Question 11.13: In Fig. 11.21, assume at Boring B-25 that the uppermost soil...
In Fig. 11.21, assume at Boring B-25 that the uppermost soil layer (silt, silty sand, and peat layer) extends from elevation -2 to -5 m and the light gray silty sand layer extends from elevation -5 to -8 m. It is anticipated that the site will be subjected to significant earthquake shaking and that these two layers will liquefy during the earthquake. Use k = 0.4 and \phi_{w}=15^{\circ} for the 3 m thick silt-peat layer and use k = 0.5 and \phi_{w}=20^{\circ} for the 3 m thick light gray silty sand layer. Using the data from Prob. 11.5, determine the downdrag load on the pier for liquefaction of the two layers.
Calculate the downdrag load for each layer.
For the 3 m thick silt-peat layer:
Average \sigma_{v}^{\prime}=(1.5)(9.2)=13.8 kPa
Using Eq. (11.14):
Q_{D}=2 \pi R L_{1} \sigma_{v}^{\prime} k \tan \phi_{w}= 2π (1.0/2)(3)(13.8)(0.4) tan 15°
= 14 kN
For the 3 m light gray silty sand layer:
Average \sigma_{v}^{\prime}=(4.5)(9.2)=41.4 kPa
Using Eq. (11.14):
Q_{D}=2 \pi R L_{1} \sigma_{v}^{\prime} k \tan \phi_{w}= 2π (1.0/2)(3)(41.4)(0.5) tan 20°
= 71 kN
Total Q_{D}=14+71=85 kN