Chapter 5 Project Implementation Plan
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CHAPTER 5 PROJECT IMPLEMENTATION PLAN CHAPTER 5 PROJECT IMPLEMENTATION PLAN 5.1 Construction Method 5.1.1 General The construction of the Line 2 East and West Extensions will require careful planning and organization, given the magnitude of the works, time constraints and the location of the works on busy national and arterial roads within Metropolitan Manila and Rizal Province. The challenges faced during construction will be: to adopt rapid construction techniques while still ensuring quality, the planning and organization of all construction activities to ensure smooth flow of construction and the avoidance of delays on critical path activities, the organization and supervision of sufficient work teams and construction equipment and proper coordination with other contractors as necessary the construction and organization of a suitable temporary casting yard close to the site to implement well planned traffic management plans to ensure minimal impact on traffic, with traffic re-routing plans as necessary incorporating utility relocations, or design changes imposed by utility locations, into the construction planning, at all times to assure safety of construction operations. 5.1.2 Viaduct 5.1.2.1 Foundations The viaduct foundations comprise of conventional bored piles and pile caps. The bored piles will be constructed using high torque powered rotary drilling rigs mounted on crawler cranes with telescopic kelly bars and using a set of various buckets, augers and chisels. Excavation typically will be carried out under a bentonite slurry without the use of temporary casings. Following the completion of the boring and the placement of the steel rebar cage in the pile excavation, concrete is placed using a tremie pipe while the bentonite slurry is pumped away. Critical issues during construction will be: proper mixing and recycling of the bentonite slurry to ensure the formation of a waterproof lining (“cake”) on the face of the excavation and allow clean placement of concrete ensuring that the end of the tremie pipe is always sufficiently embedded in the wet concrete as the bored pile concreting progresses avoidance of cold joints due to breakdown in supply of concrete overcasting of the pile and chipping back, or baling of the contaminated concrete while wet, to ensure good quality concrete at the pile head. To allow sufficient space for the construction of the pier pile caps and to accommodate the construction equipment, a minimum width of 8m will typically be required as a work space on the central reserve of the affected roads. A typical section of the construction work space arrangement is given in Figure 5.1-1. 5 - 1 MARCOS HIGHWAY RECTO AVENUE Source: JICA Study team Figure 5.1-1 Typical Work Space Layout for Foundation Construction Notwithstanding delays caused by utility relocations, the construction period for a typical bored pile pier foundation will depend on the number and size of piles per foundation, required depth of pile, soils encountered, etc. The piling work is on the critical path for the pier construction, since once the piles are constructed, multiple teams can be mobilized to complete the remaining reinforced concrete works for the piers. During the construction of the existing LRT Line 2, the contractor scheduled to construct up to two (2) piers per month per section between stations (about 1km on average between stations). The East Extension may require four (4) or more drilling rigs to complete the piling work on a similar schedule. 5.1.2.2 Substructure The viaduct substructures comprise of conventional reinforced concrete pier columns and pre-stressed concrete pier heads. The columns should be constructed using standardized steel forms to promote a good quality of finish and reduce construction cycle times. The pier head formwork will supported on falsework anchored to the pier columns to minimize required construction area and allow operation within the provided construction work space. Critical issues during construction will be: 5 - 2 Table 5.1-1 Duration for 1 pire Construction Foundation/Footing Column Pier Head Footing(Foundation) Excavation Piling Work Work Pile Driving Reinforcement Concrete Reinforcement Concrete Survey Leveling 6days Placing/Form Placing / Placing/Form Placing / Instllation etc. Concrete （a pile/day） Placing Curin Placing Curing Preliminary Sheathing Works 1day Pile Head Treating 3days 1day 10days 3days 1day 6days 3days 3days 3days 3days accurate surveying of column location and vertical checking of steel forms proper quality control of column formed surfaces and joint areas proper handling methods for the steel forms to prevent damage and deformation Typical progress photographs of the existing LRT Line 2 pier column construction are shown in Photo 5.1-1 and Photo 5.1-2. Photo 5.1-1 Pier Column Construction – LRT Line 2 5 - 3 Source: LRTA library photo Photo 5.1-2 Pier Column Construction – LRT Line 2 5.1.2.3 Superstructure The viaduct will comprise precast post-tensioned concrete elements, pre-fabricated at the casting yard and erected at site. Precast concrete units will be delivered with low-bed trailers of 50 to 100 tons capacity. Advantages of precast concrete over concrete cast in-situ are: Rapid construction on site with minimal impact on traffic, units can be delivered during night time work shifts Quality can be controlled and monitored much more easily in the pre-cast yard making it easier to control the mix, placement, steam curing and formed finish Weather is eliminated as a factor in the pre-casting process with covered and protected casting beds in the casting yard Less labor is required On site, precast elements can be installed immediately, there is no waiting for elements to gain strength Repeatability—multiple units of the same precast element can be made; and by maximizing repetition, the contractor can maximize the value from a mold and a pre-casting set-up Depending on the final form of structure adopted, the precast elements will either be PC Box segments, weighing 30 to 40 tons each, or AASHTO girders, weighing up to 50 tons each. The segments or girders units will be provided with lifting points for ease of erection. 1) PC Box Segment Erection The PC Box segments will be erected using a double steel truss, or a single steel box girder, self propelling overhead erection gantry, depending on the type of PC Box girder segment erected. The 5 - 4 erection gantry will typically be designed for the project by a specialist sub-contractor hired by the main contractor for the segment erection. The gantry will be long enough to be self propelled across two viaduct spans, with a total length of at least 60m long and have a lifting capacity of at least 150 tons. A typical erection sequence of a PC Box segment is as follows: 1. Erect and install the erection gantry support legs on the pier heads by crawler cranes or truck mounted cranes. 2. Assemble the erection gantry on the constructed support legs by crawler cranes or truck mounted cranes. 3. PC Box segment is delivered by trailer to the erection gantry, the segment is lifted by winch from a rail mounted movable gantry crane supported above the gantry. 4. The PC Box segment is rotated if necessary and launched forward by the gantry crane to its required location and then supported from the gantry by four (4) hydraulic jacks, one side of which (2 jacks) is hydraulically linked to provide a determinate 3 point lift. 5. Successive segments are similarly placed, adjusted and leveled. Segments are placed working backward so that the furthest segment is the first positioned. 6. When all of the segments for a span are positioned, the segment joints are epoxied and joined, the pre-stressing tendons are installed and stressed, and the complete span is lowered onto the bearings and prepared anchor rods before final grouting of the tendon ducts. 7. The erection gantry is then launched to the next span, and the procedure is repeated. The position of the gantry legs can be adjusted laterally on beams attached to the pier heads such that the erection gantry can negotiate curved viaduct sections. During the construction of the existing LRT Line 2, a total of three (3) erection gantries were used with both smaller steel plate box girder and larger steel truss girder designs for the main longitudinal gantry girders, to enable lifting of both single box segments and multiple cell box segments respectively. A typical erection cycle for one viaduct span, twin single box type, is given below: Table 5.1-2 Duration for 1 span Erection Span Girders Segments Epoxy & Stressing of Anchor Rod Grouting of (Twin Single transported and Joining of Tendons Grouting and Tendon Ducts Box Type) erected Segments Final Lowering Box Girder 1 Day 1 Day 2 Day 2 Day 3 Day 4 Box Girder 2 Day 3 Day 4 Day 4 Day 5 Day 6 Launching of erection girder to next span 2 – 3 Days Total Cycle Time for One (1) Span 8 – 9 Days For the Line 2 East and West Extension projects the number of erection gantries required for each extension will be controlled by the overall construction schedule. The East Extension may require as many as three (3) erection gantries to complete the PC Box spans in the case of a compressed construction schedule. A typical progress photograph of the existing LRT Line 2 PC box girder construction is presented in Photo 5.1-3 showing a truss type erection gantry used to erect multiple cell box segments. An illustration of a typical steel box girder type erection gantry, used to erect the twin box segments, is given in Figure 5.1-2. 5 - 5 Source: LRTA library photo Photo 5.1-3 PC Box Girder Erection – LRT Line 2 (Truss Type Erection gantry) Source: Study Team Figure 5.1-2 Elevation on typical Erection Gantry (Steel Box Girder Type) 2) AASHTO Girder Erection The AASHTO girders, if specified in the detailed design, will be erected using crawler cranes or truck mounted cranes.