Fully Automatic Unsaturated Soil Consolidation Apparatus
Models BTU-1U / 1UM
Description

This equipment is a fully automatic unsaturated soil consolidation apparatus, models BTU-1U and BTU-1UM, used for one‑dimensional consolidation tests on unsaturated soils under controlled matric suction. It can determine compression characteristics, coefficient of consolidation, pre‑consolidation pressure, and other parameters. The axis‑translation technique is used, applying pore air pressure while maintaining pore water pressure (typically zero) to control suction. Main features:

Specimen size: Ø61.8×H20 mm (other sizes optional)
Axial stress: 1U – 0‑800 kPa automatic loading; 1UM – 0‑3200 kPa automatic loading
Normal displacement: 12.7 mm, resolution 0.01 mm
Load cells: 1U – 0‑2.4 kN (corresponding to 0‑800 kPa); 1UM – 0‑10 kN (0‑3200 kPa), accuracy ±0.1% FS
Pore water pressure: 0‑0.1 MPa, accuracy 0.1 kPa, resolution 0.1 kPa
Volume change measurement: 0‑100 mL, accuracy ±0.01 mL, resolution 0.001 mL
Pore air pressure: 0‑0.9 MPa, accuracy ±0.1% FS, resolution 1 kPa
Ceramic disk: 1.5 MPa high‑air‑entry (imported from USA)
Control method: 20‑key membrane keypad + 240×128 LCD
Data acquisition: Includes data logger and Windows software
Flushing module: Equipped with automatic diffused air flushing device; optional temperature control system (5‑40 ℃)

Test Standards (International)

ASTM D2435(One‑dimensional consolidation of soils)
ASTM D4186(Constant rate of strain consolidation – CRS)
ASTM D4546(Load‑unload‑reload consolidation)
ASTM D6836(Unsaturated soil test methods, including axis‑translation)
ISO 17892‑5(Consolidation test)
BS 1377‑6(Consolidation test)

The equipment can meet the requirements of these standards for loading, displacement measurement, suction control, etc., and is especially suitable for unsaturated soils.

Specification

Parameter

BTU-1U

BTU-1UM

Instrument name

Fully automatic unsaturated soil consolidation apparatus

Fully automatic unsaturated soil consolidation apparatus (high stress)

Specimen size

Ø61.8 × H20 mm (other sizes optional)

Axial stress

Micro‑computer controlled automatic loading, 0‑800 kPa, stepless

Micro‑computer controlled automatic loading, 0‑3200 kPa, stepless

Normal displacement

12.7 mm, resolution 0.01 mm

Load cell

0‑2.4 kN, accuracy ±0.1% FS

0‑10 kN, accuracy ±0.1% FS

Pore water pressure

0‑0.1 MPa, accuracy 0.1 kPa, resolution 0.1 kPa

Volume change measurement

0‑100 mL, accuracy ±0.01 mL, resolution 0.001 mL

Pore air pressure

0‑0.9 MPa, accuracy ±0.1% FS, resolution 1 kPa

Ceramic disk

1.5 MPa high‑air‑entry (imported from USA)

Control method

20‑key membrane keypad + 240×128 LCD

Data acquisition

Data logger + Windows acquisition/processing software

Flushing module

Automatic diffused air flushing device

Optional

Temperature control system (5‑40 ℃)

Detail

Axis‑translation for unsaturated soils– Applies pore air pressure (uₐ) while keeping pore water pressure at zero (or controlled), giving matric suction s = uₐ – u_w. The ceramic disk has a 1.5 MPa air‑entry value, allowing suction control from 0‑1500 kPa.
Two stress ranges–

1U: max. 800 kPa, suitable for shallow unsaturated soils or low‑stress tests.
1UM: max. 3200 kPa, suitable for deep unsaturated soils or high‑stress conditions.

High‑precision volume measurement– Volume change resolution 0.001 mL, precisely monitoring drainage/absorption volume changes.
Automatic diffused air flushing device– Periodically flushes air bubbles that accumulate under the ceramic disk, preventing blockage and ensuring stable suction control; also measures diffused air volume for drainage correction.
Pore water pressure sensor– Range 0.1 MPa, accuracy 0.1 kPa, suitable for low water pressures in unsaturated soils.
Optional temperature control– 5‑40 ℃ system for studying temperature effects on unsaturated soil consolidation.
Software functions– Fully automatic consolidation tests (step loading, CRS, CRL, creep, etc.); real‑time display of stress, displacement, volume change, pore pressure curves; automatic calculation of consolidation parameters (Cv, av, Cc, Pc, etc.).

Application

Unsaturated soil consolidation characteristics– Determine compression index, coefficient of consolidation, and pre‑consolidation pressure under different suctions.
Expansive and collapsible soils– Study the effect of water content (suction) changes on compressibility.
Landfill covers– Evaluate compression and long‑term settlement of unsaturated soils.
Nuclear waste repositories– Consolidation behaviour of buffer materials (e.g., bentonite) under suction.
Deep unsaturated soils– The 1UM model can simulate normal stresses up to 3.2 MPa, suitable for deep soil layers.
Temperature‑suction‑consolidation coupling– With optional temperature control, study temperature effects on unsaturated soil consolidation.

Advantages

Specialised unsaturated design– Axis‑translation with high‑air‑entry ceramic disk (1.5 MPa) provides stable suction control.
Two stress ranges– 800 kPa and 3200 kPa options, covering shallow to deep unsaturated soils.
High measurement precision– Volume change 0.001 mL, pore water pressure 0.1 kPa, displacement 0.01 mm – meeting research requirements.
Automatic diffused air flushing– Ensures long‑term suction control accuracy, reduces manual intervention.
Fully automatic software– Supports step loading, CRS, CRL, creep, etc.; automatic parameter calculation.
Optional temperature control– 5‑40 ℃ for temperature effect studies.
High sensor accuracy– Load, pore water pressure, and pore air pressure all ±0.1% FS.
Easy operation– LCD + keypad, coupled with Windows software.

What To Choose

Select the model based on testing requirements:

Requirement

Recommended Model

Reason

Routine unsaturated soil consolidation (normal stress ≤800 kPa)

BTU-1U

Lower cost, suitable for most shallow unsaturated soil tests

Deep unsaturated soils or high‑stress conditions (normal stress >800 kPa, up to 3200 kPa)

BTU-1UM

High stress range, 10 kN load cell

Need high suction control (>500 kPa, up to 1.5 MPa)

Both models (1.5 MPa ceramic disk)

Sufficiently high

Need long‑term suction control (e.g., creep, drainage equilibrium)

Both (automatic flushing device)

Ensures long‑term stability

Study temperature effects

Either model, with optional temperature control (5‑40 ℃)

Requires additional order

Only saturated soil consolidation (no unsaturated need)

Choose a conventional consolidometer (lower cost)

Unsaturated features add cost

Limited budget and low suction requirement (<500 kPa)

Consider model with 500 kPa ceramic disk (e.g., BTU‑2U series)

Lower cost

Process Flow

Example:Unsaturated soil CRS consolidation test (controlled suction, constant rate of strain) using BTU-1U or 1UM

Ceramic disk preparation

Soak the 1.5 MPa ceramic disk in de‑aired water and vacuum saturate (remove air bubbles).
Install the ceramic disk into the consolidation cell base, ensuring a good seal. Connect the flushing lines.

Specimen preparation

Cut undisturbed unsaturated soil or prepare remoulded specimen using a Ø61.8×20 mm cutting ring.
Measure initial water content and density.

Specimen installation

Place the specimen on the ceramic disk, then install porous stone and loading plate.
Position the consolidation cell in the loading frame and install the displacement sensor.
Connect the pore air pressure line (to the top of the specimen) and the pore water pressure sensor (below the ceramic disk).
Connect the volume change measurement system (to the drainage line).

Apply suction

Apply target pore air pressure (e.g., 200 kPa) via the pore air pressure controller.
Drainage line open to atmosp , so matric suction s = uₐ = 200 kPa.
Start the automatic diffused air flushing device; record volume change until drainage stabilises (suction equilibrium).

CRS consolidation test

In the software, select “CRS consolidation module”.
Set a constant strain rate (e.g., 0.01 mm/min).
Set maximum axial strain (e.g., 20%) or maximum axial force (according to model capacity).
Start the test: the loading piston moves downward at a constant rate, applying continuous loading.
Software records axial force, axial displacement, volume change, pore pressure, and time in real time.
Plots stress‑strain curve and pore pressure‑strain curve.

Stop condition

Automatically stops when the preset strain or maximum load is reached.

Disassembly and cleaning

Unload, release pore air pressure, remove the specimen, weigh and dry to measure final water content.
Clean the consolidation cell, ceramic disk, and sensors; run the flushing device to clean lines.

Data processing

Based on CRS theory, the software calculates: coefficient of consolidation (Cv), compression index (Cc), pre‑consolidation pressure (Pc), and coefficient of permeability (k) (indirectly).
Plots e‑log p curve, Cv‑σ′ curve, etc.
Generates a test report.

For step‑loading consolidation: Set a load sequence (e.g., 25, 50, 100, 200, 400, 800 kPa); at each load step, record displacement and volume change over time; software calculates Cv, av, etc.
For creep consolidation: Apply a constant load and record displacement and volume change over a long period to analyse the secondary consolidation coefficient Cα.

Summary:The BTU-1U/1UM are fully automatic unsaturated soil consolidation apparatuses using axis‑translation for suction control, equipped with a 1.5 MPa high‑air‑entry ceramic disk and an automatic diffused air flushing device. The 1U model has a maximum axial stress of 800 kPa, while the 1UM reaches 3200 kPa. Volume change resolution is 0.001 mL, and pore water pressure accuracy is 0.1 kPa. They support step loading, CRS, CRL, creep, and optional temperature control (5‑40 ℃). They are suitable for studying compression characteristics, consolidation parameters, and temperature effects of unsaturated soils. Selection should be based on the required maximum normal stress: shallow unsaturated soils choose 1U, deep or high‑stress conditions choose 1UM.

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