By: Tina Chi
Engineering Rome 2019
December 4th, 2019
All Photos are by the author unless otherwise stated.
*Featured Image Provided By: Steve Muench
As a student at the University of Washington studying construction management with a focus on heavy civil transportation projects, I was fascinated by Rome’s public transportation system. I wanted to know how their system was being expanded through the construction of new stations that will increase ridership to different parts of the city. Luckily on my study abroad trip, I had the opportunity to visit two parts of the Metro Line C Extension. On Thursday, September 12, 2019, our class visited the 3.2 shaft Celimontana and the Fori Imperiali Station near the Colosseum. At this site, I had the chance to learn about the project’s organizational management, to observe the equipment bring used to complete the project and to learn about risks that caused potential delays in their schedule.
Because the Metro Line C Extension is a multibillion euro project, there needed to be multiple organizations to fund and oversee the completion of the project. The Metro Line C Extension is publicly funded by the Italian government, Region Lazio, and the City of Rome. This public funding is given to Roma Metropolitane who oversees all the design and construction of metro lines (romametropolitane). However after the project is completed, Roma Metropolitane will not be running and maintaining the line. The line will be turned over to ATAC Roma, a public transportation entity who operates all the metro lines in Rome as well as surface vehicles, regional railways, park & ride areas, and metered parking (ATAC Roma). Another major player of this project is the general contractor, Metro C S.c.p.A., who is a joint venture between five entities: Astaldi, who has a 34.5% stake, Vianini Lavori S.p.A. who has a 34.5% stake, Hitachi Rail STS who has a 14% stake, Consorzio Cooperative Costruzioni who has a 7% stake, and cmb who has a 10% stake (Metro C). These percentages associated with each contractor shows the risk allocation and payment for the bond (Padovan). All of these entities are required because the project needs expertise knowledge on public funding, procurement, design, construction work, contracts, operations which will not monopolize the transportation in Italy.
Metro Line C Extension Project Details
The Metro Line C Extension is a 25.5 km extension with 30 planned stations. 30 new trains with 6 cars each will be assigned to this line that holds 1,200 passengers. Maximum speed allowed will be 80 km/h and headway will range from 90 – 180 secs (Metro C). This project features Automatic Train Control (ATC) which essentially allows the train to be driverless through automation. With ATC, the train can be located through GPS, direction and time can be established, and quick and accurate calculations can be made to ensure safe acceleration and braking. ATC eliminates operator errors but still allows supervision from the Graniti Depot Operating Control Center (Depot-OCC). From <http://www.railway-technical.com/signalling/automatic-train-control.html> The Scada system, another piece of technology for facilities management, is currently being implemented on this project. Scada is in one offsite facility that remotely operates other station facilities such as the lights and elevators. Because this systems control is centralized, it conserves energy and reduces oversight of maintenance work. From <https://www.toshiba.co.jp/sis/railwaysystem/en/products/information/scada.htm> One system that has not yet been introduced in the United States is the platform screen door system. The platfrom screen doors provide a guard for riders between the platform and the guideway. Engineers will need to ensure that train doors perfectly line up with the platform doors and that they open at the same time. Implementing this system as a safety measurement will prevent deaths and injuries of passengers from train collisions. Overall, The estimated cost for the construction and administration of the extension is 3.7 billion euros and rising because of unforeseen conditions of archaeological discoveries that delay the project and poor financial record keeping. The Metro Line C Extension is now expected to be completed in 2024 (wantedinrome).
3.2 Shaft Celimontana Project Details
The 3.2 Shaft Celimontana is one of the underground stations on the Metro C Line across from Piazza Celimontana. This shaft has a circular diameter of 34.80 meters and a depth of 59 meters. This shaft consists of 6 total floors. There are two technical floors at heights of 20.55 and 27.18 meters above sea level and three intermediate floors at -4.90, 3.35 and 11.60 meters below and above sea level. There is also one platform floor where passengers will meet the metro at -14.46 meters below the sea level (Metro C). When first excavating down, contractors had to consider the soil conditions. After reading a study on the soil conditions on Metro Line C, researchers found the area to be most of sand and silt (Burghignoli). The benefit of having this type of soil condition is that it is easy to excavate out with construction equipment. However the problem with sand or silt soil conditions is that it is fine-grained which will increase the change of settlement. Therefore contractors had to devise a plan to reinforce the walls while conducting their mass excavation to prevent cave-ins. The contractors ended up using the “down-up” method to construct the shaft. While excavating downwards, some horizontal sections were reinforced by circular beams and horizontal reinforced concrete walls were casted on the way up (Noegroho).
Fori Imperiali Station Project Details
The Fori Imperiali Station is located near the Colosseum and facing the Basilica of Maxentius. This station has the dimensions of 30-50 meters for the width, a length of 240 meters, and a depth of 32 meters below the ground level. To access the station there are two entrances, one on each side of the station. Because the Fori Imperiali Station is a transfer point between Metro Line B to C, each entrance is designated to one of the line. At the entrance, there is additional access by staircases, two escalators, and elevators. There is a total of five levels in the Fori Imperiali Station: the lobby level, the mezzanine level which serves as a connection with Metro Line B, two equipment room levels, a platform level for passengers to board Metro Line C, and an under-platform level (Metro C). To construct this station, contractors chose to excavate based on the top-to-bottom method. First, contractors cast two permanent diaphragm walls along the perimeter with soil nails as temporary shoring. Next, contractors implemented the top-to-bottom method by casting slabs against the ground that bisect the diaphragm walls (Metro C). One of the considerations of this site is that contractors did not have much space for material staging. This area also has heavy pedestrian foot traffic so shipments from vehicles in and out of site had to be planned at quieter times of the day.
Fori Imperiali Station Gantry Crane w/Clamshell
One piece of equipment that I rarely see in the United States is the gantry crane. On the site tour, I had the opportunity to learn more about it’s uses on the construction site. The first gantry crane I observed was at the 3.2 Shaft Celimontana. (Note that a gantry crane is a crane that moves horizontally on rail to vertically lift and move equipment and materials) What struck me was that I have never seen one used for chain rigging wooden planks to lower down into the shaft. Because of the depth of the shaft and limited space onsite, the contractors had limited options on equipment selection so they decided to use the gantry crane. The second gantry crane I saw had a clamshell attachment at the Fori Imperiali Station. At the station, two excavators were used to excavate the hard soil and the gantry crane with a clamshell attachment moved it to the ground level where another excavator moved the soil into a truck to be hauled off. Clamshells are typically used for marine construction for soft and loose soils because it has less of a digging force compared to backhoe excavator. Ultimately, the choice of the gantry crane depends of cost of the equipment and productivity which is dependent on the type of soil, depth of cut, and the bucket size of the clamshell as well as the cycle time which was exceptionally long (Schaufelberger, Migliaccio).
Assuming the clamshell is a heavy duty bucket with a rated volume of 6 cubic yards, the clamshell can carry 21,645 lbs.
(6 LCY) (3,600 sec/hr) / (600 sec. cycle time) (1.25 LCY/BCY) = 28.8 BCY/hr.
Hydraulic Backhoe Excavator
Hydraulic backhoe excavators are a type of excavating equipment with a bucket and cutting teeth on the end of a boom. The excavator can be used to move all types of soil. Excavators were common around the 3.2 Shaft Celimontana and Fori Imperiali Station. On the job site, we saw the excavators work with the gantry cranes to dump soil into the nearby trucks to be hauled off. One of the risks that the superintendents need to be wary of is the lifting capacity of the excavator. According to SAE international, operators must be wary of the rated lifting capacity of 75% of the load before the excavator tips. This is different from being on level ground where the rated lifting capacity is 87%. Other considerations when selecting whether or not to use an excavator on the job site include operator skill level, soil conditions, depth and angle of cut, and size of bucket (Schaufelberger, Migliaccio). Because this was a relatively simple operation with loose soil, using an excavator would be the best selection for the task.
Assuming the material is a rock earth mixture, the fill factor would be between 1.00-1.05
(2 LCY excavator) * (1.025 fill factor) (3600 sec./hr) / (30 sec cycle time) (1.35 LCY/BCY) = 182 BCY/hr
Trucking and Site Logistics
Trucking in and out of the Fori Imperiali Station is a challenging task to plan. At the Fori Imperiali Station, trucks were hauling off excavated soil. There are many considerations when looking at the site logistics next to the Colosseum. There is heavy pedestrian foot traffic because it is a tourist spot so pedestrian safety is a top priority. Because of cautious driving and traffic, contractors would have to plan a route at a certain time of day to receive on time deliveries. Choosing a less congested time will improve the cycle time and maximize productivity rates. The contractor can also have a staging area for material so delay of long lead items will not affect the critical path of their schedule. Another consideration is that the trucks also cannot be too large or it will damage the asphalt roads. The size and weight will depend on local jurisdiction as well as international organizations who have measured standards for rated heaped capacities such as The International Organization for Standards (ISO), Society of Automobile Engineers (SAE) international, and the Committee for European Construction Equipment. These organizations will help the contractor select a type of truck based on the total weight of differing load and heap capacities. For instance, choosing bottom dump or end dump trucks when backfilling which have different load capacities (Schaufelberger, Migliaccio). Otherwise, calculating cycle times will be a continuous tracking effort in order to predict accurate times of deliveries and hauls.
Because Metro Line C is close to historical monuments, contractors knew that there would be many archeological artifacts nearby and must take precaution upon discovery. Preventive surveys took place 10-12 meters below the surface before mass excavation to locate the archaeological sites. At the end of the surveys, archaeologists have done their own excavation at 54 sites to produce quality finds (Metro C). Another archeological consideration is the preservation of above ground historical buildings and monuments. To decrease settlement around buildings where the tunnel boring machine will be digging under, contractors implemented compensation grouting. Compensation grouting will solidify the soil and ground by inserting tubes filled with a cement mixture to grout 1,530 cubic meters after drilling alongside the TBM (Trevi Spa). Through the collaboration of archeologists and contractors, preservation of Ancient Rome’s culture and history is made possible in maintaining a record to study the past.
After studying about construction in Rome by visiting the site and talking to officials, I have gained a better understanding of the considerations made on construction equipment. Because of the tight site space, there is limited selection on large equipment that can be put onsite. Archeological preservation affects certain layers of excavation below the surface and influences shafts and tunnel boring. The long cycle time affects productivity rates of heavy machinery. Safety of pedestrians around the site affects trucking routes and times. Overall, because of the unforeseen conditions that may occur during construction, there is increased risks of a longer schedule and increased cost. However with constant monitoring of time and money, the risks can decrease as the project advances.
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