3410 TERMINAL AVE 2018-03-09 - Laserfiche WebLink

SHAN eiWILSON,INC subsurface profile used in the design of piles on bent G. Based on this analysis,the use of a D- I 62 series hammer would result in approximately 40-50 blows per foot. The analysis of the D-46 series hammer resulted in hammer blows that exceeded 100 blows per foot, which based on our experience is larger than the typically observed during pile driving. Based on these analyses, we recommend that the selected hammer have a minimum energy rating of 150,000 ft-lbs which is approximately the energy of D-62 series hammers. I The WEAP analyses performed by Shannon&Wilson should be considered preliminary. There are many parameters in this analysis that depend on the Contractor's means and methods of , installation, therefore, we recommend that a WEAP driving analysis be performed by the Contractor prior to mobilization to the project site to select the proposed hammer type and size. The Contractor may consider choosing a hammer that can drive both 18-and 24-inch closed end steel pipe piles in the subsurface conditions at this site. 7.1.3 Vibratory Hammer A vibratory hammer may be used to initially set the closed-end pipe piles. It would likely be difficult to install the piles into dense beach deposits or glacially overridden soils with a vibratory hammer. In addition, if vibratory hammers are used in the bearing soils,the glacially overridden soils could be disturbed,resulting in a reduction in the pile side resistance. 1 Vibratory hammers are rigidly connected to the pile using hydraulic clamps. They use paired counter-rotating eccentric masses, synchronized by a gear system and driven by one or more hydraulic motors. The eccentric masses typically rotate at about 1,200 to 3,000 revolutions per minute, or about 20 to 50 Hertz. The continuous energy impulses transferred from the hammer and pile to the soil travel outwards away from the pile wall and tip as stress waves. In granular soils, such as these present at the project site,the stress waves induced by the vibration would cause movement and loss of contact pressure between individual soil particles. As a result,the ' internal friction of the soil and the contact friction between the soil and pile are reduced, allowing the pile to penetrate the soil. As noted above,this process can also result in reduced pile resistance if oversized vibratory hammers are used. We recommend that Shannon& Wilson,Inc. review the Contractor's hammer selection as compared to the anticipated soil conditions. I If a vibratory hammer is used to install the piles,we recommend that production piles be installed to within about 10 feet of the expected tip elevations for bents D through G and within I 20 feet of the expected tip for bents B and C,then be impact driven to the final cut off elevations. 21-1-21962-003-R2.docx/wp/cp 21-1-21962-003 12