Posted in Soil Mechanics

Breaking Down Sieve Data for both Lab and Textbook Problems

One of the core things students learn in a basic Soil Mechanics course is how to analyze and chart the results of sieve tests on soils.  Texts such as Soils and Foundations Reference Manual and Verruijt, A., and van Bars, S. (2007). Soil Mechanics. VSSD, Delft, the Netherlands. usually present the concept but don’t always give a detailed explanation of how these things are actually analyzed.  The example below is from Materials Testing and is based on the use of their forms DD-1206 and DD-1207, which of course we furnish as well.

Let’s consider this example, presented below:

5-849-Figure-2-39

This is a sample sieve analysis result.  For the lab (especially when sample washing is involved) it can get this complex, and the procedure is described in Materials Testing.  To look at this more schematically (and this is common for most “textbook” problems) the following simplifications are done:

  1. There are no losses in the process of sieve analysis.  This is obviously unrealistic but these should be kept to a minimum.  For textbook type problems this means that Blocks 8 and 23 are the same.
  2. The tare (sieve or pan) weight is removed from consideration.  This means that typically Column 15 is the first column in the problem, given the soil weights retained on each sieve.  The weight that “hits the pan” is in Block 22.
  3. Washing losses and errors are not considered, which means that Blocks 21 and 24 are set to zero.

With these out of the way, we can proceed to the analysis.  The top sieve in the stack (the 2″ sieve) retained no soil (it doesn’t always happen this way) so it has zero soil retained and all passing.  The next sieve (the 1 1/2″ sieve) retained 83.7 g (Column 15.)  For the cumulative weight retained (Column 16) we add the value of Column 15 just above it to this one, thus 0 + 83.7 = 83.7 g.  The next sieve (the 3/4″ sieve) retained 161 g, so for the cumulative weight retained for this sieve we add in the same way, thus 83.7 + 161 = 244.7 g.  We keep going in the same way “down the stack” until we have all of the cumulative weights retained for each sieve computed.

This is terrific, but what we really need is the percentages of the total sample each cumulative retained value represents.  This is what goes in Column 17.  These values are obtained by dividing each result in Column 16 by the total sample weight in Block 23 and multiplying them by 100 to obtain a percentage.  In this way, the cumulative percent retained for the 2″ sieve is obviously zero, for the 1 1/2″ sieve 83.7/4381.4 x 100 = 1.9%, for the 3/4″ sieve 244.7/4381.4 x 100 = 3.7%, and so on.

We can also compute the percent passing.  An easy way to do this is to start by noting that 100% passes the whole sieve stack.  We can than successively subtract the cumulative retained percentage as we go down.  Thus the percentage of the 2″ sieve is again obviously 100 – 0 = 100%, for the 1 1/2″ sieve 100-1.9 = 98.1%, for the 3/4″ sieve 98.1-3.7 = 94.4% (note that we use the percentage passing from the previous sieve each time) and so on.

We then plot the results on the sieve curve as follows:

5-849-Figure-2-42

It’s a temptation these days to use a spreadsheet and its semi-logarithmic plotting features.  I would avoid this: using a dedicated form like this has two advantages:

  1. It lines up the grain sizes and sieve designations for you.
  2. It can be plotted either from the percent passing size (left) or percent retained side (right.)

It’s also possible to use a tool such as the Spears Lab Spreadsheet, but this takes a lot of practice and is a little tricky to use, especially for “textbook” type problems where the tare is not considered.  It’s easy to get a really stupid looking result; I have seen quite a few over the years.

Posted in Pile Driving Equipment, STADYN

STADYN Project: Some GRLWEAP Screen Shots from the Original Project

While looking through some files, I found these from the original STADYN project, from the comparison case with GRLWEAP.  I’m passing these along to give you an idea of the graphical output of this program.  My thanks to Jonathan Tremmier of Pile Hammer Equipment for allowing me to use this copy of GRLWEAP.

Screenshot 2015-10-19 11.18.08
This is the “main screen” of GRLWEAP, giving a schematic view of the hammer/pile/soil system and allowing for input of parameters.
Screenshot 2015-10-19 11.18.32
This is the “bearing graph” output of the program, also giving a graphical representation of the system.
Screenshot 2015-10-19 11.19.06
This is the force-time and impedance*velocity-time trace for the pile head. Comparing the two is an important element when this data is gathered in the field.

 

Posted in Academic Issues

University of Tennessee at Chattanooga-Lee University Articulation Agreement

It finally happened:

This ceremony took place last month at UTC.  I was the “matchmaker” for the agreement; after UTC signed a similar agreement with Covenant College, I thought “why not Lee?”  Being well embedded and known in the Church of God (and my wife a Lee graduate,) I reached out to Dr. Debbie Murray, Lee’s Vice President for Academic Affairs.  Her response and that of from Dr. Paul Conn, Lee’s President, was positive. Then I approached UTC’s Dean of the College of Engineering and Computer Science, Dr. Daniel Pack, and he was receptive.  The rest, as they say, is history.

An articulation agreement like this specifies that the students spends three years at Lee and two at UTC, obtaining an engineering degree at the end.  Making this available is a step forward for both institutions.  Additionally Lee students won’t have to make a major move (if any) to complete their degree, since the two institutions are about 30 miles apart.

This has been one of the most gratifying things I have been involved with both in my years in the Church of God and at UTC.

I have had deep reservations about the frequently uncritical way data is used to “advance” science, and now I see I’m not the only one.  I think our better way is to develop our understanding of the phenomena around us and use that for predictive methods rather than just extrapolating data, with all of the biases and inherent danger in extrapolation of any kind that follows.

Some people seem to think that if you have a problem or an issue, all you need to do is to collect enough information about it, and that will tell you the answer. Robert McNamara has provided a stark counter-example. As well as being the Secretary of Defence during the Cuban missile crisis and president […]

via Collecting the wrong information — The Logical Place

Collecting the wrong information — The Logical Place

Posted in Academic Issues

Keep Going Against the Obstacles

In my teaching at UTC, one of the people I’d see in the hallway was Chris Land.  He’d always speak to me and I to him.  This past weekend he walked for his Mechanical Engineering degree:

He’s one of those people who makes teaching worthwhile, even in the midst of its frustrations.  He helps to keep us going.