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)

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)

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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