instrumentation and monitoring of underground works

7/25/2019 Instrumentation and Monitoring of Underground Works

1/11

International Conference and Exhibition on Tunnelling and Underground Space (ICETUS2015)IEM Kuala Lumpur 3-5 March 2015

Instrumentation and Monitoring of Underground Works for KVMRT

S.Vasagavijayan1, C.E. Ooi

1, I.R. Shaiful

1, and

S.Satkunaseelan1

1MMC Gamuda KVMRT (T) Sdn. Bhd., Level 7, Corporate Building (Block E), Pusat

Komersial Southgate, No.2 Jalan Dua, Off Jalan Chan Sow Lin, 55200 Kuala Lumpur.Email: [email protected]

ABSTRACT: Instrumentation and monitoring form the vital link between design hypothesis and actual performance of construction work. It

is impossible to fully define the subsurface condition and its response to underground works. As a result instrumentation and monitoring

forms a crucial component of the risk management procedure to achieve these objectives. The use of different types of instruments andmonitoring frequency to capture the impact of underground works to surrounding ground and structures within the zone of influence arediscussed in this paper. These instrument readings are referred to the pre-established design threshold values defined as AAA (Alert, Actionand Alarm) with a complete AAA response procedure. A proactive action plan can be implemented based on evaluation of the monitoring

data thus ensuring thesafety of job site and surroundings.

KEYWORDS: Risk management, Instrumentation control, Underground works, Data evaluation, Proactive action

1. INTRODUCTION

The 9.5km twin-bored KVMRT tunnels comprises of 7 undergroundstations, 2 portals, 6 shafts and some cut and cover tunnels. Thetunnel alignments pass through challenging geological formations(Kenny Hill and Karstic Limestone) and constructed entirely in the

heart of Klang Valley. For ease of reference sites within Kenny Hill

formation was termed UG1 and UG2 for sites in the KarsticLimestone formation. In order to ensure smooth operation of thismega project, instrumentation and monitoring plays an importantrole in providing vital and timely information to the entire

construction and design team, client, stakeholders and public atlarge. Various types of instruments were placed on the surface and

sub-surface to monitor the surrounding ground conditions andstructures during tunnelling and excavation works. Close to 10,000

instruments were installed and monitored in this mega project.

As construction progresses, exact geotechnical observations and

behaviour monitored using instrumentation assisted construction

team and designers to make a judgment, evaluate and make changesto construction methodology or design parameters, if necessary.Hence, instrumentation monitoring plays an integral part inachieving better control of construction, design verification, safety

of the structures besides legal protection and related economicissues.

All monitored geotechnical parameters were observed and compared

with pre-established design threshold values defined as AAA (Alert,Action and Alarm). A well-documented response procedure was putin place to ensure all involved in the project are receptive to the

instrumentation monitoring results and work proactively to ensure

safe job site and surroundings.

2. INSTRUMENTATION IN KVMRT UNDERGROUND

WORKS

The list of some major instruments used in the KVMRT (UG)project and its function is summarised in Table 1. In this paper, theperformance of some selected instruments in relation to excavationand tunnelling works will be discussed.

2.1 Water Standpipes

During the site investigation stage, some of the SI boreholes wereconverted into water standpipe to monitor the seasonal fluctuation of

water level along the tunnel alignment. For station excavation work,

water standpipes installed at least 1 month before any active

construction works starts. The water table of the surrounding isrequired to verify the design assumption prior to excavation worksso that control measures or re-analysis can be implemented if thereare any changes to the water table level that could impact the

surrounding ground and structures during excavation. As a controlmeasure to maintain ground water level where drawdown is

anticipated, gravity recharge wells with control valves maybe pre-installed subject to the field permeability of the ground.

Table 1 List of Instruments for KVMRT (UG) Project

Measurement of water level from a standpipe is done using a dipmeter which beeps when immersed in water thus providing the

depth of ground water table at this specific water standpipe. Figure 1

shows measurement being taken at a water standpipe in KVMRTMerdeka Station.

Instrument Type Function

Deep Levelling Datum Survey referencing point

Surface Settlement Marker Measure settlement and displacement

Displacement Market Measure ground displacement

Building Settlement Marker Measure structure or building settlement

Optical Prism Measure structure or structuralsettlement, displacement, convergence

Water Standpipe Measure ground water level

Vibrating Wire Piezometer Measure pore water pressure

Inclinometer in Wall Measure wall deflection

Inclinometer / Extensometer Measure deflection and settlement in thesub-surface

Rod Extensometer Measure settlement at specific depth

Tilt meter Measure tilting of structure or building

Load Cell Measure magnitude of applied load

Strain Gauge Measure changes in strain

Heave Stake Measure heaving during excavation

Vibration & Noise Monitoring Measure vibration and noise duringblasting/tunnelling/construction works

Gravity Recharge Well To recharge ground water level

Sub-surface Settlement Marker Measure sub-surface settlement

Electro-level Beam Sensor Measure high accuracy/resolution beamtilting/distortion

Tape Extensometer Measure deformation/convergencebetween two points


2/11


Figure 1 Water standpipe measurement taken at vicinity of KVMRT

Merdeka Station

Based on the water drawdown simulated in analysis due toexcavation or tunnelling work in different ground condition, the

AAA values adopted differ from station to station. The AAAthreshold values adopted for KVMRT Cochrane Station andMerdeka Station are as shown in Table 2.

Table 2 AAA threshold value for water standpipe at KVMRTunderground stations constructed in different geological conditions.

AAA Level

(Water Drawdown)

Cochrane Station

(Limestone)

Merdeka Station

(Kenny Hill)

ALERT 1.0m 2.1m

ACTION 1.5m 2.6m

ALARM 2.0m 3.0m

The water level measured during the excavation stage was used to

counter check the design assumption and to carry out re-analysisbased on the real measurement which is able to provide saving interm of cost and time for construction work. At KL Sentral Station,

the water level based on the monitoring is found to be lowercompared to the water level assumed in the original analysis. The re-

analysis based on the water table measured shows that there is lessactive force and deflection on the existing diaphragm wall comparedto the original design analysis. This has resulted to the omission ofone level of strut (final level) for the stretch of approximately 56m

over the total length of station of 149m. The wall deflection andstruts loading, and ground anchor loading were found to be wellwithin Alert Level throughout the excavation stage as well as themovement of the nearby Muzium Negara building.Saving of time

and cost for construction work has been achieved through this re-analysis study.

2.2 Inclinometers in Wall and Soil

Inclinometers are typically used to measure deflection of the casinginstalled in vertical boreholes. In this project, inclinometers wereused to measure deflection due to sub-surface soil movement anddeflection in the diaphragm wall (D-Wall) and secant bored pilewall (SBP Wall) that was constructed prior to deep excavation

works. The length of inclinometers installed in this project is

generally long where the length reaches 65m at some site due todeep excavation depth. Combination of inclinometer in soil and inwall was used in this project.

Inclinometers play an important role in providing vital information

on the performance of the retaining structure (D-Wall or SBP wall)during excavation works. The quality and accuracy of data is

paramount in ensuring safe construction at all time. To ensurereliable and accurate deflections are recorded, besides the

Figure 2 Schematics of inclinometer installation for KVMRT (UG)project

measurement technique and probe quality, it is important to socket

the inclinometer casing into hard stratum to ensure that there is nomovement at the toe of the inclinometer casing which acts as thereference point for the deflection measurement of the remaining

casing above it. In this project, the inclinometers were socketed 3minto rock or 5m into hard layer (SPT>50). A typical sketch of

inclinometer installation is shown in Figure 2.

Figure 3 Example of deflection profile for inclinometer in wall at

KVMRT Merdeka Station

A typical inclinometer deflection profile is shown in Figure 3. The

inclinometer deflection shown was upon completion of base slab forthe KVMRT Merdeka Station that was constructed by bottom up

method where temporary retaining wall was restrained by temporarystrutting system until the excavation reaches the final excavation


3/11


level (FEL). In this particular case all inclinometers deflection at

different stage of excavation was below the AAA threshold valueand demonstrates that the construction methodology, ground

conditions, etc. were well within the design judgements.

Figure 4 Comparison of inclinometer reading of INW11 with

relevant section of Plaxis analysis output at Merdeka Station

The comparison of inclinometer reading with the Plaxis outputdeflection based on design analysis give an understanding of theperformance of temporary retaining wall while construction is on-going. The comparison graphs are shown in Figure 4. If the

performance is better than the predicted profile by analysis,optimization could be proposed subjected to site condition and re-analysis.

2.3 Ground Settlement Markers (GSM) & Tunnel Array

Monitoring the surface ground condition will be essential in areasthat are close to public access such as roads, utilities, buildings andstructures. GSM are markers installed on the ground and

measurement of ground level at this marker is taken using survey

instruments at specific monitoring frequency depending on theconstruction activity. In this project, GSMs were installed within thezone of influence of station excavation work and tunnelling work.

GSMs were used to determine the impact of station construction onits surrounding and also the impact of tunnelling on the surfacealong the tunnel alignment. This information was used to counter

check the design assumptions. Volume loss calculations based on

the GSM readings serves as a reference for tunnel team to adjusttheir TBM operational parameters.

Figure 5 Example of tunnel GSM array type D and D1

For tunnelling related works, the GSMs were installed in arrays

(shown in Figure 5) to capture cross sectional settlement that will beused to calculate the volume loss and to adjust the TBM parameters

for more effective tunnelling ahead. A typical settlement plot forarray GSM during TBM mining from Semantan NP to KVMRT KLSentral Station is as shown in Figure 6.

Figure 6 Array settlement profile during tunnelling boring works

The estimated volume loss for this array (CH1+450) was 0.13%which is within the 1% as per assumed for building impact

assessment design.

2.4 Optical Prisms and Automatic Total Station (ATS)

Optical prism provides information of point movement in x,y,zdirection with minimum 0.5mm accuracy. Most commonly theseinstruments are installed on sensitive structures and are read on areal-time basis using an Automatic Total Station (ATS). In this

project the numerous ATS were used to monitor various critical and

sensitive structures such as railway, historical buildings, bridges,stadium where close monitoring is required. The KVMRT tunnelswere crossing below the existing SMART Motorway tunnel andreal-time monitoring works for the upper and lower deck using ATS

were implemented. Figure 7 (a) and (b) shows a picture of the

optical prisms and ATS that was mounted on the lower deck of theSMART Motorway tunnel.

Due to some of the sites being located at the urban area (i.e. BukitBintang Station) where the buildings are densely built, it is achallenge to find a suitable location to place the ATS to aim at all

Figure 7 (a)

Optical Prism


4/11


Figure 7 (a) Optical prism and Figure 7 (b) ATS at lower deck usedto monitor the SMART Motorway tunnel during KVMRT

tunnelling works

desired monitoring points (optical prism) as there is a possibility ofline of sight obstruction.

A typical plot of the optical prism movement in the z-directionwhich denotes the settlement is shown in Figure 8. The effect ofboth TBM mining below the SMART tunnel is very minimal.

Figure 8 Settlement plot from optical prisms at SMART Motorway

in relation to KVMRT tunnelling works

2.5 Electrolevel Beam Sensor (EL Beam)

The electrolevel beam sensor (EL Beam) is used to monitordifferential movement and rotation of structures with high precision.Horizontal EL Beams sensors can be used to measure settlement and

heave whereas the vertical EL Beams is used to measure lateralmovement and tilt. At the vicinity of KVMRT Maluri Station, thereis a LRT station and track viaduct that fall within the influence zone

of the station excavation and tunnelling works. In view of this,

structural strengthening (underpinning) works were carried out forthe effected piers and instrumentation and monitoring was essentialthroughout the KVMRT construction work. Stringent AAAthreshold values were adopted to ensure necessary precautionary

measures can be taken before any serious damage is caused to thestructure or affect the train operations. Thus, a total of 12 nos. of ELBeams were installed at numerous locations along Maluri LRTviaduct as per layout in Figure 9. The monitoring of these EL Beams

was automated using a data logging system and were monitored onhourly basis.

Since the EL Beam is electrolytic based, it is sensitive to

temperature. Even though EL Beam is equipped with temperature

Figure 9 EL Beam layout for Maluri LRT viaduct. (Inset - EL Beaminstalled on the beams of this structure)

correction within the instrument itself, the measured data must be

corrected against the surrounding temperature fluctuations. For this

project, we have established the system temperature correlation foreach individual EL Beams. All these instruments are installed

outdoor and are prone to expansion and contraction effects due tosurrounding temperature change and the actual recorded values canbe affected under this circumstances. Figure 10 shows the distortion

values for 2 nos. EL Beams with and without correction. Normally acyclic pattern can be observed on the measured readings that are

affected by consistent daily temperature fluctuations. Uponcorrection this cyclic effect can be minimized or eliminated thusreflecting the actual distortion values.

Figure 10 EL Beam readings before and after system temperature

correction

The distortion values were significantly lower with minimalfluctuations upon applying temperature correction. For example forEL Beam 1, the maximum recorded distortion of 0.257 mm/m has

significantly reduced to 0.048 mm/m after the correction. Thedistortion due to the temperature fluctuation would have triggered a

false alarm since the Alert level was set at 0.25mm/m.

The impact of tunnelling and station excavation works on the MaluriLRT viaduct was also monitored by other instruments such asoptical prisms, BSM, tilt plate and vibrometer besides the EL Beam.The vibration and distortion have not breached the AAA limit

during TBM crossing as seen in Figure 11 and Figure 12.

Figure 7 (b)

LRT Viaduct

KVMRT Tunnels


5/11


Figure 11 Recorded vibration values at the LRT Pier during TBMcrossing

Figure 12 Tunnelling impact on distortion at Maluri LRT viaduct

3. INSTRUMENTATION MONITORING CRITERIA AND

DATA MANAGEMENT

Upon installation of instruments, monitoring works commences.The frequency of monitoring works varies in accordance to the

instrument type, sensitivity of structure and impact of constructionactivity. Monitoring results are submitted by the specialist

monitoring contractors to the projects instrumentation team. Theinstrumentation result will be sent out to the Supervising consultant

(SC), site team, client and other related personnel for action afterchecking process is done. If there is any reading that breached the

AAA level, prompt notification will be sent to relevant parties

immediately so that required mitigation measure can be carried outin a timely manner. Monitoring data for the instruments in theKVMRT (UG) project is also available via an on-line monitoring

system for easy and immediate access for defined users.

3.1 Monitoring Criteria for Tunnelling and Excavation Works

As mentioned earlier in this paper, instruments are installed

minimum 1 month prior to any construction activity. This 1 month

monitoring records is known as baseline record and will be used toestablish the baseline for a specific instrument before starting ofconstruction work at site. Information about the construction impact

based on the instrument response will be meaningful only if a goodbaseline has been established.

The monitoring frequency changes from weekly basis duringbaseline period to daily basis when excavation works commence

until backfilling of the station box. For deep excavation works, the

monitoring frequency adopted for KVMRT (UG) sites for varioustype of instruments are listed in Table 3.

Table 3 Monitoring frequency during excavation for various types

of instruments

For tunnelling works the monitoring frequency is adopted based onthe TBM progress and an example of monitoring requirement for

UG1 tunnelling works is described in Table 4.

Table 4 Monitoring Frequency for bored tunnel in UG1

DISTANCE MONITORINGFREQUENCY (UG1)

50m behind the TBM and 25m in front of

cutter head

Daily

Between 50m to 100m behind the TBM Twice a week

100m to 300m behind the TBM Weekly

300m behind the TBM End of monitoring

*Monitoring frequency is Indicative only and if necessary can be varied

These monitoring criteria (as per Table 3 and Table 4) are applied

for all instruments within the influence zone of excavation and

tunnelling. The frequency of monitoring could be changed subjectedto the site condition especially when a more closely monitoring isrequired at particular area.

As this project is carried out in the heart of the city, sensitive and

critical structures located within the influence zone has been preidentified and special instrumentation and monitoring requirementswere used to monitor them while the work is on-going. Some of the

sensitive structures are including National Museum, Syariah Court,KTMB HQ, Bangunan Stesen Keretapi, Stadium Negara, and etc.

Figure 13 Real-time monitoring of mural at the National Museum

Insert: Automatic Total Station


6/11


3.2 On-line Instrumentation Monitoring System

The monitoring data submitted to the instrumentation team on adaily basis is also checked and updated constantly on to a web-based

on-line monitoring system which is capable of managing largecapacity data from real-time monitoring instruments as well as TBMparameters and progress. A caption of this on-line monitoring screen

is shown in Figure 14.

Figure 14 Web-based instrumentation and TBM monitoring system

This system allows multiple users to login simultaneously and canbe accessed via computer or even smart phones provided they areconnected to internet. This system is able to send prompt via SMS

or email to relevant personnel immediately if there is any breachingof AAA level. This would help to create a good communication linkso that mitigation or safety measure can be carried out in a timelymanner.

4. AAA RESPONSE PROCEDURE AND ACTION PLANS

Upon any monitored instrument breaching the AAA limit, a series

of predefined procedures has been put in place to ensure immediate

and appropriate measures are taken by parties involved.

4.1 AAA Level and Respective Action

When Alert Level is breached, a joint site inspection will be carried

out by the instrumentation team, Supervising Consultant (SC), andrespective site team to check on the instrument and surroundings.

Table 5 AAA Action Plan

Upon the breaching of the second AAA level which is Action Level,besides the site visit, a plan will be put forward in order to ensure

relevant control measure are taken before the instrument breaching

the Alarm level. In the event when instrument breaches Alarm level,site works will be reassessed with respective mitigation measure if

required or works within the area of concern could be suspended

upon SCs advice. In all the above AAA breach, AAA report will becreated and documented for circulation. Details of AAA action plan

are summarized in Table 5.

4.2 AAA Report

AAA reports are created for every level of AAA that is breached. A

notification is sent out and a brief report describing the site activityrelated to the breached instrument will be created by instrumentationteam. Within the stipulated timeframe, the brief AAA report will be

jointly completed by the instrumentation team with input from SC

and construction team detailing immediate response, site activity,site instruction, review of subsequent monitoring, action plan andrecommendation by the SC as listed in Table 6. A sample of AlertReport is shown in Appendix 1. This report will be circulated to the

parties involved for action to be taken as per recommendations.

Table 6 Reporting items of a AAA report and parties responsible

Reporting Item Responsibility

Immediate response ST, I&M,

Site activity (Ongoing Activity) ST

Site inspection I&M

Site instruction SC

Affected instruments I&M, SC

Review on subsequent monitoring data SC

Other actions if necessary ST,SC

Action plan ST, SC, D&T

Conclusion/Recommendations SC

Legend: ST (Site Team), I&M (Instrumentation and Monitoring Team), SC

(Supervising Consultant), D&T (Design and Technical Team)

Instrumentation monitoring is often related to emergency responseplan (ERP) especially when concerning public safety. During the

TBM mining work at KTM rail track, the ERP was drafted together

with KTMB personnel for effective and comprehensive action to be

taken when necessary. The response plan in the event of anyinstrument installed on the track breach the AAA level is presentedat Appendix 2

5. LESSONS LEARNT & RECOMMENDATIONS

Instrumentation is a vital link between design and construction. Theaccuracy of the instrumentation data is important as designers and

contractor will use these data to verify the design assumption and tocheck on the performance of the construction work or the impact tothe surrounding. Accuracy and verification of monitoring data mustbe done at all level by the specialist contractor before official

submissions and upon this if any abnormal results are observed byinstrumentation team or supervising consultant, the monitoring data

must be checked thoroughly to avoid false alerts that could cause

serious detrimental effects to the project and its safety.

Automated system is recommended to be applied on the instrument

that is prone to wear and tear due to frequent measuring action suchas inclinometer. New instruments and technology such as fiber opticsensing system can be implemented as an alternative. This could

help to solve the line of sight problem on the surveying as our tunnelconstruction involved a long distance and located in the highly

dense urban area.

QA/QC procedures to ensure that the basic tools like the measuring

instruments and datum are properly maintained, certified andcomplied in order to ensure that the true instrumentation response is

captured.

Due to the mega scale of this project which involves thousands of

data to be assimilated daily, a data management system capable ofdisplaying information with the added functionality such as

restricted access and alert capability is crucial in creating aneffective monitoring system so that proper action/counteractions canbe implemented in a timely manner.


7/11


6. CONCLUSION

Instrumentation plays an important part in the construction ofKVMRT (UG) tunnels and related stations, shafts and portals. A

combination of various types of instruments serves as important

information to verify the design assumption, to check theperformance of the construction work and to ensure safety byproviding early warning. Thus the selection of instrumentation and

location should be carefully considered and not to exhaust withinstruments and voluminous data leading to lack of appreciation tothe data acquired. Instrumentation requirement should not be a case

of just putting them in regular grid pattern hoping to capture any

unforeseen events but more importantly placed in location thatwould provide beneficial information for design and constructionimprovement. A comprehensive procedure to address the instrumentthat breached AAA creates an effective monitoring system enabling

the mitigation measure to be established in a timely manner which

enhances the safety. Tunnelling impact on surrounding ground andimproving the TBM parameters based on instrumentation results andoptimizing design parameters are key indicator for continuous

success in future projects.

7. REFERENCES

Azlan Adnan, Reza Vafaei, Reni Suryanita, Patrick Tiong, Mohd.Izzuddin Ali and S.Vasagavijayan Structural Health Monitoring

System for Seismic Performance of DBKL Building 2, Seminaron Sustainable Housing, ISI, UTM 2010, October 2010.

Burland, J.B and Wroth, C.P. (1974) Settlement of Buildings andAssociated Damage, SOA review, Conference on Settlement of

Structures, Cambridge, Pentech Press. London, pp 611-654Burland J.B., Standing J.R. and Jardine F.M. (2001) Building

Response to Tunnelling Case studies from construction of theJubilee Line Extension, London. Thomas Telford publishers,

London.Grafinger H. (1997) Digital image measuring system Aninnovative development for the evaluation of geometric and

thematic data in tunnel construction.Hamidah M.S, Mohd Faizal M.J, Muhd Norhasri M.C, Noorli I,Vasagavijayan S (2013) Strain Behavior of Exposed SteelReinforcement Bars Using FBG Sensor International Civil andInfrastructure Engineering Conference, Kuching Malaysia, pp 281-

285Kavvadas M. (1998) Analysis and performance of the NATM

excavation of an underground station for the Athens Metro", Proc.4th Int. Conf. on Case Histories in Geotechnical Engineering, St.

Louis, Missouri USA, March 1998, paper No 6.11.Kavvadas M. (1999) "Experiences from the construction of theAthens Metro project", Proc. 12th European Conference of SoilMechanics and Geotechnical Engineering, Amsterdam, June 1999,

Invited lecture, Vol 3, pp 1665-1676.

Mihalis I. and Kavvadas M. (1999) "Ground movements causedby TBM tunnelling in the Athens Metro Project ", Proc. Int. Symp.on the Geotechnical Aspects of Underground Construction in Soft

Ground, Tokyo, Japan, June 1999, pp 269-274

Terzaghi K. (1946) An Introduction to Tunnel Geology, inRock Tunnelling with Steel Supports , edited by R.V. Proctorand T.L. White. The Commercial Shearing and Stamping Co,Youngstown, Ohio, USA.

Tunnels and Tunnelling (2001) European Practice in geotechnicalinstrumentation for tunnel construction control, Tunnels and

Tunnelling International, April 2001, pp 51-54.Tunnels and Tunnelling (2001) European Practice in geotechnical

instrumentation for tunnel construction controlPart 2, Tunnelsand Tunnelling International, May 2001, pp 48-50.

Vasagavijayan S. Fiber Bragg Grating Sensor Based Hill-slopeIntelligent Monitoring System, Proc. Int. Conf. on Slopes, K.

Lumpur, Aug. 2006

Vasagavijayan S. Structural Health Monitoring using Fiber Bragg

Grating Sensor, National Seminar on Material and StructuralIntegrity, Nov.2008, Kuala Lumpur.

Vasagavijayan S. A New Approach to Fiber Optic SensingCapability for Simple & Robust Monitoring ApplicationsConference of Sensors and Systems, USA, 2009.

Vasagavijayan S. Sensitivity of Horizontal Positioned FBG Sensor

in a Cylindrical FBG Load cell for Cable Prestressing MonitoringApplication, Proc. Photonics Global Conference, Dec. 2012,Spore.

.


8/11


Appendix 1


9/11



10/11


Appendix 2


11/11


instrumentation and monitoring of underground works

Documents