EOSC433: Geotechnical Engineering Practice & Design

Size: px

Start display at page:

Download "EOSC433: Geotechnical Engineering Practice & Design"

Brittany Flora Watson
5 years ago
Views:

EOSC433: Geotechnical Engineering Practice & Design Lecture 1: Introduction 1 of 31 Dr.

principles, approaches, and tools used in geotechnical design.

although many of the analytical and numerical techniques reviewed are also used in soil

Geotechnical rock engineering design has largely evolved from different disciplines of

1 EOSC433: Geotechnical Engineering Practice & Design Lecture 1: Introduction 1 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) Overview This course will examine different principles, approaches, and tools used in geotechnical design. The examples and case histories reviewed will focus primarily on rock engineering problems, although many of the analytical and numerical techniques reviewed are also used in soil engineering design. Geotechnical rock engineering design has largely evolved from different disciplines of applied mechanics. It is a truly interdisciplinary subject, with applications in geology and geophysics, mining, petroleum and geotechnical engineering. 2 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) 1

Overview What makes it unique is the complexity and uncertainty involved when interacting with the natural geological environment. Rock masses are complex systems! Often, field data (e.g. geology, geological structure, rock mass properties, groundwater, etc.

2 Overview What makes it unique is the complexity and uncertainty involved when interacting with the natural geological environment. Rock masses are complex systems! Often, field data (e.g. geology, geological structure, rock mass properties, groundwater, etc.) is limited to surface observations and/or limited by inaccessibility, and can never be known completely. 3 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) Course Outline Maximum flexibility will be given with respect to the lecture content provided and as to how the course will evolve! Week 1: L1 - Introduction coarse overview; rock as an engineering material; design methodologies; phenomenological vs. mechanistic approaches. Week 2: L2 Observational Approach Terzaghi s observational approach; empirical design; rock mass classification vs. characterization; GSI. Week 3: L3 Kinematic Feasibility structurally controlled failure; wedge volume calculations; block theory. Lab Case histories (Campo Vallemaggia, Gotthard Tunnel). Lab Mohr s circle & stress-strain problem set. Lab stereonet wedge volume exercise; computeraided analysis (UNWEDGE). 4 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) 2

3 Course Outline Week 4: L4 In Situ Stress stress as a boundary condition; stress & strain tensors; in situ stress determination (direct vs. indirect methods). Lab joint scanline mapping exercise; rock mass classification & SWEDGE assignment. Week 5: L5 Stress-Controlled Failure Griffith s cracks; linear elastic fracture mechanics; crack initiation and crack damage; stable and unstable crack propagation. Lab Mid-term exam (Feb. 9, 2006). Week 6: Mid-Term Break Week 7: L6 Limit Equilibrium Analysis factor of safety; probabilistic analysis. Lab SLIDE exercise. 5 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) Course Outline Week 8: L7 Stress Analysis Kirsch equations; boundary-element method. Week 9: L8 Analysis of Yielding Rock constitutive behaviour of rock; failure criterion; elasto-plastic yield; finite-element analysis. Week 10: L9 Analysis of Jointed Rock joint stiffness & strength; scale-effects; distinct-element analysis. Lab EXAM 2D exercise. Lab PHASE 2 exercise. Lab UDEC exercise. 6 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) 3

Course Outline Week 11: L10 Rock Support support vs. reinforcement strategies; ground response curves; support interaction curves.

Week 13: L12 Instrumentation monitoring in design; instrumentation types; data management. Lab RocSupport exercise. Lab Group Presentations. Lab Group Presentations. 7 of 31 Dr.

will be required (<10 pages) based on an analysis performed using any analytical, empirical or numerical method (or combination thereof) as applied to a case history to be

4 Course Outline Week 11: L10 Rock Support support vs. reinforcement strategies; ground response curves; support interaction curves. Week 12: L11 Excavation Methods blasting; mechanical excavation (TBM); construction and use of empirical design charts; Matthew s method. Week 13: L12 Instrumentation monitoring in design; instrumentation types; data management. Lab RocSupport exercise. Lab Group Presentations. Lab Group Presentations. 7 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) Term Report/Group Presentations Oral Presentations of Group Reports Several groups will be formed, for which a short consulting report will be required (<10 pages) based on an analysis performed using any analytical, empirical or numerical method (or combination thereof) as applied to a case history to be assigned. For example, a distinct-element analysis (e.g. using the program UDEC) of the GjØvik Olympiske Fjellhall/Underground Hockey Cavern in Norway using geometries and material properties obtained from the literature. 8 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) 4

5 General Information Course: EOSC 433 Lectures: Tuesdays from 13:00 to 15:00 (Room 121, EOS Main) Labs: Thursdays from 13:00 to 15:00 (Room 203, EOS Main) Grades: mid-term exam 15% labs 20% term paper/presentation 15% final exam 50% Contact Info Office: 356 EOS South Phone: (604) Course Web Page 9 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) General Information Text Book The textbook (optional) to be used for this course is: Engineering Rock Mechanics - An Introduction to the Principles by J.A. Hudson and J.P. Harrison, Elsevier Science: Oxford, Lecture Notes PDF s of these Powerpoint slides will be made available for download via the course web page (hopefully the day before the lecture at the latest). 10 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) 5

Rock as an Engineering Material A common assumption when dealing with the mechanical behaviour of solids is that they are: homogeneous continuous isotropic However,

As a solid material, rock is often: heterogeneous discontinuous anisotropic 11 of 31 Dr.

6 Rock as an Engineering Material A common assumption when dealing with the mechanical behaviour of solids is that they are: homogeneous continuous isotropic However, rocks are much more complex than this and their physical and mechanical properties vary according to scale. As a solid material, rock is often: heterogeneous discontinuous anisotropic 11 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) Rock as an Engineering Material Homogeneous Continuous Isotropic sandstone strength equal in all directions Heterogeneous shale Discontinuous fault Anisotropic strength varies with direction high low sandstone joints 12 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) 6

Rock as an Engineering Material The key factor that distinguishes rock engineering from other engineering-based

$Hoek s GSI Classification intact rock rock mass ground response fractured rock 13 of 31 Dr.$ should consider the material and the forces involved.

We have the intact rock which is itself divided by discontinuities to form the rock mass structure.

7 Rock as an Engineering Material The key factor that distinguishes rock engineering from other engineering-based disciplines is the application of mechanics on a large scale to a pre-stressed, naturally occurring material. Hoek s GSI Classification intact rock rock mass ground response fractured rock 13 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) Influence of Geological Factors In the context of the mechanics problem, we should consider the material and the forces involved. As such, five primary geological factors can be viewed as influencing a rock mass. We have the intact rock which is itself divided by discontinuities to form the rock mass structure. We find then the rock is already subjected to an in situ stress. Superimposed on this are the influence of pore fluid/water flow and time. With all these factors, the geological history has played its part, altering the rock and the applied forces. 14 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) 7

8 Influence of Geological Factors Intact Rock The most useful description of the mechanical behaviour of intact rock is the complete stress-strain curve in compression. From this curve, several features of interest are derived: deformation moduli (E, ν) brittle fracture parameters peak strength criteria the post-peak behaviour Cumulative Damage, ω AE cohesion damage Normalized Stress (σ/σ cd ) Lockner et al. (1992) Relative Cohesion Eberhardt et al. (1999) 15 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) Influence of Geological Factors Intact Rock Strength, or peak strength, is the maximum stress, usually averaged over a plane, that the rock can sustain. After it is exceeded, the rock may still have some load-carrying capacity, or residual strength. high stiffness high strength very brittle medium stiffness medium strength med. brittleness low stiffness low strength brittle low stiffness low strength ductile 16 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) 8

Influence of Geological Factors - Discontinuities Discontinuities such as faults and joints may lead to structurallycontrolled instabilities whereby blocks form through the intersection of several

Erik Eberhardt EOSC 433 (Term 2, 2005/06) Influence of Geological Factors In Situ Stress When considering the loading conditions imposed on the rock mass, it must be recognized that an in situ

9 Influence of Geological Factors - Discontinuities Discontinuities such as faults and joints may lead to structurallycontrolled instabilities whereby blocks form through the intersection of several joints, which are kinematically free to fall or slide from the excavation periphery as a result of gravity. Hoek et al. (1995) 17 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) Influence of Geological Factors In Situ Stress When considering the loading conditions imposed on the rock mass, it must be recognized that an in situ pre-existing state of stress already exists in the rock. In the case of an underground excavation, such as a mine or tunnel, no new loads are applied but the pre-existing stresses are redistributed. Total = In Situ + Excavation- Stress Stress Induced Stress 18 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) 9

Influence of Geological Factors In Situ Stress

Erik Eberhardt EOSC 433 (Term 2, 2005/06) σ 1

Stress Relaxation Stress Path σ 3 20 of 31 Dr.

10 Influence of Geological Factors In Situ Stress Martin et al. (1999) 19 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) Influence of Geological Factors In Situ Stress σ 1 Unstable Stress Concentration Stable Wedge In-Situ Stress Relaxation Stress Path σ 3 20 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) 10

Influence of Geological Factors Groundwater Many rocks in their intact state have a very low permeability compared to the duration of the engineering construction, but

Thus the study of flow in rock masses will generally be a function of the discontinuities, their connectivity and the hydrogeological environment.

$Other aspects, such as groundwater chemistry and the alteration of rock and fracture surfaces by fluid movement may also be of concern. 21 of 31 Dr.$ construction and subsequent activities are generally only designed for a century or less.

construction and subsequent activities are generally only designed for a century or less.

11 Influence of Geological Factors Groundwater Many rocks in their intact state have a very low permeability compared to the duration of the engineering construction, but the main water flow is usually via secondary permeability (e.g. joints). Thus the study of flow in rock masses will generally be a function of the discontinuities, their connectivity and the hydrogeological environment. A primary concern is when the water is under pressure, which in turn acts to reduce the effective stress and/or induce instabilities. Other aspects, such as groundwater chemistry and the alteration of rock and fracture surfaces by fluid movement may also be of concern. 21 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) Influence of Geological Factors - Time Rock as an engineering material may be millions of years old, however our engineering construction and subsequent activities are generally only designed for a century or less. Thus we have two types of behaviour: the geological processes in which equilibrium will have been established, with current geological activity superimposed; and the rapid engineering process. The influence of time is also important given such factors as the decrease in rock strength through time, and the effects of creep and relaxation the 1991 Randa rockslide, Switzerland. 22 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) 11

Rock Engineering Design Given the large scale of many of

designing these structures in the optimal way.

rock mechanics principles and rock engineering experience at

Erik Eberhardt EOSC 433 (Term 2, 2005/06) Integrated Risk

12 Rock Engineering Design Given the large scale of many of these projects, there is considerable economic benefits in designing these structures in the optimal way. In practice, it quickly becomes evident that one ignores rock mechanics principles and rock engineering experience at considerable physical and financial peril. 23 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) Integrated Risk Assessment Düzgün & Lacasse (2005) 24 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) 12

13 Site Investigation & Data Collection Willenberg et al. (2004) Geological investigations geological model Rockmass processes Geophysical investigations 25 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) Site Investigation & Data Collection Geological investigations Geophysical investigations geological model Rockmass processes failure kinematics Geotechnical monitoring Stability analysis Willenberg et al. (2004) Controlling mechanism(s) 26 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) 13

Design Methodology Successful engineering design involves a design process, which is a sequence of events within which design develops logically.

14 Design Methodology Successful engineering design involves a design process, which is a sequence of events within which design develops logically. Bieniawski (1993) summarized a 10 step methodology for rock engineering design problems, incorporating 6 design principles: Step 1: Statement of the problem performance objectives Step 2: Functional requirements and constraints Design Principle 1: Clarity of design objectives and functional requirements. 27 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) Design Methodology Step 1: Step 2: Step 3: Step 4: Step 5: Statement of the problem performance objectives Functional requirements and constraints design variables & design issues Collection of information geological characterization, rock mass properties, in situ stresses, groundwater, etc. Concept formulation Analysis of solution components design variables & design issues Design Principle 1: Clarity of design objectives and functional requirements. Design Principle 2: Minimum uncertainty of geological conditions. Design Principle 3: Simplicity of design components (e.g. geotechnical model). 28 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) 14

Step 5: Analysis of solution components observational, analytical, empirical, numerical methods Step 6: Synthesis and specification for alternative solutions shapes & sizes of excavations, rock

15 Step 5: Analysis of solution components observational, analytical, empirical, numerical methods Step 6: Synthesis and specification for alternative solutions shapes & sizes of excavations, rock reinforcement options and associated safety factors Step 7: Step 8: Evaluation Optimization lessons learned Step 9: performance assessment Step 10: consideration of non-rock engineering aspects (ventilation, power supply, etc.) Recommendation - feasibility study - preliminary & final designs Implementation efficient excavation & monitoring Design Principle 3: Simplicity of design components. Design Principle 4: State of the art practice. Design Principle 5: Optimization of design (through evaluation of analysis results, monitoring, etc.). Design Principle 6: Constructability (can the design be implemented safely and efficiently). 29 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) Design Methodology Hoek & Brown (1980) have also proposed a similar design methodology: 30 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) 15

16 31 of 31 Dr. Erik Eberhardt EOSC 433 (Term 2, 2005/06) 16

Rock Mechanics and Rock Engineering

Rock Mechanics and Rock Engineering Overview Rock mechanics is the theoretical and applied science of the mechanical behaviour of rock and rock masses. Rock mechanics deals with the mechanical properties