Bishop Stress Path Triaxial Apparatus

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Bishop Stress Path Triaxial

1. Description

This equipment is a Bishop Stress Path Triaxial Apparatus (BTU-TTS-5S), designed based on the Bishop-type stress path pressure cell. It is specifically used for studying the mechanical properties of saturated soils under complex stress paths. The system is equipped with a high-precision submersible load cell, an LVDT displacement sensor, a multi-channel data acquisition unit, and multiple pressure/volume controllers, enabling fully automatic control from saturation and consolidation to stress path shearing. The software includes advanced modules such as linear stress paths (p-q or s-t, with 6 forms), low-frequency cyclic loading, and k0 consolidation.

2. Test Standards

• ASTM D7181(Consolidated Drained Triaxial Compression Test)
• ASTM D4767(Consolidated Undrained Triaxial Compression Test)
• ASTM D2850(Unconsolidated Undrained Triaxial Compression Test)
• BS 1377(British Standards for soil testing)
• SL 237-1999(Chinese specification for soil testing)

3.Specification (Parameter)

4. Detail (technical details)

• Bishop stress path pressure cell: Bishop-type design suitable for saturated soil tests; max cell pressure 2000 kPa, axial force 10 kN.
• Submersible load cell: Mounted inside the pressure cell to avoid piston friction; accuracy as high as ±0.05% FS; optional ranges 5kN or 10kN.
• LVDT displacement sensor: British brand, accuracy ±0.15% FS, range 50mm, suitable for conventional specimen deformation measurement.
• Three independent volume controllers:
  • Axial pressure: 3MPa / 250cc
  • Back pressure: 2MPa / 250cc
  • Cell pressure: 2MPa / 250cc

Enables independent and precise control of cell pressure, back pressure, and axial pressure, as well as volume change measurement.

• Data acquisition unit: 10 channels, supporting 2 digital signals (e.g., LVDT, load cell) and 8 analog signals (e.g., pore pressure, volume change); 16-bit resolution.
• Stress path module: Provides 6 types of linear stress paths (p-q or s-t forms); custom paths can be defined – suitable for simulating complex stress histories.
• Low-frequency cyclic module: Supports low-frequency cyclic loading under load control mode, for simulating seismic or traffic loading.
• k0 module: Enables k0 consolidation and swelling tests.

5. Application

• Stress path studies on saturated soils: simulate stress changes during excavation, filling, unloading, and other practical engineering scenarios
• Constitutive model parameter calibration: e.g., Cam-clay model, Duncan-Chang model
• Foundation and slope engineering: strength and deformation characteristics under different stress paths
• Cyclic loading tests: soil response under subway or traffic loading (low-frequency cyclic module)
• k0 consolidation tests: determine coefficient of lateral earth pressure at rest
• Teaching and research laboratories: advanced soil mechanics testing

6. Advantages

• Bishop-type pressure cell: optimized for saturated soil stress paths, reducing errors
• High-precision submersible load cell: directly measures specimen load, avoiding piston friction
• Three independent volume controllers: independent control of cell pressure, back pressure, and axial pressure; accurate volume change measurement
• Rich software modules: covers conventional triaxial to advanced stress paths, low-frequency cyclic, k0 consolidation
• Cost-effective configuration: 10kN axial force, 2000kPa cell pressure – sufficient for most saturated soil testing needs
• Modular upgradability: additional stress path forms or cyclic loading functions can be added as needed

7. What To Choose (selection guide)

8. Process Flow

• Specimen preparation→ Prepare saturated soil specimen of Ø39.1mm or 50mm
• Mount pressure cell→ Install specimen, submersible load cell, LVDT; connect cell/back/axial pressure lines
• Saturation stage→ Back pressure saturation and B-check to verify saturation level
• Consolidation stage (optional)→ Isotropic consolidation or k0 consolidation
• Shearing or stress path stage:
  • Conventional CD/CU/UU shearing
  • Linear stress path (p-q or s-t, 6 forms)
  • Low-frequency cyclic loading (requires advanced loading module)
• Data acquisition→ 10-channel DAQ simultaneously records axial force, displacement, pore pressure, volume change, cell pressure, back pressure
• Post-processing→ Software generates stress path diagrams, stress-strain curves, effective stress paths, failure envelopes, etc.
• Report output→ Automatically generates standard-compliant tables and curves; supports printing and export