preliminary report on geotechnical investigation …

PRELIMINARY REPORT on GEOTECHNICAL INVESTIGATION PROPOSED MULTI STOREY BUILDING CORNER MARSDEN AND MACQUARIE STREETS PARRAMATTA Prepared for CROWN LANDMARK PTY LTD Project 71342 Revision 1 March 2010

PRELIMINARY REPORT on GEOTECHNICAL INVESTIGATION PROPOSED MULTI STOREY BUILDING CORNER MARSDEN AND MACQUARIE STREETS PARRAMATTA Prepared for CROWN LANDMARK PTY LTD Project 71342 Revision 1 March 2010

Douglas Partners Pty Ltd ABN 75 053 980 117

96 Hermitage Road West Ryde NSW 2114 Australia

PO Box 472 West Ryde NSW 1685 Phone (02) 9809 0666 Fax (02) 9809 4095 [email protected]

Proposed Multi Storey Building Project 71342 Rev 1 Corner Marsden and Macquarie Streets, Parramatta March 2010

TABLE OF CONTENTS Page 1. INTRODUCTION.......................................................................................................... 1 2. BACKGROUND ........................................................................................................... 2 3. SITE DESCRIPTION.................................................................................................... 4 4. GEOLOGY ................................................................................................................... 5 5. FIELD WORK............................................................................................................... 6

5.1 Field Work Methods ......................................................................................... 6 5.2 Field Work Results ........................................................................................... 6

5.2.1 Soil Stratigraphy ................................................................................... 6 5.2.2 Water Levels......................................................................................... 7 5.2.3 Strata Permeability ............................................................................... 8

6. LABORATORY TESTING ............................................................................................ 8 7. PROPOSED DEVELOPMENT................................................................................... 10 8. COMMENTS .............................................................................................................. 10

8.1 Geotechnical Model........................................................................................ 10 8.2 Excavation Conditions.................................................................................... 11 8.3 Vibration ......................................................................................................... 12 8.4 Excavation Support ........................................................................................ 12

8.4.1 Diaphragm Wall .................................................................................. 13 8.4.2 Secant Pile Wall.................................................................................. 14 8.4.3 Soldier Piles and Jet Grouting ............................................................ 14 8.4.4 Design Parameters ............................................................................. 14

8.5 Ground Anchors ............................................................................................. 15 8.6 Foundations.................................................................................................... 16 8.7 Groundwater Control ...................................................................................... 16 8.8 Acid Sulphate Soils ........................................................................................ 17 8.9 Further Work .................................................................................................. 18

APPENDIX A: Plans and Sections APPENDIX B: Borehole Results and Notes Relating to this Report APPENDIX C: Results of SPOCAS Testing APPENDIX D: Results of In Situ Permeability Tests

of 18


BOK:jlb Project 71342 Rev 1

10 March 2010

PRELIMINARY REPORT ON GEOTECHNICAL INVESTIGATION

PROPOSED MULTI STOREY BUILDING CORNER MARSDEN AND MACQUARIE STREETS

PARRAMATTA

1. INTRODUCTION

This preliminary report presents the results of a geotechnical investigation carried out by

Douglas Partners Pty Ltd (DP) for a proposed multi-storey building at the corner of Marsden and

Macquarie Streets, Parramatta. The work was commissioned by Mr Russel Strahle of Crown

Landmark Pty Ltd, developers for the project.

It is understood that the proposed development will now involve six levels of basement parking

over about two thirds of the site, a podium of three levels of commercial and retail outlets and a

twenty two level residential tower above the podium. The investigation was required to provide

information on subsurface conditions for the design of foundations and excavations, and to

assess groundwater levels and possible methods of designing a structure to accommodate

groundwater inflows. Some preliminary information on Acid Sulphate Soils (ASS) is also

provided in this report

The investigation comprised:

• Four additional boreholes to 16 boreholes drilled previously by Douglas Partners on the site;

• In situ testing to assess the engineering properties of the strata, to obtain samples for

identification purposes, and to enable laboratory testing to assess acid sulphate soil

conditions;

of 18


• Installation of standpipe piezometers for groundwater level measurements and for short

duration pump tests to assess the hydraulic characteristics of the local soils;

• Engineering evaluation and reporting.

Details of the fieldwork and laboratory testing are given in this report, together with some

preliminary comments relating to possible design and construction issues.

The investigation was limited to assessing the local soil and rock conditions on the site and the

geotechnical constraints imposed to the proposed development. The Douglas Partners

investigation did not include the assessment of contamination of soils and groundwater. The

investigation was carried out in accordance with DP’s proposal dated 27 July 2009.

A previous report for this project dated January 2010 was prepared on the understanding that

the development would comprise five basement levels to RL -5.3 m AHD. The increased depth

of excavation now proposed means that twelve of the eighteen bores completed during the

current and 1988 investigations have not penetrated below the proposed excavation level.

Moreover, the other six bores have finished only 0.6 – 1.6 m below excavation level. Therefore,

further testing will be needed during construction to confirm foundation conditions for pad

footings.

This report supercedes in every respect the preliminary report dated January 2010.

2. BACKGROUND

Douglas Partners has previously undertaken investigations on this site in 1962, 1980 and 1988.

These investigations comprised augered and cored boreholes to depths of up to 20 m below

ground surface level and in-situ testing to determine the engineering properties of the soils.

The two previous investigations carried out by DP on the current site in 1980 and 1988 (Project

Nos. 6746 and 11581) comprised a total of 16 boreholes (Bores 1 – 16) located at the positions

as shown in Drawing 1. The boreholes were drilled using auger/rotary rigs employing

of 18


continuous spiral flight auger and rotary methods in the upper clays and sands, with NMLC core

drilling used to penetrate the underlying rock, recovering 50 mm diameter continuous core

samples.

The detailed results of Bores 1 – 16 are given in Appendix B, together with accompanying notes

defining classification methods and descriptive terms. It is noted that the strength descriptions

for rock used in these borehole logs have been changed to be consistent with the current

Australian Standard for site investigation. Table 1 shows the relationship between terms in the

old discontinued classification system and the current one.

Table 1 – Strength Description and Terms for Shale / Siltstone

Previous Term Is50 (MPa) Current Term

Extremely weak < 0.03 Extremely low strength

Very weak 0.03 – 0.1 Very low strength

Weak 0.1 – 0.3 Low strength

Medium strong 0.3 – 1 Medium strength

Strong 1 – 3 High strength

Is(50) is Point Load Strength Index

Levels shown on borehole logs were determined using the current survey drawings, assuming

that the existing site levels are the same as or similar to the levels at which the boreholes were

drilled during the previous investigations. This is probably correct because the boreholes drilled

in 1988 (BH9 – 16) and three unlisted boreholes drilled in 1962 were levelled relative to

temporary benchmarks which were assigned levels of RL 100.0 ft (1962) and RL 100.0 m

(1988). These temporary benchmarks were on the kerb of surrounding streets and as the street

levels appear to have not changed and the boreholes were all at about street level it is

considered reasonable to assume that site levels have not changed substantially in the years

since the original investigations.

of 18


The principal strata penetrated by the boreholes during the previous investigations comprised:

Filling – Shallow filling at most locations, mainly to depths of 0.2 m – 1.4 m. The filling was

quite variable, but comprised mostly clay or sand soils with varying fractions of gravel, rubble

and topsoil.

Alluvium – Initially very stiff silty and sandy clays, becoming medium dense sands and silty

sands below depths of 5 m – 8 m. Somewhat different conditions were encountered in Bore 15,

near the middle of the site, where mainly sandy soils were encountered for the full depth to rock,

except for a 2 m thick layer of hard sandy clay around a depth of 3 m.

Residual Clay – A thin layer of hard shaly clay, generally less than 1 m thick but not present at

all locations. The shaly clay exhibited the characteristics of weathered shale from which the clay

was derived.

Rock – Shale at first, grading into laminite which, in the deeper boreholes (Bores 1, 8 and 9),

was underlain by fine and medium grained sandstone. The rock was mostly medium strength to

high strength, except for an upper weathered zone and minor defects in the form of seams and

joints as noted in the logs. The rock strength increased progressively with increasing depth, with

the laminite and sandstone beds containing generally high strength rock.

Groundwater was encountered in all of the boreholes at depths of 2.2 m – 6.2 m. Although

monitoring of groundwater in the boreholes did not extend over a sufficiently long period of time

to establish a definitive pattern, the lowest water table levels appear to be associated with the

lower portion of the site.

3. SITE DESCRIPTION

The currently undeveloped site (132 – 142 Marsden Street) is approximately rectangular with an

area of about 4900 m2. It is bounded on three sides by existing streets, having frontage to

Hunter Street (approximately 65 m), Marsden Street (85 m) and Macquarie Street (54 m). The

site is also bounded to the southwest by an existing two storey building and at the northwest by

of 18


31 – 39 Macquarie Street, which is a multistorey reinforced concrete building with one level of

basement car parking.

The site has a 2 – 3 m cross-fall in a northerly direction from Hunter Street to Macquarie Street

and has recently been used mainly as an open, generally unpaved car park (but with some

areas of remaining concrete floor slabs and bitumen pavements).

At the time of the current fieldwork, the site was occupied by two large corrugated iron sheds,

which it is understood are being used by archaeologists to study the remains of historical

building(s) that formerly occupied the site. It is further understood that the portion of the site

occupied by these sheds will not form part of the final site development.

A Douglas Partners report of July 2001 (6746A) noted that eight groups of piles had been

installed sometime after the previous investigation had been carried out in 1980. The piles were

intended for support of a then proposed building. These pile groups comprised closely spaced

auger grouted piles, presumably drilled to bedrock. It is assumed that these pile groups are now

buried by the current site filling and the proposed excavation may encounter these piles which

will then have to be removed unless they can be utilised for the current development. However,

for this reuse to be feasible, full details of the pile design and installation would need to be

available.

4. GEOLOGY

Reference to the Sydney 1:100,000 Geological Sheet indicates that the site is underlain by

Quaternary alluvium comprising silty sand, silt and clay, with bedrock in the area mapped as

Ashfield Shale within the Wianamatta Group of the Triassic Age.

It would appear that the site lies within a former channel of the Parramatta River because the

fieldwork has confirmed the presence of sand and clay to considerable depth overlying siltstone

(shale) and then sandstone. Further, at other locations in Parramatta the medium strength rock

is overlain by several metres of weathered rock which is mostly absent on this site, possibly due

to erosion by river flow in the former channel.

of 18


5. FIELD WORK

5.1 Field Work Methods

The field work for the current investigation comprised four boreholes (BH101-104) drilled with a

truck-mounted auger/rotary drilling rig to supplement the information already available for the

site. The boreholes were drilled initially through the soils to depths of between 14.5 m and

14.7 m using a 100 mm diameter continuous spiral flight auger and rotary drilling. Standard

penetration tests (SPTs) were carried out at regular depth intervals to assess the soil strength

and to obtain samples. Disturbed auger samples were also retrieved for identification and

laboratory testing purposes. The boreholes were then advanced into the bedrock using NMLC

size (50 mm diameter) diamond core drilling equipment to total depths of between 20.0 m and

20.35 m.

The locations of the previous and current boreholes are shown on Drawing 1 in Appendix A.

The assumed surface levels for boreholes from the previous investigations, used to produce

cross-sections, were taken from current contour/survey plans of the site. It is assumed that the

current levels of the site are the same as or similar to the levels at which the previous

geotechnical testing was carried out.

Following installation of two standpipe piezometers, short term pump tests were conducted to

evaluate the permeability of the alluvial soils. The tests were performed by adding water to

surface level in each of the piezometers and then recording the fall in water level with time.

5.2 Field Work Results

5.2.1 Soil Stratigraphy Details of the conditions encountered in the twenty boreholes drilled on the site are given in

Appendix B, together with notes defining classification methods and descriptive terms. Colour

photographs of the rock core recovered from each borehole are also included.

of 18


The recent boreholes encountered the following typical conditions:

FILLING – minor cemented sand / roadbase filling in all boreholes ranging from 0.3 m to 0.5 m

depth, with BH101 encountering a 0.1 m thick layer of concrete at 0.5 m overlying crushed

sandstone filling to 1.4 m depth.

SANDY CLAY/CLAYEY SAND AND CLAY – generally stiff and very stiff with varying

percentages of sand and clay. A very soft, 1.0 m thick layer of sandy clay was encountered in

BH102 at 7.0 m depth.

SAND - generally medium dense with a loose layer in BH103 at 8.0 – 10.0 m and a dense layer

in BH104 between depths of 8.0 m and 11.5 m.

CLAYEY SAND – encountered in BH102 only, medium dense to 14.0 m depth.

SHALE / SILTSTONE –variably weathered, initially extremely to very low strength grading to

medium and high strength, with some very high strength rock in BH101.

SANDSTONE – fresh, high strength with a very high strength layer in BH103.

Cross sections summarising the subsurface conditions at the boreholes completed during the

previous and current investigations are presented in Drawings 2, 3 and 4 in Appendix A.

5.2.2 Water Levels No free groundwater was observed in the boreholes during augering. The use of water for

flushing the boreholes during rotary and core drilling precluded groundwater observations below

about 2–3 m depth.

Groundwater level monitoring wells were installed at boreholes BH101 and BH104 to allow long

term monitoring of groundwater levels. A measurement was made of groundwater levels in the

standpipes piezometers on 21 October 2009. Table 2 presents a summary of the observed

groundwater levels.

of 18


Table 2 – Summary of Observed Groundwater Levels

Borehole Date Depth to

Groundwater (m)

Reduced Level (AHD) of

Groundwater

101 21-10-2009 4.55 5.95

104 21-10-2009 4.65 5.55

5.2.3 Strata Permeability The results of the short term permeability tests (SLUG Tests) are provided in Appendix D and

are summarised in Table 3 below.

Table 3 – Results of Permeability Tests

Borehole Estimated Hydraulic Conductivity (m/sec)

BH101 3.5 x 10-5

BH104 2.2 x 10-6

6. LABORATORY TESTING

Selected samples of rock core from the boreholes were tested for point load strength index

values (Is(50)). The results are presented on the borehole logs at the appropriate depths. The

tests gave (Is(50)) values mostly in the range of 0.6 MPa to 2.9 MPa indicating medium to high

strength rock, but with some (Is(50)) values of between 3.9 MPa to 5.0 MPa indicating very high

strength bands in BH101 and BH103. Inferred unconfined compressive strengths (UCS) range

from about 12 MPa to as high as 100 MPa (based upon an assumed UCS: (Is(50)) ratio of 20).

Soil samples, selected from three borehole locations, were tested to assess whether Potential

Acid Sulphate Soils (PASS) are present on the site. These tests included pH screening of 12

soil samples from the three boreholes and then detailed SPOCAS testing on four samples which

gave screening results indicative of PASS. Tables 4 and 5 present a summary of the laboratory

results. The detailed laboratory test result sheets are included in Appendix C.

of 18


Table 4 – Results of DP Laboratory pH Screening Bore No.

Depth (m) pHF pHFOX Strength of

reaction* Soil Description

101 10.0-10.45 7.98 6.10 1 Grey brown sand

101 13.0-13.45 7.78 1.90 1 Dark grey sand with some wood fragments

102 1.0-1.45 7.01 6.41 1 Grey and red brown clay 102 4.0-4.45 6.84 6.09 1 Light grey and brown sandy clay

102 7.0-7.45

7.83 7.50 1 Light grey and orange brown

clayey sand 102 8.5-8.95 7.67 7.07 1 Grey clayey sand 102 10.0-10.45 7.55 4.33 1 Dark grey clayey sand 104 8.5-8.95 8.47 7.22 1 Light brown sand 104 10.0-10.3 8.23 6.75 1 Light brown sand 104 10.3-10.4 8.17 5.93 1 Grey slightly silty sand 104 11.5-11.95 7.65 5.93 1 Light brown and grey sand 104 13.0-13.45 7.45 2.86 1 Grey sand

Notes: * Strength of reaction key: F after reaction number indicates a bubbly/frothy reaction 1 Denotes no or slight effervescence BOLD Selected for SPOCAS testing 2 Denotes moderate effervescence pHF pH in distilled water 3 Denotes vigorous effervescence pHFOX pH when oxidised in H2O2 4 Denotes very vigorous effervescence,

gas evolution and heat

Table 5 - Results of Laboratory Analysis for SPOCAS

Sample location and

depth SPOS (%)

SKCL

SP pHKCl pHox TPA

(Mol H+/ tonne)

TSA (Mol H+/ tonne)

101/13-13.45 0.66 0.021 0.68 5.7 2.4 280 278 102/8.5-8.95 <0.005 <0.005 <0.005 6.8 4.7 <5 <5

102/10.0-10.45 <0.005 <0.005 <0.005 6.7 4.9 <5 <5 104/13.0-13.45 0.030 0.007 0.037 6.2 3.9 <5 <5 Action Criteria*

(more than 1000 tonnes disturbed)

0.03 - - 4 3.5 18 18

Action Criteria* (less than 1000

tonnes disturbed)

0.06 - - 4 3.5 36 36

Notes: SCR Chromium Reducible Sulphur TAA Total Actual Acidity TPA Total Potential Acidity TSA Total Sulphidic Acidity (TPA-TAA) * Action Criteria based on ‘Medium Texture’, sandy loams to light clays Results in bold exceed the ASSMAC action criteria (Ref 1).

of 18


One sample tested (BH 101, 13.0 m to 13.45 m) exceeded the ‘Sulphur Trail’ and the ‘Acid Trail’

action criteria, indicating the presence of a minor amount of PASS beneath the site.

7. PROPOSED DEVELOPMENT

It is understood that the proposed development will comprise a multistorey residential and

commercial building with a six level basement. The supplied drawings by Bates Smart show

that the building is generally rectangular with the basement covering approximately two thirds of

the site.

The proposed basement level of the development is at approximately RL -8.3 AHD, with

excavations required to depths of approximately 18 m across the basement area.

No information has been provided to Douglas Partners on the likely foundation loads but given

the scope of the proposed development it is probable that the building will impose loads of about

15,000 – 20,000 kN on the building footings based upon an average building column spacing of

7.5 – 8.0 m.

8. COMMENTS

8.1 Geotechnical Model

The investigation indicates that the site is underlain by a relatively uniform strata sequence

comprising minor surface filling over saturated alluvial soils to depths of about 13 – 15 m,

overlying bedrock. The upper 6 – 8 m of alluvial profile includes sand, sandy clay and clayey

sand whereas the lower proportion of the alluvium is predominantly loose or medium dense

sand with some dense layers. Bedrock is at a depth of 13 – 15 m below the site and apart from

a 1 – 2 m extremely low or very low strength weathered zone, the material is generally medium

or high strength siltstone and sandstone.

of 18


Summary interpreted geological sections are given on Drawings 2 – 5 in Appendix A.

8.2 Excavation Conditions

The field investigation indicates that excavation to depths of about 13 m below existing surface

level should be relatively straightforward as the majority of the excavation will be through filling,

clay, shaly clay sand and extremely low to very low strength siltstone. All of these materials

should be easily removed using conventional earthmoving equipment although much of the

material will be saturated because it will be excavated from below the standing water table.

Further comments on dewatering and retention systems that are suitable for the site conditions

are given below.

Excavation below 13 – 15 m depth will take place through medium or high strength bedrock and

this will require heavy ripping with a dozer of at least D10 capacity and possibly with the

assistance from hydraulic rock breakers. The production rate for excavation of medium and high

strength bedrock may not be economical by ripping alone and therefore the use of hydraulic

rock breakers to split the rock may be necessary. In addition, the use of hydraulic rock

breakers, rock headers or rock saws may be required to remove material in the corners of

excavation and for trimming the face of the rock excavation.

The excavation rate that can be achieved in Ashfield Shale varies considerably and is

dependent upon the degree of jointing in the rock, the overall rock strengths, the type of

machinery being used and the skill of the operator. Some of these factors vary between

individual contractors and it is therefore recommended that a single unit rate be used for

excavation and that bulk excavation tenderers be required to make their own assessment of the

equipment required to carry out the work. This can be achieved by utilising the borehole

information provided and the core photographs, but it is recommended that contractors be

invited to inspect the cores before submitting their final price.

The investigation indicates that high and very high strength rock is generally at or slightly above

the base of the excavation. It is, however, possible that these units could be encountered in the

lower 2 – 4 m of the proposed bulk excavation, thus requiring heavy ripping.

of 18


8.3 Vibration

Vibration and noise associated with rock excavation, particularly the use of rock hammers may

result in some vibration and possibly complaints from occupants from neighbouring buildings

that are founded on piles to rock. However, it is unlikely that vibration will be a significant

problem for this site because excavation of rock will take place at a depth of about 15 m below

existing surface levels and presumably in excess of 10 m below basement levels of adjoining

structures. It is therefore likely that any vibration which is transmitted to pile foundations of

adjoining buildings will be dampened significantly before reaching areas where it could be felt by

people occupying these buildings.

The recommended maximum peak particle velocity from AS 2187 Explosives Code for various

structures subject to vibration is 10 mm/sec for houses and low rise residential buildings and

25 mm/sec for commercial and industrial buildings or structures of reinforced concrete or steel

construction. However, these values of peak particle velocity are meant to limit damage to

structures and do not take into consideration personal comfort. For this reason it is

recommended that the lower vibration level of 10 mm/sec be set for this particular site. This

takes into consideration that the excavation of rock using rock hammers or heavy ripping

equipment will be located well below street level and therefore there will be significant

dampening of any vibration due to excavation on the site.

8.4 Excavation Support

In order to be able to carry out the excavation to depths of about 18 m below existing site level a

permanent retaining wall system will be required to support the surrounding ground in both the

short term while excavation is being undertaken and also in the long term when the building

structure is competed. These retaining walls will also be required to fully seal the perimeter of

the site to prevent groundwater inflow as significant flows are likely through the sand strata

between depths of 6 m to 15 m below current site level. Further comments are given on

potential groundwater flow and dewatering in Section 8.7 below.

Three different types of retaining structures could be utilised for this site with each requiring

temporary anchors for support until the permanent structure is completed. Alternatively, top-

of 18


down construction techniques could be used such that the permanent support structure is

installed progressively as the excavation is deepened.

The three types of retaining structures that would be suitable for this site are:

• A diaphragm wall;

• A secant pile wall;

• A close spaced soldier pile wall with jet grouting.

8.4.1 Diaphragm Wall Given the conditions on this site it is suggested that a diaphragm system wall be adopted as this

will provide a permanent seal for the site and a low risk option that will prevent substantial

groundwater inflow in the short and long term. Secant pile walls can sometimes achieve an

acceptable seal to groundwater inflow but when installed to depths of 18 m or more some

misalignment of the piles could occur, thus resulting in substantial groundwater inflows into the

site. Close spaced soldier piles with jet grouting have been used previously on sites close to

Sydney Harbour but control of the jet grouting is often difficult and it can result in areas that are

not properly sealed. The lack of a complete seal can only be identified when excavation takes

place and at this stage secondary grouting is required to provide a complete seal.

Diaphragm walls are the most expensive type of structure but provide a clean finish to the inside

wall and would completely seal the site from all but minor groundwater seepage which may

occur as upflow through the siltstone and sandstone bedrock. The installation, however, does

require a considerable amount of plant because temporary support of the alluvial soils is

achieved by using bentonite. A de-sanding unit is required to clean the recycled bentonite and

grout pumps are necessary because of the very high volumes of concrete that must be used to

form the diaphragm wall. In addition, cranes will require access to the site for lifting

reinforcement cages and for inserting blockouts between each wall panel.

Diaphragm walls are constructed using a large grab which excavates the soil in panels with each

panel then cast using concrete tremmied into the bentonite supported excavation. The joints

between the panels are sealed with a waterstop so that a complete water tight wall is achieved.

The construction, however, is relatively slow but when diaphragm walls are socketed into

bedrock they provide a significant load capacity for the structure.

of 18


8.4.2 Secant Pile Wall Secant pile walls are formed by drilling alternate soft concrete piles and then installing

intermediate hard concrete piles by cutting into the previously drilled soft piles. This overlap

ensures that piles are sealed but even at relatively shallow depths some misalignment can occur

so that minor gaps appear in the wall. Secant pile walls are normally drilled through a top

template so it is necessary to excavate on adjoining sites to position the template so that the

outside of the secant pile wall will be directly along the boundary. Alternatively, the template can

be set-up entirely within the subject property but this means that the basement area is slightly

smaller than the overall site dimensions.

The potential for misalignment on deep secant pile walls is very high but if the secant pile wall

can be installed with only slight misalignment at the bottom of the wall a secant pile wall can

form a relatively water tight structure with only minor seepage. It may, however, be necessary to

also undertake jet grouting if misalignment does occur because the very high groundwater

pressures near the base of the excavation will probably mean that it is not feasible to patch any

minor gaps in the secant pile wall should they occur.

8.4.3 Soldier Piles and Jet Grouting A close spaced soldier pile wall with jet grouting is the third possible alternative which could be

considered for temporary retaining structures on this site. Essentially the piles would be drilled

at spacings of approximately 2 pile diameters and then the intermediate area jet grouted to

provide a complete seal. Jet grouting is quite effective in sandy or gravelly soils but sometimes

difficulties occur in clayey soils in achieving sufficient penetration to arch between the soldier

piles and to form a complete seal. It may therefore be necessary to undertake secondary

grouting as the excavation proceeds to ensure a completely watertight site.

8.4.4 Design Parameters Regardless of which wall type is chosen, temporary anchors will need to be installed to provide

support until the permanent structure is erected unless ‘top-down’ construction techniques are

adopted. Further advice on the design of ground anchors is given below.

In carrying out the design of a propped or anchored temporary and permanent retaining walls it

is suggested that a rectangular pressure distribution be assumed over the central 80% of the

of 18


wall height, tapering to zero at the top and bottom of the excavation. A design horizontal active

pressure of 7H (where H is the height of the excavation) could be adopted.

In order to ensure that an effective groundwater cut off is provided, it is suggested that the

retaining walls be taken to a depth of at least 1 m below the bulk excavation level. This will also

be required to ensure that sufficient toeing of the retaining wall is achieved to prevent substantial

horizontal movement of the toe of the wall when excavation is completed.

8.5 Ground Anchors

In order to provide temporary support for the retaining wall it will be necessary to install ground

anchors around the perimeter of the building. The only other alternative that is considered

feasible would be to adopt ‘top-down’ construction whereby the ground-floor slab is cast

immediately after the perimeter walls are installed to prop the excavation. Earthworks could

then be commenced and each successive floor slab installed as excavation continues

downwards. Top-down construction is normally much more expensive than conventional

techniques but avoids the need to install ground anchors under adjoining buildings or roadways.

In addition, very long anchors will be needed due to the very high loads and the low soil-grout

adhesion values that can be adopted for design.

The ground anchors should be drilled at approximately 30˚ below the horizontal and preferably

taken down to bedrock to obtain relatively high load capacity. However, for the upper row of

anchors it is unlikely that anchoring into bedrock would be feasible because the length of the

anchors will probably be in excess of 30 m and for the conditions encountered on this site it will

be extremely difficult for these anchors to be successfully installed through water charged

alluvial soils using normal construction techniques. For design purposes however, it is

suggested that a grout-soil adhesion value of 30 kPa be used with a grout-rock adhesion value

of 800 kPa for anchors drilled into medium high strength siltstone and sandstone.

In deciding whether temporary ground anchors are feasible it will be necessary to take into

consideration the likelihood that they will need to be installed between pile foundations of

adjoining buildings. If ground anchors are not feasible then ‘top-down’ construction is the only

of 18


alternative because it will not be possible to install a fully cantilevered retaining system that will

support the soil until the final structure is erected.

8.6 Foundations

At this stage, it would appear that the excavation to 18 m below existing surface level will mean

that medium or medium to high strength rock will be exposed in the base of the excavation. On

this basis, it is suggested that an allowable bearing pressure of 6000 kPa be used for footings

supported by medium / high strength rock. This bearing pressure is based upon limiting

settlement to less than 1% of the least footing dimensions but if higher settlements will not

severely affect the structure, increased bearing pressures could be adopted.

In order to verify the foundation design bearing pressure and to be able to provide an opinion on

the adequacy of the founding materials prior to pouring of concrete it will be necessary to carry

out detailed spoon testing of at least 50% of the footings immediately after excavation to check

that there are no soft seams below founding level. This is especially important as many of the

bores were discontinued above the now proposed bulk excavation level.

8.7 Groundwater Control

The investigation indicates that the groundwater level is approximately 4 m below current

surface levels and that the alluvial soils are saturated. It will therefore be necessary to design a

retention system which cuts off any groundwater inflow. It will also be necessary to

depressurise the bedrock during construction to prevent significant upflows through the bedrock

strata until after the building is erected. Likewise, it will be necessary to provide an under

drainage system beneath the lower basement floor slab to prevent uplift pressures on the floor

slab once construction is completed.

The investigation did not include hydraulic conductivity testing of the bedrock strata but testing

of the Ashfield Shale and other similar formations containing medium and high strength

sandstone lenses indicates permeability values of less than about 10-7 m/sec. Adopting this

value as the upper limit it is calculated that the upflow beneath a diaphragm or secant pile wall

of 18


installed to a 1.0 m depth below excavation level would be of the order of 0.2 m3 / day per m2 of

excavation floor area. It must be noted, however, this is based upon a hydraulic conductivity of

the bedrock strata of 10-7 m/sec and it may well be one or two orders of magnitude lower. If the

flow rates calculated on the basis of this hydraulic conductivity are much higher than can be

economically handled by an underfloor drainage and pump out system it would be necessary to

fully tank the basement to prevent any inflow of groundwater. Alternatively, it may be worthwhile

performing in-situ permeability testing on the bedrock to refine the estimate of potential upflow of

groundwater beneath the floor slab. A secondary consideration when deciding whether to tank

the basement or design a depressurised basement would be the quality of the groundwater.

Groundwater from within the Ashfield Shale is known to contain relatively high totally dissolved

solids and it may therefore be necessary to treat the groundwater before disposal to the

stormwater drainage system.

On the understanding that the perimeter walls will be effectively sealed into the bedrock there

will be a need to lower the groundwater levels within the site before excavation commences.

This could be achieved by large diameter bores sunk into the alluvial soils or by spear points.

On the basis of a drainable porosity of 0.20 (20%) for the alluvial soils it is estimated that

approximately 9000 m3 of water would need to be pumped from the site before the excavation

reached the full depth of approximately 18 m below current site level.

8.8 Acid Sulphate Soils

Testing indicates that some of the sandy soil at depths of about 8 – 13 m below the current

surface level is potential acid sulphate soil and will therefore require treatment before disposal.

However, only one of the 4 samples tested displayed characteristics of PASS with Total

Potential Acidity (TPA) and Total Sulphur Activity (TSA) above the guideline values. Therefore

only some of the soil will require treatment, on the basis of current testing, but it is not possible

at this stage to distinguish between soils requiring treatment and that which does not.

Consequently, it is recommended that further testing be undertaken when excavation is

underway to determine the extent of treatment. In the meantime, it would be prudent to assume

that 25% of the soils will need to be treated and disposed of as general solid waste (non

putrescible).

APPENDIX A Plans and Sections

SOIL CONSISTENCYvs - very softs - softf - firmst - stiffvst - very stiffh - hard

2

1

CORE LOSS

Clay

Cnr Macquarie & Marsden Streets, Parramatta

10101 103

A A'

Concrete

Sandstone coarse grained

Sandstone fine grained

SandN - Standard penetration test value

- Water levelSubsurface profile is accurate at borelocations only and may vary away frominvestigation locations

vl - very loosel - loosemd - medium densed - densevd - very dense

SITE MAPLEGEND DISTANCE ALONG PROFILE (m)

ELE

VATI

ON

(AH

D)

Proposed Multi Storey Building71342

Sandy Clay

Shale

Siltstone

Silty Clay

ROCK STRENGTHEL - Extremely LowVL - Very LowL - LowM - MediumH - HighVH - Very High

Clayey Sand

Filling

1: 250 (H)

Crown International Holding Group CROSS SECTION A-A'DRAWING No:

PROJECT No:

REVISION:10.3.2010

CLIENT:

DRAWN BY:

APPROVED BY:

SCALE:

DATE:

OFFICE:

TITLE:

LD

-20

-15

-10

-5

0

5

10

15

20

0 10 20 30 40 50 60 70 80

-20

-15

-10

-5

0

5

10

15

20

st

md

vst

EL

M

H

N = 7

N = 20

N = 14

10

vst

st-vst

md

md

d

VL-L

M

H

H-VH

H

refusal

N = 19

N = 13

N = 16

N = 12

N = 21

N = 12

N = 32

N = 34

refusal

101

st

st

md

vst

M

H,M-H

H

VH

H

N = 14

N = 18

N = 13

N = 13

N = 24

N = 5

N = 37

N = 22

TESTS / OTHER

N = 29

refusal

103

md

NOTE


3

1

TESTS / OTHERN - Standard penetration test value

- Water level

Filling

Topsoil


11216

B B'

Sandy Clay

Clayey Sand

Silty Sand

Sandvl - very loosel - loosemd - medium densed - densevd - very dense


ELE

VATI

ON

(AH

D)


Shale


Shaly Clay


Clay

Silty Clay

1: 250 (H)

Crown International Holding Group CROSS SECTION B-B'DRAWING No:

PROJECT No:

REVISION:10.3.2010

CLIENT:

DRAWN BY:

APPROVED BY:

SCALE:

DATE:

OFFICE:

TITLE:

LD

-20

-15

-10

-5

0

5

10

15

20

0 10 20 30 40 50 60 70 80

-20

-15

-10

-5

0

5

10

15

20

h

vst

st

st

d

md

md

VL-L

M

M

HH

N=14

N=13

N=10

N=7

N=30

N=35/150mm

N=13

N=23

N=30/50mm

1

vst-h

st

vst

M

H

N = 17

N = 13

12

h

md-d

md

EL-VL

M

H

N = 14

N = 30

refusal

N = 23

16

h

Subsurface profile is accurate at borelocations only and may vary away frominvestigation locations

NOTE

-20

-15

-10

-5

0

5

10

15

20

0 10 20 30 40 50 60 70 80

-20

-15

-10

-5

0

5

10

15

20

vst

vst

L-M

H

N = 9

N = 20

13

h

h

md-d

md

EL-VL

M

H

N = 14

N = 30

refusal

N = 23

16

vst

st-vst

md

md

d

VL-L

M

H

H-VH

H

refusal

N = 19

N = 13

N = 16

N = 12

N = 21

N = 12

N = 32

N = 34

refusal

101

l

st

vst

md

vs

d

md

md-d

EL-VL

M

H

N = 9

N = 10

N = 17

N = 16

N = 1

N = 38

N = 17

N = 13

N = 29

refusal

102


4

1

TESTS / OTHERN - Standard penetration test value

- Water level

CORE LOSS

Clay


13

16

101

102

C C'

Concrete


Sandy Clay



ELE

VATI

ON

(AH

D)


Shale

Shaly Clay

Siltstone

Silty Sand


Clayey Sand

Filling

1: 250 (H)

Crown International Holding Group CROSS SECTION C-C'DRAWING No:

PROJECT No:

REVISION:10.3.2010

CLIENT:

DRAWN BY:

APPROVED BY:

SCALE:

DATE:

OFFICE:

TITLE:

LD


NOTE


5

1

N - Standard penetration test value- Water level

Filling

Topsoil


15

9

103

104

D D'

Sandy Clay

Clayey Sand

Silty Sand



ELE

VATI

ON

(AH

D)


Shale


Shaly Clay

Laminite

Siltstone



Clay

Silty Clay

1: 250 (H)

Crown International Holding Group CROSS SECTION D-D'DRAWING No:

PROJECT No:

REVISION:10.3.2010

CLIENT:

DRAWN BY:

APPROVED BY:

SCALE:

DATE:

OFFICE:

TITLE:

LD

-20

-15

-10

-5

0

5

10

15

20

0 10 20 30 40 50 60 70 80

-20

-15

-10

-5

0

5

10

15

20

h

vst

st

st

d

md

md

VL-L

M

M

HH

N=14

N=13

N=10

N=7

N=30

N=35/150mm

N=13

N=23

N=30/50mm

1

md

hEL-VL

L

M

MH

5

st-vst

md

vstEL-VL

M-H

H

H

N = 20

N = 17

9

st

st

md

vst

l-md

M

H,M-H

H

VH

H

N = 14

N = 18

N = 13

N = 13

N = 24

N = 5

N = 37

N = 22

N = 29

refusal

103

st

st

md

d

md

EL-VL

M-H

H

H

N = 15

N = 10

N = 15

N = 13

N = 14

N = 39

refusal

N = 24

N = 18

104


TESTS / OTHER NOTE

APPENDIX B Borehole Results

Notes Relating to this Report

NOTES RELATING TO THIS REPORT Introduction

These notes have been provided to amplify the geotechnical report in regard to classification methods, specialist field procedures and certain matters relating to the Discussion and Comments section. Not all, of course, are necessarily relevant to all reports.

Geotechnical reports are based on information gained from limited subsurface test boring and sampling, supplemented by knowledge of local geology and experience. For this reason, they must be regarded as interpretive rather than factual documents, limited to some extent by the scope of information on which they rely.

Description and Classification Methods The methods of description and classification of soils

and rocks used in this report are based on Australian Standard 1726, Geotechnical Site Investigations Code. In general, descriptions cover the following properties - strength or density, colour, structure, soil or rock type and inclusions.

Soil types are described according to the predominating particle size, qualified by the grading of other particles present (eg. sandy clay) on the following bases:

Soil Classification Particle Size

Clay less than 0.002 mm Silt 0.002 to 0.06 mm Sand 0.06 to 2.00 mm Gravel 2.00 to 60.00 mm

Cohesive soils are classified on the basis of strength

either by laboratory testing or engineering examination. The strength terms are defined as follows.

Classification Undrained

Shear Strength kPa Very soft less than 12 Soft 12—25 Firm 25—50 Stiff 50—100 Very stiff 100—200 Hard Greater than 200

Non-cohesive soils are classified on the basis of

relative density, generally from the results of standard penetration tests (SPT) or Dutch cone penetrometer tests (CPT) as below:

Relative Density SPT “N” Value (blows/300 mm)

CPT Cone Value (qc — MPa)

Very loose less than 5 less than 2 Loose 5—10 2—5 Medium dense 10—30 5—15 Dense 30—50 15—25

Very dense greater than 50 greater than 25 Rock types are classified by their geological names.

Where relevant, further information regarding rock classification is given on the following sheet.

Sampling Sampling is carried out during drilling to allow

engineering examination (and laboratory testing where required) of the soil or rock.

Disturbed samples taken during drilling provide information on colour, type, inclusions and, depending upon the degree of disturbance, some information on strength and structure.

Undisturbed samples are taken by pushing a thin-walled sample tube into the soil and withdrawing with a sample of the soil in a relatively undisturbed state. Such samples yield information on structure and strength, and are necessary for laboratory determination of shear strength and compressibility. Undisturbed sampling is generally effective only in cohesive soils.

Details of the type and method of sampling are given in the report.

Drilling Methods. The following is a brief summary of drilling methods

currently adopted by the Company and some comments on their use and application.

Test Pits — these are excavated with a backhoe or a tracked excavator, allowing close examination of the in-situ soils if it is safe to descent into the pit. The depth of penetration is limited to about 3 m for a backhoe and up to 6 m for an excavator. A potential disadvantage is the disturbance caused by the excavation.

Large Diameter Auger (eg. Pengo) — the hole is advanced by a rotating plate or short spiral auger, generally 300 mm or larger in diameter. The cuttings are returned to the surface at intervals (generally of not more than 0.5 m) and are disturbed but usually unchanged in moisture content. Identification of soil strata is generally much more reliable than with continuous spiral flight augers, and is usually supplemented by occasional undisturbed tube sampling.

Continuous Sample Drilling — the hole is advanced by pushing a 100 mm diameter socket into the ground and withdrawing it at intervals to extrude the sample. This is the most reliable method of drilling in soils, since moisture content is unchanged and soil structure, strength, etc. is only marginally affected.

Continuous Spiral Flight Augers — the hole is advanced using 90—115 mm diameter continuous spiral flight augers which are withdrawn at intervals to allow

Issued: October 1998 Page 1 of 4

sampling or in-situ testing. This is a relatively economical means of drilling in clays and in sands above the water table. Samples are returned to the surface, or may be collected after withdrawal of the auger flights, but they are very disturbed and may be contaminated. Information from the drilling (as distinct from specific sampling by SPTs or undisturbed samples) is of relatively lower reliability, due to remoulding, contamination or softening of samples by ground water. Non-core Rotary Drilling — the hole is advanced by a rotary bit, with water being pumped down the drill rods and returned up the annulus, carrying the drill cuttings. Only major changes in stratification can be determined from the cuttings, together with some information from ‘feel’ and rate of penetration. Rotary Mud Drilling — similar to rotary drilling, but using drilling mud as a circulating fluid. The mud tends to mask the cuttings and reliable identification is again only possible from separate intact sampling (eg. from SPT). Continuous Core Drilling — a continuous core sample is obtained using a diamond-tipped core barrel, usually 50 mm internal diameter. Provided full core recovery is achieved (which is not always possible in very weak rocks and granular soils), this technique provides a very reliable (but relatively expensive) method of investigation. Standard Penetration Tests

Standard penetration tests (abbreviated as SPT) are used mainly in non-cohesive soils, but occasionally also in cohesive soils as a means of determining density or strength and also of obtaining a relatively undisturbed sample. The test procedure is described in Australian Standard 1289, “Methods of Testing Soils for Engineering Purposes” — Test 6.3.1.

The test is carried out in a borehole by driving a 50 mm diameter split sample tube under the impact of a 63 kg hammer with a free fall of 760 mm. It is normal for the tube to be driven in three successive 150 mm increments and the ‘N’ value is taken as the number of blows for the last 300 mm. In dense sands, very hard clays or weak rock, the full 450 mm penetration may not be practicable and the test is discontinued.

The test results are reported in the following form. • In the case where full penetration is obtained with

successive blow counts for each 150 mm of say 4, 6 and 7 as 4, 6, 7 N = 13

• In the case where the test is discontinued short of full penetration, say after 15 blows for the first 150 mm and 30 blows for the next 40 mm as 15, 30/40 mm. The results of the tests can be related empirically to the

engineering properties of the soil. Occasionally, the test method is used to obtain

samples in 50 mm diameter thin walled sample tubes in clays. In such circumstances, the test results are shown on the borelogs in brackets.

Cone Penetrometer Testing and Interpretation Cone penetrometer testing (sometimes referred to as

Dutch cone — abbreviated as CPT) described in this report has been carried out using an electrical friction cone penetrometer. The test is described in Australian Standard 1289, Test 6.4.1.

In the tests, a 35 mm diameter rod with a cone-tipped end is pushed continuously into the soil, the reaction being provided by a specially designed truck or rig which is fitted with an hydraulic ram system. Measurements are made of the end bearing resistance on the cone and the friction resistance on a separate 130 mm long sleeve, immediately behind the cone. Transducers in the tip of the assembly are connected by electrical wires passing through the centre of the push rods to an amplifier and recorder unit mounted on the control truck.

As penetration occurs (at a rate of approximately 20 mm per second) the information is plotted on a computer screen and at the end of the test is stored on the computer for later plotting of the results.

The information provided on the plotted results comprises: — • Cone resistance — the actual end bearing force

divided by the cross sectional area of the cone — expressed in MPa.

• Sleeve friction — the frictional force on the sleeve divided by the surface area — expressed in kPa.

• Friction ratio — the ratio of sleeve friction to cone resistance, expressed in percent. There are two scales available for measurement of

cone resistance. The lower scale (0—5 MPa) is used in very soft soils where increased sensitivity is required and is shown in the graphs as a dotted line. The main scale (0—50 MPa) is less sensitive and is shown as a full line.

The ratios of the sleeve friction to cone resistance will vary with the type of soil encountered, with higher relative friction in clays than in sands. Friction ratios of 1%—2% are commonly encountered in sands and very soft clays rising to 4%—10% in stiff clays.

In sands, the relationship between cone resistance and SPT value is commonly in the range:—

qc (MPa) = (0.4 to 0.6) N (blows per 300 mm) In clays, the relationship between undrained shear

strength and cone resistance is commonly in the range:— qc = (12 to 18) cu

Interpretation of CPT values can also be made to allow estimation of modulus or compressibility values to allow calculation of foundation settlements.

Inferred stratification as shown on the attached reports is assessed from the cone and friction traces and from experience and information from nearby boreholes, etc. This information is presented for general guidance, but must be regarded as being to some extent interpretive. The test method provides a continuous profile of engineering properties, and where precise information on


soil classification is required, direct drilling and sampling may be preferable.

• Water table levels will vary from time to time with seasons or recent weather changes. They may not be the same at the time of construction as are indicated in the report.

Hand Penetrometers

• The use of water or mud as a drilling fluid will mask any ground water inflow. Water has to be blown out of the hole and drilling mud must first be washed out of the hole if water observations are to be made.

Hand penetrometer tests are carried out by driving a rod into the ground with a falling weight hammer and measuring the blows for successive 150 mm increments of penetration. Normally, there is a depth limitation of 1.2 m but this may be extended in certain conditions by the use of extension rods.

More reliable measurements can be made by installing standpipes which are read at intervals over several days, or perhaps weeks for low permeability soils. Piezometers, sealed in a particular stratum, may be advisable in low permeability soils or where there may be interference from a perched water table.

Two relatively similar tests are used. • Perth sand penetrometer — a 16 mm diameter flat-

ended rod is driven with a 9 kg hammer, dropping 600 mm (AS 1289, Test 6.3.3). This test was developed for testing the density of sands (originating in Perth) and is mainly used in granular soils and filling.

Engineering Reports

• Cone penetrometer (sometimes known as the Scala Penetrometer) — a 16 mm rod with a 20 mm diameter cone end is driven with a 9 kg hammer dropping 510 mm (AS 1289, Test 6.3.2). The test was developed initially for pavement subgrade investigations, and published correlations of the test results with California bearing ratio have been published by various Road Authorities.

Engineering reports are prepared by qualified personnel and are based on the information obtained and on current engineering standards of interpretation and analysis. Where the report has been prepared for a specific design proposal (eg. a three storey building), the information and interpretation may not be relevant if the design proposal is changed (eg. to a twenty storey building). If this happens, the Company will be pleased to review the report and the sufficiency of the investigation work.

Laboratory Testing Every care is taken with the report as it relates to interpretation of subsurface condition, discussion of geotechnical aspects and recommendations or suggestions for design and construction. However, the Company cannot always anticipate or assume responsibility for:

Laboratory testing is carried out in accordance with Australian Standard 1289 “Methods of Testing Soil for Engineering Purposes”. Details of the test procedure used are given on the individual report forms.

• unexpected variations in ground conditions — the

potential for this will depend partly on bore spacing and sampling frequency

Bore Logs The bore logs presented herein are an engineering

and/or geological interpretation of the subsurface conditions, and their reliability will depend to some extent on frequency of sampling and the method of drilling. Ideally, continuous undisturbed sampling or core drilling will provide the most reliable assessment, but this is not always practicable, or possible to justify on economic grounds. In any case, the boreholes represent only a very small sample of the total subsurface profile.

• changes in policy or interpretation of policy by statutory authorities

• the actions of contractors responding to commercial pressures. If these occur, the Company will be pleased to assist

with investigation or advice to resolve the matter.

Interpretation of the information and its application to design and construction should therefore take into account the spacing of boreholes, the frequency of sampling and the possibility of other than ‘straight line’ variations between the boreholes.

Site Anomalies In the event that conditions encountered on site during

construction appear to vary from those which were expected from the information contained in the report, the Company requests that it immediately be notified. Most problems are much more readily resolved when conditions are exposed than at some later stage, well after the event.

Ground Water

Where ground water levels are measured in boreholes, there are several potential problems;

Reproduction of Information for Contractual Purposes

• In low permeability soils, ground water although present, may enter the hole slowly or perhaps not at all during the time it is left open. Attention is drawn to the document “Guidelines for the

Provision of Geotechnical Information in Tender Documents”, published by the Institution of Engineers,

• A localised perched water table may lead to an erroneous indication of the true water table.



Australia. Where information obtained from this investigation is provided for tendering purposes, it is recommended that all information, including the written report and discussion, be made available. In circumstances where the discussion or comments section is not relevant to the contractual situation, it may be appropriate to prepare a specially edited document. The Company would be pleased to assist in this regard and/or to make additional report copies available for contract purposes at a nominal charge.

Site Inspection The Company will always be pleased to provide

engineering inspection services for geotechnical aspects of work to which this report is related. This could range from a site visit to confirm that conditions exposed are as expected, to full time engineering presence on site.

Copyright © 1998 Douglas Partners Pty Ltd

APPENDIX C Results of SPOCAS Testing

APPENDIX D Results of In Situ Permeability Tests