Apollo 12 Regolith and Mega-Regolith Characterization

The first step in the SPORE project is to gather as much relevant data as possible on the Lunar regolith and mega-regolith at the Apollo 12 site.

Check out the Lunar Homestead Experimental Location page for why I chose the Apollo 12 site for Lunar Homestead projects. That page is now obsolete but it still does a good job explaining why the site was selected.

Apollo 12 regolith parameters at a glance

Geomechanical (mechanical strength properties)
- Compressive strength
- Coefficient of friction
- Shear strength
  - Cohesion (three estimates) = 0 to 0.7 kPa / 0.1 to 3.1 kPa / 0 to 1 kPa (1, pg 508).
  - Friction angle (three estimates) = 28º to 35º / 13º to 56º / 51º to 59º (1, pg 508).
  - Values for Peak Shear Stress are all over the place. I’m not sure how they could be used for any sort of planning.
- Hardness
- Rheology
- Angle of repose
- Tensile strength
- Fracture behavior
- Impact resistance
Physical
- Particle density
- Bulk density
  - The shape and thickness of the drive core tubes disturbed the regolith sample, changing the bulk density value (1, pg 485).
  - From core samples (three different estimates) =
    - 1.6-2 g/cm³
    - 1.55-1.9 g/cm³
    - 1.7-1.9 g/cm³
- Relative density
- Porosity
- Thermal properties
- Surface area
- Friability
- Permeability
Grain Specific
- Grain size
- Grain size distribution
- Grain shape
- Magnetic grain properties
- Grain shape distribution
- Electrostatic charging
Chemical
- Glass composition
- Bulk chemistry
- Reactivity as volatile/soluble minerals
- Surface reactivity (including damage)
Mineralogical
- Mineralogical composition as function of grain size
- Modal mineralogical composition
- Soil texture
Multicategory
- Implanted solar particles
- Agglutinates with nanophase Fe

Apollo 12 mega-regolith parameters at a glance

There are no Apollo 12 mega-regolith samples. See the Lunar mega-regolith page for more information.

Apollo 12 regolith parameters

At this point I don’t know which parameters are critical and which are useless. So I’ll just collect everything and figure it all out later.

Relative density (takes particle packing into account)

Relative density description — [Lunar Sourcebook (pg 495)]

According to the Lunar Sourcebook, the most significant geotechnical variable is the relative density of the regolith , as it controls the other physical properties as well(1, pg 476).
The bulk density of any soil sample can vary over a wide range depending on how the particles are packed (1, pg. 494).
Two soils with the same bulk densities can have very different relative densities and display different behaviors. The converse (same relative but different bulk) is not true however (1, pg 495).
In-situ relative densities for Lunar regolith:
- Top 15 cm = 65±3% (1, pg 497).
- 0-30 cm = 74±3% (1, pg 497).
- 30-60 cm = 92±3% (1, pg 497).
- Observations based on boulder tracks estimate that the top 400 cm of slopes has a relative density of 61%, indicating that slopes are significantly looser than plains areas (1, pg 499).
- A relative density of 65-75% is the practical limit for terrestrial soil field compaction. Shock waves from meteoroid impacts has shaken and densified the Lunar regolith (1, pg 495).

Regolith bulk density — [Lunar Sourcebook (pg 492)]

Porosity (the volume of void space between the particles divided by the total volume)
- Intergranular (the volume of space between individual particles)
  - Affects both bulk and relative density (1, pg. 481).
- Intragranular (the volume of reentrant surfaces on the exterior of the particles)
  - Has a strong effect on bulk density (1, pg. 481).
- Subgranular (the volume of enclosed voids within the interior of the particles)
  - The actual subgranular porosity of individual Lunar regolith particles is poorly understood (1, pg. 481).
- Void ratio (the volume of void space between the particles divided by the volume of the “solid” particles).
- Soil breccia = 35% void space (2, pg 241)
- Best estimates of in-situ Lunar regolith porosity (inter- and intragranular combined)

Regolith porosity — [Lunar Sourcebook (pg 492)]

Compressibility (the volume change when a confining stress is applied to soil)
- Compression index (the decrease in void ratio that occurs when stress is increased by an order of magnitude)
  - Range 0.01 – 0.11 (1, pg 501).
  - Recommended typical value
    - Loose = 0.3 (1, pg 501).
    - Dense = 0.05 (1, pg 501).
  - Agglutinates crush under relatively low confining stress, decreasing the void spaces (1, pg 503).
- Useful when figuring out structural foundations and footings.
Shear strength
- Governs ultimate bearing capacity, slope stability, and trafficability (1, pg. 506).
- Cohesion best estimate = 0.1 to 1 kPa (1, pg 506).
- Friction angle = 30º to 50º (1, pg 506).
- Values for Peak Shear Stress are all over the place. I’m not sure how they could be used for any sort of planning.
Permeability (the quantity of flow of a fluid through a porous medium in response to a pressure gradient)
- I only found 2 possible papers on this topic and both were behind paywalls. It doesn’t seem like there has been much research in this area.
- No direct measurements have been made on Lunar samples (1, pg 517).
- Test firing of the Surveyor 5 vernier engine on the Lunar surface produced an estimate of 1-7 x 10^-12 m² to a depth of 25 cm (1, pg 517).
- JSC-1A viscous flow permeability of 1 × 10^-12 m² to 6.1 × 10^-12 m² for bulk densities from 1550 to 2000 kg m^-3(3).
Diffusivity (defines the molecular flow of a gas through a porous medium in response to a concentration gradient)
- Diffusivity depends on the gas concentration, the pressure and temperature, and the particle size and shape distributions in the soil (1, pg 517).
- No direct experiments have been run on Lunar samples. However tests were conducted using a basaltic Lunar soil simulant with a void ratio of 0.6. The tests were run at room temperature under very low vacuum conditions (1, pg 517).
  - Helium = 7,7 cm²/sec
  - Argon = 2.3 cm²/sec
  - Krypton = 1.8 cm²/sec
- More reactive gases and decreased temperatures will increase “sticking time” (1, pg 517).
Bearing capacity (the ability of a soil to support an applied load)
- Ultimate bearing capacity (the maximum possible load that can be applied without causing gross failure)
  - For a 1 meter footing on the Lunar surface = ≈6000 kPa (1, pg 517)
  - Ultimate bearing capacity increases proportionally with the width of the footing, making it more than sufficient to support any conceivable structure (1, pg. 518).
- Allowable bearing capacity (load that can be applied without exceeding a given amount of settlement)
  - Significantly less than the ultimate bearing capacity. Allowable bearing capacity controls the design of a foundation (1, pg 519).
  - Need to be calculated based on specific design requirements.
Slope stability (the ability of the soil to stand without support)
- Uncompacted regolith (“dumped”) (1, pg 522).
  - Relative density = 30-40%
  - Safety factor = 1
  - Height = 10 meter
  - Angle = nearly 40º
- Compacted (once disturbed, the regolith will not return to its original dense state) (1, pg 521).
  - Relative density = 65-75%
  - Safety factor = 1
  - Height = 10 meter
  - Angle = 45º
- Natural slopes
  - Very little is known (1, pg 522).
Trafficability (the capacity of a soil to support a vehicle and provide sufficient traction)
- Almost any vehicle with round wheels and a maximum ground contact pressure of 7-10 kPa will work (1, pg 522).
Soil cohesion
Soil friction
Tool-soil adhesion
Soil weight (lifting/blanket)

Apollo 12 mega-regolith parameters

There are no Apollo 12 mega-regolith samples. See the Lunar mega-regolith page for more information.

Resources

Lunar Sourcebook (www.lpi.usra.edu/publications/books/lunar_sourcebook)
Lunar Stratigraphy and Sedimentology (lunarhomestead.com/resources/lunar-resources/)
Permeability of JSC-1A: A lunar soil simulant (www.sciencedirect.com/science/article/pii/S0019103510004835)