Figure Ex. 17.3 depicts a drilled pier with a belled bottom. The details of the pile and the soil properties are given in the figure. Estimate (a) the ultimate load, and (b) the allowable load with Fs = 2.5.

Question

Figure Ex. 17.3 depicts a drilled pier with a belled bottom. The details of the pile and the soil properties are given in the figure. Estimate (a) the ultimate load, and (b) the allowable load with [latex]F_{s}=2.5[/latex].

Accepted Answer

Based load

Use Eq. (17.8) for computing [latex]q_{b}[/latex]

[latex]q_{b}=9 c_{u}[/latex] (17.8)

[latex]q_{b}=9 c_{u}=9 imes 200=1,800 kN / m ^{2}[/latex]

Base load [latex]Q_{b}=\frac{\pi d_{b}^{2}}{4} imes q_{b}=\frac{3.14 imes 3^{2}}{4} imes 1,800=12,717 kN[/latex]

Frictional load

The effective length of shaft [latex]L^{\prime}=25-(2.75+1.5)=20.75 m[/latex]

From Eq. (17.24) [latex]f_{s}=\alpha c_{u}[/latex]

[latex]f_{s}=\alpha c_{u}[/latex] (17.24)

For [latex]\frac{c_{u}}{p_{a}}=\frac{100}{101} \approx 1.0, \quad \alpha=0.55[/latex] from Fig. 17.15

Hence [latex]f_{s}=0.55 imes 100=55 kN / m ^{2}[/latex]

[latex]\begin{aligned}&Q_{f}=P L^{\prime} f_{s}=3.14 imes 1.5 imes 20.75 imes 55=5,375 kN \&Q_{u}=Q_{b}+Q_{f}=12,717+5,375=18,092 kN \&Q_{a}=\frac{18,092}{2.5}=7,237 kN\end{aligned}[/latex]

Question 17.3: Figure Ex. 17.3 depicts a drilled pier with a belled bottom....

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