• When the pile group was subjected to two-way cyclic lateral loading (i.e., back and forth lateral
loading) at the pile head, the shadowing effect was not appreciably diminished.
• Although the two-way cyclic lateral loading did not influence the shadowing effect, there was densification of the soil adjacent the piles related to sand falling into the voids around the pile as it was
pushed back and forth. For 100 cycles of loading, about 9 in. (23 cm) of ground surface settlement
directly around the pile was observed due to this effect of sand falling into the voids created by
pushing the pile back and forth. This densification effect of the sand caused by the back and forth
lateral loads appeared to improve the soil resistance at subsequently larger lateral loads.
• Cyclic lateral loading in only one direction would not produce as much densification as the twoway cyclic lateral loading and would result in a greater loss of soil resistance with increasing cycles
Solution From Table 11.1, for sand having a medium density, use a value of horizontal displacement divided by height of pile subjected to passive resistance of:
1
/
2
(0.002 +0.006) =0.004
Horizontal deflection of pile head for passive resistance in the upper 5 ft (1.5 m) of soil =
(0.004)(60 in.) =1/4 in. (0.6 cm)
To determine passive resistance, use Eq. (6.26):
P
p
=1.5k
p
g
tDH2
=1.5 [tan
2
(45°+34°/2)](125)(1.0)(5)
2
=16,600 lb (72 kN)
of load. In this respect, the results of the experiment show the beneficial effects of back and forth
cyclic loading but the worst case would be lateral loading in only one direction. The results of the
study clearly show the importance of the nature of the loading.