Figure A Values of As and Ac (after Reese et al. 1975)

225
Figure A P-y curve in stiff clay with no free water – static loading (after Welch and Reese 1972).
Figure A P-y curve in stiff clay with no free water – cyclic loading (after Welch and Reese 1972).

Static Loading For static loading, the following procedure can be used to construct the p-y curve for stiff clay with no free water (below water surface) as shown in Figure A
1. Obtain input parameters, including the undrained shear strength C
u
, effective unit weight γ′ with depth, and pile diameter D. Obtain the value of ε
50
from stress-stain curves or from Table A.
2. Calculate the ultimate soil resistance per unit length of pile (p
u
) as the smaller value calculated from Equations A and A. When using Equation A, the average shear strength from the surface to the depth under consideration should be used. Take J = 0.5.

226 3. Calculate y
50
using Equation A. Construct the p-y curve using the following equation 0.5 �
𝑦𝑦
𝑦𝑦
50
�
1 Equation A)
5. For y ≥ 16y
50
, pis equal to p
u
for all values of y.
Cyclic Loading
For cyclic loading, the following procedure can be used to construct the p-y curve for stiff clay with no free water as shown in Figure A
1. Construct the p-y curve for short-term static loading using the previously described procedure. Determine the number of cycles of load application, N.
3. For several values of p/p
u
, obtain the parameter C, which characterizes the effect of repeated loading on deformation. Welch and Reese (1972) developed the following relationship from laboratory tests that should be used, in the absence of additional information, to estimate the parameter C as = 9.6 Equation A)
4. For the same p values used to calculate p/p
u
in Step 3, compute the deflection y
c
for cyclic loading conditions with the following expression 𝑦𝑦
𝑠𝑠
+ 𝑦𝑦
50
𝐶𝐶 log 𝑁𝑁 Equation A) where y
c
is the deflection after N load cycles y
s
is the deflection upon initial loading and C and N as defined previously.
5. Obtain the p-y curve the soil response after N cycles of load.

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