08 31/12/08 25/01/09 19/02/09 16/03/09 10/04/09 05/05/09 30/05/09 24/06/09 19/07/09 [mngf] [ C] 8 cote du niveau d'eau température Drawdown 9 m Water table Temps

13 Treatment of water outside the North tunnel portal excavation stream Water coming from the tunnel (60 m 3 /h) Inspection and coarse filter Buffer reservoir Excavator for mud Discharge regulation reservoir (6,5x3m) ph control Mobile treatment station with press-filter (8x3m; discharge m 3 /h) HCl ph regulation OUTPUT: 5,5 < ph < 9,5 Suspended particles < 50 mg/l Hydrocarbons < 2 mg/l Retention reservoir (1200 m 3 ) ph 5,5 7,5 9,5 Time OUTPUT Up hill Down hill

14 at excavation concluded Use of extensive water monitoring French law (Loi sur l eau) asks the constructor to perform an extensive monitoring of surface and ground waters, and after the tunnel excavation. This extensive monitoring have provided data in real time, which have permitted to: interpret the problems and find quickly the correct solutions; constantly verifying the reference hydrogeological model; in case of claims have easy relations with the public authorities and citizens. Design of water monitoring network Interesting to note that the springs Mas Courtoise, which was known but not included in the monitoring network, was dried. The choice not to include it in the monitoring was forced by the owner absence. For future, any logistic problem should not justify such a choice. Back-analysis of the DHI method This project has allowed to perform a back-analysis of the Drawdown Hazard Index (DHI), which is a predictive probabilistic model for spring drawdown.