Customized state-of-the-art segment production

Transcription

1 Customized state-of-the-art segment production Jörg Riechers Product Manager, Herrenknecht Formwork Technology GmbH, Germany. ABSTRACT Efficient mechanized tunneling projects, using segments for its structural lining, depend on a harmonized segment production at highest standards in segment quality and accuracy. As a result of a consequent product management, Herrenknecht Formwork has successfully established itself as the world market leader for the supply of segment moulds, handling equipment and carousel plants. Up to now, more than 4,000 moulds were manufactured for 140 realized projects. Herrenknecht Formwork designs and supplies customized equipment for any type of segment production at highest standards. With three workshops in Germany, Slovenia and China, Herrenknecht Formwork is able to offer and manufacture equipment at short notice and in outstanding quality. Due to short project lead times and an increasingly growing demand, contractors often rely on mould manufacturers project experience with regards to the selection of a suitable variant of segment manufacturing, determination of suitable sets of moulds for an efficient manufacturing as well as on comprehensive concrete and curing concepts. Based on increasing world-wide interest in multipurpose tunnels, enabling either a temporary or permanent use of its overall or partial structure for more than the essential purpose, Herrenknecht Formwork is aware of the importance of cutting-edge developments. Especially for tunnels with segmental lining, for conveyance of water and sewage water, Combisegments has been developed. This segment embedded corrosion-protective liner (CPL) is extended by a liner frame and a mechanically integrated gasket, whereby e.g. welding at radial and circumferencial joints and conventional gasket gluing become obsolete. In addition, Herrenknecht Formwork is active in the field of thermally activated tunnel structures, whereby conventional segmental lining is turned into a heat exchanger for heating of municipal properties. This paper compares segment productions using immovable stand moulds and a manufacturing carousel with associated handling equipment. In this context, influencing factors such as tunnel length, regional labour cost, lead and assembly time as well as cycle times of segment production are taken into consideration. In addition, new and promising product developments are introduced. INTRODUCTION Each tunnel project is individual as regards technical requirements, geographical, topographical, infrastructural, climatic and most important geological aspects. Therefore, the segment production plant has to be exactly adapted to the local conditions of the project. This is the only way of ensuring that each segment is in the right place at the right time as well as in required quality. This presents a huge challenge to the planners and contractors, to ensure that reinforcement production, concrete mixing, segment production and handling merge into in an optimal workflow for installation in the tunnel.

2 Together with the first use of mechanical tunnel boring machines in the 19 th century, technical solutions for pre-fabrication of reinforced concrete segments were developed stepwise. Based on increasing project demands, on both accuracy and efficiency of segment manufacturing, two types of manufacturing established themselves: stationary segment production and carousel production. SEGMENT PRODUCTIONS IN SPOTLIGHT Stationary production A stationary production line is characterized by a precisely defined positioning of used segment formworks during production. Consequently, the moulds are fixed on the floor during the whole production period (Figure 1). Concrete can be supplied both by trucks, specially developed flying bucket systems with concrete distribution buckets as well as by means of overhead cranes. Figure 1: Stationary segment production (left) and connection of vibrator interface to the mould (right) [Herrenknecht Formwork, 2011]. In order to ensure an efficient concrete compaction, vibration is supplied either by pneumatic or electrical vibrators and distributed by its fastening positions underneath each formwork bottom. Both vibratory methods enable supply of sufficient vibration energy at usually 6,000 RPM, although systems differ both in terms of investment costs and costs for installation but as well with regards to possibilities for adjustments and synchronization of frequency and RPM of used vibrators. Latter aspects directly affect quality of concrete compaction related to parameters as concrete slump and influencing natural frequency of concrete moulds. Operating manuals and maintenance recommendations should be considered by all means, independent of chosen equipment. An accelerated concrete curing can be achieved either by integrated heating installations, located in the base frame of each mould, or by means of heating tubes/ radiators installed on the factory floor (Figure 2). In order to achieve optimal curing conditions in terms of temperature and humidity, furthermore, tarps or insulated hoods for covering each mould are used after filling and compaction. Figure 2: Heating tubes / radiators pre-installed at the later position of neighbored moulds [Herrenknecht Formwork, 2010].

3 Carousel production In contrast, when concrete segments are produced by means of a carousel system, the moulds are moved on rails to pass different working stations for the purposes such as mould cleaning, concreting, finishing, etc. For curing, the filled moulds are moved in a special curing chamber with an appropriate heating system and afterwards pre-stored indoor before being stacked outside near to the segment plant. The main elements of the carousel plant are as follows (Figure 3): Concreting system with concrete hopper, concrete supply, automatic mould cover for large moulds (if required), concreting table, concreting chamber Carousel-type rail system, thrust bars, cross transfer trolleys with rail system, clamping Reinforcement supply with monorail and magazine for reinforcement cages Heating system with curing chamber, heating, pipes Demoulding equipment, e.g. vacuum lifter Finishing and evacuation line including rotator, gasket gluing station (if necessary, please refer to Combisegments ), etc. Figure 3: Carousel segment production [Herrenknecht Formwork, 2009]. The carousel plant is equipped with several control units for automated operation of the different components such as movement of the moulds on the rails by means of thrust bars, movement of the cross transfer trolleys, movement of the cranes, doors of the curing chamber, handling equipment, etc., thus reduction in the share of manual works. The core part of the carousel plant is the concreting chamber. With its automatic doors, its steel/ brick structure with noise insulating panels and its control panel separated from the concreting chamber by a window, it guarantees a maximum of safety and noise reduction (issue of working without ear protection) with less manpower required (Figure 4). After concreting and stripping the surface, the filled moulds are pushed into the curing chamber where they remain usually for approx. 6 to 10 h in dependence of e.g. the segment size, characteristics of the concrete, ambient temperature. The curing chamber guarantees optimum conditions for a controlled and accelerated concrete curing due to adjustable heating radiators (55 65 C). To improve the efficiency, moulds are often covered with tarps, in order to create high humidity at a certain temperature beneath cover and concrete surface. Optionally, a steam distribution system in the chamber can be used to control humidity conditions (Figure 4). Especially in the beginning of the curing phase, a sufficient supply of heat and humidity accelerates the curing process, i.e. hydration of cement.

4 Figure 4: Operation panel for the concreting station (left); filled moulds in the curing chamber (right) [Herrenknecht Formwork, 2013]. For each type of production, appropriate handling and logistic equipment is required and made available according to customer requirements by Herrenknecht Formwork. When starting planning of a segment production plant, construction companies, precasting companies and suppliers of the equipment have to choose the appropriate production type and related equipment. They are usually facing the question of advantages and disadvantages of each production type related to a certain project. Therefore, the most important selection criteria have to be defined, for example as follows. Criteria for selection of the production mode As already mentioned in the introduction, the local conditions of the project are crucial for selection of the production mode. However, there are further aspects that have to be considered: number of TBMs, expected advance rate, project time, production time and schedule, setup time, space requirements, labour requirements versus availability of (skilled) labour, cost of labour, project budget, forecast for follow-up projects as well as climatic conditions. In the following, these aspects will be pointed out and their influence on the selection of the production mode shall be explained. Local conditions Local conditions have to be divided into different categories either referring to location of the tunneling site or national regulations regarding safety, working time, importation of goods, etc.. When the project is located in a large city, for example, space requirement of the production plant is one of the decisive criteria. If there is already an existing precast plant, stationary moulds can be integrated into the existing factory more easily. By contrast, in case of a remote tunneling site, logistic and infrastructural conditions have to be determined and evaluated. Here, for example, a just-in-time supply of the necessary wear and spare parts for a highly automated carousel plant could be challenging. Figure 5: Remote project location in Palomino, Dominican Republic [Herrenknecht AG, 2008]. In addition, the wage level of the country has to be considered. In a country with low wage costs, stationary production tends to be more efficient as personnel costs would probably be lower than the additional cost for the automated carousel plant.

5 As regards the national regulations, some countries, for instance Brazil, impose strict safety regulations, i.e. one person may only be responsible for one special function. In such a case, the approval for a stationary production plant, usually operated by a certain number of teams with alternating tasks, is rather difficult to obtain. In contrast, an authorization for a carousel plant with only few people responsible for the same production procedure would be comparatively easier. Customs procedures are another important aspect. In some countries, customs clearance of complex equipment, including parts from different suppliers, lead to delays in shipment. Non-functioning carousels, due to missing equipment or required spare parts, cause expensive production downtimes. Tunneling advance rate Precast concrete segments have to be available in the tunnel just-in-time in order to guarantee continuous advance of the TBM. As storage capacity is restricted in most of the cases, the segment production speed has to be adjusted to the tunneling speed. Segment production speed can mainly be defined by the number of sets of moulds used as well as the number of working hours per week. The latter is often limited by national regulations. By the way, a set of moulds consists of a certain number of segments required for forming a segmented ring. According to Herrenknecht Formwork s experience, the number of production cycles with each set of moulds per day is 2-3 for carousel plants and in dependence of the optimization degree between 1-2 and 2 up to 3.25 for stationary moulds. However, from the aspect of tunneling speed alone the appropriate production mode cannot yet be derived, as both systems are able to fulfill such requirements, as for example stationary moulds with an efficient heating system, together with favorable climatic conditions, sufficient qualified employees within a team of colleagues used to working together can achieve more than three production cycles per day as a best performance. Project time schedule/ setup time This aspect may be decisive in case of a tight project schedule. Due to the high degree of automation, the carousel system requires more time for conception, design, construction and setup compared to stationary mould production lines. Further, a more intensive and time-consuming training of the operator s personnel is required which in turn leads to minor cost increase. In order to get an impression, stationary moulds can usually be commissioned within e.g. one or two weeks (depending on the number of moulds, personnel capacity, etc.), whereas commissioning of a carrousel production plant takes e.g. two to three months (depending on the scope of supply and services). This period, however, strongly depends on the client s support for preparation works, e.g. construction of a suitable foundation for the segment plant, and provision of suitable personnel. Expected operation period of the plant The calculated operation period often depends on the tunnel length or also on the overall infrastructure development of the region or country, i.e. if any subsequent projects can be expected. In case of a short operation period, a stationary production would probably be more efficient as a carousel solution. Comparatively higher investment cost for additional carousel equipment cannot be justified in case of a small-series production. In contrast, if the number of segments required is comparatively high in combination with large dimensions, which is basically attributable to the tunnel length and diameter, the operator could benefit from the lower personnel requirement of the carousel. Otherwise, this saving of personnel cost could be offset the higher the investment costs of the carousel equipment. In case of different projects to be realized in a certain area, the carousel plant can easily be adjusted and re-used for follow-up construction lots/ projects, even for rings with different diameters. In this case, the number of sets of segment moulds required for each diameter would be smaller compared to stationary production. Thus, it is important to determine and evaluate important parameters resulting in a balanced calculation.

6 Comparison of different aspects Time, available land plot, personnel requirement, production capacity The following Table 1 briefly summarizes differences between selection criteria and indicates labour requirements and costs as well as an assumption of usually required time for the entire chain from design to production launch. This comparison reflects a metro project with an internal diameter of 5,400mm, external diameter of 6,000mm, ring configuration 6+1 using segments with right / left conicity and a width of 1,400mm. The tunneling job itself and the segment manufacturing have been executed in Moscow. In order to evaluate efficiency of production methods for a required avg. casting capacity of 15 rings/ day, a stationary production plant with eight sets of moulds at seven moulds/ set has been compared with a carousel production plant which only requires six sets of moulds. Table 1: Differences in assumed requirements for stationary and carrousel productions. Assumed requirements (avg.) Period for conception of the factory (hours of supplier) Period for design and construction Plot of land a) for production line b) for indoor storage with evacuation line Carrousel production with 6 sets of moulds approx. 200 h (batching plant and cranes not included) approx. 800 h (without evacuation/ finishing line) h for moulds = total: 1,400 h a) 18m x 65m = 1,170m² b) 18m x 55m = 990m² total approx. 2,000 m² Stationary production with 8 sets of moulds approx. 100 h approx. 600 h a) 21m x 85m = 1,785m² b) 21m x 50m = 1,050m² total approx. 2,835 m² Period for assembly, commissioning and training of client s personnel (weeks) Labour for assembly, commissioning and training of client s personnel (labour of supplier) Additional personnel from the client for setup (usually made available by the client) persons 1 2 persons persons 5-6 persons Effort for maintenance per month approx. 50 h approx. 16 h Personnel for production per shift (please refer to Table 2) persons persons Requested avg. production capacity 15 rings/ day 15 rings/ day Scheduled production cycles per day (assuming 24 working hours); higher rates possible in other projects max. 2 Production rate (rings/ day) It should be noted that given figures on daily productions cycles are related to this specific reference production and precasters schedule of production. By means of an example, during segment castings in Abu Dhabi at CCI, outstanding performances up to 3.25 cycles/ day could be achieved at average rates of 3 cycles/ day. Table 2 summarizes different types of work necessary for production of precast segments, divided in types of production. The numbers listed refer to recent project experience with the metro project in Moscow and similar projects. It should be noted that indicated information depend basically on required production capacity related to project aspects as well as on the qualification of available personnel, national health and safety regulations, etc..

7 Table 2: Comparison of necessary works for production and the required number of persons. Required type of work (job steps) Carrousel production employees per shift Stationary production employees per shift Demoulding 2 3 Cleaning of the mould 2 3 Preparation of mould: installation of insert parts and reinforcement 2 3 Closing of the mould and final check Concreting Finishing 3 3 Covering of filled mould 0 2 Turning, storage Total number of employees Based on previously discussed influencing parameters and this project example, it becomes clear that several criteria have to be considered referring to the tunnel project itself, e.g. tunnel length, tunneling speed and project schedule as well as local conditions, e.g. infrastructural, social, and environmental. Therefore, without considering these aspects, it is not possible to state that a carrousel system is favorable in general. Comparatively, small but important equipment accessories such as vibrators (pneumatic or electrical) offer potential for further improvements of production efficiency. The presented reference project and related comparison between both production modes show clearly that each of both can fulfill the requested production rate. Based on experience of Herrenknecht Formwork the following net diagram (Figure 6) shows essential decision criteria and its emphasis related to each production mode. Personel for production 1 Assembly, commissioning, training Design and conception 0,75 0,5 0,25 0 Labour costs Production capacity Required land plot Occupational safety Stationary Carousel Investment costs 0,5: basis = stationary mode 1: higher (effort/ capacity/ quality) Figure 6: Net diagram for illustrating differences between production modes by means of different criteria. In this specific case, two different precasters have chosen a carousel production after internal and external consultation. The land plot of precasting plants is located in Odinzovo, a city with limited available industrial areas, not far from Moscow. In addition, higher production rates in this specific case at low labour requirements per shift including safety issues influenced their decision. This tendency can be confirmed by a close look on already 27 carousel production plants being designed and assembled by Herrenknecht Formwork. Geographically, they are distributed as follow: 14 in Europe & Russia, 8 in South Central America, 3 in Asia & Pacific and 2 in Israel. The majority of all carousels were located in an urban area in densely populated regions. Nevertheless, as a conclusion, it can be highlighted that a careful, detailed assessment of the above mentioned aspects at the beginning of the project is crucial for a successful and cost-efficient segment production and consequently for a successful tunnel project.

8 CUTTING-EDGE SOLUTIONS FOR PRECAST CONCRETE SEGMENTS Especially for segmental lined tunnels with highest demands on durability, e.g. for conveyance of water and sewage water, Herrenknecht AG and Herrenknecht Formwork developed Combisegments. The designation Combisegments describes a composite product consisting of a common reinforced concrete segment incorporating an advanced corrosion resistant lining element. Based on first project experience with Combisegments in Moscow in 2009 using GRP as lining material, further improvements have been implemented in order to achieve both highest quality standards and a simplified usability during segments manufacturing and tunneling. A Combisegments lining element consists of a Telene -pdcpd (poly-dicyclopentadiene) corrosionprotective liner, extended by a liner frame and a mechanically integrated gasket, whereby e.g. welding at radial and circumferencial joints after/ during tunneling becomes obsolete. Manufacturing of Combisegments can be integrated into usual production cycles without additional equipment or additional training of labour. Based on its design, a Combisegments lining element is simply placed centered at the bottom of the Combisegments -mould, with its smooth surface facing the base plate. Mechanical fixation of this liner is achieved after closing mould shutters by means of an integrated groove system. After demoulding, fastening of required sealing frames by means of adhesive, resulting in additional effort for the precaster, is no longer required due to already integrated EPDM gasket within the Combisegments lining element (Figure 7). Thus, investment for a gasket gluing station is not necessary as well as costs for consumables, application tools and additional wage costs do not apply (cf. chapter Segment Production in Spotlight). Figure 7: Combisegments -mould (ID 2000) - handling demonstration [Herrenknecht Formwork, 2013]. Based on increasing world-wide interest on multipurpose tunnels, enabling either a temporary or permanent use of its overall or partial structure for more than the essential purpose, Herrenknecht Formwork is active in the field of thermally activated tunnel structures, whereby conventional segmental lining is turned into a heat exchanger for heating of municipal properties. The so called Energy Lining Segment Energietübbing was developed by the companies Ed. Züblin AG and REHAU AG & Co.. Together with Herrenknecht Formwork, three world-wide known companies have jointed their expertises to provide tailored concepts and equipment turning tunnels into a source of renewable energy. Energy lining segments are equipped with absorber pipes fastened at the reinforcement cage. By integrating coupling pockets into segments, achieved by using special mould components, access to protruding absorber pipes is achieved, whereby segments respectively erected rings can be connected to thermal cycles after tunneling (Figure 8).

9 Figure 8: Energietübbing with absorber pipes (red), fixed to a reinforcement cage [Ed. Züblin AG, Geotechnical & Tunneling Division]. SUMMARY AND CONCLUSION In summary it can be stated that besides core competences in design, manufacturing and delivery of perfectly project harmonized equipment increasing demands are being placed on equipment manufacturer. Throughout the entire project cycle a holistic consultancy and service is increasingly of importance and, in turn, offers business opportunities for experienced solutions suppliers. By means of an exemplary metro project in Moscow criteria for the selection between methods of segment production stationary and carousel have been discussed. It became apparent that the decision between stationary and carrousel production depends on numerous infrastructural and economic aspects and should be based on a thorough evaluation of all criteria relevant for the corresponding project. In addition to this competence, two cutting-edge solutions were introduced: Combisegments and Energietübbing. Combisegments meets requirements on durability with simultaneous advantages during production and tunneling. Unlike conventional liners, this solution enables one-pass segmental lining without subsequent welding at radial and circumferencial joints, after being manufactured accelerated without the need of a gasket gluing station. Based on increasing world-wide interest in multipurpose tunnels, the Energietübbing - Energy Lining Segment turns tunnels into a source of renewable energy. Since being a well-experienced system supplier with a modern philosophy and a wide-ranging team of experts in mechanical engineering and civil engineering, Herrenknecht Formwork meets the challenge to develop, design and supply customized solutions for state-of-the-art, sustainable traffic and utility tunneling.