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