ENGINEERING GEOL Flashcards
Young Geomorphic Features of an Active Faulting
Fault Scarps
Triangular Facets
Fault Sarplets
Fault Rifts
Fault Slice Ridges
Shutter Ridges
Offser Stream
Enclosed Depression
Fault Valleys
Fault Troughs
Side Hill Ridges
Fault Saddles
Active Fault
?Has history of strong equakes an surface rupture
?demonstrated to have an interval of recurrence short enough to be sigificant during the life of a particular project
?Reccurence time period considered significant for individual projects will vary with the consequence of activity
Potentially Active
?Tectonic faults w/c has not ruptured in historic time but available evidence indicates that rupture occurred in the past
?Reccurence Period could be short enough to be of significance to particular projecst
Activity Uncertain
?reported fault for which insufficient evidence is available to define the past activty or its recurrence
Tentatively Active
?Predominant evidence suggest that the fault may be active even though its recurrence interval is very long or poorly defined
Tentatively Inactive
?Predominant evidence suggesst fault is not active
Inactive
?Surface faulting has not occurred in the recent past
?Reccurence interval is long enough to be significant in particular projects
Seismic Hazards
Description
Ground Rupture
?faulting/displacement along a fault
?defornation is permanent
Fault Creep
?Slow aseismic displacement along a fault
?creeping doe not guaranee that fault will not move catastrophically
Ground motion
?Near Source - 3-5km
Ground acceleration decreases as a function of distance
Liquefaction
takes place when loosely packed, water-logged sediments at or near the ground surface lose their strength in response to strong ground shaking
Differential Settlement
occurs when structure partly founded on rock and partly on soil
EQ Induced Landslide
Mass wasting triggererd by ground motion
Tsunamis
?Occurs along coastal areas
?Triggeed by movement along trenches, sbumarine faults, volcanoes and landslinde
?Rquirements to be Tsunamogenic Activity:
1) Epicenter offshore
2) Relatively Shallow depths
3) Sufficiently Strong
4) Vertical Motion
Seiches
?Refers to standing/oscillatory waves in large lakes, ponds or reservoirs
Induced Seismicity
?Large reservoirs, geothermal extraction and reinjections, mining and nuclear explosions
?Limited to small and moderate Eqs
?May aactually be beneficial
Deterministic
?Worst case scenario
?Based on a single event
?Based on desigh earthquake and shortest distance to EQ Generator
Probabilistic
?Statistical Treatment of historical data
?Highly quantitative
?Fails to consider concept of sesmic gaps
?Increasingly required for major projects
Basic Principles
Soli mechanics (Cohesion and Friction Angle)
Modes of Failure
1) Circular Failure
?occurs in thick soils
?need to saturate the entire slope
2) Parallel Failure -
?occurs in high steep slopes
?thin mantle of residual soil above bedrock fails with the Rock-Soil interface as sliding plane
?no need to saturate entire slope
?Root of trees can trigger as it spread out along the interface
?Prolonged shaking of trees
Assessments Needed
landslide Mapping
use of remote sensing prior to field work
Topographic Survey
Geotech Investigation
?Detailed Topo Mapping
?Geotech Drilling
?Soil sampling w/ lab testing
Slope Stabiliy Analysis
?Normal Conditions
?Saturation
?Seismic Loading
Lithologies that are not so susceptible to slope failure but is highly susceptible to weathering might lead to detoriation of strength parameters and eventually fail in the future
Mitigating Measures Reducing Hazard
?Earthmoving (Benching, Unloading, Butress)
?Improvement of surface and subsurface drainage
?Soil Nails, Shotcrete
?Retaining Walls, Gabions Walls (Broken rocks in a wiremesh Basket)
Mechanically stabilize Earth
?Piling
?Bio Engg (Vetiver, Peanut plant, Hydroseeding Wattling)
Mitigating Measures Reducing Exposure
Non Construction
Relocation/Realignment
Evacuation
Regulation of traffic/access
Mitigating Measure Reducing Vulnerability (Protecting popuation, structures etc)
?IECs
?Landuse Zoning and planning
?Slope Stability
?Site-ing
?Engg:
Catch Walls,
Protection works,
Check Dams,
Tunneling
Slopes
1) Natural
2) Man-Made (Cut slope, back filled slopes/embankments)
Morpholgical Indications of Slope Failures
1) Amphitheater
2) Headscar
3) Escarpement
4) Teracettes
5) Ponded Water
6) Tension Cracks
7) Lateral Escarpments
8) Hummocy terrain of landslide debris (bukol bukol)
9) Difference in Vegetation or Titled Trees
Factor Affecting Slope Hazard
1)Slope: Steeper
2)Geology: Siltstone, Shale, Marls.
3) Fracture: Highly Fractured
4) Weathering: Intensely Weathered
5) Alteration: Hydrothermally Altered Rocks
6) Groundwater: Saturated rocks
7) Rainfaill: Prolonged Periods of Rain
8) Vegetation: Less Vegetation more suscpetible, Strong winds can shake trees can induce parallel failures
Secondary Impacts of Landslides
1) can dam rivers
2) Landslide derbis can be remobilized as debris flows
3) Can lead to massive siltation
4) Can impact communities, agricultural land, facilities, bridges and dams down streams
Hazard
Description
Flash Flood
type of floods which are more limited in extent and occur with limited warning and can be deadly because they produce a rapid rise in water levels and can have a devastating flow velocity
Influenced by:
1) Rainfall Intensity and Duration
2) Topgraphy
3) Surface Conditions
Inundation/Sheet Flow
Overflowing of Water
Debris Flow
Often related to damming/blockage of water then subsequently breached (na block ng matagal, naipon tapo na breach kaya may sudden high volume of discharge)
Blockage can be because of: Landslide debris, log jams, spillways, culverts and bridges acting as obstructions
?High Water content
?Poorly Sorted Debris
?High Velocity
?Large Volume
?Often Channelized
?Can travel large distance
?Trigerred by intense rainfall
Siltation
Increase mudding which can choke streams
Bank Erosion
Erosion of river banks
Channel Migration
Changing of the path of River
Scouring
Downward erosion of rivers or erosion of riverbed and riverbanks
Gully Erosion
V-type erosion deeper than rills
Sheetflow-Rills-Gullies
Special Problems
Description
Foundation in Limestone
?Can result in loss of foundation
?Can still pose problems even w/o collapsing
Tunneling
?Can result in water loss
?Safety issue can cause sudden influx of water in case water-filled cavity is intercepted
?Tunnel can collapse into sinkhole
?Rockfall on tunnel lining
?Difficulty in grouting or backfilling
Groundwater Contamination in Limeston
?No filtration
?Concentrated flows instread of intergranular flow
Sources of Contamination:
?Domestic waste water
?Leaking Septic tanks
?Dump sites/Landfills
?Used oil from talyers
?inflow of mud due to change in land cover (Kaingin)
?Salt water instrusion for coastal areas/small islands
COASTAL HAZARDS
Mitigation Elimination of Hazard
Tsunamis
None
Coastal Erosion
Coastal Protection
Coastal Flooding
Regulation of Groundwater extraction
Coastal Protection (Tarbuck)
Descrption
Hard Stabilization
This general term which refers to strucures build to protect a coast from erosion or to prevent the movement of sand along a beach
Jetties
These are usually build in pairs and extend into the ocean at the entrance to rivers and habors which constricts the flow of water into a narrow zone which prevents deposition of the sand into the channel during the ebb and flow caused by the rise and fall of tides.
This may also act as dam agains which longshore current and beach drift deposit sand
Longer than groin
Groin
A barrier build at a right angle to the beach, usually in series, to trap sand that is moving parallel to the shore and are usually built using large rocks or wood.
Breakwater
The purpose of this structure is to protect boats from the force of large breaking waves by creatig a quiet water zone near the shore
Seawall
Designed to armor the coast and defend from the force of breaking waves by reflecting the force of unspent waves seawards
Beach Nourishment
This practice involces adding large quantities of sand to the beach system which makes buildings along the shoreline less vulnerable to destruction by storm waves and enhances recreational use. Sand is pumped by dredges from offshore or trucked from inland locations .
Relocation
Aside from Beach nourishment what is the other alternative to hard stabilization?
Elimination of Hazards
Sabo Ams
Elimation of exposure
Non Construction, Relication realignment
decreasing Vulnerability
Hydrology and Hydraulic Studies
Diking
