Appendix D Geotechnical report · MCU18/0013

Project No. 304-2014
November, 2004 Page 10

 

Footing bases should be individually recompacted, eg. by vibrating plate compactor, to
remedy disturbance of the sand foundation during excavation. Testing of footing bases is
recommended to confirm the compaction status of the foundation. If footing beams
cannot be cast on the same day as excavation, a concrete blinding layer of at least

50mm thickness is recommended across the footing base.
6.3.4 Deep Foundations

Deep foundations using piles are considered as an alternative solution for the proposed
residence. The choice of suitable pile types should be made from non-vibration piling

methods.

Push-in preformed piles, continuous flight auger (CFA) or bored piles are considered
suitable pile types, although the construction of the latter may be problematic in loose

sand, where collapse of the pile hole is likely.

Depending on the load requirements, and the piling contractors design, it is
recommended that the piles are founded in material which is at least medium dense, and

at a minimum depth of 3m below existing ground surface.
The design of piles in cohesionless soils may be carried out using the following method:
Ou =Q0+Qs ultimate pile resistance
where:

QO» =Ap-Pa- (Ng -1) ultimate base resistance

QO; =As+pa+ Ks + (tand) ultimate skin friction

As;= area of pile shaft

Ap= __ areaof pile base

Pa= effective overburden pressure at depth d
Pa= average effective overburden pressure
K,= lateral earth pressure coefficient

6 = __ pile-soil angle of friction

N,= bearing capacity factor

(Nq = 60 for medium dense sands, N, = 100 for dense sands)

 

# SOIL SURVEYS ENGINEERING