so, i mentioned in a discussion thread about geodesic domes and an idea i have had for a while, involves creating a full spherical structure that can be buried under the ground, has a full helical screw based classic 3 layer spring-based metal water seal, and in the lower section, has a valve system that can be set to push or pull water into it to create balance so it stays mostly upright like how it works in ships, with a bilge pump that can push water out from any leakage to maintain the air in the upper part (combined with a large compressed air cylinder), and underneath, tethered by heavy chain to a very large block of cement that acts as a tether so it can be fully immersed, and maintain safe dry part above, similar to how it is done in submarines for controlling flotation depth. the other part was using the classic "truncated icosohedron" aka "buckyball" with a screw-based tensioning system at 5 points in the structure to create tensegrity that resists compression by spreading the force across the whole sphere.

here's claude's summary of the concept and explanation of how it works. turns out it is a bit similar to existing tsunami survival shelters:

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Your Hybrid Geodesic Tensegrity Structure Concept

You're describing a remarkably ambitious multi-function structure:

1. Buried earth shelter (withstands soil loading)

2. Sealed pressure vessel (watertight lower section)

3. Ballast-controlled flotation device (submarine-style buoyancy)

4. Moored vessel (anchored but can float when needed)

5. Self-righting submersible (can surface after complete immersion)

Structural Form: Truncated Icosahedron

The football pattern (12 pentagons, 20 hexagons, 60 vertices) is ideal because:

- Distributes stress evenly in all directions

- Natural for both compression (soil loading) and external pressure (submersion)

- The two polar pentagons become your screw-cap access points

Tensegrity with Cables Through Pipes

Using https://tensegritywiki.com/index.php?title=Tent of running cables through hollow struts provides:

- Hidden turnbuckle mechanisms for tension adjustment inside tube ends

- Protection of tension members from soil, water, and debris

- Ability to use the cable network to pre-stress the structure for both soil loading from above and hydrostatic pressure from submersion

The double-layer tensegrity approach (inner and outer cable shells with struts between) would be particularly appropriate here, as it creates a thicker structural envelope that can handle multi-directional loading.

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Buried Earth Shelter Considerations

According to https://www.structuralbasics.com/earth-pressure-calculation/, your dome must handle:

- Vertical soil load: Several feet of earth = significant downward pressure

- Lateral earth pressure: Increases linearly with depth (behaves like hydrostatic pressure)

- Groundwater pressure: If the water table rises, additional hydrostatic loading

The geodesic dome's ability to distribute loads evenly makes it suitable for this. https://www.motherearthnews.com/green-homes/underground-homes-geodesic-domes-zmaz78mazjma successful buried geodesic structures, and https://www.monolithic.org/domes are explicitly rated for underground and underwater construction.

Key advantage: When buried, the dome is in compression from all sides - the strongest loading condition for this geometry.

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Ballast Tank & Buoyancy Control

Your concept mirrors submarine engineering. According to https://www.navalunderseamuseum.org/wp-content/uploads/2020/06/Ballast-and-Buoyancy.pdf:

- Main ballast tanks: Control diving/surfacing (your lower sealed section)

- Trim tanks: Adjust attitude to maintain vertical orientation

- Depth control tanks: Fine buoyancy adjustments

https://oceanbuilders.com/blog/variable-buoyancy-and-ballast-for-floating-pods-and-other-structures/ uses exactly what you describe: fiberglass water tanks with pumps that add/remove water to control height and level.

Your bottom pentagon cap would incorporate:

- Intake valve (flood to descend/add ballast)

- Pump outlet (bilge to ascend/reduce ballast)

- Threaded pressure-rated seal

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Screw-Thread Pentagon Caps

For pressure vessel end caps, https://www.eng-tips.com/threads/asme-code-for-pressure-vessel-caps.472046/ recommend:

- Threaded caps with O-ring or gasket sealing (not threads alone)

- Ellipsoidal or torispherical heads for smooth stress transition

- At high pressures, the cap design resembles "a bolt with a much wider head"

https://www.seascapesubsea.com/product/watertight-enclosure-end-caps-domes-and-flange-caps-2-3-4/ use:

- Anodized aluminum flange caps with dual radial O-rings

- Anti-rotation features

- M10 threaded holes for cable/valve penetrators

- Ratings to 950m depth

Your pentagon caps could be machined with internal threads matching external threads on the dome's polar pentagon frames, with multiple O-ring grooves.

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Mooring Systems

For your dual anchoring approach:

Helical Screw Anchors into Rock

https://www.foundationtechnologies.com/products/applications/mooring/ provide:

- 4-5x the holding strength of alternatives

- ~100 lb anchor can deliver 20,000+ lbs holding force

- For solid rock: drill a hole with hydraulic sinker drill, use expanding rock anchors

Chain & Weight Anchor System

https://marineconstructionmagazine.com/article/mooring-systems-and-floating-docks/ use:

- Heavy chain or cable rode

- Dead weight or mushroom anchor as backup

- Elastic/flexible tether sections to absorb shock loads

Key: Use a https://seaflex.com/products/seaflex-mooring-system/ that can handle 35m+ water level variation - your tether must allow the structure to rise from buried position to floating while remaining anchored.

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Existing Analogues

Several products validate your concept:

1. http://survival-capsule.com/Products.html (Seattle): Aircraft-aluminum spheres, watertight, can be tethered or free-floating, onboard oxygen for submersion, 2-10 person capacity

2. https://www.tajima-motor.com/safeplus/shelter/e/: FRP floating tsunami shelter, self-righting, survives 10m/s impacts and 3m water drops

3. https://canada.constructconnect.com/dcn/news/technology/2016/03/floating-concrete-bunkers-key-to-tsunami-survival-1014407w: Precast concrete modules, sealed watertight, self-righting with controlled buoyancy, endorsed by Tsunami Society International

4. https://newatlas.com/tsunami-proof-shelter-backyard/31355/: DIY 22-foot plywood/epoxy capsule built in a backyard

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Design Considerations for Your Specific Concept

Challenges unique to your buried-then-floating approach:

1. Breakaway from soil: When floodwaters wash out the soil, the structure must cleanly separate - consider smooth exterior, sacrificial soil barrier, or designed failure points in soil contact

2. Transition loading: Structure goes from compression (buried) to tension on tethers (floating) - the tensegrity cable system must handle both

3. Valve design: Bottom intake valve must handle:

- Soil/debris infiltration prevention when buried

- Reliable operation after years of dormancy

- Both gravity-fed intake and pump-driven discharge

4. Air supply: When submerged, you need either:

- Stored compressed air (like survival capsules)

- Snorkel system once at surface

- Your top cap design allowing air intake at "just barely submerged" position

5. Self-righting: With water ballast at bottom and air volume at top, you should naturally orient vertically, but ensure center of buoyancy is well above center of mass

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This is a genuinely novel design concept. The closest existing products (tsunami capsules) assume free-floating deployment, not burial and controlled emergence. The tensegrity-through-pipes approach for a structure that must handle both burial compression and flotation tension is particularly interesting.

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additionally, i have the idea of using a convex tensegrity frame that underpins two levels of flooring, so the top is sleeping/refuge area, directly exposed to the pentagon cap above that is normally open for ventilation but can be sealed for submersion and when brought to buoyancy above so that the water level is below the opening, so once it is washed away, it can be carefully floated up until the center of gravity of the structure is below the surface, ensuring it maintains upright/horizontal alignment, and as the waters subside, it can then be brought carefully back down. probably needs folding supports that can be pulled outwards using cables so when the water is all gone, it has stability and pins itself into the mud, the weight of the ballast tank providing central orientation, and of course, rope ladders that can be thrown out from the top opening to climb down and out.

here is the notes about the additional tensegrity based flooring design:

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Interior Layout: Equatorial Floor Placement

Your truncated icosahedron has a natural "equator" - a ring of 10 hexagons around the middle. The floors positioned at the bottom and top of these equatorial hexagons create three distinct zones:

╱ Top Pentagon Cap (air intake) ╲

╱ ╲

│ Upper dome space (headroom) │

├────────────────────────────────────┤ ← Upper Floor (sleeping)

│ Living/workspace zone │

├────────────────────────────────────┤ ← Lower Floor (workshop/lab/kitchen)

│ Ballast chamber │

╲ ╱

╲ Bottom Pentagon Cap (valve) ╱

This places approximately 76" (per the https://www.sonostarhub.com/blogs/the-sonostar-r-d-lab/second-floor-in-a-geodesic-dome) of clear height in the main living zone between floors.

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Tensegrity Floor Design: Convex/Upwardly Oriented

Your insight about making the floors slightly convex upward (domed toward the ceiling) is structurally elegant. This works via two complementary mechanisms:

1. Inverted Catenary Principle

According to https://lbcc.pressbooks.pub/structuraldesign/chapter/chapter-4-catenary-cables-and-arches-2/, a hanging chain naturally forms a catenary curve. Invert that curve and you get the optimal shape for compression - pure compressive stress with no bending moments.

Your convex floor acts as an inverted catenary membrane:

- Loads (people, furniture, equipment) push down

- The convex shape converts this into outward thrust at the perimeter

- The dome's rigid equatorial ring absorbs this thrust

- The floor remains in pure compression under load

2. Tensile Membrane Action

At the floor level, https://novumstructures.com/news_and_insights/what-is-a-cable-net-system-design-principles-real-world-use/ provide:

- Pre-tensioned cables forming a load-bearing mesh

- Nodes at cable intersections spreading loads evenly

- The dome's frame acts as the "anchoring frame" absorbing tension forces

The slight upward curvature means:

- Center of floor is above the perimeter attachment points

- Under load, the floor wants to flatten, which increases tension in cables

- This "self-stiffening" behavior prevents sagging or wobble

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Floor Construction Options

Option A: Pure Cable Tensegrity Floor

Following https://tensologic.com/engineering/engineering-principles-of-tensegrity-structures/:

Compression struts (radial, angled slightly upward from perimeter to center)

│

├── Connected by tension cables (circumferential rings + diagonal bracing)

│

└── Deck panels rest on strut network

- Struts don't touch each other - suspended in cable network

- Pre-stressed during assembly for stiffness

- Self-equilibrating: automatically distributes stress across structure

- Advantage: If one element fails, loads redistribute rather than collapse

Option B: Cable Net with Rigid Deck

Similar to https://www.loftnets.com/en/65-guardrail-net:

- High-strength cable net (stainless steel or Dyneema)

- Pre-tensioned with turnbuckles at perimeter attachment

- Rigid deck panels (marine plywood, aluminum honeycomb, or composite) resting on net

- Net rated for 100+ kg/m² loading

Option C: Tensioned Membrane Floor

Using https://membranes.novumstructures.com/product-system/membrane-systems/:

- PTFE or reinforced fabric membrane stretched across frame

- Catenary cables in perimeter pockets

- Double-curved surface (your convex dome shape)

- More flexible/resilient - absorbs wave motion if floating

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Attachment to Dome Structure

The floors anchor to the dome at the vertices of the equatorial hexagons. In your tensegrity dome:

1. Cable-through-pipe struts of the dome frame run to equatorial vertices

2. At each vertex, a hub node connects multiple struts

3. Floor cables/struts attach to these same hub nodes

4. Tension in floor cables adds to the dome's overall pre-stress

This creates structural integration - the floors aren't just sitting inside the dome, they're part of the tensegrity system, adding to overall rigidity.

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Lower Floor: Special Considerations

The workshop/lab/kitchen floor above the ballast chamber has unique requirements:

Watertight Separation

- This floor must seal the ballast chamber from living space

- Consider a hybrid design: rigid sealed deck with tensegrity support structure below

- Deck hatches for access to ballast system maintenance

Weight Distribution with Variable Ballast

When ballast chamber fills/empties, the load on this floor changes:

- Empty: Floor spans open space, carries only its own weight + contents above

- Full: Water pressure pushes up against floor underside

The convex-upward shape handles both:

- Empty: Works as inverted catenary (compression to perimeter)

- Full: Water pressure adds upward force, reducing effective load

Bilge Pump Integration

- Pump mounting points on floor underside or ballast chamber walls

- Intake at lowest point of ballast chamber (bottom pentagon)

- Discharge routing through dome frame (could run through same pipes as tensegrity cables)

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Upper Floor: Sleeping Level

The sleeping area floor benefits from:

Vibration Isolation

Tensegrity floors naturally dampen vibrations:

"Tensegrity structures are self-equilibrating and automatically distribute internal stresses across the structure. This allows them to adapt to varying loads without losing structural integrity." - https://www.engineeringmechanics.cz/pdf/21_5_355.pdf

Wave motion when floating would be absorbed rather than transmitted directly.

Thermal Separation

The air gap between floors provides insulation - critical when buried (ground is 55-57°F year-round according to https://www.motherearthnews.com/green-homes/underground-homes-geodesic-domes-zmaz78mazjma).

Emergency Egress

Upper floor positions sleeping area closest to top pentagon cap - shortest path to surface when structure floats up.

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Load Path Summary

External loads (soil, water pressure, wave action)

↓

Dome shell (tensegrity struts in compression, cables in tension)

↓

Equatorial hub nodes

↓

Floor tensegrity systems (convex upward)

↓

Floor deck surfaces

↓

Interior loads (occupants, equipment, stored supplies)

All loads ultimately transfer to the dome's continuous tension network, which distributes stress throughout the entire structure. The https://www.ansys.com/blog/design-floating-structures-tensegrity notes that this self-distributing property is why tensegrity works well for floating structures with dynamic, unpredictable loading.

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This floor system complements your overall design beautifully - it adds structural stiffness to the dome while creating usable horizontal surfaces, and the convex profile naturally handles the varying load conditions between buried, floating, and submerged states.

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nostr:npub12h6h8dj3ale4rk6hkpsp6gcz9kx9xtucyhd3pftn86lnn0j25gdsa9qpsf i think this might be right up your alley