Earthquake Activated Electro-Osmosis
GeoSierra has been researching and developing the technologies to utilize electro-osmosis to prevent damage to existing structures during an earthquake event. One of the most destructive effects of the stress waves generated during a seismic event results from their induced shaking or vibratory shearing of saturated, loose fine sand or silty sand, causing a phenomenon known as liquefaction. When loose sands and silts are subjected to repeated shear strain reversals, the volume of the soil contracts and results in an immediate rise in the pore water pressure within the soil. If the pore water pressure rises sufficiently high, then the effective stress reduces to zero, and the soil mass will lose all shear strength.
Such temporary loss of shear strength can have a catastrophic effect on earthworks or structures founded on these deposits. Major landslides, settling or tilting of buildings and bridges and instability of dams or tailings ponds have all been observed in recent years and efforts have been directed to prevent or reduce such damage.
View our in situ Liquefaction Assessment Tool and our Earthquake Liquefaction Prevention and Seismic Base Isolation videos.
To view the ASCE paper of Hocking & Hebner (2006) go to the ASCE's library website at ASCE or view the Alaskan Way Viaduct.
The electro-osmosis technology involves reducing the pore water pressure build up in soils during an earthquake event by activating an electro-osmotic gradient away from the foundation of the structure. This negates the impact of the earthquake shaking and by reducing the soil pore water pressure maintains the soil shear strength and foundation structural stability. Soil liquefaction prevention by electro-osmosis can be retrofitted to protect existing structures with minimal disruption or disturbance to the structure.
A seismic switch monitors local seismic precursor events, such as early arrival ground motion, and electrically energizes the electrodes beneath the structure to move the groundwater by electro-osmosis away from the foundation of the structure and thus maintain structural stability of the foundation by preventing liquefaction of the sub-base soils during an earthquake event. The energized electrodes are completely safe and there is no potential for any electrical shock to persons or the structure.
High Rainfall and Liquefaction Induced Failures
The electro-osmosis system can be activated by high rainfall events, pore fluid pressure measurement, accelerometer readings, etc. so as to mitigate slope failures, tailings dam and dam failures. In these cases, the system may be powered up for hours or days with a backup generator, to provide warning and time to excavate from the dangerous incipient failure.
Videos Earthquake Liquefaction Prevention, Liquefaction Assessment Tool and Seismic Base Isolation.