Triple Rheological Direct Shear Apparatus

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Triple Rheological Direct Shear Apparatus BTU-TRA Series (TRA-1 / TRA-2 / TRA-3)

Description

This series consists of triple rheological direct shear apparatuses, models BTU-TRA-1, BTU-TRA-2, BTU-TRA-3, designed for simultaneous direct shear testing of three specimens, with particular suitability for rheological (creep) studies. The three models differ mainly in automation level and data acquisition method:

• BTU-TRA-1: Basic model, LCD display, no data acquisition
• BTU-TRA-2: Data acquisition model, equipped with data logging system
• BTU-TRA-3: Fully automatic model, servo closed‑loop control

Common features:

• Triple unit (tests three specimens simultaneously)
• Specimen size: Φ61.8 × H20 mm (standard cutting ring)
• Shear rate: 0.00001‑6 mm/min, stepless adjustment
• Maximum normal stress: 0.4 MPa (same for all three models)
• Maximum shear stress: 0.4 MPa for TRA-1; 0.8 MPa for TRA-2/3
• Test modules: direct shear, cyclic shear, rheological direct shear (TRA-2/3 also include standard consolidation)
• Later upgrade options: temperature control module (0~+90 ℃) and high pressure (1.6 MPa)

Test Standards (International)

• ASTM D3080(Direct shear test)
• ASTM D7608(Residual strength – reciprocating shear)
• ASTM D5321(Interface shear – similar principle)
• ISO 17892‑10(Direct shear test)
• BS 1377‑7(Direct shear test)
• ASTM D6519(Creep/rheological tests – may refer to soil rheology testing standards)

The equipment meets the requirements of these standards for shear rate, normal stress control, and displacement measurement.

Specification

Detail

• Triple unit design– Three specimens can be sheared simultaneously (different normal stresses or identical conditions), greatly improving efficiency.
• Low normal stress range– Maximum 0.4 MPa, suitable for soft soils, peat, high‑water‑content soils, and other low‑stress conditions.
• Shear stress difference– TRA-1 max shear stress 0.4 MPa; TRA-2/3 0.8 MPa – the latter can test higher strength materials.
• Loading methods–
  • TRA-1/2: lever loading (weights) – simple, reliable, but requires manual weight changes.
  • TRA-3: servo closed‑loop loading – automatic normal stress control, capable of complex stress paths.
• Sensor configuration–
  • TRA-1: 3 load cells (one horizontal shear force per unit? normal force calculated from lever weights, no sensor) + 3 displacement sensors.
  • TRA-2/3: 6 load cells (normal + horizontal per unit), 3 displacement sensors (one horizontal per unit).
• Acquisition method–
  • TRA-1: LCD display only, manual recording.
  • TRA-2: external data logger, automatic recording.
  • TRA-3: servo closed‑loop, automatic control + acquisition.
• Test modules– All models support direct shear, cyclic shear, and rheological direct shear. TRA-2/3 additionally include standard consolidation (step loading).
• Rheological direct shear– Long‑term creep tests measuring shear displacement over time.
• Upgrade options–
  • Temperature control (0~+90℃): for temperature‑creep coupling studies.
  • High pressure (1.6 MPa): raises maximum normal stress from 0.4 MPa to 1.6 MPa, suitable for stiffer soils.

Application

• Rheological studies– Determine time‑dependent deformation (creep) of soft soils, peat, high‑organic soils, etc.
• Cyclic shear– Simulate strength degradation under earthquake, wave, or traffic loading.
• Soft soil engineering– Subgrade settlement, long‑term slope stability analysis.
• Triple high‑efficiency testing– Simultaneous direct shear or creep tests at three different normal stresses for rapid strength parameter determination.
• Teaching demonstrations– Visualise shear failure and creep phenomena.
• Temperature effects– With optional temperature control module, study temperature influence on soil rheology.

Advantages

• Triple unit design– Obtain three data sets in one test, three times the efficiency of a single‑unit apparatus.
• Extremely low shear rate– 0.00001 mm/min, suitable for long‑duration creep tests.
• Modular upgrade path– Upgrade from basic (TRA-1) to data acquisition (TRA-2) or fully automatic (TRA-3).
• Multiple test modes– Direct shear, cyclic shear, rheological direct shear, consolidation, etc.
• Later expandability– Optional temperature control and high‑pressure upgrades increase capability.
• Lever loading (TRA-1/2)– Simple, reliable, no power required, low cost.
• Servo closed‑loop (TRA-3)– High‑precision automatic control, suitable for complex stress paths.
• High‑resolution displacement measurement– Suitable for monitoring small creep deformations.

What To Choose

Select the model based on testing requirements and budget:

Note: The servo closed‑loop system of TRA-3 automatically controls normal stress, which is highly beneficial for maintaining constant stress during creep tests. For long‑term rheological studies, TRA-3 is strongly recommended.

Process Flow

Example:Creep shear test on soft soil (constant normal stress) using the fully automatic triple rheological direct shear apparatus (BTU-TRA-3)

• Specimen preparation
  • Cut three undisturbed or remoulded soft soil specimens using a Φ61.8×20 mm cutting ring.
  • Measure initial water content and density; saturate if required.

• Specimen installation
  • Place the three specimens into the lower shear boxes of the three units, install upper boxes, porous stones, and loading plates.
  • Position the triple shear box assembly in the direct shear loading frame.
  • Connect the normal and horizontal loading rods for each shear box; install displacement sensors (one horizontal per unit, and optional vertical displacement sensors).

• Apply normal stress
  • In the software, set independent target normal stresses for each shear box (e.g., 50, 100, 200 kPa).
  • The servo system automatically applies and maintains constant normal stress.
  • Record normal displacement (consolidation) until stable (stability criterion can be set).

• Set shear parameters
  • Select the “rheological direct shear test” module.
  • Set the shear stress level (e.g., 70% of peak strength) or set a shear rate (e.g., 0.0001 mm/min for creep).
  • Set test duration (e.g., 72 hours) or displacement limit.
  • Choose control mode: stress control (constant shear stress) for creep.

• Start shearing
  • Start the horizontal servo system to apply the set shear stress (or rate).
  • The software records horizontal shear force, horizontal displacement, normal displacement, and time for each shear box in real time.
  • Plot creep curves (shear displacement vs. time).

• Stop condition
  • Automatically stops when the preset time or displacement limit is reached.

• Disassembly and cleaning
  • Unload normal force, retract horizontal pistons, remove specimens.
  • Record failure mode, clean shear boxes.

• Data processing
  • Software plots creep curves, calculates creep rate, long‑term strength, etc.
  • For cyclic shear tests, calculate modulus degradation, damping ratio, etc.
  • Generate test report.

For TRA-1 or TRA-2:

• TRA-1 requires manual reading of values; cannot automatically plot curves.
• TRA-2 can automatically acquire data, but normal stress must be applied manually using weights; shear stress/rate is set via the controller.

Summary:The BTU-TRA series triple rheological direct shear apparatus offers three configurations from manual lever‑loading to fully automatic servo closed‑loop. It is suitable for direct shear, cyclic shear, and rheological (creep) tests on soft soils, peat, and similar materials. The triple design greatly improves efficiency. Selection should be based on data acquisition needs, automation level, and budget. Later upgrades include temperature control (0~90 ℃) and high pressure (1.6 MPa) to expand the application range.