Geotechnical report_Morrison · 132008.169

Job No. ME09/068

Referring to BH1 and BH2 the SPT ‘N’ value drops off in the yellow sand which appears to
relate to the clay fines content. Continuing into the sandstone may have merit for heavy loads
where the allowable base resistance increases to 1.5MPa.

3.3.2 Screw Piles

Screw piles offer a satisfactory alternative for loads up to 50 tonnes. Specialist contractors
will offer a pile type and spiral dimensions for the loadings required.

All piles should be hot dipped galvanized and should be drilled to a minimum depth of 7
metres on the lower slopes and 5 metres in the northern part of the site represented by DP4
and DP6.

Allowable base resistance may be taken as that applicable for drilled concrete piles as

as Q>p = a = 1.0MPa

Shaft resistance on the other hand is zero.

Ultimate tension or pull out resistance is the mass of a 30 degree tapered cone of sand above
the pile spiral base plate based on an average sand density of 17.5kN/m?,

4.0 SLOPE STABILITY

The natural cleared slope at 20 to 25 degrees has a Factor of Safety (As ay )

of 1.2 to 1.6 and below the house site with trees remaining of 1.4 to 1.7 and therefore has a
very low risk of movement. Heavy rainfall however may cause local over steepening if runoff
is concentrated on the slope as all of the sand (dune sand and Teewah sand) is highly
erodible.

Preferably all storm water runoff should be taken to the natural drainage below the site.

5.0 GROUNDWATER

Seepage in the sand will occur after heavy rain but there is no groundwater table as such. In
the northern part of the site seepage can be expected at the sand/clay interface represented
by test pit TP2 at about RL42.5m,

All retaining walls should be well drained with a gravel filter and pipe protected by a geofabric
surround,

6.0 LIMITATIONS

The use of drilled piles will require inspections at construction to confirm the base and shaft
friction and the working load capacity as the dynamic probes did not allow adequate soil
identification.

Screw piles on the other hand may be approved by meeting the contractor's torque capacity
correlation appropriate at the pile working load.

Recommendations given in this report are based on information supplied regarding the
proposed construction in conjunction with the findings of the investigation. Any change in
construction type may require additional testing and/or make recommendations invalid.

 

Ref 00558 — Adrian Slinger MORRISON GEOTECHNIC
71 Seaview Terrace Sunshine Beach