words, maps, and photographs which might identify the site...

William C Cromer Pty. Ltd. 74A Channel Highway Taroona, Tasmania 7053 Australi a

Mobile 0408 122 127 Fax 03 6227 9456 www.billcrom er.com.au email [email protected]

NEW GIRL GUIDES HALL RECREATION GROUND

BOX HILL ROAD CLAREMONT

GEOTECHNICAL SUMMARY

In general accordance with AS1726 (1993) Geotechnical Site Investigations

SITE (SOIL TEST) CLASSIFICATION

In general accordance with AS2870 (1996) Residential slabs and footings – Construction

AND

WIND LOAD CLASSIFICATION In general accordance with AS4055 (2006) Wind loads for housing

Municipality Client Location Proposed development Date of inspection

WILLIAM C. CROMER PTY. LTD. ACN 009 531 613 ABN 48 009 531 613

ENVIRONMENTAL, ENGINEERING AND GROUNDWATER GEOLOGISTS C C W

Words, maps, and photographs which might identify the site of this report have been deleted

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Geotechnical summary, site (soil test) and wind classifications DATE

William C Cromer Pty Ltd 74A Channel Highway Taroona Tasmania 7053

Environmental, engineering and groundwater geologists

Mobile 0408 122 127 email [email protected]

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Refer to this report as Cromer, W. C. (2011). Geotechnical summary, site classification and wind classification, new Girl Guides Hall, Box Hill Road, Claremont. (Unpublished report for Claremont RSL by William C. Cromer Pty. Ltd., 19 January 2011; 29 pages including 12 pages of CSIRO information bulletins). William C Cromer Pty Ltd may submit hard or electro nic copies of this report to Mineral Resources Tasmania to enhance the geotechnical data base of Tasmania. Important Note Permission is hereby given by William C. Cromer as author, and the client, for this report to be copied and distributed to interested parties, but only if it is reproduced in colour, and only distributed in full. No responsibility is otherwise taken for the contents. This report includes three copyrighted CSIRO information bulletins which cannot be copied. Purchase originals of these from CSIRO Publishing Phone (03) 9662 7500, Fax (03) 9662 7555 www.publish.csiro.au, or William C. Cromer Pty. Ltd. The CSIRO documents form an integral part of this report and shall not be omitted from copies of it.

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SUMMARY STATEMENTS

Geotechnical risk Risks associated with a variety of geotechnical hazards potentially affecting a new Girl Guides Hall on the Box Hill Road recreation ground in Claremont are mainly in the Very Low to Moderate range (see Attachment 4) and can be addressed by standard management techniques. Reactive and low strength clayey soil, and surface drainage, are higher risks. Recommendations are made to manage the risks.

AS2870 Site Classification In accordance with Australian Standard 2870 (2011) Residential slabs and footings, the proposed development site (encompassed by area abcd in Attachment 2 to this report) is classified as Class P (it would have been Class E based on soil reactivity alone). Footings for Class P sites require certification by a suitably experienced engineer. It is recommended that footings be piered to depths around 1.5m. The reasons for the Class P classification are discussed in Attachment 4.

AS4055 Wind Classification In accordance with Australian Standard 4055 (2006) Wind loads for housing, the following wind load classification apply to the development site: Wind region A Terrain Category classification TC2 Topographic classification T1 Shielding classification NS Wind classification N2 Max. Design Gust Wind Speed for house 26m/s (Vh, s); 40m/s (Vh, u)

W. C. Cromer Principal 19 January 2011 This report is and must remain accompanied by the f ollowing Attachments Attachment 1. Location, aerial photography and published geology of the property (1 page) Attachment 2. Satellite image of the property showing test pit locations, and the area abcd to which the AS2870 site

classification applies (1 page) Attachment 3. Test pit logs, interpretation of site geology; AS2870 site classification and Notes for Designers,

Builders and Owners (6 pages) Attachment 4. Summary of geotechnical hazards, risks and consequences to development site, and suggested

risk treatment practices (1 page), and Terminology used in geotechnical risk assessment (1 page)

Attachment 5. Three 4-page CSIRO pamphlets (13 pages): CSIRO Information sheet BTF 18. Foundation Maintenance and Footing Performance: A Homeowner’s Guide (replaces Information Sheet 10/91; dated 2003) CSIRO Building Technology File No. 19. A builder’s guide to preventing damage to dwellings. Part 1 – Site investigation and preparation (February 2003) CSIRO Building Technology File No. 22. A builder’s guide to preventing damage to dwellings. Part 2 – Sound construction methods (August 2003) Designers, builders and developers are encouraged t o read these publications, and the other Attachments to this report.

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Attachment 1

(1 page) Location, aerial photography and published geology of the property

Sources: www.thelist.tas.gov.au, Google Earth and Mineral Resources Tasmania

Aerial photography

Location

Geology source: Calver, C. R., Latinovic, M., Forsyth, S. M., Clarke, M. J. and Ezzy, A. R. (2004). Map 2, Glenorchy – Geology. Tasmanian Landslide Hazard Series. Mineral Resources Tasmania. Key to rock types and colours Light brown = Unconsolidated Tertiary-age sediments (clay, sand, gravel, etc)

Published geology

Approx. metres All images same scale

0 200

GN

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Attachment 2

(1 page) Satellite imagery of the property showing test pit locations,

and the area abcd to which the AS2870 site classifi cation applies Source: Google Earth

GN

0

Approx metres

10 20

Deleted

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Attachment 3 (6 pages including this page)

Test pit logs, interpretation of site geology, AS28 70 site classification and Notes for Designers, Builders and Owners

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Gravelly CLAY: brown; moderate plasticity

Topsoil

CLAY: patchy grey and light yellow; high plasticity; trace to some silt and sand

End as required, 1.8m in unconsolidated Tertiary sediments

Soil over Tertiary sediments U50

0.3 – 0.6m

U50 0.7 – 1.0m

Excavation log Pit A

Sheet 1 of 1

Project Location Coordinates

RL

Datum

Dimensions (m) Depth 1.8 Length 2 Width 0.5

Exposure type Equipment

Operator

Date dug Date logged

Logged by Checked by

Materials Soil type, colour, plasticity or

particle characteristics, secondary and minor components

Notes

Samples and tests

metres

Gra

phic

log

Wat

er

Structure, geology and interpretation

William C. Cromer Pty. Ltd. Environmental, enginee ring and groundwater geologists

16

18

GDA94

RL

Dep

th

Pen

etra

tion

Moi

stur

e co

nditi

on

Con

sist

ency

D

ensi

ty in

dex Hand

penetr-ometer

(kPa)

25

50

100

200

400

Consistency (silt, clay, sandy clay, silty clay) VS = Very soft (<25kPa; exudes in fingers when squeezed); S = Soft (25-50kPa; easily penetrated by fist); F = Firm (50-100kPa; easily penetrated by thumb); St = Stiff (100-200kPa; indented by thumb, penetrated with difficulty); VSt= Very Stiff (200-400kPa; easily penetrated by thumbnail); H = Hard (>400kPa; indented by thumbnail with difficulty); Fb = Friable (crumbles or powders when scraped by thumbnail) Relative density (sand and gravel) VL = Very loose (ravelling); L = Loose (easy shovelling); MD = Medium dense (hard shovelling); D = Dense (picking); VD = Very dense (hard picking)

1 2 3

US

CS

m

She

ar

Van

e

(kPa)

Dyn

amic

co

ne

pene

trom

(Blows per 100mm)

2 4 6 8 10

Strength

Water level

Water inflow

Water outflow

GNE = Groundwater not encountered

Water

Moisture D = Dry M = Moist W = Wet

Penetration

V and H scale

m

1 2 3 4

Refusal

No resistance

Graphic log key

CLAY (CH, CL)

SAND (SP)

SILT (SM)

GRAVEL (GP, GW)

COBBLES (63-200mm) BOULDERS (>200mm) SHELLS SHELL FRAGMENTS ROOTS FRACTURES

New Girl Guides Hall Recreation Ground, Box Hill Road, Claremont23 December 2010 23 December 2010

W. C. Cromer W. C. Cromer

Test pit 1.5t excavator; 0.4m bucket; 4 teeth

Seaton Waterfield

520938mE; 5262220mN

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Ponded rainwater

N S 0.25

0.25

W S GC

CH M>>PL S

F

46

58

60

Dynamic cone penetrometer

U50 0.3 – 0.6m

U50 0.7 – 1.0m

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Sandy SILT: brown; low plasticity

Topsoil

Silty CLAY and CLAY: grey brown grading to olive brown below about 0.6m; high plasticity; trace sand; occasional cream/white sand patches

End as required, 1.8m in unconsolidated Tertiary sediments

Soil over Tertiary sediments

U50 0.6 – 0.9m

Excavation log Pit B

Sheet 1 of 1

Project Location Coordinates

RL

Datum

Dimensions (m) Depth 1.8 Length 2 Width 0.5

Exposure type Equipment

Operator

Date dug Date logged

Logged by Checked by

Materials Soil type, colour, plasticity or

particle characteristics, secondary and minor components

Notes

Samples and tests

metres

Gra

phic

log

Wat

er

Structure, geology and interpretation

William C. Cromer Pty. Ltd. Environmental, enginee ring and groundwater geologists

16

18

GDA94

RL

Dep

th

Pen

etra

tion

Moi

stur

e co

nditi

on

Con

sist

ency

D

ensi

ty in

dex Hand

penetr-ometer

(kPa)

25

50

100

200

400

Consistency (silt, clay, sandy clay, silty clay) VS = Very soft (<25kPa; exudes in fingers when squeezed); S = Soft (25-50kPa; easily penetrated by fist); F = Firm (50-100kPa; easily penetrated by thumb); St = Stiff (100-200kPa; indented by thumb, penetrated with difficulty); VSt= Very Stiff (200-400kPa; easily penetrated by thumbnail); H = Hard (>400kPa; indented by thumbnail with difficulty); Fb = Friable (crumbles or powders when scraped by thumbnail) Relative density (sand and gravel) VL = Very loose (ravelling); L = Loose (easy shovelling); MD = Medium dense (hard shovelling); D = Dense (picking); VD = Very dense (hard picking)

1 2 3

US

CS

m

She

ar

Van

e

(kPa)

Dyn

amic

co

ne

pene

trom

(Blows per 100mm)

2 4 6 8 10

Strength

Water level

Water inflow

Water outflow

GNE = Groundwater not encountered

Water

Moisture D = Dry M = Moist W = Wet

Penetration

V and H scale

m

1 2 3 4

Refusal

No resistance

Graphic log key

CLAY (CH, CL)

SAND (SP)

SILT (SM)

GRAVEL (GP, GW)

COBBLES (63-200mm) BOULDERS (>200mm) SHELLS SHELL FRAGMENTS ROOTS FRACTURES

New Girl Guides Hall Recreation Ground, Box Hill Road, Claremont23 December 2010 23 December 2010

W. C. Cromer W. C. Cromer

Test pit 1.5t excavator; 0.4m bucket; 4 teeth

Seaton Waterfield

520928mE; 5262208mN

0.5

1.0

1.5

2.0

2.5

3.0

3.5

N S 0.25

0.25

D Fb SP

CH M<>PL VSt 104

176

200

Dynamic cone penetrometer

U50 0.7 – 1.0m

176

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Geology and Soils Geology The published geological map (Attachment 1) of the Glenorchy area indicates the site is underlain by Tertiary-age unconsolidated sediments. There are no outcrops in the vicinity, but the materials exposed in test pits A and B (see logs, this Attachment) are consistent with the published geology. Both test pits intersected only high plasticity clay to depths of up to 1.8m. Soils The soil around the Girl Guides Hall is a thin topsoil of gravely clay and sandy silt about 0.1m thick. All or some of it may have been imported. Evidence of slope instability at the site No evidence. General area is almost flat and at a low risk of slope instability. Fill Not observed Bearing capacities of materials See the test pit logs. The clay in test pit A was of low strength in the upper 0.5m or so because of its high moisture content. This in turn is because the northeastern corner of the site is poorly drained, and water ponds there after rain. The clay in pit B was of higher strength in the surface 0.5m or so, but of lower strength at greater depths. The shear vane results (see test pit logs) suggest that the clay in test pit A is of inadequate bearing capacity, and that in test pit B is probably of adequate bearing capacity. Shallow groundwater Groundwater was not observed in either test pit. AS2870 site classification Soil reactivity and shrink swell testing To test the reactivity of the subsoil materials, and to assist in site classification in accordance with AS2870, two undisturbed sample from pit A, and one from pit B, were collected for testing1 to estimate their Shrink-Swell Indices (Iss). The test results were: Pit A (0.3 to 0.6 CLAY (CH); light olive brown; high plasticity; on Tertiary sediments

Initial moisture content 28% Swelling strain 0.7% Shrinkage strain 7.9% Shrink swell index (I ss) = 4.6%

Pit A (0.7 to 1.0 CLAY (CH); light olive brown; high plasticity; on Tertiary sediments


1 Although William C. Cromer Pty. Ltd. is not NATA registered, testing was performed essentially in accordance with AS1289.7.1.1-1998. Methods of testing soils for engineering purposes. Method 7.1.1. Soil reactivity tests – Determination of the shrinkage index of a soil – Shrink-swell index. Standards Australia. From the Shrink-Swell index, the maximum ground surface movement can be estimated, and hence the site classification.

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Pit B (0.6 to 0.9 CLAY (CH); light olive brown; high plasticity; on Tertiary sediments


These values of Iss are towards the high end of the moderate range. I have assumed a range of 4 – 5% to be fairly representative of soils at the site. When this range is applied to the clay thicknesses in each test pit the following estimated ground surface movements2 result:

Test pit A Estimated ground surface movement in the range 75 – 95mm (Class E) Test pit B Estimated ground surface movement in the range 75 – 95mm (Class E)

These estimated ground surface movements are in keeping with site observations: the northeastern side of the building has risen by a similar amount relative to the rest of the structure, probably because of the different moisture contents. Site classification On the basis of clay reactivity alone, the AS2870 class at the development site (area abcd in Attachment 2) would be Class E, but variably inadequate clay bearing capacity and the need to improve site drainage means Class P is more appropriate to alert designers and builders. Footings for class P (and E) sites require certification by an engineer experienced in footing design. Notes for designers and builders Variability of subsurface conditions’ Subsurface conditions encountered during construction which appear to differ significantly from those described here should be immediately brought to my attention. Footings It is understood a slab on ground is contemplated for the new Girl Guides Hall. While a stiffened slab could be designed to cope with uniform ground surface movements for Class E sites, differential ground surface movement remains a possibility, and a slab on ground might tilt. It is therefore suggested that piers to depths of at least 1.5m or so be part of the footing design to support the slab. Drainage All surface and roof runoff shall be adequately controlled and diverted away from the development. The present ground surface needs to be regraded to prevent ponding of water. Fill Presumably no fill will be used on site.

2

Notes 1 Regional suction base depth = 2m 2 Change in suction at surface = 1.5pF 3 Assumes layer will be completely dry and completely wet at surface during a 50 year period 4 AS2870 classifications

Class Ground surface movement A 0 – 10mm S 10 – 20mm M 20 – 40mm H 40 – 70mm E >70mm

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Preventing damage to buildings In conjunction with the site specific suggestions in the present report, read the CSIRO Bulletins BTF19 and 22 in Attachment 6. Notes for owners and occupiers Information bulletins Read the CSIRO Bulletin BTF18 in Attachment 6 of this report.

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Attachment 4 Summary of geotechnical issues, risks and consequen ces to development site, and suggested risk treatment practices (1 page), Terminology used in geotechnical risk assessment (1 page), and Examples of good and poor hillside engineering prac tices (2 pages)

Table 4.1 Summary of potential geotechnical issues, risks and consequences to development site, and suggested risk treatment prac tices

A B C D

Issue Likelihood of occurrence

Consequences to property

Level of risk to property Risk treatment

1 Surface soil erosion Unlikely Minor Low Control stormwater and surface runoff. Prevent surface ponding. See this report.

2 Tunnel erosion Unlikely Minor Low As for hazard 1

3 Soil creep Rare Minor Very low As for hazard 1

4 Shallow-seated landslide (involving, for example, soil, boulder beds, talus, colluvium, etc)

Rare Minor Very low As for hazard 1.

5 Deep-seated landslide (involving, for example, boulder beds, talus, colluvium, bedrock etc)

Barely credible Major Very low As for hazard 1

6 Foundation movement due to reactive soils

Almost certain Medium Very high See this AS2870 site classification report by William C. Cromer Pty. Ltd. Design footings accordingly.

7 Low strength materials (eg uncontrolled fill, soft soils)

Likely Medium High As for Hazard 6

8 Vegetation removal/planting

Unlikely Minor Low Avoid removing or planting deep rooted/large trees close to the building

9 Flooding Unlikely Minor Low As for hazard 1

10 Waterlogging, restricted drainage

Likely Medium High As for hazard 1

11 Riverbank collapse Not applicable

12 On-site wastewater disposal

Not applicable

13 Site contamination from previous activities

Unlikely Minor Low Visual examination during development; manage if required

14 Earthquake risk Almost certain (magnitude <5); Likely (magnitude>5)

Insignificant to Minor

Low to Moderate Generally accept risk. A similar risk or range of risks exists throughout Tasmania.

15 Sea level rise Not applicable

Notes

1. The assessments in Columns A, B and C are unavoidably subjective to varying degrees.

2. See the next page for an explanation of the terms used in this table.

3. Further reading: Australian Geomechanics Society Subcommittee (2007). Landslide Risk Management. Aust. Geomechanics 42(1) March 2007

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Terminology used in geotechnical risk assessment (1 page)

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Examples of good and poor hillside engineering prac tices (2 pages)

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Attachment 5 (13 pages including this page)

Three 4-page CSIRO pamphlets CSIRO Information sheet BTF 18. Foundation Maintenance and Footing Performance: A Homeowner’s Guide (replaces Information Sheet 10/91; dated 2003) CSIRO Building Technology File No. 19. A builder’s guide to preventing damage to dwellings. Part 1 – Site investigation and preparation (February 2003) CSIRO Building Technology File No. 22. A builder’s guide to preventing damage to dwellings. Part 2 – Sound construction methods (August 2003)

Deleted

words, maps, and photographs which might identify the site...

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