Automation in Construction 15 (2006) 627 – 639 www.elsevier.com/locate/autcon
Automated construction of the Paghuashan tunnel for Taiwan High Speed Rail (THSR) project Pao H. Lin a,*, H.P. Tserng b, Ching C. Lin c a b
Department of Civil Engineering, Feng Chia University, Taichung 407, Taiwan Department of Civil Engineering, National Taiwan University, Taipei 106, Taiwan c China Engineering Consultants, Inc., Taipei 106, Taiwan Accepted 30 August 2005
Abstract The Taiwan High Speed Rail (THSR) project is the most significant infrastructure development in Taiwan, and the largest Build – Operate – Transfer (BOT) project in the world. The project is required to be completed and in operation as soon as possible. The THSR’s longest main tunnel, at 7364 m long crossing Paghuashan hills, was considered as the most critical sub-phase of the project. To ensure effective control of this critical phase, the joint venture contractor brought highly efficient construction equipment and fresh planning ideas into Taiwan. The main tunnel_s excavation work was carried out using a method minimizing harmful loosening of adjacent groundmass. Engineering records reveal that the Paghuashan project was implemented successfully. The project was completed two months ahead of schedule, and even recorded the best monthly excavated length of 250 m, marking a significant milestone in the progress of the THSR project. This paper introduces the cycle of excavating and lining technique used in constructing this key tunnel, and an the analysis of work productivity through the utilization of these automated equipment and facilities. This investigation also provides detailed insight and experience for future long tunnel construction, particularly in bidding for Design – Build (DB) contracts. D 2005 Elsevier B.V. All rights reserved. Keywords: Tunnel; Automation; Taiwan; BOT
1. Introduction Taiwan has vast uninhabited mountainous regions. About 95% of the national population of 24 million live on the narrow strip of coast in the western part of the island. Conventional intercity transportation options cannot easily manage the increased traffic loads, resulting in service quality deterioration. Considering the expected rapid growth in demand for intercity travel, and with Government officials looking to the example of Japan with its highly advanced system of dedicated high-speed routes linking major cities, which have famously transformed medium and long-distance travel between major population centers, the Taiwan High Speed Rail Project (THSR), emphasizing safety, mass transit, restricted land use, energy * Corresponding author. Tel.: +886 4 2451 7250x3147; fax: +886 4 2451 6982. E-mail addresses:
[email protected] (P.H. Lin),
[email protected] (H.P. Tserng). 0926-5805/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.autcon.2005.08.002
efficiency and minimal pollution, is expected to alleviate the overcrowding traffic, and improve the regional development balance significantly. The Taiwanese Government drew up a detailed proposal to construct a new 345-km route, capable of running trains up to 300 km/h between the island’s north and south within a 90-min travel time. The THSR revolutionizes the concept of space afforded by its fast linking, making one-day commuting along the extensively developed west corridor a reality [5]. The shortage of public funds to finance new infrastructure projects has led the government to adopt the BOT infrastructure delivery approach, where the private sector finances, designs, builds, operates and maintains the facility for a stipulated period of time, then transfers it to the government. In July 1998 the concessionaire, Taiwan High Speed Rail Company, and the government, signed a 35-year concession agreement including a commitment to raise the cash to construct the line from private sources. Physical work on the project began in early 2000. Over 300 km of the line’s total 345 km length was built either in tunnels or on viaducts, owing to the densely-populated
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corridor through which the system passes. The system is scheduled to commence commercial operation in late 2005. The THSR Project is the largest transportation infrastructure initiative in Taiwan, and the first major Taiwan national public facility involving private investment. The US$13 billion makes this project one of the largest construction projects of the late 20th century. The THSR project undoubtedly bears significant expectations, not only in terms of the socio-economic development in Taiwan, but also as a milestone of industrial technology initiatives. Therefore, the concessionaire and all consortia recognized the requirement to implement the project on time, within budget and to quality specifications. Delayed delivery of civil work of the THSR project will affect the progress of succeeding trackwork and core system integration, therefore the severe penalties are set to discourage time extensions. In the preplanning phase of the THSR project, tunneling was quickly identified as a key sub-task. The project includes approximately 47 km of tunneling of which 39 km are mined and 8 km are Cut and Cover tunnels. Because of the high complexity and uncertainty in tunnel excavation, the major tunneling work of the 48 tunnels was placed on the critical path of civil construction scheduling. The longest main tunnel, 7364 m long, crossing the Paghuashan hills is considered as the most crucial mission in the critical path of the entire THSR project. To ensure effective management of this vital tunnel project, the joint venture between Bilfinger Berger AG of Germany and the local contractor Continental Engineering Corp. introduced many new characteristic and highly efficient automatic construction equipment and fresh planning ideas. The main tunnel excavation work was typically carried out using a backhoe tunnel excavator, minimizing harmful loosening of the adjacent groundmass. Data including engineering records demonstrate that the Paghuashan project was performed successfully. The upper half of tunnel section had an average excavation length of 133 m per month, and was completed two month earlier than scheduled. Further, the Paghuashan tunnel even recorded the best monthly excavated length of 250 m in the THSR project. This paper investigates and analyzes automation in excavation and con-
struction of this critical tunnel, including general geological information, construction techniques, support measures, working productivity, equipment and facilities, management approach and the overall success, and helps provide detailed insight and experience for future long tunnel constructions, particularly for contracts with Design – Build under significant pressure to be completed on time. 2. Paghuashan tunnel project The THSR project contains five major tunnels over 2 km long, of which the longest is the Paghuashan tunnel with mining over 7.3 km. The Paghuashan tunnel consists of a major twin-track tunnel with typical horseshoe-shaped cross-sections of 130 m2 excavated faces and two emergency adit tunnels. The tunnel is aligned approximately north – south, and ranges in elevation with respect to sea level from 100 to around 154 m. The overburden varies from a few meters up to a maximum of approximately 90 m. The THSR alignment normally follows the most populated region along the western coast of the island, and therefore the tunnels do not cross mountain ranges with high overburden. Fig. 1 illustrates the alignment section layout with the elevation of the Paghuashan tunnel, and Fig. 2 shows its typical section geometry. Most tunnels in Taiwan have been in either rocks or soil. Gravel formation encountered at the Paghuashan tunnel, which kept properties between rock and soil, is a rare occurrence in Taiwan [14,15]. To avoid the likely effect of groundwater on excavation, the level of the Paghuashan tunnel inverts were designed to be above the groundwater table by several meters, as shown in Fig. 1. The next section discusses geological conditions in detail. 3. General geological situation The THSR enters the Paghuashan terrace from the north and leaves it in a southerly direction to enter the alluvial plains west of the Paghuashan Terrace. The Toukoshan Formation in the northern zone of the Paghuashan anticline, in which the Hill level Groundwater level Rail level
-0.97 %
1.52 % Slope 0.3 %
Adit B TK177+812
Adit A TK175+020
17
17
TK
TK
0.3 % 1.47 %
3+ 02 1 3 TK +2 5 17 0 3 TK +5 17 00 3 TK +7 17 50 4 TK +0 17 00 4 TK +2 17 50 4 TK +5 17 00 4+ TK 7 17 50 5 TK +0 17 0 0 5 TK +2 17 50 5 TK +5 17 00 5+ TK 7 17 5 0 6 TK +0 17 0 0 6 TK +2 17 50 6 TK +5 17 00 6+ TK 7 17 50 7 TK +0 17 00 7 TK +2 17 50 7+ TK 5 17 00 7 TK +7 17 50 8 TK +0 17 00 8 TK +2 17 50 8+ TK 5 17 00 8 TK +7 17 50 9+ 17 000 9k TK +2 17 50 9 TK +5 17 00 9+ TK 7 18 50 0 TK +0 18 00 0+ 25 0
240 220 200 180 160 Elevation 140 120 (M) 100 80 60 40 20 0
Tunnel Chainage Fig. 1. Alignment layout of Paghuashan tunnel.
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Fig. 2. Typical cross-section of Paghuashan tunnel.
Paghuashan tunnel was excavated, is of early Pleistocene age (1 million years ago). The sediments of the lower levels of this formation therefore experienced a compaction under a load of several hundred meters of overburden. The deposition of this predominantly coarse sediments with gravel and cobbles occurred in rivers with high flowing velocities and changing flow directions. In areas of lower velocities lenses of sands or sandy gravel were deposited and in areas with very low flowing velocities layers and lenses of silt, sandy silt and clayey silt were deposited. It is very likely that occasionally also thin layers of gravel or cobbles with no or only little contents of sand were deposited. The investigations and the tunnel areas excavated has shown that sandy gravel with a differing content of cobbles are the most frequent type of ground in the area of the tunnel. Further, evidence during excavation of the tunnel has shown that even with a cover of only 6 – 7 m, the sandy gravel, sandy silts and sands are Table 1 Rock classification for the Paghuashan tunnel Rock Type
Descriptions
S1
Clast-supported cobble
S2
Matrix-supported cobble
Cobble is round or almost round, between high level contents of cobbles are sand and silt matrix, which are tight, its behavior is cobble clast-supported Cobble is round or almost round between lower level contents of cobbles are sand and silt matrix, which are tight, its behavior is fine matrix-supported Collapsed or diluvial cobble deposits between clast or matrix-supported, usually distributed at the wing of Paghuashan, and its tightness is inferior Fine to coarse silt and sand with few cobbles in between, tightness ranges from loose to quite dense Silty clay or mudstone, over-consolidated
S3
Secondary deposit cobble
S4
Sand/sandstone
S5
Clay/mudstone
compacted to a high degree [7,13]. According to the report of geotechnical assessment and rock classification of this tunnel by Sinotech Co.[8], soils in the Paghuashan areas can be classified into clast-supported, matrix-supported, secondary gravel deposit and sand/silt or clay/mudstone. Table 1 lists the detailed descriptions for every rock type. 4. Support classification The mined tunnels were excavated and supported following the principles of the New Austrian Tunneling Method (NATM). This method considers the behavior and reaction of the surrounding groundmass, together with the installation of a flexible support system consisting of elements such as shotcrete, steel ribs, wire mesh and bolts. The appropriate excavation class was determined by the ground behavior, considering the geological and hydro-geological, overburden, experience gained under similar conditions and geotechnical monitoring results. In practice, the Geotechnical Engineer was responsible for the evaluation of the ground encountered and interpretation of the monitoring results and would propose the appropriate excavation and support system to be applied. Five excavation and support classes were developed for the tunnel, namely classes A, B, C, D and D0 [9]. The difference between each class is the Table 2 Support classification associated with rock type Rock type
S1
S2
S3
S4
S5
Portal
Overburden height (m) Support class Estimated deformation (mm)
H > 11.5
H > 11.5
–
H > 70
H < 11.5
A 100
B 150
B 150
H < 11.5 or 34.5¨70 C 150
D 200
D0 200
630
P.H. Lin et al. / Automation in Construction 15 (2006) 627 – 639 100
7000 6000
5317
5000
length 73.14
80
percentage 60
Length 4000 (M) 3000
40
2000
1135
607
15.61
1000
211
8.35
%
20 2.9 0
cl
cl as s
as s
D o
C
B as s cl
cl
as s
A
0
Support classification
Fig. 3. Percentage of various support types.
cycling length of the unsupported cavity, and the amount of the support measures as a criterion for the temporary stability. Class A signifies very good ground conditions, consisting mainly of gravel and cobbles or matrix-supported with no or little sand, silty sand, sandy clay or clay layers. The excavation face is stable without, or with very minimized, afterbreaking, without requiring pre-supporting measures. Class B signifies good or fair underground conditions, with sand, silty sand, sandy clay or clay layers generally predominant within the gravel matrix. Excavation can be performed without pre-supporting measures. In Class C the underground conditions are to be considered poor and layers of loose sand, silty soil, clay or sandy clay are predominant in and around the tunnel cross-section. The excavation face is generally stable, but heavy afterbreaking may require support of the face, pre-supporting measures may be necessary. Classes D and D0 signify very poor and critical conditions of loose sand, silty soil or soft clay [9]. The excavation and support classes associated with rock types can be shown as Table 2. Fortunately, apart from short sections at portals with very shallow overburden and crossing few fault areas, the tunneling conditions for classification of all mined tunnel sections were almost identical. Fig. 3 shows the computed
Fig. 5. Special excavator with backhoe in tunneling.
percentages of various support classes with their excavation lengths in the Paghuashan tunnel. Support classes A and B predominate over others as 15.6% and 73.1%, respectively, and the other classes have relatively low percentage weights. Obviously, the good to very good underground conditions were predominant in and around the Paghuashan tunnel. In situ monitoring is an integral part of NATM. Monitoring cross-sections for deformation measurement with three target bolts in the crown and two in the bench were provided within the tunnel with an average spacing of 10 m [13]. During excavation and support work for the mined tunnel, frequent measurements allowed a continuous monitoring of the actual behavior of ground and initial support and to assess the relevant design assumptions. The original design exhibited many rock bolts set in the supporting system. The results of the regular deformation measurements and the data from the measuring sections provided a back analysis and a confirmation of the given geotechnical parameters. With the homogenous conditions, compactness, low deformability and almost self-supporting ground, rock
Fig. 4. Profile of excavated stages for Paghuashan tunnel.
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bolts were found not to be essential support elements. Thus, the joint venture contractor redesigned the support system excluding the rock bolts, which resulted in a shortened time cycling about 160 min and accelerated construction progress. For comparison, the original planning for a cycle time is about 390 min. The analysis of production rate will be conducted in details in Section 5.3. 5. Tunnel excavation 5.1. Planning and excavation
Fig. 6. Loader and dumper equipped with giant wheels.
Fig. 7. Automated shotcrete equipment. (a) Wet spraying system. (b) Practical shotcrete spraying in Paghuashan tunnel. (c) Radio remote controller [6].
As well as the north and south portals, the excavated faces of the tunnel still include the other four faces from the two adits bound to the north and south directions, respectively. The mined tunnels were constructed with the Sequential Excavation and Support(SES) NATM method, which was most appropriate for the tunnel size and geometry, and which was identified as the most advantageous in terms of schedule at the gravel formation. The tunnel cross-section was excavated in stages, reducing the open surface of each face, which typically consisted of a top heading, bench and invert, thereby decreasing the potential for collapse. The tunnel was driven with top heading-bench-invert sequencing. The distances between top heading, bench and invert excavation were restricted only by logistics. That is, sufficient space was required to provide for machinery and equipment such as the backhoe excavator, shotcrete rig, drilling jumbo, lifting platforms and bulk materials adjacent to the face. A length of at least 50 m was physical for regular advances. Fig. 4 depicts the separation of excavated stages of this tunnel. The finished tunnel cross-section area must be at least 90 m2 to accommodate the aerodynamic requirements of high-speed train travel at 300 km/hr [13]. The excavation was typically executed by minimizing harmful loosening of the adjacent groundmass. A specially designed backhoe tunnel excavator was employed to loosen the ground (see Fig. 5). The joint at the backhoe_s mechanical arm
Fig. 8. Expression for monitoring points at selected tunnel section.
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P.H. Lin et al. / Automation in Construction 15 (2006) 627 – 639 60 40 20 S1
Displacement (mm)
0
S2 S3
-20
S4 -40
S5 S6
-60 S7 -80 -100
0
0
50 0+
0
25 0+
18
TK
0
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0
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17
25 17
3+ 17
TK
TK
TK
17
3+
00
0
-120
Tunnel Chainage Fig. 9. 3-D optical monitoring measurements for tunnel settlements.
equipment is shown as Fig. 7. The machine had a human oriented control system, which could operate the robot with 8- of freedom. The remote control enabled the operator to manipulate the spraying jet not only in automatic, but also in semi-automatic and if needed in manual mode. It helped maintain the distance and the angle to the surface, and the thickness within the design tolerances. The equipment help reduce rebound material to a minimum of about 11%. This automated shotcrete equipment debunks the conventional wisdom that the success of a shotcrete operation is dependent entirely upon the skill of the operator [1,2,4]. This automated shotcrete system results in machine spraying with high speed,
can freely adapt to in situ circumstances to motion within 180-. Excavation with a backhoe Liebherr 932 was shown to yield a regular excavation line without disturbing the ground behind the excavation surface. Due to the tunnel’s limited working space, the loader and dumper for mucking were equipped with large wheels that narrow down their turning radius, as shown in Fig. 6. During excavation, the tunnel face and exposed sidewalls exhibited mostly good stability without significant overbreak. If required, temporary support was usually attained with an array of rock bolts from the spring line to the crown, lattice girders spaced at 1 –1.5 m, and shotcrete ranging in thickness from 175 to 350 mm. The automated shotcrete 80 60
C1 40 C2
Displacement (mm)
20 0
C3
-20
C4
-40 C5 -60 -80
C6
-100
C7
Fig. 10. 3-D optical monitoring measurements for tunnel convergences.
2 18 50 q5 00
0
TK
00 TK
18
0+
0 75 TK
18
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Tunnel Chaniage
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17
00
0
-120
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3500
633
quality and efficiency, instead of a mostly manual, time consuming process.
daily on a length starting about 30 m ahead of the face and ending 50 m behind the face (readings every day). Then, weekly readings were executed for one month. 3D precision displacement monitoring is an optical measurement method used for determining 3D displacements of the linings in underground excavations. It is a modern alternative to the classical convergence and roof settlement measurements. Underground displacement measurements can be linked to above-surface monitoring, with all deformation data compiled in one common database. This provides a complete picture about the history and development of deformations [10]. The field measurements in settlements and convergences at the tunnel monitoring sections can be shown in Figs. 9 and 10. The deformation almost ranges from 0 to 60 mm, and few points reach to a maximum of approximately 100 mm. The results show that all deformation was controlled under safety and expected estimates.
5.2. Site monitoring
5.3. Analysis of production rate
Field monitoring and frequent measurements allowed a continuous provision of the actual behavior of ground and initial support. In this way, it could be assessed whether the actual monitoring results were within the acceptable limits. Evaluation of all monitoring results had to be performed on a daily basis and irrespective of reaching any threshold values [10]. The tunnel monitoring sections consisted of five to seven optical monitoring points for the three-dimensional (3D) monitoring of tunnel lining deformation, and pressure cells at selected sections. Fig. 8 illustrates the seven monitoring points at a tunnel section. The sections were generally installed at regular intervals of about 10 m along the tunnel. Its main purpose was the appraisal of deformation of the outer lining, the verification of the stabilization with time, the appraisal of stress intensities in the lining and the general lining behavior. During the excavation stages of top heading, bench and invert, the readings were taken
Typically, the excavation process included ten working crew members, two shifts in a day with 24 h of working. The geological survey and construction planning were exhaustive, and the required exploratory measures and the encountered ground conditions at the tunnel faces were continuously monitored and provided on a daily basis. The contractor could know well the geological conditions within the entire length of the track and made appropriate decisions on the ground classification, excavation sequences and support systems to be applied. The Paghuashan tunneling predominantly had a short cycle length of 80 cm to shorten the excavated face exposure time. Fig. 11 plots the detailed cycle length distribution with corresponding total numbers of excavated cycle. The average cycle time for top heading excavation was about 160 min for a cycle length of 80 cm. Fig. 12 illustrates the average time for each task in a cycle. For comparison, the
cycle number
3000
C y c l e s
2762
80
percentage
2433
2500
60
2000
1000
%
1457
1500
40 877
29
26
907
883 20
15
500
9
10
9
150
2 0
0 0.6
0.7
0.8
0.9
1
1.1
1.2
Cycle Length (m)
Fig. 11. Distribution of cycle length.
Time(Minute)
Time Task item
60
120
180
240
300
360
420
480
540
600
Mucking Installation of lattice girder & wire mesh Shotcrete Top heading excavation Mucking Installation of lattice girder & wire mesh Shotcrete Top heading excavation Mucking Installation of lattice girder & wire mesh Shotcrete Average cycle time
note cycle length 0.8m
Top heading excavation
(160min/cycle)
Fig. 12. Analysis of average time for each task in top heading excavation.
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Table 3 Average monthly excavation progress in Taiwan Year
Total length of tunnels (m)
Numbers of tunnels
Average length of tunnels (m)
Average cross-sectional area (m2)
Average excavation progress (m/month)
1972 – 1981 1982 – 1986 1987 – 1991 1992 –
29,198 38,798 39,999 129,443
33 79 50 116
912 485 800 2353
29.8 23.7 39.7 63.4
68.3 50.3 32.5 58.0
and vault lining. Automated construction equipment specific to the lining work of the Paghuashan tunnel was introduced by the joint venture contractor. The average production rates were based on a learning period and a routine period with a regular production to the actual capacities of the equipment in use, and were based on a shift system similar to the excavation phase, with approximately 24 working days per month. Both the invert and vault lining work, especially concreting, were continuously working cycles, where each crew member would take over a particular task. The average advance rates were attainable, considering the lengths of the three lining sections (north, south, and center parts) which were running concurrently. The three sections were equipped with regard to formwork shutters and labors, that the work could proceed without affecting each other.
original planning with rockbolt setting task for a cycle time is about 390 min. Thus, the elimination of rockbolt task indeed resulted in an accelerated construction progress. The multi-skilled crew with experiences in multi-tasks operation, led by an experienced foreman and directed by a geological engineer, managed the in situ geological conditions well, completing the top heading excavation two months ahead of schedule. An average production rate of 130 m per month was achieved, with a peak monthly rate of 250 m per working face. It made a significantly advanced progress record compared with the average tunnel excavation performance in Taiwan. Table 3 shows the average excavation progress for rock tunnel construction in Taiwan for reference [3]. It shows that the average monthly progress varies from 30 to 70 m. Due to the complex geological conditions, it is still difficult to compare the tunneling progress on a completely similar basis. However, there was a road tunnel initiated by the National Road Bureau (NRB) in the Paghuashan area with a very similar soil formation. This NRB tunnel is known as the second longest road tunnel with over 4900 m in Taiwan. In contrast, the NRB tunnel was carried out in suffering from serious ground water problems, resulting in an average excavation progress of 39 m per month. Fig. 13 illustrates the detailed average monthly progress for each excavated face in the top heading and bench tunneling in the Paghuashan tunnel. The invert excavation was generally proceeded as the top heading and bench excavation were entirely finished. The invert closure helped stabilize the tunnel.
6.1. Invert lining Invert lining work was undertaken by an invert shutter, with a length of approximately 40 m. The invert shutter system comprised a formwork frame, face shutter including support device, moving frame, crane beam including trolley, concrete distribution system, hydraulic system and working platforms. Fig. 14 illustrates the side and front views of this system. The wagons and shutters in the rear of the invert shutter were railbound, that is, they used the same rail (lane width = 8.9 m), which was fixed on top of the finished invert banquette (underside of cable trough position). This approach guaranteed a uniform base level for all wagons, and eased the survey control. Only the last wagon in the line, the platform wagon for void grouting and surface finishing, moved on tires. All wagons had a central clearance of 3.5/4.5 m (width/height) for throughway. The wagons were self-mobile [12]. The invert
6. Lining work The inner lining of the tunnel were begun when the excavation was completed, and can be categorized into invert 200 180 160 140 120 100 80 60 40 20 0
102
133 130 Top heading
e in lL
N
po
Al
o
S
lt rta
Bench
So
ut h
Ad it
B it Ad
B
to
to
N
S to
N Ad
it
A
A
to
o lt Ad it
rta po th or N
176 156 156 158 147 134 130 112 6264
S
Excavation length (Meter/Month)
179
Fig. 13. The average monthly progress in top heading and bench excavation.
P.H. Lin et al. / Automation in Construction 15 (2006) 627 – 639
635
(a) side view
Front Wall Truss & Support Beams
End Wall Truss & Support Beams
Moving Frame Shutter Face Shutter
Forwork Frame
(b) front view
(Unit:mm) Crane Beam incl. Trolley
Moving Frame
Formwork Frame
Face Shutter
Fig. 14. The invert shutter system.
Time Task item
Time(Minute) 60
120
180
240
300
360 420
480
540 600
Installation of invert reinforcement Moving and setting of main truss formwork Relief of face shutter and joint formwork Installation of face shutter and joint formwork Overlapping of invert reinforcement Check before pouring Pouring Curing Total Time
720(Minute/Block) Fig. 15. Analysis of cycle time for invert lining.
660
720
780 note
636
P.H. Lin et al. / Automation in Construction 15 (2006) 627 – 639 Formwork Crown Element
(a) cross section
Cross Beams of Carrier Frame
Bracing Devices
Formwork Side Element
Wheels & Chassis
Supporting structure for reinforcement
(b) crane wagon
Transport Beam
FrameWork Cross framework with column and swinging out alighting gear
Fig. 16. The vault shutter system.
Time Task item
Time(Minute) 60 120 180 240 300 360 420 480 540 600 660 720 780 840 900 960 1020 1080 1140 1200 1260 1320 1380 1440
Relief of Formwork Clean of Formwork Descending of Formwork Moving & lifting of vault reinforcement Move out of crane wagon Setting up of crown formwork Overlapping of crown & side reinforcement Setting up of right side Formwork Setting up of left side formwork Seal of side formwork Pouring Curing Total Time
1400(Minute/Block) Fig. 17. Analysis of average cycle time of vault lining.
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Fig. 18. Installation of reinforcement for vault lining.
concrete cycle consisted of the following phases: move frame to next block; remove side/face shutters; install gap reinforcement; install face shutter and side shutters, and pour concrete. During regular production, one invert cycle lasted 8 to 9 h, leaving about 3 to 4 h for hardening, before removing the face shutter. The frame posters were positioned on blocks aged at least 12 h (central) or 24 h (rear) [12]. High quality and fast progress could be achieved by the invert shutter system with average monthly progress 550 m. Fig. 15 plots the average cycle time for each invert lining task. The Twin Invert Shutter was found to be able to cast 2 blocks (each block 12.5 m) in 24 h. 6.2. Vault lining Shotcrete was applied for sealing, and as initial lining. The wet shotcrete technique was employed, i.e., cement and aggregate were batched by weight and mixed with water and admixtures when brought to site. One or two layers of wire mesh fabric were positioned within the shotcrete lining as reinforcement. The lattice girder was placed inside the shotcrete lining and wholly embedded in the shotcrete. To counter uncohesive loose sand or fine gravel layers in the crest of the top heading, steel lagging sheets could be used for pre-supporting to minimize possible break. Typically, the shotcrete lining’s tolerance was constrained to 5 cm over the theoretical borderline between shotcrete lining and inner lining. The required clearance for the waterproofing system (fine graded shotcrete layer, geotextile and membrane) had to be incorporated into the designed inner lining thickness. All support measures exceeding this tolerance had to be reprofiled. Thailand labor crews performed the profiling, concreting and excavation work. The crews were guided as far as possible by the same supervisors at site, easing the transition into the lining work. The vault was lined with reinforced cast-in-place concrete, using mechanized formwork systems, while the vault shutter was applied to carry out all casting work. The wagon length was approximately 16 m. The vault shutter comprised the carrier frame, formwork, working platform, concrete distribution system, vibrating system and hydraulic system. The vault reinforcement was separated into ‘‘wall’’ and ‘‘arch’’ reinforcements. The vault reinforcing system consisted of lifting, reinforcing and crane wagons, to lift, assemble and move the vault reinforcement, respectively. Fig. 16 illustrates the vault
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shutter and crane wagon of the vault reinforcing system. The nominal thickness of the vault concrete was 40 cm in the normal underground sections, rising by 10 cm close to the portals and at shallow overburden zones. The regular block length was 12.5 m. A vault concrete cycle consisted of the following working phases: remove face shutter, open spindles, lower and clean formwork, take over crown reinforcement and move to block, splice wall/crown reinforcement and close gap, position formwork and close spindles, install face shutter, and pour concrete, start during installation of face shutter. Approximately 6 h after the concrete pouring finished, the pipes, installed in the crown for void grouting, were pulled back. The holes were then inspected. The water proofing membrane could be visible. At regular production, a vault cycle lasted 12 – 14 h, leaving about 10– 12 h for hardening, before the face was removed [11]. Fig. 17 plots the average cycle time of each task in the vault lining. Figs. 18 and 19 display the practical construction system for vault lining, demonstrating the working shutter system in site. The entire process in the above description for inner lining working can be depicted by the seven steps presented in Fig. 20. 7. Excavation machines and equipment Heavy equipment, such as tunnel excavators, shotcrete machines and drilling jumbos, was imported to ensure the attainable construction speed. The major equipment was transported in coordination with construction to the assigned working areas. Table 4 summarizes the key equipment. The equipment operator would perform a visual check on the equipment twice a day before and after the working shift, and reported the results to the mechanical supervisor. Once a week, the mechanical department inspected the equipment on site, and once a month, the equipment was maintained and checked in the machine yard on site. Defective or worn-out parts were replaced immediately with original spare parts only. In the other side, breakdown of key equipment (excavator, shotcrete unit, loader, dumper and drilling jumbo) could lead to work interruption. The excavator, owing to its long working duration, and the shotcrete unit, since it provided immediate tunnel support once the round was open, were treated as critical
Fig. 19. Concrete distribution system of vault lining.
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Step 1: Invert lining works with invert shutter system Step 2: Reprofiling and checking shotcrete surfaces by profile wagon Step 3: Waterproofing works Step 4: Fabrication of wall reinforcement Step 5: Fabrication of arch reinforcement Step 6: Lifting of arch cage to the carrier frame Step 7: Pouring concrete with vault shutter system Fig. 20. Illustration of process sequence for inner lining working.
equipment items. A qualified and mobile maintenance team in the workshop would do the best to keep that the equipment was always in good order and that immediate action could be undertaken if a breakdown occurred. The workshop operated a Planned Preventive Maintenance (PPM) system, inspecting all key equipment daily and either repairing any defects or logging them for the next routine service [9]. To guarantee the continuation of tunnel work in case of a serious breakdown, sufficient spare equipment valued at more than US$1 million was always made available at short notice. In case of a major breakdown that the repair failed to be implemented in an accepted term, the required equipment was immediately ordered from neighboring work sites (bench drive or next nearby tunnel drive). Moreover, for each excavated face, the construction equipment with highest utilized rate was the shotcrete unit with 61% usage, but also had the highest breakdown rate with 6.2%. By comparison, the excavator had the lowest usage rate, with 44% of idle time. Therefore, in the excavation cycling process, the shotcrete task occupied the longest cycling time, while the excavator task occupied the shortest
time. Thus, an unnecessarily over excavated cross-section could be avoided and the shotcrete time for compensating tolerances could be eliminated to benefit the entire tunneling progress. 8. Conclusions The construction of the Paghuashan tunnel, the longest in the Taiwan High Speed Rail Project, significantly influenced the construction schedule of the whole project, and has been the focus of attention from the project participants since its construction in early 2001. This paper analyzes the automated excavation and construction of this critical gravel tunnel, including the general information of geological condition, construction method, support measures, working productivity, equipment, facilities, management approach and the overall performance. The practical working data and experiences were gathered and recorded for advanced analysis. The productivity analysis and comparison of this study also provide a detailed insight and valuable experience in cycling for future long gravel tunnel construction, particularly for
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Table 4 List of major excavating equipment for Paghuashan tunnel Equipment
Specification
Brand
Quantity
Manufacturer
Excavator Excavator Wheel loader Shotcrete mobile Drill jumbo Dumper Dumper Dumper Twin invert shutter Profile wagon Water membrane wagon Side wall reinforcing wagon Vault reinforcing system – lifting wagon
Litronic 932T Litronic 912T CAT966G Meyco Suprema Tamrock Paramatic 206 Kaelble/KV25N Bell/B25 C6*6 CAT D25 L = 40 M L = 13 M L=6 M L = 13 M
Liebherr Liebherr Caterpillar MBT Tamrock Kaelble Bell Caterpillar Bernold Bernold Bernold Bernold
5 2 6 6 5 6 6 4 2 2 2 2
Germany Germany U.S.A. Switzerland Finland Germany South Africa U.S.A. Switzerland Switzerland Switzerland Switzerland
L = 10 M
Bernold
2
Switzerland
L = 30 M L = 12.5M
Bernold Bernold
2 5
Switzerland Switzerland
Vault reinforcing system – crane wagon Vault shutter
Design and Build bidding contracts. The key factors to successful performance of this tunnel construction can be summarized as follows: (1) Design – Build (DB): The contract was awarded based on the Design – Build tender, which gave the joint venture contractor full flexibility in meeting the ongoing-design of the New Austrian Tunneling Method according to the practical conditions encountered in complex excavation. Thus, construction hazards can be avoided or mitigated. Design – Build contracts have dominated changeable tunneling construction, and significantly benefit overall performance. (2) Well-planned construction management: Aside from the existing better geological conditions encountered in tunneling, well-organized international joint venture contractors are very important to achieve good average advance rates. Experienced foremen and multi-skilled crews can be teamed together to achieve good construction progress, maintain equipment and facilities to decrease the breakdown and idle time. Daily inspection and observation for overall control in working environment can in most cases help construction safety and productivity. (3) Automated tunneling construction: The application of automated equipment and facilities can advance tunneling techniques and improve construction productivity. Although the automated equipment and additional facilities may raise construction cost, the advantages of assuring progress within schedules justify the cost, premium, especially when contracts include large liquidated damage.
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