In our newest SCS Advice from the Field, Ali Khatami makes his case for the landfill chevron pattern…
For at least the past 50 years, our industry has referred to the design pattern for the bottom of landfill cells as herringbone. But, it’s time to break the long-standing herringbone reign and give credit to the true holder of the crown: the chevron pattern. A chevron pattern visualizes the actual geometry used by landfill designers over the decades.
The schematic views of both patterns are shown below:
Now, here’s a sketch of a landfill single-cell design:
Note the cell base area with elevation contours that resemble the chevron pattern, with the leachate collection pipe located along the centerline of the cell. The cell base area is sloping toward the leachate collection pipe to convey landfill leachate at the base to the pipe, then the pipe conveys the leachate to the leachate sump located at the low end of the pipe. The pattern at the base can easily be duplicated in either direction of the cell area, developing a multi-cell design resembling the chevron pattern shown above.
In this case, the straight lines connect the low points (representing leachate collection pipes) and the high points (representing the divider berms separating adjacent cells). The zig-zag lines in the pattern remind landfill engineers of the elevation contours for the landfill bottom design geometry.
Meanwhile, with the herringbone pattern, the adjacent “tiles” or rectangular shapes are in a perpendicular position to each other and do not resemble the zig-zag lines in the chevron pattern. The herringbone pattern cannot be representative of the elevation contours, leachate collection pipes, and the boundary lines between adjacent cells like the chevron pattern. Additionally, the angle of line segments in the zig-zag in the chevron pattern can vary to any desirable value, which allows representation of changes to the disposal cell base slope (an important parameter in landfill design). On the contrary, the tile position in the herringbone pattern has to maintain perpendicular angles throughout and therefore it loses the ability to represent various base slopes.
One may draw lines along interface boundaries of the herringbone features and come up with the chevron pattern. But why stretch the truth when the chevron is already clearly the pattern? It is not apparent how or why the herringbone association took hold in the first place, but it’s about time that changed.
Admittedly, it took nearly four years to scientifically support the validity of the Special Relativity Theory from the time it was published by Albert Einstein in 1916. And it took nearly 50 years to physically detect the existence of Higgs boson particle from the time it was theorized by Peter Higgs in 1964. So, I suppose we can wait for formal recognition of chevron designation for landfill design.
Why such a big deal!?
The chevron validation may be insignificant compared to the scientific validations of Einstein’s and Higgs’ work. For landfill engineers, attune to details, it could be considered big because anything new, and more accurate in the landfill design field is a cheering matter!
Throughout the history of science, new findings supported by scientific evidence have replaced prior theories or concepts when progress is desired. Change of the pattern association, in this case, may not qualify as a scientific finding; however, it is a clear and noteworthy correction to what landfill engineers have been using over the past many years.
About the Author:
Ali Khatami, Ph.D., PE, LEP, CGC, is a Project Director and a Vice President of SCS Engineers. He is also our National Expert for Landfill Design, Construction Quality Assurance, and Elevated Temperature Landfills. He has over 40 years of research and professional experience in mechanical, structural, and civil engineering.