The evaluation of the vertical ultimate capacity of the micro-pile depends on the type of micro-pile considered. In the present work we consider root-type micro-piles and Tubifix micro-piles.

Root-type micro-piles:

The vertical ultimate capacity is expressed through the following formula:

So it is expressed as the product between the side area of the pile and the limit tangential strain on the pile-soil interface. The τlim is evaluated through the following formula:

Where γt is the specific gravity of the soil, zm is the level of the midpoint of the pile working length, K0 is the lateral pressure coefficient at rest, ϕ is the angle of inner friction of the soil, a is a dimensionless adhesion coefficient and c is the foundation soil cohesion.

Tubifix micro-piles:

In this case too, the vertical ultimate capacity is expressed through the following formula:

In this case, however, a different method is used to calculate the limit interface t. In particular, Bustamante’s theory is used. According to said theory, the limit tangential strain is calculated as follows:

•if F is different from zero:

•if F is equal to zero and if c is higher than zero:

Two events can occur depending whether it is a question of a single or repeated injection:

Single injection:

Should the limit strain so calculated turn out to be lower than the value of 0.5, then the following formula must be used:

Repeated injection:

Should the limit strain so calculated turn out to be lower than the value of 0.5, then the following formula must be used:

In all the previous formulas, plim is the limit pressure detected by Ménard’s pressure meter inserted in N/mm².