Impacts of Basement Excavation on Ann St Abutment … George St Redevelopment Impact of Basement...

300 GEORGE ST REDEVELOPMENT

IMPACT OF PROPOSED BASEMENT EXCAVATION ON THE

ANN STREET ONRAMP STRUCTURES

BONACCI GROUP

DOCUMENT HISTORY

ISSUE REVISION DATE AUTHOR REVIEWER

Issued for DTMR Review A October 11, 2013 R. West

RPEQ 13523

J. Velosa

RPEQ 2586

Issued for DA B November 1, 2013 R. West

RPEQ 13523

J. Velosa

RPEQ 2586

300 George St Redevelopment

Impact of Basement Excavation on Ann Street On-Ramp

2

1 INTRODUCTION

The proposed redevelopment of the old Supreme Court site in Brisbane, located at 300 George St,

involves the construction of an integrated commercial, residential and retail development consisting

of three high-rise towers, located over a common podium with seven levels of underground

basement.

The existing site is bounded by George St to the east, Adelaide St to the south, North Quay to the

west and Ann St on the north.

Aerial Photo of Existing Site

Immediately adjacent to the existing site is the Ann Street on-ramp onto the Riverside Expressway,

which consists of a single lane, five span continuous, post-tensioned curved concrete box girder

bridge with insitu concrete abutments and approach structure at the Gorge St end.

2 SCOPE AND LIMITATIONS

The purpose of this report is to identify the impacts on the existing Ann Street Bridge and supporting

structures to enable the Department of Transport and Main Roads (TMR), to develop a set of

compliance measures which would form part of the Development Application.

TMR have advised (email on the 20/8/2013) that;

• the developers are to ensure that the displacements of footings / piles supporting existing bridges / on-ramp are such that the performance of these structures are not compromised;

• lateral displacements arising from excavations and how this will be managed should they be adverse and impair on the functionality of adjacent buildings and other road assets should be documented;



3

The main body of the Report discusses the overall impacts due to the excavation and proposes a way

forward to reach approval for the Development. The detailed analysis and discussion is included in 3

main appendices as follows:

• Analysis of soil behavior and resulting movements on structures. Prepared by Golder

Associates

• Analysis of the 5 span bridge deck, columns and Abutment A (River side). Prepared by Nick

Stevens Consulting

• Analysis of Abutment B (George St side) and approach structure. Prepared by Bonacci

This report is based on information currently available and may include further analysis on receipt of

further information. The intention is however to inform TMR on our key findings at key stages in the

process and assist TMR in drafting the relevant and appropriate conditions for the proposed

development in a timely manner.

It is understood that the On-ramp was temporarily closed to traffic in 2006, following the discovery

of excessive twist in the box girder. The Report does not address the state of the structure “as is”,

however it recognizes that the excavation impacts will add to the current status.

Traffic loads were assumed to be those included in the prevailing Code at the time of construction of

the bridge (early 1970), i.e T44.

3 ON-RAMP STRUCTURE

The On-ramp structure is described in detail in Appendix C and drawings are included in Appendix D.

The following details are of particular significance:

• The approach ramp from George St is a suspended slab/beam arrangement supported on

side walls which in turn are supported on bored piles. These piles are found on low to

medium strength weathered rock. The space underneath the slab is void.

• The River end of the approach structure is supported vertically on a pile cap which also

supports the abutment. The support is via a sliding joint. The pile cap covers 6 raked and

vertical bored piles.

• The abutment supports the end of the bridge girder via 2 pot bearings and a central restraint

in both longitudinal and transverse directions

• The side walls of the approach structure and abutment wall are covered with a decorative

concrete block veneer.

• The first bridge column coming from George St is supported on a high level pad footing. The

remaining columns are on piles

The Positive Stop Barrier constructed in 2009 is a separate steel portal frame supported on piles.

Due to the flexibility of the frame it will not be further discussed in this report.

.



4

4 BASEMENT EXCAVATION IMPACT

The proposed basement involves the construction of a composite steel soldier and shotcrete wall to

retain the surface soils and medium-low strength rock, and a solid shotcrete wall facing to the more

competent rock below. The wall is tied back progressively with stressed anchors as the excavation

progresses. The lowest basement level B7 is approximately 20m below the surface.

Appendix A gives further details on the excavation and retention.

Impacts on the On-ramp are:

• Short term. As the excavation progresses the relaxation of the soil mass invariably causes

settlement and horizontal displacement of the wall. This happens regardless of the amount

of stressing used in the tie backs. The soil movement causes pile settlement and potentially

horizontal displacement. More importantly is the potential differential settlement between

piles which imposes additional stresses on the structure.

• Long term. The basement slabs, which prop the excavation in the long term, will undergo

shrinkage and creep over time. Whilst the majority of the movement will occur in the initial,

say 2 years, while the stressed anchors are still effective, a residual movement can be

expected after that. This effect has been considered in our analysis

5 FINDINGS OF THE ANALYSIS

Key findings are summarized below:

• Per Golders geotechnical analysis, dated 30/10/13 and attached in Appendix A, the expected

maximum short term settlement is in the order of 2mm (where the wall is supported by the

ground anchors) and 7mm maximum long term settlement, allowing for shrinkage of the

basement slabs over 30 years.

• Our preliminary analysis has considered 10mm as differential settlement between piles to

cater for uncertainty and cover the worst possible scenario. This movement is considered to

be manageable, involving only light repair measures to the approach structure if it was to

eventuate. For the Ann Street bridge girder, the impacts of a 20mm settlement has also

been reviewed, with the results included in the separate report by Nick Stevens, attached in

Appendix B.

• The current twisting of the bridge girder at Abutment B with the inside (North) bearing

lifting during periods of high temperature will not be aggravated. This is because the

abutment is almost certain to rotate in the other direction

• Lateral movement at abutment B will not impact the bridge deck. However a potential

opening of the expansion joint at abutment A has to be addressed.



5

6 PREVENTATIVE MEASURES AND MONITORING OF BRIDGE STRUCTURES DURING

EXCAVATION

Although every effort has been made to protect these structures, it is possible that the resulting

relaxation of the soil/rock around and under the existing Ann Street structures may result in

settlements greater than the 10mm allowed for in our review.

The approach adopted to minimize these risks and to rectify possible damage is as follows:

1. Design of the new basement such that potential soil movement is minimized

• Increasing perimeter wall stiffness alongside the ramp structure and providing additional

soldiers in the vicinity of the bridge foundations

• Provide additional redundant ground anchors in the vicinity of the existing bridge to

allow for additional prestress to be applied to the wall.

2. Design of the retention system and construction sequence to minimize movement

• Reduced spacing and higher stressing forces on the ground anchors

• Excavate the basement walls with hit and miss excavation to minimize movement of the

unrestrained wall.

• To minimize the resulting movement in the wall due to shrinkage of the carpark slabs, a

gap will be left between wall and slab, for as long as possible to allow the slabs to

stabilize. This gap will be closed with a fine concrete mix as late as practical during the

construction of the development (minimum of 18months, but possibly even later as this

is not disruptive to progressing the basement construction).

3. Implement a monitoring programme

• Main Roads have requested that a comprehensive monitoring programme be

implemented by an independent Consultant. It is assumed that movements to be

measured would include vertical and lateral displacements as well as rotations and tilt.

4. Develop contingency plans to deal with worst case scenarios

• The structural review of the bridge deck and its bearings has concluded that:

(i) the bridge deck can tolerate differential vertical deflection in the order of 10mm

without being affected, and can accommodate a 20mm maximum settlement

with minor impact.

(ii) Possible twisting of the deck due to settlements of the piles would actually

improve the current state of the bridge bearings.

(iii) Lateral displacement can also be tolerated provided the existing bearings have

sufficient reserve travel to accommodate the expected horizontal movement.

Prior to commencing site activities it is envisaged that the current status of the bearings (at

abutments and piers) will be surveyed and inspected. This would form part of the

independent assessment and monitoring programme mentioned above.



6

In the unlikely event that the predicted displacements are exceeded and the deck

performance is compromised, the bearings would need adjustment. The process to

implement these adjustments would have to be developed with Main Roads in order to

ultimately obtain their approval.

A review of the Ann St Approach Structure has revealed that relatively small differential settlements

between piles may overstress the walls and cause cracking in the walls of this structure. Although

the walls have more than enough reserve structural capacity to support the design loads, the

resulting cracks may make the structure more vulnerable to corrosion. Should the settlements of the

piles exceed the allowable range, the strategy is to monitor the structure during excavation and to

repair any cracks that may occur should the movements exceed the permissible values. This would

involve removing and reinstating the existing block wall veneer and then injecting the cracks with an

approved repair method.

7 CONCLUSIONS

A detailed structural design review has been undertaken for the Ann Street bridge girder, abutment

and approach structures for the case of a 10mm maximum vertical and horizontal displacement. This

exceeds a maximum calculated displacement of 7mm as determined by Golders Associates in their

report dated 30/1/13.

A structural review of the bridge girder and abutment indicates that these structures can

accommodate these displacements without distress, and potentially have sufficient capacity to

accommodate up to 20mm displacement with minor impact.

The approach structure is much more sensitive to differential settlements between the supporting

piles, due to its very high stiffness, and may crack if the differential settlements exceed predictions.

Should this occur, any cracking will not substantially reduce the load capacity of this structure, and is

primarily a durability concern with any resulting damage be rectified to TMR’s satisfaction.



7

8 APPENDIX A – ANN ST BOUNDARY WALL ANALYSIS RESULTS – GOLDER ASSOCIATES



8

9 APPENDIX B – EFFECTS OF ABUTMENT SETTLEMENT ON ANN ST RAMP

SUPERSTRUCTURE - NICK STEVENS CONSULTING

Nick Stevens Consulting Pty Ltd ABN 51 070 172 271

Nick Stevens BE PhD (Toronto) MIE Aust RPEQ

1/54 Kersley RdKenmore Q 4069PO Box 655Kenmore Q 4069

Ph +617 3878 6286M +614 1902 4983

Report

On

Effects of Abutment Settlement on the Ann StRamp Superstructure

Client Bonacci Group (Qld) Pty Ltd

Project 300 George St – Ann St Ramp Abutment

Issue Date 29 October 2013

Document No: NSC270-TR-02 Rev 0

1.0 Introduction

Bonacci are providing engineering services for the design of the proposed developmentat 300 George St. This site is immediately adjacent to the abutment for the Ann Staccess ramp onto the Riverside Expressway. This structure is a 5 span curved posttensioned concrete box girder.

The excavation for the proposed development will extend to well below the foundinglevels for the Ann St Ramp abutment. Hence some movement of the abutment can beexpected as a result of the excavation.

Bonacci have engaged Dr Nick Stevens of Nick Stevens Consulting Pty Ltd (NSC) toinvestigate the effects of any settlement at the abutment on the bridge superstructure.

A preliminary assessment of the issue has already been undertaken and is reported on indocument NSC270-TR-01. That assessment indicated that the ramp would be relativelytolerant to small settlements at Abutment B.

This assessment includes a more detailed analysis model. Also, as a result ofgeotechnical modeling by others, Bonacci have now provided design and extreme casesettlements which will form the basis of the assessment.

This report summarizes the results of the assessment.

2.0 Description of the Structure

The structure is a 5 span, double cell concrete box girder. It is post tensioned, and wasconstructed in stages. The staged construction can be expected to have had an effect onthe long term final stress state in the bridge.

The Department of Transport and Main Roads (TMR) chainage for this structureincreases from the river end to the city end so in accordance with standard practice, inthis report, the abutment and pier numbering starts from the river end. Abutment A is



the column supporting the river end and Abutment B is the abutment on Ann St whichis of interest. Pier 4 is the Pier on Ann St which also may be affected by the excavation.

Abutment B is supported on piles, however Pier 4 is supported on a high level spreadfooting.

The articulation of the superstructure is as follows:

Abutment A: Two bearings effectively preventing twist about the bridge centreline. Free to move along bridge centre line, but restrained transversely.

Piers 1 to 4: Vertical support only – free to move longitudinally and transverselyand to rotate in any direction.

Abutment B: Two bearings effectively preventing twist about the bridge centreline. Restrained longitudinally and transversely.

The restraints at the abutments are independent of the bearings and are located under thecenterline of the girder.

The bearings at Abutments A and B that are on inside of the ramp curve are referred toas the inner bearings, and those on the outside of the curve are referred to as the outerbearings.

In 2006 it was discovered that a combination of prestressing effects and long termcreep and shrinkage had caused the girder to twist significantly with the inside edge ofthe curved girder lifting up. A hot top temperature condition further exacerbates thistwist. The twist is to the extent that the inner bearing at Abutment A has permanentlylifted off, and the inner bearing at Abutment B lifts off consistently on hot days.

3.0 Expected Settlements

The design settlements for the abutment that were provided by Bonacci are:

Design Case:

Horizontal: 5 mm transverse to ramp centreline at level of bearings.

Vertical: 10 mm at the centreline of the abutment.

Rotation: 10 mm differential across the width of the abutment. This will bemeasured on the outside of the abutment blockwork walls which are 7470 apart.This is equivalent to +/- 1.9 mm at the bearings.

Extreme Case:

The extreme case that will be assessed is twice the design case.

4.0 Analysis Model

NSC has developed software over a period of years for the analysis of bridges. Thesoftware automates the creation of the analysis model, based on the structure alignment,and can also accommodate varying girder cross section geometries. It also manages all



of the load combinations to determine the most critical load effects at all locations onthe structure. The software can also include staged construction effects and posttensioning, but there is a considerable amount of work in inputting all the tendonprofiles so this has not been done at this stage.

Figure 1 shows the Spacegass model that the software creates.

Figure 1 Spacegass model of Ann St Ramp

5.0 Analysis Results

For the purpose of determining load effects in the girder due to settlements at AbutmentB, the Spacegass model was modified at Abutment B to remove the members modelingthe abutment and to provide nodal supports directly to the bearings. This alloweddisplacements to be applied at the underside of bearing level.

The model was analysed for the following displacements:

Abutment B 10 mm vertical down (both bearings)

Abutment B rotation about longitudinal axis consisting of +/- 1.9 mm verticaldisplacement of the bearings (clockwise looking towards the abutment).

Abutment B 5 mm transverse displacement

It was found that the transverse displacements at Abutment B produced only negligibleload effects in the superstructure and columns. When the articulation of the bridge isconsidered this is not surprising. Hence this displacement is not considered further inthe discussion on load effects and stresses, however the effect of this movement on theavailable travel on bearings and expansion joints will need to be considered.

Figures 2 and 3 show the box girder bending moment diagram in the end spans due tothe settlements and rotations at Abutment B. Figure 4 shows the torsions in the girderdue to the rotation at Abutment B. The torsions due to the settlement at Abutment Bwere negligible.



Figure 2 Bending Moments due to 10 mm settlement at Abutment B

Figure 3 Bending moments due to rotation at Abutment B

Figure 4 Torsions due to rotation at Abutment B



The key load effects at Piers 3 and 4 and Abutment B due to the design settlements aresummarized in Table 1 below.

The magnitude of these loads is directly related to the Young’s Modulus Ec adopted forthe concrete girder which was 32800 MPa. The short term modulus for the 40 year old6000 psi concrete used may well be higher than this. On the other hand, the settlementswould initially be applied over a matter of days or longer, and so some creep wouldoccur over this time.

Table 1 Load Effects due to movements at Abutment B

Load Effect Design CaseExtreme

Case

Shear at Abutment (kN) 26 52

Torsion at Abutment (kNm) 408 816

Moment at Pier 4 (kNm) -684 -1368

Shear at Pier 4 (kN) -17 / 26 -34 / 52

Torsion at Pier 4 (kNm) 407 814

Moment at Pier 3 (kNm) -55 -109

Shear at Pier 3 (kN) 2 / -17 4 / -35

Torsion at Pier 3 (kNm) 351 702

Table 2 Summary of stresses due to movements at Abutment B and Pier 4

Load Effect Stress Description DesignCase

ExtremeCase

Shear at Abutment Shear in web (MPa) 0.02 0.04

Torsion at Abutment Shear in flange (MPa) 0.44 0.88

Moment at Pier 4 Bending at top (MPa) 0.39 0.78

Shear at Pier 4 Shear in web (MPa) 0.02 0.04

Torsion at Pier 4 Shear in flange (MPa) 0.44 0.88

Moment at Pier 3 Bending at top (MPa) 0.03 0.06

Shear at Pier 3 Shear in web (MPa) -0.01 -0.02

Torsion at Pier 3 Shear in flange (MPa) 0.30 0.61

The stresses corresponding to the above load effects are summarized in Table 2. Theseare a useful indicator of the significance of the settlement. For the stresses due to



bending, the tensile (positive) stresses are of most interest, as this could potentiallycause cracking when combined with the existing stresses. The maximum tensile stressof 0.39 MPa at Pier 4 for the design case and 0.78 MPa for the extreme case are themost significant results.

To assess the impact of these settlements the load effects due to the settlements need tobe added to the ULS loads and compared with the capacity. Similarly, the stresses needto be added to the estimated current stress state and compared with allowable values.

6.0 ULS Load effects

The ULS load effects due to dead load, superimposed dead load, traffic loading andthermal effects have been calculated using the bridge analysis software. These loadeffects do not include prestress secondary effects or construction staging effects.

Table 3 below summarizes the calculated load effects and compares them with the loadeffects due to settlement.

Table 3 Comparison of Settlement effects with ULS load effects

Load Effect

ULS LoadEffect

Settlement Effects

CommentDesignCase

ExtremeCase

Shear at Abutment (kN) -2315 26 52 Beneficial

Torsion at Abutment (kNm) 1985 / -3169 408 816 Beneficial

Moment at Pier 4 (kNm) -22431 -684 -1368 Detrimental

Shear at Pier 4 (kN) -3925 / 3544 -17 / 26 -34 / 52 Detrimental but verysmall

Torsion at Pier 4 (kNm) 1524 / -2750 407 814 Beneficial

Moment at Pier 3 (kNm) -25820 -55 -109 Detrimental

Shear at Pier 3 (kN) -4059 / 4191 2 / -17 4 / -35 Beneficial

Torsion at Pier 3 (kNm) 1797 / -2113 351 702 Detrimental – buttotal torsion lessthan at Pier 4

It can be seen that in many cases the shears and torsions due to settlement are beneficial– that is they are in the opposite direction to the controlling load effect at the location inquestion. The torsion at Pier 3 is detrimental in that when it is added to the positivetorsion at the pier, the positive torsion is larger than the magnitude of the maximumnegative torsion at the pier.



6.1 ULS Bending Only

Generally the moments due to settlements at the piers are detrimental and the momentcapacity has been checked at these locations. Table 4 summarises the ULS bendingmoments, the ULS bending moments including the settlements, and the calculatedsection capacities.

Table 4 Comparison of bending capacity with ULS and additional settlement moments

Location

M*

(DL+Traffic+Thermal)

(kNm)

M* including SettlementEffects (kNm) ϕMu

(kNm)DesignCase

ExtremeCase

Pier 4 -22,431 -23,115 -23,799 -35,300

Pier 3 -25,820 -25,875 -25,930 -39,600

When considering these results it needs to be born in mind that the ULS load effects(M*) do not include secondary prestress effects or construction staging effects.

Secondary prestress effects would usually be beneficial over an internal pier. The effectof construction staging effects cannot be determined without additional information anda more detailed analysis. It would be considered likely however, that the constructionstaging would have been planned to minimize any detrimental effects that it might haveon the final stress state in the bridge.

Nevertheless there is a significant amount of reserve capacity at both piers and it is clearthat the design and extreme settlements can be tolerated from a ULS capacity point ofview.

6.2 Combined ULS Bending Shear and Torsion

To confirm that the presence of shear and torsion does not significantly reduce theavailable negative moment capacity at Pier 4 a combined moment, shear, and torsioncapacity assessment was undertaken. The assessment was undertaken at a sectionlocated a girder depth D from the centreline of Pier 4, towards Abutment B. Table 5summarizes the load effects used.

Since it is a box girder, the effect of torsion is to increase the shear in one outside weband decrease it in the other. The approach taken in the assessment was to increase theshear force so that all three webs carried the same shear as the most heavily loaded weband then to assess the section for bending and shear only.

The shear force in an outer web due to torsion was calculated to be 142 kN. In thesection assessment, torsion was ignored, and the shear force was increased by 3x142 =426 kN.



Table 5 Load effects used for combined moment, shear, and torsion capacity check

Load EffectULS including

PE, Trafficand Thermal

ExtremeSettlement

Effects*

Combinedeffects

AssessmentEffects withincreased V*to account for

Torsion

M* (kNm) -18461 -1340 -19801 -19801

V* (kN) 2512 50 2562 2988

T* (kNm) -997 0 -997 0

*No rotation included as the effects of rotation are beneficial to the torsions and negligible to other loadeffects at Pier 4

The bending and shear capacity was checked using the Response 2000 softwareavailable from the Department of Civil Engineering at the University of Toronto. Thissoftware uses the Modified Compression Field Theory to model the shear behaviour andhence it rationally captures the interaction between bending and shear capacity.

The capacity reduction factors used in the assessment were 0.6 for concrete and 0.8 forreinforcing steel and prestressing steel. The prestress losses were assumed to be 40%.

The load on the section was increased proportionally (i.e at a constant M/V ratio). Thecapacity was reached at ϕMu= -29754 kNm and ϕVu= 4469 kN. That is, with ϕMu/M* =ϕVu/V* = 1.50

While this does not constitute a code check, it clearly shows that the ULS capacity ofthe girder including the effects of the extreme settlements is adequate.

7.0 SLS stresses

Table 6 summarizes the SLS moments, and estimated SLS stresses at the locations ofinterest. The stresses have been calculated assuming total prestress losses of 30% and40%. The prestress losses have not been calculated at this stage, so these conservativeassumptions were made. As noted previously the SLS moments include thermal effectsbut do not include staged construction effects or prestress secondary effects.

In addition Table 6 shows the bending stresses for the design settlement cases. Whencombined with the existing SLS stresses the total stress should satisfy the current TMRcriteria which is that at all times the tensile stress shall be less than 0.25√f’c = 1.60 MPa.



Table 6 Summary of SLS stresses - existing and due to settlements

LocationSLS

Moment(kNm)

SLS Bending

Stresses σx (MPa)

Stresses due to

Settlements σx (MPa)

30 %Prestress

Losses

40 %Prestress

Losses

DesignCase

ExtremeCase

Pier 4

(Stress at Top)-16066 -2.18 -0.61 0.39 0.78

Pier 3

(Stress at Top)-18507 -2.35 -0.73 0.03 0.06

The presence of coexisting torsion will increase the principle tensile stresses at the topof the girder. The results in Table 7 account for this. In this table the total coexistingtorsion (including torsion due to settlement) has been used to calculate the co-existingshear stress at the top of the girder. The effective allowable stress in the table is the

maximum longitudinal stress σx which when combined with the shear stress will keepthe maximum principal stress below 1.60 MPa.

It can be seen that the worst case is at Pier 4 (Maximum M* case) with the extremesettlements and with 40% prestress losses. In this case the most tensile stress of +0.19MPa is still less than the effective allowable stress of 1.58 MPa.

Table 7 Comparison of total stresses with settlement and the effective allowable stresswhich accounts for the effects of torsion

Location

Direct Stresses σx with DesignCase Settlements (MPa)

Direct Stresses σx with ExtremeCase Settlements (MPa)

30%Prestress

Losses

40%Prestress

Losses

EffectiveAllowable

30%Prestress

Losses

40%Prestress

Losses

EffectiveAllowable

Pier 4

Max M* case

(Stress at Top)

-1.79 -0.22 +1.60 -1.40 +0.19 +1.58

Pier 4

Max T* case

(Stress at Top)

-2.29 -0.72 +1.37 -1.90 -0.33 +1.17

Pier 3

(Stress at Top)-2.32 -0.70 +1.43 -2.29 -0.67 +1.32



8.0 Effect of Girder Twist

The analysis discussed above has assumed that both bearings at both abutments arealways in contact and able to carry compression loads. However this is not currently thecase.

As noted in Section 2 above twisting of the box girder has occurred. The twisting hasoccurred to such an extent that the inside bearing on Abutment B lifts off on hot days,and the inside bearing at Abutment A has lifted off permanently. This was investigatedby NSC in 2006/2007 and in the resulting report (NSC188-TR-02 Rev 0) arecommendation was made to raise the inner bearings at the abutments so that so thatthey will remain in contact under all loading conditions. This work has not yet beenundertaken but is planned for the future.

The effect of the settlements on the bridge in its current condition with the two innerbearings inactive has also been investigated. This investigation has concentrated onassessing the effect at Pier 4 which has shown to be the most critical location.

A rotation of Abutment B when it is only supported on one bearing has no effect on theload effects in the girder. Hence this component of the settlement is ignored. The effectsof settlements at Abutment B when only the outer bearing is in contact are only slightlyless than the results above for the normal case, and so the previously reported loadeffects will be used in the assessment.

Table 8 summarizes the ULS and SLS load effects due to dead load, traffic and thermaleffects at Pier 4 for the normal case and the case with the inner bearing inactive. It canbe seen that as a result of the inner bearings being inactive, the bending moments haveincreased by about 5%, the shears have increased by a smaller amount, but the torsionshave become significantly more negative. The maximum torsion magnitude hasincreased by about 85%.

Table 8 The effect of inactive inner bearings on the load effects (DL, traffic, andthermal) at Pier 4

Load effect

ULS SLS

As DesignedInner

BearingsInactive

As DesignedInner

BearingsInactive

M* (kNm) -22341 -23498 -16066 -16828

V* (kN) -3925 / 3544 -4033 / 3594 -2759 / 2493 -2834 / 2526

T* (kNm) 1524 / -2750 776 / -5086 720 / -1836 -335 / -3029



8.1 ULS Effects

Based on bending alone, the ULS Capacity at Pier 4 from Table 4 is -35,300 kNm. TheULS load effect, including the extreme case settlement, is -23498 – 1340 = -24838 kNmwhich is still comfortably below the capacity.

The combined bending, shear and torsion capacity at distance D from Pier 4 wasassessed using the same methodology as described previously. Two cases wereconsidered; the load case that gave the maximum moment, and the load case that gavethe maximum torsion. These were combined with the extreme settlement case. Table 9summarizes the design loads including the settlement effects, and the adjusted loadswith the torsion accounted for by a higher shear force.

Table 9 Load cases used for combined bending, shear and torsion assessment with innerbearings inactive

Load effect

Maximum M* Load Case Maximum T* Load Case

ULS Loadeffects

includingExtreme

Settlement


Torsion

ULS Loadeffects

includingExtreme

Settlement


Torsion

M* (kNm) -20820 -20820 -11398 -11398

V* (kN) 2602 3167 2426 4599

T* (kNm) -1323 0 -5086 0

For the maximum M* load case, the capacity was reached at ϕMu= -29703 kNm andϕVu= 4497 kN. That is, with ϕMu/M* = ϕVu/V* = 1.42

For the maximum T* load case, the capacity was reached at ϕMu= -14410 kNm andϕVu= 5810 kN. That is, with ϕMu/M* = ϕVu/V* = 1.26

These capacity ratios are lower than for the case with both bearings active, however themargins are still acceptable for the extreme settlement case.

8.2 SLS Stresses

The increased torsions with the inner bearings inactive reduce the effective allowable

longitudinal stresss σx and the higher bending moments will increase the longitudinalstresses. However, the absence of torsions due to rotation at abutment B means that theeffective allowable stress is the same for both the design and extreme case settlements. ,

Table 10 summarizes the stresses at the top of the section at Pier 4 for the case with theinner bearings inactive. For the controlling load case, and with 40% prestress losses andextreme settlements, the longitudinal stress was calculated to be +0.60 compared withan effective allowable stress of 1.37. This is satisfactory, although the margin to allow



for uncertainties is quite small. On the other hand, it is a very conservative case with40% prestress loss and the extreme settlements.

Table 10 SLS stresses at Pier 4 with inner bearings inactive

Location

Direct Stresses σx with DesignCase Settlements (MPa)

Direct Stresses σx with ExtremeCase Settlements (MPa)

30%Prestress

Losses

40%Prestress

Losses

EffectiveAllowable

30%Prestress

Losses

40%Prestress

Losses

EffectiveAllowable

Pier 4*

(Stress at Top)-1.34 +0.21 +1.37 -0.95 +0.60 +1.37

9.0 Summary and Conclusions

9.1 Limitations

This assessment has not considered secondary prestress effects and construction stagingeffects.

At the critical sections at the Piers, the secondary prestress effects are expected to befavourable. While the construction staging effects are unknown, it is unlikely that theyare large. When combined with favourable secondary prestress effects any nettunfavourable effect would be expected to be small.

Hence the comparisons of ULS load effects with capacities, and of SLS stress levelswith allowable levels, that are given in this report should give a reasonable indication ofthe risk to the structure of the settlements that have been considered.

9.2 Twist of Girder

Due to long term creep and prestress effects, the box girder has twisted so that the innerbearing on the River End is never in contact, and the inner bearing on the City end is notin contact on hot days. As a result, two cases have been considered: With the innerbearings fully in contact, and with the inner bearings inactive.

The amount of twist that has occurred at Abutment B is high compared with theexpected rotation of the abutment due to settlements. Hence, if the excavation takesplace with the ramp in its current state, the rotations can be tolerated with negligibleeffect on the superstructure.

Generally the case with the bridge in its current state with the inner bearings inactivecontrols for the ULS capacity and SLS stress assessment.



9.3 ULS Capacity

It was generally found the there is a significant reserve of capacity at the Piers and thatthe additional load effects due to the design case settlements and the extreme casesettlements could be easily accommodated.

Pier 4 was found to be the critical location for ULS effects. The capacity ratios(ϕMu/M*) calculated at Pier 4 are given in Table 11. It can be seen that the worst case isfor the extreme settlements with the bridge in the current condition. In this case there isstill a 26% reserve of capacity.

Table 11 Calculated Capacity Ratios (ϕMu/M*) at Pier 4

Description ofCapacity Check

No Twist – Both Bearingsactive

Current State – Innerbearings inactive

DesignSettlement

Case

ExtremeSettlement

Case

DesignSettlement

Case

ExtremeSettlement

Case

Moment Only atPier 4

1.53 1.48 1.46 1.42

Combined BendingShear and Torsion atD from Pier 4

Not Assessed 1.50 Not assessed 1.26

9.4 SLS Stresses

Pier 4 is also the critical location for SLS stresses. The increase in stress at the top of thegirder at Pier 4 due to the design and extreme settlement cases are 0.39 MPa and 0.78MPa respectively. These are relatively small.

Table 12 summarizes the margin between the calculated longitudinal stress at the top ofthe section and the effective allowable tensile stress. The effective allowable tensilestress is the stress which, when combined with the shear stress due to torsion, will resultin a principal tensile stress of 0.25√f’c = 1.60 MPa.

It can be seen that generally the margins of stress are acceptable. The worst case has amargin of 0.77 MPa. This is satisfactory, although the margin to allow for uncertaintiesis quite small. On the other hand, it is a very conservative case with 40% prestress lossand the extreme settlements.



Table 12 Margins between predicted and allowable longitudinal stresses at the top of thegirder at Pier 4

Stress Condition

No Twist – Both Bearingsactive

Current State – Innerbearings inactive

DesignSettlement

Case

ExtremeSettlement

Case

DesignSettlement

Case

ExtremeSettlement

Case

Top stress at Pier 430% prestress losses (MPa)

3.39 2.98 2.71 2.32

Top stress at Pier 440% prestress losses (MPa)

1.82 1.39 1.16 0.77

9.5 Horizontal Bearing Movements

Horizontal movements at Abutment B do not cause any significant loads in thesuperstructure. However any horizontal movement at Abutment B causes movements ofsimilar magnitudes at other bearings on the bridge and accordingly the ability of thesebearings to accommodate such movement needs to be checked.

The extreme case of a 10 mm transverse movement at Abutment B towards theexcavation would result in a 10 mm opening of the expansion joint at abutment A. Theavailable travel on these bearings and the expansion joint would already have beenreduced over time due to long term shrinkage and creep. This needs to be checked.

To this end, a request should be made to TMR for any information that they haveregarding the current locations of the bearings within their travel range. It may be thatuseful information was collected in this regard during the 2006 / 2007 investigationsinto the twisting of the ramp.

9.6 Conclusions

The findings of this investigation indicate that the design case settlements proposed as aresult of the excavation can be tolerated without any significant adverse effect on thecapacity or stress levels in the Ann St ramp superstructure.

The investigation also indicates that the extreme case settlements will not significantlyaffect the capacity of the ramp superstructure. Due to the limitations noted above, thereis some risk that serviceability stress levels at the top of the girder at Pier 4 may exceedthe allowable limits for the extreme settlement case. This is particularly the case for theramp in its current state with both the inner bearings not active for some periods.

The available travel on the bearings at Abutment A and the columns must be checked todetermine what horizontal movements can be tolerated at Abutment B. This will requireadditional information from TMR.



9

10 APPENDIX C – STRUCTURAL REVIEW OF AR3 AND APPROACH RAMP - BONACCI

300 GEORGE ST REDEVELOPMENT

STRUCTURAL REVIEW OF ABUTMENT AR3, APPROACH

STRUCTURE AND POSITIVE STOP BARRIER

BONACCI GROUP

DOCUMENT HISTORY

ISSUE REVISION DATE AUTHOR REVIEWER

Issued for DTMR Review A October 11, 2013 RJW JV

Issued for DA B October 30, 2013 RJW JV



2

CONTENTS

1 SCOPE OF THIS REPORT................................................................................................................... 3

2 MODELLING INPUTS AND ASSUMPTIONS ....................................................................................... 3

3 DESIGN LOADS ................................................................................................................................ 3

4 ABUTMENT AND APPROACH STRUCTURAL MODEL ....................................................................... 4

5 ABUTMENT AND APPROACH MODELLING RESULTS ....................................................................... 6

6 ABUTMENT AND APPROACH STRUCTURAL CAPACITY ................................................................... 9

7 PROPOSED ALLOWABLE SETTLEMENTS ........................................................................................ 13

8 SUMMARY AND DISCUSSION ........................................................................................................ 14

9 APPENDIX A – SPACEGASS MOVING LOAD ANALYSIS ................................................................... 15



3

1 SCOPE OF THIS REPORT

The purpose of this report is to review the impacts of differential settlements due to the basement

excavation and retention system on the existing Ann Street Bridge Abutment AR3, the insitu

concrete Approach ramp to the abutment and the Positive Stop Barrier.

Limitations of this Report

The purpose of this report is to verify that the existing bridge and abutment structures have

sufficient capacity to resist the additional loads applied to them by the excavation of the basement

for 300 George Street. Hence, this report is limited to a review of only those elements directly

impacted by the excavation and does not constitute a verification or certification of the existing

structures, either complete or in part.

2 MODELLING INPUTS AND ASSUMPTIONS

As the basement is excavated, the soils immediately adjacent the retention system will relax due to

the release of earth pressure adjacent the excavation, with the amount of relaxation dependent on

the stiffness of the retention system and the post-tensioning of the ground anchors. To quantify this

effect, a detailed geotechnical analysis has been undertaken by Golders Associates to determine the

magnitude of expected soil displacements. (Golders Report 137632111-003-L, Rev 0, 9/10/13)

3 DESIGN LOADS

The following design loads have been used to verify the existing bridge structures during excavation

of the basement;

Vehicle Loading:

The design vehicle loading for the bridge for the purposes of this review is the T44 load. This report

does not consider the increased design loadings in the current version of AS5100, as this review is a

verification of the existing capacity of the structure and is not intended to constitute a basis for

increasing the current rated capacity of the bridge and its supports.

The dynamic load allowance for the review of the bridge and supporting structures is taken as 0.4 for

moving loads and 0.0 for stationary traffic.

Accompanying Vehicle Loads:

For the purposes of review, several combinations of design loading have been checked, including a

single T44, and a two T44’s following eachother 6m part. Additionally, the design vehicles have been

checked for a deviation up to 2m from the centerline of the bridge.

A moving load analysis was undertaken using Spacegass to identify the critical load cases for each

support and this analysis is attached in Appendix E for reference.



4

4 ABUTMENT AND APPROACH STRUCTURAL MODEL

To determine the impacts of the expected soil movements on the bridge abutment and approach

structure, a 3D Finite Element Model was constructed in order to quantify the stresses imposed on

the structures due to displacement of the soil during excavation of the basement.

The following cases have been considered as part of our detailed structural analysis of the Ann

Street Abutment and Approach Structure;

Case 1: Differential Settlement of Piles along Site Boundary (Tilting of Abutment/Approach

Structure)

Case 2: Differential Settlement of Abutment Relative to Approach Structure

ABUT APPROACH STRUCT.

PILES SETTLE

PILES FIXED



5

Case 3: Differential Settlement of Approach Structure Relative to Abutment

Model Restraints:

Piles for the abutment have been modeled as beam elements with end bearing restraints and

ignoring the effects of skin friction. The structure is assumed to be completely supported on the

piles, with no additional support allowed for due to bearing on the soil between the piles.

Global X/Y restraints have been provided to both the abutment and approach structure to prevent

twisting of the model during analysis.

All piles for the bridge and abutment are assumed to be founded in the MW rock, with an end

bearing stiffness of 1500kPa/mm. The structure is assumed to be completely supported on the piles,

with no additional support allowed for due to bearing on the soil between the piles.

ABUT APPROACH STRUCT.

PILES FIXED

PILES SETTLE



6

5 ABUTMENT AND APPROACH MODELLING RESULTS

Individual 3D FEA models were created using Strand 7 to determine the effect of differential

settlement of individual piles, and the overall combined stress results are presented for discussion

below.

In all cases presented, stresses are plotted for the critical load case which is 2/T44 trucks offset 2m

from the centerline of the bridge and located over the central piles on the approach structure. All

stresses presented below are based on in- service design loads.

In critical load cases the loads applied to the structure exceed the tensile capacity of the concrete

(calculated as 2.26MPa) and as such the approach structure is expected to crack under differential

settlement which will reduce the stiffness of the structure. To model this effect, the concrete

modulus was reduced to 60% of Ec to model the behavior of a cracked section.

Case 1: Existing Condition – No Displacement



7

Case 2: 10mm Tilt Full Length

Case 3: 5mm Tilt of Abutment Only



8


Case 4: 5mm Tilt of Approach Structure Only



9


Discussion on Analysis Results:

Due to the high bending stiffness of the approach structure, it has limited capacity to articulate and

redistribute differential settlements of the piles. This is indicated most clearly in case 5 where a

10mm settlement of the central piles on the approach structure results in the structure spanning the

full 24.4m to the end piles with minimal additional vertical loads applied to the internal piles.

This effect also occurs in reverse, as illustrated in case 3, where a 10mm differential settlement of

the abutment results in very high loads to the internal piles, and high local bending stresses in the

approach structure as it cantilevers over the internal supports.

6 ABUTMENT AND APPROACH STRUCTURAL CAPACITY

Abutment and Approach Structure Piles: 1050mm Dia. RC Concrete

Pile loads have been checked for all cases and the maximum pile load is 2159kN under the approach

structure in Case 3. The geotechnical end-bearing capacity of the pile is defined in the TMR

drawings as 15T/sqft, or 1.6MPa working, which correlates to a maximum working capacity of

1,400kN. (Neglecting any contribution of skin friction to the capacity of the pile)

The structural capacity of the pile has been calculated at 15,900kN ULS, which far exceeds the

applied loads. Maximum design moments are 723kN.m working, or 1084kN.m ULS (Case 2),

compared to a calculated bending capacity of 1986kN.m @ balanced failure.

As such, the piles have sufficient reserve structural capacity to resist the additional loads due to a

differential settlement of 10mm, however, in extreme circumstances differential settlements may

overload the geotechnical capacity of the piles. This is not considered critical to the structure,

however, as yielding of the soils will shed load to the adjacent piles and hence reduce the overall



10

stresses in the approach structure. As such, the design approach of assuming these piles are fixed

supports with minimal movement is conservative.

Approach Structure:

The approach structure is a 4,000psi (28MPa) reinforced concrete structure constructed in the mid-

1970s. Due to the age of the concrete, it has been assumed that the concrete properties for this

structure are equivalent to N32 concrete. Reinforcing to the structure is defined as structural grade

deformed bars with 400MPa yield strength.

A review of tensile stresses in the approach structure due to differential settlements has been

undertaken, with the critical case being differential settlement between the approach structure and

the bridge abutment.

A review of peak stresses for these two cases with results as follows;

Load Case Average Reo

Stress @ Top of

Wall (375mm

Thick, 7N20)

Average Reo Stress

just below top of

wall (225mm

Thick, N12-300 EF)

Average Reo

Stress in Deck

(150mm Thick,

N12-100)

Average Reo Stress

@ base of Wall

(750W x 450D

Footing, 8N24)

5mm Abutment

Settlement

1.73MPa Tens 0.77MPa Tens 1.40MPa Tens -2.24MPa Comp

10mm Abutment

Settlement

2.49MPa Tens 1.39MPa Tens 2.49MPa Tens -3.18MPa Comp

5mm Approach

Settlement

-1.24MPa Comp -0.84MPa Comp -1.29MPa Comp 2.25MPa Tens

10mm Approach

Settlement

-1.82MPa Comp -1.06MPa Comp -1.82MPa Comp 3.63MPa Tens

Assuming the above stresses are carried only by the reinforcing in tension, the following reinforcing

stresses have been calculated for each case;

Load Case Average Reo

Stress @ Top of

Wall (375mm

Thick, 7N20)

Average Reo

Stress just below

top of wall

(225mm Thick,

N12-300 EF)

Average Reo

Stress in Deck

(150mm Thick,

N12-100)

Average Reo Stress

@ base of Wall

(750W x 450D

Footing, 8N24)

5mm Abutment

Settlement

133MPa 236MPa 185MPa Comp.

10mm Abutment

Settlement

191MPa 426MPa 340MPa Comp.

5mm Approach

Settlement

Comp. Comp. Comp. 210MPa

10mm Approach

Settlement

Comp. Comp. Comp. 340MPa



11

From the above analysis the approach structure can reasonably accommodate 5mm differential

settlement without distress, however, a 10mm settlement will result in cracking occurring over the

central piers.

It is important to note, however, that the critical case for the approach structure is differential

settlements along its length, and that settlements across the width of the structure are not critical.

In this instance, the structure can accommodate up to 10mm of differential settlement between the

northern and southern sides, provided that the differential settlement along the length of the

structure is less than 5mm between any two piles.

Additionally, it is noted that any cracking that occurs in the approach structure will not adversely

affect its traffic carrying capacity and the structure will remain stable. However, substantial cracks

may lead to ongoing durability problems if the cracks were not adequately repaired.

Abutment Structure:

The bridge abutment is a 1200 deep pier cap, 6.6m long by 7.8m wide and is supported on 6

1050mm diameter cast insitu concrete piles. The bridge bearings are located on a 2.6m high

reinforced concrete pedestal. Concrete strength is 4,000psi (28MPa equivalent) and reinforcing is

grade 400 structural deformed bar.

Analysis results for the abutment are below;




12


Load Case Pier Cap Mxx Pier Cap Myy

10mm Abutment Tilt +580kN.m/m

-535kN.m/m

+895kN.m/m

-509kN.m/m

10mm Approach Tilt 570kN.m/m

-531kN.m/m

896kN.m/m

-527kN.m/m

For the purposes of review, the following equivalent moment capacities were determined based

upon the geometry of the pile cap and the reinforcing indicated on the TMR drawings;

Load Case Reo Top Top Moment @

200Mpa

Reo Btm Btm Moment @

200Mpa

Mxx N12-300 100kN.m/m N28-150 900kN.m/m

Myy N12-300 100kN.m/m N32-150 1100kN.m/m

Cracking

Moment

N/A 815kN.m/m N/A 815kN.m/m

From the above it is apparent that with 10mm differential tilt across the abutment, the applied

moments are less than the cracking moment for the pier cap for negative moments, and well within

acceptable limits for sagging moments.

As such, the abutment structure can withstand 10mm differential settlement across any dimension

with no detrimental effects.



13

Positive Stop Barrier Structure (PSB):

The positive stop barrier structure is founded on six 900dia insitu concrete piles nominally 3m long,

and connected by a 1200 deep by 3000 wide footing beam. Additionally, the structure is anchored

by 12 rock anchors embedded 4m into the MW Phyllite.

The comparatively light self weight of this structure, combined with the very high strength of the

footing beams and shallow embedment of the piles means that this structure will simply rotate to

accommodate any settlements due to excavation and a 10mm differential settlement is not

considered to have an adverse impact on the PSB.

7 PROPOSED ALLOWABLE SETTLEMENTS

From the analysis above, the following maximum allowable displacements of the bridge foundations

are proposed:

Element Maximum Permissible Settlement

Abutment AR3 - 10mm across width of roadway (tilt), 5mm parallel

Approach Structure - 10mm across width of roadway (tilt), 5mm parallel, and

maximum of +/-5mm differential to abutment structure



14

8 SUMMARY AND DISCUSSION

A detailed structural analysis has been undertaken on the impacts of differential settlements on the

foundations of the Ann Street Abutment, Approach Structure and Positive Stop Barrier. Form this

analysis it has been confirmed that the foundations for these structures have a moderate capacity to

resist differential settlements, but that careful monitoring and control will be required during

construction to ensure these limits are not exceeded.

The proposed deflection limits are nominally 10mm maximum total across the width of the on-ramp,

and 5mm maximum differential along the length. These limits are within the expected movement

predicted by the geotechnical analysis, as provided by Golder Associates in their separate report.



15

9 APPENDIX A – SPACEGASS MOVING LOAD ANALYSIS



10

11 APPENDIX D – DRAWINGS OF PROPOSED BASEMENT AND EXISTING STRUCTURE

North

Rev Description Date By

COPYRIGHT All rights reserved.These drawings, plans and specifications and the copyright therein are the property of the BonacciGroup and must not be used, reproduced or copied wholly or in part without the written permissionof the Bonacci Group.

DateProject Director Approved

Drawing No RevProject Ref

App

Sheet

Scale

Drawn

Designed

Date

File

: P

:\P

roje

cts\

B3966_330_G

eorg

e_S

t\D

wg\S

truct

\Aca

d\B

onN

SW

Base

ment D

raw

ings\

S-D

D-B

-0010.d

wg

P

lotted:

30.1

0.1

3 a

t 6:1

8 P

M B

y: C

hris

Eden

BONACCI GROUP ( NSW ) Pty LtdABN 29 102 716 352Consulting Engineers, Structural - Civil - InfrastructureLevel 6, 37 York Street, Sydney, NSW 2000 AustraliaTel: +61 2 8247 8400 Fax: +61 2 8247 8444sydney @bonaccigroup.comwww.bonaccigroup.com

P4

SHORING PLAN

S-DD-B-00102001406

300 GEORGE STREETBRISBANE

North





App

Sheet

Scale

Drawn

Designed

Date

File

: P:\P

roje

cts\

B3966_330_G

eorg

e_S

t\D

wg\S

truct

\Aca

d\B

onN

SW

Base

ment D

raw

ings\

S-D

D-B

-0011.d

wg

P

lotted:

30.1

0.1

3 a

t 6:1

7 P

M B

y: C

hris

Eden


P4

SHORING ELEVATIONSSHEET 1

S-DD-B-00112001406


North





App

Sheet

Scale

Drawn

Designed

Date

File

: P

:\P

roje

cts\

B3966_330_G

eorg

e_S

t\D

wg\S

truct

\Aca

d\B

onN

SW

Base

ment D

raw

ings\

S-D

D-B

-0012.d

wg

P

lotted:

01.1

1.1

3 a

t 10:3

9 A

M B

y: M

ark

Gib

bin

s

BONACCI GROUP ( NSW ) Pty LtdABN 29 102 716 352Consulting Engineers, Structural - Civil - InfrastructureLevel 6, 37 York Street, Sydney, NSW 2000 AustraliaTel: +61 2 8247 8400 Fax: +61 2 8247 [email protected]

P3


S-DD-B-00122001406


North





App

Sheet

Scale

Drawn

Designed

Date

File

: P

:\P

roje

cts\

B3966_330_G

eorg

e_S

t\D

wg\S

truct

\Aca

d\B

onN

SW

Base

ment D

raw

ings\

S-D

D-B

-0013.d

wg

P

lotted:

30.1

0.1

3 a

t 6:1

6 P

M B

y: C

hris

Eden


P2


S-DD-B-00132001406


North





App

Sheet

Scale

Drawn

Designed

Date

File

: P

:\P

roje

cts\

B3966_330_G

eorg

e_S

t\D

wg\S

truct

\Aca

d\B

onN

SW

Base

ment D

raw

ings\

S-D

D-B

-0014.d

wg

P

lotted:

30.1

0.1

3 a

t 6:1

5 P

M B

y: C

hris

Eden


P1


S-DD-B-00142001406


North





App

Sheet

Scale

Drawn

Designed

Date

Bonacci Group Pty LtdABN 42 060 332 345Consulting Engineers, Structural - Civil - InfrastructureLevel 6, 37 York Street, Sydney, NSW 2000 AustraliaTel: +61 2 8247 8400 Fax: +61 2 8247 [email protected]

File

: P:\P

roje

cts\

B3966_330_G

eorg

e_S

t\D

wg\S

truct

\Aca

d\B

onN

SW

Base

ment D

raw

ings\

S-D

D-B

-0015.d

wg

P

lotted:

30.1

0.1

3 a

t 6:1

4 P

M B

y: C

hris

Eden P3

SHORING DETAILS

S-DD-B-00152001406


North





App

Sheet

Scale

Drawn

Designed

Date

Bonacci Group Pty LtdABN 42 060 332 345Consulting Engineers, Structural - Civil - InfrastructureLevel 6, 37 York Street, Sydney, NSW 2000 AustraliaTel: +61 2 8247 8400 Fax: +61 2 8247 [email protected]

File

: P

:\P

roje

cts\

B3966_330_G

eorg

e_S

t\D

wg\S

truct

\Aca

d\B

onN

SW

Base

ment D

raw

ings\

S-D

D-B

-0016.d

wg

P

lotted:

30.1

0.1

3 a

t 6:2

7 P

M B

y: C

hris

Eden


P2

SHORING SECTIONS

S-DD-B-00162001406




12

12 APPENDIX E – RESPONSE TO TMR INFORMATION REQUEST

Project: 300 George Street Redevelopment

Reviewed Submission: 300 George Street - Impact of Basement Structures on Ann Street

Item TMR Comment Designers Response TMR Comment TMR Acceptance 1 Instrumentation and Monitoring

A comprehensive Instrumentation and monitoring is required to validate your impact assessment and the design assumptions, among the others. Please, therefore, submit the related instrumentation and monitoring drawings. The drawings should indicate the location of the instrument, trigger (review) level for each stage of excavation, monitoring frequency and the action plan.

Noted. A detailed monitoring and assessment program will be coordinated with the project surveyor, TMR and the design team prior to excavation of the basement commencing.

2 Golder Associates’ Report Please include the followings in the Golder’s report:

• The geological sections and the borehole locations.

• a plan showing Sections AN1-A, AN1-B and AN2.

• Assumed long term and short term stiffness of the struts and the anchors

• Assumed construction sequence and the allowance made for any ‘over-excavation.’

• The effects of rising water level (perhaps due Brisbane River) above RL -4.5 m

Awaiting Input from Golders



• Effects of shear zones or faults within the rock mass; and, demonstrating adequacy of the current geological info and the design approach to address this issue?

• Sensitivity of the soil parameters on the predicted settlements/deflections.

• Justification for the sensitive/critical soil parameters.

• Effects of groundwater drawdown.

3 Impact Assessment Updates Please note that the current impact assessment is based on limited, partial or preliminary information. The actual impact may vary depending on the final design. Hence the impact assessment needs to be updated (once the design has been finalized) and submitted, together with relevant drawings, for our review.

The impact assessment will be updated as required during the excavation.

4 Long Term Settlement Section 5 of BONACCI’s report states that “ The expected maximum long term settlement could be up to 30 mm, if a proper construction staging was not implemented. We believe this movement is unacceptable and will therefore adopt measures to prevent it from happening.”

The 30mm maximum long term settlement was based upon incorrect design loads in the geotechnical model and allowing 10mm shrinkage for the slabs. The slab shrinkage has since been reduced to 5mm through the use of control joints in the slab and isolating the retention wall from the slabs for a



In view of this, please clarify the followings:

• ‘L ong term’ here means how long? • How the 30 mm settlement was

estimated? • Where this settlement is expected to

occur? • What are the measures to be taken to

limit this settlement? And to what value it needs to be limited?

minimum of 18 months during construction (To allow the slab to shrink freely, before the ground anchors are released) In this context, “long-term” refers to a case 30 years after construction is complete and the majority of the shrinkage of the basement structure is complete. Contingency measures have been identified should the displacements exceed those calculated, and these are included in the current version (Rev B) of the Bonacci Report, section 6.

The Department of Transport and Main Roads (DTMR) have reviewed the documents for conformance with DTMR technical requirements. It should be

noted that DTMR have not carried out any proof calculations or risk analysis. The responsibility for the design rests with the RPEQ Certifier

PN 22/10/13

Impacts of Basement Excavation on Ann St Abutment … George St Redevelopment Impact of Basement...

Documents

Transcript of Impacts of Basement Excavation on Ann St Abutment … George St Redevelopment Impact of Basement...