This paper–which is part of the STADYN project–was presented at the IFCEE 2018 conference in Orlando, FL, 7 March 2018. The slide presentation for the paper is below.
Back in the Saddle at the Deep Foundations Institute
Vulcan Iron Works was involved in its industry in a number of ways other than simply selling and renting its product. One of these was its years in the Deep Foundations Institute. Although Vulcan was not a charter member of the organisation, it joined very shortly after its beginning and was active during the 1980’s and early 1990’s, until about a year before the merger with Cari Capital. This webmaster was the Program Chairman for the 1992 DFI Annual Meeting in New Orleans.
So it is with pleasure that I have joined the DFI once again, continuing another tradition of the “Old Vulcan.” My thanks to Theresa Engler, DFI’s Executive Director, who helped make this a reality.
Mating Pipe Piles to Pipe Pile Caps
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.
Some other information is shown below.
Pulling Adapters for Vulcan Extractors
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 Heppenstall tongs, which were similar to the clamp used by the Nilens extractor.
- The Wood Pile Puller.
New Version of TAMWAVE Online Wave Equation Program Now Available
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:
- TAMWAVE: Pile Toe Resistance, and Some More on Pile Shaft Resistance
- TAMWAVE 1: Entering Basic Soil and Pile Properties
- TAMWAVE 2: Modifying the Soil Properties
- TAMWAVE 3: Basic Results of Pile Capacity Analysis
- TAMWAVE 4: Shaft Resistance Profile, ALP and CLM2
- TAMWAVE 5: Wave Equation Analysis, Overview and Initial Entry
- TAMWAVE 6: Results of Wave Equation Analysis
- TAMWAVE 7: Analysis for a…
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TAMWAVE 7: Analysis for a Cohesive Soil
With the analysis of the concrete pile in cohesionless soils complete, we turn to an example in cohesive soils.
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…
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TAMWAVE 6: Results of Wave Equation Analysis
With the data entered for the wave equation analysis, we can now see the results. There’s a lot of tabular data here but you need to read the notes between it to understand what the program is putting out. If you are not familiar at all with the wave equation for piles, you need to review this as well.
Time Step, msec | 0.04024 |
Pile Weight, lbs. | 15,000 |
Pile Stiffness, lb/ft | 600,000 |
Pile Impedance, lb-sec/ft | 57,937.5 |
L/c, msec | 8.04688 |
Pile Toe Element Number | 102 |
Length of Pile Segments, ft. | 1 |
Hammer Manufacturer and Size | VULCAN O16 |
Hammer Rated Striking Energy, ft-lbs | 48750 |
Hammer Efficiency, percent | 67 |
Length of Hammer Cushion Stack, in. | 16.5 |
Soil Resistance to Driving (SRD) for detailed results only, kips | 572.7 |
Percent at Toe | 35.39 |
Toe Quake, in. | 0.220 |
Toe Damping, sec/ft | 0.07 |
For those familiar with the…
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TAMWAVE 5: Wave Equation Analysis, Overview and Initial Entry
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…
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TAMWAVE 4: Shaft Resistance Profile, ALP and CLM2
With the basic parameters established, we can turn to the static analysis of the pile, both axial and lateral.
Shaft Resistance Profile
Depth at Centre of Layer, feet | Soil Shear Modulus, ksf | Beta | Quake,inches | Maximum Load Transfer, ksf | Spring Constant for Wall Shear, ksf/in | Smith-Type Damping Constant, sec/ft | Maximum Load Transfer During Driving (SRD), ksf |
0.50 | 48.4 | 0.163 | 0.0022 | 0.009 | 4.03 | 45.394 | 0.009 |
1.50 | 83.9 | 0.163 | 0.0038 | 0.027 | 6.99 | 19.911 | 0.027 |
2.50 | 108.3 | 0.163 | 0.0050 | 0.045 | 9.02 | 13.572 | 0.045 |
3.50 | 128.1 | 0.163 | 0.0059 | 0.063 | 10.68 | 10.543 | 0.063 |
4.50 | 145.3 | 0.163 | 0.0067 | 0.081 | 12.11 | 8.730 | 0.081 |
5.50 | 160.6 | 0.164 | 0.0074 | 0.098 | 13.38 | 7.509 | 0.098 |
6.50 | 174.6 | 0.164 | 0.0080 | 0.116 | 14.55 | 6.623 | 0.116 |
7.50 | 187.6 | 0.164 | 0.0086 | 0.134 | 15.63 | 5.948 | 0.134 |
8.50 | 199.7 | 0.164 | 0.0091 | 0.152 | 16.64 | 5.414 | 0.152 |
9.50 | 211.1 | 0.164 | 0.0097 | 0.170 | 17.59 | 4.980 | 0.170 |
10.50 | 222.0 | 0.164 | 0.0102 | 0.188 | 18.50 | 4.618 | 0.188 |
11.50 | 232.3 | 0.164 |
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TAMWAVE 3: Basic Results of Pile Capacity Analysis
With the soil properties and lateral loads finalised, we can proceed to look at the program’s static results. These are shown below. We will concentrate on cohesionless soils in this post; a sample case with cohesive results will come later.
Pile Data | |
Pile Designation | 12 In. Square |
Pile Material | Concrete |
Penetration of Pile into the Soil, ft. | 100 |
Basic “diameter” or size of the pile, ft. | 1 |
Cross-sectional Area of the Pile, ft^{2} | 1.000 |
Pile Toe Area, ft^{2} | 1.000 |
Perimeter of the Pile, ft. | 4.000 |
Soil Data | |
Type of Soil | SW |
Specific Gravity of Solids | 2.65 |
Void Ratio | 0.51 |
Dry Unit Weight, pcf | 109.5 |
Saturated Unit Weight, pcf | 130.5 |
Soil Internal Friction Angle phi, degrees | 32 |
Cohesion c, psf | |
SPT N_{60}, blows/foot | 20 |
CPT q_{c}, psf | 211,600 |
Distance of Water Table from Soil Surface, ft. | 50 |
Penetration of Pile into Water Table, ft. | 50 |
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