When you hear this phrase, perhaps your thoughts go immediately to the 1920’s song, or the 1950’s movie that popularized that song.
Either way, this phrase would not conjure up images of working on a compacted clay liner—rain and earthwork generally do not mix very well. So, allow me to open up your mind and take you through another performance that is sure to captivate your mind!
Several years ago, I was doing compacted clay liner CQA within a few miles of a site my friend was working on. My friend, with about 5 years of CQA experience, knew I was rained out and told me to stop by. Given we were in the midst of a heavy rain forecast to last the rest of the day, I thought we were going to get together and go to lunch. The windshield wipers could hardly keep up with the rain as I approached his worksite. My eyes nearly popped out of my head as I struggled to peer through the windshield!
There before me was all of the construction equipment—not parked as you would expect, but running as if this was the perfect weather for earthwork construction. There were the scrapers, tires spinning frantically trying to forge their way over the near frictionless surface to place yet another lift; dozers grading the lift of clay when not called elsewhere to help a hapless scraper; and the rubber-tired padsfoot compactor churning through the material like a roto-tiller, being driven by my CQA buddy! Memory doesn’t serve me well as I cannot remember if the water truck was making passes, but I would not be surprised if it had been! I didn’t venture too close to the area, afraid my non four-wheel drive work truck would get stuck or something would inadvertently run me over!
Eventually my buddy dismounted the compactor and came over to talk to me. He asks me: “Have you ever seen anything like this in your life?” I don’t even know how long it took me to respond, but I am dead certain my answer was simple—“No”! Then I began to talk to my buddy about the project and things that were going on, trying to understand the logic for why they were working so feverishly in the rain.
As it turns out, the moisture requirement for the soil was hard to obtain. Even on sunny days with little wind, moisture seemingly could not be applied fast enough to meet the moisture requirement, which fell within what you would normally expect to see for soils like that. (I was working with similar soils only a few miles away.) The contractor was simply paying huge expenses in hauling water to the material during construction, so now was enjoying the benefit of Mother Nature providing free moisture.
When asked my opinion, I shared that the soils looked way too wet. But even under these conditions, the technician was having a difficult time getting the test to meet the minimum moisture requirement according to the nuclear density gauge.
The first thing we talked about was not the soil conditions, but why my buddy was running the compactor in the first place. If I was the business owner, I don’t think there would be any answer that would suffice, but it basically boiled down to wanting to keep the client/contractor happy.
My next suggestion was checking the gauge he was using against my gauge. We were not willing to do this in the heavy rain. However, when we did check the gauge, we found out the moisture was off significantly and was reading way too low and required a significant correction to be entered into the gauge. So, why would this technicians’ gauge require a moisture requirement and the one I was using would not? Good question!
You see, the gauge I was using already had a moisture correction in it, as well as a density correction. Although the soils in this area sometimes warrant a minor correction for the gauge in either moisture or density, this was far beyond the norm—never in my life had I considered it would take a thunderstorm to provide the required moisture.
Back at my site a few weeks prior, I first suspected there was a problem with the gauge I was using: the compactor would not obtain the required soil densities, even when it was walking completely on top of the soil—a ‘dozer could stand up on it’s blade when cutting the soil and still my density would fail! I immediately compared the soil proctor I was using with those previously used, and they were very consistent, as were the soil descriptions and classifications. To me, this ruled out an error in the soils lab, or a significant change in soil type.
The office was dumbfounded as to what the problem could be. Even using basic gauge correction factors we used on other site projects and soils, the soil would still not meet the density requirement. Another gauge was brought out for side-by-side comparisons, and yielded similar, but not identical results—although no test would pass with the second gauge either. My immediate suggestion was to run sand cone and microwave moisture tests for a relatively quick assessment of the gauges. The sand cone comparison suggested the gauges were off by over 15 PCF on density, and about one-third of that on moisture. So, why did we never have this problem before? Anyone want to venture any guesses?
The answer was not so obvious at first. As it turns out, the company I was working for decided to invest in a portable calibration system for the gauges instead of sending them out every year for calibration. The person who ran the calibrations was downright offended that I even suggested this was the source of the problem; however, sending one gauge off for calibration quickly showed the rest were off when performing side-by-side testing upon it’s return.
The script of this story may not be as nomination worthy as the musical version of Singin’ In The Rain but to an industry insider it may parallel the level of comedy while providing a serious lesson. Who was a fault here? Is it the CQA technician for not recognizing a serious problem existed in the field? Perhaps it is the experienced contractor who should have demanded an explanation? The facility owner for not recognizing there is a problem? The CQA project manager who received phone calls daily from the field technician describing the outrageous amount of water being added to the soil? The junior engineer who calibrated the gauges?
What thoughts do you have?
UPDATE: I received this response from a reader. I thought it was quite good and that I would post it to further the discussion. Thank you, Chris!
I enjoyed this story especially. We had a similar situation in the not too distant past. For that job, the Contractor was required to hire their own soils testing firm to test for embankment compaction and we would only review their results and do a sandcone correlation every ten NG tests.
For two weeks the Contractor worked and reworked the same 6” lift, as the testing firm was reporting that the moisture was too high in the soil, causing the density to be just under passing, all the while compactor cleats and dozer blades showed that the material appeared as hard as a rock, similar to your story. The Contractor was very irate and morale on the site was low.
Meanwhile, we had not only been doing sandcone correlations on every tenth test, but on every test we could within a reasonable amount of time with the equipment we had. As our data set expanded, it became clear that the soils testing firm’s gauge was very consistently reading the moisture 4% higher than our own oven contents, and the compaction results of our sandcones were passing. When the moisture offset was applied to past and future NG results, we found them all to be passing, and the job was able to move forward.
The real clincher in this story for me was that one of the two soils firm technicians did not even know what the sandcone apparatus was and asked me what I was doing when I started placing my plate and digging my sample in his previous test location. Thousands of dollars in wasted man and machine hours demonstrated how important correlation and calibration testing can be.
Chris Thiel
CQA Technician
Thiel Engineering
