Example 5.11 A clay stratum 8.0 m thick is located at a depth of 6 m from the ground surface. The natural moisture content of the clay is 56% and Gs = 2.75. The soil stratum between the ground surface andthe clay consists of fine sand. The water table is located at a depth of 2 m below the ground surface. The submerged unit weight of fine sand is 10.5 kN/m3, and its moist unit weight above the water table is 18.68 kN/m3• Calculate the effective stress at the center of the clay layer.

The other important factor in the prediction is the value of n in Eq. (16.8a). The values obtained from the experimental test results are also given in Fig. 16.20. The values of n are equal to unity for vertical and negative batter piles and increase linearly for positive batter piles up to a maximum of 2.0 at + 30° batter.

In the absence of plate load tests, estimated values of kl and hence ks are used. The values suggested by Terzaghi for k1 (converted into S.I. units) are given in Table 14.1.14.5 PROPORTIONING OF CANTILEVER FOOTING Strap or cantilever footings are designed on the basis of the following assumptions:1. The strap is infinitely stiff. It serves to transfer the column loads to the soil with equal and uniform soil pressure under both the footings.

Eq. (10.35) is the same as Eq. (10.29) obtained by the conventional method of analysis. Bishop (1955) suggests that the accuracy of the analysis can be improved by taking intoaccount the forces E and T on the vertical faces of each slice. For the element in Fig. 10.23(b), we may write an expression for all the forces acting in the vertical direction for the equilibrium condition asN' cosO = W + (Ii - T2 ) - ul cosO-FR sin 0 (10.36) If the slope is not on the verge of failure (Fs > 1), the tangential force Ft is equal to theshearing resistance FR on ed divided by Fs•

Block diagram (a) represents a specimen in the plastic state, which just fills a container of known volume, Vo. The mass of the specimen is Mo. The specimen is then dried gradually, and as it reaches the shrinkage limit, the specimen is represented by block diagram (b). The specimen remains saturated up to this limit but reaches a constant volume Vd . When the specimen is completely dried, its mass will be Ms whereas its volume remains as Vd .

Example 12. 1 A strip footing of width 3 m is founded at a depth of 2 m below the ground surface in a (c -l/J) soil having a cohesion c =30 kN/m2 and angle of shearing resistance l/J = 35°. The water table is at a depth of 5 m below ground level. The moist weight of soil above the water table is 17.25 kN/m3. Determine (a) the ultimate bearing capacity of the soil, (b) the net bearing capacity, and (c) the net allowable bearing pressure and the load/m for a factor of safety of 3. Use the general shear failure theory of Terzaghi.

Example 15.23 A reinforced concrete pile 30 ft long and 15 in. in diameter is embedded in a saturated clay of very stiff consistency. Laboratory tests on samples of undisturbed soil gave an average undrained cohesive strength Cu =2500 Ib/ft2• Determine the net pullout capacity and the allowable pullout loadwith Fs = 3.

Step 3 Continue Step 1 and Step 2 until convergence is reached in the values of T and Pe • The final values obtained for Pt =10 X 103 lb are T =51.6 in, and P e =12.32 X 103 lbsStep 4 The ground line deflection may be obtained from Eq (16.23).