Attachment 5 - Geotechnical Assessment · MCU18/0015

RTI 11/055 Folio B396

 

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November 2003 -12- 03632248-001

 

7.3 Footing Design

Based upon the results of the investigation, we anticipate that the foundation conditions for
the proposed structures will comprise either deep sand or shallow clay / rock. It is our
preliminary assessment that the Lodge together with Cabins 3B, 4A/B, 5A/B and 6B will have
deep sand foundations, whilst the other structures will encounter shallow clay / rock
foundation conditions.

Golder Associates should carry out inspections of footing excavations during construction to
confirm allowable bearing pressures.

7.3.1. Deep Sand Foundations

Footings supporting structures on deep sand foundations will need to penetrate through the
loose sand to found in the underlying medium dense (or denser) sand. «Footings could
comprise bored piers, however significant fall-in is expectedyfrom the loose upper sand
resulting in construction difficulties unless the piers afe-installed using a casing/liner. Grout-
injected (CFA) piles would also be a suitable method for the proposed, construction.

Spoil from pile excavation should not be stockpiled on the slope, and similarly, any drilling
fluids used in drilling the piles should notbe discharged_onto the slope.

Piles founded in medium dense sand could be=designed using an allowable end bearing
pressure of 500 kPa and allowable shaft adhesion of 20 kPa, A specialist piling contractor
should confirm allowable pile capacities.

Apart from vertical\loads imposed by ‘the supported structure, final pile depth will also be
dependent upon bracing requiremenis to resist the potentially significant lateral loads exerted
on the piles by movement of loose sand. If localised instability develops in the loose surface
sand directly up the slope from a pile, heavy loads will be placed on the pile as the sand
attempts to flow down.the slope past the pile.

Estimation of lateral forces on piles should be based on an assumption that lateral ground
movements occur along the interface between loose and medium dense sand. The average
depth of the zone of loose sand is 3 m. Calculation of lateral forces on piles should be carried
out in accordance with the method outlined in the figure below.

Golder Associates