Risk Management Applied to Mechanized Tunnelling in Urban Area Piergiorgio GRASSO - GEODATA, Italy

Transcription

1 Risk Management Applied to Mechanized Tunnelling in Urban Area Piergiorgio GRASSO - GEODATA, Italy ITA CBT Seminario SAT2008 Sao Paolo, June

2 Contents Peculiar aspects of Tunnelling in urban areas Demanding requirements: how to face it? The need of a Risk Management Plan: a robust approach Implementing a RMP Identification Quantification Primary response to the identified risks (mitigation measures, including correct design-construction choices) Evaluation of residual risk and control criteria Predefinition of countermeasures to face the residual risks Control: use of a Plan for Advance of Tunnel (PAT) ITA CBT Seminario SAT2008 Sao Paolo, June

3 Tunnelling in urban area Tunnelling is increasingly being seen as an environmentally preferable means of providing infrastructure to densely populated urban areas The demands for tunnels in urban area comes from various markets: Underground transportation systems (metro, railways, highways) Utilities (DSS, water supply, flood mitigation, hydro, pipeline) Underground shopping centres and pedestrian systems ITA CBT Seminario SAT2008 Sao Paolo, June

4 Tunnelling in urban area ITA CBT Seminario SAT2008 Sao Paolo, June

5 ITA CBT Seminario SAT2008 Sao Paolo, June

6 Difficult tunneling context ITA CBT Seminario SAT2008 Sao Paolo, June

7 The challenges The increasing number of new challenging projects that involves tunnels in urban area or long and deep tunnels, which have always represented one of the most complex and ambitious engineering undertakings, together with the pressing market requirements continuously lead to new difficulties to be overcame. The real challenge is give certainty in an uncertain context in terms of: Quality Cost and Time Safety during the construction and the exploitation stages Durability ITA CBT Seminario SAT2008 Sao Paolo, June

8 Risk Management Approach No construction project is risk free. Risk can be managed, minimized, shared, transferred, or simply accepted, but it cannot be ignored. (Managing Geotechnical Risk, Sir Michael Latham, 1994) Risk should be properly managed by: -Risk identification; -Risk quantification; -Definition of the responses to risk: Control of residual risk. ITA CBT Seminario SAT2008 Sao Paolo, June

9 Risk Management Approach In cases where the initial risk level is not acceptable, the relevant mitigation measures should be identified and designed. After application of the mitigation measures the "residual risk level" is reached. ITA CBT Seminario SAT2008 Sao Paolo, June

10 Risk Management Approach Observational Method + Flexible Approach PAT + = Full RMP Monitoring of behaviour behavior -Underground structure -Surrounding ground -Structure above Prediction -Design Analysis -Design Analysis -Threshold values -Treshold values -Pre-definition of counter measures Design Optimization & Application of pre-defined counter measures Concept of iterative design through the use of a Plan for Advance of Tunnel (PAT) ITA CBT Seminario SAT2008 Sao Paolo, June

11 Plan for the advancement of the Tunnel: PAT Geological conditions Supervision Training Clientcontractor team Workmanship Structure Performance Ground treatment & Construction Method Monitoring Interpretation Risks management Successful Project PAT The use of the control techniques and the continuous updating of the designconstruction protocol, called PAT, help to stabilize actively the equilibrium, otherwise known as unstable, of the observational method. ITA CBT Seminario SAT2008 Sao Paolo, June

12 What happens without a RMP Collapses can heavily injure third parties and/or cause serious damages to people and private properties. ITA CBT Seminario SAT2008 Sao Paolo, June

13 Implementing a RMP: Identification Define Reference Design Scenario Creation of a team of specialists Collection of published and unpublished data, including site investigation data Risk sessions to identity risks, and rank in terms of prob./likelihood and impact, using checklists, heuristics, risk software, RES (Hudson), etc. Creation of a register of risks Produce a geo model and estimate likeliest ground conditions, and variations ITA CBT Seminario SAT2008 Sao Paolo, June

14 Implementing a RMP: Identification The use of Risk Register ITA CBT Seminario SAT2008 Sao Paolo, June

15 Implementing a RMP: Identification The use of Risk Register ITA CBT Seminario SAT2008 Sao Paolo, June

16 Implementing a RMP: Identification FAMILY OF HAZARDS Compiling the Risk Register Design CAUSES Construction (mechanized) Factual data and input information GEOLOGY Factual data and input information HYDROGEOL. -Insufficient data collection -Insufficient field work of experiences geologists -Local experts not involved -Lack of site investigations to reduce local uncertainties -Lack of geological model validation during preconstruction activities (boreholes to install in-ground monitoring equipments) -Lack of geological model validation during construction (probing ahead, face mapping) -Insufficient data collection -Late start in the collection of data -Groups of available data statistically not meaningful -Insufficient tests both on site and in labs -Ground failure mechanisms related to tunnelling not fully understood -TBM is not equipped to probe ahead -Face mapping is not systematic during cutterhead maintenance and whenever possible -Lack of strict controls of face pressure to maintain face stability -Recruited personnel without enough experience -Insufficient piezometers -Insufficient correlation studies of rainfall data vs. piezometric readings -Late start in the installation of monitoring instruments -Monitoring instruments not installed ITA CBT Seminario SAT2008 Sao Paolo, June

17 Implementing a RMP: Quantification Risk quantification is based on a combination of: objective (statistical) and judgmental approaches (experts opinion). Judgmental quantification becomes necessary when: - the nature and extent of the data is not suitable to statistical manipulation; - or, the statistical analysis of data cannot identify the specific problem such as a fault of cohesionless material). ITA CBT Seminario SAT2008 Sao Paolo, June

18 Implementing a RMP: Quantification Qualitative Risk Analysis ITA CBT Seminario SAT2008 Sao Paolo, June

19 RMP: Example of a RMP Showing hazard identification, risk quantification, response likelihood impact Impact has the following implications: technical, planning, cost, safely Likelihood scale: 1 Improbable 2 Remote 3 Occasional 4 Probable 5 Frequent Every hazard is identified. Related impact and likelihood are scored in order to estimate the associated risk. Response in terms of design, construction, logistics, etc. are defined. residual risks evaluation... ITA CBT Seminario SAT2008 Sao Paolo, June

20 Principi d Acaja Porta Susa XVIII Dicembre Pozzo 11 Pozzo 10 ITA CBT Seminario SAT2008 Sao Paolo, June

21 RMP: Response to risk - investigations ITA CBT Seminario SAT2008 Sao Paolo, June

22 RMP: Response to risk - investigations Principi d Acaja Pozzo 11 Porta Susa Pozzo 10 XVIII Dicembre Unit 1: topsoil Unit 2: sandy gravel cement. < 25% Unit 3: sandy gravel cement % Unit 4: sandy gravel cement. >50% Geology and hydrogeology ITA CBT Seminario SAT2008 Sao Paolo, June

23 RMP: Response to risk - investigations ITA CBT Seminario SAT2008 Sao Paolo, June

24 RMP: Response to risk - investigations BUILDINGS STATIONS TUNNEL Systematic collection and management of the information through a GIS based system, via web. GROUNDWATER CONGLOMERATE UTILITIES EXISTING HISTORICAL TUNNELS ITA CBT Seminario SAT2008 Sao Paolo, June

25 RMP: Response to risk - investigations PRINCIPI D ACAJA PORTA SUSA POZZO N 11 XVIII DICEMBRE POZZO N 10 ITA CBT Seminario SAT2008 Sao Paolo, June

26 Implementing a RMP: Mitigation measures Choice of correct excavation method as primary countermeasure The TBM cutterhead has to be designed for excavating in hard rock. The confinement has to guarantee the face stability in weak rock and cohesionless soils. ITA CBT Seminario SAT2008 Sao Paolo, June

27 Implementing a RMP: Mitigation measures Selecting the correct method, including the correct and specific machine is a necessary, but not always sufficient, condition for success. It is necessary that all the stakeholders participate in the project to the best of their capabilities for addressing the following aspects: The Owner needs to develop and use a list of criteria for the selection of the Contractor and the Designer. The Designer must arrange all the known elements necessary for a correct work development and for doing adequate investigations. The Designer must also be aware of the state-of-the-art machines for tunnel excavation, and collaborate with the constructors in selecting the best solutions for the identified problems. The machine Manufacturer must efficiently combine the need of mechanical engineering with the aspects related to tunnel construction. The Contractor must always operate the selected machine in a careful and rigorous manner The Contractor must utilize only skilled and well-trained personnel. ITA CBT Seminario SAT2008 Sao Paolo, June

28 RMP: selection of the best alternative Construction of a 4.5km long shallow tunnel in urban environment with a EPB shield that can excavate in both open and close modes depending on the geological and surface conditions. Elements of the Modeling Approach - subdivision of the alignment in OF and CFcompatible regions; excavation duration [months] chainage - definitions of distributions of likelihood and size of incident when operating in OF when conditions require CF; - exponential function to take into account the increases in the time and cost arising from repeated occurrence of incidents. ITA CBT Seminario SAT2008 Sao Paolo, June

29 Quantifying the impact of a set of risks: use of DAT Simulation of hazard & inadequacy 40 chainage excavation duration [months] chainage excavation duration cost accident simulation Distribution of time and cost duration ITA CBT Seminario SAT2008 Sao Paolo, June

30 Implementing a RMP: Mitigation measures Mitigation (during design, before excavation) Kovari, 2004 Where the excavation technique and the procedures are not sufficient to properly reduce the residual risk at acceptable standards, consolidation works will have to be designed. Kovari, 2004 ITA CBT Seminario SAT2008 Sao Paolo, June

31 Implementing a RMP: Mitigation measures The correct excavation technology is the primary response to risks (e.g., EPB shield integrated with a secondary face support system) Secondary Face Support System pump SFSS = injection of bentonite slurry into the chamber as an "active manner to keep the pressure always at the desired value ITA CBT Seminario SAT2008 Sao Paolo, June

32 Implementing a RMP: Mitigation measures Countermeasures (design & during excavation) The continuous and validated monitoring of the excavation parameters is a fundamental part of the RMP recorded pressure operational range Extracted weight ITA CBT Seminario SAT2008 Sao Paolo, June

33 Implementing a RMP: Countermeasures Countermeasures (during excavation) Recorded pressure at the face (7 sensors) Secondary face support system ITA CBT Seminario SAT2008 Sao Paolo, June

34 Implementing a RMP: Countermeasures Countermeasures (during excavation) ITA CBT Seminario SAT2008 Sao Paolo, June

35 Implementing a RMP: Countermeasures Countermeasures (during excavation) Ring n Example of smooth pressure management P1 P2 P3 P4 P5 P6 P7 4,0 4,0 3,5 3,5 3,0 3,0 2,5 2,0 1,5 1,0 2,5 2,0 1,5 1,0 0,5 0,0 0,0 05:24:00 05:40:40 05:57:20 06:14:00 06:30:40 06:47:20 07:04:00 07:20:40 07:37:20 07:54:00 Bulkhead pressures (bar) Bulkhead pressures (bar) ,5 ITA CBT Seminario SAT2008 Sao Paolo, June

36 Implementing a RMP: Countermeasures Countermeasures (during excavation) ITA CBT Seminario SAT2008 Sao Paolo, June

37 Implementing a RMP: Systematic Control The management of the operational data, together with the monitoring readings (exactly like the flight recorder of an airplane), make it possible to implement the countermeasures in the shortest possible time, in order to avoid the plane crash (or the tunnel collapse) as a consequence of the accident, and not to use the black box just to investigated the causes of the crash ITA CBT Seminario SAT2008 Sao Paolo, June

38 A successful example The experience of the Nodo di Bologna tunnel construction ITA CBT Seminario SAT2008 Sao Paolo, June

39 The experience of the Nodo di Bologna tunnel construction Project layout A trench tunnel, double track from km to km A launch shaft, from to km Two tunnels, single track, excavated by EPB TBMs from km to km An emergency shaft at km A ventilation shaft at km N Pk S.Ruffillo Job Site Camp A transition shaft from km to km A NATM tunnel, double track from km to ITA CBT Seminario SAT2008 Sao Paolo, June

40 The experience of the Nodo di Bologna tunnel construction Typical cross section m Twin-tunnels (9,4 m diameter 6,1 km length) running mainly below the existing National Railway (Milan-Naples Line) Interferences with buildings, historical bridges and facilities ITA CBT Seminario SAT2008 Sao Paolo, June

41 The experience of the Nodo di Bologna tunnel construction Geological profile Pliocenic Clays Yellow loose Sands Sands and sandy Gravels with Clay lenses ITA CBT Seminario SAT2008 Sao Paolo, June

42 The experience of the Nodo di Bologna tunnel construction Geological profile Silty Clays with sandy Gravel lenses Silty Clays and Sand layers ITA CBT Seminario SAT2008 Sao Paolo, June

43 The experience of the Nodo di Bologna tunnel construction Choice of the EPB excavation methodology The correct choice of machine operated without the correct management and operating controls is as bad as choosing the wrong type of machine for the project BTS/ICE, 2005 Geological and Geotechnical conditions: variable ground conditions, with presence of gravels and pebbles of up to 100 mm in diameter, multi-level aquifer The experience of two Contractors of J.V. in the use of EPB machines Environmental problems: lack of space in Bologna and its suburbs both for the slurry disposal and for the treatment plant ITA CBT Seminario SAT2008 Sao Paolo, June

44 The experience of the Nodo di Bologna tunnel construction EPB tunnel excavation advanced in two distinct periods 1st phase July 2003 up to October from pk up to pk (1st TBM) and pk (2nd TBM) = 3530m / 15 months Geotechnical complexities Contractual constraints Settlements problems ITA CBT Seminario SAT2008 Sao Paolo, June

45 The experience of the Nodo di Bologna tunnel construction Recorded settlements Recorded settlements ST20pk Vp1=1,1% Vertical displacements [mm] TBM1 (Peck) TBM2 (Peck same behaviour as TBM1) TBM1 + TBM2 (Peck recorded data) TBM1 (Recorded data) Distance from TBM1 axis [m] ITA CBT Seminario SAT2008 Sao Paolo, June

46 The experience of the Nodo di Bologna tunnel construction Recorded settlements Recorded settlements ST20pk Vp2rel.=1,9% Vertical displacements [mm] TBM1 (Peck) TBM2 (Peck same behaviour as TBM1) TBM1 + TBM2 (Peck) TBM1 (Recorded data) TBM2 (Recorded data) Distance from TBM1 axis [m] ITA CBT Seminario SAT2008 Sao Paolo, June

47 The experience of the Nodo di Bologna tunnel construction During the excavation it was verified that, due to the small distance between the two tunnels, the ground encountered by the 2nd EPB machine was more disturbed by the 1st tunnel excavation and presented poorer geotechnical characteristics. As a consequence of this effect, during the EPB excavation it was necessary to apply more restrictive control parameters, and a higher level of excavation control when the second tunnel was excavated. ITA CBT Seminario SAT2008 Sao Paolo, June

48 The experience of the Nodo di Bologna tunnel construction 2nd phase (adoption of EPB excavation management system): May 2005 up to May 2006 Application of Risk Analysis Approach with implementation of PAT May 2005 up to May 2006 (end of excavation pk ) = 9260m / 12 months ITA CBT Seminario SAT2008 Sao Paolo, June

49 The experience of the Nodo di Bologna tunnel construction Monitoring of behaviour Prediction -Design Analysis -Treshold values -Pre-definition of counter measures -Underground structure -Surrounding ground -Structure above Design Optimization and Application of pre-defined counter measures Plan for the Advancement of the Tunnel (PAT) ITA CBT Seminario SAT2008 Sao Paolo, June

50 The experience of the Nodo di Bologna tunnel construction EPB excavation management system OPERATIONAL ELEMENTS APPLIED 1.Plan for the Advancement of the Tunnel (PAT) for each 300 m of tunnel: definition of excavation procedures, TBM control parameters and countermeasures 2.Permanent site team with Tunnel engineer for each shift, for checking TBM data and the respect of excavation procedures 3.Technical Desk with Client, Contractor and Consultant: for excavation and monitoring analysis ITA CBT Seminario SAT2008 Sao Paolo, June

51 The experience of the Nodo di Bologna tunnel construction Countermeasures and controls to reduce settlements Control of Face-support Pressure Longitudinal grouting Excavation chamber always full of materials with proper density Balances & scanner to measure the extracted material Secondary Face Support System (SFSS) ITA CBT Seminario SAT2008 Sao Paolo, June

52 The experience of the Nodo di Bologna tunnel construction EPB parameters and threshold values 1. FACE SUPPORT PRESSURE ITA CBT Seminario SAT2008 Sao Paolo, June

53 The experience of the Nodo di Bologna tunnel construction ITA CBT Seminario SAT2008 Sao Paolo, June

54 The experience of the Nodo di Bologna tunnel construction EPB parameters and threshold values 2. EXTRACTED MUCK WEIGHT AND VOLUME ITA CBT Seminario SAT2008 Sao Paolo, June

55 The experience of the Nodo di Bologna tunnel construction EPB parameters and threshold values 3. TAIL VOID GROUTING VOLUME AND PRESSURES ITA CBT Seminario SAT2008 Sao Paolo, June

56 The experience of the Nodo di Bologna tunnel construction Calculated parameters for evaluation of risk Angular distorsion: for buildings; Absolute and differential settlements: for topographical sections and bridges and viaducts Volume loss (VL) : for topographical sections ALL THE DATA ANALYSED AND AUTOMATICALLY COMPARED WITH PREDEFINED ALARM LEVELS CALCULATED BY THE EXCAVATION CONSULTANT Volume loss calculation 24 ITA CBT Seminario SAT2008 Sao Paolo, June

57 The experience of the Nodo di Bologna tunnel construction Face-support pressure Muck extracted Calculated parameters for evaluation of risk BACK-ANALYSIS OF SURFACE SETTLEMENTS CONTINOUSLY COMPARED WITH EPB PARAMETERS: Backfilling (grouting operations) BEST WAY FOR EVALUATE THE GROUND RESPONSE TOWARDS TBM EXCAVATION AND THE INTERFERENCE OF ONE TBM WITH THE EXCAVATION BY THE OTHER LATER ON ITA CBT Seminario SAT2008 Sao Paolo, June

58 The experience of the Nodo di Bologna tunnel construction Monitoring results: 1st TBM Phase 2 Phase 1 ITA CBT Seminario SAT2008 Sao Paolo, June

59 The experience of the Nodo di Bologna tunnel construction Pontevecchio bridge Active monitoring for compensation control during excavation: Bridge settlements/heaves measuring by a real time hydrostatic leveling system (1 reading every 15 minutes) 93 points on 3 levels; ±0.5mm precision Road and piers settlements by manual topographical leveling (2 readings/day) Structure cracks monitoring by automatic electrical crack meters ITA CBT Seminario SAT2008 Sao Paolo, June

60 The experience of the Nodo di Bologna tunnel construction Active settlement control with compensation grouting technique during excavation, performed by controlled grout injection through valved pipes installed below bridge foundations. The Pontevecchio case: Compensation grouting operations 9 arches, 130 m long, 10 m cover (between footing and tunnel crown) 2,7 and 5 mm allowed differential settlement between arches 96 grout pipes (HDD Technology) in 2 layers, 5 m above the TBMs crown railway bridge Ponte vecchio Via Emilia Levante Bologna 10 m grouting pipe array with maximum length of 68m 11, ,5 5,0 18,0 fill sand sandy gravel, silt content <10% twin tunnels 9,4 m in diameter tunnel 9,4 m in diameter grouting pipe array with maximum length of 68m ITA CBT Seminario SAT2008 Sao Paolo, June

61 The experience of the Nodo di Bologna tunnel construction Pontevecchio bridge This very challenging passage has demonstrate that an adequate excavation control system, together with a modern technique of intervention (the socalled compensation grouting ) led to exceptional results. In this case the difference of the settlements between two adjacent piles of the bridge has been maintained below the design limit, i.e. 2.7 mm.! Actual lecture Previous lecture ITA CBT Seminario SAT2008 Sao Paolo, June

62 The experience of the Nodo di Bologna tunnel construction TBMs performances (2nd period of excavation) Total Excavation Length [m] Avg. Daily advancement Best day Best month Avg. Last 3 months (daily) TBM (68%) 8,2 ring 12.3m 25 ring 37.5m 788 rings 13,5 ring 20.25m TBM (77%) 9,3 25 ring 1182 m 14,5 ring 13.95m 37.5m (April 06) 21.75m Excavation shifts: 24 hrs/d - 7 days/wk ITA CBT Seminario SAT2008 Sao Paolo, June

63 The experience of the Nodo di Bologna tunnel construction ITA CBT Seminario SAT2008 Sao Paolo, June

64 A new challenge: Bologna Metro Alignment High Speed Railway Tunnel Metro line 1 Major stations and key points Railway station Node Historical area Piazza Maggiore ITA CBT Seminario SAT2008 Sao Paolo, June

65 A new challenge: Bologna Metro Piazza Maggiore station Piazza Maggiore ITA CBT Seminario SAT2008 Sao Paolo, June

66 A new challenge: Bologna Metro Piazza Maggiore station Piazza Maggiore is Bologna s real heart ITA CBT Seminario SAT2008 Sao Paolo, June

67 A new challenge: Bologna Metro ITA CBT Seminario SAT2008 Sao Paolo, June

68 Conclusions Risks traditionally have been managed indirectly through the engineering decisions taken during the project development. By the use of techniques of Risk Management throughout the tunnel project development it is ensured that potential problems are identified in due time, such that the appropriate risk reducing measures can be implemented. The use of risk management from the early stages of a project, where major decisions such as choice of alignment and selection of construction methods can be influenced, is essential. ITA CBT Seminario SAT2008 Sao Paolo, June

69 Conclusions Be wise a priori: the unexpected is no longer acceptable from a risk management point of view. Use a systematic risk management approach to allow for reliable technical solutions and to ensure Certainty of results (in terms of safety, time & cost, quality and durability) in Uncertain context. ITA CBT Seminario SAT2008 Sao Paolo, June

70 Thank you for your attention ITA CBT Seminario SAT2008 Sao Paolo, June