Posted in Geotechnical Engineering

Retaining Wall Collapse on I-295 Project in Bellmawr, New Jersey

An MSE Retaining Wall suffered a dramatic failure last week closing the right northbound lanes of I-295 indefinitely. The wall is part of the Direct Connection Project to reduce congestion on I-295/I-76/Route 42 in Bellmawr, […]

Retaining Wall Collapse on I-295 Project in Bellmawr, New Jersey
Posted in Deep Foundations, Geotechnical Engineering, Pile Driving Equipment

Reconstructing a Soviet-Era Plastic Model to Predict Vibratory Pile Driving Performance — vulcanhammer.info

The latest in our series of monographs on vibratory pile drivers, this one takes us back to the beginnings of vibratory pile driving in the Soviet Union. It was prepared for the ReSEARCH Dialogues at the University of Tennessee at Chattanooga in April 2021. The vibratory driver that started it all: the Soviet BT-5, used […]

Reconstructing a Soviet-Era Plastic Model to Predict Vibratory Pile Driving Performance — vulcanhammer.info
Posted in Academic Issues, Civil Engineering, Geotechnical Engineering

My Review for the FE Exam Civil/Geotechnical Section

Over the years, my department has asked me to give a review session for my students before they take the FE exam. In this time of COVID, I’ve committed all my other lectures to video, and this one is now no exception:

I mention a few of things in the intro I’d like to elaborate on:

  • About ten years ago, it was brought to my attention that my students weren’t doing well on the FE Exam geotechnical section. My response to that was simple: “I’ll fix that problem.” I did that by aligning what I taught in class with what was in the FE “cheat sheet” (I’m sure NCEES loves that designation.) I don’t subscribe to the idea that we should only be “teaching to the test” but the FE exam’s geotechnical requirements are pretty basic, so that wasn’t much of a conflict. What has been tricky is that they’ve shifted around what they require over the years. But my students’ performance on the test has improved.
  • Since COVID I’ve put my lectures online. If you need to investigate some topics in detail, I’ve got them either at my Soil Mechanics or Foundations pages.
  • Once you’ve digested what’s presented in the video, you can and should solve sample problems. I just don’t recommend that you start your preparation doing that.
Posted in Uncategorized

In Memoriam: GZA Founder Donald T. Goldberg — GeoPrac.net

His contributions and legacy are reflected in the values of the company he built and the leadership he provided to the industry he loved. President and CEO Patrick Sheehan reflects on Don’s legacy. “It would be […]

In Memoriam: GZA Founder Donald T. Goldberg — GeoPrac.net

Since 2004 this site has hosted Goldberg’s classic document Lateral Support Systems and Underpinning.

Posted in Academic Issues, Soil Mechanics

The “Line of Optimums” Approach for Compaction

There are some things in geotechnical engineering that don’t get really good (if any) coverage in many textbooks, which means that those who go on into that part of civil engineering are blindsided by their appearance. One of these is the “line of optimums” approach for compaction evaluation. The only formal textbook I know of that covers it is Soils in Construction, for which I must credit my co-author, Lee Schroeder. It also appears in the Soils and Foundations Reference Manual.

The line of optimums approach seeks to answer a key question in compaction: how much compactive energy is necessary to effect a given compaction? We have the Standard Proctor and the Modified Proctor test, but when we’re trying to determine a specific compactive effort for a particular soil and project, we need more flexibility.

I discuss this in my class video for Soil Mechanics: Compaction and Soil Improvement, but let’s consider an example, in this case from Rebrik (1966).

Compaction Chart with Multiple Compactive Energies and Line of Optimums, from Rebrik (1966)

Lines 1, 2, 3 and 4 represent compaction curves for a soil, but with a different number of blows (25, 50, 100 and 150, as shown in the chart.) The energy variation is explained in my video. In any case with the increase in compactive energy is a closer packing of the soil particles. The peak dry density/unit weight also increases with compactive energy, although the water content decreases (which makes sense as the void ratio decreases with greater compaction.) Line 6 through the peaks in the compaction curve is referred to as the “line of optimums.” Once we establish this line we can make a determination of the compactive effort we will need based on the result we are looking for, taking into consideration the degree of relative compaction we are prepared to allow for.

Line 5 is the zero air voids curve.

The line of optimums method is a good one for compaction evaluation, and we hope that this little presentation helps you to understand it.

Reference

  • Rebrik, B.M (1966) Vibrotekhnika v burenii (Vibro-technology for Drilling.) Moscow, Russia: Nedra.