Changes Application - MCU15/0023.02

ProjectNo.112-14608
January,2013   REF:   1-14608,2013-01-15,BR VER O.                                           Page14

     Preformed driven or pushed piles may also be suitable, however the environmental
     constraints that may be present at this site might preclude driven piles due to the noise
     and vibration associated with this method.        Pushed-in piles avoid these problems, but a
     push-in rig of sufficient reaction capacity may not be able to successfully negotiate the
     sloping site. Specialist contractors should be approached if this pile type is considered.


     Skin Friction


     Average values for ultimate unit skin friction for straight sided piles are shown in Table 4.


     Vesic (1966) showed that at a penetration depth equivalent to 10 - 15 pile diameters, a
     peak value of unit skin friction is achieved. Research has not yet established whether the
     peak value is a constant in all conditions or whether it is related to grain size or angularity.
     At present a maximum value of 11OkPa is given in the literature.


     In the case of bored piles in cohesionless soils, some sand may be loosened due to the
     boring operation. However, pressurised grout is expected to bond any disturbed material
     and hence dense sand parameters can be used.


     TABLE 4                  AVERAGE ULTIMATE SKIN FRICTION VALUES

                                                     Sands
                      Relative Density            Average Ultimate Unit Skin Friction for Straight
                                                                  Sided Piles (kPa)
                Less than 0.35 (loose)                                   10
              0.35 - 0.65 (medium dense)                               10 - 25
                  0.65 - 0.85 (dense)                                  25 - 70
             More than 0.85 (very dense)                              70 - 110
     Note: (1) Highvaluesmaybepossiblesubjectto roughnessof the rocksocket.


     End Bearing Capacity


     For piles founded in sand, research has shown that at a certain depth a maximum value
     of base resistance is reached which is not exceeded no matter how much deeper the pile
     is installed. Published pile test results indicate that the maximum value is 11,000 kPa for
     grout injected piles.


     Piles founded within the critical thickness of about 10B (B - pile thickness) of the top of
     the lower level medium dense sands, as encountered in Borehole 1 at a depth of 16.90m,
     will result in a reduction of the ultimate base resistance.




                                                             :#. SOIL SURVEYS ENGINEERING