Twin Track Installation Methodology And Construction Schedule For Viaduct

Twin Track Installation Methodology

The twin tracks should be installed using prefabrication method. This means that the components of the tracks would be manufactured in a factory and transported on site for installation. The key steps of manufacturing the tracks are: cleaning and preparing the formwork systems; installing the reinforcement and dowels for the rail fasteners; pre-stressing; concreting; cutting through the pre-stressing wires; lifting the slabs and storing them; processing the rail support point mechanically; assembling the rail fastenings; and delivering the components to the site for installation.

Since the method used in FFB slab track Bogl system, there are ten key steps involved in installation process. The first actual installation process starts by installing the reinforced concrete base layer or the hydraulically bound layer. These layers constantly reduce stiffness and load transfer besides being binding layers. Additionally, they support the slab tracks. The second step is preventively pegging out the slab joints and track axles on the viaduct. The third step is transporting the slabs to the specific location to be installed. The fourth step is to deposit the slabs and align the slab tracks. The fifth step is to adjust and fix the slabs. Horizontal and vertical adjustment is done using computer-aided surveying system and spindle devices. The sixth step is to seal the transverse and longitudinal joints of the slabs and fill them using specially prepared grout (Max Bogl, 2015). The seventh step is to underpour the slab. The eight step is coupling the slabs in the longitudinal direction so as to obtain a uniform, unbroken band with high resistance to transverse and longitudinal displacement. Longitudinal coupling resists what is known as whipping effect (which is the warping of a slab ends as a result of thermal differences) (Max Bogl, 2018). The ninth step is to fill the transverse joints. The last step is to assemble the rails.

Different machines and equipment will be needed for the installation process of slab tracks. Some of these include: rail fasteners, rail welding equipment, rail sleepers, point heaters, computer-aided surveying and alignment systems, grout mixers, spindle devices, cranes, trucks, multi-purpose gantries, concreting trains, concrete pumps, concrete finish machines, hergie machine, plasma devices, gauge holder, track adjustment devices, drilling machines, concrete shuttle, construction trains, and rail safety equipment, among others (Anon., 2015); (Rhomberg Sersa UK Limited, (n.d.)).

a2. First TCD

a3. Second TCD

Safety is a very important aspect of installing the twin slab tracks. The following is the safe work method statement for the installation of slab tracks:

• All workers on site must wear appropriate personal protective equipment (PPE)
• All workers must be frequently trained on how to identify hazards, prevent/manage them and report them to the right personnel.
• The site must be properly fenced or hoarded to prevent external interference or protect the public against potential hazards associated with ongoing works.
• Heavy loads should only be lifted by machines
• Only trained and certified personnel should be allowed to operate machines, plant and equipment
• Machines, plant and equipment must be maintained properly and inspected before every use
• All materials, machines, plant and equipment should be stored in designated areas when not in use
• All working areas must have adequate lighting at all times
• Proper signage should be erected to give directions or alert people about ongoing activities or prohibited areas
• There must be emergency exits, properly labelled and lit.
• All works will be supervised by qualified personnel.
• Workers at height will always use full body harnesses and other fall arrest systems.
• There will be a safety manager who will be responsible for all safety matters on site. This includes keeping records of safety incidents, training, etc.
• The safety manager will develop a comprehensive safety and health management plan that will guide all works.
• There will be a first aid officer on site at all times.
• There will be a specified communication procedure to be used in case of any safety incident.

List of Equipment Needed for Installation

Floor cycle time is a common term used in construction industry (especially for construction of high-rise buildings) to mean the time duration that is taken to complete one floor, from start to finish. Since floors of a high-rise building are typically the same, it means that the processes and resources (including materials, machines and labour) of constructing each floor are the same. Therefore it is assumed that the resources and time spent to complete each floor is equal. In the construction of the power tower in this project, the details of the power tower in terms of dimensions and materials are the same. So if the power tower is divided into sections of equal length, from the bottom to the top, the time that will be required to complete one section will be the same across all sections. It therefore means that the total time duration that will be required to construct the entire power tower can be determined by multiplying the time taken to complete one section with the number of sections (Anon., 2015). For this reason, the time that will be spent to construct one section of the power tower will be the floor cycle time for this project. Knowing floor cycle time helps in ensuring that resources all appropriately allocated and managed (Leung & Tam, 2015). It also helps the project manager to identify opportunities for saving construction time.

Floor cycle time helps in identifying opportunities that can be used to reduce the time duration of the project. Therefore floor cycle time is considered the fastest time that can be spent to complete a typical section of the structure being built. It means that floor cycle time is exclusive of any delays and losses of the project. The aspect of floor time is also related to learning curve. In simple words, the contractor learns from the experience of constructing one section of the structure and uses these lessons to reduce the time spent to construct the subsequent section (Jarkas & Horner, 2011). The concept of learning curve is that construction of subsequent section(s) or floor(s) involves repeating the same activities that were done in the previous section(s) or floor(s) (Malyusz, 2016). With that in mind, learning curves helps in increasing labour productivity and reducing floor cycle times (Panas & Pantouvakis, 2018).

There are several opportunities for saving construction time as construction of the power tower proceeds upwards. One of the greatest opportunities is to capitalize on the concept of learning curve. As construction of the power tower proceeds upwards, relevant stakeholders involved can assess the efficiency and success of constructing previous sections and identify areas where they succeeded and failed. They should then use these lessons to maximize the successes and improve on the failures. Some of the likely opportunities to save construction time in this project include: ensuring that lead items are delivered on time through use of cutting-edge logistics systems; avoiding errors and reworks by hiring trained workers only; using specialized equipment and systems (such as formwork and scaffolding systems); using innovative construction methods; continuous training of workers on site on how to increase productivity; ensuring strict adherence to health and safety management guidelines; using high performance construction materials; using technological tools and systems to operate machines and equipment, facilitate coordination and collaboration of stakeholders, and supervision; and ensuring quick resolution of any conflicts. All these opportunities, which are derived from learning curve concept, can help reduce construction time by improving efficiency and productivity, and avoiding unnecessary delays (Srour, et al., 2015). 

Construction Schedule for Track Installation Contract

Three types of cranes have been suggested for this project. These are: tower crane, crawler crane and mobile crane. The capacities of these cranes are as follows:

• Tower crane

Hammerhead tower crane is recommended for this project due to its versatility and efficiency. The tower crane will be used for the construction of the power tower. It is most suitable for lifting and placement tasks (Bruton, 2017). The recommended model of tower hammerhead crane for this project is M1680D. This has a maximum load of 200 tons at 15m, a minimum boom length of 36m, a tip load of 16 tons at 80m, and a maximum boom length of 82.6m (Favelle Favco, 2018).

• Crawler crane

This crane will mainly be used for lifting heavy loads, components and machines during construction and installation processes (Thomas, 2014). The recommended model of crawler crane for this project is 14000 Lattice Boom crawler crane from Manitowoc. This crane has a maximum capacity of 200 tons, main boom length of 89m, fixed jib length of 24.4m, and luffing jib length of 51.8m (Manitowoc, 2018).

• Mobile crane

The mobile crane will be used for the lifting and positioning of various materials and components, including the positioning of the SRS into position on top of the power tower. This crane will also be used for the movement of heavy components from one place to another on the site (TNT Cranes, 2017). The recommended model of mobile crane is LTC 1050-3.1 from Liebherr. The maximum load capacity of this mobile crane is 50 tons. It has a maximum hoist height of 48m, telescopic boom of 36m and maximum radius of 39m. The crane has three axles (Liebherr, 2018).

Site layout design is another very important aspect of ensuring that the cranes works efficiently and safely on the site (Sanad, et al., 2008); (Wang, et al., 2015). Each crane has to be positioned where it will perform the intended work efficiently and without interfering with other ongoing activities or posing safety risks to workers on site (Huang, et al., 2011). In other words, the position of the cranes on site has to be optimized. This can be achieved through use of computer simulation models together with physical inspection of the site (Abdelmegid, et al., 2015); (Irizarry & Karan, 2012).

Below are examples of a crane site layout and logistics plan on a construction site. The diagram in Figure 1 shows the position of the crane, its entire structure and how it is in a position that enables it reach the desired working zone. The crane is positioned such that it does not interfere with other activities. It is also positioned such that the job cuts across the entire structure that is being built. This means that it can be used to lift and position loads on any part of the structure. The diagram in Figure 2 shows the position of the tower crane relative to other elements such as the concrete mixers, security fence, emergency fence, entry gates and working zone, among others. As stated before, the crane should be positioned where it will perform maximally, reaching the entire working zone, and without creating safety risks to workers on site.

Difference in Time Between Two Installation Methods

Long lead items refers to the products, materials, equipment or machines that must be identified at the earliest time possible so as to as to start procuring them immediately. These items should be identified during design stage of the project and the list issued to the relevant stakeholders to plan on how they will be delivered on time. The reason for identifying long lead items as early as possible is because their procurement process is complex and time consuming. This can mean that the items have long bureaucratic processes or take long to be designed, created/manufactured, processed or shipped. Considering the magnitude, complexity and importance of this project, there will be several long lead items. It is possible that some specialized equipment and materials may have to be sourced overseas. Most of the components of the power tower and solar receiver system will also have to be customized, tested and certified by relevant government agencies before they can be used. Therefore the long lead items have a lot of processes and bureaucracies that must be planned ahead (preferably before commencement of actual construction).

A delay in delivery of long lad items has a great impact on construction schedule. Considering the attention given to these items, any delay will cause the entire project team to panic. Since most of these items are likely to be on critical path of the project, it means that construction cannot proceed until they are delivered. In other words, a delay in delivery of long lead times interrupts the whole construction schedule and if radical measures are not taken, the project period will have to be extended. This also has direct implications on the overall cost of the project.  

However, there are several steps that can be taken to try and ensure that long lead items are delivered on program. These steps include: ensuring that the project team identifies long lead items during design stage and hands them over to the relevant department to start procuring immediately; monitoring the progress of procurement and manufacturing processes of these items to ensure that they are on time; facilitating coordination, collaboration and communication between all stakeholders involved in acquiring the long lead items; and ensuring speedy resolution of any issues that may affect delivery of the long lead items (WorkPack, 2018).   

Even though this project is quite complex (considering its design, it is relatively new in this location and the expectations are very high), there are numerous opportunities to save construction time as discussed above. Using these opportunities together with the concepts of learning curve and floor cycle time, ensuring on program delivery of long lead items and benchmarking with similar projects that were completed before, construction time can be significantly reduced. Therefore the estimated construction time duration for the reinforced concrete power tower is eight months. But for this to be achieved, the project team has to prepare a comprehensive construction schedule and ensure that all resources (including long lead items) are provided on time, competent personnel are involved at each stage of the construction process, high performance concrete is used, and that there is proper coordination, collaboration and communication among all stakeholders.

Safe Work Method Statement for Track Installation Work

The perceived key risks and hazards associated with the construction of power tower include:

• Working at height

The power tower is very high – up to 150m. Tradesmen will be working at this great height hence they will be exposed to hazards due to factors such as mobility restriction. Any slight mistake while working at height is always catastrophic.  

• Moving objects

There will be a lot of movement of people, machines and equipment on construction site. The commotion can cause accidents, injuries or even fatalities.  

• Falling objects

There is a possibility of objects falling from height and injuring people downward or on the ground. These objects may fall from lifting equipment such as cranes or from tradesmen working at height.

• Slips, trips and falls

Considering the use of different machines and materials, and the numerous activities that will be undertaken on site, slips, trips ad falls will be very common.

• Material and manual handling

There will be a lot of lifting and moving materials and components n site by workers, both manually and by use of machines. This exposes workers to risks of being injured.  

• Noise

The construction of the power tower will involve use of heavy machines and equipment, which will produce significant amount of noise. The activities will also involve hitting, lifting and contact of different components that produce noise.

It is very important for the project manager to develop a comprehensive health and safety management plan for this project so as to prevent, minimize or manage these risks and hazards.

The following assumptions are made to solve this problem:

• Stage 1 and 3 started at the same time while stage 2 started 6 months later
• The client made full advance payment at the start of each stage
• To recover the advance payment, the client retained or deducted 20% of progress payment for stage 1 and 2 and 10% for stage 3, starting from the first month of payment until all the advance payment was recovered.
• The S-curve payments for stage 1 and 2 were the same.

1. Client’s monthly payments to contractors

A summary of monthly payments made by the client to the contractors are as shown in the table below:

Month	Stage 1 ($Million)	Stage 2 ($Million)	Stage 3 ($Million)	Developer Monthly Payment ($Million)
	Prog. Pay	Adv. Pay	Ret.	Total Pay	Prog. Pay	Adv. Pay	Ret.	Total Pay	Prog. Pay	Adv. Pay	Ret.	Total Pay
0	0	23	0	23	–	–	–	–	0	3	0	3	26
1	4.6	-0.92	-0.46	3.22	–	–	–	–	1.2	-0.12	-0.12	0.96	4.18
2	2.3	-0.46	-0.23	1.61	–	–	–	–	1.2	-0.12	-0.12	0.96	2.57
3	4.6	-0.92	-0.46	3.22	–	–	–	–	1.8	-0.18	-0.18	1.44	4.66
4	4.6	-0.92	-0.46	3.22	–	–	–	–	1.5	-0.15	-0.15	1.2	4.42
5	5.75	-1.15	-0.575	4.025	–	–	–	–	1.5	-0.15	0.15	1.2	5.225
6	5.75	-1.15	-0.575	4.025	0	20	0	20	3.3	-0.33	0.33	2.64	26.665
7	8.05	-1.61	-0.805	5.635	4	0.8	-0.4	2.8	3.3	-0.33	0.33	2.64	11.075
8	10.35	-2.07	1.035	7.245	2	-0.4	-0.2	1.4	4.2	-0.42	0.42	3.36	12.005
9	11.5	-2.3	-1.15	8.05	4	-0.8	-0.4	2.8	3	-0.3	0	2.7	13.55
10	11.5	-2.3	0	9.2	4	-0.8	-0.4	2.8	3	-0.3	0	2.7	14.7
11	10.35	-2.07	0	8.28	5	-1	-0.5	3.5	2.4	-0.24	0	2.16	13.94
12	9.2	-1.84	0	7.36	5	-1	-0.5	3.5	2.1	-0.21	0	1.89	12.75
13	6.9	-1.38	0	5.52	7	-1.4	-0.7	4.9	0.9	-0.09	0	0.81	11.23
14	5.75	-1.15	0	4.6	9	-1.8	-0.9	6.3	0.6	-0.06	0	0.54	11.44
15	6.9	-1.38	0	5.52	10	-2	1	7	–	–	–	–	12.52
16	2.3	-0.46	0	1.84	10	-2	0	8	–	–	–	–	9.84
17	2.3	-0.46	0	1.84	9	-1.8	0	7.2	–	–	–	–	9.04
18	2.3	-0.46	0	1.84	8	-1.6	0	6.4	–	–	–	–	8.24
19	–	–	–	–	6	-1.2	0	4.8	–	–	–	–	4.8
20	–	–	–	–	5	-1	0	4	–	–	–	–	4
21	–	–	–	–	6	-1.2	0	4.8	–	–	–	–	4.8
22	–	–	–	–	2	-0.4	0	1.6	–	–	–	–	1.6
23	–	–	–	–	2	-0.4	0	1.6	–	–	–	–	1.6
24	–	–	–	–	2	-0.4	0	1.6	–	–	–	–	1.6

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