three 80 ft (24.4 m) long piles were driven: 1) a 30 in (760 mm) diameter control pile, which was a conventional steel pile driven using standard impact methods, with and without a bubble curtain, 2) a 30 in (760 mm) diameter double-wall pile and 3) a 30 in (760 mm) diameter mandrel- driven double-wall pile. The piles were received in 40 ft (12.2 m) lengths, and additional sections were welded onsite using a splice- or roller-bed. The double-wall and mandrel piles were fabricated on these beds (i.e., inner piles were inserted into the outer piles) prior to lifting and installation. The piles were lifted using a conventional crane in routine fashion, and the piles were driven using an APE D46 diesel hammer. Each pile was located the same distance from the sound measurement devices, which were deployed at distances of 33 ft (10 m), 330 ft (100 m) and 1,640 ft (500 m). At a distance of 33 ft (10 m), the double-wall and mandrel piles showed a reduction in peak noise levels (the maximum peak overpressures and underpressures) greater than 20 dB in underwater noise compared to a 6 dB reduction for the bubble curtain. The cumulative sound measurements (RMS – mean pressure levels, and SELcum – cumulative energy exposure levels) also showed a reduction in noise levels in excess of 15 dB. The MCT Pile reduced the noise levels below the biological thresholds for every sensitive species except fish, whereas the standard pile with bubble curtain generated noise levels that exceeded all but two established thresholds. Noise Level Mandrel Peak RMS SELcum 196 172 188 Double Wall 196 173 190 to the first test: 1) a 30 in (760 mm) diameter control pile, which was a conventional steel pile driven using standard impact methods (i.e., no bubble curtain was used for this test because it did not fit within or around the template used to drive the piles); 2) a 30 in (760 mm) diameter double-wall pile and 3) a 30 in (760 mm) diameter mandrel- driven double wall pile. The foundation contractor received the Control Double Pile Mandrel Pile Test Pile Penetration 39 ft (11.9 m) 40 ft (12.2 m) 37 ft (11.3 m) Number of Blows 290 412 324 Blows/ft (last 3 feet) 16 18 17 Drivability performance of the three test piles The piles installed at the Vashon test site 76.5 ft (23.3 m) long piles from a barge: a standard or control pile, a fully fabricated double-walled pile, and a partially fabricated mandrel pile. The piles were lifted using a conventional crane in routine fashion, and the piles were driven using an APE D80-23 diesel hammer. Each pile was placed into the template, fitted with dynamic drivability instrumentation, and then impact driven to the desired depth. An eight-channel pile driving analyzer (PDA) system was used to collect and analyze the data. The configuration of the driving template precluded the use of a bubble curtain, so no noise attenuation was provided during installation of the control pile. The double walled pile was lifted, placed into the template, instrumented, and then driven similar to the control pile. For the mandrel pile, the contractor lifted the outer pile, set it down vertically, and temporarily braced it to the barge. The crane operator lifted the inner pile, and then threaded the inner pile into the external pile while hoisting the outer pile Measured Sound Levels Single Wall (control) 212 189 204 Fish 206 --- 187/183 Noise levels for the test piles and biological thresholds for sensitive species A second full-scale test occurred on December 7-8 2015, at the Vashon Island Ferry Terminal in Puget Sound near West Seattle, Wash. At this test site, three 76.5 ft (23.3 m) long piles were driven within a steel driving template in a manner similar Cetacean Injury --- 180 --- up to ensure the bottom seal was free of water when the piles were coupled at the shoe. After the mandrel pile was fabricated, it was set into the driving template, the dynamic instrumentation was affixed, and then the pile was impact driven. were driven to approximately 40 ft (12.2 m) of penetration to test the drivability performance of the new technology. The MCT Pile showed statistically equivalent drivability to conventional piles over the last 3 ft (0.9 m) of driving. Sound measurement devices were deployed at distances of about 33 ft (10 m) and 330 ft (100 m) from the piles. At a distance of 33 ft (10 m), the double wall and mandrel piles showed a reduction in the peak noise levels in excess of 13 dB. The RMS and SELcum levels showed a reduction in excess of 9 dB and 7 dB, respectively, when compared to the standard pile. Observations during pile driving and from the noise data suggest the following: • The interaction between the test piles and the steel driving template generated an unanticipated addition or source of underwater noise. The physical contact between the piles and the template during driving resulted in vibration and, therefore, noise. • The flexible coupling that worked very well during the first test in soft sediment was reused, and was found not to work as well during the second test. The O-rings within the coupling were not optimized Established Biological Thresholds Cetacean / Pinniped Disturbance --- 160 --- Pinniped Injury --- 190 --- Murrelet Injury --- --- 202 Murrelet Non- Auditory --- --- 208 for the substrate and were, therefore, too soft. This will not be a factor in any future deployments, as the flexible couplings will be uniformly fabricated from stiffer materials to ensure superior performance in any soil condition. DEEP FOUNDATIONS • MAR/APR 2017 • 67
