Automatic Unsaturated Soil Stress Path Triaxial Apparatus

Product Specification

                                                          Automatic Unsaturated Soil Stress Path Triaxial Apparatus

1. Description

This equipment is a Fully Automatic Unsaturated Soil Stress Path Triaxial Apparatus (BTU-TTS-U series), specifically designed for unsaturated soil mechanical property studies. It adopts adual-chamber pressure celland anindependent total volume change measurement system, enabling precise control of pore air pressure, pore water pressure, and cell pressure, thereby allowing unsaturated soil testing under complex stress paths. The apparatus is also compatible with saturated soil test modules and can be optionally upgraded with temperature control and multi-field coupling functions.
 
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2. Test Standards

• ASTM D6836(Test methods for hydraulic and mechanical properties of unsaturated soils)
• ASTM D5298(Filter paper method for soil-water potential)
• ISO 17892 series(Geotechnical laboratory testing)
• SL 237-1999(Chinese specification for soil testing – unsaturated soil section)
• Common methodologies from research literature on unsaturated soil triaxial testing

 
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3. Specification (Parameter)

 
Other common specifications:

• Total volume measurement system: independent, continuous measurement, unlimited range
• Ceramic disk: 500 kPa high air-entry value (imported from the USA); optional 15 Bar (~1.5 MPa)
• Software modules: unsaturated/saturated soil tests, stress path, rheology, etc.

 
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4. Detail (technical details)

• Dual-chamber pressure cell: simultaneous loading of inner and outer chambers, reducing the influence of cell deformation on volume change measurement.
• Independent total volume measurement system: does not rely on volume controller accumulation; enables continuous and accurate volume change measurement, especially suitable for long-duration or large-deformation tests.
• Pressure/volume controller: high precision, large volume capacity; can be used independently for pressure loading and volume measurement.
• Independent pore air/water pressure control: allows independent application and measurement, enabling matric suction control.
• High air-entry ceramic disk: 500 kPa standard; optional 15 Bar (~1.5 MPa) for higher suction ranges.
• Shearing speed: up to 60 mm/min (TTS-4U) and as low as 0.00001 mm/min, covering tests from rapid shearing to rheology.
• Upgradability: can be upgraded to a bidirectional equal-pressure permeability unsaturated soil triaxial apparatus, as well as temperature control and multi-field coupling systems.

 
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5. Application

• Unsaturated soil mechanics research: e.g., loess, expansive soil, residual soil, compacted fill
• Slope stability analysis: strength changes under rainfall infiltration
• Landfill cover and liner systems: unsaturated hydraulic characteristics
• Subgrade and compacted earthworks: influence of moisture change on bearing capacity
• Buffer materials for nuclear waste repositories: e.g., bentonite in high-level radioactive waste disposal
• Climate change and geotechnical engineering: effects of drying-wetting cycles on soil mechanical behavior

 
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6. Advantages

• Truly fully automatic: full-process automatic control for unsaturated soil testing, reducing human error
• Dual chamber + independent volume change measurement: high volume change accuracy, unaffected by pressure cell flexibility
• Wide pressure and speed range: adapts to various unsaturated soil materials and testing requirements
• Modular design: upgradeable to permeability, temperature control, multi-field coupling – strong expandability
• Compatible with saturated soil tests: one device meets both saturated and unsaturated soil testing needs
• Imported ceramic disk: high air-entry value, stable and reliable performance

 
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8. What To Choose (selection guide)

 
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9. Process Flow

 
Based on typical unsaturated soil triaxial test procedures and the characteristics of this equipment:
 

• Specimen preparation→ Prepare unsaturated soil sample to dimensions (e.g., Ø61.8×H125 mm); install ceramic disk and saturate it
• Mounting & sealing→ Place specimen in dual-chamber pressure cell; connect pore water and pore air pressure lines
• Suction equilibrium→ Apply target matric suction using axis translation technique (air pressure > water pressure); wait for equilibrium
• Consolidation stage (optional)→ Apply net cell pressure; record volume change and drained/exhausted volumes
• Stress path or shearing stage:
  • Constant stress path (constant suction)
  • Constant strain shearing (CU, CD modes)
  • Suction change path (e.g., wetting test)
  • Rheology or low-frequency cyclic loading (optional modules)
• Data acquisition→ Record axial force, displacement, pore water pressure, pore air pressure, total volume change, cell pressure
• Post-processing→ Plot unsaturated soil failure envelope (suction‑dependent), stress-strain curves, volume change curves, etc.
• Optional upgrade procedures: temperature control, permeability, multi‑field coupling – performed according to corresponding modules