Automatic Temperature-Controlled Unsaturated Soil Triaxial Apparatus
1. Description
This equipment is a Fully Automatic Temperature-Controlled Unsaturated Soil Triaxial Apparatus (Multi-unit capable), model BTU-TTS-1UT. It is a specialized device that integrates a temperature control system into an unsaturated soil triaxial apparatus, enabling complex coupled tests involvingstress path, temperature control, and drying-wetting cycles. The system adopts a dual-chamber pressure cell, high-precision pressure/volume controllers, and four-dimensional control software (axial stress, radial stress, pore air pressure, pore water pressure). It is suitable for studying thermo-hydro-mechanical coupled behaviour in environmental geotechnical engineering.
2. Test Standards
TheBTU-TTS-1UT Fully Automatic Temperature-Controlled Unsaturated Soil Triaxial Apparatus (Multi-unit capable)is designed and manufactured to meet or exceed the requirements of the following latest international standards:
- ASTM D6836-25— Soil Water Characteristic Curve (SWCC) Determination
- ASTM D5298-16— Measurement of Soil Potential (Suction) Using Filter Paper
- ASTM D3999-11— Modulus and Damping Properties of Soils Using Cyclic Triaxial Apparatus (includes unsaturated soil)
- ASTM D7012-23— Compressive Strength and Elastic Moduli under Varying Stresses and Temperatures
- ASTM D4767-11(2020)— Consolidated Undrained (CU) Triaxial Compression Test
- ASTM D7181-20— Consolidated Drained (CD) Triaxial Compression Test
- ASTM D2850-26— Unconsolidated-Undrained (UU) Triaxial Compression Test
- ISO 17892-9:2018— Consolidated triaxial compression tests on water saturated soils
- ASTM D2434-26— Constant Head Permeability of Coarse-Grained Soils
- ASTM D5084-24— Hydraulic Conductivity Using Flexible Wall Permeameter
- EN ISO 17892-8:2018— Unconsolidated undrained triaxial test (European)
- BS 1377-7:1990— Shear strength tests (total stress / stress path)
3. Specification (Parameter)
| Parameter | Specification |
| Model | BTU-TTS-1UT |
| Specimen size | Ø39.1mm × H80mm |
| Dual-chamber pressure cell | Max. pressure 2MPa |
| Cell pressure/volume controller | 0~2 MPa, resolution 1kPa, absolute accuracy ±1kPa |
| Pore water pressure/volume controller | 0~2 MPa, resolution 1kPa, absolute accuracy ±1kPa |
| Axial load capacity | Max. 10kN, accuracy ±0.1% F.S |
| Axial stroke | Max. 100mm |
| Loading speed | 0.00001~10 mm/min, stepless adjustment, with fast forward/rewind |
| Pore air pressure controller | 0.001~900kPa, absolute accuracy ±1kPa, resolution 0.1kPa |
| Ceramic disk | 500kPa high air-entry value (imported from the USA) |
| Temperature control range | -5℃ ~ +100℃, accuracy ±0.1℃ |
| Software version | BTU V3.11, includes 4D control, drying-wetting cycles, creep modules |
| Multi-unit capable | Supports parallel connection of multiple pressure cells |
Software modules: Data acquisition, unsaturated soil consolidation, unsaturated soil strain triaxial testing, unsaturated soil stress path, four-dimensional control, unsaturated soil triaxial creep, drying-wetting cycle test module, temperature control test equipment.
4. Detail (technical details)
- Dual-chamber pressure cell: Designed for drying-wetting cycle tests, enabling independent or simultaneous loading of inner and outer chambers during drying and wetting processes.
- Four-dimensional control: The software can independently control axial stress, radial stress (cell pressure), pore air pressure, and pore water pressure, achieving true multi-field coupled testing.
- High-precision volume controllers: Cell and pore water controllers have a resolution of 1kPa and absolute accuracy of ±1kPa; pore air pressure controller has accuracy ±1kPa and resolution 0.1kPa.
- Axial loading system: Maximum thrust 10kN, accuracy ±0.1% F.S; speed range 0.00001~10 mm/min, stroke 100mm, with fast forward/rewind function.
- Temperature control system: -5℃ ~ +100℃, accuracy ±0.1℃, capable of simulating freezing-thawing, high temperature, constant temperature, and other thermal conditions.
- Drying-wetting cycle module: Supports drying (increase air pressure / decrease water pressure) and wetting (decrease air pressure / increase water pressure) cycles, combined with stress path and temperature control – suitable for climatic environmental geotechnics.
- Multi-unit capable: Suggests the ability to connect multiple pressure cells in parallel for simultaneous testing of multiple specimens.
5. Application
- Environmental geotechnical engineering: soil mechanical response under coupled drying-wetting cycles and temperature variations
- Climate change and infrastructure: effects of rainfall-evaporation cycles on slopes, subgrades, landfill covers
- Freeze-thaw studies: unsaturated soil behaviour at sub-zero temperatures (-5℃)
- Nuclear waste repository buffer materials: thermo-hydro-mechanical coupling (e.g., bentonite)
- Foundation treatment in hot and humid regions: soil strength and deformation under high temperature and high humidity
- Energy piles and ground source heat pumps: influence of temperature on pile-soil interface mechanical properties
- Teaching and cutting-edge research: multi-field coupled soil mechanics instruction and research
6. Advantages
- Wide temperature range: -5℃ ~ +100℃, covering both freezing-thawing and high-temperature scenarios
- Truly fully automatic temperature-controlled unsaturated soil triaxial apparatus: no manual intervention required for temperature and suction paths
- Dual-chamber pressure cell: specifically designed for drying-wetting cycles, accurate volume change measurement
- Four-dimensional independent control: axial stress, cell pressure, pore air pressure, pore water pressure – each independently controlled
- High-precision sensors and controllers: pressure accuracy ±1kPa, thrust accuracy ±0.1% F.S
- Rich software modules: includes consolidation, strain triaxial, stress path, creep, drying-wetting cycles, temperature control
- Multi-unit capable: supports parallel connection of multiple pressure cells for higher testing efficiency
- Imported ceramic disk: 500kPa high air-entry value, stable performance
8. What To Choose (selection guide)
| Requirement | Recommended configuration | Reason |
| Only routine unsaturated soil stress path tests | TTS-U series may suffice | TTS-1UT has excess functionality, higher cost |
| Need drying-wetting cycles + triaxial shearing | TTS-1UT + drying-wetting module | Core advantage of this model |
| Need sub-zero (freeze-thaw) testing | TTS-1UT (-5℃ temperature control) | Covers below-zero temperatures |
| Need high temperature (e.g., >50℃) simulation | TTS-1UT (up to ~100℃) | Suitable for geothermal or extreme climate studies |
| Need four-dimensional control (stress + air + water pressures) | TTS-1UT standard configuration | Software already includes this |
| Need to test multiple specimens simultaneously | Multi-unit configuration (multiple pressure cells) | Improves efficiency |
| Teaching laboratory comprehensive demonstration | Single-unit TTS-1UT | Full functionality, suitable for demonstrations |
9. Process Flow
- Specimen preparation→ Prepare an unsaturated soil specimen of Ø39.1mm × H80mm
- Install ceramic disk and specimen→ Install the high air-entry ceramic disk (pre-saturated) and place into the dual-chamber pressure cell
- Set temperature→ Set target temperature (e.g., -5℃ or +60℃); wait for temperature to stabilize (accuracy ±0.1℃)
- Saturation and suction equilibrium→ Apply pore air pressure and pore water pressure using axis translation technique to reach target matric suction
- Drying-wetting cycles (optional)→ Perform drying (increase air pressure / decrease water pressure) and wetting (decrease air pressure / increase water pressure) according to a programmed sequence; record volume and water content changes
- Consolidation stage→ Apply net cell pressure; record volume change
- Shearing or stress path stage→ Perform constant strain shearing or custom stress path (four-dimensional control)
- Creep stage (optional)→ Maintain constant stress; record creep deformation
- Data acquisition→ Record throughout: axial stress, radial stress, pore air pressure, pore water pressure, volume change, temperature, displacement, axial force
- Post-processing→ Software generates stress-strain curves, suction path diagrams, drying-wetting cycle effect curves, temperature influence curves, etc.
- Multi-unit extension (if applicable)→ If using a multi-unit system, conduct parallel or comparative tests on multiple specimens simultaneously
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