sectional area for a steel H-Pile. First, steel is selected and then H-Pile type. Then the available sections are displayed, as shown in Figure 2, to simplify data entry and avoid errors during the data entry process. If pipe piles are selected, the diameter and wall thickness are entered and, for any other sections, the area is entered. For concrete piles, the operator can select from square or cylindrical cross sections to establish the cross sectional area. For square piles, the side dimension is entered; for cylindrical cross sections, the diameter and wall thickness are entered. For any other cross section, the area is entered. The speed of the wave propagation is measured, and from that the modulus can be determined and entered directly. The modulus can also be determined automatically during driving by measuring the wave speed. If this option is used, changes in wave speed during driving are automatically determined and the modulus adjusted. The total pile length and the length below gages are required in the analysis. Also, note that the permitted steel stress, permitted concrete compression stress, permitted concrete tension stress and the effective prestress are entered. This information is used in preventing damage. The hammer type and the specific hammer are entered. Of course, this is not required in the analysis, but it can be a useful piece of information when reviewing the data. Pile Check uses the power of modern computers to perform the computations necessary to do the required signal matching using a powerful high- performance optimization technique. If there is no shaft or toe resistance on the pile, the stress and proportional velocity waves will follow the same line as they propagate down the pile. That is: F = (EA/c) v. Where F is the force at some point along the length of the pile, E is the modulus of elasticity, c is the velocity of wave propa- gation and v is the particle velocity at the same point on the pile. If resistances to penetration are present, upward traveling waves are generated and the force and proportional velocity waves will separate. So, to determine the resistances, and hence the capacity, equivalent resistances must be applied to bring the two waves back 54 • DEEP FOUNDATIONS • SEPT/OCT 2012 The forces and stresses are known so they can be used to limit the driving stresses in the pile. During driving, the maximum compression and maximum tension stresses are displayed by Pile Check. The operator enters the limiting stress for steel piles, the limiting compression and tension stresses, and the effective prestress for concrete piles. This system will prevent the excessive pounding that sometimes occurs when a steel pile is driven to rock. If it then continues to be beaten, the pile toe will surely be damaged. In addition to the toe stress reaching the limit, in most cases the pile will have some shaft resistance. Imagine the unnecessary capacity that the pile has. together. The resistances used are the stan- dard static and dynamic values used by the Smith Model in the Wave Equation Analysis. A very powerful optimization analysis ad- justs the resistances so that the differences between the force and velocity curves are minimized. This process is known as signal matching. The sum of the static resistances determined is the predicted pile capacity. What has been described so far produces results that are standard in current dynamic testing systems. The basic methods used by Pile Check in signal ma t ching ana l y s e s of f e r othe r opportunities for useful capabilities. We used the standard Smith lumped mass- spring wave propagation analysis, which determines the propagation of the measured force wave. The force is determined as a function of time at each of the elements along the pile. Since, the force is known at all elements, all of the time, the critical stress conditions can be detected. For steel piles the compression stress will probably be critical, so the limiting stress will probably be the yield stress, or a somewhat smaller value to add some conservatism. When the stress during driving is within 5% of the limiting value, a large yellow rectangle appears on the screen as shown in Figure 3. When the limiting stress is reached, the warning turns red. The location of the limiting stress is also given. For concrete piles, when the compression stress is within 5% of the limiting concrete stress minus the effective prestress, the yellow light appears. When it reaches the limit, the light turns red. When the concrete tension stress reaches the limiting concrete tension stress plus the effective prestress, the yellow warning appears and, when the limit is reached it turns red. The location of the critical stress is given. Figure 3. Stress alert warning
