Pipe pile caps have been around as long as pipe piles, but mating them to a pile hammer via a pipe cap may be new to some users. The diagram above (which, as you can see, dates from 1931) shows how this is done.
The cross-section shows three diameters of pipe piles mating with a pipe cap. Pipe caps typically have steps to mate with more than one size of pipe pile. It’s also possible to drive pipe caps “flat face” (with no steps) but you lose the alignment assistance of the cap when you do.
The outer two pipes mate with “male steps,” those which face the inside diameter of the pipe. It’s necessary thus to know the ID of the pile, which usually means the OD and the wall thickness. A little clearance is allowed to make mating simpler and to take into account the fact that pipe pile isn’t always perfectly round (especially at the ends, where it gets bent.)
On the small onshore caps, the steps are typically straight. On the offshore caps, Vulcan typically put in a draft angle to make stabbing the pile easier.
With caps with multiple steps, it’s possible for the steps to interfere with each other because the diameter of one step is too small to accommodate the OD of the pile below it. To avoid this problem requires some layout before the cap is machined.
Male pipe caps can be used with wall thicknesses thinner than originally intended with the use of welded shims.
The inner pile mates with the “female” portion of the cap, i.e., the OD of the pile. This eliminates the ID mating problem but requires a completely different cap design.
Vulcan pile extractors were largely designed to extract sheet piling. The standard connection had two (2) or three (3) holes that needed to be burned into the sheeting. While this provided a very durable connection, it was time consuming and is not really applicable to piling such as wood piling.
Above is a diagram, taken from Vulcan’s literature around 1960, showing various types of pulling adapters for piling other than sheeting. In addition to these there were two other types of connections that were used on Vulcan extractors:
The completely revised TAMWAVE program is now available. The goal of this project is to produce a free, online set of routines which analyse driven piles for axial and lateral load-deflection characteristics and drivability by the wave equation. The program is not intended for commercial use but for educational purposes, to introduce students to both the wave equation and methods for estimating load-deflection characteristics of piles in both axial and lateral loading.
We have a series of posts which detail the theory behind and workings of the program:
The analysis procedure is exactly the same. We will first discuss the differences between the two, then consider an example.
Differences with Piles in Cohesive Soils
The unit weight is in put as a saturated unit weight, and the specific gravity of the soil particles is different (but not by much.)
Once the simulated CPT data was abandoned, the “traditional” Tomlinson formula for the unit toe resistance, namely $latex q_t = N_c c $, where $latex N_c = 9 $, was chosen.
The ultimate resistance along the shaft is done using the formula of Kolk and van der Velde (1996). This was used as a beta method, for compatibility with the method used for cohesionless soils. Unless the ratio of the cohesion to the effective stress is constant, the…
With the static analysis complete, we turn to the wave equation analysis. TAMWAVE (as with the previous version) was based indirectly on the TTI wave equation program. Although the numerical method was not changed, many other aspects of the program were, and so we need to consider these.
Shaft and Toe Resistance
Most wave equation programs in commercial use still use the Smith model for shaft and toe resistance during impact. Referencing specifically their use in inverse methods, Randolph (2003) makes the following comment:
Dynamic pile tests are arguably the most cost-effective of all pile-testing methods, although they rely on relatively sophisticated numerical modelling for back-analysis. Theoretical advances in modelling the dynamic pile-soil interaction have been available since the mid-1980s, but have been slow to be implemented by commercial codes, most of which still use the empirical parameters of the Smith (1960) model. In order to allow an appropriate…
With the first step out of the way, we can proceed to the second: allowing the user to modify the properties of the soil. This option must be used with care since it is easily possible to put together a set of soil properties that is physically unrealistic if not impossible.
Also, if you have chosen a sand or clay, you have chosen the methodology you will use. Adding cohesion to a sand or gravel, for example, will have no effect on the subsequent performance of the model.
Finally, depending upon the choice of a free or fixed head, you are given the option of entering lateral loads and/or moments for the pile head. In this case we have opted to add a lateral load of 10 kips to the pile and no moment. The default is zero for both load and moment; this will produce some coefficients but…
TAMWAVE stands for Texas A&M Wave Equation. The TTI wave equation was developed at Texas A&M in the late 1960’s and early 1970’s, and was a successor to Smith’s original wave equation program. In reality this is more than a wave equation program; it is a driven pile analyser which, in addition to the wave equation program, analyses the static performance of a driven pile for both axial and lateral loads. It is not intended to be used on actual projects, but as an educational tool for students. Most of the software in current use is expensive, and predecessors such as SPILE, WEAP87 or COM624 are hard to use (they’re DOS programs) or methodological obsolescence issues. (With WEAP87, there are not as…