Page 55 - Unit2.docx

Example 5.6

Determine the design bearing capacity of a pile 22m pile driven in to clay with
characteristic undrained shear strength 20KPa and 2.0kPa increase per metre
depth. Piling condition is assumed to be favourable and the safety class 2. The
pile is cut at 2.5m below the ground level. Top diameter of the pile is 280mm
and growth in diameter is 9mm/m.
© It's Engg. Life

Figure 5-4 Example 5.6

*Often it is assumed that cohesive strength of the soil in the fires three meters is
half the values at the bottom.

solution:

First decide which part of the pile is heavily loaded. To do so, divide the pile
which is in contact with the soil in three parts or sections (see fig.4.2) in this
example the pile is divided into three 3.5m parts

Calculate and decide diameter of the pile at the mid point of each 3.5m
section (0.280+0.009(y ) ; y growth per meter from the end point.
i
i

Calculate the shear strength of the soil at the mid point of each 3.5m section C
mi
= (22 - 2(y ) ). Shear strength at the end of the pile = (20MPa + 2MPa (22m))=22
i
MPa

Decide the values of the partial coefficients from table (20-2 - 20-4)

ymi(see fig. dmi=
Part 5.4) (0.280+0.009⋅ yi Cmi = (22 - 2⋅

(yi)
m m

T(top) 8.75 0.259 23.3 26.9
section