MicroPile Techonology

Pile vs Micropile technology: I worked a couple of years on a Technical Committee (named MicroPile Study Group) on MicroPile Technology. As a part of the MC Study group, I had witnessed the live test on micro-pile, and became part of FE simulations. Oops, I also published a technical paper on Finite Element simulation of micro pile model test results. So, let me try to introduce you what is micropile technology.

Piles are structural material mainly made of either steel sections, or reinforced concrete columns or timbers, and embedded into ground, and usually placed vertically. There are two types of piles: bearing piles and frictional pile, and sometime, you may find combined type. Bored piles are usually bearing type, but not necessarily always. Driven piles are almost always frictional. Lateral confinement from adjoining soil mass helps the pile trans large stress into soil despite of being it very slender. When I was at AIT for Masters degree in Soil Engineering, a veteran pile expert in Bangkok used to give us lecture on Pile Technology used in Bangkok and surrounding areas. One time, he was surprised, and also not sure whether the pile really works, because he was telling us that there were some piles have length equal to greater then 80m long. He was raising his eyebrow that whether such slender structural elements can really transfer loads down to 80m below the foundation ? I am not sure either. But, my guess would be that if these elements are penetrated well inside the sand layer, and if the joints are good enough they might not be conventional piles, but might be behaving like micro-pile that works in tension, but does not work in compression.

So, micropiles are basically slender piles used to reinforce and strengthen foundations existing structure by inserting into the foundations. The micropiles can be considered very similar to soil nail in their actions. Good in tension and practically useless in compression. Lizzi introduced micropiles in 1950 in Italy, and their use is now getting wider, especially, after 1994 California Earth Quake (EQ), and Kobe EQ in Japan in 1995 (I was printing last pages of my Ph.D. thesis that morning, I was alone in the lab, and it was very scary moment because the whole building was shaking continously for several 10s of seconds). Because of strong EQ related lateral loading, and because of weaker design standards against EQ loads at the time majority of old buildings or engineering structures were made in West Coast in US, and in Japan, Japanese and US govt needed a solution to reinforce and strengthen the existing structures' foundations made long time before the current design standards against EQ loading were introduced. They saw Micropile as a very effective tool, and it having very high prospectus in reinforcing the existing foundations. This is a new technology outside Italy. It has a lot of research area and prospectus to develop and mature.