COSMOS 2012: Earthquakes in Action COSMOS 2012

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1 COSMOS 2012

2 What is SFSI and why is it important? Soil issues in Earthquakes Structures where SFSI important Retaining structures (lateral earth pressure) Foundations (spread and pile footings, bearing capacity) Soil remediation methods

3 What is SFSI? Soil-Foundation-Structure interaction is tightly coupled between: Earthquake Soil Structure Designers need to understand where they are building their structure so they can predict frequency range of future earthquakes and design structures around them What are the soil conditions underneath? What are the expected seismic demands? Need to investigate soils to see if issues exist (might have to remediate)

4 COSMOS 2012: Earthquakes in Action Liquefaction The process by which sediment that is very wet starts to behave like a liquid. Occurs because of the increased pore pressure and reduced effective stress between solid particles generated by the presence of liquid Often caused by severe shaking, especially associated with earthquakes.

5 Site Amplification effects Soil layers cause significant amplifications (enlargements) to wave vibration during earthquake which is related to distance of center of earthquake, size and properties of the soil conditions. Soil layers are like a filter for seismic waves. At some frequencies the waves are dampened while some see dynamic amplification of the waves.

6 To show how your Geophysics and Structural Engineering courses relate to each other and go hand in hand for earthquake engineering.

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8 Retaining Walls: Structures that hold back the lateral pressure from soil or rock from a building, structure or area. Prevent downslope movement or erosion and provide support for vertical or near-vertical grade changes Dams: used to retain water, typically made from reinforced concrete

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13 Shallow Footings Good for lighter weight structures Relies on bearing capacity of soil Must be a competent layer of soil beneath to work Rock is ideal

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17 Pile Footings (good in liquefiable regions) Driven Piles (steel H-pile and Reinforced Concrete) Requires softer soil strata - cannot drive through solid rock CIDH Piles - Cast-in-drilled-hole Up to 12 in diameter Reinforced concrete Ideal for sites with layers of rock that can be drilled through Common for bridge applications

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29 Mechanically Stabilized Earth: MSE is soil constructed with artificial reinforcing. It can be used for retaining walls, bridge abutments, dams, seawalls, and dikes.

30 In-situ soil alteration/improvements to improve performance during earthquakes Soil replacement Vibro-compaction Vibro-replacement Dynamic compaction Explosive compaction Drain systems The premise of soil alteration is that improvement of soil density will reduce liquefaction potential. Factors which influence choice of remediation technique include Impacts to the environment, Structure type Settlement tolerances, Soil permeability, Drainage path, and Cost.

31 Course sand for backfill: for certain sand condi4ons that are granular

32 Gravel for backfill: for more silty condi4ons

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