HAMMER-PIPE ENERGY TRANSFER EFFICIENCY FOR PIPE RAMMING

摘要

The amount of energy transfer from the hammer to the casing is a critical consideration for assessingof the constructability of the required length and diameter of pipe with a given hammer. Due to various contractorselectedpipe-hammer connections and natural sources of energy loss (e.g., thermal, frictional, etc.), the energytransfer efficiency of pipe ramming hammers must be less than 100 percent; however, actual hammer- pipe energytransfer efficiencies, defined as the ratio of actual energy transferred to the rated hammer energy, have not beenreported to-date. Overestimates of hammer- pipe energy transfer could result in corresponding overestimates ofdriving stresses and penetration rates; likewise, over-estimates of driving stress could lead to excessive anduneconomical wall thickness. This study focuses on the characterization of hammer- pipe energy transferefficiencies for commonly used pneumatic and hydraulic hammers observed during production and test piperamming installations. The observed energy transfer was found to depend on the type of hammer, the hammer-pipeconnection (e.g., collets vs. ram cones), the hammer alignment, and the degree of tension on restraining chains.Observations of energy transfer indicate that hammer efficiency can vary widely; average observed efficienciesranged from 20 to 50 percent. Additionally, a parametric study on pipe drivability is presented, and confirmed theimportance of energy transfer on the rate of pipe penetration. The characterization of pipe-hammer energy transferprovided herein can form the basis for a rational evaluation of pipe drivability for a given hammer and pipegeometry, and can help owners, engineers, consultants, and contractors determine the likelihood of a successfulcasing installation.