In a fascinating leap from the lab to the lunar surface, researchers from Wuhan University have been investigating how moon soil behaves under pressure. Using advanced GDS Dynamic Back-Pressure Direct Shear and other systems, the team has published groundbreaking findings in the prestigious journal Acta Geotechnica. Their study, inspired by actual lunar samples brought back by China’s Chang’e-5 mission, focuses on a simulated regolith called WHU-1, developed to mimic the real thing. The results could play a crucial role in shaping future lunar exploration and construction.
Summary of the Research:
1. Background
The Moon’s extreme environment (surface gravity of 1.6 m/s², vacuum pressure of 10⁻⁹ Pa) poses unique challenges for engineering mechanics. Traditional geotechnical theories developed on Earth cannot be directly applied due to differences in gravity and atmospheric conditions. The Chang’e-5 mission returned only 1,731 grams of lunar soil, and the scarcity of these samples has limited research progress. To overcome this limitation, the team developed a high-fidelity lunar soil simulant called WHU-1, based on the particle characteristics of the Chang’e-5 samples. WHU-1 has a median particle size (D50) of just 30.96 microns, with sharp-edged grains, mineral composition closely resembling real lunar regolith, and superior gradation. This material provides a solid foundation for systematic mechanical testing of lunar soil.
2. Overview of Test Methods
Using a GDS dynamic cyclic triaxial testing system and a dynamic back-pressure-controlled shear test system, the researchers conducted triaxial compression tests and direct shear tests on the WHU-1 simulant. The triaxial tests were performed under varying confining pressures, using either water or air as the confining medium. The direct shear tests provided different lateral confinement conditions compared to the triaxial tests. These experiments enabled the team to analyse how confining medium, lateral constraints, and environmental pressure influence the mechanical behaviour of WHU-1.
LH picture - GDS Instruments Dynamic Triaxial Test System (DYNTTS) with the stress state diagram of the specimen.
RH Picture - GDS Instruments Direct Shear System (DYNBPS)
3. Key Findings
(1) Triaxial Test Results:
Under back-pressure-controlled conditions, water loading in weak lateral confinement caused significant pressure differences, leading to underestimation of cohesion and overestimation of internal friction angle. Radial stress and environmental pressure strongly influenced inter-particle interactions, forming multiple shear bands and resulting in varied failure modes. Lowering environmental pressure changed the shear strength relationship from linear to quadratic, highlighting the need for further tests in vacuum conditions.
(2) Direct Shear Test Results:
In direct shear tests, shear force concentrated along a single plane, leading to a nonlinear strength response with increasing load. In contrast, triaxial tests, which offer uniform confinement, provided more stable cohesion and friction angle values under high stress. These findings stress the importance of selecting the appropriate test method based on specific stress conditions.
(3) WHU-1 Material Properties:
WHU-1 showed higher cohesion due to its finer particle size distribution and broader gradation. This suggests that the Chang’e-5 lunar regolith may have higher internal friction and cohesion than Apollo-era samples.
About the Equipment
GDS Dynamic Back-Pressure Shear Apparatus (DYNBPS)
The DYNBPS is used for static and dynamic direct shear testing with pore pressure control, allowing realistic simulation of field conditions in the lab. It enables modeling of landslides that accelerate after initial failure, and supports cyclic shear testing while monitoring and controlling pore pressure.
Features and Advantages:
| Key Feature | Benefit |
| Motor actuator | Long service life, high precision displacement control; suitable for small-strain, creep, and dynamic tests (up to 5Hz) |
| Realistic simulation | Simulates dynamic and seismic geotechnical issues like slope stability |
| Detachable underwater load cell | Enhances testing accuracy for soft soils |
| Closed-loop control | For both shear force/displacement and axial force/displacement |
| External shear box | Manual configuration outside pressure vessel |
| Counterweight system | Provides economical back-pressure with minimal fluctuation during dynamic testing |
Supported tests:
- Static back-pressure direct shear
- Dynamic stress-controlled direct shear
- Dynamic strain-controlled direct shear
Upgrades:
- Bender elements
- Small-strain sensors
GDS Advanced Dynamic Triaxial Test System (DYNTTS)
The DYNTTS is a high-end system integrating a triaxial pressure chamber and dynamic actuator, capable of applying dynamic loads up to 5Hz. Axial loading is driven by a motorized base screw from the chamber bottom.
It offers extensive customization: upgrades for local strain sensors, bender element testing, unsaturated soil testing, etc. Load capacity can be upgraded from 10kN to 60kN. Sample sizes range from 100mm to 300mm. Temperature control upgrades allow testing from -20°C to +85°C.
Features and Advantages:
| Key Feature | Benefit |
| High-precision motor control | Suitable for both small-strain static and large-strain dynamic tests |
| Interchangeable load cells | Supports soft to very stiff soils (1–60kN range) |
| Built-in counterweight | Maintains stable confining pressure during cyclic tests (up to 5Hz) |
| Interchangeable bases/caps | Enables multi-diameter testing in one chamber |
| Direct axial force/displacement control | Accurate axial load/displacement application |
| Adaptive control (standard) | Enhances dynamic load control precision |
Results
The following results are extracts from Acta Geotechnica (SCI Zone 1, IF=5.6) titled "Influence of loading conditions on mechanical behaviors of lunar regolith simulant WHU-1 based on Chang’e-5 returned samples".
Fig 1 shows the sampling locations along with the typical particle morphology.
Fig 2 shows the mineral composition, particle size distribution, and chemical composition of the Chang’e recovered samples.
Fig 3 shows comparison of WHU-1 simulant with other samples taken from previous lunar missions.
Fig 4 shows sample failure analysis from a number of different triaxial tests.
