1 - GEOTECHNICAL INVESTIGATION REPORT - 150320 LAR Road Investigation Ridgewood Geotech 23042015_Rev1-Combined

1.0 Introduction
At the request of Lambert and Rehbein (L&R), Red Earth Engineering Pty Ltd (REE) has
undertaken a geotechnical investigation along a section of Top Forestry Road, Ridgewood
for the purposes of providing geotechnical advice regarding the suitability of the proposed
L&R design for the road pavement upgrade and widening.

REE understands that as a Noosa Shire Council requirement for a proposed development at
136 Top Forestry Road, Ridgewood, the existing unsealed gravel pavement of Top Forestry
Road will need to be upgraded from Old Ceylon Road to the property at number 136. This is
to accommodate a higher frequency of vehicle movements including heavy vehicles, to
increase the pavement width and to seal this section of the road. This involves a pavement
upgrade length of approximately 1.4 km. It is understood that the proposed pavement
design is based on an assumed subgrade CBR of 15%. Some sections of the roadway are
to be widened through existing cuts. Lambert & Rehbein Concept Drawing B14101-SK-005
indicates that the design for the steepest cut batter to achieve the required formation is 1
Horizontal to 1.333 Vertical (approximately 55 degrees).

This document presents the result of field investigations and laboratory testing, as well as
engineering recommendations and comments related to the proposed upgrade.

2.0 Site Description
The proposed road redevelopment extends along Top Forestry Road, Ridgewood from Old
Ceylon Road towards the west for approximately 1.4 km. The current roadway is in a rural
community near the township of Cooroy and is gravel surfaced with a formation width of
approximately 5 m to 6 m. The roadway is constructed along a series of cut benches and fill
embankments. Cut faces typically vary between 1 m and 2 m in height, however in one
section they are up to approximately 4 m in height. Fill embankments typically range from
between 1 m to approximately 3 m height.

Prior to carrying out the field investigation it was noted that the pavement surface had
recently been graded and levelled. There was no evidence of significant rutting or other
surface deformation. The fieldwork was undertaken during a heavy rainfall period. There
was no evidence of significant erosion of fill batters or infiltration of surface run-off into the
pavement surface or adjacent shoulders. Some old and small zones of slumping within the
upper 0.5 to 1 m of cut faces (i.e. typically in the residual soil/extremely weathered profile)
was noted in some areas.

3.0 Geology
Reference to the 1:100,000 Australian Geological Map – Gympie Special indicates that the
investigation site is underlain by rock of the Early-Middle Triassic age and part of the Kin Kin
Beds. Rock types include Arenite, Argillite and Phyllite.

4.0 Fieldwork
Two activities were undertaken simultaneously as part of the geotechnical investigation.
One was auger hole drilling within the existing road pavement and the other was a stability
assessment of existing cuts.




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