Genting Tunnel Design

Chapter 41

DESIGN AND CONSTRUCTION OF THE NEW TUNNEL AT GENTING SEMPAH, MALAYSIA S.J. Porter,1 M.T. McRae,2 and R. Wright3 1

Hyder Consultants, Australia; 2Jacobs Associates, El Segundo; 3 Transfield Tunnelling, Malaysia ABSTRACT

The new tunnel at Genting Sempah is part of a privately funded infrastructure project that involves duplicating the existing highway extending from the Gombok Toll Plaza near Kuala Lumpur to Karak, in Malaysia. The 60 km long tollway includes an 800 m long, twolane highway tunnel with excavated dimensions of 10.5 m wide by 8 m high. The majority of the tunnel extends through slightly to moderately weathered, moderately to highly jointed quartz porphyry. Excavation of the tunnel was performed using drill and blast methods and the primary tunnel support consists of rock dowels and shotcrete except for short sections adjacent to the portals where steel sets were utilized. A portion of the tunnel encountered sheared and altered material that was successfully supported using rock dowels and shotcrete. The final lining for the tunnel consists of mesh and fiber reinforced shotcrete. The flexible nature of the primary support and shotcrete final lining resulted in considerable cost savings and expedient construction methods. INTRODUCTION

The Kuala Lumpur-Karak Highway is located northeast of Kuala Lumpur in central Malaysia. An existing two lane highway is being duplicated by private investors under a Build-Own-Operate-Transfer (BOOT) contract with the Malaysian Government. The Kuala Lumpur-Karak Highway is approximately 60 km in length. Mid-length it passes through the Genting Highlands - an area famous in that part of Asia for its casino and resorts as well as its natural beauty. The highway crosses the highlands at Genting Sempah (“Sempah” meaning saddle). A two lane bi-directional tunnel, approximately 900 m in length passes through the saddle. As the highway is being duplicated to provide two lanes in each direction it has been necessary to construct a second tunnel, parallel to the existing alignment through the saddle. Refer to Figure 1 for a site plan. At the time of preparation of this paper the excavation and lining of the tunnel were complete and fit-out was in progress. MTD Prime, a Malaysian public company has the “Concession” from the Government to build and operate the toll road. They will own the toll road during the “Concession Period”, after which time ownership will transfer to the Government. MTD Construction has a contract with MTD Prime to design and construct the highway duplication. MTD Construction have in turn contracted Transfield Constructions, an Australian company with locally owned opera-

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1997 RETC PROCEEDINGS

tions in Malaysia, to design and construct the new tunnel at Genting Sempah due to their expertise in tunneling. The construction cost of the t unnel is approximately U.S. $12 million.

Figure 1. Site Plan

DESIGN/CONSTRUCTION OF NEW TUNNEL AT GENTING SEMPAH

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Transfield engaged Hyder Consulting in Australia to undertake the design of the tunnel, including the geotechnical investigations, temporary and permanent tunnel support and mechanical and electrical services. Jacobs Associates provided specialist expertise in the design of the tunnel support. GEOLOGY Geologic Setting

The tunnel is located below the Genting Sempah Pass, a low point of the Genting Chain which is a major range of mountains trending from the northwest to southeast and delineating the watersheds of the Gombak River to the west and the Kenyol River to the east. The slopes in the vicinity of the tunnel are very steep with gradients ranging from 30 to 70 percent. There are few natural outcrops in the area of the tunnel due to the 2 to 5 m cover of lateritic soils over much of the area. The combination of steep slopes and a continuous soil cover makes the characterization of the rock mass quite difficult. The majority of the rock within the region has undergone tectonic deformation associated with the Genting thrust belt, the major fault zone of the area. Most of the faults are low angle thrust faults developed in response to east-west lateral compression. Geologic Units

The great majority of the tunnel extends through a quartz porphyry that has also been described as a rhyolite porphyry and includes porphyritic rhyolite, rhyolite, rhyodacite, dacite and rhyolitic tuff breccia. Generally the rock is moderately to highly jointed and most joints have been recemented with secondary minerals, mainly calcite, kaolin and chlorite, and subordinately with quartz. Generally the rock encountered at tunnel depth is slightly t o moderately weathered. However, the weathering profile is highly variable and the highly fractured and faulted material tends to be more highly weathered. The weathering, alteration, shearing and close jointing has largely destroyed the original texture of the parent rock. The three rock classes, defined during the geologic characterization, are summarized below: • Class A - Slightly altered/fresh rock • Class B - Altered rock, zones disturbed by weathering and faulting • Class C - Highly altered, cataclastic to mylonitic rock The unconfined compressive strength of the samples of intact rock tested during the geological investigation for the original tunnel ranged from 24 to 240 MPa. A seismic refraction survey was performed during the geotechnical investigation for the new tunnel and included surface seismic refraction, surface-to-borehole, borehole-tosurface, and cross-hole seismic methods. Typically the recorded compression wave velocities close to tunnel depth are in the range of 3500 to 5000 m/sec. Lower velocity materials were generally limited to depths less than 25 m. Geologic Structure

The predominant joint sets within the rock mass are subvertical, followed by those inclined from 31o to 60o with a third set having an inclination of less than 31o. The average

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spacing of the subvertical joints is approximately 50 mm, 100 to 200 mm in the intermediate system, and 300 to 900 mm in the subhorizontal set. Typically the subvertical joints are undulose with thin coatings of calcite. The intermediate joint set are typically rough planar to irregular, and commonly stepped with some porous zones. The subhorizontal set can generally be characterized as clean, uncoated, planar and smooth. Groundwater

In general the groundwater level is relatively close to the ground surface. Reportedly, water inflows into the existing tunnel were significant during construction but have been successfully controlled in the completed tunnel. Rock Mass Classification

The Norwegian Geotechnical Institutes Q-System (Barton et. al., 1974) was used to characterize the rock mass during the geologic investigation. The Q values were assessed based on inspection of the rock core obtained from the exploratory drilling. Q was est imated to range between 0.01 to slightly great er than 0.1 which corresponds to ex tremely poor rock using the Q-systems descriptive terminology. DESIGN General Arrangement of Tunnel

The alignment of the new tunnel was chosen to take advantage of the natural landform, allowing its length to be minimized to approximately 800 m (approximately 100 m shorter than the existing tunnel). The tunnel profile is a typical horseshoe shape with a finished width of approximately 10 m and a height of approximately 8 m (see Figure 2). Near the eastern portal the new tunnel is located as close as 17 m to the existing tunnel with the separation increasing rapidly away from the portal to a maximum of 30 m. The finished tunnel will incorporate two 3.75 m lanes, shoulders on each side, and a 650 mm wide emergency walkway. Architectural wall panels will be provided on each side of the tunnel. The tunnel services will incorporate ventilation, lighting, traffic controls, communications, fire emergency services, drainage and a central monitoring and control system.

Figure 2. Tunnel Cross Section


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Design of Tunnel Support

The design of the tunnel support was developed using empirical methods (Terzaghi, 1946, Wickham, Tiedemann, and Skinner, 1974, Bieniawski, 1993, and Barton et. al., 1974) and the past experience of the designers. Based on observations made during a visit to the site, it was surmised that many of the discontinuities within the rock mass are healed, and these healed discontinuities were “broken” during the drilling and sampling process such that the assessment of the rock mass based on inspection of the core was misleading. This conclusion was confirmed by the results of the seismic refraction survey. Grimstaad and Barton (1993) provide the following relationship between compression wave velocity and the Q-value: ( Vp 3500 ) −

q

=

10

1000

where Vp is the compression wave velocity in m/sec. Using a conservative estimate for Vp of 3000 m/sec provides a Q value of 0.3 which is significantly higher than the upper end of the estimated range for Q (i.e., 0.1) developed during the geotechnical investigation. Four tunnel “support types” were developed for the range of rock conditions anticipated along the tunnel and general rock mass descriptions were defined to aid in the selection of the appropriate support type. These descriptions are presented below in Table 1. Table 1. Description of Rock Conditions for Different Support Types Support Type 1

2 3 4

General Rock Description Fresh to slightly weathered (altered) rock, with tight, rough to slightly rough, moderately to closely spaced joints, slightly weathered walls. Fresh to moderately weathered (altered) rock with tight, slightly rough, closely spaced joints, moderately weathered walls. Moderately weathered (altered) rock, with coated, very closely spaced joints, highly weathered walls; rock includes numerous sheared zones. Crushed and sheared, moderately weathered (altered) rock, with gouge zones

Support Types 1 to 3 utilize rock dowels and shotcrete for primary tunnel support. The rock dowels are 3.3 m long, untensioned and full column grouted with cement grout. The longitudinal spacing between the dowels ranges from 1.5 to 2 m and the circumferential spacing ranges from 1.25 to 1.5 m. Steel sets or lattice girders and shotcrete were the specified primary support measures for Type 4 ground and the contractor elected to use steel sets. The sets consist of 200UC60 sections. Shotcrete was specified to be applied as necessary to control raveling in Type 1 ground, whereas a minimum shotcrete thickness of 50, 100, and 100 mm was specified for Types 2, 3, and 4 ground, respectively. All primary shotcrete was specified to be reinforced with collated fibrillated polypropylene (CFP) fibers to reduce rebound and improve the flexural toughness, and increase the fatigue and impact resistance. Fiber reinforcement also helps reduce shrinkage cracking which, in t urn, reduces the permeability of the shotcrete. A reinforced shotcrete wallplate was designed and in-

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stalled at the base of the top heading in Type 4 ground. The final lining for the tunnel consists of mesh (F41) and fiber (CFP) reinfor ced shotcrete, 125 to 150 mm thick. It was considered that the two types of reinforcing would optimize the performance of the lining as the mesh provides a quantifiable flexural strength and the fiber reinforcement provides the benefits listed above. Drainage for the tunnel is provided by str ip drains, spaced at 5 m, installed behind the layer of primary shotcrete. The layout of the tunnel support for Type 3 ground, the most prevalent along the tunnel, is shown on Figure 3. CONSTRUCTION

The tunnel was excavated by drill and blast methods. Excavation was carried out using a heading and bench method due to the size of the tunnel and generally poor rock conditions. A heading from the east, approximately 500 m in length, was constructed first due to the accessibility of this portal area. After development of the western portal, involving a large open cut excavation, a western heading commenced. At this time, advancement of the eastern heading was stopped and the bench removal operation undertaken. Following the completion of the bench excavation, t he final lining was installed in the eastern heading. After breakthrough, the bench removal and final lining operations were completed in the western heading.

Figure 3. Tunnel Support Measures in Type 3 Ground Excavation/Primary Support Sequence

The excavation and primary support sequence was typically as follows: (i) drill face; (ii) charge face;


(iii) (iv) (v) (vi) (vii)

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blast and dissipate smoke by ventilation; scale loose material from the crown and sidewalls; remove muck from face; apply shotcrete to crown and walls; and install rock dowels. Face Drilling and Blasting

Drilling of the face was carried out using an Atlas Copco H135 drill rig with two drill booms and a man basket. The heading drilling comprised approximately 80 holes in a burn cut pattern. The length of drilled hole was varied according to the ground conditions. The holes were charged using locally produced Emulite cartridge explosives and non-electric detonators. Lighter charges were placed in the perimeter holes to control overbreak. As the separation to the existing tunnel is only 17 m at the eastern portal and 30 m maximum, care was taken to control blast vibration levels at the existing tunnel. Vibrations were monitored in the existing tunnel adjacent to each blast. Blasting v ibration was successfully controlled and the recorded vibrations were consistently within the specified maximum peak particle velocity of 50 mm/s and no damage to the existing tunnel was observed. As a precaution, the existing tunnel was cleared of traffic prior to each blast. Mucking Operations

Mucking was carried out using a Caterpillar 966F rubber tired loader and articulated dump trucks. The mucking operation included scaling of all loose material from the tunnel crown and walls. Air quality was monitored regularly to ensure diesel fumes were being effectively removed by the ventilation equipment.

Figure 4. Tunnel Mucking Operation in Top Heading Shotcrete

Wet mix shotcrete was batched at an on-site batch plant. It was applied to the walls

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and roof of the tunnel using an Alive 285 shotcrete machine and Alive 305 remote boom. The shotcrete was applied immediately after mucking. Where c onsidered necessary for stability, however, the boom allowed application of shotcrete over the top of the in-place muck pile. Rock Dowels

The Type 3 support employed for the majority of the tunnel required installation of eleven 3.3 m long rock dowels over the crown of the tunnel and in the side walls as necessary. After drilling the pattern of holes, the dowels were installed with prefixed grout tubes and centralizers. The collars were sealed and the dowels grouted using an MAI pump. Quality Control for Tunnel Support

The Project was undertaken as a “Quality Assurance” (QA) contract and, hence, the responsibility for quality control was totally with the Tunnel Contractor. This responsibility included the selection of the appropriate tunnel support type based on the encountered geotechnical conditions. During the early stages of the project, inspectors and “check engineers” were employed by the Client to overview the work of the Contractor. However, in the later stages of the project, the Client had full confidence in the Contractors quality control methods and these additional quality assurance personnel were no longer required. This resulted in immediate cost savings as well as providing the Contractor additional flexibility in planning the sequence of construction activities which helped in completing the project early and within budget. The following were the principle quality control testing measures for the tunnel support specified by the designers and implemented by the Contractor: • • • • •

•

material testing for concrete and shotcrete such as cube and slump tests; test panel field trials for shotcrete; cores for thickness measurement and strength testing for the final shotcrete lining; Schmidt hammer testing of the final shotcrete lining; pull-out tests on rock dowels at commencement of work and tensile load tests of the rock dowels at a rate of approximately 2 percent during tunneling; and convergence monitoring. Excavation and Support Performance

As noted earlier, the predominant support type used was Type 3. Type 4 support was employed near the portals and approximately 100 m of Type 2 support was used. The maximum advance rate achieved was 36 m per week in the heading and 65 m per week in the bench. The primary tunnel support measures used for the great majority of the tunnel, consisting of rock dowels and shotcrete, proved to be very effective apart from two minor collapses in the tunnel crown that occurred shortly after installation of the rock dowels and shotcrete. These occurred in the time before the support had reached a significant propor-


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tion of its design strength. The use of accelerated grout with the dowels may have provided earlier support and alleviated this problem. Resin grouted dowels were not used because obtaining the required bond with resin cartridges may have proved difficult to achieve consistently in the ground conditions encountered and because of corrosion considerations. Convergence was measured using survey equipment at regular intervals along the tunnel and at locations with poor ground conditions selected by both the client and the contractor. No appreciable convergence was measured and there was no evidence of stress related cracking in either the primary or final shotcrete linings. The shotcrete final lining proved to be an economical alternative to a cast-in-place concrete lining as the surface profile of the shotcrete can follow the excavated profile quite closely, resulting in considerable savings in materials alone. Tunnel Fit-out

Civil works commenced in the eastern heading following completion of excavation and lining. Blinding concrete was placed in the invert to minimize deterioration of the tunnel floor and to ensure an even thickness of the overlying no-fines concrete drainage layer. The tunnel drainage system was constructed and then the no-fines concrete placed and roller compacted. The pavement, consisting of 230 mm of reinforced concrete, was then constructed. Finally, the precast concrete new jersey barriers, cable ducts, pulling pits and walkway were installed. At the time of preparation of this paper the mechanical and electrical services fit-out was in progress. This work is being undertaken by Siemens under a subcontract to Transfield. Following behind the mechanical and electrical works will be the final construction activity the installation of the architectural wall panels. The tunnel operating and emergency services will then be tested and commissioned and the new tunnel at Genting Sempah will be ready to receive traffic. CONCLUSIONS

The design process used for the new tunnel at Genting Sempah illustrates several important points. First, it shows that with today’s communication technology it is possible to perform a fast-track design remote from the construction site - in this case with parts of the design performed on two continents. Second, the design and successful completion of the tunnel validates the use of empirical design methods for tunnels with diameters of approximately 10 m. Finally, this project highlights the importance of using a number of exploratory methods to characterize a rock mass and showed that borings alone, especially in a rock mass with healed discontinuities, can provide an unfavorable and perhaps misleading view of rock mass quality. The construction of the tunnel was completed ahead of schedule and within budget and is another example of the efficiency and economic benefits of using rock dowels and shotcrete for permanent tunnel support. The quality assurance contract used for the project was successful and indicates that in many cases it may be beneficial t o assign some, if not all, quality assurance responsibility to the Contractor on a design-build project.

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1997 RETC PROCEEDINGS BIBLIOGRAPHY

Barton, N.R., Lien, R. and Lunde, J., 1974, Engineering Classification of Rock Masses for the Design of Tunnel Support, Rock Mech. 6, 189-239. Grimstaad, E. and Barton, N., 1993, Updating the Q-System for NMT. Proc. Int. Symp. on Sprayed Concrete - Modern Use of Wet Mix Sprayed Concrete for Underground Support, Fagernes, Oslo. Lang, T.A., 1961, Theory and Practice of Rockbolting, Tans. American Inst. Min. Engrs, 220, 333-348. Terzaghi, K., 1946, Rock Defects and Loads on Tunnel Supports. In Rock Tunneling with Steel Supports, (eds R.V. Proctor and T.L. White) 1, 17-99. Youngstown, OH: Commercial Shearing and Stamping Company. Wickham, G.E., Tiedemann, H.R., and Skinner, E.H., 1972, Support Determination Based on Geological Predictions, In Proc. North American Rapid Excavation and Tunneling Conf., Chicago, 43-64.

Genting Tunnel Design

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