Down to Earth

In 2009 Baziw Consulting Engineers, Ltd. entered into a strategic alliance with VMS. Through this alliance BCE can focus their attention on product development and training of their clients in the use of that equipment, while VMS provides marketing and sales support. As part of that effort I want to introduce SC3-DAC Pro .

SC3-DAC Pro is a Windows® program that facilitates the data acquisition of triaxial Seismic Cone (SC) time series data, and provides the user with automatic real-time preliminary interval SH-wave velocities estimates and Vertical Seismic Profile (VSP) displays. The data can then be analyzed in more detail using the SC3-RAV seismic data analysis software.

The development and release of SC3-DAC Pro fits BCE’s mission of providing our clients with state-of-the-art seismic data acquisition and analysis systems that allow better and faster diagnostics of the sub-surface. In the first release of SC3-DAC Pro preliminary estimates of right and left side SH-wave interval velocities are generated automatically during a Seismic Cone Penetration Test (SCPT). Future releases of this software will also provide the user with automatic estimates of the absorption values (QS and QP), interval P-wave velocities, and the interval low-strain elastic constant.

SC3-DAC Pro includes the following features:
�� Configurable for either geophones or accelerometers.
�� Configurable for either contact Switch or Sensor Triggers.
�� Suitable for P-Wave and S-wave.
�� Option for a time delay in collecting data.
�� Maximized data sampling rate.
�� Option for Data Stacking.
�� Bandpass, high pass, low pass, and notch digital filters.
�� Automatic full waveform SH-wave interval velocity estimates.
�� Displays of peak particle accelerations, velocities, and displacements.
�� VSPs with trend line estimation.

Please visit the BCE website for more information on this product or contact us by e-mail for more information (info@bcengineers.com)

There are certain concepts that seem so obvious that you often don’t realize how recently they were first formulated. PDCA or “Plan, Do, Check, Act” is one of those concepts. First proposed by Edwards Deming in the 1950’s, it describes the continuous cycle of planning your work, then executing that plan, followed by checking whether everything is proceeding in accordance with the plan, and finally taking corrective actions to improve the execution. This concept applies to any business, including pile driving, and pile driving simulation is the perfect tool to implement this. In this article the advantages of these simulations will be highlighted, hopefully leading to a more widespread use of this technique prior to actually driving the piles, because unfortunately there are still too many instances where pile driving simulation is viewed as a tool only suitable to analyze problems after the fact.

Pile driving simulation programs have been around since 1960, but the application didn’t become widespread until after the introduction of PCs. From then on engineers could perform driveability studies from behind their desks, which allowed them not only to predict whether the pile could be driven to a certain depth with a particular hammer, but also to optimize the pile driving process (by selecting the most appropriate hammer/pile combination). Obviously, the accuracy of these studies is directly (and predominantly) dependent on the accuracy of the soil investigation data and the soil models available in the simulation programs used to process these data. While a more elaborate model may make the data entry more cumbersome, the use of a very basic soil model may not accurately predict the outcome (as some engineers have experienced the hard way). But with good soil data and a detailed soil model these simulations can provide the user with realistic assessment of any pile driving project.

Such a piledriving simulation should therefore always be used to plan the actual work (the “P” in PDCA), eliminating the practice of basing a pile driving set-up on intuition, which is generally justified by pointing out that based on experience the chances that something will go wrong are minimal and that therefore there is no reason to incur the additional cost associated with a simulation. It is true that with local experience a workable set-up can be established for most cases, but the problem with this approach is that the set-up may not be optimal and therefore more costly. But a simulation can also be seen as an insurance policy to virtually eliminate the chances that a pile cannot be driven to the required depth. And the premium for that insurance (i.e. the cost of performing a simulation) is very reasonable given the potential expenditures associated with resolving a problem situation.

The next step in the cycle is “D”: doing the work. Let's assume that a contractor begins work on site without having access to the simulation data. In many respects this is similar to going on a trip without a map: you know your starting point and your destination, but you have no idea what to expect in between. Just as a map is a good idea for a trip, having access to a graph showing the expected blow count (in case of impact hammers) or penetration speed (in case of vibro hammers) as a function of the depth is a good idea when driving piles, because only then will you be able to determine whether the work is progressing according to plan, which brings us to the next step in the cycle.

This next step is “C”: checking the actual progress against the planned progress. As long as everything is basically going according to plan, the simulation is of limited value at the job site. It is when things are not going as planned when the simulation becomes an essential tool. As an example, the design engineer may have assumed that a pipe pile will plug as it is driven to the target depth, but actual pile driving results may indicate that this is not the case (as the pile is driven into the ground more easily than predicted), which would obviously affect the bearing capacity of the pile. It is essential that issues like these are identified before the pile foundation is finalized to allow for corrective action(s) if necessary. But without a pile driving simulation these issues cannot be identified, which means that not only the “C” step in the cycle is eliminated, but also the final “A” step.

After the differences between the predicted results and the actual results have been identified, it is important that these differences are carefully reviewed to determine their actual cause and whether any corrective action is appropriate (the “A” step). Too often this is when a simulation is done for the first time: only when it was impossible to drive the piles to the target depth the process was simulated to determine the actual cause of the problem. But when used to analyze the differences between the predicted and the actual results, pile driving simulation programs can provide valuable insight regarding the site conditions, especially when several alternatives are simulated (e.g. in case of a pipe pile with and without a plug). This enhanced insight can then be used to assess whether corrective actions are appropriate.

In conclusion, simulating pile driving is a valuable tool to determine in advance whether the pile driving can be done successfully and whether it can be done more economically. It also provides a clear road map to avoid any surprises during project execution (you will know how long it will take to drive a pile), and finally it may provide some insight in case the actual progress is not as predicted. Hopefully these reasons are enough to convince everybody involved with pile driving that driving piles without simulation (using a program like Profound’s PDPWAVE) and without the results readily available on the job site is simply not a good business practice.

I was recently asked whether there is such a thing as the perfect in-situ soil test, probably in response to a presentation that I had given a few weeks earlier, in which I enthusiastically described the advantages of CPT. The answer is obviously no: there is no single test that provides the most reliable information on the various soil parameters for all soil types. Having said that, CPT is generally speaking a very appropriate testing method in soils other than rock and gravel, providing good data on a very wide range of soil parameters. As such it is clearly the most versatile in situ soil test available. What is even more important, especially here in North America, is that CPT provides information on more soil parameters than SPT in all soil conditions other than gravel. Moreover, for those soil parameters that can be derived from both the SPT and the CPT results, CPT provides generally more accurate results and the results are available within minutes after the test was done (before the test equipment leaves the test site). In other words, CPT is a very useful test to provide an all-around characterization of the soil in a very short period of time. Not perfect, but in my opinion by far the best in the class of in-situ soil tests.

In recent weeks we have spent a lot of time emphasizing the use of generic language in specifications. Far too often we see specifications where the author(s) seem(s) to have been at a loss trying to describe the functional requirements of a piece of equipment or a test. The easy way out in those cases is to mandate the use of a particular piece of equipment by including a brand name in a specification. The problem with that approach is that in doing so the author(s) in effect creates a monopoly or at the very least express(es) a clear preference for that particular piece of equipment. Especially for specifications issued by government entities this is not appropriate and quite often even illegal, but above all completely unnecessary. In most cases there is a specification out there that describes the function of that particular piece of equipment or that test (ASTM international has published close to 12,000 standards) and a simple statement that equipment or a test in accordance with a certain ASTM standard must be used quite often will resolve the issue.

When it comes to foundation testing the same applies. ASTM D4945 (Standard Test Method for High-Strain Dynamic Testing of Piles), ASTM D1143 (Standard Test Methods for Deep Foundations Under Static Axial Compressive Load), and ASTM D7383 (Standard Test Methods for Axial Compressive Force Pulse (Rapid) Testing of Deep Foundations) are just a few examples of detailed functional specifications that are reviewed (and, if necessary, revised) on a regular basis to keep them up to date.

So authors of specifications for foundation testing wishing to fairly describe a CAPWAP or a Statnamic test using generic wording should just refer to the appropriate ASTM specification (ASTM D4945 and ASTM D7383 respectively). Contractors will then have the freedom to use any brand of equipment which meets those ASTM standards.

Let's assume that you want to see a doctor to get a diagnosis for a potential medical problem. When you make the appointment you get told that the doctor won't be able to see you (as a matter of fact, he is not even close to where you are), but instead a nurse will see you and run some tests on you. She will then forward the test results to the doctor and that doctor will then determine what treatment, if any, you need. I fully expect that you would not accept something like that, but you may be wondering why I am mentioning this.

The reason is that it is similar to a practice that is strongly promoted by some in the geotechnical industry: take the measurements during a Dynamic Load Test, send them to somebody who has never been on the job site, and that person will determine the capacity of the pile. To me that makes about as much sense as the example I mentioned at the beginning of this message. The outcome of a Dynamic Load Test determines whether a pile can be accepted as is, but in order to properly analyze the data you need to be fully aware of the local conditions, and that is impossible if it is done by somebody who has never set foot on the job site.

I'm sure that some of you disagree with the above and I look forward to hearing from you. Hopefully your response will address the need for awareness of local site conditions during a load test and how somebody far away could possibly have this knowledge, because that is really what this issue is all about.