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Reference Document - Slope Stability Risk Assessment
REFERENCE DOCUMENT
MCU20/0084 ABN: 26 602 913 673
NOOSA COUNCIL
15 OCTOBER 2020 E: [email protected]
-
P: (07) 5568 0180
A: 5/10-12 Claude Boyd Parade,
Bells Creek, QLD, 4551
protestengineering.com
Viktoria Dioszegi Project Number: PTP/03499
328 Upper Pinbarren Road, Letter Number: PTP/03499 – 0001
Upper Pinbarren, QLD, 4568 Project Name: 328 Upper Pinbarren Road,
Upper Pinbarren, QLD,
4568
Email: [email protected]
Slope Stability Risk Assessment Report
328 Upper Pinbarren Road, Upper Pinbarren – Proposed “Mango Tree” Cabin
RPD: Lot 3 on RP851976
Area: 256,500 m2
Regulatory Authority: Noosa Shire Council
HAZARD CLASSIFICATION ‘Low’
Figure 1 – Site for proposed building footprint - facing west
AIM
1. To establish the hazard classification for the above block with regards to slope instability;
2. To establish that a development will not adversely affect the stability of the above site; and
3. To recommend any measures that would improve stability.
PTP/03499 – 328 Upper Pinbarren Road, Upper Pinbarren (Mango Tree Cabin) 13 August 2019
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Page 2
ABN: 26 602 913 673
E: [email protected]
P: (07) 5568 0180
A: 5/10-12 Claude Boyd Parade,
Bells Creek, QLD, 4551
protestengineering.com
INTRODUCTION
Protest Engineering (Protest) were commissioned by Viktoria Dioszegi to undertake a Geotechnical
Stability Assessment for the proposed “Mango Tree” cabin located at 328 Upper Pinbarren Road,
Upper Pinbarren. The location of the site is shown in Figure 2 – Site Location below.
The investigation and assessment comprised of determining the hazard risk of the natural slope due
to proposed construction. The slope assessed is shown in Figure 3 – Assessed Slope with two sections
of the slope derived from lidar data shown in Figure 4 and 5 – Slope Section.
Figure 2 – Site Location
PTP/03499 – 328 Upper Pinbarren Road, Upper Pinbarren (Mango Tree Cabin) 13 July 2019
Page 3
ABN: 26 602 913 673
E: [email protected]
P: (07) 5568 0180
A: 5/10-12 Claude Boyd Parade,
Bells Creek, QLD, 4551
protestengineering.com
Figure 3 – Assessed Slope (facing south west down slope)
PTP/03499 – 328 Upper Pinbarren Road, Upper Pinbarren (Mango Tree Cabin) 13 July 2019
Page 4
ABN: 26 602 913 673
E: [email protected]
P: (07) 5568 0180
A: 5/10-12 Claude Boyd Parade,
Bells Creek, QLD, 4551
protestengineering.com
Figure 4 – Slope section east-west orientation (maximum angle 14.1)﮿
Figure 5 – Slope section south-north orientation (Maximum angle 4.26)﮿
SOIL PROPERTIES
Two boreholes undertaken by Protest have been used as a basis for the natural soil profile. Beneath
the topsoil/grass layer, residual, firm to very stiff clayey silts were encountered to borehole
termination at 2.0 m depth. Detailed borehole logs are attached. The clayey silts encountered were
classified as moist at the time of investigation. No Groundwater seepage was encountered at the time
of investigation.
RETAINING WALLS
All retaining walls should be designed as per AS4678. Any retaining walls are required to have a factor
of safety of 1.5 minimum. This office does not take responsibility for the integrity of any existing
retaining walls including rock walls, or future retaining walls unless specifically designed by this office.
RECOMMENDATIONS
a. From our findings, the hazard risk of the natural slope is considered to be ‘Low’, which is
should be acceptable.
b. Attached are drainage and earthworks recommendations as per the Australian Geotechnical
Society examples of good hillside construction practices. See AS2870 for further
recommendations.
c. Stormwater is to follow a stormwater management plan.
d. Effluent disposal may be by use of trenches.
PTP/03499 – 328 Upper Pinbarren Road, Upper Pinbarren (Mango Tree Cabin) 13 July 2019
Page 5
ABN: 26 602 913 673
E: [email protected]
P: (07) 5568 0180
A: 5/10-12 Claude Boyd Parade,
Bells Creek, QLD, 4551
protestengineering.com
Table 1 – Assessment Data
Criteria COMMENT
History: Based on the Noosa Shire Council website this area is
tagged with susceptibility to landslide.
Current Stability: No signs of instability in the slope.
Stability of Adjoining Properties: Residential block with proposed new dwelling
construction. Will have no stability effects on
surrounding properties.
Requirement for Retaining Structures: Dependant on excavations and design. If required,
retaining walls are to be designed by appropriate
engineers. If retaining walls are greater than 2.5 m, this
office should be advised.
Special Design Features Required: Nil.
Special Surface or Sub-Surface Drainage Nil.
Measures:
Evidence of Previous Instability: Nil.
Assessment of Surface Drainage: Good – Flow generally heading towards the southwest.
Attached is an example of prudent site drainage
measures.
Assessment of Sub-Surface Drainage: N/A
Building Site Stability: With respect to the assessed hazard risk, Protest
Engineering zone this site as ‘low’.
Long Term Stability of Building Site and Building: Provided the (soil) information is correct, good practice
for surface drainage is followed, the engineer designs
were carefully followed, the site and dwelling stability
should be considered as ‘low’ hazard.
PTP/03499 – 328 Upper Pinbarren Road, Upper Pinbarren (Mango Tree Cabin) 13 July 2019
Page 6
ABN: 26 602 913 673
E: [email protected]
P: (07) 5568 0180
A: 5/10-12 Claude Boyd Parade,
Bells Creek, QLD, 4551
protestengineering.com
Table 2 – Site Information
COMMISION As requested, a geotechnical engineer from Protest
Engineering visited the site on the 2nd of August 2019.
The weather was fine.
SITE Residential block (256 500m2). Existing residential
dwelling at the west of the site. Proposed new
residential dwellings towards the centre of the site.
GEOLOGY Referencing the Queensland Geology Map the geology of
the site is; Middle Triassic aged Kin Kin Beds comprising
Strongly cleaved and commonly kinked mudstone with
thin siltstone laminae; minor volcanilithic sandstone.
CONCENTRATION OF WATER RUN-OFF Upper slope runoff generally to the southwest of the
block.
EFFLUENT DISPOSAL On-site Disposal by trenches
GROUND WATER Nil.
INFLUENCING HAZARD FEATURES OUTSIDE THE Nil.
BLOCK
EXISTING EARTHWORKS Nil.
PTP/03499 – 328 Upper Pinbarren Road, Upper Pinbarren (Mango Tree Cabin) 13 July 2019
Page 7
ABN: 26 602 913 673
E: [email protected]
P: (07) 5568 0180
A: 5/10-12 Claude Boyd Parade,
Bells Creek, QLD, 4551
protestengineering.com
Table 3 – Landslide Susceptibility Analysis, using Macgregor & Taylor Method 2001 AG-Journal.
Criteria Description Level Factor
Natural Surface Slope Between 5 and 15 Low 0.5
degrees
Slope Shape Planar Moderate 0.9
Site Geology Sedimentary Moderate 1
Soils Residual soil >3m deep High 1.5
Evidence of Groundwater Minor moistness Moderate 0.9
Concentration of Surface Water Upper slope Moderate 0.9
Evidence of Instability No sign of instability Low 0.5
Relative Susceptibility
0.27
Relative Susceptibility 0.27
Hazard Rating Low
Hazard Risk Acceptance Low
Protest Engineering Reviewed By:
Sean Kelly James Tayler RPEQ#1407
Geotechnical Engineer Checking Engineer for Protest Engineering
Attachments: 1: Hillside Construction
2: Effluent and Surface Water Disposal
Attachment 1 – Hillside Construction (As per AGS):
PTP/03499 – 328 Upper Pinbarren Road, Upper Pinbarren (Mango Tree Cabin) 13 July 2019
Page 8
ABN: 26 602 913 673
E: [email protected]
P: (07) 5568 0180
A: 5/10-12 Claude Boyd Parade,
Bells Creek, QLD, 4551
protestengineering.com
PTP/03499 – 328 Upper Pinbarren Road, Upper Pinbarren (Mango Tree Cabin) 13 July 2019
Page 9
ABN: 26 602 913 673
E: [email protected]
P: (07) 5568 0180
A: 5/10-12 Claude Boyd Parade,
Bells Creek, QLD, 4551
protestengineering.com
Attachment 2 – Effluent and Surface Water Disposal (As per ASG):
PTP/03499 – 328 Upper Pinbarren Road, Upper Pinbarren (Mango Tree Cabin) 13 July 2019
Page 10
DCP1
BH3
BH4
Notes:
1. Test locations are approximate and are
shown with reference to site features.
Borehole Location and Number
CLIENT TITLE Job No.
Viktoria Dioszegi Test Location Plan: PTP_034996
1 Issue for Report 09/08/19 KM SK 328 Upper Pinbarren Creek Road, Pinbarren Drawing No.
Issue Description Date DRN CHK APP 1
Page 11
BORE 3
CLIENT Viktoria Dioszegi DATE 02/08/2019
PROJECT Slope Stabilities and Site Classification EASTING
LOCATION 328 Upper Pinbarren Creek Road, Pinbarren NORTHING
PROJECT NUMBER PTP/03499 SURFACE ELEV.
DRILLER Protest RIG 4wd mounted drill rig LOGGER KM
Sampling & Testing
Drilling Method
Graphic Log
Strength Dynamic
Casing
Material Description (Consistency, Results & Penetrometer Test
Type (blows per 100 mm)
Comments
Water
Relative Density,
RL Depth Rock Strength)
(m) (m) 5 10 15 20
TOPSOIL
Medium Dense 3
CH clayey SILT trace sand and gravel, stiff, orange, high plasticity, fine
to medium angular gravel, fine to coarse sand, moist 3
3
3
red-brown
3
No groundwater seepage encountered at the time of investigation.
0.5
4
0.6
4
D 4
3
0.9
4
1.0
Stiff 5
4
4
4
3
1.5
4
5
5
8
6
2.0
Bore terminated at 2 m.
Target depth achieved.
PROTEST-BORE LOGS.GPJ GINTDATATEMP_PROTEST.GDT 9/8/19
2.5
3.0
Remarks:
Auger to 2.0 m;
Page 12
BORE 4
CLIENT Viktoria Dioszegi DATE 02/08/2019
PROJECT Slope Stabilities and Site Classification EASTING
LOCATION 328 Upper Pinbarren Creek Road, Pinbarren NORTHING
PROJECT NUMBER PTP/03499 SURFACE ELEV.
DRILLER Protest RIG 4wd mounted drill rig LOGGER KM
Sampling & Testing
Drilling Method
Graphic Log
Strength Dynamic
Casing
Material Description (Consistency, Results & Penetrometer Test
Type (blows per 100 mm)
Comments
Water
Relative Density,
RL Depth Rock Strength)
(m) (m) 5 10 15 20
TOPSOIL
Medium Dense 5
CH clayey SILT trace sand and gravel,stiff, orange, medium plasticity,
fine angular gravel, fine to coarse sand, moist. 3
2
3
3
No groundwater seepage encountered at the time of investigation.
0.5
stiff, red-brown.
4
5
5
6
4
1.0
Stiff 4
4
5
3
3
1.5
3
4
5
6
6
2.0
Bore terminated at 2 m.
Target depth achieved.
PROTEST-BORE LOGS.GPJ GINTDATATEMP_PROTEST.GDT 9/8/19
2.5
3.0
Remarks:
Auger to 2.0 m;