[beresd]

Hi there,

I am not actually a chemistry student, but a final year civil engineering student - however, I very much need the help of some chemists on my thesis...

I am doing my final year project on a phenomenon that occurs to steel piles when embedded in sand - where it has been found that the capacity of piles (that is, the maximum weight each pile can sustain without "failing" by being pushed deeper into the ground), increases over time. Upon removing the piles from the ground, they are covered with a layer of sand seemingly bonded to the steel.

I wanted to ask if there is a chemical reaction at work here - is the steel somehow reacting with silaceous or calcerious sand to form this bond? As far as I know (and I have only just started on this), the reaction, if there is one, occurs in both types of sand. As with most ground conditions, some amount of moisture will always be present, if that in any way explains it.

Sorry for the strange question, any help at all will be greatly appreciated, as I have found almost nothing on it though searching

[Arkcon]

OK, my curiosity is piqued -- how can you tell the sand has undergone a chemical reaction with the steel, and not just compressed itself into surface imperfections?

[beresd]

I am going by what my supervisor, who is a geotechnical professor has told me to look into. From what he has said, it seems the sand is too strongly bonded to the steel for it to be a purely physical interaction. Also, the capacity increases 3-5 fold if left long enough (a year), not an insignificant amount, so the reasoning is that would not occur just with the sand being compressed into the steel surface.

However, we are not sure it is a chemical reaction, which is why I am asking the question

[Borek]

What if iron corrodes and corrosion products (rust) while not reacting chemically with the sand, form something that 'glues' sand and iron together?

[Arkcon]

From what he has said, it seems the sand is too strongly bonded to the steel for it to be a purely physical interaction. Also, the capacity increases 3-5 fold if left long enough (a year), not an insignificant amount, so the reasoning is that would not occur just with the sand being compressed into the steel surface.

However, we are not sure it is a chemical reaction, which is why I am asking the question

See, both of those explanations are interesting, but they're just not ... quantitative ... enough for me to really believe there's a chemical reaction.  But this may be a well known phenomena, something a building engineer or metallurgist would know about.  Or maybe a hot topic of research for surface chemists.