03 - Soil Failure Potential
The potential for soil to fail in the event of an earthquake depends on the distance to an active fault and the local topography. Important features are the geological type and characteristics of the soil, such as material composition, water content and stability. Failures can include, but are not limited to, surface rupture, slump, sink holes or liquefaction.
Overall, secondary effects can often account for a large portion of the damage following an earthquake.
The following issues are indicative of potential soil problems associated with seismic shaking:
- High ground water levels (approximately 10 m below ground surface).
- Sand or silty soils.
- Sloping ground, especially in the vicinity of rivers or lakes.
- Areas where mining activities have taken place or are on-going.
- For new structures, a geotechnical investigation is always conducted to determine the type of foundations required even before starting design of the structure. If the structure is in an earthquake zone additional geotechnical tests to determine liquefaction potential should be conducted. Most structural design codes, especially in seismic countries, define the soil parameters, which require special strengthening measures. Besides suitable foundations, eg. piles, soil strengthening measures may need to be applied as well. These include lowering the ground water table, replacing the soil, strengthening the soil by compaction or geotextiles or other measures.
- Foundation strengthening measures for existing building include, eg. injection grouting of the soil, micropiling, dewatering and densification, geotextiles, etc.