STORMWATER MANAGEMENT AND ROAD TUNNEL (SMART).pdf

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STORMWATER MANAGEMENT AND ROAD TUNNEL (SMART)

DESIGN CHALLENGES TO CUT-AND-COVER TUNNELSBY

Ir. Vince Tan Pik Sing&

Ir. Chin Yew Thai

Sepakat Setia Perund ing (Sdn.) Bhd.

ABSTRACT

The SMART Project is an innovative project and first of its kind in the world. It combinedthe dual functions of drainage and traffic tunnels. The cut-and-cover tunnels weredesigned as cast in-situ box sections. They were cast underground with soil cover asdeep as 16 meter. The top-down construction was designed for certain length of thetunnels where restricted by land uses at the vicinity area. Temporary drainage systemwas designed to divert the stream discharge into Sungai Kerayong in order to constructthe cut-and-cover tunnels. Permanent cast in-situ reinforced concrete drainage channelwas designed to run across the cut-and-cover tunnels.

1. INTRODUCTION

There are four major types of structures in the project namely:

1.1 Inlet and outlet hydraulic structures.

1.2 Stormwater-cum-motorway tunnels.

1.3 Stormwater tunnels.

1.4 Motorway tunnels.

FIGURE 1 in Page 2 shown the general layout and alignment of the tunnels andhydraulic structures at the Inlet and Outlet Systems of the SMART Project.


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Figure 1: General layout of tunnel alignment and hydraulic structures systems

2.0 INLET AND OUTLET HYDRAULIC STRUCTURES

As the SMART Project is mainly a hydraulic project that designed for dischargingstormwater to overcome flash flood problem in the city center. Thus, there were a lot ofrelevant hydraulic structures were introduced at the inlet and outlet systems to cater forspecific hydraulic design needs and functions. The hydraulic structures that weredeveloped in the SMART Project are as follows:

NORTH INGRESS-EGRESS

SOUTH INGRESS-EGRESS

NORTH INGRESS-EGRESS

TBM TUNNEL

OUTLET SYSTEM

INLET SYSTEM


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2.1 Inlet System:

2.1.1 Sungai Klang Diversion Weir.

2.1.2 Sungai Klang Offtake.

2.1.3 Baffle Walls in Holding Pond.

2.1.4 Tunnel Intake

2.2 Outlet System:

2.2.1 Tunnel Outfall

2.2.2 Intake from Attenuation Pond

2.2.3 Attenuation Pond Culvert to River

2.2.4 Outfall to Sungai Kerayong

3.0 STORMWATER-CUM-MOTORWAY TUNNELS

The dual function tunnels are circular section with 11.8m internal diameter and wereconstructed with tunnel boring machine (TBM). The TBM construction method for thistype of tunnels minimized the extent of disturbance to the existing buildings above it. Thetunnels have two deck slabs to serve traffic and diversion of stormwater.

The dual function tunnels are approximately 3km long, which is joining the North andSouth Junction Boxes and Ventilation Shafts to holding pond at Kampung Berembang,

Ampang, and attenuation pond in Taman Desa nearby Sungai Besi Old Airfield. SeeFigure 2 in Page 4 for typical cross section details of the stormwater and motorwaytunnel.

4.0 STORMWATER TUNNELS

This stormwater tunnel was also constructed with tunnel boring machine but withoutprovision of deck slabs for traffic. It is approximately 9.7km long and formed part of thetotal 12.7km long tunnel. The tunnel has a similar circular cross section as dual functiontunnels and solely for discharging stormwater. It was finished with links of pre-castconcrete linings. Each link was formed by 9 numbers of 500mm thick x 1700mm widepre-cast reinforced concrete segments.


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The tunnels are joining the holding pond at Kampung Berembang, North Junction Boxes,ventilation shafts, South Junction Boxes and attenuation pond at Taman Desa nearbySungai Besi Old Airfield. See Figure 3 in Page 5 for typical cross section details of

stormwater tunnel.

Figure 2: Typical cross section details of stormwater-cum-motorway tunnel


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Figure 3: Typical cross section details of stormwater tunnel

5.0 MOTORWAY TUNNELS (CUT-AND-COVER TUNNELS)

The motorway tunnels were constructed by cut-and-cover method. Thus, they are alsonamed cut-and-cover tunnels. All South and North Ingress and Egress Tunnels are cut-and-cover tunnels. Each of the cut-and-cover tunnels was designed with single/doubledeck slabs. Each deck slab has single/double traffic lanes. The south cut-and-covertunnels are located nearby Sungai Besi Old Airfield along Kuala Lumpur-SerembanHighway. However, the north cut-and-cover tunnels are located at Kampung PandanRoundabout, which is joining to Jalan Sultan Ismail and Jalan Tun Razak.

The tunnels were constructed by open cut excavation. It was back filled with wellcompacted and selected earth to match the existing ground levels or designed finishedground levels. This construction method caused a lot of disturbance to existing servicessuch as M&E cables, water, gas and sewer pipelines as well as surrounding buildingsalong or adjacent to the alignment of the tunnels. Deep open excavation may cause lossof ground water and lead to displacement and settlement at the vicinity ground if properprecaution measures are not dully taken with care and attention.


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The tunnels were designed to cater for light vehicle traffic with maximum height of 2.1mand maximum driving speed limited to 60km per hour. It was not designed for diversion

of stormwater purposes. The motorway tunnels were not designed for motorcyclists

either. It was designed for both single/double decks with maximum two lanescarriageway at each deck.

6.0 DETAILS OF CUT-AND-COVER TUNNELS

The total overall length of the four lines of carriageway of the cut-and-cover tunnels isapproximately 4.5km. The overburden of earth back filled on top of the tunnels variesfrom 3m to 16m. The tunnels consist of three major types geometrically i.e. single cell,double-deck single cell and double-deck twin cells.

The clear headroom of the box tunnels varies from 3.1m to 3.6m. Its clear width variesfrom 8m to 14m, depends on numbers of lanes of the carriageway. However, the twincells box tunnels have constant headroom and internal clear width of 3.6m and 8mrespectively. The clear headroom of double deck box tunnels is fixed at 3.6m for lowerand upper decks, both with internal clear width vary from 8m to 14m.

The troughs were designed at the end of cut-and-cover tunnels, approaching groundlevels. It was designed for earth back filled varies from 3m to 7.2m with internal clearwidth varies from 8m to 21m depending on the numbers of lanes of the carriageway.

See Figures 4 to 11 in Pages 6 to 11for typical cross section details of the cut-and-cover tunnels and troughs:

Figure 4: Typical cross section details of box tunnel for single lane traffic


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Figure 5: Typical cross section details of double deck box tunnel for single lane traffic

Figure 6: Typical cross section details of box tunnel for double lane traffic


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Figure 7: Typical cross section details of double deck box tunnel for double lane traffic

Figure 8: Typical cross section details of double deck box tunnel at split


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Figure 9: Typical cross section details for combination of two double-deck box tunnels

Figure 10: Typical cross section details of single cell box tunnel constructed with top-down construction method


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Figure 11: Typical cross section details of trough or U-section

7.0 DESIGN CONSIDERATIONS FOR CUT-AND-COVER TUNNELS

In order to achieve a sound and cost-effective design, massive technical discussionsand meetings were carried out regularly. Every design parameters and requirements ofthe codes of practice were taken into consideration during design stage. The aspects ofdesign considerations for the cut-and-cover tunnels were as follows:

7.1 OPTIMUM DESIGN

The design of tunnels and troughs was not only to meet the code of practices andloading requirementsto achieve a sound structure, optimum design was also animportant aim. During detailed design stage, various sizes of cross sections of tunnelsand troughs were studied and examined in order to achieve the most cost-effectivetunnel section.


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The final cross section of the tunnels and troughs achieved a balance stage of utilizationof concrete section capacity and strength capacity provided by steel reinforcement to

produce the most economical design of the structures. The design process of thestructures was tedious but it was an essential exercise to ensure that output of thedesign was not only to meet the requirements of code of practices, but also the mostcost-effective design of the structure.

7.2 TYPES OF DESIGN LOADS

The tunnels are underground structures subjected to the following primary load cases:

7.2.1 Live load surcharge on top of finished ground level

7.2.2 Overburden earth filled on top of finished ground level

7.2.3 Lateral live load surcharge

7.2.4 Long term and short term lateral earth pressure

7.2.5 Lateral ground water pressure

7.2.6 Uplift pressure due to ground water

7.2.7 Superimposed dead load inside tunnel

7.2.8 Live load inside tunnel

7.2.9 Self-weight of structure

With the above-mentioned primary load cases, the tunnels were analyzed with allpossible different load combinations to cater for temporary and long term conditions. Thedesign of the tunnels were based on the worst case of load combinations and taken intoaccount of service and ultimate limit states to meet durability and performance

requirements of the tunnels.

7.3 FUTURE LOADING/POSSIBLE SURROUNDING LOADS

During detailed design stage, there was proposed Kuala LumpurPutrajaya DedicatedHighway interfaced with North Ingress and Egress of SMART Tunnels. Thus, thehighway engineer design team, structural engineers and geotechnical engineers as wellas contractor met frequently to discuss and identify possible loads that would affect theSMART Tunnels design. The contractors and design consultants of the proposed


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Dedicated Highway were advised to avoid its piled foundation encroach on the proposedalignment of the SMART Tunnels. However, certain area of the troughs has no choice tobe designed to cater for additional loading surcharge induced by the new proposed

reinforced earth wall of the Dedicated Highway.

7.4 TUNNEL SECTIONS

Prior to proceed with detailed structural design of the tunnels and troughs, a lot of effortswere made to determine types of cross sections for the tunnels and troughs. Exchangeof design information and requirements between structural engineers, highwayengineers, mechanical and electrical engineers were regularly carried out in order toproduce a practical and cost-effective design output.

The major design issues govern the sections of tunnel/trough included soil profile,overburden back filled on top of the tunnels, lateral earth pressure on the wall of thetroughs, underground water table, openings and recesses for mechanical and electricalservices. The highway engineers will design the alignment and gradients of the tunnel toincorporate the design information and requirements provided by structural engineers,mechanical and electrical engineers to avoid any abortive works. However, the structuralengineers will incorporate the required openings and recesses for mechanical andelectrical services into the design of tunnels and trough.

7.5 CONCRETE DESIGN MIX

It is one of the important aspects needs to be taken into consideration in order toproduce durable end products that could meet design and performance requirements.

As most of the dimensions of the tunnel cross section were thicker than 1m, the heatgenerated during hydration process of concrete after casting would pose a potential riskto thermal cracks. Thus, design mix of concrete with pulverised-fuel ash (PFA) wasintroduced to prevent possible cracks caused by excessive heat generated duringhydration process of concrete. However, instruments such as thermometers wereinstalled in different points and orientations throughout the casting area of tunnel to

ensure the generated heat during hydration of concrete was closely monitored andunder control.

7.6 SERVICEABILITY ASPECTS

Since cut-and-cover tunnels are underground structures, thus water tightnessrequirement is a very important issue to be tackled for the structures. The tunnels andtroughs were designed with maximum 0.25mm crack width by taking into considerationof exposure conditions.


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All the construction joints of tunnel located at base slabs, walls and roof slabs were

provided with re-injectable type of water proofing system to cater for any possibleleakage of ground water getting into the tunnel. Any leakage at construction jointscaused by ground water will be injected with epoxy grout to stop the ground water.

Waterstop was not provided at the construction joints because the thickness of tunnelcross section was too thick to used. Installation of waterstop such as out of alignment,detached during construction, etc caused the construction joint becomes weak point forleakage.

7.7 GEOTECHNICAL DESIGN ASPECTS

The geotechnical design information playing a crucial and important role in determinationof a project cost as well as the safety of a structure. This is especially important forSMART Project that involved works mainly deep underground excavation and tunnelingsuch as the cut-and-cover tunnels and tunnels constructed with TBM as well ashydraulic structures.

The ground water tables as advised by the geotechnical engineers for North and SouthIngress and Egress Tunnels were estimated at 0.5m and 1.5m respectively below

finished ground level. Based on this design information, all the design of tunnels andtroughs were required to counterbalance uplift force caused by the ground water. Earthfilled and self-weight of the structure are normally used to provide the counterbalanceforce. However, in certain cases toes were introduced to the tunnels and troughs so thatmore weight of earth could be imposed onto the toes to increase the counterbalanceweight against uplift force. This method was more cost-effective as compared withthickening walls and slabs of the tunnel.

Due to constraints of the site and limited working space, toes were unable to beintroduced for some stretches of tunnels and troughs located at the North Ingress andEgress. In order to overcome the floatation problem, after tedious cost-effective studies,

soil nails/rock bolts were eventuallyprovided underneath base slab of the tunnels andtroughs depending on types of ground conditions. Each of the soil nails or rock boltswere designed with 100KN working tensile force based on the geotechnical engineersadvice and recommendation. See Figures 12 and 13 in Page 14 for typical crosssection details of the tunnel and trough with integrity of rock bolts:


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Figure 12: Typical cross section details of tunnel integrated with rock bolts

Figure 13: Typical cross section details of trough integrated with rock bolts


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Extensive instrumentation was used for monitoring of possible ground displacement and

settlement. Thus, any early discovery of ground movement could prevent unnecessarydamages and remedial cost to adjacent buildings or structures.

The cut-and-cover tunnels in SMART Project were majority directly supported on rockexcept a small stretch of tunnels that located nearby Sungai Kerayong at South Ingressand Egress were supported on piled foundation. Transition zone between rock and piledfoundations had been carefully taken care for. Soil treatment was also carried out tolocalized area, which was limited to maximum 2m deep. Temporary retaining walls wereintroduced when deep soil replacement was necessary.

7.8 TOP-DOWN CONSTRUCTION METHOD

Apart from Open Cut Excavation Method for construction of the tunnels, Top-downConstruction Method was used in part of the South Ingress and Egress Tunnels close toSungai Besi Old Airfield. The construction method was adopted due to constraints ofexisting site conditions and tight construction schedule. Also, the traffic flow at thestretch of Sungai Besi Old Airfield along Kuala Lumpur-Seremban Highway was veryheavy and difficult to be diverted for other construction methods.

The top-down construction works began from upper portion toward lower portion of thebox tunnel. It was very different and reversed from conventional construction method inthe sequence of construction. The construction sequences were to cast the roof slab ofthe tunnel first. Then proceed with the base slab and wall construction.

Openings of 4.5m x 8.0m, 4.8m x 8.0m and 6.0m x 8.0m sizes were cast in the roof slabof the tunnel. The openings were required to provide accesses for excavationunderneath the roof slab and casting of r. c. base slab and walls. Upon completion of thebase slabs and walls, the openings were cast back with concrete.

Based on the top-down construction method, temporary structural strut system for thetunnels was not required. The tunnels were no longer directly supported on shallowfoundation conventionally but supported by reinforced concrete contiguous bored piles(CBP) at both sides. The CBP walls were acting as temporary retaining wall as well aspart permanent wall of the tunnels. The reinforced concrete contiguous bored piles were800mm diameter. See Figures 14 to 16 in Pages 16 and 17 for part layout and typicaldetails of openings for top-down construction:


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Figure 15: Typical 4.8m x 8m opening details in tunnel roof slab for top-downconstruction

Figure 16: Typical 6m x 8m opening details in tunnel roof slab for top-downconstruction


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7.9 EXISTING SERVICES OF CABLES AND PIPES

This aspect was always occurred during construction at developed area. Cautiousattention and careful verification of the location, alignment and orientation of the existingservices were carried out to prevent any damages and interruptions to the services.Thus, all the existing services such as water pipes, sewer pipes, gas pipes, M&E ductsor cables, etc were made available during design stage to avoid unnecessarydisturbance during construction.

At South Ingress and Egress, there was no choice to reduce the base slab thickness of atunnel to isolate the existing 1.2m diameter concrete sewer pipe touching tunnel. Thesewer pipe was running across underneath the box tunnels.

7.10 INTERFACES WITH TEMPORARY WORKS

As the tunnels were built with open cut excavation method, a lot of temporary worksystems were introduced into this project. These included temporary retaining sheet pilewall propped by a few layers of horizontal struts, which restrained by the king postsvertically. Due to the support system of the temporary retaining walls, king posts wereinstalled at certain area to provide restraint for the temporary struts. Thus, the king postswere cast with the base slab of trough and tunnels. The reinforcement details of thebase slab were modified to suit the construction works.

7.11 INTERFACES WITH EXISTING RIVER

Besides dealing with existing services in the SMART Project, at the South Ingress andEgress, the double-deck box tunnels were running across an existing branch river ofSungai Kerayong. The river was approximately 14m wide and 4.5m deep from finishedground level. The invert level of the riverbed is about 2.5m above roof slab of the boxtunnels. The cross section of the tunnels is 11.8m wide x 10.2m high underneath theriver.

In order to carry out construction works of the tunnels, a temporary drainage system wasintroduced to divert the flow of the river. After completion of the tunnel constructionworks, the river was reinstated to match the original alignment and sizes of the existingSungai Kerayong. Soil treatment was also carried out underneath of the river.


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8.0 CONCLUSION

The design and construction of the cut-and-cover tunnels in the developed downtown ofKuala Lumpur, indeed was a great challenging task to the design engineers as well ascontractors. This is especially difficult for the works carried out nearby Kampung PandanRoundabout and Sungai Besi Old Airfield along Kuala Lumpur-Seremban Highway,which involved heavy traffic flow and existing services, highway flyovers and high risebuildings.

The construction of SMART Project was challenging. However, the effectivemanagement during detailed design and construction stages made it successfullyimplemented on the site. The good lines of communication and coordination betweenconsultants, contractors and authorities played an important role for achievingthe

smooth and successful implementation of the ever first type of tunnels in the world thatnot only function for discharging stormwater but also for traffic purpose.


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REFERENCES

British Standards:

BS 5400 - Steel, concrete and composite bridges

Part 1 - General statement

Part 2 - Specification for loads

Part 4 - Code of practice for design of composite bridges

BS 6031 - Earthworks

BS 8002 - Earth retaining structures

BS 8004 - Foundations

BS 8081 - Code of practice for ground and anchorage recommendation for soil and rockanchorage system of grout or mechanical pipe

BS 8110 - Structural use of concrete:

Part 1 - Code of practice for design and construction

Part 2 - Code of practice for special circumstances

BS 8007 - Design of concrete structures for retaining aqueous liquids

Departmental standards:

BD 14/82 - Design manual for roads and bridges




BA 24/87 - Design manual for roads and bridges




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