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Seismic/Liquefaction Mitigation

Liquefaction can occur when a site with saturated relatively loose, cohesionless soils (usually sands or silts) experience strong earthquake ground motion. When seismic forces excite the saturated granular layers, the loose soil structure tends to contract generating excess pore water pressure, accompanied by a reduction in soils’ strength. This causes the soil to behave as a viscous liquid rather than soil.

The consequences of liquefaction for shallow foundations include the reduction in foundation support through the loss of bearing capacity, excessive settlement, lateral spreading, and flow failures. In deep foundations, liquefaction can cause reduction in lateral capacity, additional downdrag forces, and/or additional demand on the piles from lateral spreading or flow failures.

Hayward Baker Inc. is actively involved in research related to earthquake engineering, which is the scientific field concerned with protecting society as well as the natural and the man-made environment from the effects of earthquakes by limiting the seismic risk to socio-economically acceptable levels.

In situ remediation of loose cohesionless soils with geotechnical construction techniques has become a common practice in geotechnical engineering. Earthquake drains can provide adequate soil liquefaction mitigation by providing a drainage path for the dissipation of the pore pressures before reaching dangerous levels. Vibro replacement stone columns and vibro compaction use displacement and vibratory energy to densify loose cohesionless soils at depth. Jet grouting allows surgical treatment of liquefiable soil layers. Compaction grouting reduces liquefaction potential of loose granular soils through ground densification. Vibro Piers® (compacted aggregate piers) permit construction on shallow spread footings while densifying surrounding liquefiable soils during their construction. Wet soil mixing cements liquefiable soils particles together to form stiff foundation elements that help absorb the earthquake forces. Anchors, micropiles, and jet grouting provide seismic retrofit of existing foundations. Dynamic compaction is an economical soil densification technique typically used on open sites to improve a range of porous soils. Hayward Baker is the most experienced geotechnical contractor with the full range of techniques for seismic mitigation and liquefaction mitigation methods.

The presence of liquefiable soil does not mean the building site has to be abandoned, or that expensive deep foundations are required. Soils can be stabilized to mitigate the potential for liquefaction with a number of ground improvement techniques. The most commonly used to date are vibro compaction, vibro replacement, deep soil cement mixing, dynamic compaction, and compaction grouting. Cement grouting, chemical grouting, or jet grouting are also viable options. Working with owners and their geotechnical engineers, Hayward Baker Inc. can assist in selecting the most appropriate technique for the application and the soils.

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