Pile Design and Construction Practice, Fifth edition

362 Piles to resist uplift and lateral loading
Design resistance of deadman anchor in strong chalk �0.8�1000���0.215�
10/1.4�3860 kN.
Total design resistance of pile and anchor � 148 � 3860 � 4008 kN, which is greater
than the design uplift of 2100 kN.
Checking the uplift resistance of the overlapping cones using the UPL limit-state factors,
Table 6.2 gives a partial factor of 1.25 on the angle of shearing resistance. Therefore the
characteristic resistance due to the submerged weight of the cones and the frictional resistance
surrounding them is equal to 2747 � 3755/1.25 � 5751 kN. From Table 6.1 the partial
factor to obtain the design value of the favourable stabilizing action is 0.9.
Design value � 0.9 � 5751 � 5175 kN.
Vertical component of variable destabilizing action � 2800 � sin 71.5��2655 kN.
Table 6.1 gives a partial factor of 1.5 for variable unfavourable actions. From equation 6.4:
V dstd � 1.5 � 2655 kN � 3983 which is less than the design resistance of 5175 kN.
If shear connectors are to be provided equation 6.6 can be used to calculate the required
bond length. It is not strictly valid for the geometry of the connection but this example will
illustrate the use of the equations. Assume a characteristic grout compression strength of
25 N/mm 2 at 3 days and a modular ratio of 18. For a shear key upstand height of 10 mm and
a spacing of 150 mm, the ratio h/s of 0.067 gives C s � 1.0. Assume a bond length to anchor
tube diameter greater than 12 to give C L � 0.7.
From equation 6.7, stiffness factor:
K � 1
18� 568
200� �1
�� 168 600
�
16 16� �1
� 0.04
From equation 6.6, characteristic bond strength:
10
� 0.04�0.7 �9�1 � 1100�
150��25 � 11.5 N/mm 2
For work of this kind special grout monitoring would not be used. Hence a safety factor of
6 should be used giving,
Allowable bond strength N/mm2 �
1329 � 1000
Required bond length over anchor � � 1323 mm
� � 168.3 � 1.9 11.5
� 1.9
6
Therefore provide 1323/150 � 8.8, say 9 shear keys spaced at 150 mm centre over a
distance of 1.3 m over anchor tube and pile.
Example 6.4
A vertical bored and cast in-situ pile 900 mm in diameter is installed to a depth of 6 m in a
stiff over-consolidated clay ( cu � 120 kN/m ). Find the ultimate
2 , c��10 kN/m2 , ���25�