Slope Stability Report

Dean & Vanessa McDonald                                                                          21505-001-Rev0
                                                                                                 4 February 2022

Approximately 15 m downslope from the building pad, an access track was observed to be cut into the
natural slope with exposed weathered phyllite cut batters up to 2 m height. The cutting was located at the
toe of fill battering back to the shed building pad as seen in Text Figure 5 below.




Text Figure 5: Exposed weathered phyllite batter on downslope access track
The building pad exposed weathered phyllite to the west and comprised previously placed ‘uncontrolled’ fill
to the east. The ‘uncontrolled’ fill appeared to comprise gravelly clay with weathered phyllite cobbles. To
make an appraisal of the strength of the fill materials at the building pad, Tectonic undertook two standalone
DCP tests (designated DCP1 & DCP2). DCP1 and DCP2 were undertaken about 3 m back from the fill
batter crest.
DCP1 and DCP2 indicated initially stiff / medium dense materials to 0.3 m to 0.5 m BGL, then firm to stiff /
loose to medium dense materials to 2.5 m BGL in DCP1 and 1.5 m BGL. These were underlain by stiff to
very stiff (or stiffer) / dense (or denser) materials, which are inferred to be residual soils grading to weathered
phyllite as observed in cut batters.
DCP reports are attached at the end of this report.
2.2    Topography
As illustrated in Text Figures 6 & 7 overleaf, the proposed shed site is located in the south-western corner of
the allotment, mid slope and to the east of Old Ceylon Road which generally traces a southerly dipping
ridgeline. The allotment generally falls north to south with a natural gully that bisects the property.
Downslope to the east of the proposed shed site is a dam that catches surface runoff from the natural gully.

Text Figure 6 overleaf indicates the topographic features observed during the site walkover, noting that
ground slopes were recorded using a hand-held clinometer. The inferred natural ground slope across the
development site (prior to earthworks) was about 15°, with slopes of 10° to 12° observed above the cut
batter, and slopes of 15° to 20° downslope of the access track down into the dam.

As stated previously, the proposed development area had been altered previously by cut and fill earthworks
to create a relatively level building platform. Upslope cuts in the order of up to 4.5 m depth were battered at
15° to 25°. Fill was estimated up to 2.5 m height, with downslope fill batters typically ranging up to 25°. Text
Figure 7 overleaf appears to show the previous natural contours before the earthworks were completed. It is
noted that a slight gully was present through the location of DCP1 which is in line with the deeper fill inferred
from the DCP results. The building platform slopes slightly downslope from west to east.




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[OCR of page images]
Dean & Vanessa McDonald 21505-001-RevO
4 February 2022

 

Approximately 15 m downslope from the building pad, an access track was observed to be cut into the
natural slope with exposed weathered phyllite cut batters up to 2 m height. The cutting was located at the
toe of fill battering back to the shed building pad as seen in Text Figure 5 below.

 

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Text Figure 5: Exposed weathered phyllite batter on downslope access track

The building pad exposed weathered phyllite to the west and comprised previously placed ‘uncontrolled’ fill
to the east. The ‘uncontrolled’ fill appeared to comprise gravelly clay with weathered phyllite cobbles. To
make an appraisal of the strength of the fill materials at the building pad, Tectonic undertook two standalone
DCP tests (designated DCP1 & DCP2). DCP1 and DCP2 were undertaken about 3 m back from the fill
batter crest.

DCP1 and DCP2 indicated initially stiff / medium dense materials to 0.3 m to 0.5 m BGL, then firm to stiff /
loose to medium dense materials to 2.5 m BGL in DCP1 and 1.5 m BGL. These were underlain by stiff to
very stiff (or stiffer) / dense (or denser) materials, which are inferred to be residual soils grading to weathered
phyllite as observed in cut batters.

DCP reports are attached at the end of this report.
2.2 Topography

As illustrated in Text Figures 6 & 7 overleaf, the proposed shed site is located in the south-western corner of
the allotment, mid slope and to the east of Old Ceylon Road which generally traces a southerly dipping
ridgeline. The allotment generally falls north to south with a natural gully that bisects the property.
Downslope to the east of the proposed shed site is a dam that catches surface runoff from the natural gully.

Text Figure 6 overleaf indicates the topographic features observed during the site walkover, noting that
ground slopes were recorded using a hand-held clinometer. The inferred natural ground slope across the
development site (prior to earthworks) was about 15°, with slopes of 10° to 12° observed above the cut
batter, and slopes of 15° to 20° downslope of the access track down into the dam.

As stated previously, the proposed development area had been altered previously by cut and fill earthworks

to create a relatively level building platform. Upslope cuts in the order of up to 4.5 m depth were battered at

15° to 25°. Fill was estimated up to 2.5 m height, with downslope fill batters typically ranging up to 25°. Text
Figure 7 overleaf appears to show the previous natural contours before the earthworks were completed. It is
noted that a slight gully was present through the location of DCP1 which is in line with the deeper fill inferred
from the DCP results. The building platform slopes slightly downslope from west to east.

 

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geotechnical & environmental engineers.

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