## Pile foundation design under static loading

he static design of the pile foundations has to be carried out in accordance with EC7. A procedure is outlined below for cohesionless soils. A similar approach can be used for cohesive soils ith suitable odification.

The pile capacity can be determined as a combination of the base capacity and the shaft capacity:

Base capacity Shaft capacity

9.2.1 Base capacity he base capacity depends on the bearing capacity of the soil at the pile tip level. It can be calculated using:

Friction angle (f)

Figure 9.4 Bearing capacity factor N for deep foundations

Friction angle (f)

Figure 9.4 Bearing capacity factor N for deep foundations

Qb = qb • Ab where Ab = base area of pile shaft qh = S • Nq

The bearing capacity factor, N , for a deep foundation can be obtained using the chart shown in Figure 9.4. These types of charts were originally proposed by Berezantzev et al (1961) and subsequently modified by several researchers.

9.2.2 Shaft capacity

The shaft capacity is obtained by estimating the shear stress generated along the shaft, which can be calculated as:

where K depends on type of pile and installation (driven or cast in situ piles), s'v is the effective stress at the elevation where shear stress is being calculated and 8 is the friction angle between the pile and the soil. For driven piles, Ko<1, so choose 1 conservatively. In order to obtain the shaft capacity due to skin friction, we need to integrate the shear stress over the surface area of the pile using the follo ing equation:

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