MINIMIZING DEFECTS OCCURRENCES ON SFRC TUNNEL SEGMENT OF KLANG VALLEY MRT PROJECT

Transcription

1 Journal of Engineering Science and Technology Special Issue on 4th International Technical Conference 2014, June (2015) School of Engineering, Taylor s University MINIMIZING DEFECTS OCCURRENCES ON SFRC TUNNEL SEGMENT OF KLANG VALLEY MRT PROJECT MOHAMMED HAKIMI B. ABDUL RAZAK, AMIRUDDIN ISMAIL* Sustainable Urban Transport Research Centre (SUTRA) / Department of Civil and Structural Engineering, Universiti Kebangsaan Malaysia, Malaysia *Corresponding Author: aismail@ukm.edu.my Abstract Steel Fibre Reinforced Concrete (SFRC) precast segment has become more demanded and common for major tunnelling works in the world. In general the impact of demand along with the fast progress of the tunnelling works will eventually affected the quality of the SFRC precast segment where past projects showed the typical defects occur on the tunnel lining were mainly on concrete spalling, leakages between the segmental lining and cracks on the precast segment. This study will focus on the factors that encourage the occurrence of these defects in order to implement a new method and procedure in minimize the defects on the precast segment. The data collected such as inspection record, visual inspection, and questionnaire distributed which aim on the method of construction were analysed and SPSS were used for descriptive of the data. The obtain results revealed that when the suggested method from the survey was implemented during the construction of the Section 2: Tunnel from KL Sentral Station to Pasar Seni Station, the numbers of leakages were dropped at 40.9% by installing a secondary lining of Ethylene Propylene Diene Monomer (EPDM) gasket. For spalling, by using lifting cage during handling of the SFRC segment bring the number of occurrences dropped at 32.4% and using protective pad for segment storage show the cracks across the segment dropped at 34%. On top of the quality control procedure and common method of works, this result revealed that by improving the area that involved workmanship does give a biggest impact in minimizing the defects on SFRC precast segment. Keywords: Tunnel, SFRC precast segment, Quality, Defects. 1. Introduction In general, the use of SFRC Precast segment for tunnelling works has been widely used as the fibre reinforcement is inessential for integrity, quality, production and safety [1]. The quality requirement of the SFRC precast segment 13

2 Minimizing Defects Occurrences on SFRC Tunnel Segment of Klang has increased as part of the design life on the tunnel itself [2]. Every tunnelling works in the world will try to avoid and minimize the defects on the tunnel lining but during the construction works, an area which involves quantity, progress, procedures and human error has eventually lead to defects occurrences on the SFRC precast segment. Past research that has done many experiments and testing from the manufacturing of the segment until the installation stage of the segmental lining. Research such as tensile and bend test were done to determine the mechanical properties of the steel fibre [3]. Finite element analysis use to calculate the segment stress distribution which will lead to cracks [4]. Study on differential settlement of the tunnel to determine the contribution of leakages [5]. These researches were mainly focused on the durability of the material which the results show a positive used of SFRC precast segment for tunnel lining. This paper however will focused more on the method of construction where workmanship will be monitored and analyse as workmanship itself has always been an important key in quality control of the SFRC segment. The case study of the existing study is the tunnel works for the Malaysian Klang Valley Mass Rapid Transit (KVMRT) which is currently the longest underground tunnel in Malaysia that stretch for 9.5 km in the heart of Kuala Lumpur. This case study however will be divided into two section of the tunnel where Section 1: Tunnel from Semantan portal to KL Sentral Station (1.2 km) and Section 2: Tunnel from KL Sentral Station to Pasar Seni Station (1.25 km). This is a single case study where section 1 tunnel will be the phase of data collection to determine the type of defects and the factors that lead to the defects occurrence. In section 2 tunnel, the suggested method from the study will be incorporated during the tunnelling works from KL Sentral Station to Pasar Seni Station. The project records for Section 1: Tunnel from Semantan Portal to KL Sentral Station was obtained and Table 1 shows the type and number of defects occur on SFRC precast segment during the construction of the tunnel lining. The most common defects are leakages and were recorded at 2,037 or 86% of the total occurrences. This is followed by concrete spall or damage of the SFRC precast segment which is at 340 occurrences or 14% of the total occurrences. The cracks on the SFRC precast segment has been recorded as the lowest defects occurrences, which is at 44 or 1.8% of the total occurrences Table 1. Type and number of defects for section 1 tunnel. Leakages Spalling Cracks North Bound South Bound Total The highest defect recorded which is the leakages was mainly occurring on the radial or circumferential joint of the SFRC precast segment. Figure 1 shows the typical joint leakages between the segmental linings. In general one of the main contributions for the leakages between the segmental linings is the high groundwater table or differential settlement of the tunnel [5]. In this case, 15 numbers of water standpipes were installed along the north and south bound

3 15 M. H. B. A. Razak and A. Ismail tunnel. The reading recorded by geotechnical department is from 1.0 m to 1.5 m below ground level for a period of 9 months. Table 2 revealed that both south and north bound tunnel having the average of 1.12 m (m.b.g.l). Table 2. Water table reading for south and north bound tunnel. From Chainage (m) To Depth (m.b.g.l) Type of Soil / Rock 0 8 m 8 m Silty SAND / Silty SILT Bedrock Limestone 0-10 m Mainly 10 m SAND Bedrock Limestone 0-10 m Mainly 10 m SAND Bedrock Limestone 0-10 m Mainly SAND Bedrock Limestone Indicative Average Groundwater Level (m.b.g.l) 1.5 m 1.0 m 1.0 m 1.0 m As for the waterproofing lining, past research on tunnel waterproofing show that the use of Ethylene Propylene Diene Monomer (EPDM) gaskets as lining does play a role in minimize the leakage between the segmental linings [6-8]. However, in this project where the precast segment is using the same waterproofing method, the occurrences of leakages is still highly recorded. From the surveillance and survey done at the project site, many has agreed that the main cause is the inclination of the thrust jack that damage the EPDM gasket thus resulting in leakages between the segmental linings. Fig. 1. Joint leakages between the tunnel segmental linings. The second highest defect recorded according to Table 1 is the concrete spall on the SFRC precast segment. Many researchers have agreed that these defects were categorized as normal defect to be recorded during the manufacturing and delivery stages [2]. From this project inspection record has revealed that concrete

4 Minimizing Defects Occurrences on SFRC Tunnel Segment of Klang spall or damage on the precast segment was normally detected during handling and installation stages. Figure 2 shows the concrete spall at the edge and surface of the precast segment. Although the installation of the segmental is semiautomated by the TBM erector, there are few stages where lifting is still using the manual hoist chain which contributed to the spall. Fig. 2. Concrete spall at the edge and surface of the precast segment. Cracks on the SFRC precast segment has been recorded as the lowest defects on the tunnel lining, affected only on 44 segments out of 17,280 segments install for section 1 tunnel. Although it is the lowest numbers of defect recorded, cracks on the precast segment are considered a major type of defects and required a high attention the rectification works. Figure 3 shows the cracks on the SFRC precast segment. Fig. 3. Cracks on the SFRC precast segment. Past research showed that there were a few factors that lead to the cracks such as eccentricity or inclination of the thrust jack, non-smooth ring joints and during casting phase [9-12]. All the factors were typical to any other tunnel project and same for this case as where the excavation is operated by Earth Pressure Balance (EPB) type of Tunnel Boring Machine (TBM). If the proper installation process is done according to the procedure, the numbers of crack should have been minimized [11].

5 17 M. H. B. A. Razak and A. Ismail 2. Materials and Method The methodological for this research consists of the project quality record that will determine the type and numbers of defects recorded for section 1 and section 2 tunnels. A questionnaire is distribute at the project site and the data collected will be interprets using SPSS and Microsoft Excel. For the data collection, a survey was done at the project site with the respondents for these surveys are the engineers, technicians, general labours and supervisors at the project site that is handling the tunnel activity. The questionnaire is kept simple, brief, using dichotomous type in order to get the firm result. They filled in questionnaire forms at the project site office and at construction site. There will be three parts of questionnaires where first part (Part A) is on leakages, the second part (Part B) is on concrete spalling and the third part (Part C) is on cracks. For example under part A, leakages type of defects, respondent will be given 3 choice of answer based on the common factor discovered at the project site. At the end of every section, the respondent will be asked on their opinion on how to reduce the defects mentioned in the questionnaire. Table 3 shows the distribution of the questionnaire at the construction site. A total of 83 questionnaires were collected in three months (from December 2013 to February 2014). SPSS Statistics version 17.0 package and Microsoft Excel 2010 were used to analyse the data. Table 3. Distribution of the questionnaire at the construction site. Total Respondents : 83 Survey distributed : 110 Response rate : 75.45% N.B Tunnel Job Title S.B Tunnel Job Title Number of survey respondents Percentage of survey respondents Tunnel Engineer Tunnel Supervisor Technician QA/QC Engineer Construction Manager TBM operators Total North Bound Tunnel Engineer Tunnel Supervisor Technician QA/QC Engineer Construction Manager TBM operators Total South Bound Total With this information gathered for the Section 1: Tunnel from Semantan Portal to KL Sentral Station, the result will be incorporated during the construction of

6 Minimizing Defects Occurrences on SFRC Tunnel Segment of Klang Section 2: Tunnel from KL Sentral Station to Pasar Seni Station in order to evaluate and minimize the defects on the tunnel lining using this SFRC precast segment. 3. Results and Discussions 3.1. Leakages type of defects For leakages type of defects under part A questionnaire, based on Fig. 4, shows 77% respondents agreed that leakages occur on the segmental lining due to the damaged waterproofing lining, Ethylene Propylene Diene Monomer (EPDM) gasket, 12% agreed that leakages occur because of the ground water table and 11% stated that due to mix error on the backfilling grouting. Each answer selected will lead to the sub section of questionnaire based on the respondent answer. This paper shows the demographic result of the highest percentage answered by the respondents. Figure 4 revealed that 70% respondents agreed that the damage of waterproofing lining happened during the installation of the segmental because of the inclination of thrust jack. Figure 5 shows the inclination of the thrust jack 22% revealed that the EPDM gasket is not properly intact and checked before installation and 8% agreed that the waterproofing lining is damaged during unloading and lifting of the precast segment. The last section of Fig. 4 shows that when respondents were asked their opinion on how to avoid damage on the waterproofing lining 82% respondent suggesting installing another strip of the EPDM gasket as a secondary waterproofing lining will minimize the leakages. Another 9% respondents agreed that to double check the EPDM gasket is intact before installation and another 9% stated that proper handling of the segment during installation also play a role in minimize the occurrence of leakages. Figure 5 shows an example when the thrust jack pressing the EPDM gasket during excavation resulting damages to the lining and Fig. 6 shows the installation of secondary strip of gasket lining to avoid the potential damages. Part A : Leakages Why do you think the leakages occur on the lining? Frequency Percent A.1 Due to damage of waterproofing lining A.2 Due to high water table A.3 Error in mixing for grouting Total If your answer is due to damage of the waterproofing A.1, what do you think that may lead to this damage? A.4 Inclination of thrust jack A.5 EPDM gasket not properly intact A.6 EPDM damage during lifting works Total If your answer is due to inclination of thrust jack A.2, what is your suggestion to avoid this defect? Install secondary strip of lining Proper handling of the segment To check the intact of the gasket Total Fig. 4. Questionnaire data for the Leakages type of defects.

7 19 M. H. B. A. Razak and A. Ismail Fig. 5. Inclination of thrust jack that damage the EPDM gasket. Fig. 6. Secondary strip install at the precast segment Spall and damaged of the precast segment From the project surveillance record, most of the spall or damaged of the precast occur during handling of the segments whether during unloading or during installation of segmental lining. From the questionnaire, based on Fig. 7, revealed that 55% respondents stated that the segment was damaged due to poor handling at the project site. This is including the belt use by the crane is placed at the end of the segment. 32% respondents agreed that when installing the last key segment, the aggressive movement of the segment erector does make the segment spall and 12% believe that damage may occur at the manufacturer storage yard. Part B : Spall and damaged on segment Why do you think spall and damage occur? Frequency Percent B.1 Due to poor handling at project site B.2 Due to movement of segment erector B.3 Already damage from manufacturer Total If your answer is due to poor handling at the site B.1, what is your suggestion to avoid this defect? Improved the inspection during delivery To use a lifting cage for unloading work To improved workmanship on erector Total Fig. 7. Questionnaire data for spall and damage of segment. From the survey result, last section on Fig. 7 shows that when respondents were asked their opinion on how to avoid spall or damaged on the precast segment, 46% suggested that to improve the inspection during delivery of the precast segment. 48% agreed that to use a lifting cage when unloading instead of using belt. Others 7% stated that the segment erector to be handle properly during installation Cracks on the precast segment. From the survey, 84% stated that during transportation and during stacking at the project site, the segments were placed directly to the concrete support without

8 Minimizing Defects Occurrences on SFRC Tunnel Segment of Klang having any rubber pad and cause the segments lay on uneven surface. This is including the uneven timber support that was stacked between the segments which distributed an uneven load to the segments which may lead to cracks when shoving. 12% respondents believe that the segments was cracks due to uneven thrust load during shoving and 4% respondents say that the segment already crack at the manufacturer after casting phase. Figure 8 shows the factor that may lead to the occurrence of cracks on the precast segment. When the questionnaire asked the respondents on how to avoid the cracks occurrences on the segment, from Fig. 8 revealed that 84% suggest that to apply a protection between the concrete support and the segment to avoid any movement or uneven load distribution to the segment during transportation and during storage. 10% of the respondents stated that to make sure the stacking in on even load and 6% suggest improving the inspection during delivery of the segments. Part C : Cracks on the precast segment Why do you think cracks can occur? Frequency Percent C.1 Segment placed directly on support C.2 Due to uneven thrust load C.3 Cracks occur at the manufacturer Total If your answer is due to segment stacking C.1, what is your suggestion to avoid this defect? To apply protection on concrete support To make sure stacking is on even load To improved inspection during unloading Total Fig. 8. Questionnaire data for cracks on the precast segment. Figure 9 shows the precast segment lay on concrete support without protection and the use of gunny sack as padding between the segment and the concrete support during the construction of section 2: Tunnel from KL Sentral Station to Pasar Seni Station. Fig. 9. Precast segment placed directly to the concrete support and using gunny sack as protection during Section 2 Tunnel.

9 21 M. H. B. A. Razak and A. Ismail From the data collected on the survey, the highest percentage from the opinions on how to minimize the occurrences of these defects were incorporated during the tunnelling works for Section 2: Tunnel from KL Sentral Station to Pasar Seni Station. The suggested method as follow; For the leakages between the segmental linings, the respondents suggested that installing a secondary gasket on the segment lining will minimize the leakages. Figure 6 shows the secondary lining install at the SFRC precast segment before installation of tunnel lining. For the concrete spall or damage on the segment, the respondents suggested using a lifting cage during unloading of the precast segment. For the cracks, the respondents believe that to apply a protection between the segments during stacking/transportation. Figure 9 shows that gunny sack will used as protective pad to avoid any uneven load distribution during stacking Upon completion of Section 2: Tunnel from KL Sentral station to Pasar Seni station, data collected from the joint inspection revealed that the total number of leakages between segmental lining recorded is 833 nos. The concrete spall type of defects recorded is 110 nos. and cracks on the segment are recorded at 15 nos. Figure 10 shows the comparison numbers of the defects recorded for both Section 1 and Section 2 tunnel. The opinion from the respondents were incorporated during construction of section 2 tunnel show an improvement when the suggested method from the respondents were implement during the tunnelling works. Table 4 shows that the percentage for Leakages was dropped at 40.9%, the Spall at 32.4% and Cracks at 34.1% Leakages Spall/Damage Cracks Section 1: Tunnel Semantan to KL Sentral Station Section 2: Tunnel KL Sentral station to PasarSeni station Fig. 10. Comparison of defects occurrences between section 1 and 2 tunnel. Table 4. Percentage of defects occurrences between section 1 and 2 tunnel. Section 1 Tunnel Section 2 Tunnel Percentage Leakages Spall and damage Cracks

10 Minimizing Defects Occurrences on SFRC Tunnel Segment of Klang Conclusion Upon completion of Section 1 : Tunnel from KL Sentral Station to Pasar Seni Station, the main contractor has issue a Non Conformance Report for the defects recorded. The suggested method from this questionnaire on how to minimize the leakages, spall and cracks were used in replying the Non Conformance Report as a preventive action. During the construction of Section 2: Tunnel from KL Sentral Station to Pasar Seni Station these preventive actions were used until completion of the tunnel works. With the decreased percentage on all the defects during the construction of Section 2 Tunnel, this study indicates that a simple improvement on the method and workmanship does give a big impact in minimizing the defects. The suggested method from the project site personnel who is handling the SFRC precast segment eventually lead to a better quality result of this project. This is proven when the data revealed using suggestion implemented on the Section 2: Tunnel from KL Sentral Station to Pasar Seni Station. The highlight finding of this study is: The EPDM gasket will always get damaged due to inclination of the thrust jack. Having to install a secondary lining that act as a primary gasket will eventually reduce the leakages. As convenient and economical using belting type of lifting method, the result will always lead to spall or damage on the segment. By using lifting cage, longer time used during lifting but the numbers of spall on segment has been minimized. On top of all experiments and analysis done on cracking of the segments by past research, a simple improvement on the protection of the segment during stacking or transporting actually help in reducing the cracks. This cracks maybe not visible during stacking due to uneven load or no protection on the support but after a certain load transferred to the segment during shoving, the cracks will occur. The finding of this research can be conclude that the standard quality control implemented at any tunnelling project should have been improved in the area of workmanship according to the project surrounding and behaviour in order to minimize the occurrences of the tunnel lining using SFRC precast segment Acknowledgment The authors would like to acknowledge the Sustainable Urban Transport Research Centre (SUTRA) and Department of Civil and Structural Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia and MMC Gamuda KVMRT Semantan North Portal Tunnel Team for their support given to accomplish this study. References 1. De Rivaz, B. (2008). Steel fiber reinforced concrete (SFRC): The use of SFRC in precast segment for tunnel lining. Proceedings of India World Tunnel Congress on Underground Facilities for Better Environment and Safety. New Delhi, India,

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