REPORT ON STABILITY RISK ASSESSMENT 4A WRIGHTS ROAD, … · REPORT ON STABILITY RISK ASSESSMENT 4A...

$: REPORT ON STABILITY RISK ASSESSMENT 4A WRIGHTS ROAD, … · REPORT ON STABILITY RISK ASSESSMENT 4A WRIGHTS ROAD, GLENELLA CHRIS AND COLIN WINDSOR Version 1 5 May 2014 L:\PROJECTS\ENGINEERING$
4A WRIGHTS ROAD, GLENELLA

CHRIS AND COLIN WINDSOR

REPORT ON STABILITY RISK ASSESSMENT

5 May 2014 Job No. U23702

rachelsm

Received (Auto Date)

REPORT ON STABILITY RISK ASSESSMENT 4A WRIGHTS ROAD, GLENELLA

CHRIS AND COLIN WINDSOR Version 1 5 May 2014 L:\PROJECTS\ENGINEERING REPORTS\U23702 Chris&Colin Windsor_5A Bald Hill Road\U22597_4A Wrights Rd_Slope stability_rev 2.doc Page i

Cardno Ullman & Nolan Geotechnic Pty Ltd

ABN 45 103 205 205

71 Connors Road

Queensland 4741 Australia

Telephone: 07 4952 5255

Facsimile: 07 4952 5455

International: +61 7 4952 5255

Email: [email protected]

Web: www.cardno.com.au

Document Control

Version Date Author Reviewer

Name Initials Name Initials

1 16 July 2009 W S Sitana WSS Trudie Bradbury TB

2 5 May 2014 T Bradbury TB Karen Gates

"© 20014 Cardno Ullman & Nolan Geotechnic Pty Ltd All Rights Reserved. Copyright in the whole and every part of this document belongs to Cardno Ullman & Nolan Geotechnic Pty Ltd and may not be used, sold, transferred, copied or reproduced in whole or in part in any manner or form or in or on any media to any person without the prior written consent of Cardno Ullman & Nolan Geotechnic Pty Ltd.”


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REPORT ON STABILITY RISK ASSESSMENT

4A WRIGHTS ROAD, GLENELLA

TABLE OF CONTENTS

1. INTRODUCTION ................................................................................................................. 1

1.1 Details of Development ................................................................................................ 2

1.2 Site Location and Description ...................................................................................... 2

1.3 Method and Scope of Investigation .............................................................................. 3

1.3.1 Scope of Works ................................................................................................ 3

1.3.2 Method of Investigation ..................................................................................... 3

1.4 Qualifications of Responsible Individuals ..................................................................... 4

2. DESCRIPTION OF EXISTING CONDITIONS .................................................................... 4

2.1 Geology ........................................................................................................................ 4

2.2 Topography .................................................................................................................. 4

2.3 Groundwater ................................................................................................................ 4

2.4 Surface Drainage ......................................................................................................... 4

2.5 Vegetation .................................................................................................................... 5

2.6 Existing Buildings and Structures ................................................................................ 5

3. ASSESSMENT OF LAND STABILITY ............................................................................... 5

3.1 Preliminary Evaluation ................................................................................................. 5

3.2 Existing Conditions ...................................................................................................... 5

3.2.1 Surface Features .............................................................................................. 5

3.2.2 Sub-surface Features ....................................................................................... 6

3.3 Geotechnical Constraints to Development ................................................................... 6

3.3.1 Hillside Instability .............................................................................................. 6

3.3.2 Debris Fall ......................................................................................................... 7

3.3.3 Cut Batter Stability ............................................................................................ 7

3.3.4 Failure within Fill ............................................................................................... 8

4. DESCRIPTION OF PROPOSED DEVELOPMENT ............................................................ 8

4.1 Site Layout ................................................................................................................... 8

4.2 Proposed Development Components .......................................................................... 8

4.3 Potential Geotechnical Effects ..................................................................................... 8


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5. ASSESSMENT OF DEVELOPMENT IMPACTS ................................................................ 8

5.1 Site Layout ................................................................................................................... 8

5.2 Roadworks, Driveways and Other Pavements ............................................................ 8

5.3 Earthworks (excavation, material usage) ..................................................................... 8

5.4 Foundations ................................................................................................................. 9

5.5 Surface Drainage ......................................................................................................... 9

5.6 Wastewater (treatment & Disposal) ............................................................................. 9

5.7 Overall Effect of Development on Stability ................................................................... 9

6. MEASURES RECOMMENDED TO MITIGATE IMPACTS ............................................... 10

6.1 General ...................................................................................................................... 10

6.2 Hillside Instability ....................................................................................................... 10

6.3 Debris Fall .................................................................................................................. 10

6.4 Cut Batter Stability ..................................................................................................... 11

6.5 Failure within Fill ........................................................................................................ 11

6.6 Foundation ................................................................................................................. 11

6.7 Earthworks ................................................................................................................. 11

6.8 Site Management ....................................................................................................... 11

7. SUMMARY AND CONCLUSIONS ................................................................................... 13

8. LIMITATIONS ................................................................................................................... 14

APPENDICES APPENDIX A Engineering Geological Map

APPENDIX B Engineering Geological Cross Section

APPENDIX C Descriptive Engineering Borehole Logs & Dynamic Cone Penetrometer Results

APPENDIX D AGS (2007) Management & Maintenance of Sloping Sites

APPENDIX E Site Photos

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Cardno (Qld) Pty Ltd Trading as Cardno Ullman & Nolan Geotechnic ABN 57 051 074 992

71 Connors Road Mackay QLD 4740 Australia PO Box 5630 Mackay MC QLD 4741 Australia Phone: 61 7 4952 5255 Fax: 61 7 4952 5455 www.cardno.com.au

Our Ref U23702 Contact Andrew Williams

5 May 2014

1. INTRODUCTION

Chris and Colin Windsor 4A Wrights Road Glenella QLD 4740 REPORT ON STABILITY RISK ASSESSMENT 4A WRIGHTS ROAD, GLENELLA Dear Sir/Madam We are pleased to present the results of slope risk assessment undertaken by Cardno Ullman & Nolan Geotechnic (Cardno UNG) at the above site. This report clarifies information from the initial inspection in light of supply of certification of retaining walls, and a stability assessment of the proposed pool area. Initial site investigation was undertaken on 16th June 2009. The objective of this investigation was to establish the risk of instability at the site under current conditions, identify constraints to proposed development and effects of proposed development on stability of the site. The data collected was then used in the assessment and recommendation of mitigation measures where appropriate and comment on the suitability of the site for the proposed development. Assessment is generally undertaken in accordance with the following:

The Australian Geoguide for Slope Managment and Maintenance AS2870-1996 “Residential Slabs & Footings” Building Services Authority (BSA) New Building Services Board

Subsidence Policy (September 2004). The investigation was undertaken to satisfy Mackay Regional Council’s requirement of certifying a very low risk to instability with sites having slopes in excess of 15 percent. An additional investigation was undertaken on the 1st May 2014, this was targeted at the area of the proposed pool in front of the house. The name of the report has also been changed. The site was previously known as 5A Bald Hill Road


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1.1 Details of Development

The proposed development consists of a constructing a new dwelling in Lot 20, 4A Wrights Road, Glenella. A shed is also proposed on a platform formed from cut and fill operation at the north-western corner of the lot. 1.2 Site Location and Description

The subject site is located in Glenella. A gravel access road leads from Wrights Road to the site. Wrights Road is off Bald Hill Road. The site is legally known as Lot 20 on SP163592. Site location is shown on Figure 1.

Fig 1 Aerial view showing site location, proposed pool area west of the house. Proposed shed area north west corner of block (source MiMaps).



1.3 Method and Scope of Investigation

1.3.1 Scope of Works

Cardno UNG submitted a quote (MG18713) on 5th June 2009 after invitation from the client. The quote was subsequently accepted by the client on 12th of June 2009. The scope of works is to undertake a slope risk assessment of the site with respect to the proposed development. Particulars of scope of works are as outlined in our quote (MG18713). 1.3.2 Method of Investigation

The method of investigation included desktop study which involved the review of published geological maps and aerial images from Google Earth and Mackay Regional Council, MiMaps. The aim is to collect background information and delineate areas of interest that may need particular attention during field work. Site classification report by Integrated Environmental Services Australia (IESA) was also reviewed. Field work involves detailed engineering geological mapping and sub-surface investigation in the form of machine boreholes and dynamic cone penetrometer testing. A typical cross section was also measured across the site (see site map, Appendix A and cross section in Appendix B). Field work is undertaken to assess existing terrain (slopes, natural features, landslip features, drainage) and confirm surface and sub-surface material properties (lithology, groundwater, failure planes, foundation conditions), with regards to stability issues.

Results from in-situ and site observations are synthesised and used in slope stability analysis after the methods of AGS (2007)1. The findings are presented in this report along with recommendations.

The soil classification descriptions and field tests were generally undertaken in accordance with the following Australian Standards:

AS1726-1993 “Geotechnical Site Investigations”, AS2870-1996 “Residential Slabs and Footings”, and AS1289 “Methods of Testing Soils for Engineering Purposes”.

Engineering geology map showing geomorphic features and test locations is presented in Appendix A. Cross section measured across the site is shown in Appendix B.

Logs of machine boreholes are presented in Appendix C. Foundation dimensions and structural loads were not available at the time this report was produced.

1 Australian Geomechanics, “The Australian GeoGuide for Slope Management and Maintenance” Ref AGS (2007e); Journal and News of the Australian Geomechanics Society, Vol 42, No 1 March 2007



1.4 Qualifications of Responsible Individuals

A team comprising geotechnical engineers and engineering geologist with a combined experience of more than 50 years in slope stability and land development are involved in this project. Individuals in this group are also members of recognised engineering and earth sciences institutions, associations and societies.

2. DESCRIPTION OF EXISTING CONDITIONS

2.1 Geology

Published geological map of Mackay2 indicates Glenella to be underlain by rhyolitic to dacitic ignimbrite; surbodinate poorly sorted volcanolithic sandstone and conglomerate; minor altered basalt of the Carmila Beds and Lizzie Creek Volcanic Group (early Permian). Dykes and veins are shown to be locally oriented north-south.

The subject site is located on elevated land.

2.2 Topography

The topography of Glenella is predominantly flat with occasional raised land features.

The subject site is located on the western flanks of a knoll feature, hence resulting in steep, west trending topography within the study site (see photo 1).

2.3 Groundwater

Free water was not encountered in the boreholes at the time of investigation nor was there any natural seepage noted in the existing cut batters or on the slopes. However as is the case with jointed rockmass, it is anticipated that a seasonal groundwater regime exists during the wet season where groundwater is predominantly fracture controlled flowing from higher to lower heads. 2.4 Surface Drainage

Surface drainage is controlled by the direction of natural sloping ground and previous earthworks. Natural ground slopes trend generally west hence surface water travels in the same direction. A natural flowpath exists to the north of the site. Surface water also flows down a formed access track leading into the cut platform to the west of the site. A swale drain exists along the southern boundary discharging into a field pit at the south-western corner of the lot.

Surface drainage is shown on engineering geology map (Appendix A).

2 Australia 1:100 000 Geological Series, Mackay Queensland, Sheet 8755, March 2006.



2.5 Vegetation

The site has been cleared in recent times and is covered in light grass and weed with clusters of trees and palm trees distributed sporadically across the site (see photos 1 -3). 2.6 Existing Buildings and Structures

Buildings exist downslope of the site to the west, another exist immediately east. A number of structures also exist to the north of the site. The subject lot has a house and a series of retaining walls constructed on it

3. ASSESSMENT OF LAND STABILITY

3.1 Preliminary Evaluation

Google Earth and MiMap images did not show any obvious signs of recent or past deep seated instability for the images viewed. This is subsequently confirmed during site inspection and discussed in this report.

3.2 Existing Conditions

The following discussion is on existing surface and sub-surface conditions observed at the time of inspection for the site.

3.2.1 Surface Features

Natural ground slopes are gentle to steep (8 to 21), generally trending west. Original sections of the slope where cuts have been undertaken are steep to extremely steep (46 to 54°). The surface of the lot has been partially cleared around the house and the pad for the proposed shed. Landscaping has been undertaken with planted gardens (see photos 1-3). A few trees and palm trees exist on the slopes. A vegetable garden and minor landscaping exists immediately west of the western boundary within adjoining lot 29. An unsealed access road exists along the eastern boundary of the lot (see photo 2). An unsealed access tracks leads from the bitumen running along the northern boundary leading to a building platform at the north-western corner of the lot where the shed is proposed (see photo 5). The building platform was formed from a cut and fill operation. Rock retaining walls exist along cut and fill batters on the building platform (see photos 3, 4, 6, 9, 10 & 12). Site geomorphology indicates a wedge of fill has been placed to form the building platform (see cross section, Appendix B). This is confirmed with samples retrieved from the machine boreholes. Smaller step-type retaining structures are present up to the house, with a link-block wall immediately east of the house

Surface features are shown on engineering geology map (Appendix A).



3.2.2 Sub-surface Features

The local lithostratigraphy of the site generally comprised a veneer of topsoil overlying a variable thickness of colluvium (cobbles, boulders and blocks and fines) overlying ignimbrite. Where cuts have been performed extremely to slightly weathered, jointed ignimbrite was observed. Joints are plotted on site map (Appendix A). A wedge of fill exists on the platform with increasing thickness west. Borehole 2 indicates a fill thickness of 0.60m overlying residual soils. Dynamic cone penetrometers (DCP) testing indicate the underlying material within the building platform to be dense. The pad in front of the house has been created by cutting only and no fill is present in this area; the natural ground can be seen through the grasses and DCP testing in this area confirms the present of dense soils. Ground model for the site is synthesised from site observation and machine borehole sampling. The inferred ground model is presented on cross section A (Appendix B). No freewater or seepage was observed in boreholes or on slopes at the time of investigation.

3.3 Geotechnical Constraints to Development

Geotechnical constraints inferred from site observations and sub-surface investigation are discussed in table 5 for the proposed lots. The discussion follows the methods of AGS (2007) where qualitative risk is determined from the ‘likelihood’ and ‘consequences’ of an adverse event taking place. 3.3.1 Hillside Instability

Due to the steep nature of the site, hillside instability is considered possible. The mode of instability could be erosion and shallow failure in topsoil/colluvium and residual soils. The annual probability for this event is in the range of 200 to 2000 years. Such failures can be instigated by slope saturation from protracted rainfall, bush fire or by vegetation clearance and slope modification.

The consequences of such an event occurring is considered minor to medium and may be in the form of sediment inundation necessitating clean up; however, where boulder size material is involved the consequence will be significant especially for existing dwelling on lower slopes to the west of the site. Boulder release is discussed under ‘Debris Fall’.

Erosion is noted at the foot of the rock retaining walls and at the edge of the cut platform where surface water enters the rear of the retaining walls and discharges onto the edge of the platform (see photos 9-11). The risk from erosion and shallow failure of the slope above and below the building platform is assessed to be low. This is based on existing slope conditions at the time of investigation. Risk from global instability is considered to be very low.



3.3.2 Debris Fall

At the time of investigation cobbles and gravels were noted on the surface within the colluvium (See photos 5 & 8).

Loose material can pose a threat when they roll down slopes and release their energy upon impact. The amount of energy is a function of the size and density of the material, the geometry of the slope and other site specific material parameters. Of equal importance is the presence of source rock. Elevated area east of the lot has been developed hence there is no source for debris fall upslope of the lot. There was no fresh material noted on the natural slopes or on the cut platform.

From site investigation, the likelihood from material release is considered negligible to possible with a recurring interval between 200 to 1000 years for the majority of the slope. The consequence of material release is assessed to be moderate for existing dwelling downslope and proposed shed. However, debris fall from the existing rock retaining walls is considered unlikely as the walls have been engineered. Based on current slope conditions the risk from boulder release is considered low. Further discussion on the rock retaining wall is discussed under ‘Cut Batter Stability’. 3.3.3 Cut Batter Stability

Active erosion and scouring is noted at the foot of the unbounded rock retaining walls and at the edge of the cut platform (see photos 9-11)). Close inspection of the rock retaining walls indicate lack of drainage at the back of the walls. As such surface and sub-surface water enters the top and rear of the walls and exit at the foot of the walls causing erosion and scouring as observed during site inspection. Surface run-off from the existing access track discharges directly onto the building platform resulting in erosion at the edge of the platform. Further erosion is to be expected every time water reaches the walls. A recurrence interval of 1 to 100 years is assessed. This may occur during periods of protracted rainfall and at locations of concentrated surface run-off discharge. The consequence from failures may require cleaning up and removal of material from rear of proposed garage, hence it is categorised to be insignificant to medium. However, if erosion persists over a period of time it may result in the failure of the rock retaining walls. Failure of the retaining walls may have significant consequences on the existing dwelling downslope of the site, especially if boulders are dislodged downslope. Cardno UNG have been provided with Forms 15, 16 and 21 for the retaining walls on the site. Based on this premise, and assuming maintenance measures outline in section 6.4, the risk of failure of the retaining walls can be assessed as very low.



3.3.4 Failure within Fill

Forms 15, 16 and 21 have been sighted for the retaining walls around the proposed shed and at the rear of the property, hence the fill on the formed building platform for the shed is considered controlled fill.

Erosion is noted at edge of fill where surface run-off is discharged. A very low risk to failure of fill material is assessed and is discussed under sub-section 6.5.

4. DESCRIPTION OF PROPOSED DEVELOPMENT

4.1 Site Layout

Site layout for the proposed development is shown on engineering geology map (Appendix A). 4.2 Proposed Development Components

The proposed development will comprise a dwelling at the top of the slope and a shed toward the north-western corner of the site. Access roads will lead from the existing sealed road onto the dwelling and shed. 4.3 Potential Geotechnical Effects

The proposed development may have the potential effect of accelerating settlement of the existing uncontrolled fill and risk to failure of rock retaining walls. Mitigation measures to ensure a very low risk to instability are discussed under Section 6.0.

5. ASSESSMENT OF DEVELOPMENT IMPACTS

5.1 Site Layout

The proposed site layout is assessed to have very low impacts on the stability of the site. This can be maintained by implementing recommendations outlined in this report. 5.2 Roadworks, Driveways and Other Pavements

Inspection of existing sealed bitumen pavement did not show any signs of distress or fatigue. The proposed access to service the shed and dwelling is considered feasible. The access roads will need to be built on underlying weathered Ignimbrite rock as opposed to the colluvium. 5.3 Earthworks (excavation, material usage)

We understand the house platform has been levelled through cut, with no fill placed around the house or on the level of the proposed pool. Retaining structures less than 1m high have been constructed leading from the proposed pool area to the house. Rock was found at the eastern side of the house site while installing the retaining wall. A pad has been cut at the western frontage of the house which is the site of the proposed pool. We understand that this pad is comprised of cut only, with no fill. DCP testing was undertaken at various locations over the pad to determine the depth to rock over it, with indications being that the rock (presumably causing DCP refusal) is within



0.5m of the surface at the eastern side of the block nearest the house, and within 2m of the surface at the western extremity of the pad 5.4 Foundations

At the time this report was initially produced foundation dimensions were not available. It is envisaged all proposed structures will be socketed into underlying rock which should result in very low impact to landslip potential. Founding the dwelling in the colluvium is not recommended. The steep nature of the site means structures will need to piled and socketed into underlying rock. Where benches have been formed, shallow foundations can be utilised but should also be founded in underlying rock not colluvium. The house has since been constructed. 5.5 Surface Drainage

Under current conditions, natural surface drainage discharges onto the back of the retaining walls and at edge of the building platform, where the shed is proposed. All surface water should be diverted away from the retaining walls and building platform to prevent scouring, riling and erosion. 5.6 Wastewater (treatment & Disposal)

A septic system exists on the site, we understand that no on-site disposal is undertaken. 5.7 Proposed Swimming Pool

A pool is proposed for the cut pad on the western side of the house. We understand no fill is present on this pad, however, the proximity to slopes is notable and adequate set-back will be required so that no load is placed on the slopes. We understand that the proposed pool is 4.5m wide, with the cut platform approximately 12.5m wide, adequate space is present for a set-back of at least 3.5m from the base of either the retaining wall or the slope. An inspection of the site by a pool designer should be undertaken to ensure that the pool design is suitable for the block 5.8 Overall Effect of Development on Stability

The overall effect of the proposed development on the stability of the site and adjoining land and structures is considered to be of very low impact not withstanding recommendations outlined in this report.



6. MEASURES RECOMMENDED TO MITIGATE IMPACTS

6.1 General

This section discusses mitigating measures for issues identified under sub section 3.4 and sections 4 and 5. The measures provided are considered applicable to the proposed development. We note Mackay Regional Council (MRC) requires the risk level to be certified as very Low. The assessment is undertaken according to AGS (2007) where a low of level risk is recommended throughout the life of the property. This can be achieved via good construction and maintenance practice and landscaping design. To safeguard against instability and ensure the long term performance of the slopes and effectively maintain a Very Low Risk to Property and an Acceptable level to Risk to Loss of Life, consideration should be given to the following discussions.

6.2 Hillside Instability

Risk from erosion and shallow failures on the natural hillside (within the colluvium and topsoil) can be kept very low by effective slope management practices. It is strongly recommended that surface run-off is diverted at the top of the slope and discharged safely away from the slopes to prevent scouring, riling and erosion. Grass and other vegetation cover should be encouraged on the slopes. Vegetation assist slope stability via root binding effects and control moisture via evapotranspiration. Modification of the slope via earthworks may affect its stability. Any future earthworks on the slopes may require geotechnical input. The swimming pool should maintain a set-back of at least 3.5m from either the retaining wall at the eastern side of the platform, or the slope at the western side. We recommend that an inspection of the ground conditions be undertaken once the excavation is completed to ensure that ground conditions are commensurate with design expectations 6.3 Debris Fall

Debris fall originating at the top of the slope is considered unlikely as most of the site has been developed. A regular check should be made on the slopes say every two to five years or after heavy rainfall to clear loose boulders on the slope that are directly above the building footprint. The most likely source of debris fall is the existing rock retaining walls. Surface water should be prevented from entering the rear of the walls. Ongoing maintenance and regular checking of the walls is recommended.



6.4 Cut Batter Stability

Surface geomorphic processes naturally shape slopes to grades that ensure long term stability. The current existing batters are between 46 to 54 degrees from horizontal. Exposed ground should be vegetated to prevent scouring, riling and erosion. Surface run-off should be directed away from rock retaining walls to prevent scouring, erosion and riling. Appropriate drainage should be provided at the rear of the rock retaining walls. Surface drains should be lined to prevent water entering the slope via soil pores and joints in rock. Water provides destabilising mechanisms in slopes in the form of pore water and hydrostatic pressures. 6.5 Failure within Fill

It is recommended that the proposed shed is located within the footprint as shown on drawing 09-0233 by HR Design Group. Erosion has been noted within the fill and in the location of the retaining wall, this will require ongoing maintenance to ensure it does not propagate. Surface water should also be directed away from the building platform. 6.6 Foundation

The steep nature of the site means structures will need to be socketed into underlying rock. This can be achieved via piles where structures are to be founded on sloping ground. Where platforms have been created shallow foundation can be utilised but will need to be founded on natural ground. A geotechnical professional should be present during foundation investigation to confirm design intents have been achieved.

6.7 Earthworks

It is recommended that any earthworks is undertaken in accordance with AS3798-1996 “Guidelines on Earthworks for Commercial and Residential Developments” and local authority requirements. It is recommended that the earthworks contractor be familiar with site conditions. It is strongly recommended that all design and construction should be undertaken following and recognizing best practice for sloping sites. These are summarized in AGS (2007) figure shown in Appendix F.

6.8 Site Management

In order to minimise foundation movement, it is important that proper site management for the existing soil conditions are observed by both the builder at the time of the construction and the owner throughout the life of the proposed development.



We recommend that appropriate drainage be provided around houses to ensure adequate foundation performance and prevent scouring. It is also recommended that the ground around the building platform should slope away at 1 in 20 for 2m and then collected via surface drains and disposed of safely away from the slopes. Roof run-off should be collected and piped to a storage tank or discharged a safe distance away from slopes. It is recommended that future shrubs and trees be planted at a distance at least equivalent to their mature height away from the building to avoid shrinkage movement in the in-situ soils. On-site disposal of sewage is not recommended. It is strongly recommended that sewer should be connected to a public system. This report has been prepared based on the understanding that following the design and construction of the building, this document is passed onto the owner of the property, and that it is that person’s obligation to ensure that the document is passed onto future owners.



7. SUMMARY AND CONCLUSIONS

Findings and recommendations from our investigation are summarised as follows.

From site inspection no obvious past or recent instability was noted under static conditions within the study site. However, erosion is noted at the foot of the rock retaining walls and at the edge of the platform.

A fill wedge is noted to the south of the building platform. Fill thickness up to 0.6m was encountered in borehole two.

It is strongly recommended that foundation for the proposed structures be founded in natural ground. Under no circumstances should foundations be placed on colluvium.

A geotechnical professional should be present during foundation excavation to confirm foundation intents have been achieved.

The proposed shed should be located within the building footprint as shown on drawing 09-0233.

The proposed pool should be positioned with at least a 3.5m set-back on either side of the cut platform.

Surface run-off should be diverted away from the dwelling and exposed ground to prevent scouring, riling and erosion. Drains should be lined to prevent water entering the slopes.

Loose and unstable material (boulders) should be removed and regular inspections undertaken on slopes to remove or secure unstable boulders.

All cut batters should be retained to ensure long term stability. Appropriate drainage should also be provided at the back of the retaining walls. Forms 15, 16 and 21 have been sighted for the large retaining walls on the site

Disposal of sewage and stormwater on the surface is not recommended. It is assessed the proposed development will not alter the present state of stability of the

subject land or have an adverse impact on adjoining land and structures. It is the responsibility of the developer to ensure that all requirements of consenting and

local authorities are met. It is strongly recommended that all works performed on the slopes should be done

according to AGS (2007) ‘Management and Maintenance of Sloping Sites’. A copy is attached in Appendix D.

From our site inspection, sub-surface testing and analysis, we conclude the site is suitable for the proposed development and has a very low risk to land instability. This can be maintained throughout the life of the property by implementing recommendations outlined in this report.



8. LIMITATIONS

The findings presented in this report have been based on the investigation described in this report. There are always some variations in subsurface conditions across the site, which cannot be fully defined by investigation. It is likely that the measurements and values obtained from sampling and testing during the investigation will represent the extremes of conditions that may exist within the site. Hence it is recommended that if any ground conditions other than those described in this report are encountered during construction, further advice should be immediately sought from Cardno UNG. It is recommended that Cardno UNG be commissioned to provide a review of design and documentation to confirm that the intents of the geotechnical report are properly reflected in the designs. Similarly, inspection of the footing excavations is considered a prudent means of ensuring that ground conditions meet design expectations. This report has been prepared specifically for Chris and Colin Windsor and the project designers. Information contained in this report should not be construed as appropriate for any other purposes or for other users. Thank you for your commission to undertake this investigation. Should you have any queries, please do not hesitate to contact Trudie Bradbury at our Mackay office. Yours faithfully,

Karen Gates Trudie Bradbury Senior Geotechnical Engineer Senior Engineering Geologist for Cardno Ullman & Nolan Geotechnic


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APPENDIX A

Engineering Geological Map



APPENDIX B

Engineering Geological Cross Section



APPENDIX C

Descriptive Engineering Borehole Logs & Dynamic Cone Penetrometer Results

0.10

0.50

1.50

2.50

4.00

SM

SM

CL

SM

SM

L

D

D - M

M

Silty Clayey Sand; dark brown, fine to medium grained, with rootsMPS 2 LL 35 P75 45

Extremely Weathered Rock; yellow-brown mottled orange, recoversas silty clayey sand, fine grainedMPS 1 LL 25 P75 35

Extremely Weathered Rock; orange-brown, recovers as sandy siltyclay, fine grained sandMPS 1 LL 30 P75 55

Extremely Weathered Rock; brown mottled grey-orange, recovers assilty clayey sand, fine to medium grainedMPS 1 LL 25 P75 30

Extremely Weathered Rock; orange-brown, recovers as silty clayeysand, fine to coarse grained, with fine grained, angular to sub-angulargravelMPS 5 LL 25 P75 40

BH 1 TERMINATED AT 4.00 m

STRATA

Gra

phic

Log

Moi

stur

e

Dep

th (m

)

RL

(m N

/A)

Cla

ssifi

catio

n

Con

sist

ency

TESTINGVISUAL SOIL DESCRIPTION

Description(SOIL NAME; plasticity/grain size, colour, particle

shape, secondary components, minor constituents)(ROCK NAME; grain size, colour, minor constituents)

Contractor : Cardno UNGDrill Rig : Jacro 350Mounting : TruckDiameter:Coords : N/A

Hole Commenced : 22.6.09Hole Completed : 22.6.09Logged By : KPChecked By : TBSurface R.L. (m) : N/A

BOREHOLE LOGBorehole No. : BH 1

Sheet : 1 of 1

Client : Darrin HartProject : Slope Stabilty AssessmentJob No : U22597Site : 5A Bald Hill RoadLocation : Refer to Map

CU

_LIB

_05.

GLB

Log

CU

BO

RE

HO

LE L

OG

U22

597_

LOG

S.G

PJ

<<D

raw

ingF

ile>>

16/

07/2

009

12:3

2 8

.2.0

02

very softsoftfirmstiff

very stiffhard

very looseloose

medium densedense

very dense

DMW

DryMoistWet

MPSLLP75

UDNPP

CM

Moisture Visual Description Method Bit SupportConsistency SamplingCasing

MudRollerBlankV bit

TC bitDiamond

Maximum particle sizeLiquid Limit

% passing 75um sieve

RBVTD

AWPHCR

AugerWashbore

PercussionHammer

CoreRotary air flush

VSSFStVStHVLLMDDVD

Undisturbed Sample & Size in mmDisturbed Sample

Standard Penetration Test & ResultPocket Penetrometer Value

Bulk Sample

Sup

port

Met

hod

& B

it

TestingSampling

DRILLING

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0.20

0.60

0.90

2.30

3.50

CI

CH

CH

CL

CL

St

St - VSt

VSt

M

D

Sandy Clay; dark brown mottled brown-grey, low plasticity, fine tocoarse grained sand, trace organic inclusions (FILL)

MPS 2 LL 40 P75 65Clay; brown, low plasticity, with organic inclusions (FILL)

MPS 1 LL 60 P75 95

Clay; red-brown, low plasticity, trace sand (RESIDUAL SOIL)

MPS 2 LL 55 P75 90

Extremely Weathered Rock; yellow-brown, recovers as sandy clay,fine grained sandMPS 1 LL 30 P75 55

Extremely to highly Weathered Rock; yellow-brown, recovers assandy clay, fine grained sand, occasional light brown pocketsMPS 1 LL 25 P75 50

BH 2 TERMINATED AT 3.50 mRefusal

STRATA

Gra

phic

Log

Moi

stur

e

Dep

th (m

)

RL

(m N

/A)

Cla

ssifi

catio

n

Con

sist

ency

TESTINGVISUAL SOIL DESCRIPTION

Description(SOIL NAME; plasticity/grain size, colour, particle

shape, secondary components, minor constituents)(ROCK NAME; grain size, colour, minor constituents)

Contractor : Cardno UNGDrill Rig : Jacro 350Mounting : TruckDiameter:Coords : N/A

Hole Commenced : 22.6.09Hole Completed : 22.6.09Logged By : WSChecked By : TBSurface R.L. (m) : N/A

BOREHOLE LOGBorehole No. : BH 2

Sheet : 1 of 1

Client : Darrin HartProject : Slope Stabilty AssessmentJob No : U22597Site : 5A Bald Hill RoadLocation : Refer to Map

CU

_LIB

_05.

GLB

Log

CU

BO

RE

HO

LE L

OG

U22

597_

LOG

S.G

PJ

<<D

raw

ingF

ile>>

16/

07/2

009

12:3

2 8

.2.0

02

very softsoftfirmstiff

very stiffhard

very looseloose

medium densedense

very dense

DMW

DryMoistWet

MPSLLP75

UDNPP

CM

Moisture Visual Description Method Bit SupportConsistency SamplingCasing

MudRollerBlankV bit

TC bitDiamond

Maximum particle sizeLiquid Limit

% passing 75um sieve

RBVTD

AWPHCR

AugerWashbore

PercussionHammer

CoreRotary air flush

VSSFStVStHVLLMDDVD

Undisturbed Sample & Size in mmDisturbed Sample

Standard Penetration Test & ResultPocket Penetrometer Value

Bulk Sample

Sup

port

Met

hod

& B

it

TestingSampling

DRILLING

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

UNGR 92 G

(-/12/05)

Page 1 of 1 71 Connors Road, Mackay Laboratory

CLIENT: Darrin Hart JOB NO: U22597 LAB REF NO: 09-2936AB

PROJECT: TESTED BY: WS/SM DATE: 15.07.09

LOCATION: 5A Bald Hill Road, Glenella CHECKED BY: CM DATE: 15.07.09

TEST PROCEDURES : AS 1289.6.3.2 CLIENT REF: -

Test No.: A Test No.: BTest Location/Chainage : Test Location/Chainage :Ground Surface R.L. (m) : Ground Surface R.L. (m) :Depth Below Ground Depth Below GroundSurface at start of Test (mm): Surface at start of Test (mm):Soil Description : Soil Description :

Soil Moisture Condition: Refer to Logs Soil Moisture Condition: Refer to LogsDepth to Groundwater (m) : Depth to Groundwater (m) :

Cumulative Depth Below Penetration Cumulative Depth Below PenetrationNo. of Starting Level Rate No. of Starting Level RateBlows (mm) (mm/blow) Blows (mm) (mm/blow)

13 100 8 15 100 719 200 1728 300 11 Refusal38 400 1061 500 ### 4

#############################################

###############

Accredited No. 910

Certificate No. 09-2936A

Date of Issue 15.07.09

ULLMAN & NOLAN Technical Services Pty Ltd

A.C.N. 103 205 205DYNAMIC CONE PENETROMETER

- -

Slope Stabilty Assessment

Refer to Logs Refer to Logs

DCP A

Refer to Logs

DCP B

Refer to Logs

00

This document is issued in accordance with NATA's accreditationrequirements.

Authorised Signatory ...........................................................C. A. Murray

UNGR 92 G

(10/10)

Page 1 of 1 Mackay Laboratory

CLIENT: JOB NO: U22597 LAB REF NO: 14-1169AB

PROJECT: TESTED BY: WC DATE: 01.05.14

LOCATION: 4A Wright Street CHECKED BY: CM DATE: 01.05.14


Test No.: Test No.:Test Location/Chainage : Test Location/Chainage :Ground Surface R.L. (m) : Ground Surface R.L. (m) :Depth Below Ground Depth Below GroundSurface at start of Test (mm): Surface at start of Test (mm):Soil Description : Soil Description :

Soil Moisture Condition: Dry Soil Moisture Condition: DryDepth to Groundwater (m) : Depth to Groundwater (m) :


20 100 5 12 100 835 200 7 29 200 645 300 10 49 300 549 400 25 65 400 652 500 33 77 500 857 600 20 87 600 1068 700 9 96 700 1178 800 10 106 800 1086 900 13 115 900 1192 1000 17 125 1000 10

101 1100 11 136 1100 9113 1200 8 146 1200 10119 1300 17 152 1300 17128 1400 11 159 1400 14134 1500 17 175 1500 6142 1600 13 199 1600 4154 1700 8 224 1700 4164 1800 10189 1900 4

*DB

Accredited No. 910

Certificate No. 14-1169A


Colin Windsor

-

Pool Area Centre

-

--Natural Natural

CARDNO ULLMAN & NOLAN GEOTECHNIC PTY LTD

- -

Slope Stability Assessment

DYNAMIC CONE PENETROMETER

71 CONNORS ROAD MACKAY QLD

Pool Area West side

A B


Authorised Signatory ...........................................................

C A Murray

UNGR 92 G

(10/10)

Page 1 of 1 Mackay Laboratory

CLIENT: JOB NO: U22597 LAB REF NO: 14-1169CD

PROJECT: TESTED BY: WC DATE: 01.05.14

LOCATION: 4A Wright Street CHECKED BY: CM DATE: 01.05.14


Test No.: Test No.:Test Location/Chainage : Test Location/Chainage :Ground Surface R.L. (m) : Ground Surface R.L. (m) :Depth Below Ground Depth Below GroundSurface at start of Test (mm): Surface at start of Test (mm):Soil Description : Soil Description :

Soil Moisture Condition: Dry Soil Moisture Condition: DryDepth to Groundwater (m) : Depth to Groundwater (m) :


11 100 9 8 100 1318 200 14 24 200 626 300 13 40 300 630 400 25 58 400 640 500 10 78 500 560 600 5 103 600 485 700 4

*DB

Accredited No. 910

Certificate No. 14-1169C


Colin Windsor

-

Pool Area South East

-

--Natural Natural

CARDNO ULLMAN & NOLAN GEOTECHNIC PTY LTD

- -

Slope Stability Assessment

DYNAMIC CONE PENETROMETER

71 CONNORS ROAD MACKAY QLD

Pool Area South West

C D


Authorised Signatory ...........................................................

C A Murray



APPENDIX D

AGS (2007) Management & Maintenance of Sloping Sites

AUSTRALIAN GEOGUIDE LR8 (CONSTRUCTION PRACTICE)

HILLSIDE CONSTRUCTION PRACTICE

Sensible development practices are required when building on hillsides, particularly if the hillside has more than a low risk of instability (GeoGuide LR7). Only building techniques intended to maintain, or reduce, the overall level of landslide risk should be considered. Examples of good hillside construction practice are illustrated below.

WHY ARE THESE PRACTICES GOOD?

Roadways and parking areas - are paved and incorporate kerbs which prevent water discharging straight into the hillside (GeoGuide LR5).

Cuttings - are supported by retaining walls (GeoGuide LR6).

Retaining walls - are engineer designed to withstand the lateral earth pressures and surcharges expected, and include drains to prevent water pressures developing in the backfill. Where the ground slopes steeply down towards the high side of a retaining wall, the disturbing force (see GeoGuide LR6) can be two or more times that in level ground. Retaining walls must be designed taking these forces into account.

Sewage - whether treated or not is either taken away in pipes or contained in properly founded tanks so it cannot soak into the ground.

Surface water - from roofs and other hard surfaces is piped away to a suitable discharge point rather than being allowed to infiltrate into the ground. Preferably, the discharge point will be in a natural creek where ground water exits, rather than enters, the ground. Shallow, lined, drains on the surface can fulfil the same purpose (GeoGuide LR5).

Surface loads - are minimised. No fill embankments have been built. The house is a lightweight structure. Foundation loads have been taken down below the level at which a landslide is likely to occur and, preferably, to rock. This sort of construction is probably not applicable to soil slopes (GeoGuide LR3). If you are uncertain whether your site has rock near the surface, or is essentially a soil slope, you should engage a geotechnical practitioner to find out.

Flexible structures - have been used because they can tolerate a certain amount of movement with minimal signs of distress and maintain their functionality.

Vegetation clearance - on soil slopes has been kept to a reasonable minimum. Trees, and to a lesser extent smaller vegetation, take large quantities of water out of the ground every day. This lowers the ground water table, which in turn helps to maintain the stability of the slope. Large scale clearing can result in a rise in water table with a consequent increase in the likelihood of a landslide (GeoGuide LR5). An exception may have to be made to this rule on steep rock slopes where trees have little effect on the water table, but their roots pose a landslide hazard by dislodging boulders.

Possible effects of ignoring good construction practices are illustrated on page 2. Unfortunately, these poor construction practices are not as unusual as you might think and are often chosen because, on the face of it, they will save the developer, or owner, money. You should not lose sight of the fact that the cost and anguish associated with any one of the disasters illustrated, is likely to more than wipe out any apparent savings at the outset.

ADOPT GOOD PRACTICE ON HILLSIDE SITES

174 Australian Geomechanics Vol 42 No 1 March 2007

AUSTRALIAN GEOGUIDE LR8 (CONSTRUCTION PRACTICE)

WHY ARE THESE PRACTICES POOR?

Roadways and parking areas - are unsurfaced and lack proper table drains (gutters) causing surface water to pond and soak into the ground.

Cut and fill - has been used to balance earthworks quantities and level the site leaving unstable cut faces and added large surface loads to the ground. Failure to compact the fill properly has led to settlement, which will probably continue for several years after completion. The house and pool have been built on the fill and have settled with it and cracked. Leakage from the cracked pool and the applied surface loads from the fill have combined to cause landslides.

Retaining walls - have been avoided, to minimise cost, and hand placed rock walls used instead. Without applying engineering design principles, the walls have failed to provide the required support to the ground and have failed, creating a very dangerous situation.

A heavy, rigid, house - has been built on shallow, conventional, footings. Not only has the brickwork cracked because of the resulting ground movements, but it has also become involved in a man-made landslide.

Soak-away drainage - has been used for sewage and surface water run-off from roofs and pavements. This water soaks into the ground and raises the water table (GeoGuide LR5). Subsoil drains that run along the contours should be avoided for the same reason. If felt necessary, subsoil drains should run steeply downhill in a chevron, or herring bone, pattern. This may conflict with the requirements for effluent and surface water disposal (GeoGuide LR9) and if so, you will need to seek professional advice.

Rock debris - from landslides higher up on the slope seems likely to pass through the site. Such locations are often referred to by geotechnical practitioners as "debris flow paths". Rock is normally even denser than ordinary fill, so even quite modest boulders are likely to weigh many tonnes and do a lot of damage once they start to roll. Boulders have been known to travel hundreds of metres downhill leaving behind a trail of destruction.

Vegetation - has been completely cleared, leading to a possible rise in the water table and increased landslide risk (GeoGuide LR5).

DON'T CUT CORNERS ON HILLSIDE SITES - OBTAIN ADVICE FROM A GEOTECHNICAL PRACTITIONER

More information relevant to your particular situation may be found in other Australian GeoGuides:

• GeoGuide LR1 - Introduction • GeoGuide LR2 - Landslides • GeoGuide LR3 - Landslides in Soil • GeoGuide LR4 - Landslides in Rock • GeoGuide LR5 - Water & Drainage

• GeoGuide LR6 - Retaining Walls • GeoGuide LR7 - Landslide Risk • GeoGuide LR9 - Effluent & Surface Water Disposal

GeoGuide LR10 - Coastal Landslides • GeoGuide LR11 - Record Keeping

The Australian GeoGuides (LR series) are a set of publications intended for property owners; local councils; planning authorities; developers; insurers; lawyers and, in fact, anyone who lives with, or has an interest in, a natural or engineered slope, a cutting, or an excavation. They are intended to help you understand why slopes and retaining structures can be a hazard and what can be done with appropriate professional advice and local council approval (if required) to remove, reduce, or minimise the risk they represent. The GeoGuides have been prepared by the Australian Geomechanics Society, a specialist technical society within Engineers Australia, the national peak body for all engineering disciplines in Australia, whose members are professional geotechnical engineers and engineering geologists with a particular interest in ground engineering. The GeoGuides have been funded under the Australian governments’ National Disaster Mitigation Program.

Australian Geomechanics Vol 42 No 1 March 2007 175



APPENDIX E

Site Photos



Photo 1. View north across site.

Photo 2. View south along sealed driveway at top of lot.

Existing platform (proposed shed location)

Proposed Dwelling



Photo 3. View east, upslope of site.

Photo 4. View south-west onto building platform, note approx. fill line.

Cut platform (Proposed shed location)

Proposed Dwelling

`Fill



Photo 5. View east upslope along access track leading from building platform.

Photo 6. View south along building platform, note rock retaining walls.



Photo 7. Weathered rock exposure within building platform.

Photo 8. Typical colluvium cover.



Photo 9. View at rear rock retaining wall, note unbound nature of boulders & erosion at toe of wall, see geo-pick for scale.

Photo 10. View south along edge of rock retaining wall, note erosion.

Erosion



Photo 11. View along foot of lower wall, note erosion.

Photo 12. View at retaining wall, note size of material, see hammer for scale.



APPENDIX F

Certifications

REPORT ON STABILITY RISK ASSESSMENT 4A WRIGHTS ROAD, … · REPORT ON STABILITY RISK ASSESSMENT 4A...

Documents

Transcript of REPORT ON STABILITY RISK ASSESSMENT 4A WRIGHTS ROAD, … · REPORT ON STABILITY RISK ASSESSMENT 4A...