Contenido Engineering Geology for Underground Works

This book contains a careful analysis of geological and environmental issues and a correct reconstruction of the conceptual model
This leads to optimal design solutions
This book presents a synthesis of current knowledge about all the issues needed to ensure the safety to the workers during construction and to the users

The construction of tunnels involves the resolution of various complex technical problems depending on the geological and geological-environmental context in which the work fits.

Only a careful analysis of all the geological and geological-environmental issues and a correct reconstruction of the conceptual model can lead to optimal design solutions from all points of view (including financial) and ensure the safety of workers during the construction and users in the operation phase.

It was therefore felt that there was a need to collect in one volume the state of current knowledge about:
•all the geological and environmental issues related to the construction of underground works
•the different methodologies used for the reconstruction of the conceptual model
•the different risk typologies that it is possible to encounter or that can arise from tunnel construction, and
•the most important risk assessment, management and mitigation methodologies that are used in tunneling studies

Table Contents

1.1 Introduction
1.2 Lithological and Structural Features
1.2.1 Lithological Features
1.2.2 Structural Features
1.3 Tectonic Setting
1.3.1 Faults
1.3.2 Folds
1.4 Scale Effect
1.5 In Situ Stress State
1.6 Morphological Conditions
1.6.1 UndergroundWorks at Shallow Depth
1.6.2 Portals
1.7 Hydrogeological Setting
1.7.1 AggressiveWaters
1.8 Weathering and Swelling Phenomena
1.8.1 Weathering
1.8.2 Swelling
1.9 Geothermal Gradient
1.10 Seismic Aspects
1.11 Gas, Radioactivity and Hazardous Materials
1.11.1 Gas
1.11.2 Radon
1.11.3 Asbestos
References

2 Environmental-Geological Problems due to Underground Works

2.1 Introduction
2.2 Surface Settlements
2.3 Slope Instability
2.4 Interaction with SurfaceWater and Groundwater
2.5 Inert Waste
2.6 Noises and Vibrations During Excavation
References

3 Geological Conceptual Model for Underground Works Design

3.1 Introduction
3.2 Geological Studies and Investigations
3.2.1 Characterization of Shallow-Overburden Stretches
3.2.2 Characterization of Medium-High Overburden Stretches
3.2.3 Hydrogeological Surveys
3.3 Geological-Technical Characterization
3.4 Geomechanical Classifications
3.4.1 Bieniawski Classification (or of the RMR Index, Only Relevant for Rock Masses)
3.5 Rock Mass Excavability Index RME
3.5.1 Rock Mass index RMi
3.5.2 Surface Rock Classification SRC
3.5.3 Barton Q-System Classification
3.5.4 QTBM Classification System
3.6 Hoek-Brown Constitutive Model for Rock Mass
3.7 Strength of Discontinuities
3.7.1 Patton Criterion
3.7.2 Barton Equation
3.7.3 Ladanyi and Archanbault Criterion
References

4 Underground Excavation Analysis

4.1 Introduction
4.2 Discontinuous Medium and Equivalent Continuum
4.3 Convergence and Confinement
4.4 UndergroundWorks at Shallow and Great Depth
4.5 Analysis Methods of the Excavation Behaviour
4.5.1 Block Theory
4.5.2 Characteristic Lines
4.5.3 Numerical Methods
4.5.3.1 Distinct Elements Method
4.5.3.2 Finite Elements or Finite Difference Methods
4.6 Squeezing and Time-Dependent Behaviour
4.6.1 Singh et al. (1992) Empirical Approach
4.6.2 Goel et al. (1995) Empirical Approach
4.6.3 Hoek and Marinos (2000) Semi-Empirical Method
4.6.4 Jehtwa et al. Method (1984)
4.6.5 Bhasin Method (1994)
4.6.6 Panet Method (1995)
4.7 Rock Burst
4.8 Face Stability Assessment
4.8.1 Shallow Overburden
4.8.1.1 Undrained Behaviour of Cohesive Soils
4.8.1.2 Grain Material with Drained Behaviour
4.8.1.3 Stability of the Excavation Face by Tamez (1985)
4.8.2 High Overburden
4.8.2.1 Face Stability as a Function of Characteristic Strength of Rock Mass
4.8.2.2 Face Stability with Convergence–Confinement Method
4.8.2.3 Face Stability as a Function of Shear Strength
4.8.2.4 Face Stability in Relationship to the Tensional Field and Mechanical Characteristics of RockMasses
4.8.2.5 Face Stability with the Ground Reaction Curve Method
4.8.2.6 Face Stability Caquot Method
4.9 GroundWater Influence
4.9.1 Assessment of Tunnel Inflows
4.9.1.1 The Draining Process from an Advancing Tunnel
4.9.2 The Influence ofWater on the Mass Behaviour
References

5 Geological Risk Management

5.1 Introduction
5.2 Definitions and General Concepts
5.3 Geological Risk Assessment for UndergroundWorks
5.3.1 Qualitative Methods for Risk Analysis
5.3.2 Quantitative Methods for Risk Analysis: Safety Methods
5.3.3 Monte Carlo Method for Quantitative Risk Analysis
5.3.4 Risk Evaluation
5.4 Applicative Example: The Decision Aid in Tunnelling (DAT)
5.5 From Risk Assessment to Risk Mitigation
References

6 Risk Mitigation and Control

6.1 Introduction
6.2 Excavation Methods
6.2.1 Shielded and Pressurized TBM
6.3 Injections
6.3.1 Injections via Impregnation and Fracturing
6.3.2 Jet-Grouting.
6.4 Freezing
6.5 Cutter Soil Mix (CSM)
6.6 Anchors
6.6.1 Nails
6.6.2 Bolts
6.6.3 Tiebacks
6.7 Drainage
6.8 Reinforced Protective Umbrella Methods (RPUM)
6.8.1 Forepoling
6.8.2 Jet-grouting Vaults
6.8.3 Precutting
6.8.4 Pretunnel
6.9 Linings
6.9.1 First Stage Linings
6.9.1.1 Shotcrete
6.9.1.2 Steel Ribs.
6.9.2 Final Linings
6.9.2.1 In Situ Cast Concrete (Unreinforced and Reinforced)
6.9.2.2 Waterproofing andWater Management Systems
6.9.2.3 Prefabricated Linings
6.9.2.4 Single-Shell (Monocoque) Linings
References

7 Ground-Structure Interaction

7.1 Rabcewicz Theory
7.2 Method of Hyperstatic Reactions
7.3 Evaluation of the Loads Acting on the Linings
7.3.1 Vertical Loads
7.3.1.1 Soils: Caquot and Kerisel’s (1956) and Terzaghi’s (1946) Formulations
7.3.1.2 Rock masses: Terzaghi’s (1946) Classification and Approaches Based on Bieniawski’s Characterization
7.3.2 Horizontal Loads
7.3.3 Inclined Loads
7.3.4 Loads Assessment on the Lining in Case of Tunnel Under Groundwater Table
7.4 Nailing
7.4.1 Method of the Confinement Pressure
7.4.2 Homogenization Method
7.4.3 Modelling of the Cross Section with Continuum Discretization Methods
7.5 Spiling
7.6 Forepoling
7.7 Stabilization of the Excavation Face: Number and Length of the Forepoles
7.8 Characteristic Lines: Analysis of the Linings
7.9 Numerical Methods
7.10 Seismic Aspects
7.11 Final Considerations
References

8 Monitoring

8.1 Introduction
8.2 Geomechanical Surveys
8.3 Measurements of Convergence
8.4 Measures of Rock Deformations
8.4.1 Face Extrusion
8.4.2 Radial Deformations
8.5 Measures on Linings
8.5.1 Assessment of the Strain with ‘Strain Gauges’
8.5.2 Assessment of the Stress
8.6 Measurements of Pressure and Flow Rate
8.6.1 Piezometers
8.7 Measures of Acoustic Emissions
8.8 Monitoring in Excavation by TBM
8.8.1 Measure of the Machine Parameters
8.8.2 Geophysical Seismic Surveys
8.8.3 Geoelectic Surveys of the Cutting Head (Shielded TBM)
8.9 Surface Settlements and Surrounding Infrastructures Monitoring
8.9.1 Settlement Gauges and Multibase Extensometers
8.9.2 Inclinometers
8.9.3 Other Instruments for Buildings and Facilities Monitoring
8.9.4 Settlements Monitoring
Index