Lyntas/mining_domain_knowledge_reference_dataset huggingface dataset:
Area: Marine Facilities
Construction Equipment
The primary piece of equipment required for marine-based construction is the marine derrick.
A marine derrick is essentially a flat deck barge that has a duty-cycle crawler crane mounted on it. In order to drive piles and drill into rock the crane must be able to accommodate various driving and drilling rig equipment. Both vibratory and impact hammers will be required for the initial setting of the piles. The drill rig will typically be a diesel powered drill unit capable of accommodating various types of drill bits.
The size of crane is dictated by the capacity requirements of the heaviest pile and by the length of crane boom required for properly handling and pitching the longest pile. Because the floating marine equipment can be brought relatively close to the work face, the crane will have a smaller lift radius than other construction methods and therefore the capacity requirements will be less onerous. Local marine contractors have duty-cycle cranes with capacities ranging up to 350 tons which, depending on boom length, can easily pick loads ranging up to 60 to 100 tons based on a 15 m to 10 m lift radius.
For the heaviest or longest piles, in-situ field splicing is an alternative, if cranes with the necessary capacity or boom length are not readily available. Although field splicing is not uncommon, it should be limited due to the time and expense required to make field welds over open seas as well as associated quality issues. Field splicing may also be difficult to execute, if the piles sink into the weak seabed material under their own weight.
Area: Marine Facilities
Cantilever Construction Method
The Cantilever Construction Method, also known as the cantitravel, over-the-top or cantilevered bridge method, is a common method of constructing pile-and-deck trestles which has been used successfully around the world. This method uses a span by span approach for building the trestle using a mobile work platform that is supported above tidal waters. The pile guides and templates are cantilevered out from the main work platform to facilitate a work front that is located a full span away from the last finished bent. This method produces a minimum amount of disturbance to the existing ground or seabed, while still allowing work to proceed from the elevated construction platform which is supported on the same pile foundations used to support the final structure.
To accommodate the Suspension Bridge construction, the working platform would be required to progress from the LNG berths towards the SW Anchor Block to avoid interference between work fronts. In this situation the first few Trestle bent foundations at the LNG berths would need to be installed using marine-based methods. Once these initial bents were erected, the working platform and crane for the Cantilever Method would be assembled and erected on these bents. The working platform would then complete the rest of the trestle advancing towards the bridges SW Anchor Block.
When cantilever construction is used, the construction methodology must be taken into account during the design phase to make the construction process as efficient as possible.
Area: Marine Facilities
The structural design is typically optimized to suit the construction methodology in terms of the selected member sizes, spans, materials, connections, detailing, etc.
As mentioned above, the working platform, also known as a cantitraveler or cantilevered bridge is a primary piece of equipment required for cantilever construction. A photo of a typical cantitraveler platform is shown in Figure 3-2. A cantitraveler or cantilevered bridge is basically a customized mobile working platform which provides:
 A support platform for a crawler crane and associated equipment such as vibratory hammers, impact hammers, and drilling equipment;
 Integral guides and templates used to locate, drive and install foundation piles; and
 A platform which facilitates the installation of superstructure elements and the finishing of connections between foundations and superstructure elements.
For cantilevered construction, the exact sequence of construction operations will vary from project to project depending on various factors such as trestle layout and overall construction methodology. Regardless of the actual construction sequence however, a main benefit for this type of construction is the repeatability of the construction cycle for each pile foundation.
Area: Marine Facilities
In general terms the construction cycle for any given pile foundation starts with the installation of the piles. The installation of the piles is followed by the erection and assembly of the transverse pile cap which essentially completes the pile bent foundation. Depending on the construction process, once a pile bent is completed, trestle deck elements may be erected or temporary bracing installed to provide longitudinal stability to the bent. Upon completion of the cycle, the platform is advanced forward one span to begin a new cycle and initiate construction on the next pile bent. Possible construction sequences and techniques for pile installation and drilling which may be used for the PNW LNG trestle are described in more detail in the following sections.
Area: Marine Facilities
Construction Equipment
Selection and design of the required construction equipment is integral with both the trestle design and the chosen construction methodology. The design of the trestle itself will typically be developed with consideration of the intended construction equipment, sequencing and overall process. Likewise the design of the construction platform will also be developed to facilitate an efficient construction process. Both design of the trestle and the construction platform will be based on the optimization of various interrelated parameters including trestle span length, construction platform dimensions, crane size, weights of components, structural interferences, structural connections, etc.
The two main pieces of equipment for cantilevered construction is the construction platform and the crane. The construction platform can come in various shapes and sizes, but there are two basic types which are most commonly used consisting of:
 Cantitraveler platform; and
 Cantilevered bridge.
Both types of construction platforms and the crane requirements are described below.
Area: Marine Facilities
Cantitraveler Platform
A cantitraveler platform as shown in Figure 3-2 is made up of a main carriage frame that supports a work deck for the crawler crane, equipment, and personnel. The main frame of the cantitraveler is mounted on steel wheel bogies which ride on rails attached to the top flanges of heavy rail girders.
The rail girders are separate components designed to bear on the trestle pile caps and take the large construction loads from the cantitraveler and transfer them directly to the pile foundations. The rail girders are necessary to support the heavy construction loads, since it would be uneconomical to design the deck elements of the final trestle structure to support such loads. The rail girders are typically individual simple span girders which can be picked up by the cantitraveler crane and leapfrogged from the back span to the fore span allowing the cantitraveler to index forward as each pile bent foundation is completed. Because the main carriage of the cantitraveler is usually positioned over a single span it also allows the crane to install deck elements in the back span behind the cantitraveler or in some cases the fore span in front of the cantitraveler once the next pile bent is complete. A cable system comprised of winches, pulleys and sheaves that are restrained in the trestle superstructure is used to advance the cantitraveler.
The guides or templates used for positioning, setting and installing the piles are typically located at the ends of truss frames cantilevered out from the side of the main carriage frame.
The pile guides or templates are customized to suit the trestle layout and can be adjusted or dismantled as required.
Area: Marine Facilities
Cantilevered Bridge
Another type of platform which may be used in cantilevered construction is the cantilevered bridge as shown in Figure 3-3. A cantilevered bridge is comprised of a steel through-truss which extends over multiple spans of the trestle. The bridge has a platform on its upper chords for supporting a crawler crane and has a rail mounted gantry crane running between the main trusses. The functionality of the cantilevered bridge is similar to that of the cantitraveler in that the bridge supports a crawler crane for installing the foundation piles, has built-in piling templates for positioning the piles, and also facilitates the installation of trestle deck components. A cable system with winches, pulleys and sheaves is employed to advance the cantilevered bridge from span to span, similar to the cantitraveler system.
Unlike the cantitraveler system however, the cantilevered bridge does not use wheels and rail girders to facilitate movement. Instead, the cantilevered bridge bears directly on the foundation pile caps and is typically slid forward on guides and bearing pads attached to the pile caps.
Another primary difference between the two platform types is the method by which trestle deck elements are erected and installed. Since the cantilevered bridge covers multiple spans and the top platform and bracing prevents the crawling crane from gaining access to the trestle deck below, the bridge is equipped with an internal gantry crane that can be used to erect and install trestle deck elements in the spans covered by the bridge.
Area: Marine Facilities
Crane
The required crane size is directly related to the trestle span and weight of the structural members required to be installed by the crane. As the spans increase, the crane reach increases and a larger crane is required to lift the same weight at the extended reach. Also, as the span increases, in general, so will the pile size and the size of hammers required for the installation. The crane size quickly limits out and sets the maximum span length.
The Trestle section of the LNG Jetty is located further from the shore well past the outer edge of Flora Bank. In this area the bedrock is much deeper than it is near Lelu Island and it is estimated that pile lengths may be as long as 80 m to 100 m or greater with corresponding weights of 60 to 75 tonnes or more. To lift a 60-tonne pile to accommodate a 36 m trestle span would require a 600-tonne capacity crane. This is a very large crawler crane size and may be impractical for the Cantilever Method. However, it is also likely not possible to pitch and drive such long piles since the required size of crane boom would be excessively high.
Therefore it may be necessary to splice the piles in-situ, which will not only reduce the length of piles required to be handled and pitched but will also bring down the required lifting capacity for the crane.
Another method of keeping the crane size to a minimum is to reduce the size of the trestle spans and hence the required lifting radius of the crane, or alternatively use temporary spud piles to allow the crane to get close to the work front.
Area: Marine Facilities
The maximum size of crawler crane that local marine contractors have in their fleets is 350 tonnes. Although the trestle designs currently call for 36 m spans, as discussed above, it is likely that the trestle span will need to be reduced or temporary spud piles used to accommodate the Cantilever Method. Past projects in BC have been limited to spans between 12 and 16 m using locally available equipment. Clearly, with the scope of this project, the crane equipment will be optimized for the installation method and we expect a span length of 25 to 30 m can be reached.
Area: Marine Facilities
Construction Sequencing
The basic construction cycle for building a trestle span, as shown in Figure 3-4, consists of the following general construction steps:
1. Installation of piles;
2. Installation of pile cap;
3. Installation of temporary longitudinal bracing;
4. Transfer of rail girders;
5. Movement of cantitraveler platform; and
6. Installation of longitudinal girders and deck elements.
Area: Marine Facilities
Depending on the design and geotechnical conditions, the pipe piles may be either driven into the seabed overburden material, or driven through the overburden material and then drilled into the underlying bedrock to achieve the required bottom fixity. Various techniques for driving and drilling piles are described in more detail below in Sections 3.4 and 3.5
Area: Marine Facilities
After all the piles for a particular bent have been installed and cut-off to the proper elevation, the pile cap is erected and attached to the pile heads thus completing the pile bent foundation.
The connection between the pile heads and the pile cap varies depending on the type of materials used in the design:
1. For a steel pilecap, a basic field weld would be used to directly connect the pile cap to the steel pipe piles.
2. If a cast-in-place concrete pilecap is used, reinforced concrete plugs would be cast into the pile heads with the reinforcement extending up into the pilecap to provide the connection. Formwork would be set up above the water, supported on the pipe piles, reinforcement for the pile cap placed, and finally the pile cap would be poured. The formwork would be removed after several days of curing time.
3. If a precast concrete pile cap is used, concrete infill plugs would be cast in the pile heads similar to the cast-in-place construction. The infill plug reinforcement cages would extend up through holes in the precast units to provide the connection to the pilecap. The pilecap is complete when infill concrete is poured into the precast unit to monolithically join the elements together. The precast option does not require formwork like a regular cast-inplace pilecap would. But, regardless of which concrete option is used, those elements that have some amount of cast-in-place concrete will require at least 7 days curing before loads may be placed on the structure.
Upon completion of a pile bent, the crane on the cantitraveler will install bracing to stabilize the bent in the longitudinal direction. Once the new pile bent is stabilized, the rail girders are advanced to the next position and the cantitraveler is moved to the next span to initiate the next construction cycle.
Throughout the above process, there are several options for installing the trestle superstructure and deck elements. One option is to install the trestle girders or deck elements with the crane on the cantitraveler before it is moved into the next position. The trestle girders may either be installed in the fore span in front of the cantitraveler or the back span depending on the selected construction methodology. Another option is to allow the cantitraveler to be moved forward and immediately begin on the next bent foundation while a second smaller crane follows behind on the finished trestle deck and provides a second work front by installing the trestle superstructure and deck elements on the back spans behind the cantitraveler.

As shown in Figure 3-5 the basic construction sequence described above for a cantitraveler platform is essentially the same for a cantilevered bridge with some minor exceptions as follows:
1. Installation of piles;
2. Installation of pile cap;
3. Pull back cantilevered bridge and install longitudinal trestle girders in the new span;
4. Place guides and bearing pads on new pile foundation;
5. Move cantilevered bridge forward onto new pile foundation and install deck elements in span behind cantilevered bridge; and
6. Index the bridge forward to begin new cycle.
Area: Marine Facilities
Similar to the Marine-Based Method, placement of scour protection around the perimeter of each pile would be conducted soon after pile installation. The scour protection could be placed via marine-based methods using tidal windows and a flat deck barge equipped with an excavator or front end loader and a stockpile of riprap. This work could be conducted simultaneously as the cantilever platform advances along the trestle length. Alternatively the cantilever platform crane could be used to install the scour protection as each bent is completed prior to the erection of deck elements.
Area: Marine Facilities
Cantilever Construction Schedule and Equipment Profile
Mobilization and start-up includes assembly of the construction platform and crane over open waters. The initial pile bents will be installed using marine-based methods and then the cantilever work platform can be erected from barges using marine derricks so that the balance of the trestle can be completed with the Cantilever Construction Method.
The assembly of the construction platform and the initial start-up of the trestle construction may take a few weeks to a month depending on the geotechnical conditions and the number of initial trestle bents that need to be constructed.
Once the start-up process is completed, typical cantilever construction can achieve an average productivity rate of approximately 2 days for one complete span (including the foundation and superstructure). This productively rate however, is typical for projects where the spans are less than what is proposed for the PNW LNG trestle and where the piles are only driven into the overburden soils.
For the PNW LNG project, the spans may be up to 36 m and the local geotechnical conditions require the piles to be driven into the overburden soils and drilled into the underlying bedrock. Of the various construction activities that make up a typical production cycle, the pile drilling operations will be the most time consuming, especially if the piles are required to be socketed to significant embedment depths. It is estimated that pile drilling and socketing may take up to 3 to 4 days per pile, and since the piles must be drilled sequentially, a typical span with a 4 pile bent may require 14 to 18 days to complete. For pile bents with additional piles, add 3 to 4 days per pile to complete the given span. If the piles are not required to be socketed into the rock, such as for the spans in deeper water, the productivity rate will improve.
Area: Marine Facilities
Once the trestle is complete, disassembly of the heavy construction crane and travelling platform will be conducted using floating marine derricks which will lift the crane and platform components onto flat deck barges for demobilization. The disassembly and demobilization process is estimated to take several weeks.
The overall estimated schedule duration for the construction of the trestle structures is 14 months. However since the Trestle is not a critical path item, there is enough schedule float to allow for longer Trestle construction times without delaying the overall project.
Area: Marine Facilities
Although marine derricks and scows would not be required for the Cantilever Construction Method other than the initial mobilization, delivery of piles and other construction materials will be required using supply barges. In shallow waters the supply barge movements would be dependent on tidal windows while for those sections of the Trestle in deeper waters they will not. Although the supply barges are not subject to tidal restrictions in the deeper waters around the outer trestle, it is unlikely the EPC contractor will allow the equipment to stay in open water overnight. Thus regardless of the water depths, the supply barges will be moved between the construction site and a safe anchorage or staging area daily. The anchorage or staging area could be located in Port Edward. However to mitigate possible marine traffic congestion in Porpoise Channel, the supply barges could transit to a location within the inner harbour of Prince Rupert.
In general the construction of the trestle via Cantilever Construction methods should not be an impediment to marine traffic. The work face will occur in a relatively small area in open waters and only one round-trip transit per day would be expected from the supply barge. A safety zone would be enforced around the work site which may prohibit vessels from approaching closer than 50 m. Work site restrictions would be promulgated through a variety of channels, such as Notices to Mariners, in accordance with the Marine Communication Plan.
Area: Marine Facilities
Pile Driving Techniques
The pile installation techniques described below are applicable to either Cantilever or Marine Based Methods.
The steel pipe piles proposed for the trestle foundations will be supplied in approximately 12 m (40 ft) long sections and will require welding to be assembled and spliced into their final length. Because the seabed overburden material at the project site is predominantly comprised of weak marine clay, it is anticipated the steel pipe piles will sink some distance into the overburden material under their own weight, essentially setting themselves into the seabed. This can make in-situ field splicing of the pile sections difficult. As a result, the piles will likely need to be preassembled and spliced lengths that can be practically handled prior to being transported to site.
An efficient way of transporting long piles to site is on flat deck barges, which can be kept at the project site and used to stockpile the piles. When it comes time to install a pile, the barge can be brought into position during the tidal windows, and then the pile can be picked and pitched by a crane. For relatively long piles, the rigging may need to be adjusted in order the pick and pitch the pile without exceeding the bending strength of the pile. Once the pick is complete the barge can be moved away to a secure anchorage until it is required again.
Stockpiling the piles on a flat deck barge is also advantageous in that it avoids any requirements for a pile lay-down area on Lelu Island.
Area: Marine Facilities
Once a pile is positioned by a crane and set into the seabed, it needs to be driven through the overburden material until it reaches bedrock. A pile may be driven either closed-ended or open-ended depending on the design requirements and geotechnical conditions. However if the pile is required to be socketed into the bedrock, it will need to be driven open-ended, and cleaned out prior to rock drilling.
For the driving operation, either an impact or vibratory hammer may be used. Although impact hammers have the ability the drive piles through harder material, they are much noisier than vibratory hammers and do cause greater underwater pressure disturbances.
Fortunately it is anticipated that a vibratory hammer will be adequate enough to advance the pile through the weak overburden material until the pile tip is seated close to bedrock.
For the last few meters above the bedrock however, an impact hammer will likely be required to advance the pile through any harder till layers until the pile tip actually reaches bedrock.
Area: Marine Facilities
Once the bedrock is reached, the impact hammer will drive the piles approximately 1 m into the bedrock to properly seat the pile and/or seal it for socketing. Although an impact hammer will be noisier than a vibratory hammer, it will only be required for a short duration to drive the pile the remaining depth and tap it into the bedrock.
Measures such as the use of bubble curtains may be employed to mitigate underwater overpressures from the pile driving operations and keep underwater acoustics within allowable limits. Typically the overpressure limit for pile driving is set at approximately 30 kPa, but may vary at the regulators discretion.
If the pile is designed to be only seated on the bedrock, then the pile installation is complete.
However, if the pile is designed to be socketed into the bedrock, the overburden material left inside the pipe will need to be cleaned out prior to the drilling operation. A grab hammer will typically be used to clean out the pile, however if the material is weak and loose enough it may be possible to flush or airlift it out of the pile. The removed material is stockpiled on a barge for disposal. Filter cloth and other materials may be used on the barge to reduce turbidly caused by any remaining water runoff from the stockpile.