GEGN 468 - Final Exam
Given a particular geological scenario, recommend the most appropriate slope stability analysis method/tool
"Limit Equilibrium" analysis just considers equilibrium forces Evaluates "will it move or not", NOT "how will it move" Limit - basically force balance that gives idea of stability (make assumptions on block with perfectly planar failure surface) - slide assumes shape Numerical - idea about progressive development, mechanisms difference from idealized case - shape of geometry is Also Circular vs. Non Circular failure
Differentiate between limit equilibrium analysis and numerical analysis
"Limit Equilibrium" analysis just considers equilibrium forces Evaluates "will it move or not", NOT "how will it move" Limit - basically force balance that gives idea of stability (make assumptions on block with perfectly planar failure surface) - slide assumes shape Numerical - idea about progressive development, mechanisms difference from idealized case - shape of geometry is
Assess whether construction of a concrete or embankment dam is most appropriate for a given hypothetical dam planning scenario
80% of dams under 30 m are embankment dams 60% of dams over 150 m are concrete Embankment dams are better for wide valleys, whereas concrete dams are better for narrow valleys Material requirements Availability of suitable foundation material is also important
Define anisotropy, isotropy, heterogeneity, and homogeneity
Anisotropy - material properties are DEPENDENT on directionality Isotropy - material properties are INDEPENDENT from directionality Heterogeneity - material composition DIFFERENT thru space Homogeneity - material composition SAME thru space
Identify falling and sliding wedges for underground excavations based on structural data on a stereonet
Falling: Triangle over center Sliding: Triangle not over center
Recall the approximate magnitude of changes in slope factor of safety that can be caused by groundwater changes
Can decrease it from 1.8 to 0.6
Describe what type of engineering geology information might need to be mapped for a given scenario
Depends on scenario given - consider which types are applicable
Explain the principles of an earth pressure balance shield TBM
Chamber is filled so there is no pressure gradient from outside to inside the excavation Screw conveyor = uses gradient to transport the soil Lots of soils don't perform well in chamber - mixed with chemical additives, foam, etc How to manage pressures Manage advance speed (change rate) Change screw conveyor speed (how much comes out)
Identify grain size distributions as "Poorly Graded", "Well Graded", or "Gap Graded" and the associated implications for soil permeability
Clay: <.002mm Silt: 0.002<g<0.05mm Sand: 0.05mm<g<2mm Gravel: 2mm<g<75mm Poorly Graded - all the same size, high permeability Well graded - all different sizes, low permeability Gap Graded - missing section
Describe the observational method as applied to tunneling
Basically setting up the ground model with triggers, construction control, monitoring, review then checking if trigger criteria is exceeded then make preplanned modifications and revise the ground model
Compare and contrast the Mohr-Coulomb and Barton-Bandisshear strength criteria for rock joints
Mohr-Coulomb(assumes smooth failure plane): shear strength = normal pressure*tan (failure angle) Barton-Bandisshear(accounts for roughness): shear strength = normal pressure*tan (failure angle+ Joint Roughness Coefficient*log(jcs/normal pressure))
Identify strike and dip of a planar structure from a stereonet representation of that structure
Plane striking NS, dipping vertically Plane striking 20o, dipping vertically Plane striking 20o, dipping 10o Plane striking 200o, dipping 70o Plane striking 50o, dipping 50o The line perpendicular to 4 (the "pole" to 4) The line of intersection of 3 and 5
Differentiate between different types of engineering geology maps
Planning: Engineering Geology and Land Use Interpretive: Geological hazards, home site suitability, resource suitability Engineering: UCS, Rock Quality, Slope Stability, excavation, infiltration, corrosivity Observational: Topographic bedrock geology
Explain the influence of pore pressure on shear strength using words and/or a Mohr Circle diagram
Pore pressure moves circle left, therefore increasing the cohesion, and increasing the angle of friction
Describe the function of internal drainage systems in embankment dams
Prevents piping underneath foundation Prevents settlement due to underlying soft material
List the limitations of ground reaction curve analyses
Primarily based on perfectly plastic behavior (continuum!) Limited to isotropic in-situ stress conditions Despite limitations, still a good starting point Limitations can be overcome by constructing a ground reaction curve through numerical modeling
Relate given soil conditions to potential excavation failure modes
Raveling & running Gravitationally-driven fallout of Cohesionless material Squeezing Stress-induced deformation of continuum (cohesional) materials Flowing Saturated sands Swelling Chemical/mineralogical; not stress induced
Recall the trend that relates GSI to the ratio of intact and Rockmass stiffnesses
Recall the typical stiffness ranges (with order of magnitude accuracy) of different geomaterials
Recommend appropriate slope monitoring and/or mitigation techniques for a given scenario and provide justification for the selected approach
Regional Scale: Satellite Imagery Local Scale to Site Scale: Airborne or Terrestrial Imagery (photogrammetry, LiDAR); instrument installation; visual inspection Geodetic Extensometers Crackmeters Radar
Describe key influences of Rockmass structure on rockmass geotechnical behavior, including why the influence is significant
Faults and fractures (discontinuities) Bedding Planes (discontinuities) Other Discontinuities Fold Foliation/Schistosity
Classify a uniaxial compressive strength value as "relatively high", "moderate", or "relatively low"
High 110-221 MPa 16000-32000 psi Medium 55-110MPa 8000-16000psi Low <28MPa <4000psi
Relate characteristic factors of high and low strength rocks and soils to associated geotechnical issues
High Strength Rock - Equipment wear and difficult excavation Low Strength Rock - slope failure, settlement under load, deformation underground, change over time Hard Soils - Expansive and Collapse Soft Soils - settlement of foundation, slope failure, high erosion, raveling Organic Soils - subsidence
Critique, in the form of a written argument, conventional (stereonet-based) practice for assessing rockfall instability potential
Human Error Orientation Continuity Spacing Condition of wall rock Aperture Infilling Water conditions
List key geological factors that affect intact rock properties
Key factors for clastic rocks: Grain to grain frictional resistance (interlock depends on grain characteristics) Cementation (silica/carbonates strong; clay/gypsum weak) Mineralogy (quartz strong, platy minerals weak) Age (degree of compaction, cementation, and lithification) Key factors for crystalline rocks: Amount of platy minerals (e.g. high presence of micas in low - grade metamorphic rocks) Amount of weak minerals (halite, gypsum, etc.)
List and describe commonly applied approaches for groundwater management for slope stability applications
Minimize infiltration Provide drainage to avoid pressure buildup Avoid other mitigation measures which limit drainage (e.g. shotcrete w/o drains)
Relate the concept of a ground reaction curve to the concept of non-Instantaneous deformation and excavation face advance using words and/or diagrams
The yielding support allows the rock to deform initially and then applies a loading later when the support pressure needed is significantly less
Explain the physical significance of joint friction angle for a planar sliding block
When you zero out cohesion the w's cancel - angles cancel them out Implicitly talking about mohr coulomb
List the key Rockfall protection ditch design parameters and relate these to both slope geometry parameters and the associated rock movement mode expected
Width and depth depends on rolling, falling and bouncing behavior
Label and describe different elements of a ground reaction curve
X axis: Inward Radial Displacement Y axis: Support Pressure Pcr - critical support pressure - defined by initiation of plastic failure of rock surrounding tunnel Below Pcr: Plastic Displacement Above Pcr: Elastic Displacement Dashed line: plastic displacement assumed (used in modeling)
Use the Q-system tunnel support chart to design excavation support
Y axis: Span Height/ESR X axis: Q value
Describe in words and/or diagrams the procedures, principals, and limitations of the point load test
a point load is applied to a sample to determine strength I=P/D^2 not great for weak rocks - will crush on impact also correlation factor (K) is not unique and high potential for human error
Explain why embankment dams typically have a central low permeability core
central core or hearting of highly impermeable material (which, with any below ground cutoff, will effectively seal the dam against seepage);
Explain the impact of groundwater on slope stability
effect on F.S.(reduced normal stress on shear plane) as well as change in plane geometry Landslide instability Ice wedging Erosion Pore pressure decreases shear strength or water along sliding plain
Describe the method of slices as applied to slope stability calculations
effective angle of shearing resistance is not constant over the failure surface failure surface might pass through several different materials Calc weight and resisting moment Add cohesion, frictional resistance and resisting force
Explain earthquakes in the context of elastic rebound theory
o As opposite sides of a fault are subjected to forces, they accumulate energy and slowly deform until their internal strength is exceeded. At that time, a sudden movement occurs, releasing the accumulated energy, and the rocks snap back to their original undeformed shape. o GROUND BEHAVES BRITTLE
Explain the limitations of the Richter Scale
o Because of limitations imposed by seismographs and the emphasis on measuring a single peak amplitude, the Richter scale underestimates the energy released in earthquakes with magnitudes greater than 6.5, since the values calculated after measuring very large seismic waves tend to cluster, or "saturate," near one another. o Richter scale could not be used to calculate the total energy released by an earthquake or describe the amount of damage it did
Recall which materials typically have strength dominated by cohesion and which have strength dominated by friction
o Cohesion • Prominent in clays and intact rock • Primarily due to the attraction between particles (e.g. electrostatic and molecular forces) • Varies with moisture content in clays o Friction • Prominent in coarse soils and rock joints • Due to interactions between mineral surfaces • Friction is controlled by base friction + geometrical factors and confining stress (non-linearity!)
Compare and contrast deterministic and probabilistic analysis in the context of engineering geology problems
o Deterministic: one solution one most likely outcome o Probabilistic: variability inherent in analysis - result is probability that things will happen
Recall key geotechnical parameters that are commonly used to decide rock excavation methods
o Discontinuities are weaker than intact rock o Dependency on loading direction o With multiple joint sets, Rockmass strength is controlled by the most critical set for any given loading scenario o Equations in Hoek et al. (2002) and Hoek & Diederichs (2006) • Assumes fully persistent joint sets!
Describe, using mathematical terms, the relationship between earthquake magnitude, earthquake energy, and earthquake wave amplitude
o Energy (and waves) propagate in all directions! • Energy is contained in a single ray path for multiple wave types (P, SV, SH) • Multiple wavefronts, however, Real waves are not mono frequency ENERGY - EXPONENTIAL INCREASE W/ MAGNITUDE MAGNITUDE LOGARITHMIC W/ AMPLITUDE
Explain why different Rockmasses may have different jointing patterns
o Existing structures depend on the genesis of the rock mass o Cooling Joints -Basalt o Orthogonal Jointing • Require a flip of the principal stresses o Conjugate Joints • Created by unidirectional loading (e.g. tectonic) or unidirectional unloading (e.g. erosional) • Angle tells you about genesis!
Recall definitions of key terms related to earthquakes
o Focus: The point where the earthquake originates (on a larger fault plane) o Hypocenter: The estimated location of the focus o Epicenter: The projected of the hypocenter onto the Earth's surface (doesn't need to be on the fault trace!) o Origin Time: Time of the initial motion o Travel Time: Time for waves to reach a point of observation
Recall the purpose/use of the "Q-Slope" system
o For unsupported slope design in rockmasses o Applies "O-Factor" to account for orientation
Explain why modeling earthquake loading as a static force leads to a conservative estimate of slope stability
o Inherently conservative; treats dynamic loading as a constant force equal to the maximum transient force o Acceptable F.S. might be 1-1.1 instead of 1.3-1.5 o Could model as a horizontal force OR as a resultant vector including a vertical force equal to 2/3 the horizontal force
Explain the conditions under which risk mitigation is appropriate
o MITIGATION COST < RISK COST No Mitigation- MITIGATION COST > RISK COST Mitigation
Explain the differences between MCE, MPE, and MDE
o Maximum Credible Earthquake (MCE) • Largest EQ that may reasonably be expected to occur along a given fault or seismic source under the current tectonic setting • Recurrence interval typically ~2,500 o Maximum Probable Earthquake (MPE) • The largest EQ a fault is expected to generate within a specific time period of interest (e.g. 30 or 100 years) o Maximum Design Earthquake (MDE) • The EQ selected for design or evaluation of a structure; this EQ would generate the worst case loading scenario which is expected for the structure
Explain the limitations of empirical Rockmass classification approaches in general
o Non-uniqueness! o Think about key features for relevant application o Don't use empirical systems outside the range of conditions they were designed for!
List the factors that control earthquake-induced liquefaction potential
o Older deposits tend to be more stable (more o compaction) Coastal areas tend to have higher potential o (less geometric confinement) Tends to occur in uniform, Cohesionless soils
Explain, using examples, the difference between primary, secondary, and tertiary damage associated with earthquakes
o Primary • Ground Shaking • Damage occurs throughout the entire period of strong ground motion • "Bracketed Duration" is the duration of shaking above a certain threshold acceleration (often 0.05g) and is defined as the time between the first and last peaks of motion about this threshold o Secondary • Tsunamis (e.g. Japan) • Ground motion • Landslides • Liquefaction • Settlement o Tertiary • Physical • Supplies of parts, expertise to use them, ... • We don't realize how much routine maintenance is required to keep things going! • Social • Hospitals overwhelmed • Water compromised • Food shortages • Looting, unrest
List factors affecting the stiffness of rocks and soils
o Soils • Types of solids • Size and arrangement of grains • Porosity (density) o Rocks • Mineralogy o Porosity • Structure
List common Rockmass attributes considered in rockmass classification schemes
o Spacing oContinuity/persistence/length o Orientation o Surface roughness oWeathering/alteration/aperture/infilling o Rockmass with (statistically!) similar major lithologic and structural characteristics o Common to lump similar Lithologies together o Typically controlled by structural changes (e.g. controlled by faults, lithological changes, folds)
Relate compactant/dilatant post- yield behavior to landslide stability
o Volume change effects on pore pressure o Impact on landslide stability • System hardening versus weakening
Compare and contrast earthquake intensity and magnitude scale concepts
o Want something more objective than intensity o Requires correction for distance from source o Quantification of energy released by earthquake
Explain the difference between physical cohesion and apparent cohesion
on stress vs shear plot, fitting and extrapolation can lead to cohesion
Explain how dam reservoir level changes can lead to slope Instabilities
pore water pressure
Distinguish between different slope instability modes from photos and/or diagrams
do it
Assess the suitability of a given location for a dam foundation based on given geological/geotechnical data
do it!
Estimate the most likely epicenter location (and the uncertainty associated with this estimation) using a graphical method based on data from three or more seismograph stations
do it!
Given information about seismicity in a given area and a specific design application in that area, suggest and justify a Maximum Design Earthquake for that application
do it!
Hypothesize the highest likelihood dam failure mechanisms for a given geological/construction scenario
do it!
Explain the principles of the GLQ system
eAb(c)(d) e = modifier (cemented, expansive, hydrocompacted) A = genetic symbol (alluvial, colluvial, eolian) b = lithologic symbol (clay, silt, sand) c = qualifier (f - from morphology, sw - slope wash) d = thickness (arabic #)
Describe the general process of earthquake hazard assessment
• Is a fault or seismic source zone present • Is the fault "active" or "capable" • The fault length • The type and magnitude of expected displacement • The geologic history of displacements and age of most recent movement • Relationship of the fault to regional tectonic features • An estimated magnitude that might be expected • The estimated PGA at the site of interest • Site specific conditions that might result in ground failure or modification of ground motion
Estimate the weight of a potentially unstable rock block in two-dimensions
step one of class activity Expected to do geometry · Apply the appropriate equation to determine the factor of safety of an unsupported potentially unstable planar block (in two-dimensions) Not derive - able to use equation sheet and know which one appropriate and apply it if no water then you cancel the weight, and no cohesion you can cancel that as well
Explain major causes of slope instability
- Material Properties - Groudwater - Loading conditions - geometrical conditions
Recall the formula for maximum tangential stress concentration around a circular excavation
3 sigma 1 minus sigma 3
Distinguish between passive and active supports
Active support applies a load immediately upon installation Passive support applies a support load only after ground deformation has occurred
Define different categories of landslide activity
Active: Currently moving Reactivated: Currently moving after having been inactive Suspended: Moved in last annual cycle of seasons Inactive: Last moved more than one annual cycle of seasons ago Dormant: If the underlying cause of the landslide has not been removed Abandoned: If the causes of the landslide are no longer present (e.g. fluvial deposition at toe) Stabilized: Human activity resulted in inactivity Relict: Developed under different geomorphic or climatic conditions
compare and contrast slope stabilization/reinforcement measures and protection measures as slope mitigation options
Avoid (relocation, removal of materials, bridge): - Best: if any alternatives exist, if small volume of excavation involved, poor soils at shallow depth - Limits: may be costly for removal or bridge Reduce Driving Forces (change line or grade, drain surface, drain subsurface, reduce weight): - Best: on slopes where lowering of ground water table, existing potential slide - Limits: could affect roadway adjacent, can't be used when sliding mass is impervious, requires lightweight materials, excavation waste could cause issues Increase resisting forces (buttress and counterweight, toe berms, anchors): - Best: existing landslide, to prevent movement prior to excavation, limited ROW - Limits: not effective on deep seated landslides, must be on firm foundation, won't stand large deformations, must penetrate below sliding surface, foundation soils must resist shear forces Increase internal strength (drain subsurface, use reinforced backfill, install in-situ reinforcement) - Best: landslide where water table is above shear surface, embankments with steep fill slopes, temporary structures in stiff soils - Limits: experienced personnel to install effective orientaiton, long-term durability of reinforcement, long term durability of anchors
Describe using words and/or diagrams how fine grained soil mechanical behavior (stiffness, strength, brittleness) changes as a function of water content (e.g. relative to Atterberg Limits)
Brittle: increases with water content Plastic: increases to peak Liquid: no shear so no change
Describe the concept of the Unified Soil Classification System
Coarse grained soils are classified based on grain size distribution Fine grained soils are classified based on plasticity Classifications are based on engineering behavior
Explain the differences between two-dimensional and three-dimensional limit equilibrium models of slope stability
Common practice to approximate using multiple cross sections 2d model always more conservative - lower FOS 3d has lateral boundary and includes resistance of these
Discuss limitations of underground wedge analysis and common approaches for managing these limitations
Conservative due to inability to accurately estimate cohesion (means analysis is conservative) Conservative due to assumption of worst case wedge geometry (can scale back wedges to nominal size) Difficult in incorporating stress clamping effects (application of field stress or taking them out of model if less than 20deg) Significance for extreme geometries
Recall methods that can be employed in the field to distinguish between different soil grain sizes
Dilatency - hit side of hand to see soil release (clean sand will be quick, clay will be non noticeable) Dry Strength - dry a piece and test breaking (clay will have high strength) Toughness - roll to 3mm diameter (weakness at plastic limit, lowe plasticity) Plasticity - roll to smallest thread possible
Compare and contrast P and S waves
Direction of propagation is different: - S-wave: particle motion is in the Z direction - P-wave: particle motion is in X direction Velocities are lower for S-waves (change based on density of material)
Describe, using words and/or diagrams, a typical slope management program framework
Drain catchment Galleries joint drains vent wells slope drains
Compare and contrast the processes and strengths/weaknesses of different excavation methods
Drill & Blast: -less start up time -explosive storage permits -slower excavation rate (3-9 m per day) -horseshoe-shaped -difficult in low overburden settings, slower in long tunnels -any ore body orientation -spoil size and consistency variable -high vibration -unpopulated areas -unique skill sets and certification Tunnel Boring Machine: -3-12mo. startup time -slightly larger footprint -excavation rate (15-50 m per day) -round -30m turn radius - deep long ore bodies -reuse easier -primarily mechanics used
Apply Rockshed design formulae to calculate the required thickness of a protective gravel layer
Estimated deformation: d=mv^2/Fdesign Fdesing = c*F c = .4 for ductile and 1.2 for brittle F = 2.8t^(-5)*R^(0.7)*E^(0.4)*tan(phi)*mv^2/2 t = thickness of gravel layer R = radius of rock E = youngs modulus v = impact velocity Typical: 20MPA and 2700psi t>d+3(phimax) t>2d t>0.5m
Recall commonly used F.S. criteria for underground excavation design
F.S. criteria in the 1.3-1.5 range often used for mining Applications F.S. closer to 2 may be used for infrastructure projects Depends on end use as well as relationship between primary support design and final lining design
Recall commonly used F.S. criteria for slope design
F.S. should be at least 1.3 temporary-1.5 permanent depending on use
Apply the appropriate equation to determine the factor of safety of an unsupported potentially unstable block (in two-dimensions), accounting for the impacts of joint water pressure
FOS = [cA+(Wsin(p)-U-Vcos(p)+tcos(p+t)*tan(phi)]/[Wcos(p)+Vsin(p)-Tsin(p+t)] unit weight water = 9.81kN/m^3 = 62.4psi
Apply the appropriate equation to determine the factor of safety of an unsupported potentially unstable block (in two-dimensions), accounting for the influence of active and/or passive bolts
FOS = [cA+(Wsin(p)-U-Vcos(p)+tcos(p+t)*tan(phi)]/[Wcos(p)+Vsin(p)-Tsin(p+t)] T - accounts for bolt strength and t is angle of tension bolt
Compare and contrast geological and geomechanical models
Geological: based on genesis (unit, formation, group)& layers of similarity Geomechanical: mechanical variability, groupings based on behavior, water and pressure gradient considered
Recall typical properties of different rock types and their associated uses for construction (Intrusive Igneous Rocks; Volcanic Igneous Rocks: Rhyolite & Andesite, Basalts, Pumice, Ash, Tuff; Sedimentary Rocks:Limestone & Dolomite, Sandstone, Chert, Shales, siltstones, mudstones, claystones; Metamorphic Rocks: Gneisses,Schists/ phyllites, Slates, Marble, Quartzite
Intrusive Igneous Rocks o e.g. Granite, Diorite, Gabbro o Aggregate use: • High durability; low absorption of water (freeze-thaw) • Crushes to equi-dimensional fragments • Can be used in concrete o Cut-stone facings: • Good unless pyrite present or mica abundant o Foundations: • Good unless heavily jointed or weathered Volcanic Igneous Rocks • Rhyolite & Andesite • High resistance to abrasion • Suitable for aggregates • Basalts • High resistance to abrasion • Vesicular varieties subject to frost damage • Pumice, Ash, Tuff • Typically weaker and softer • May be highly erodible • Potential for high seepage Sedimentary Rocks • Limestone & Dolomite o Chert nodules or beds are unfavourable o Chalk is low strength and porous o Crystalline limestone & dolomite is a good aggregate o Solution features are problematic • Sandstone o Crushes to equi-dimensional shape o Good aggregate if well cemented, low in clays o Porosity can be variable (and important, depending on the application) • Chert o Very hard (highly abrasive) o May swell with absorption of water (problem for concrete) o Presence of water in the crystal structure causes problems with freeze-thaw o Unweathered Chert is smooth (poor bond with cement) • Shales, siltstones, mudstones, claystones o Poor aggregate o Cemented shales robust against moisture change o Compacted shales -slaking issues o Easily excavated o Very weak bedding planes (problems for foundations) o Easily weathered (potential for differential weatheing) Metamorphic Rocks • Gneisses o Similar behavior to granitoids • Schists/ phyllites o Anisotropy and ratio of mica to quartz key for behavior o Potential for weathering o Potentially weak and blocky • Slates o Strong between cleavage planes o Often used for stone facings, floors, shingles • Marble o Significant weathering potential o Similar behavior to Limestones and dolomites o Commonly used for aggregates and stone facings • Quartzite o Strong; highly abrasive; difficult to excavate o Can typically maintain steep slopes; failures may be very brittle
Contrast the roles of investigation and instrumentation within a slope management program
Investigation: To provide an understanding of ground conditions for design purposes To provide input values for design calculations To check for changing ground conditions as a project advances Instrumentation: To assess and verify the performance of the design To calibrate models and constraints analyses To provide a warning of any change in ground behavior to enable intervention/remediation
List major dam foundation requirements
Issues: High stresses in weak foundation materials•Low strength discontinuities dipping downstream•High uplift pressures beneath the dam Adequate strength Similar stiffness between dam and formation - most imp for concrete dam Limited seepage through foundation - low permeability Stability against uplift - can grout curtains it or create drain holes targeted at reducing flow and pressure underneath Stability in relation to ground movement - subsidence and landslides
Recall that brittleness decreases with increased confining stress
It does!
Compare and contrast the Q, RMR, and GSI classification systems, including a discussion of their relative strengths and when they should be applied
Q- SYSTEM - LIMITATIONS - often result in a sampling bias due to a preferential orientation distribution of discontinuities. cannot account for the size (length) of the considered discontinuities They also point out that the Q-system fails to properly consider joint orientations, joint continuity, joint aperture and rock strength. - tunnel support Q-SLOPE - long-term stable, reinforcement-free slope angles can be derived These conditions include the extremes of erosive intense rainfall, ice wedging, as may seasonally occur at opposite ends of the rock-type and regional spectrum. - Maximum stable unsupported angle RMR - RMR doesn't consider stress -The greatest difference between the two systems is the lack of a stress parameter in the RMR system. Fails to provide a meaningful measure of relative block size; the ratio JW/SRF is not a meaningful measure of the stresses acting on the rockmass to be supported. - Excavation stand-up time& Excavation support GSI Good if you need an input parameter for modeling GSI should not be considered an exact value, and a range of possible values should always be considered in an analysis - Determination of rockmass parameters
Describe the different components of risk
RISK = PROBABILITY x CONSEQUENCE
Describe and compare different primary support functions for excavations in rock
Retain (holds rock loads) Reinforce (prevents stresses acting on) Soil or weak rock (non-TBM): Forepoles, steel arches, dowels in the face, bolts, mesh, shotcrete Moderately weak to competent rock: Bolts, mesh, shotcrete, steel sets
Design specifications (e.g. size, energy requirements) for rockfall fences based on Rockfall Simulation results
Rockfall Fence-Design Energy is the key design parameter (accounts for mass and velocity) E = F x d If we want to stop a 1000 kJ rockfall over 0.1 m of deformation, this would result in 10 MN of force static load of 10,000 people! To make the forces manageable, we need to allow for much higher deformations Rockfall fences started in Europe ~1960s; only in the 2000s did we develop full-scale tests and standards European guidelines: Maximum Energy Level (just stop it) and Service Energy Level (must stop two subsequent impacts) SEL = 1/3 MEL Design is made relative to MEL (F.S. 1.2 in Italy) Mass of block given by geologists (engineers); height and velocity are estimated from rockfall simulation (95th percentile) Current product ratings range be/w 100 kJ and 1000 kJ/1 ft moving 1 m/s is ~100kJ Placement of fences is based on rockfall modeling Typically lower on the slope Can't place immediately next to road (deformation) Logistical/practical considerations Posts are connected to a foundation by a hinge which can rotate to allow an even distribution of forces Energy dissipators allow displacement (d = 1 m-2 m) and control force
Describe expected excavation behavior in rock based on information about excavation depth and Rockmass characteristics
Rockmass Characteristics: Massive (brittle), Moderately Fractured (localized brittle failure), Highly Fractured(squeezing and swelling, elastic/plastic continuum, raveling) In Situ stress: low (linear elastic), medium (brittle failure) high (brittle)
Compare and contrast the meaning of design in GE and in other fields
Routine design - design based on codes or standards (e.g. pavement design) Parametric design - need to find parameters which maximize performance with well defined inputs and outputs (e.g. bridge design) Original design - scenario is unique and analysis is inexact (e.g. tunnel support design) Geological engineering design is all about uncertainty No "right" design; many "acceptable" designs Depends on risk tolerance, starting assumptions Geological engineers need to (a) appreciate when assumptions are reasonable and (b) ask questions to minimize unknown unknowns
Describe common dam foundation permeability management techniques using words and/or diagrams
Seepage through dam foundations (either through discontinuities or weathered zones) can lead to multiple problems: Uplift pressures underneath the dam foundation High hydraulic gradients (risk of erosion) Significant water loss from reservoir Slope instability in abutments and downstream from the dam
Explain the importance of joint shear strength for rock slope stability problems
Shear strength counteracts the water force as well as the weight of the sliding block
Assess the relative benefits of EPBM or slurry-shield TBM excavation for a given geological scenario
Slurry - loose sandy soil Earth Pressure Balance - soft clay
List major factors that influence land use
Space Food supply Water supply Raw materials supply Energy supply Transportation
Compare and contrast high stress excavation failure mechanisms (squeezing, spalling, And rock-bursting)
Spalling = brittle failure = crushing of compressed rock w/ strain localization shown as a shear crack. Brittle cases require support to hold newly fractured ground in place. In - situ brittle cracking strength is lower than UCS (0.3UCS to 0.5UCS) Called "CI" (UCS* in chart to right) Spalled notch shape tends to self-Stabilized Key is to hold damaged material in place Squeezing - deformation of the surrounding rock in squeezing phenomenon takes place slowly and gradually when the resulting stress state following the excavation exceeds the strength of the surrounding medium, require sequential excavation, possibly yielding support Spalling + rapid energy release = rockburst
Define soil sensitivity and how it is classified
The degree to which disturbances to soil structure such as vibrations or excavations affects strength Ratio of undisturbed strength to remolded strength 2-4: Nonsensitive(most clays) 4-8: Sensitive 8-16: Highly sensitive >16: "Quick"
Recall the typical stiffness ranges (with order of magnitude accuracy) of different geomaterials
USCS - Description - Loose; Medium; Dense GRANULAR: GW,SW - gravels/sand well graded - 30-80;80-160;160-320 SP - sand, uniform - 10-30;30-50;50-80 GM, SM - sand/gravel silty - 7-12;12-20;20-30 USCS - Description - Very soft to soft, medium, stiff to very stiff, hard COHESIVE: ML - silts with slight plasticity - 2.5-8;10-15;15-40;40-90 ML,CL - silts with low plasticity - 1.5-6;6-10;10-30;30-60 CL - clays with low to medium plasticity - 0.5-5;5-8;8-30;30-70 CH - clays with high plasticity - 0.35-4;4-7;7-20;20-32 OL - organic silt - medium(0.5-5) OH - organic clay - medium (0.5-4)
Recall (approximate) p-wave velocities for different materials
Unconsolidated Settlements 0-2 km/s Clastic Sedimentary rocks 1.5-5.5 km/s Limestones 3-5.5km/s Salt 4-5 km/s Igneous and metamorphic 4-6 km/s Ultramafic rocks 7-9 km/s
Use a travel-time chart to determine the distance of an earthquake epicenter from a seismograph station
Use 3 stations, and correlate time to distance traveled, then draw circles to find
Relate principles of support design to ground reaction curve concepts
Want to make sure design support doesn't yield prior to application at equilibrium
Explain the excavation principle of a hard rock (disk cutter) TBM
a) ridge formation due to lack of pressure and length of cracks b) overbreak due to excessive loading and longer cracks c) optimum chip size formed
Explain the principles of a slurry-shield TBM
the cutterhead acts as the means of excavation, whereas face support is provided by slurry counterpressure, namely a suspension of bentonite or a clay and water mix (slurry). This suspension is pumped into the excavation chamber where it reaches the face and penetrates into the ground forming the filter cake, or the impermeable bulkhead (fine ground) or impregnated zone (coarse ground) which guarantees the transfer of counterpressure to the excavation face. Excavated debris by the tools on the rotating cutterheads consists partly of natural soil and partly of the bentonite or clay and water mixture (slurry). This mixture is pumped (hydraulic mucking) from the excavation chamber to a separation plant located on the surface which enables the bentonite-clay slurry to be recycled. Slurry TBM Advantages Less energy required to rotate Cutterhead (frictionless fluid versus earth in chamber) Can include a rock crusher in worker chamber to handle boulders
Rank Geomaterials according their relative brittleness
• Wet clay • Sand • Pourous sandstone • Fractured limestone • Non fractured dry clay • Non porous sandstone • Basalt