eosc433: geotechnical engineering practice & design · lab – group presentations. term...

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EOSC433EOSC433::

Geotechnical Geotechnical Engineering Engineering

Practice & DesignPractice & Design

Lecture 1: IntroductionLecture 1: Introduction

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

OverviewOverview


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.

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.

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OverviewOverview


What makes it unique is the complexity and uncertainty involved when interacting with the natural geological environment.

Often, field data (e.g. geology, geological structure, rock massproperties, groundwater, etc.) is limited to surface observations and/or limited by inaccessibility, and can never be known completely.

Rock masses are complex systems!

Course OutlineCourse Outline


Week 2: L2 – Observational Approach– Terzaghi’s observational approach; empirical

design; rock mass classification vs. characterization; GSI.

Maximum flexibility will be given with respect to the lecture content provided and as to how the course will evolve!

Lab – Case histories (Campo Vallemaggia, Gotthard Tunnel).

Lab – Mohr’s circle & stress-strain problem set.

Week 1: L1 - Introduction– coarse overview; rock as an engineering material; design methodologies; phenomenological vs. mechanistic approaches.

Week 3: L3 – Kinematic Feasibility– structurally controlled failure; wedge volume

calculations; block theory.

Lab – stereonet wedge volume exercise; computer-aided analysis (UNWEDGE).

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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.



Week 8: L7 – Stress Analysis– Kirsch equations; boundary-element method.

Lab – EXAM2D exercise.

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 – UDEC exercise.

Lab – PHASE2 exercise.

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

Lab – RocSupport exercise.

Week 12: L11 – Excavation Methods– blasting; mechanical excavation (TBM); construction and use of empirical design

charts; Matthew’s method.

Lab – Group Presentations.

Week 13: L12 – Instrumentation– monitoring in design; instrumentation types;

data management.

Lab – Group Presentations.

Term Report/Group PresentationsTerm 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 OlympiskeFjellhall/Underground Hockey Cavern in Norway using geometries and material properties obtained from the literature.

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General InformationGeneral 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 SouthPhone: (604) 827-5573E-mail: [email protected]

Course Web Page –http://www.eos.ubc.ca/courses/eosc433/eosc433.htm

General InformationGeneral Information


Text Book – The textbook (optional) to be used for this course is:

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).

“Engineering Rock Mechanics - An Introduction to the Principles ” by J.A. Hudson and J.P. Harrison, Elsevier Science: Oxford, 1997.

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Rock as an Engineering MaterialRock as an Engineering Material


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

A common assumption when dealing with the mechanical behaviour of solids is that they are:

· homogeneous · continuous · isotropic



sandstone strengthequal in

all directions

Homogeneous Continuous Isotropic

sandstone

shale

Heterogeneousfault

joints

Discontinuoushighstrength

varies withdirection low

Anisotropic

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Hoek’s GSIClassification

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.

rock mass

intactrock

ground response

fracturedrock

Influence of Geological FactorsInfluence of Geological Factors


We have the intact rock which is itself divided by discontinuitiesto 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.

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.

With all these factors, the geological history has played its part, altering the rock and the applied forces.

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Influence of Geological Factors Influence of Geological Factors –– Intact RockIntact Rock


From this curve, several features of interest are derived:

· deformation moduli (E, ν)· brittle fracture parameters· peak strength criteria· the post-peak behaviour

Cum

ulat

ive

Dam

age,

ωA

E

Normalized Stress (σ/σcd)

cohesion

damage

Relative C

ohesion

Eber

hard

t et

al.

(199

9)

The most useful description of the mechanical behaviour of intact rock is the complete stress-strain curvein compression.

Lock

ner

et a

l.(1

992)

Influence of Geological Factors Influence of Geological Factors –– Intact RockIntact Rock


high stiffnesshigh strengthvery brittle

medium stiffnessmedium strengthmed. brittleness

low stiffnesslow strength

brittle

low stiffnesslow strength

ductile

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.

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Influence of Geological Factors Influence of Geological Factors -- DiscontinuitiesDiscontinuities


Discontinuities such as faults and joints may lead to structurally-controlled 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.

Hoe

k et

al.

(199

5)

Influence of Geological Factors Influence of Geological Factors –– In SituIn Situ StressStress


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

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Mar

tin

et a

l.(1

999)



Unstable

Stable

Stress PathRelaxationRelaxation

Wedge

In-Situ Stress

σ3

StressStressConcentrationConcentration

σ1

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Influence of Geological Factors Influence of Geological Factors –– GroundwaterGroundwater


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.

Influence of Geological Factors Influence of Geological Factors -- TimeTime


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 Randarockslide, Switzerland.

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Rock Engineering DesignRock Engineering Design


Given the large scale of many of these projects, there is considerable economic benefits in designing these structures in the optimalway.

In practice, it quickly becomes evident that one ignores rock mechanics principles and rock engineering experience at considerable physical and financial peril.

Integrated Risk AssessmentIntegrated Risk Assessment


Düz

gün

& La

cass

e(2

005)

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Site Investigation & Data CollectionSite Investigation & Data Collection


Rockmassprocesses

geological model

Geophysical investigations

Geological investigations

Will

enbe

rg e

t al

.(2

004)

Site Investigation & Data CollectionSite Investigation & Data Collection


Rockmassprocesses

geological model

Geophysical investigations

Geological investigations

Stabilityanalysis

Controllingmechanism(s)

failure kinematics

Geotechnical monitoring

Willenberg et al. (2004)

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Design MethodologyDesign 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:

Statement of the problem

Step 1:

Functional requirements and

constraints

Step 2:

performance objectives

Design Principle 1: Clarity of design objectives and functional requirements.



Statement of the problemStep 1:

Functional requirements and constraints

Step 2:

performance objectives

Design Principle 1: Clarity of design objectives and functional requirements.

design variables & design issues

Collection of informationStep 3:geological characterization, rock mass properties, in situstresses, groundwater, etc.

Analysis of solution components

Step 5:

Concept formulationStep 4:design variables & design issues

Design Principle 2: Minimum uncertainty of geological

conditions.

Design Principle 3: Simplicity of design

components (e.g. geotechnical model).

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Step 5:

observational, analytical, empirical, numerical methods

Synthesis and specification for alternative solutions

Step 6:

shapes & sizes of excavations, rock reinforcement options and associated safety factors

Design Principle 3: Simplicity of design

components.

Analysis of solution components

Design Principle 4: State of the art practice.

Evaluation

Step 7:

consideration of non-rock engineering aspects (ventilation, power supply, etc.)

Optimization

Step 8:

performance assessment

Design Principle 5: Optimization of design (through evaluation of

analysis results, monitoring, etc.).

lessons learned

RecommendationStep 9:- feasibility study- preliminary & final designs

Design Principle 6: Constructability (can the design be implemented safely and efficiently).

ImplementationStep 10:efficient excavation & monitoring



Hoek & Brown (1980) have also proposed a similar design methodology:

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