The surface of a saturated clay deposit is located permanently below a body of water as shown in Fig. Ex. 5.5. Laboratory tests have indicated that the average natural water content of the clay is 41% and that the specific gravity of the solid matter is 2.74. What is the vertical effective pressure at a depth of 37 ft below the top of the clay.
Question 5.5: The surface of a saturated clay deposit is located permanent...
To find the effective pressure, we have to find first the submerged unit weight of soil expressed as
\gamma_{b}=\frac{\left(G_{s}-1\right) \gamma_{w}}{1+e}
Now from Eq. (3.14a), e=\frac{w G_{s}}{S}=w G_{s} \text { since } S=1
S=\frac{w G_{s}}{e} \text { or } e=\frac{w G_{s}}{S} (3.14a)
or e=0.47 \times 2.74=1.29
Therefore,
\gamma_{b}=\frac{(2.74-1.00) \times 62.4}{1+1.29}=47.41 lb / ft ^{3}
Effective pressure, \sigma^{\prime}=37 \times 47.41=1754 lb / ft ^{2}
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