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A NEW SYSTEM FOR DYNAMIC PILE TESTING George Goble and John Sanclaria, Goble PileTest, Inc, Longmont, CO, USA Eric Stauffer, DYS Services, Denver, CO, USA ABSTRACT The use of dynamic pile testing for the determination of axial pile capacity is generally accepted and extensively used, world-wide. The existing equipment is complex and its use requires considerable training. A new dynamic pile testing system has been developed that reduces the cost of testing and increases testing capabilities by automation of the signal matching analysis so that a capacity prediction is obtained, in the field, in real time, for every hammer blow. The analysis offers the following capabilities in addition to the usual capacity determination by signal matching: (1) the equipment is simple to operate and its use can be learned from the documentation or with only very brief training, (2) a signal matching analysis that is fully automated has been developed for the determination of pile capacity, (3) the maximum compression stress and its location along the pile is determined, (4) a warning, is given if the maximum pile compression strength is nearly reached, (5) the critical stress location is also given, (6) a similar capability is available to determine the limits on tension stresses in concrete piles, and (7) selected results in tabular form, that can be transmitted to the Engineer at the end of driving if he is not on-site. An example of interesting results that take advantage of the automated signal matching capability is presented. The results show that the use of the capacity prediction from a single hammer blow can fail to represent the actual ultimate capacity of the pile. All hammer blows are not the same. INTRODUCTION AND BACKGROUND If a pile is modeled as an axially rigid element, Newton’s Second Law can be applied directly to determine the forces that resist penetration during impact. This concept was first studied by Nara and Eiber, (1958) at Case Institute of Technology. The results of that study were optimistic and further research began in 1964 with sponsorship from the Ohio Department of Transportation. If the pile top force and the acceleration are measured during impact the velocity can be calculated by integration of the acceleration. Then the capacity is RU(t) = F(t) – ma(t) – Cv(t) (1) where RU is the pile capacity, F(t) is the force measured at the pile top, m is the pile mass, a is the acceleration, C is the damping constant and v is the particle velocity. Then the capacity at the time of zero velocity is RU = F(t0) – ma(t0) (2) This method was used by Case Research Project to obtain a capacity prediction during driving using an electronic device constructed by the project. By 1970 extensive field testing had been completed and the results compared with static load tests. TRB 2012 Annual Meeting Paper revised from original submittal.
