Lyntas/mining_domain_knowledge_reference_dataset huggingface dataset:
Area: Marine Facilities
Pile Drilling Techniques
The pile drilling techniques described below are applicable to either Cantilever or Marine Based Methods.
Driving piles into rock is not feasible, unless the rock is very soft and weak. Therefore for most types of rock, drilling equipment and techniques must be employed to fix piles into the rock. Depending on the design requirements and the degree of moment capacity and fixity required at the bottom of the pile, piles may be installed into bedrock either as rock doweled piles or rock socketed piles.
For a rock doweled pile, the pile itself is inserted down the entire length of a hole drilled into the bedrock. The pile can be fully grouted in the hole or advanced with a friction fit, thereby providing fixity at the bottom of the pile as well as development of the piles full moment capacity.
A rock socket is similar to a rock dowel, but in lieu of inserting the steel pile all the way into the drilled hole, the steel pipe pile is only embedded a certain distance into the rock and the balance of the hole is filled with a cast-in-place reinforced concrete core. The concrete core also extends a certain distance up into the hollow of the pile above the rock to facilitate load transfer. The reinforced concrete core acts like an extension of the steel pile into the rock and thereby provides anchorage and a degree of fixity at the bottom of the pile. The reinforced concrete core however, will not provide the full moment capacity of the steel pipe pile therefore a rock socketed pile is not as strong as a rock doweled pile.
Area: Marine Facilities
For installing a pile into rock, initially the pipe pile must be driven a certain distance into the bedrock in order to seal the hole and prevent overburden material from sloughing in as the hole is advanced past the tip of the pipe pile. Various drill bits and techniques may be employed depending on the type of rock being drilled and whether it is a rock socketed pile or rock doweled foundation. Some typical drill bits which may be employed include down-the hole hammers, churn drills, core barrels, rock augers, tri cone bits and other rotary bits. The contractor will use the most effective bit given the local rock conditions. Drill bits are typically attached to a rotating Kelly bar operated from a diesel-powered drill unit mounted on a frame or the leads of a crane.
The installation of a rock socketed pile, involves inserting the drill bit into the pile from the top and lowering it to the bottom. The drill unit rotates the bit, grinding the rock away at the bottom of the hole and advancing it with a diameter slightly smaller than the inside diameter of the pile. The hole is drilled to the desired embedment depth while the drill tailings are simultaneously airlifted to the surface through the kellybar. Once the hole is complete and cleaned, a reinforcement cage and tremie concrete can be placed, completing the socket.
Area: Marine Facilities
For a rock doweled pile, the hole must be drilled with a diameter large enough to allow the pile itself to be inserted. However, since the drill bit is generally smaller than the piles inside diameter (so that it may be inserted into the pile) special techniques must be used to drill an oversized hole.
One method is to use a down-the-hole hammer with undercutting capability. Although the overall hammer bit is small enough to fit inside the pile, once the tip of the bit is advanced beyond the pile end, under reaming cutter wings extend out from the bit, drilling a hole slightly larger in diameter than the pile.
Another method involves the attachment of a sacrificial cutting ring to the pile itself. The drill bit is used to drill a slightly undersized hole similar to a rock socket. The cutting ring on the end of pile is advanced by rotating the pile itself, typically in the opposite direction of the drill bit, and reaming out the hole thereby enlarging it and allowing the pile to be embedded. For this method the drill unit must have the capability to rotate the pile.
Area: Marine Facilities
A third method for installing a rock dowel involves the use of a large diameter pipe casing. Using the same techniques as for piles, the oversized casing is driven down, sealed into the rock and cleaned out. Using standard rock socket drill techniques, a hole is drilled in the rock that is smaller than the casing but larger than the pile. The pile is inserted into the casing from above and grouted into the hole. The casing is then removed and positioned for the next pile.
This technique has some disadvantages compared to the previously mentioned methods in that it requires multiple handling of large long pipes, including pile insertion and casing removal. This may require a crane with a very large boom. Another disadvantage is the greater volume of material required to be cleaned out of the casing as compared to other methods where just the pile is installed. Also, when the casing is removed there may be additional disturbance and soil sloughing around the pile. This is avoided with the other methods.
For all of the above drilling techniques, the tailings from the drill process are typically extracted by airlift systems. The removed material can be run through a cyclone to extract water before it 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.
Area: Marine Facilities
MOF Construction Methodologies
There are various design configurations for the MOF and as such the construction methodology will be tailored to suit the type of marine structure selected by the EPC contractor. Unlike the other marine facilities however, the MOF also has a requirement to dredge rock and sediment within the MOF cove and its approaches to provide a water depth that can accommodate the vessels expected to offload at the facility. Both the dredging and construction methodologies for the MOF are discussed in the following sections.
6.1 Dredging Methodology
Dredging between Lelu Island and Ridley Island (Porpoise Channel) is planned to provide adequate depth for the MOF berths. Approximately 790,000 m3 of material will need to be removed for the MOF of which approximately 590,000 m3 is expected to be rock (phyllite/schist). Further description of the MOF dredging methodology is detailed in Appendix A.
The methodology used in this study was based mainly on the geotechnical information provided by PNW LNG, tidal variations and Hatchs experience in rock drilling/blasting (D&B) and dredging operations. This is a preliminary assessment and final methodology should be selected by the contractor. Dredgeate and rock material not used for onshore purposes will be disposed at sea in Brown Passage as indicated in the EA submission.
Due to the important tidal variation in the area of study, the dredging area will be divided into two regions with distinct D&B and dredging methodologies:
 Area below MSL to be performed with marine-based equipment;
 Area above MSL to be performed by land-based equipment.
Most of the dredging area is located outside a natural navigation channel and is not expected to disturb navigation activities in the area.
The site conditions, geotechnical information, dredging volume, disposal options and productivity will determ
Area: Marine Facilities
An estimated 200,000 m3 of marine sediment will have to be dredged prior to the commencement of the drilling blasting activities. All sediment will be disposed at sea in Browns Passage.
The most common equipment for dredging marine sediments is a Trailing Suction Hopper Dredger (TSHD). The TSHD is a self propelled vessel that accumulates the dredged material into its hopper and disposes this material through doors located at the bottom of the vessels hull. TSHDs come in a wide range of hopper volumes. As the hopper volumes increase so too does the vessels draft. Therefore it is suggested that a small TSHD with a capacity up to 5,000 m3 be used so that a wider dredging area can be accessed. No auxiliary equipment is necessary for a TSHD operation other than a crew vessel.
Since 90% of the sediment volume is located below MSL it is expected that the TSHD will be able to tackle most of the marine sediment dredging. A 5,000 m3 TSHDs monthly dredge production rate is estimated to be approximately 150,000 m3. This means that approximately 2 months would be required to dredge 90% of the marine sediment.
Area: Marine Facilities
Drilling and Blasting
Drilling and blasting is used to fragment the rock layers with explosives. Drilled holes are filled with explosives and laid out in a grid pattern. A common pattern for blasting operations consists of drilling holes of about 130 mm in diameter in a 3 m x 3 m square grid. The blasting material most widely used in environmental sensitive areas, as a substitute to dynamite, is water-based gel explosives.
Area: Marine Facilities
Marine-Based Equipment
The most common equipment for drilling in offshore areas is a jack-up barge (also known as a self elevating platform) equipped with multiple drilling towers.
The jack-up barge consists of a floating pontoon with movable spuds, capable of raising its hull above water surface. An example of jack-up barge is shown in Figure 6-1. Its approximate dimensions are 40 m long x 30 m wide x 5 m moulded depth.
The main advantage of using a jack-up barge is its ability to withstand heavy seas, currents and the tidal range to maintain stability for drilling activities and positioning. The main disadvantage is the jack-up barge is not self propelled and is dependent on tugs for transportation and positioning.
The jack-up barge can be positioned in most of the drilling areas, up to an elevation of +5.40m CD. This is the upper access limit-based on an estimated jack-up barge draft, when floating, of about 2 m and barge deployment occurring when tides reach their highest levels.
Even though the time span for highest tides is short in a semi diurnal tide region, the jack-up barge could be positioned fairly quickly with the help of tugs and anchors positioned on shore.
Area: Marine Facilities
Land Based Equipment
The upland area will be drilled with mobile drilling rigs and will need road access and level terrain for stability. Drilling rigs can be deployed on wheels or on tracks as shown in Figure 6-2. Therefore, it will be necessary to fill some upland areas to create level access to the rigs. Shallow areas between +5.40 m CD (draft limited depth) and HHWL (+7.40 m CD) will also have to be filled in order to allow access for land-based drilling equipment. No auxiliary equipment is required for the drilling rigs. Fill and cut to provide level access of the land-based drill rigs will not be assessed in the study.
Area: Marine Facilities
Marine Based Equipment
The most suitable equipment for recovering blasted rock is the marine backhoe dredger (BHD), as shown in Figure 6-3. BHD is a stationary water-based excavator mounted on a dedicated dredging pontoon that has a rotating table. The position and stability is maintained by three spud poles, where two spuds are fixed to the front side of the pontoon near the excavator crane and one tilting spud at the aft side. The equipment can move with the tilting spud and direction can be adjusted with the two-part articulated arm. In the dredging position the front spuds are firmly planted in the seabed. The dredger then raises itself partially out of the water to further anchor the spuds. With the pontoon slightly lifted out of the water, part of the weight of the dredger is now transferred via the spuds to the seabed, resulting in an increase in anchoring.
Because of the hydraulic action of its stick and bucket cylinders, BHDs exert positive forces pushing the bucket into the material to be excavated
Area: Marine Facilities
BHDs are becoming the dredging equipment of choice as dredging operations and projects have expanded. This equipment can dig at greater depths and have greater installed power, therefore can be utilized cost-effectively in heterogeneous soils containing a mixture of clay, sand, cobbles and boulders. Because BHDs can generate reasonable cutting force, they are also suitable for digging heavy clays, soft stones, blasted rock and soil containing fractured rocks or rubble.
BHDs are equipped with accurate positioning systems and can operate with precise underwater profiles. The bucket position is followed by the operator on a computer screen in real time and the seabed elevation is updated automatically in the dredging software once the bucket removes material from the seabed.
The suggested minimum requirement for the BHD is specified as 3,000 kW power capacity, 10 m³ bucket volume and approximate pontoon dimensions being 60 m long x 18 m wide x 4 m moulded depth, which falls into the class of mega BHD.
Area: Marine Facilities
The main advantage of using a BHD is its ability to dig into hard soils containing boulders or debris due to its hydraulic power and can reach water depths up to 20 m. The main disadvantage of BHD is that it mainly relies on the pontoons buoyancy to support its weight as the pontoon spuds do not have the capacity to carry it. The BHD has to then work with enough under keel clearance in order to allow safe water draft for dredging operations. The semi diurnal tidal variation at the MOF site will restrict the area of influence for this equipment and force it to move a great deal to cover the intertidal area. Another disadvantage of BHDs is downtime due to waves and cross-currents. Since the MOF dredging area is protected it is not expected that climate conditions will cause equipment standby.
Dredging is expected to start only after blasting is complete and surveyed. The BHD bucket dumps the rock material into a self-propelled split barge moored alongside the dredger. The suggested minimum requirement for the split barge volume capacity is 700 m³ with bow thrusters.
Auxiliary equipment involved in marine dredging includes:
 1 multicat barge (25 m long x 12.7 m wide x 2.3 m moulded depth) with 40 t crane capacity;
 Self-propelled split barge;
 1 survey and crew launch boat; and
 1 operational launch boat.
Area: Marine Facilities
It is suggested that rock disposal site be positioned on intertidal area with access to landbased equipment once water level drops. According to client communication the dredged rock will be used for civil works. Therefore, the split barge would have to dump the rock disposal material as close as possible to shore at high tide.
Dredging is expected to start only after blasting is complete and surveyed. Due to safety reasons no vessels are allowed to operate near the blasting area.
Production rate for the marine-based BHD is estimated to be 37,500 m3/month considering an operation rate of 350 hours/month and a production rate of 85.8 m3/hour with a 10 m3 bucket. Higher productivities may be achieved with a larger bucket size.
Area: Marine Facilities
Land Based Equipment
The most suitable equipment to dredge the upland areas as well as the intertidal areas that are inaccessible by a marine-based BHD, is an elevated land-based backhoe excavator mounted on an under-carriage with spread tracks as shown in Figure 6-4.
This versatile equipment can operate at water depths up to 5 m and dig into hard soils containing boulders or debris due to its hydraulic power. The main objective of the land-based backhoe is to move the blasted and disposed rock towards the upland and make it available for civil works and earth moving equipment (not part of the scope of this study).
The elevated backhoe will gradually drag and move the blast rock material upland. The estimated production rate for land-based backhoe is 60,000 m3/month considering an operation rate of 350 hours/month and production rate of 200 m3/hour with a 10 m3 bucket.
Since the total volume to be dredged by land-based equipment is approximately 118.000 m3, the estimated schedule for one land-based backhoe is about 2 months.
Land-based dredging can be performed simultaneously with the marine-based dredging.
Area: Marine Facilities
Phasing and Schedule
Marine sediment dredging equipment will have to be mobilized prior to drilling and blasting activities and rock dredging. It is recommended that the faster dredging method be selected in order to avoid delays in the schedule.
Drilling and blasting activities will be performed from the same equipment, either a jack-up barge with drilling equipment, or alternative equipment such as a specialized drill vessel.
Upland drilling and blasting activities can proceed simultaneously with marine drilling and blasting activities. Equipment production will have to be assessed in more detail in order to determine the phasing of the works for the MOF Dredging.
To speed up production, dredging with a BHD can be supplemented with an elevated landbased excavator which has the capability to reach the seabed as deep as Elev. -8.0 m CD.
The land-based excavator would dredge the foreshore and shallow waters, while the BHD would dredge the deeper waters down to Elev. -12 m CD.
As per client information, the in-water blasting window for Porpoise Channel is a 2.5-month period from November 30 to February 15, subject to site-specific changes based on species use and discussions with DFO. Blasting should be performed only during low tide. However, the proposed schedule for MOF blasting and dredging activities is 7 months. In order to achieve the blasting schedule, drilling operations should be mobilized well in advance of the actual blasting window to prepare the blasting boreholes. Also, onshore blasting is not subject to the same restrictions as in-water blasting and can be conducted outside the 2.5-month period.
Area: Marine Facilities
Construction Methodology
The exact construction methodology for the MOF will be dependent on the type of marine structure selected by the EPC contractor. Based on the currently proposed FEED designs, the MOF is comprised of two wharf structures which, depending on the design concept, may be constructed using Concrete Caissons, Steel Sheet Pile Bulkheads, or Pile-and-Deck type structures. Despite the wide variety of possible structural configurations, the required marine construction equipment will generally be similar to the other marine facilities.
Similar to the Pioneer Dock, the construction activities for the MOF can be divided into a marine scope and an upland scope. Both the marine and upland scope activities will vary depending on the selected MOF configuration.
If a Pile and Deck wharf structure is selected for the MOF, the construction methodology would be the same as for the other facilities requiring marine piles. Standard marine-based methods and equipment as described previously would be used to install the piles. Pile vibratory and drilling techniques, as described for the LNG Jetty Trestle, would be used to mitigate noise concerns during pile installation. Once the piles have been installed, the deck superstructure can be installed from the land, or from the waterside, or both, depending on the framing layout and the materials used. Typically a retaining wall is required to prevent scour or undermining of the landside abutment of the wharf. The landside abutment or interface would be constructed using land-based equipment and should not affect the marine habitat. If a revetment slope under the wharf structure is used for scour protection in lieu of a retaining wall, the riprap protection would be placed after pile installation and before the deck was constructed.
Area: Marine Facilities
For Steel Sheet Pile Bulkhead structures, a marine derrick and flat deck scow would be required similar to the Pile and Deck design. The marine derrick would use a vibratory hammer to install the sheet piles into the overburden sediments, thereby limiting noise levels.
The flat deck scow would be used to stockpile the sheet piles and equipment. The marine equipment is used primarily to install the steel sheet piles and once the bulkhead is complete, the balance of the work can be conducted by land-based equipment. When the bulkhead wall is near completion, the space between the bulkhead wall and shoreline would be filled and compacted in a series of lifts using land-based equipment. Since the activities occur behind the wall, there is less probability of generating turbidly in the water column. Anchor systems for the bulkhead wall, including walers, connections, tie-rods and concrete deadman anchors, would be installed in between lifts at the appropriate elevations. The tops of the steel sheet piles would be cut-off level and to the proper elevation. Once the backfill behind the bulkhead wall was complete a concrete cope beam and decking would be formed and installed from the land side. Finally, the marine derrick would use a clamshell grab to place scour protection in front of the bulkhead in the berth pocket to prevent undermining of the bulkhead wall.
Area: Marine Facilities
For the Concrete Caisson concept, again the basic marine construction equipment deployed would be a marine derrick and flat deck scow. In addition, a hopper barge may be used for the initial placement of the engineered fill for the caisson mattress pad. The installation of concrete caissons will require more dredging and rock blasting than the other concepts since enough space must be provided for the caissons and mattress pad upon which the caissons sit. After initial placement of the engineered fill, the marine derrick will use a special spreader bar to distribute and screed the engineered fill to produce a mattress pad with a flat level bearing surface. The concrete caissons would be fabricated in dry-dock and towed to site just prior to installation. Tugs and the marine derrick, which would likely be a spud barge, would be used for initial placement of the caissons and for ballasting the caissons to seat them on the mattresses. Once the infill panels are installed between the caissons and the caissons are fully ballasted into position, the balance of the backfilling behind the caissons and completion of the deck and cope beam on top of the caissons can be completed with landbased equipment. Finally, the marine derrick will use a clamshell grab to place scour protection in front of the caissons in the berth pocket to prevent undermining of the mattress pad.
Area: Marine Facilities
Construction Schedule and Equipment Profile
The overall estimated construction schedule for the MOF construction is 12 months.
Regardless of the configuration of the MOF wharf structures, the basic marine construction equipment deployed would be a spud barge type marine derrick and a flat deck scow. The activities performed by this equipment will be slightly different depending on the structure type being built. Work tugs would also be deployed to move the marine equipment from one work face to another. For the concrete caisson design a hopper barge may also be deployed for a brief period for placing engineered fill for the mattress pad.
The contractor may elect to mobilize two crews to work on two work faces simultaneously.
This essentially means that two sets of marine derricks and scows would be required. These construction barges would be located in the cove and would be staged so as to not block Porpoise Channel. Therefore the construction equipment should not be an impediment to marine traffic in Porpoise Channel. A safety zone would be enforced around the work site which may prohibit vessels from approaching closer than 50 m. Or the safety zone may be set up around the entrance to the MOF cove to correspond with a silt curtain deployment. In either case, work site restrictions would be promulgated through a variety of channels, such as Notices to Mariners, in accordance with the Marine Communication Plan.