Neometrix / Materials & Geotechnical Test / Triaxial Test System / NMX-TRX-73

NMX-TRX-73 · ENGINEERED-TO-ORDER CLASS — SPECIFY · FRAME · CONTROL · BUILD · TEST · PROVE

Triaxial Test System. Soil feels the stress the water leaves.

Name: Triaxial Test System
Brand: Neometrix
SKU: NMX-TRX-73

A triaxial test squeezes a soil specimen the way the ground does, from all sides, with water in its pores. It then loads the specimen until it deforms or fails, and records what it does.

The soil does not feel the total stress. It feels the total stress less the pressure of the water in its pores. So the system has to control the stress on the specimen, measure the water pressure inside it, and prove it is saturated before the test.

Discuss a triaxial system Capability note (PDF)

A single triaxial test loading frame on a plain white studio background: a rigid grey painted steel frame with a base plate, two vertical columns and a crosshead carrying a bright load cell, and standing on the base plate a clear acrylic cylindrical cell between bright stainless steel plates held by slim tie rods, with a grey-brown soil specimen inside wrapped in a thin transparent membrane, a polished ram entering the top, and three thin clear tubes with small valves leaving the base, and no people

Fig · 01 — A triaxial test frame: a clear cell holding a soil specimen in a membrane between two end caps, a ram and a load cell above it, and pressure lines leaving the base — illustrative render.

The stress

all round, then axialcell pressure, then the ram load

The water

measured insidepore pressure at the specimen

The saturation

proved before the testback pressure and a response check

The test

static or cyclicdrained or undrained

Status

engineered to orderno triaxial system claimed

ISO 9001ISO 14001ASTM D4767 reference method

Overview

Why the whole job is the water.

Because the grains carry only the stress the water leaves them, and the system has to measure and control that water.

A single triaxial cell on a plain white studio background: a clear thick-walled acrylic cylinder between a bright stainless steel base plate and top plate held by four slim tie rods, a grey-brown soil specimen inside in a thin transparent membrane between two bright end caps, a polished ram through the top plate and small stainless valves with short clear tubes on the base, and no people

Fig · 02 — A triaxial cell: a clear cylinder between two steel plates held by tie rods, a specimen inside, a ram through the top and valves on the base — illustrative render.

Soil feels the stress the water leaves.

What the system is for

It tests soil specimens to find how strong and how stiff the soil is under the stresses it carries in the ground. The specimen is sealed in a thin membrane, set in a cell, squeezed from all sides by the cell pressure and then loaded through a ram. It suits static tests for strength and stiffness, and cyclic tests for how a soil behaves under repeated loading.

Why soil feels the stress the water leaves

A soil is grains with water between them. The water carries part of the total stress, and the grains feel only the rest. That rest is the effective stress, the total stress less the pore pressure. It is the effective stress that sets the strength and the stiffness of the soil.

Why the specimen is saturated first

The rule works only when the pores are full of water. The system raises the cell pressure and a back pressure together, and then checks that the pore pressure answers a change in cell pressure almost fully.

A specimen that has not passed the check has a pore pressure reading that cannot be trusted.

Why drainage decides the test

Whether the water may leave the specimen changes the answer. In an undrained test the water is kept in, and the pore pressure rises or falls as the soil is sheared. In a drained test the water is let out, and the loading is slow enough for it to move.

Why the pressure controller is also the volume gauge

When water leaves or enters the specimen, it moves through the back pressure controller. The volume that moves is the volume change of the specimen, so the same device holds the pressure and measures the change.

Why a cyclic test needs a different system

A cyclic test reverses the load again and again on a saturated specimen and watches the pore pressure build. The actuator, the control loop and the pressure controllers have to keep up without drift. The readings have to be taken fast enough to follow each cycle.

The method

Specify, frame, control, build, test, and prove.

Six steps in a fixed order. Reading the pore pressure at the specimen, and proving the saturation check works, are the two a quick order skips.

1 · Specify

The specimen sizes, the types of test and the range of stress are stated by the customer.

2 · Frame

The frame, the actuator and the cell are sized for the specimens and the loads, static or cyclic.

3 · Control

The controllers, transducers and loops are chosen so that the pore pressure and the volume change are read at the specimen.

4 · Build

The frame, the cell, the controllers, the transducers and the software are built as one installation.

5 · Test

The transducers are calibrated and a reference specimen is run, so that the saturation check is shown to work before any customer specimen is tested.

6 · Prove

A record is kept for every test, with its stages, its readings and its saturation check, and handed over with the system.

Which test for which question

Test	What it finds	What to watch
Unconsolidated undrained	the specimen is squeezed and sheared with no drainage, for the undrained strength of the soil as it stands	it reports total stress only, so it says nothing about how the soil behaves once the water drains
Consolidated undrained, with pore pressure	the specimen is consolidated under the cell pressure, then sheared with no drainage while the pore pressure is measured	it gives the effective stress parameters, but only if the specimen is saturated and the pore pressure reading is trusted
Consolidated drained	the specimen is consolidated, then sheared slowly with drainage open, so that the pore pressure stays at the back pressure	it is slow, because the water has to move, and the volume change has to be measured with care
Cyclic	a load that reverses many times is applied to a saturated, consolidated specimen, to see how the pore pressure builds and the soil softens	the actuator and the pressure controllers have to keep up without drift, and the readings have to be taken fast

The step people underrate is the saturation check. A soil test run on a specimen that was never proved saturated reports a pore pressure that means little.

Work content

What the system contains, element by element.

Read it as a checklist: a system missing a row will run a test on paper and not report the stress the soil felt.

A single pressure and volume controller on a plain white studio background: a long bright stainless steel cylinder lying in a plain grey painted steel housing, with a lead screw driven by a compact motor at one end and two bright stainless fittings joined by a short clear tube at the other, and no people

Fig · 03 — A pressure and volume controller: a stainless cylinder driven by a lead screw and a motor, in a plain housing, with its output fittings at the front — illustrative render.

Element	What it does	What matters
Loading frame	carries the axial load	stiff and aligned, so that the ram pushes along the axis of the specimen and in no other direction
Triaxial cell	holds the specimen and the cell water	takes its pressure without leaking, with ports at the base for the drainage and pore pressure lines
Cell pressure controller	squeezes the specimen	holds the cell pressure steady for hours, and ramps it when the stage calls for it
Back pressure and volume controller	holds the water pressure and measures the volume change	the volume that moves through it is the volume change of the specimen, so it must be steady and well calibrated
Pore pressure transducer	reads the water pressure	mounted at the specimen base with no air in the line, because air makes the reading slow and soft
Load cell and displacement transducer	read the load and the deformation	mounted so that they read the specimen and not the frame
Axial actuator and control loop	apply the axial load	a slow, steady drive for static tests, and a fast actuator with a stable loop for cyclic tests
Data acquisition and test software	run the stages	the saturation, consolidation, shearing and cyclic stages, with the readings logged against time
End caps, porous discs and membranes	prepare and seal the specimen	sized for the specimens the customer names, and replaced when worn
Procedure	fixes the sequence	specify, frame, control, build, test and prove, the same for every test
Testing & documentation	prove the system first	transducers calibrated, a reference specimen run, and a record the customer can inspect

The elements that decide whether the pore pressure can be trusted are the saturation check and the pore pressure line, because a reading from a specimen that is not saturated, or from a line with air in it, looks like data and is not.

Full specification — expand

System	A rigid loading frame with an axial actuator and a load cell; a triaxial cell that applies cell pressure all round the specimen; a cell pressure controller; a back pressure and volume controller; a pore pressure transducer; a displacement transducer; for cyclic work, a fast actuator and a stable control loop; data acquisition and test software that runs the saturation, consolidation, shearing and cyclic stages; end caps, porous discs and membranes; a written test plan; and calibration, testing and documentation before handover
The One Idea	Soil feels the stress the water leaves.
Why Soil Feels The Stress The Water Leaves	A soil is grains with water between them, and the water carries part of the total stress while the grains feel only the rest, which is the effective stress, the total stress less the pore pressure, and it is the effective stress that sets the strength and the stiffness of the soil
Why The Specimen Is Saturated First	The effective stress rule works only when the pores are full of water, so the system raises the cell pressure and a back pressure together and then checks that the pore pressure answers a change in cell pressure almost fully, because a specimen that has not passed the check has a pore pressure reading that cannot be trusted
Why Drainage Decides The Test	In an undrained test the water is kept in and the pore pressure rises or falls as the soil is sheared, and in a drained test the water is let out and the loading is slow enough for it to move, so whether the water may leave changes the answer
Why The Pressure Controller Is Also The Volume Gauge	When water leaves or enters the specimen it moves through the back pressure controller, so the volume that moves is the volume change of the specimen and the same device holds the pressure and measures the change
Why A Cyclic Test Needs A Different System	A cyclic test reverses the load again and again on a saturated specimen and watches the pore pressure build, so the actuator, the control loop and the pressure controllers have to keep up without drift and the readings have to be taken fast enough to follow each cycle
Standards	ASTM D2850 is the public method for the unconsolidated undrained triaxial test on cohesive soils, ASTM D4767 for the consolidated undrained test with pore pressure measurement, ASTM D7181 for the consolidated drained test and ASTM D5311 for the cyclic triaxial test. This page prints none of their pressures, rates, tolerances or times, and no edition year: those come from the method the customer names and from the soil. Approval of a system, or of a test result, rests with the customer and the authority they name; none is claimed here
Configurations	A static triaxial system, a combined static and cyclic system, and a controller set for a customer's own frame
Scope Boundary	This page is the triaxial test system. It is not a servo-hydraulic fatigue test system, which loads metal specimens in a frame (see servo-hydraulic fatigue and structural test system), not a deep ocean pressure simulator, which squeezes equipment in a chamber (see deep ocean pressure simulator) and not a pressure calibration bench (see pressure calibration bench). A rock testing machine, a direct shear box and a consolidation cell are different equipment again. No certification is claimed here
Status	Neometrix has quoted against successive triaxial test system requirements, and no delivered triaxial test system is claimed.

Configurations

One method, three ways to build the system.

The method, the saturation check and the record are shared. What changes is how fast the load can be applied and whether the customer already has a frame.

Static triaxial system

Frame, cell and controllers

A screw-driven or hydraulic frame, a cell and pressure controllers for saturation, consolidation and shearing in drained and undrained tests.

Combined static and cyclic system

Fast actuator and stable loop

The same cell and controllers with an actuator and a control loop fast enough for cyclic loading, and software that records every cycle.

Controller set

For a customer's own frame

Cell pressure and back pressure controllers, transducers and software added to a frame the laboratory already owns.

And the part that is not equipment at all, yet decides all three: the test plan. It fixes the stages of each test, how saturation is checked, how fast the load is applied, and what is recorded. It is written from the soil and the question asked of it, not from the frame.

Where it is used

Wherever the ground carries a load, and the water decides how much.

The common thread is a soil whose strength depends on the water in it, and a design that needs that strength.

Geotechnical laboratories

Where soil from a site is tested for strength and stiffness before a foundation or an embankment is designed.

Academic and research laboratories

Where the behaviour of soil under stress, and under repeated loading, is studied and taught.

Foundation and slope design

Where strength measured in effective stress feeds the design of a footing, a cut or a slope.

Earthquake studies

Where cyclic tests show how a saturated soil softens as the pore pressure builds.

Watch

See it in motion.

A short walkthrough video of the triaxial test system.

FAQ

Common questions.

Longer answers, for readers who want the reasoning.

Q · 01 What does a triaxial test system actually do?

It tests a soil specimen under stresses like those in the ground. The specimen is sealed in a membrane and set in a cell. The cell pressure squeezes it from all sides, and a ram then loads it along its axis. The system controls both, measures the pressure of the water in the specimen and the water that moves in or out, and records the load and the deformation. From that the strength and stiffness of the soil are worked out. It does not take the sample from the ground, it does not prepare the specimen for you, and it does not replace the engineer's judgement.

Q · 02 Why does soil feel the stress the water leaves?

Because a soil is grains with water between them, and water cannot carry a shear. The water carries part of the total stress as pressure, and only the rest reaches the grains. That rest is the effective stress, the total stress less the pore pressure. Strength and stiffness follow the effective stress. Two specimens under the same total stress can therefore behave quite differently if the water in them is at a different pressure, which is why the pore pressure is a reading and not an afterthought.

Q · 03 Why is the specimen saturated first, and how is that proved?

Because the effective stress rule assumes the pores are full of water. Air in the pores makes the water pressure respond softly and slowly. The system raises the cell pressure and a back pressure together, which pushes the air into solution. It then raises the cell pressure alone for a moment and watches the pore pressure. If the pore pressure follows almost fully, the specimen is saturated. If it does not, the stage is repeated. The check goes into the record, so that a later reader can see the reading was trustworthy.

Q · 04 Why does it matter whether the test is drained or undrained?

Because the soil answers a different question in each. If the water is kept in, the pore pressure rises or falls as the soil is sheared, and the test shows the strength before the water has moved. If the water is let out, and the loading is slow enough for it to move, the pore pressure stays where it was set and the test shows the strength after the water has had time. A fast job such as a sudden load and a slow one such as a long-term embankment ask for different tests, and the system has to be able to run both.

Q · 05 Is this the same as the servo-hydraulic fatigue system, the deep ocean pressure simulator or the pressure calibration bench?

No, and the differences are worth stating precisely. The servo-hydraulic fatigue and structural test system page covers a stiff frame that loads metal specimens and structures. The deep ocean pressure simulator page covers a chamber that squeezes equipment from every side. The pressure calibration bench page covers comparing a transducer with a reference pressure. This page is the triaxial test system. A rock testing machine, a direct shear box and a consolidation cell are different equipment again. It does not replace any of them, and it does not claim what they claim a second time.

Q · 06 Has Neometrix built one of these?

We would rather answer this plainly than let a page imply otherwise. Neometrix has quoted against successive triaxial test system requirements, and no delivered triaxial test system is claimed. What stands behind the offer is adjacent: Neometrix engineers a servo-hydraulic fatigue and structural test system (see the servo-hydraulic fatigue and structural test system page), a deep ocean pressure simulator (see the deep ocean pressure simulator page) and a pressure calibration bench (see the pressure calibration bench page). The load frames, actuators, pressure controllers, transducers and data loggers are catalogue items, bought in, not invented. What Neometrix engineers is the system around them: the frame and cell, the pressure and pore-water lines, the control, the saturation check and the record, the procedure and the test plan. So the honest position is that the system is engineered to order, the neighbouring disciplines are in the building, and the first system of this exact kind will be built around the customer's own soils and specimens rather than taken off a shelf.

Q · 07 Which standard applies, and what can the system not do?

ASTM D2850 is the public method for the unconsolidated undrained triaxial test on cohesive soils, ASTM D4767 covers the consolidated undrained test with pore pressure measurement, ASTM D7181 covers the consolidated drained test and ASTM D5311 covers the cyclic triaxial test. This page prints none of their pressures, rates, tolerances or times, and no edition year: those come from the method the customer names and from the soil. The system tests a specimen and keeps a record. It does not certify a soil or a design: this page claims no certification or accreditation. No pressure, stress, rate or quantity figure is printed here, and approval for use rests with the customer and the authority they name; none is claimed here.

Q · 08 What do you need from us to quote?

Six things, and most of them describe your tests rather than the system. First, the specimens: their diameter and height, and whether they are intact or remoulded. Second, the tests: which of the undrained, drained and cyclic tests you want to run. Third, the stress range: the cell pressure and the axial load you need to reach. Fourth, the cyclic duty, if any: the loading pattern and how fast it must run. Fifth, the frame: whether you want a new one or a controller set for your own. Sixth, the record: what you want kept for each test. From that we come back with a system concept, a written test plan you can check, and a budgetary price.

The neighbouring test and pressure pages, and how they differ from this one.

Three neighbours: one loads metal, one squeezes equipment, one checks a pressure reading.

↗ Loading metal

Servo-Hydraulic Fatigue & Structural Test System

A stiff frame and a servo-hydraulic actuator that load metal and structure - a frame for solids, where this page loads soil with water in it.

↗ Squeezing equipment

Deep Ocean Pressure Simulator

High-pressure chambers that squeeze subsea equipment from every side - a chamber for equipment, where this page squeezes a soil specimen and measures the water in it.

↗ Checking a pressure reading

Pressure Calibration Bench

A gauge or transducer compared with a reference pressure built from mass, area and gravity - the check that a pore pressure reading depends on.

Browse all Neometrix product lines.

Get a quotation

Tell us the soil, the tests,
and the stresses you need.

The projects desk replies within two working days with a system concept, a written test plan you can check, and a budgetary quotation. Write to [email protected] or use the form.

Enquire — triaxial system Capability sheet (PDF) +91 7777 876 876

ISO 9001 / 14001 ENGINEERED-TO-ORDER CLASS — TRIAXIAL TEST SYSTEM SPECIFY · FRAME · CONTROL · BUILD · TEST · PROVE — SOIL FEELS THE STRESS THE WATER LEAVES ENGINEERED IN NOIDA · INDIA