In-Water Pile Driving Methods
Pile driving will occur during approved work windows with reduced currents and only during daylight hours. Pile driving will be conducted with vibratory or low/nonimpact methods (i.e., hydraulic) that result in sound pressures below threshold levels to the extent feasible. Applied energy and frequency will be gradually increased until necessary full force and frequency are achieved. If it is determined that impact hammers are required and/or underwater sound monitoring demonstrates that thresholds are being exceeded, the contractor will implement sound dampening or attenuation devices to reduce levels to the extent feasible; these may include the following:
– A cushioning block used between the hammer and pile.
– Use of a confined or unconfined air bubble curtain.
– If feasible, pile driving could be done in the dry area (dewatered) behind the cofferdam.
Pile driving will follow the criteria outlined in the most recent version of the California Department of Transportation’s Technical Guidance for Assessment and Mitigation of the Hydroacoustic Effects of Pile Driving on Fish (Caltrans 2015).