Consider a situation that we laid two different soils as a foundation of a road (as a base courses). Both of them pass the initial criteria (for example the same compaction) and based on the employed tests, they expected to have the same performance over time. But, it turned out that after subjecting to traffic loading, one of them deteriorates more rapidly. So this fact makes me get the impression that something, like a chemical reaction between the solid and fluid phase of the soil, may produce this change in performance.
Dear Ebrahim Sangsefidi
Soil physical, chemical and to some extent biological properties are inter-linked. It will be correct even to say that interactions among two properties definitely can alter the third one. So it is yet a matter of investigation to assess what chemical reactions could affect the soil strength and vice versa.
Dear Mr. Sangsefidi,
to avoid any misguidance of the discussion I would like to put something right. Constructing roads or other installations belonging to the infrastructure of a society fall outside the field of pedology or soil science. It is part of rock mechanics and engineering geology.
A road built from unbound rock fragments or aggregates making up the subbase of it does not find its foundation in the A-, B, or C horizons of a soil type but in solid rocks or what you might call the D or E horizons which mark the transition zone into the unaltered bedrock. Nobody will spread loose aggregates across the topsoil and stabilize them with asphalt or concrete. Even if you stabilize the uppermost part of the surface with lime or concrete, you normally use a scraper or caterpillar to get as close as possible to a rock providing you with a base-course to withstand lorries and limousines running on the top of it safely.
There may be traffic in the desert or in the steppe leaving tracks behind or causing jeepable roads to form after a certain period of time, but this is not road construction on purpose and design. The vehicles happened to cross the surface here and there. I know it by myself , as I was working in the Central Asian Interior.
Sorry to say your question is based upon a wrong assumption. I think it might be helpful for you to get the discussion back on track as early as possible, before it is spiraling out of reality.
Best regards
H.G.Dill
Ebrahim
Design of roads is not part of rock mechanics or engineering geology. It is part of engineering and falls in the geotechnical and the highways or highway materials fields. The black top, base and sub-base generally fall in the highway marerials field while the road foundation falls in the geotechnical field. Road sub-basaes hardly ever lie on rock and are usually on soils of not very good engineering properties.
The performance of the base course depends on a wide range of factors including the performance of the sub-base and the foundation (ie, the ground or layers below the sub-base and extending down to 1m below the black top for heavy duty roads). Chemical reactions within crushed rock can take place, such as "thaumasite" formation, but it is more likely that the cause of the performance variation lies in the mechanical properties of the base, sub-base and foundation for the two roads.
Did you do static or dynamic tests or both? Possibly they behave (nearly) the same in static tests but show different behavior in dynamic loading.
What kind of soils did you use for the road?
Dear Christain,
I mainly focus on the Dynamic tests, but I did not understand which parameters do you compare that you said: "Possibly they behave (nearly) the same in static tests but show different behavior in dynamic loading".
The soil that I am going to use is granular soil. for example, 45% gravel, 30% sand, 20%silt, and 5% clay.
Thank you for your considerations.
Kind regards,
Ebrahim
Dear Professor Dill,
Thank you for your response.
Apart from road construction, my question regards to any other compacted soil (or even uncompacted soil) that is opened to water ingression. So, my question is the effect of the effect of entering water into the soil and then evaporating and repeating this cycle for example 50 times. Mainly, I am going to focus on the chemical aspect of this interaction.
Please let me know if I am still not on the right track.
Thank you for your considerations.
Kind regards,
Ebrahim
Dear Dr. Deneys,
Let us assume that there in no mechanical difference between these to the soil (just imaginary). So, if we assume again that chemical interaction between the solid and liquid phase of the soil play a pivotal role on the compacted soil strength, what are, probably, these chemical reactions?
Thank you for your response.
Kind regards,
Ebrahim
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