In 1983, when I started to teach experimental soil mechanics to the undergraduate students in civil engineering at the University of Southern California, I thought that laboratory soil testing was well covered by textbooks. However, I stumbled on three unexpected but major problems when I attempted to select a textbook for my course: the reliance on standardized testing procedures, outdated data processing, and the absence of typical test results.
In reference to the first problem, most recent textbooks describe soil testing as a set of standardized procedures with little reference to the theories prompting these tests. They are useful for training laboratory technicians in testing companies but are less informative to student engineers. Any standardized testing procedure is not engraved in stone—it only provides guidelines which, when followed carefully, guarantee the quality and repeatability of test results. As an educator I feel strongly that standardized tests should not eclipse the principles that motivated the tests.
In reference to the problem of outdated data processing, the textbooks on soil testing that I examined were filled with complicated and numerous data sheets. They required students to write down their measurements and calculate results with hand calculators and archaic monographs, such as for the hydrometer test. In this age of personal computers, such tedious data reduction is as outdated as slide rules. To update the data processing I wrote two generations of BASIC programs for personal computers. The first generation produced poor graphics and barely improved the hand calculator results. The second generation had advanced graphic and input/output features but had to be sealed hermetically because it was too complicated. Both versions crated many difficulties in entering data and unnecessarily confused soil testing, I found myself asking more fundamental questions. Does the Computer improve or hinder students’ understanding? Do students benefit from a program they do not understand?
These concerns motivated the use of spreadsheet programs that have an open calculation structure (c.g., Lotus 123, Quatiro Pro, and Microsoft Excel). Initially, spreadsheets were intended for business purposes, but now they have mathematical functions and programmable custom functions that make them suitable for engineering. They can reduce experimental data, plot graphs, and print reports. The spreadsheet approach eased my apprehensions about using computers in teaching experimental techniques. In fact, spreadsheets enhanced the ways my students understood physical phenomena and processed their measurements. For instance, by using Stokes’ and buoyancy laws directly, instead of applying esoteric monographs they better understood the principles and limitations of hydrometer analysis. With spreadsheets. I was therefore capable of addressing two of the problems found in textbooks on soil testing: the advanced data processing techniques actually helped to emphasize the principles of soil mechanics. My students also benefited in other ways, enhancing their communication and presentation skills, and producing well-organized laboratory reports.
The third problem with existing textbooks is that there has been no way for students to know if they have performed the test correctly. In the professional world, we look to published experimental results constantly. If our results deviate significantly from normal results. We must either corred our own errors or explain the discrepancy. To establish normal test results for comparison, I have compiled typical results on soil properties from various sources and included a few useful empirical correlations between soil properties. Empirical correlations are often discredited from the scientific point of view due to their lack of physical and rational explanations; however. Some correlations are useful in the laboratory to check approximate agreement between different soil properties. With typical results and empirical correlations my students have a basic knowledge of values for soil properties and some points of reference for discussing the validity of their experimental results
Since 1983, my students have been using the spreadsheets programs com- paring their test results and gaining a thorough understanding of the theories behind the tests In effect, they have learned much more than basic standardized testing procedures. I hope that Experimental Soil Mechanics will benefit other teachers and students in geotechnical engineering.
1. Grain Size Distribution
2. Plasticity, Shrinkage, and Soil Classification
3. Density and Compaction
4. Permeability and Seepage
5. Stress – Strain – Strength Properties
7. Shear Strength
8. Elements of Experimental Techniques
9. Data Processing with Spreadsheets
Appendix: Conversion factors