Tunnels

* See also Watertight_Doors_and_Bulkheads
* See also Construction
* See also Utility Distribution
* See also Viaducts
* See also Streets
* See also Transportation_Systems
* See also Concrete_IS_Your_Friend
* See also Trams
* See also Rapture Agriculture ( which made substantial use of Tunnel-type construction )
--- --- --- --- ---
Tunnels would be a natural thing to exist as part of Rapture, with the immediate volcanic seabed. Many of facilities and other spaces would be embedded in the bedrock. I have even suggested a 'Levittown' 'Levittown' - Suburban mass-housing, built in the USA after WW2, which were the first massive neighborhood development projects. https://www.nytimes.com/2018/12/19/realestate/levittown-ny-the-original-starter-community.html type Suburb would eventually be built to handle Rapture's population expansion, and that would be largely built using the later perfected tunneling techniques to save on expenses. (( Note - New/Additional Construction in Rapture is not simple to do, it requires significant modifications to existing infrastructure - you don't simply build a house/building on a Vacant Lot. ))
Various secondary utility systems would be reached by Tunnels, which would not warrant the full Securis Door installations, so would have simpler and less expensive 'Submarine Door' type mechanisms. ( Note - On my Level Map Foundation levels, they use medium cost (but effective) Submarine-style manual bulkhead doors to seal levels used for utilities and drainage systems. )
Tunnels would be built through seabed rock strong enough and solid enough to be intrinsically watertight with minimal leakage ( Note- Such rock does not exist everywhere under Rapture ). These Tunnels would be most cost-effective when they had only minimal sealing and structural reinforcement required. Farm-used Tunnels would be built less strong ( than anything Residentially inhabited ).
--- --- ---
Utility with a 'Tram' track to move utility equipment around, and give access, and transport personnel.
--- --- ---
Tunnel Construction as an Economic Measure (For Rapture's Population Expansion) :
Technology (ex- Electric Plasma Rock cutting techniques) was first being used ( in early Phase 1 Construction of Rapture) for cutting out basement volumes (into bedrock ) enabling placement of Prefabricated buildings foundations, and embankments for the AE.
Tunneling was used for some segments of the Tram/Trolley system. You prefer to go THROUGH Hills, rather than around them, AND the construction could be more economical than the prefab Trolley Viaduct structures. 
Residential 'Tunnel' construction became the equivalent of (Real World) Levittown, with fast inexpensive mass construction techniques and prefabrication, and built-in appliances being provided. The need was for Rapture's expanding population (family growth), and new living space had to be created. Over time the population also wanted more variations of their residential options ( and some people moved from certain areas which were less desirable ).
This later city expansion had to be built with no infusion of 'new' money ( from outside - as was used for the original construction extravagances ). It was made possible by employing experience/techniques learned/developed - about what worked and what did not.
Such Simpler Tunnels were developed for "Farm" interiors to be economically expanded ( being unpopulated space volumes, with lower risks from potential catastrophic failures - floodings ). Tunnel Lining improvements were later developed for building of much safer interior spaces (useable for populated zones).
----
Tunnel.jpg
Oldsys.jpg
Muck.jpg
Overheader.jpg
Tunnel5.jpg
Smugglingtunnel.jpg
MexicanSmugglingTunnel.jpg
Tunnelz.jpg
RaptureSuburbTramStation.jpg|transit station
Tunnnnel.jpg
Motunnelly.jpg
Alternates222.jpg
Oldconstructiontunnel2.jpg
Trolleythruarcadia.jpg|Trolley from Arcadia to Ceres Green
ProblemLightingAETracks.jpg|AE Tunnels being Lit were a problem - Thats more a job for that Big Daddy 'drill'
Tunnel888.jpg|Tunnel Bore thru solid rock
Tunnnnnel.jpg
Smuggie.jpg
TunnelBallZ.jpg|Perhaps those passageways through my foundation levels look like this
SmugglersTunnel33.jpg|Airlock in some old tunnel (something which required it - under a river/whatever).
TrolleyTunnel.jpg
Modernarchedunderground.jpg
Tunelll.jpg
Tunnelzzz.jpg
SmugTun.jpg
UnderArcadia.jpg
UtilityTunnels.jpg
Tunnelzz.jpg
TunnelsUnderRapture.jpg
UnderTheStreets.jpg
TramTunnel77.jpg
Tunnelzz22.jpg
--- --- ---
Tunnels in Foundations :
The Foundations under buildings are filled with rock and concrete - bonding the structures to the seabed. These building bases would have inspection and access ways - TUNNELS through that mass of rock and concrete. Minor Leakage would be monitored/pumped and various Utility ways also connect through those pathways. With foundations being rather large and sprawling, the extensive access Tunnels would be divided into watertight sealed compartments to protect them and preserve the building above.
--- --- --- 
Round Tunnels offer a better structure to be self supporting (effectively 'arches' top and bottom) as well as making use of a semi-automated 'Boring' machine ( big driller kinda thingee ).
Linings of reinforced concrete would be used to seal the passage ( Deep 'under the sea', sea water still works its way through the rock and cracks and such ) .
Solid rock is largely self-supporting. Tunnels in solid rock thus have much of their structural strength already provided, versus a similar structure located in open water. As long as the Tunnel is small, the rock is more capable of being the majority of the support needed.
'Solid' is a relative term, but cracks/fissures which are small in dimension can be a big problem with the great water pressure existing at Raptures depth. The Tunnel Solutions (where appropriate) don't require (as much) massive construction (even at deep water pressures) IF they can make use of the great compression strength various native rock can provide.
Locating rock which is 'solid', and of other proper qualities, is the problem/task for building Rapture 'Tunnels'.
--- --- ---
Rapture Conventional Tunnel Construction Process :
The first task is to Survey, discover and verify an adequate expanse of a useable-quality rock formation. Some areas in the Mt Ryan volcanic 'crater' surface were deeply filled with loose debris and were not suitable. ( These would already have been largely avoided for Rapture's 'Building' type construction - as those also required adequate/stable support and anchoring of themselves into solid seabed ).
Intervening bad rock, when detected, would be avoided ( tunnels can be built in any direction ). OR if required, would be bridged/patched with conventional heavy concrete tunnel construction. Best would be large thick monolithic beds of solid volcanic rock, which had been deposited in one flow from the ancient undersea volcano.
The Rock Tunnels would be built with a consistent 'standard' geometry ( ie- a basic 12/20 foot usable interior diameter ) which allowed semi-automated machinery to do a bulk of the work, including transporting the bulky waste rock away to disposal sites out in the Ocean. Earlier waste rock of this type (being solid/strong rock), had been used as a basic filler aggregate component for the City's concrete building Construction ( So another use of for the Plasma Cutter's 'fracturing' technique ). Prefabricated Tunnel support and liner components would be efficiently made elsewhere in Rapture.
A complex of interconnecting tunnels would be planned out to meet the requirements for that city expansion cluster. Sufficiently extra space was allowed to compensate for likely 'bad' sections of rock which would not be Tunnel-friendly. The Tunnels would be built progressively in segments with intersections, with the transport for the growing Tunnel Construction being well planned-out. There would be mine tracks similar to the Foundation 'Tram' ( equivalent to those used by Fontaine's smuggling tunnel to Arcadia ). Tunnels would be circularly connected - always with two ways in (and out), and with many alternate paths through the Tunnel network. They could be stacked into levels, with vertical tunnels for stairwells/elevators, and where-needed, tunnels could be sloped to serve as ramps.
Cutting rock was done with Electric Plasma Cutters ( narrow extremely hot electrically-ionized gas jets like a welding rig ) followed with a water jet causing the rock to shatter. This allows you to cut/chip out blocks to form the tunnel space with fair precision. ( The technique had already been utilized to cut the huge basement/anchoring holes out of bedrock for Rapture's buildings - done from the city's construction start. )
Work was often done at above Water Pressure before the tunnel segment was sealed ( You don't want leaks/sprays of water fouling the construction process ).
Anchor bore holes (another plasma technique) would be extended intoi the surrounding rock, radiating out from the bare tunnel face. These would serve to anchor the tunnel facing, as well as find any potentially weak/leaky rock near the Tunnel. If needed, weak fractured sections could be 'strengthened' using the plasma-cutting techniques ( placing of rebar and grouting solidifying any fractured rock around the tunnel space to strengthen it and assure its pressure/structural integrity ). 
In the process, the newly-created Tunnel segment would be depressurized to One Atmosphere(RSP), and for a period the bare rock face was inspected for any leakage or shifting - identifying any weak points. Detectors with pressure and sonar sensors would be used during the 'proofing' period. Reinforced linings were then added to further seal/strengthen the inside. The lining would be solidly-fastened to the rock facing and to the reinforcement rod/post filled borehole anchors. Sampling sensors (tap traps) would be left in place outside the wall shell to allow periodic inspections for new leak activity/instability.
Emergency Pressure Doors would be added at regular intervals to contain potential failure. ( Done at many junctions to sufficiently Safety-Partition the tunnels. ) Depending on use, additional safety systems would be added appropriately ( ie- Residential areas got the most extensive measures ).
After the full set of the concrete and confirmation testing, the interior was built up to facilitate the living space. Utility areas were blocked off and filled with all the required conduits/pipes/vents/lines/machinery ( again standardized and prefabricated as much as possible ). Interior walls/floors/false ceilings were built-up and furnished/decorated appropriately.
--- --- ---
Melting Rock to Make Tunnels ? :
A means to make cheap construction used for certain purposes which use significant volumes ( like for hydroponic farming ). The initial tunnel contour would be pre-bored to its rough intended size by a semi-automated tunnel boring rig. The Tunnel size is fairly small. Something like 15 foot diameter.
Electric Plasma cutting would be used to melt and fracture volcanic Igneous Rock to cut out the Tunnel through rock strong enough to resist water pressure at depth. Areas with appropriate large masses/beds of contiguous volcanic rock with minimized fracturing/layering would be chosen for this type of construction. The Mid-Ocean rift Spreading Igneous Rock is Basalt (Volcanic rock). Basalt has high liquidus and solidus temperatures—values at the Earth's surface are near or above 1200°C/2192°F (liquidus) and near or below 1000°C/1832°F (solidus). These values are higher than those of other common igneous rocks.
This work all has to be done UNDER pressure (ambient deep water pressure). This assures that the local pressure does not collapse the broken/semi-liquefied rock in the middle of the process (a blowout). The Tunnel Interior would be kept filled with pressurized gas (280 psi is alot). The Majority of the Work to be done by Automated machinery. (( Men in Hardsuits are not suitable to do this work manually - It is far too difficult/inefficient/expensive to do the majority of the work manually. )) 
The Tunnels are built using the Metal Shield method ( Tunnel Walls supported during 'the cut' ). Mechanisms involved have to withstand direct contact with temperatures exceeding 1200°C/2192°F. At about 1,000° F Steel is at 50% strength and at about 1472°F structural Steel loses 90% of its strength - So high temperature alloys would be needed for the cutting rig. A High-temperature lubricant mix would be used to prevent the heated/liquefied rock from sticking to the mechanism. 
Waste heat must be eliminated, and the rock's cooling sufficiently controlled to minimize adjacent rock fracturing. The COLD surrounding rock ( rock subjected to temperature differentials likes to fracture, which means it would not seal well ). You thus have to cut carefully around the tunnel bore rock in small increments, allowing the walls to slowly cool down to eliminate stress fracturing. 
Probe Patching ( similar to the Plasma Cutting ) can be done to subsequently fix weak spots and cracks. You CAN do minor sealing with grout pumped into cracks, as well as using some conventional tunnel construction (ferro-concrete sections). 
Early Concept Experimentation was probably done to determine if the air pressure inside the Tunnels could be allowed to STAY at the high ambient sea pressures (minimizing leak issues), but such interior environment were discovered to have limited prospective uses ( and that more normal/less-complex open/in-sea sea-floor construction would then have served just as well for the limited uses ).
--- --- ---
Bigger Spaces - Complexes of Subterranean Construction For Rapture :
Some larger 'Cavern' spaces could be built using a similar process, with the large volume expanses requiring greater interior support ( more like the interior force distribution structures of the 'buildings' above ). Dome shape designs would be logical, as they provide an 'arch' type support of the rock walls. Internal support pillars and ribbing would be needed for the larger open spaces.
A network of transport tunnels would be built containing normal walkways ( bicycle and electro-cart accessible ), and others connecting into the City Trolley system ( which already had more than a few 'tunnel' segments built in the ~1950 Rapture Transit Trolley consolidation rebuild. ) Utilities would be connected through the same tunnels.
The city's Phase Two tunnel-type expansion might be considered as the 'suburbs' of Rapture. Designed to fit the needs of an expanding population, and having some improvements made evident from the use of the Phase One Construction. With the use of standardization to lower costs, they might also be called Raptures Levittown ( Levittown NY, 1947, was the first truly mass-produced suburb in the USA ).
Sewer and seepage control systems would all be integrated. The usual system of Safety Bulkheads would be installed to protect from any catastrophic flooding.
--- --- ---
Viaduct Tunnel (Sea Bed) Construction :
-
'Wet-Work' :
Dig out 'tunnel' (Boring Rig) with electric plasma torches.
Contour Surfacing - drilling of anchor fastening holes into the surrounding rock. 
Initial lining surface melting if the rock cooperates
Constant monitoring to maintain path through solid bedrock.
Tunnel Contour's include space for ventilation/utilities/drainage and walk space ( likely small Vehicles & Bicycles )
Anchors get set into the radial anchor holes ( filled with reinforced hydraulic concrete )
Leak testing ( most of these Tunnels are in solid rock - which still can have many small cracks )
Temporary Incremental Airlocks added to facilitate the Tunnle Construction Process
Filling with air and pump draining, and then lowering pressure to RSP
Surfacing, cleaning/wash to remove salt, etc ...
Stability inspection/retest
Wet Patching to be redone if significant weaknesses is still detected 
-
'Dry-Work' : 
Extended checking for minor leaks/seepage ( further concrete rework filling to seal large, and epoxy injections for small )
Installing the redundant pressure lining ( requiring a standard period for proper concrete settling ) 
Installing prefab safety pressure doors and valve sets (spaced to proscribed sectioning)
Final leakage testing
Install interior's lining/deck/vent conduits utility pipes and cables, leak sensors, drainage system
Install lighting and surface finishing (paint and decoration)
NOTE - Pressure Doors/Bulkheads are only PART of a safety sectioning of Rapture. There also have to be closure systems and seals for all utilities (all types) to block the water passing the boundary. Breaker systems and Taps for electrics ... power/water mains can pass through if properly insulated/shielded ( still with effective REDUNDANT cutoff valves ). Special Tunnels would be built for distance-running Utilities having additional anti-failure redundancy. 
--- --- ---
Hybrid Interconnecting Construction :
Conventional Viaducts would be built as connections to/between various Subterranean spaces out in Rapture's 'Suburb' areas. They might 'Run' for significant distances, and being more practical when running through stretches of LESS stable bedrock ( even emerging into the open water to get past various dips/ravines ).
Some long Tunnels would cross greater distances between out-lying Subterranean Clusters and the rest of the city. A few could even be build as 'roads' sufficient to operate small automobiles/trucks - as intermediate pathways connecting to the larger transport systems. (( The late Subterranean building trend was soon ended by the Terrorism, Chaos and Ruin brought by Fontaine/Atlas starting with the Kashmir Terrorist Attacks )).
--- --- ---
What Do Art Deco Tunnels Look Like ? :
The 'Suburb' expansion of Rapture was done with the less costly Plasma Tunneling technology ( instead of the early above-seabed buildings ). I suppose while the rock is molten ( with use of Ryan Technology plasma cutters and such ), molds could be applied to offer some aesthetic 'texture' to the basic construction ...
A big element of Art Deco was repeating patterns of CAST tiles/decorations added/fastened to the basic ordinary/plain concrete structure. Highlights usually being applied particularly at Portals and entranceways, intersections.
Many more mundane/utilitarian 'Tunnels', not being accesses by the public, really do not need the wasted expense of decoration (Art Deco or otherwise).
--- --- ---
Facilities like the Submarine Operations Base at Port_Of_Rapture would have been in what were effectively large 'Tunnels'.
Real Submarines being effectively long and thin, the 'Tunnel' structure would be logical.
--- --- ---
Early design Hot Water Pipeline from Hephaestus Geothermal complex. Eventually insulation had to be added to lower long distance heat loss. Tunnels for this 'aqueduct' would be driven through obstacles where required.
--- --- ---
Early Prefabricated Construction Tunnel :
Used in early days of Rapture Construction, before the first permanent buildings were installed. They connected the Construction Domes. They were designed to be quickly laid on the seabed, and then reused as the construction work moved to new areas. They were designed to handle a moderate amount of leakage/seepage, instead of having to be made to full Rapture Water Integrity Standards. Multiple Airlocks would be part of any 'Tunnel Run' to allow corrections when the leakage/seepage we not 'moderate' enough. 
--- --- ---
'Mail Rail' London - Example of a Real Underground Haulage System of Tunnels :
 
Build (operational by 1927) to haul Mail across the huge congested city of London https://www.londonxlondon.com/postal-museum-mail-rail/. ( 9 foot diameter Tunnel ). Shut down in 2003, reopened as a museum ride 2017.
--- --- ---
Logical - Tunnels beneath the Streets in Columbia ( White Folk wouldn't tolerate having the 'Servile Class' be seen on the Street they walked in 'The New Eden' ). Fink used to say : "First Hint Of Rebellion, Flood the Tunnels ..."
--- --- --- --- ---
.
.