Geotechnical Instrumentation and Monitoring for the NewMetroRail City Project, Perth, Western AustraliaP.G. McGoughInstrumentation and Monitoring Manager, Leighton Kumagai Joint Venture, PerthM. WilliamsSpecial Contracts Manager, Leighton Kumagai Joint Venture, PerthABSTRACT: The New MetroRail Project involved a significant number of deep excavations withinvarying soil types, as well as tunnelling under live railways and heritage buildings. From the onset ofthe project, significant effort and planning was put into geotechnical instrumentation and monitoring,with over 5200 instruments being installed during the life of the project over a length of less than 3kilometres. This paper details the initial planning and management process, as well as the contractualrequirements, which formed the basis for more instrumentation as the project progressed. Specificproject requirements such as compensation grouting under buildings and tunnelling under liverailways at depths of less than one tunnel diameter required specific planning measures and additionaldetailed monitoring which is discussed herein.A large number of automated instruments were used to ensure cost effective and safe collection ofdata. The types of instruments used on the project are discussed in detail with respect to theirapplicability, accuracy, reliability, repeatability and cost effectiveness. Examples are presented toillustrate the above points as well as highlight operational issues learnt. The process of data collection,management and reporting is also discussed.With construction taking place in a variety of ground conditions ranging from very soft alluvial siltsand reclaimed fill to medium dense alluvial sands and stiff clays a number of distinct response issueswere observed by the monitoring. The lessons learnt from three years of continuous monitoring ofground and building movements, groundwater movements, and instrument vibrations are discussedwith respect to this project and future projects in Perth within similar geotechnical environments.Detailed examples of ground, sheet pile and wall movements and strut loads with respect to excavationdesign are presented, along with examples of the exceptionally low volume loss from TBM operation,and resulting building responses to ground movement. An empirical method for predicting groundsettlement due to sheet pile extraction is also presented. Examples of ground vibrations induced bysheet piling, construction activities and tunnelling are presented.
1 INTRODUCTIONThe minimum required instrumentation for the project was specified in the contract documentsreferred to as the Scope of Works and Technical Criteria (SWTC), which became the guidingdocument for tendering purposes and initial estimation. To address the definition of purpose formonitoring, a Building Protection Management Plan was created by Leighton Kumagai Joint Venture(LKJV). The overall purpose of LKJV’s approach to instrumentation, monitoring and buildingprotection was summarised in the Management Plan as follows: “ to identify the controls to be implemented to ensure personal safety (construction and public), and verify design predictions to prevent damage to buildings, services and civil infrastructure as a result of LKJV construction activities.” [From LKJV’s “Building Protection Management Plan”]Appropriate management methods were also created and put in place to handle the possible influencesof construction activities due to the soft Perth soils. This included selecting “fit-for-purpose”instrumentation that was able to be monitored safely, whilst still providing accurate and timelyfeedback about construction progress. In addition to working in, with and around the constructionpersonnel, a key criteria was to minimise disruption to pedestrians, traffic flows, and retail business inthe CBD.2 INITIAL PLANNING AND MANAGEMENT PROCESS2.1 OverviewThe need for protection of workers’ safety, property and the environment was foreseen by the PublicTransport Authority (PTA) in their tender scope document “Scope of Works and Technical Criteria”(SWTC). These activities included: • Monitoring the performance of deep excavations with respect to design; • The need for controls to minimise the potential for damage to buildings, services, roads, rails and bridges from construction activities such as: - demolition; - sheet piling, bored piling or diaphragm wall construction; - tunnelling; - ground improvement activities (jet grouting, soil mixing, compensation grouting); - consolidation from groundwater drawdown. • Determining a series of baseline condition surveys to objectively determine any damage; • A process for receiving automated alerts if movement criteria were exceeded.On consideration of the complexity of the final monitoring program, LKJV added the followingadditional elements to those listed in the SWTC: • An overall management process to coordinate the activities of design, construction, survey and monitoring crews, with geotechnical and management reviews. A single document (Building Protection Management Plan) was created to bring together the requirements of: - Geotechnical Interpretive Report; - Ground Settlement, Building Protection and Repair Plan, incorporating Property Condition Surveys and Building Protection Assessments; - Instrumentation and Monitoring Plan; - Various area-specific Method Statements and Safe Work Methods (i.e., JSA’s); - Feedback from the actual results generated. • Visual approach to interpretation of monitoring data to allow for quick interpretation by a range of personnel;
• Innovative instruments and monitoring methods such as wireless electrolevel beams and terrestrial photogrammetry driven by safety or minimising disruption to the public; • Emergency Response procedures as part of the overall risk management plan to cover the event of a massive failure.Figure 1 outlines the key elements of the building protection and monitoring process. Geotechnical investigations Condition surveys in zone of influence Detailed design Assess the need for building protection Install instrumentation Protection of key and monitoring structures Construction and Tunnelling works Investigate exceptions Post construction surveys and repair Figure 1. The LKJV Building Protection and Monitoring Process2.2 Damage criteriaAfter extensive preliminary geotechnical work had been undertaken, modelling of the potential zoneof influence of the project works was performed. This determined the width of the potentialsubsidence zone, based on the predicted design level of induced settlement and TBM face loss.A key point to note is that although the Ground Settlement, Building Protection and Repair Plandetermines a zone of influence based on a designed level of settlement caused by the excavations andthe TBM, the actual performance of the TBM was expected to be considerably better than this (i.e.,less settlement). This was in demonstrated by the actual TBM operations, where up to 20mm wasdesigned for along William Street, but only around 3-5 mm was observed. The performance of theTBM with respect to design is discussed in more detail later in this paper.Once the potential zone of influence was determined, a visual Property Condition Report was preparedfor each of the following structures along or adjacent to the route of the project: • 88 buildings, from single storey to BankWest tower; • 5 bridges and footbridges, including the heritage listed Horseshoe Bridge; • Sections of roads and associated furniture along and adjacent to William and Roe Streets; • Around 30 water and sewer services using a CCTV camera.The design level settlements of the TBM had the potential to cause minor damage to some buildingsalong the route. An engineering assessment was made to determine whether this potential damagewould exceed the limits specified in the PTA’s SWTC. The damage criteria was based on the work ofBoscardin and Cording, 1989, which is reproduced as Table 1.
Table 1 - Building Damage Classification Approx. Description of Max Risk Description of Typical Damage and Likely Crack Degree of Tensile Category Forms of Repair width Damage Strain [%] [mm] Less than Less than 0 Negligible Hairline Cracks 0.1 0.05 Fine cracks easily treated during normal redecoration. Damage generally restricted to 0.05 to 1 Very Slight internal wall finishes Perhaps isolated slight 0.1 to 1 0.075 fracture in building. Cracks in exterior brickwork visible upon close inspection. Cracks easily filled. Redecoration probably required. Recurrent cracks can be masked by suitable linings. Exterior cracks visible: some 0.075 to 2 Slight 1 to 5 repointing may be required for weather- 0.15 tightness. Doors and windows may stick slightly. Cracks may require cutting out and patching. 5 to 15 or a Tuck pointing and possibly replacement of a number of small amount of exterior brickwork may be 3 Moderate cracks 0.15 to 0.3 required. Doors and windows sticking. Services greater may be interrupted. Weathertightness often than 3 impaired. Extensive repair involving removal and 15 to 25 replacement of sections of walls, especially over but also doors and windows required. Windows and door Greater 4 Severe depends on frames distorted. Floor slopes noticeably. Walls than 0.3 number of lean or bulge noticeably. Some loss of bearing in cracks beams. Services disrupted Usually Major repair required involving partial or greater complete reconstruction. Beams lose bearing, than 25 but Greater 5 Very Severe walls lean badly and require shoring. Windows depends on than 0.3 broken by distortion. Danger of instability. number of cracksFor each property, a Building Protection Assessment was undertaken by Airey Taylor Consulting thatconsidered the predicted maximum damage from the Ground Settlement Plan and the cumulativevariation from the initial damage category assessed in the Property Condition Report. The result wasthe maximum damage category that could be expected. Building protection was required if the“incremental” damage exceeded the following limits: • For heritage structures – very slight (up to 1mm crack width); • For other structures – slight (up to 5mm crack width).In addition to compliance with the PTA’s SWTC, a formal Instrumentation and Monitoring Plan wasproduced to detail the network of devices which would provide feedback for the following: • Construction management to ensure the safety of deep excavations is maintained; • TBM operators and management to control the various TBM operating parameters; • Geotechnical Manager to ensure the project’s impact on the surrounding natural and built environments is minimised and within stated limits.
3 KEY AREAS OF MANAGEMENT FOCUSIn addition to the minimum contractually-specified arrays, there were a number of key constructionactivities that needed specific management requirements: • Protection of key structures: A number of structures, buildings and services needed special treatment due to their calculated risk category. All other structures were monitored according to the Instrumentation and Monitoring Plan to confirm the validity of the design assumptions. • Incident and emergency management: With the extensive array of monitoring devices, LKJV needed a documented process to investigate any devices that showed movement “out of tolerance”, plus planning for major high risk events.These two areas are discussed in more detail in the following sections.3.1 Protection of key structuresThe main structures that needed unique building protection solutions were: • Underpinning of the Wellington Building • Removal of the Mitchell Façade • Protection of the Horseshoe Bridge arches • Compensation grouting of the buildings under which the TBM passed • Perth Rail Yard, footbridge and station platforms (where tunnelling under the live railways was at depths of less than one tunnel diameter) • Claisebrook Sewer.These are each discussed briefly below.3.1.1 Underpinning of the Wellington BuildingThe heritage-listed Wellington Building is a “classic piece of turn of the 19th century cornerarchitecture” under which the new station had to be constructed. As part of the permanent stationstructure, the Wellington Building had an array of tubular steel and grout micropiles drilled fromwithin the basement. A concrete slab was then poured in the basement but not connected to themicropiles. A series of flat jacks were placed between the top of the micropiles and the base of theconcrete slab. The slab was then clamped to the external diaphragm walls, thus forming the roof ofthe new station. Excavation was then commenced in a top down method under the WellingtonBuilding, with the former footings removed with the first level of excavation, and the weight of theslab and building supported by the micropiles and the diaphragm wall. The excavation was thencompleted to base slab level and the tubular steel piles were then cut, and tied into the base slab of thestation providing an uplift anchor. The weight of the building then sat on the roof slab of the newWilliam Street Underground Station. (WSS)To monitor the impact of the construction works, around 40 optical prisms were placed around thebuilding and read from robotic theodolites on the Advertising Tower at Perth Station, and the PostOffice Building in Forrest Place. This allowed for remote monitoring and interpretation of movementsacross the building. Being heritage listed, the damage criteria were stricter for the WellingtonBuilding, which meant a much higher density of micropiles were necessary than would be required ona purely structural basis. Additional manual monitoring such as roof and building levelling, tiltmonitoring and retro target surveying was undertaken to enhance the automated monitoring.
Figure 2 - Wellington Building, and Excavation of Exterior Brick Wall of Building Prior to Tieing Basement Slab and Capping Beam to Diaphragm Wall3.1.2 Removal of the Mitchell FaçadeOnly the façade of the Mitchell Building was heritage listed, but it was located very close to thediaphragm wall alignment for the station. This combined with safety concerns over the stability of thefaçade’s render meant that LKJV sought permission from the Heritage Council to remove the façadeto ensure its protection. Permission was granted and the façade was encased in a steel frame and cutinto pieces to be stored off site, as illustrated in Figure 3. Figure 3 - Mitchell’s Building Prior to, and during breaking up into pieces3.1.3 Protection of the Horseshoe BridgeLKJV’s first consideration for the Horseshoe Bridge was full underpinning through installation of jetgrout columns under the existing footings. However after more detailed analysis of the structure, thepotential for differential movement across the structure was still highly probable. It was determinedthat due to the flexible nature of the steel-framed structure there would be no structural damage, butthe façade heritage features (cement render arches) were susceptible to movement and needed to bepropped with timber arches to prevent damage.3.1.4 Compensation grouting of the “Gold Group”The “Gold Group” buildings (named for their importance to the project) comprise the followingbuildings facing William Street between Hay and Murray Street Malls: Friendlies Chemist, HBF,Hungry Jack’s/KFC, Walsh’s Building (McDonalds, and other retail tenancies).The route of the TBM passed either partially or wholly under these buildings, and LKJV’s BuildingProtection Assessment indicated the need for protection, with a potential design movement of 20mm.
Due to various space and access constraints, LKJV determined the best option was to workcollaboratively with Keller Ground Engineering and implement a TAM compensation groutingsystem. The details of this system are described in more detail in another paper contained herein byNobes & Williams (2007)3.1.5 Perth Rail Station tracks and platformsThe TBM passed twice underneath the station and the live railway, which needed to be kept running atall times. Due to the flexibility of ballasted rail, there was no structural problem should TBMsettlements reach the design limits, but such settlements may cause two operational issues. Firstly, iftilting of the platform edge increased relative to the track there would be insufficient clearance for thetrain, and secondly, if excessive cross cant was to occur it may lead to a derailment.Due to the success of the first stage of tunnelling up William Street (maximum 5mm settlement), itwas determined that an observational approach be taken in preference to preventative measures, withdefined management methods and actions. Elements of this observational method included: • Automatic electrolevel beams on the rail tracks; • Automatic tilt meters on the platform faces; • High density of surface, building and rail settlement points; • 24 hour/7 day week survey, with rail safety presence, and direct ring-by-ring contact with the tunnel shift engineer; • Specific management measures including: - A purpose-written Method Statement covering survey, interpretation, tunnel operations and rail safety; - Daily coordination meetings with all parties (management, survey, geotechnical, tunnel, rail and client); - Web-based access to all monitoring information for all teams; - Emergency scenario workshops.The close contact with the TBM crew allowed for parameters to be changed on a ring by ring basis onthe survey and automatic results presented. The result was that during the passage of the TBM, themaximum final rail movement was limited to less than 10mm.3.1.6 Claisebrook SewerWith the footings of the century old, brick lined, Claisebrook Sewer potentially lying within 800mmof tunnel alignment, protective measures were required. After thorough discussions with WaterCorporation, it was decided to re-line the inside of the sewer with new plastic piping. In addition tothis, LKJV determined that since a subsidence risk was still present during the passage of the TBMdue to fragile nature of the sewer, LKJV also temporarily “over-pumped” the sewer when the TBMwas within a zone of influence.3.2 Incident and emergency management3.2.1 Incident investigationsAll instruments had the following three alert levels determined in the Ground Settlement and BuildingProtection Plan: • Trigger, set at say, 80% of the “design” level as an early warning; • Design, equal to the predicted movement level; • Allowable, set at say 120% of the “design” level and at which remedial action must be taken.
For all instruments, these alert levels were entered into the instrument database (GIMS). If a level wasexceeded, an SMS and email were sent to a nominated group of people to action as appropriate. Whenalert levels were exceeded, a rigorous process was followed to ensure traceability of all decisions.This process is shown in Figure 4. If the alert was not spurious, or a transient event, a more detailedinvestigation was initiated to determine whether any changes to design or construction techniqueswould be necessary. • Monitoring frequencies were set for each instrument, and one full time person was dedicated to ensuring the instruments being read matched the progress of the construction works. During the peak months, a team of up to 19 people were dedicated to gathering, inputting, reviewing and investigating monitoring data:3.2.2 Emergency management through desktop scenariosAlthough the chance of an excavation or TBM failure (to a level requiring the assistance of emergencyservices) was remote, as a key part of the LKJV’s risk management approach, a comprehensiveemergency management process was implemented. To test our management plan so that it was a“live” document, we undertook a series of scenario workshops both internally and externally to LKJV.On 1 December 2005, around 40 representatives from LKJV, Leighton Contractors, LeightonHoldings, New MetroRail (client), Public Transport Authority (operations and infrastructure), City ofPerth, Fire & Emergency Services Authority, Police, Worksafe, Western Power, Alinta Gas, WaterCorporation, Telstra and Main Roads attended a workshop focussing on the bored tunnel section upWilliam Street. One of the key findings to come from the scenario workshops was that of the role ofthe Hazard Management Authorities (HMAs) and how to use the existing Memoranda ofUnderstandings between the HMAs and the various government and private agencies.Another workshop was held on 15 March 2006 with a similar range of external parties, but with moreattendance from railway operations personnel, which was the focus of the day. Also a number ofinternal scenario sessions were held with teams from survey, geotechnical, tunnel and rail to ensurecoordination of activities and communication. We also checked that our communication protocolswere consistent with Leighton Contractors national approach to Crisis Management, and soughtfeedback from Leighton Holdings on lessons learnt from recent crisis management activities (LaneCove Tunnel). Feedback from all sessions was used to make our procedures as user friendly aspossible. The aim was to ensure people knew what to do if something escalates from an incident to anemergency.A Building Access Checklist was also obtained for every property, which LKJV could use to raise analarm in the case of an emergency. Since LKJV’s monitoring and/or tunnelling teams will probablybe the first to know of any incident, we determined that having this information on hand was prudent.
BUILDING AND MONITORING INCIDENT FLOWCHART NEW METRORAIL CITY PROJECT Legend 1 Point of Contact Point of Contact (PC) Incident occurs Primary Secondary PC Point of Contact Building Incident Primary Contact Alternative Contact Peter McGough Kate Stone Buiding Incident Matt Williams Kate Stone IM I & M Manager Monitoring Incident Peter McGough Fugro Monitoring Incident Peter McGough Franco Roselli PD Project Director 2 Infrastructure / Infrastructure/Services Mike Wallis Area Manager CM Construction Manager Services IncidentMichael Wallis Incident Relevant Area Manager 3 AM Area Manager No further action No Is investigation GM Geotechnical Manager (Update register if required? Considerations DM Design Manager required) Establish whether incident is legitimate Yes Considerations Form W1114-CS-4018 1. Notification to Area Manager 4 2. Safety of personnel Record Incident on 3. Structural integrity of building/infrastructure/service register and review 4. New occurrence or sudden change in trend details 5. Compare to existing condition, historical monitoring/reports BUILDING INCIDENT RESPONSE and any background data PC CONTACT DETAILS 6. Review of recorded levels against control levelsLKJV M ANAGEMENT CONTACTS TELEPHONE MOBILE 7. Visit to location and visual inspection 5Rob Wallwork Project Director 9424 5604 0411 259 451 8. Estimate of damage Conduct preliminary 9. Record of construction work being undertaken at time ofTony Cariss Construction Manager 9424 5515 0419 932 132 investigation incidentK. Akabane Ass’t Construction Mgr 9424 5596 0421 404 984Kate Stone Community Relations Mgr 9424 5588 0422 001 037 PC 6F. Aikawa Design Manager 9424 5563 0422 246 067Simon Gegg William Street Station Mgr 9424 5506 0402 898 627 7Paul Farris Southern Area Manager 9424 5631 0422 001 235 No Site assessment by GM to Is further action agree and implementAshley Warner Perth Rail Yard Manager 9228 4942 0421 144 469 required? Yes - URGENT action planLKJV TUNNELLING CONTACTS TELEPHONE MOBILEHenry Yamazaki Tunnel Manager 9424 5654 0422 593 780Frank Hannagan Tunnel Superintendent 0421 053 317 GM/PC YesFrank Bonte General Foreman 0421 053 313 8S. Shigemura Senior Engineer 9424 5653 0422 653 574M. Oshima Senior Engineer 9424 5691 0413 197 300 Are only minorAndrew Shepherd Shift Engineer – Tunnel 9424 5651 0411 659 546 Yes repairs required? Special Response TeamT. Watanabe Shift Engineer – Tunnel 9424 5651 0431 120 366 Special Contracts Manager/NomineeTom Jones Shift Engineer – Tunnel 9424 5639 0422 001 021 Area Manager/NomineeTBM Direct Line 9202 1485 No Geotechnical Manager/NomineeLKJV MONITORING & GEOTECHNICAL CONTACTS TELEPHONE MOBILE LKJV geotechnical/monitoring repPeter McGough Instrumentation and LKJV Subontractor respresentative 9424 5519 0421 053 351 9 Monitoring Manager PTA Representative Complete IncidentOskar Sigl Geotechnical Manager 9424 5514 0411 659 549 Form to initiate Form W11140-CS-4019 If available: Intern’l: +65 9735 2522 AMBER warning Construction ManagerMarc Woodward Geotech Manager (alt) 9347 0000 0417 911 131 Assistant Construction Manager PCBarry Hackett Building Protection Eng. 9424 5511 0421 053 337 Design Manager/Nominee 10LKJV R AIL CONTACTS TELEPHONE MOBILE Project Director Notify PTA (& insurer)Peter Rosenbauer Senior Project Eng’r - Rail 9424 5509 0402 894 801 immediately afterVasil Calcan Senior Rail Safety Officer 0421 635 8491 initiating amberPeter Russell Rail Safety Officer 0407 193 915 warningJohn Welch Rail Safety Coordinator 9424 5541 0421 711 303 PC/GM Investigation considerationsFUGRO CONTACTS (INSTRUMENTATION & MONITORING) TELEPHONE MOBILE 11 1. Notification to Area ManagerFugro Monitoring Phone 9424 5617 0439 930 927 Undertake detailed 2. Safety of personnel investigation and 3. Structural integrity of building, infrastructure, orRitchie Mulholland Chief Monitoring Surveyor 9424 5617 0417 611 295 formal risk service Home: 9302 6256 assessment 4. Review of predicted settlement andKent Wheeler Monitoring Surveyor 9424 5584 0400 980 060 GM/PC/AM construction impactPTA CONTACTS TELEPHONE MOBILE 15 5. Quantification of damage 12 6. Review protection works to determineRichard Mann Project Director 9326 2536 0419 964 209 Notify PTA (& insurer) Verify short term adequacyEric Hudson-Smith Geotechnical Manager 9326 2060 0419 988 861 immediately after remedial action 7. Undertake condition survey to determine extent initiating red alertJock Henderson Special Projects Manager 9326 2093 0419 915 408 closed out of damage PD/CM/GMINSURANCE CONTACTS TELEPHONE MOBILE GM/AM 8. Undertake additional monitoring (eg survey) toBob Perry Marsh Ltd 9421 5666 0414 307 247 13 quantity and monitor further damage 9. Complete risk assessmentEMERGENCY CONTACTS TELEPHONE TELEPHONE 14 10. Review of incident impact on bothPTA Urban Train Control 9326 2214 Can incident No Initiate RED alert via temporary and permanent works designMain Roads Traffic Operations Centre 9428 2222 be resolved? Incident Form and constructionFire and Emergency Services (FESA) 000 1300 1300 39 PD/CM/GM State Emergency Services (SES) 9277 0555 Action considerations 1. Increase monitoring FESA and SES Operations Centre 9323 9333 9323 9322 Yes 2. Continuous monitoringWA Police 000 9222 1111 3. Review construction techniques and equipment Russell Armstrong (Incident Management 16 9222 1694 9222 1958 Verify long term 4. Review emergency procedures Unit and LEMC) 5. Review geotechnical control limits remedial actionAmbulance 000 6. Determine whether amber warning or red alert closed out Bill Thompson 0415 428 617 required GM/DM/CMWorksafe 9327 8777 1800 678 198 7. Stop work where required 8. Determine urgency of repair workCity of Perth 9461 3333 17 Police Post at City of Perth 9325 6000 Bill Strong (LEMC) 9461 5836 0418 947 908 No Repairs Sadak Hamid 9461 3885 0417 977 101 required?Transperth 131 608 9325 2277Alinta 131 352Amcom 1800 222 019 Considerations Yes 1. Identify scope of repair workOptus 131 344 18 2. Establish programme for repair workTelstra 132 203 Seek authorisation 3. Obtain quotesWater Corporation 131 375 for repairs 4. Advise PTA George Basanovic 9386 4952 0417 180 677 CM/PC 5. Advise InsurersWestern Power (generation) 131 351 6. Obtain property owner/representative approval to do work Shane Duryea 9427 4257 0407 445 076 19 Undertake repairsSynergy (retail) Business Faults 131 354 CM Residential Faults 131 353 Considerations 20 Final inspection and 1. Complete "During-construction property condition survey" sign off 2. Issue copy of survey and incident report to PTA and obtain CM/PC property owner/representative sign off. 21 Close out incident Form W1114-CS-4019 SCM/PC Form W1114-CS-4018 22 Notify PTA of close out SCM Figure 4 - Incident Notification and Investigation Process
4 INSTRUMENTATION AND MONITORING4.1 Instrumentation QuantitiesA total of 5205 instrumentation points were installed on the New MetroRail Project to monitor theinfluence of excavation, tunnelling, piling and dewatering activities. The instrumentation types, andquantities installed over the life of the project are summarised in the following table. Table 2 – Instrument Types and Quantities Instrument Type Quantity Installed Surface Settlement Pin – SSP-1 1021 Surface Settlement Retro – SSP- 2 451 Bored Settlement Point – SSP- 3 559 Deep Settlement Point – SSP- 4 19 Building Settlement Point - BSPB 449 Building Settlement Retro - BSPR 1403 Building Settlement Prism - BSPP 285 Tilt Meter, Manual - TILTM 54 Tilt Meter, Automatic - TILTA 33 Crack Meters – CM 82 Electro Level Beams - ELB 150 Strain Gauges – SG 174 Vibration Sensor - VS 12 Inclinometers - INCL 64 Extensometers, Magnetic - EXTM 187 Extensometers, Rod - EXTM 25 Vibrating Wire Piezometers - VWPZ 91 Open Hole Piezometers - OHPZ 146 5205In addition to the above, a further 180 recharge and dewatering bores were drilled on the project, mostof which were also regularly monitored for water levels.The instrumentation density installed on the project was considered to be high, with densities beingconsistently higher than minimum specifications, however a large proportion of the manual settlementpoints (SSP-1 and SSP-3) required replacement and thus approximately 800-1000 of this number waslikely to have been a replacement for points damaged by the construction process. Despite the highquantity of instrumentation, costs for instrumentation and monitoring including drilling remained verylow at approximately 3-4% of the tender price.4.2 Instrumentation TypesThe 18 types of instruments used on the project could be grouped into 7 functional types as follows: • Vertical Ground Movement • Lateral Ground Movement • Building Movement • Building Tilt • Structural Response • Vibration • Groundwater Movement
The instruments used in each of the functional groups, their suitability for purpose, reliability,accuracy, repeatability, and cost effectiveness are discussed in detail in the following sections:4.2.1 Vertical Ground MovementGround Movement, (settlement and heave) was measured using the following instruments: • Settlement Pins (SSP-1), [survey nails and bridge spikes installed in roads, bridges and footpaths] • Settlement Points (SSP-3), [steel reinforcing rods grouted 800mm deep into a borehole] • Deep Settlement Points (SSP-4), [steel reinforcing rods grouted into borehole approximately 1.5m above services] • Rod Extensometers (EXTR), • Magnet Extensometers (EXTM) • Reflective Photogrammetry Targets • Electrolevel Beams • Retro TargetsSettlement pins, settlement points and reference head on the rod extensometers were all measured bymeans of digital levelling using a Leica DNA-10 Digital Level and Barcode Staff. Typically traversesof up to several hundred metres were undertaken without control points. A misclosure limit of 3mmwas used as the acceptance criteria for these traverses. The repeatability of surveys was within +/-1.5mm of the true or mean level as illustrated by Figure 5, which was a point sufficiently away fromall excavation and tunnelling that no settlement occurred. Vibration from pedestrian traffic andmachinery was a common problem, due to the city location, with shaking of the digital level visiblethrough the optical sight. This vibration occasionally resulted in gross errors, which were muchgreater than +/- 1.5mm.Raw survey data downloaded from field was adjusted via the least squares method. Data was then“dumped” into excel spreadsheets for verification. Verified data was then exported to GIMS databasefor permanent record. Contouring or cross sectioning of data was then undertaken. Whilst apparentlytedious, the above method enabled easy verification and manipulation of large quantities of datawithout impacting on the integrity of the raw database. Typical examples of sectional and contouredoutput are shown in Figure 6 and Figure 7.The deep settlement points drilled into the ground (type SSP-3 and SSP-4) typically showed lessfluctuations than the smaller survey pins and spikes (type SSP-1) hammered into the ground and thuswere considered more reliable. The results on the project indicated that there was no discernibledifference in the total measured movement between points installed through road pavements (typeSSP-3) and those installed at the surface of the road (type SSP-1), inferring that the road base wasflexible enough to reflect the ground movements occurring at subgrade level, even where asphaltthicknesses of 100-200mm were found along William Street.An innovative drilling method was used to install settlement points in areas where coring of the uppermaterials was not required. Drilling via vacuum extraction was used to install SSP-3’s and SSP-4’s inmany areas. The method simply involved the use of a pipe connected to suction truck, whichvacuumed up the sands, thus forming a hole, as illustrated in Figure 8 and Figure 9. The method isnormally used in Perth to locate and expose buried services, but we found it was ideally suited to ourpurpose of forming shallow holes in a very quick and cost effective manner with no preparation orclean up required. The shallow holes were formed within a few minutes, with the installation of thegrouted steel settlement rods occurring immediately after hole drilling, thus the whole process wastypically complete in 10-15 minutes.
13.815 SSP_0533 Reduced Level Reduced Level (mAHD) 13.805 13.795 26-Oct-04 25-Dec-04 23-Feb-05 24-Apr-05 23-Jun-05 22-Aug-05 21-Oct-05 20-Dec-05 18-Feb-06 19-Apr-06 19-Jun-06 18-Aug-06 17-Oct-06 16-Dec-06 Figure 5 – Example of Repeatability of Settlement Point Ground Movement Profile Due to Tunnel 2 Excavation - CH 440 PMup (Chainage: 440 PMup +/- 10m, Tunnel 1, Vs = 0.00% Tunnel 2, Vs = 0.60%) 15.0 10.0 5.0 0.0Settlement (mm) -5.0 -10.0 K=0.45 Vloss = 0.70% (320m radius of curvature) (VLOSS = 0.60% if straight) -15.0 -20.0 3/08/2006 8:00 4/08/2006 8:00 -25.0 5/08/2006 8:00 Tunnel 2 Cutter Face at CH 450 approx, 2/8/06 18:00 Tunnel 2 Cutter Face at CH 430 approx, 4/8/06 03:00 6/08/2006 8:00 Design Volume Loss Curve -30.0 -35.0 -50.0 -40.0 -30.0 -20.0 -10.0 0.0 10.0 20.0 30.0 40.0 50.0 Chainage (m) Figure 6 –Example Cross Sectional Display of Figure 7 –Example Contoured Output of Tunnel Settlement with Time Settlement Data Around Major Excavation Figure 8 – Vacuum Extraction Drilling Figure 9 – Vacuum Extraction UnitRod extensometers used on the project were the multiple head grouted anchor type supplied by SlopeIndicator Company (SINCO). The heads were typically grouted 1.5 and 4.5 metres above the tunnel
crown, and during tunnel passage the differential movement of the rods relative to the fixed head wasmeasured manually with micrometer. The results obtained were consistent with tunnel activities andshow that micrometer repeatability was approximately +/- 0.25mm, as illustrated in Figure 10, butcalculated total movements were limited by the head levelling repeatability of +/- 1.5mm.The installation of the rod extensometers was a prescribed requirement on the project, with the benefitof the installed rod extensometers being questionable as the results confirmed the knowledge thatrelatively greater settlements occur at depth than at the surface. The density of the extensometersinstalled (1 per 200m) served no other benefit than to confirm this fact, with the higher density ofsurface monitoring providing a better warning of face loss or heave. Rod 1 - Diff. from Original (mm) Rod 2 - Diff. from Original (mm) Rod Head - Diff from original (mm) Surface Movement at SSP 3023 5.00 4.00 3.00 Heave from tail void Tunnel 2.00 grouting Induced (point 1.5mDiff. from Original (mm) Settlement from crown) 1.00 0.00 -1.00 -2.00 -3.00 No heave at surface -4.00 -5.00 01/ Jan/ 06 08/ Jan/ 06 15/ Jan/06 22/ Jan/ 06 29/ Jan/ 06 DateFigure 10 - Typical Example of Rod Extensometer Figure 11 - Typical Example of Magnet Output Data Extensometer DataMagnet extensometers were used adjacent to excavations in preference to rod extensometers. Thetype of magnets used on the project consisted of magnetic strips attached to corrugated plastic pipe,which slid over standard inclinometer piping. The magnets were installed at intervals of 3-5m downthe inclinometer hole. The inclinometer and magnet were then grouted into place, initial readingstaken; a period of equalisation (~30 days) was then foregone before secondary readings were taken.Readings were taken via lowering a probe down the centre of the inclinometer pipe until it reaches thebottom magnet position. The tape is then pulled up and as it passes each magnet, two beeps are heard;the depth at which the second beep is heard is recorded for each magnet. The method is prone to grosserrors. The repeatability of the measurements is approximately +/- 5mm as illustrated in Figure 11,with gross movements with depth clearly visible once excavation induced settlement commences. Thesettlement of the top of the inclinometer was also checked via regular levelling and compared to theobserved results. The magnet extensometers were considered highly suitable for the intended purposeof measuring large movements where accuracies of +/- 5mm were acceptable. Magnet extensometersprovided a cost effective solution without the need for multiple boreholes or expensive rodextensometers, or alternatively they provided additional information at minimal cost from an existingplanned inclinometer. Experience from this project would suggest that at least 5 readings be taken toestablish an average baseline value before any excavation or external loading commences.Settlement monitoring was also undertaken with retro reflective targets located on rail tracks or surveyspikes in areas where access for regular levelling was not possible. This method of survey wasundertaken using Leica Total Stations and was slightly less repeatable than digital levelling, withhigher degrees of scatter in the measured results. Repeatability using this method was in the range of+/-2mm. This reduced repeatability is likely to be a result of human error as the surveyor focuses onthe centre of the target to get the correct result. As discussed later in the building monitoring section,the effect of one or two face readings is also likely to have impacted on the repeatability of the resultsobtained from this type levelling.Due to the need to focus on the target, the resulting retro target survey is slower than compared todigital levelling. However as this method only requires one surveyor for the majority of the survey,the operational costs incurred can be less than or equal to digital levelling in many cases. Experience
on the project indicates that using retro targets for long term settlement monitoring should only beconsidered where access is limited for level surveys, or where automated instrumentation cannot beinstalled. In contrast, for short term high density monitoring of restricted access areas, retro targetswould provide a cost effective solution as they only cost a few dollars each to supply and install, andthe degree of repeatability can be negated by small traverse lengths and high frequencies ofmonitoring. Figure 12 - EL Beams installed along centreline of Figure 13 - Proximity of Retrieval Box Excavation active rail line to Active Rail LineAutomated Electro-Level (EL) Beam monitoring was also used to monitor settlement of the traintracks as excavation and tunnelling occurred in the Perth Rail Station and Perth Rail Yard. EL Beamswere required as access to the active rail area was limited with trains operating 18-20 hours per day,and excavation was occurring within 1m of active tracks (Figure 12 and Figure 13), and tunnellingoccurred directly below the active train lines of Perth Train Station. Chains of EL beams were used toobtain settlement profiles along the centreline of rail tracks, and transverse movements were alsomeasured every few metres. The ends of each EL beam chain were regularly verified via levelling andsettlement profiles adjusted for end settlement if applicable. Some EL Beams were in place for almost2 years, and despite the vibrations from regular train traffic (every 2-30 minutes), extreme heat, andweather, the EL beams showed no creep effects, with the repeatability of the entire chain remaining inthe range +/- 1.0mm of a mean value. A typical settlement profile and the fluctuation in the readingsobserved over a 6 hour period where no construction activity was occurring is shown in Figure 14,illustrating the high degree of repeatability.The EL beam results were also consistent with excavation and tunnelling activities, with retro targetmonitoring undertaken during tunnelling confirming the accuracy of the individual EL Beams asshown in Figure 15, as well as highlighting the immediate response of the ground/rail as the TBMpassed underneath the beam shown. The sub millimetre accuracy of individual EL beams washighlighted in their ability to resolve the daily 2mm variation in track height due to thermal effects.As a result of this EL beam monitoring, there was continuous train operation throughout the 3 years ofthe project, even with excavations within 1m of active trains as illustrated in Figure 13.An innovative method of settlement monitoring using photogrammetry and auto target recognitionsoftware was trialled on the project. Reflective targets mounted on the sides of “Cat’s Eyes” on theroad above the tunnel, on kerbs and on buildings, were monitored for movement. The aim of thephotogrammetry was to reduce the time the surveyors were spending on William Street, which was abusy one way street through the centre of Perth CBD. By using photogrammetry, thus reducing thesurvey time on the road, the risk of injury to our surveyors was reduced significantly as normal surveyrequired a moving method of traffic management (cars with flashing arrow boards and surveyorsworking in front) in order to maintain traffic flow. In addition to the safety risks, the reduced cost oftraffic management and survey time was a benefit of this method of monitoring.
Figure 14 - Typical Repeatability of EL Beam Located on the Railway (15min readings over 6 hr period) Longitudinal Settlement - EL_001_5L01 at CH 23.143m 10 8 6 Cumilative Movement (mm) 4 2 0 -2 -4 -6 -8 -10 12-May-06 13-May-06 14-May-06 15-May-06 16-May-06 17-May-06 18-May-06 19-May-06 20-May-06 21-May-06 22-May-06 23-May-06 24-May-06 Cumilative Date EB 527 EB 526 Figure 15 - Comparison of EL Beam Data with Retro Target SurveyingThe reflective targets were typically 15-20mm in diameter and glued to the side of the “Cat’s Eyes” asshown in Figure 16. Additional points were also installed on the adjacent kerbs and buildings, asillustrated in Figure 17. Once an initial photo model was generated (from multiple photos), softwareautomatically determined the location and change in movement of each reflective point in subsequentphotos, with each model only requiring four control points. The photogrammetry software used was3DM Calib Cam by Adam Technology, with an example model with automated target pointsrecognised and labelled shown in Figure 18. Typically two photogrammetry surveys per day wererun, with greater than 100m of tunnel coverage in each photo model.There was good correlation with manual level surveys as illustrated in Figure 19 (Note: SSP 3005 =manual level, SSP 2317 – 2319 = Photogrammetry Level), however due to the low levels of tunneldeformation in the study area there was insufficient data to confirm the repeatability of the systemrelative to levelling. The system proved to be fit for purpose and has numerous applications formonitoring of buildings and structures at low cost. The safety benefits of the system cannot beunderstated as it significantly reduced the period the surveyors were exposed to life threateninginjuries such as being hit by a car. If adopted at the start of a project the quantities of building andsettlement monitoring surveys would be reduced significantly thus saving hundreds of thousands ofdollars annually to similar projects of this type.
Figure 16 - Reflective Target on Cat’s Eyes Figure 17 - Reflective Targets on Kerbs/Buildings Figure 18 - Photogrammetry Model with Automatic Target Recognition Generated from Figure 17 432 4 434 2 Photogrammetry Points 0 436S ettlem ent [m m ] -2 438 -4 Levelling 440 -6 Point 442 -8 -10 444 13/11/05 23/11/05 3/12/05 13/12/05 23/12/05 2/01/06 12/01/06 22/01/06 Date SSP_3005 SSP_2317 SSP_2318 SSP_2319 #N/A Figure 19 - Comparison of Photogrammetry Surveys with Level Surveys
Settlement monitoring was the most time consuming and costly exercise on the project. The cost of asurveyor and assistant was approximately A$1500 per day over 2.5 years (approximately A$500,000per annum per survey crew), and 2-3 crews were operating at most times throughout the project. Inaddition to this, daily traffic control at A$1000-A$2000 per day was also required when surveyingabove the tunnels, and on highly trafficked streets where excavation induced settlement was occurring.Experience shows that substantial cost savings in survey would have been possibly gained in usingautomated EL beams mounted below footpaths and roads given that each EL beam costs in the orderof A$2500-A$3000 for a 3m beam length.The use of automated instruments would also have reduced the quantity of engineer supervision on theproject whilst providing highly desirable continuous information to tunnelling and constructionpersonnel. The density of EL Beam readings would also have benefited the end users, as readingswould be spaced at 3-5m intervals rather than the 12-25m centreline spacing than was only possiblewith manual monitoring.4.2.2 Lateral Ground MovementLateral ground movement was measured primarily through inclinometers installed adjacentexcavations and between tunnels. The lateral movement of several sheet piled structures and rail lineswas also measured using retro targets.The inclinometers and casing used on the project were supplied by SINCO and were found to beextremely reliable with approximately 8km of readings (spaced at 0.5m intervals) being undertakeneach week, or more impressively approximately 800,000 readings per year totalling over 400km.During the 2.5 year monitoring period, only the wheels and springs required replacement once.Repeatability of measurements in holes up to 40m deep was found to be less than +/-1mm over the40m, and did not change throughout the project. The results obtained were consistent withexpectations, with the development lateral ground movements and ongoing creep consistent withexcavation activities.Given the quantity of readings obtained by monitoring personnel and the high potential for backinjury, a simple extension piece which fitted over the quick connect collar of the casing was developedat the start of the project. The purpose of the extension piece was to extend the reading height toapproximately waist height (as shown in Figure 20) reducing the need for bending over the holecontinuously as is the common procedure (as shown in Figure 21). As a result there were no recordedback injuries or complaints from monitoring personnel over the life of the project despite the millionsof readings taken. Figure 20 - Inclinometer Measurement with Figure 21 - “Normal” Inclinometer Measurement Extension Piece to Waist Height requiring bending over the boreholeAutomated Inclinometers (IPI’s) were also used on the project in high traffic areas where access forperiods greater than 5 minutes was not possible, or posed an unacceptable risk to monitoring personnelsafety. The IPI’s were used to monitor ground deformations between the two tunnels along William
Street, and in a bus lane adjacent a bridge founded on stone columns. The IPI’s generally performedvery well and produced excellent results, and were stable for periods of more than 1 year. Theresponse of individual sensors was excellent, with a repeatability less than +/-0.2mm as illustrated inFigure 22 below, with the overall accuracy of a 24m chain approximately +/- 0.5mm as illustrated inFigure 23. There was a small proportion of sensors that showed minor creep movements, howeverthese were replaced by the supplier under warranty. It should be noted that in Figure 23, thetemperature sensors recorded increased temperatures after the tunnel passed which was possibly linkedto the exothermic heat generated during curing of the tail void grout. Sensor 1 Relative Movement From Bottom of Hole (RL From -12.985mAHD to -9.985AHD) 5.0 24 Temperature Increase after Tunnel Passage 4.0 23 3.0 22 Relative Movement (mm) 2.0 21 Temperature (0C) 1.0 20 0.0 19 -1.0 18 Response to Tunnelling -2.0 17 -3.0 16 -4.0 15 -5.0 14 04- 05- 06- 07- 08- 09- 10- 11- 12- 13- 14- 15- 16- 17- 18- 19- 20- Jan-06 Jan-06 Jan-06 Jan-06 Jan-06 Jan-06 Jan-06 Jan-06 Jan-06 Jan-06 Jan-06 Jan-06 Jan-06 Jan-06 Jan-06 Jan-06 Jan-067Pt Moving Average Trendlines fitted to Data Date / Time Figure 22 - Typical Repeatability of Individual IPI Sensor BH 2178 A-Axis From Initial 20/01/2006 7:30 Chainage 261.57 15 18/01/2006 6:00 10 16/01/2006 6:00 14/01/2006 6:00 Reduced Level (mAHD) 5 13/01/2006 6:00 0 12/01/2006 6:00 Bored Tunnel Level 11/01/2006 6:00 -5 9/01/2006 6:00 -10 7/01/2006 6:00 -15 4/01/2006 6:00 -10 -5 0 5 10 West East Created: 20/01/2006 7:30 7Pt Average Cummulative Displacement (mm) Figure 23 - Typical Repeatability of IPI Chain (for 16 day period shown in Figure 22)
Whilst expensive to install, the IPI’s are recommended for where long term monitoring of largeexcavations is required in developed countries (i.e. cost of manpower is expensive). A typical 30metre IPI and datalogging system may cost approximately A$20,000-A$25,000 to purchase, howeverif that instrument is logged every two days over a period of 1 year, the cost of two monitoringpersonnel to undertake the same manual inclinometer surveys would also cost in the region ofA$20,000 or more. Whilst the cost benefits are neutral over 1 year, the benefits lie in the continuousinformation gained and ability to warn of impending failures at any time. Additional benefits are thatconstruction personnel can have unrestricted site access, allowing continuous traffic/machinery flowabove (assuming the instruments are located under 1m of fill), and importantly the IPI’s can beretrieved and re-used at other locations thus reducing the overall cost for longer and larger projects.The IPI’s were located in highly trafficked areas, and hence restrictions on installation time and areaavailable for drilling were present, so a drilling technique new to Australia; sonic drilling, was utilised.Sonic drilling allowed rapid dry coring of the borehole from the surface, through 100-200mm ofasphalt, to depths of approximately 30 metres in one night. The continuous coring was of great benefitin geological logging, whilst the dry drilling method was very beneficial environmentally as no sumpsor mud tanks were required to contain wash cuttings, thus also saving valuable clean up time. Themachine used was also compact and thus traffic management was confined to two lanes, and the IPIinstallation was completed in one night. The cost savings compared to traditional rotary methods weresubstantial. The sonic core method was also used to drill and install SSP-3’s and Rod Extensometersabove the tunnel centreline, and to sample jet grout and soil mix columns. The method allowed rapidcoring (in the order of a few minutes) through the thick surface asphalt and crushed rock road baseinto the subgrade, with the machine quickly mobilised to the next drill location in 5-15minutes. Figure 24 – Sonic Drill Rig in William Street Figure 25 – Sonic Rig Showing Coring Barrel and Catch Tray for Water from Core Barrel4.2.3 Building MovementBuilding movement (settlement and heave) was monitored using the following instruments: • Building Settlement Points (BSP), [bolts installed into buildings, bridges and structures] • Retro-Reflective Targets (BSPR) • Optical Prisms (BSPP) • Reflective Photogrammetry Targets • Electrolevel Beams