Download landslides and related phenomena

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Transcript
El Salvador, Jan. 2001
How can Factor of Safety (FS) Change?
•Safety Factor(FS)
•FS =1.25; minimum for slope
•FS = 10; minimum for a structure
•Change of FS
•Time
•Erosion
•Water
FS = RF/DF
Finish Factor of Safety Example
from last lecture
FS = SLT/ W sine 
S = shear strength of clay
L = length of the slope
T = unit thickness
W sine  = driving force
Using numbers in text, the
SF is only 1.125. Needs to
be 1.25 or greater
Calculations show that
about 50 m3 must be
removed for FS = 1.25
Note Assumptions:
1.
Planar Slip surface
2.
Not considering effect of fluid pressure
– what is it?
Engineering Properties of Soils: Worked
Example of Soil Shear Strength
USGS Experimental
Debris-Flow Flume
Show flume video
Vaiont
Worked Example – Estimating debris
flow speed from the scar and deposit
Subsidence
• Causes
– Withdrawal of fluids (gas, oil, water)
– Collapse of surface soil and near-surface
rocks
• Karst topography (Kars Mts., Slovenia)
• Result from dissolution
– Limestone or dolomite
– Gypsum and salt
Carbonates and Landforms in Fla. Sinkholes
Sinkholes
• May be natural or man made
• Water table
– High
• Dissolution
• Vertical flow
• Pressure change
– Low
• Decreases support
SINKHOLE DAMAGE
Sinkholes
OrlandoWinter Park, FL
Sinkholes
West central Florida sinkholes
Sinkhole
Formation
Sinkholes
• Types of sinkholes
– Solution or subsidence sinkhole
•
•
•
•
Occur where limestone is exposed at or near the surface
Covered by soil and insolubles as the depression forms
Usually not large
Bowl shaped: steepness determined by rate of subsidence
Sinkholes
• Types of sinkholes
– Cover-subsidence sinkholes
•
•
•
•
Cover is mainly non-cohesive, permeable sand
Develop by gradual subsidence
Generally only a few feet in diameter and depth
Generally remain small, cavities are filled as fast as they develop
Sinkholes
• Types of sinkholes
– Cover collapse sinkholes
• Clayey, cohesive overburdens can bridge LS cavities
• Changes in water table level (pumping effect) weakens
the bridging overburden, resulting in collapse
• Lack of support on falling water table
• Upward pressure in the case of a rising water table
Sinkhole Map
Sinkholes
• Detection Methods
– Drilling
– Ground penetrating
radar
– Resistivity
Sinkholes
12/22/04: Deltona's Howell Blvd
The Informed Volusian
Sinkholes
Caves
• Common in karstic terranes
• Mostly form by the dissolution of
limestone
• Mechanisms
– Acidic meteoric and groundwater (most
caves)
• CaCO3 + H2CO3Ca+2 + 2 HCO3-1
– Biological Activity (more recent idea)
• H2S + 2O2 + Biological activity H2SO4
• H2SO4 + CaCO3 + 2H2O CaSO4•2H2O + HCO3-1
Crystals in Cave
Gypsum Crystals:
Selenite (variety)
Size: 20 X 50 feet
Other Subsidence
In Florida
• Oxidation of Histosols
Perception of
the Landslide Hazard
• Negligible
• Residents are not easily swayed by technical
information
Cause of Portuguese
Bend Landslide
Portuguese Bend
Oft reported mass movement
Mass movement resulting from
expansive soil.
Document related concepts
no text concepts found
Similar