Advanced Triaxial Testing Equipment
NL 5019 X

Standard : BS 1377:7, BS 1377:8, ASTM D4767, ASTM D2850, ASTM D7181, AASHTO T297

Advanced Triaxial Testing Equipment

Triaxial Testing Equipment is used to measure the behavior of soils under different stress-strain and shear strengths, providing soil insights into their mechanical properties, including strength and deformation characteristics. The data is used for many soil engineering purposes such as ground, foundations, slopes, excavations, and embankments.

The test is mostly performed on cylindrical soil samples of Ø 38 mm to 150 mm, with a height twice its diameter. The soil sample is then subjected to different levels of confining pressure while also applying stress along its vertical axis while applying fluid pressure in perpendicular directions and deformations are recorded until failure. This allows engineers to simulate various stress conditions that the soil might experience in the field. By measuring the soil's response to these stresses, engineers can determine parameters such as shear strength, cohesion, and internal friction angle, which are crucial for designing foundations, retaining structures, and other geotechnical projects.

Three Types of Triaxial Tests Can Be Performed

Unconsolidated Undrained (UU) Test:

• In the UU test, the soil sample is not subjected to any consolidation (i.e., no application of axial stress to compact the sample) before the test begins.
• The confining pressure is applied to the soil sample, and then it is rapidly sheared without allowing time for consolidation.
• During the shearing process, pore water pressure is allowed to build up without being dissipated (undrained condition).
• This test is typically used to assess the undrained shear strength of soils, which is crucial for analyzing the stability of quick-loading conditions such as during an earthquake or rapid construction.

Consolidated Undrained (CU) Test:

• In the CU test, the soil sample is first subjected to a process of consolidation, where an axial load is applied gradually over time to compact the soil.
• Once the consolidation process is complete, the confining pressure is applied to the soil sample, but no drainage of pore water is allowed during the shearing process.
• The CU test is used to determine both the drained and undrained shear strength of soils under different levels of confinement.
• This test is particularly useful for analyzing soil behavior in conditions where drainage is restricted, such as beneath the foundation of a structure.

Consolidated Drained (CD) Test:

• In the CD test, similar to the CU test, the soil sample is first subjected to consolidation to remove any excess pore water and achieve a stable state.
• However, in the CD test, drainage of pore water is allowed during the shearing process, meaning that excess pore water pressure is dissipated as the test progresses.
• The CD test is used to determine the drained shear strength of soils under different levels of confinement.
• This test is relevant for analyzing soil behavior in situations where drainage is unrestricted, such as in embankments or slopes subjected to steady-state loading conditions.

A) Triaxial Load Frame - NL 5019 X / 003 & 006 - P 001

Triaxial Load Frame is used to apply axial and confining pressures to the soil sample while allowing for precise control and measurement of these pressures. The frame consists of a precise CNC machined high-performance and advanced load frame which is heavy-duty with a rigid two-column design, providing extremely stable and consistent loading during the test. High-accuracy microprocessor control system loading for precise speed control to perform tests within 0.00001 to 9.99999 mm/min. High-quality luxury touchpad panel for monitoring and recording various parameters such as axial load, confining pressure, deformation, and pore water pressure.

Key Features of Triaxial Load Frame

• Large easy-to-read LED screen display. 
• Versatile high-quality keypad. 
• Connectable to datalogger for computer control, parameters display, and analysis. 
• Full variable speed setting from 0.00001 to 9.99999 mm/min. 
• Adopt a silent and stable operation, ensuring no vibration during the test. 
• Designed to perform dedicated Triaxial tests – UU, CU, and CD. 
• Ideal for research laboratories and advanced testing that require high-quality tests and high repeatability.

Technical Specifications of Triaxial Load Frame

Accessories for Triaxial Load Frame

B ) Advanced Pressure Volume Controller

NL Scientific Advance Pressure Volume Controller provides both the required pressure and volume measurements of water. The oil-free mechanism uses a high-precision stepper motor ensuring the pressure supplied is consistent & self-adjusts to preset pressure should there be an increase or decrease of pressure. Fine control of water pushes water at 1mm³ resolution for precise back pressure measurement.

Features of Advanced Pressure Volume Controller

• Easy set pressure via keypad and display. 
• Convenient table top size, to replace conventional bulky, noisy & dangerous air compressor. 
• Long lasting high precision & silent stepper motor operation. 
• Dual-purposed – acts as either the main controller for cell pressure or volume change. 
• Connect PC for display & easy control of pressure and volume change.

Technical Specification of Advanced Pressure Volume Controller

C) Compatible Version Laptop with Stress Path Triaxial Testing System Software

Automatic data acquisition function, with steps for a complete triaxial test from saturation, consolidation & shearing. The software allows users to perform complete triaxial tests with ease, which are the standard UU, CU & CD tests. Simple & clear setting of basic test information. Even beginners will find it easy to use, as the software is designed to be user-friendly for any type of user.

Features of Triaxial Testing System Software

• Simple & clear setting of basic test information. 
• Selection of acquisition, saturation, UU, CU & CD functions. 
• Automatic or manual control of triaxial stages according to BS & ASTM. 
• Real-time display of cell, pore & back pressure. 
• Calibration function for all parameters display. 
• Unlimited data storage via computer hard disk. 
• Control directly triaxial frame & pressure volume controller from PC.

Triaxial Cell

Precisely made of high-quality aluminum alloy and highly resistant acrylic cell cylinder to withstand a maximum pressure of 2000 kPa. Fitted with industrial-grade quality on/off valves for cell pressure, back pressure & pore pressure hose connections. No tools are required for dismantling & assembling the cell, as the clamping rods are tightened & loosen using hand knobs.

Technical Specification of Triaxial Cell

Accessories of Triaxial Testing Equipment

Standards

• BS 1377:7 - This is a British Standard that specifies the method for the consolidation test for soils. Consolidation is a process in which soils undergo a decrease in volume due to the expulsion of water when subjected to a load. This standard outlines the procedure for determining the consolidation characteristics of soils in the laboratory.

• BS 1377:8 - Another British Standard, this one pertains to the test for permeability of soils. Permeability is a measure of how easily water can flow through a soil mass. This standard provides guidance on conducting laboratory tests to determine the permeability of soils.

• ASTM D4767 - This is an ASTM (American Society for Testing and Materials) standard that covers the testing of mechanical soil compaction methods. Soil compaction is the process of increasing the density of soil by reducing the volume of air within the soil mass. This standard outlines procedures for measuring the dry unit weight of soil in a field or laboratory setting.

• ASTM D2850 - This ASTM standard focuses on the unconsolidated undrained triaxial compression test on cohesive soils. Triaxial compression testing is a common method used to determine the shear strength and stress-strain behavior of soils. This standard provides guidelines for conducting such tests on cohesive soils, which are soils composed primarily of fine particles such as clay.

• ASTM D7181 - This ASTM standard addresses the determination of shear strength parameters of soil-rock mixtures using large-scale direct shear testing. It provides guidance on conducting direct shear tests, which are used to determine the shear strength properties of soil-rock mixtures.

• AASHTO T297 - This is a standard published by the American Association of State Highway and Transportation Officials (AASHTO), which outlines the method for determining the percentage of moisture in soils using a microwave oven. Moisture content is a critical parameter in geotechnical engineering as it affects the engineering properties of soils, such as their density and strength.

Test Procedure of Triaxial Testing Equipment

• Sample Preparation:
• Soil samples are carefully prepared according to the required specifications, such as diameter, height, and density. Special attention is given to ensuring that the sample is representative of the in-situ soil conditions.
• The sample is usually trimmed to the desired size and shape using cutting tools and molds.
• Sample Installation:
• The prepared soil sample is placed inside the triaxial cell, a cylindrical chamber equipped with porous stones or filters at both ends to allow water to flow freely while preventing soil particles from escaping.
• The sample is then saturated with water to ensure that it is fully saturated before testing begins. Saturation is typically achieved by applying water pressure or by allowing the sample to soak in water over a period of time.
• Confining Pressure Application:
• Once the sample is saturated, the confining pressure is applied to the soil sample using a pressure control system. This pressure is exerted uniformly around the sample to simulate the lateral stress that soil experiences in the field.
• The confining pressure is gradually increased to the desired level while ensuring that the sample remains intact and does not deform excessively.
• Consolidation (for CU and CD Tests):
• For Consolidated Undrained (CU) and Consolidated Drained (CD) tests, a process of consolidation is performed before shearing the sample.
• During consolidation, an axial load is applied to the sample at a controlled rate to remove excess pore water and achieve a stable state. The rate of consolidation depends on the specific test requirements and soil properties.
• Shearing:
• After consolidation (for CU and CD tests) or immediately (for UU tests), the shearing process begins. An axial load is applied to the soil sample at a constant rate while monitoring the axial deformation.
• In UU tests, drainage of pore water is not allowed during shearing, while in CD tests, drainage is permitted. CU tests fall in between, allowing drainage to some extent.
• The shearing continues until the desired deformation or failure criterion is reached, such as a specified axial strain or shear stress.
• Data Collection:
• Throughout the test, various parameters are measured and recorded, including axial load, confining pressure, axial deformation, pore water pressure, and volume change.
• Real-time data acquisition systems are often used to monitor these parameters and ensure accurate measurements.
• Data Analysis:
• Once the test is completed, the collected data is analyzed to determine key soil properties such as shear strength, cohesion, internal friction angle, and permeability.
• Analysis may involve plotting stress-strain curves, calculating failure envelopes, and interpreting the results in relation to the specific engineering application.
• Reporting:
• Finally, the test results are compiled into a comprehensive report, detailing the testing procedure, equipment specifications, sample characteristics, test results, and interpretations.
• The report provides valuable information for engineers and geotechnical professionals involved in designing and analyzing soil structures and foundations.

How to Operate Advanced Triaxial Testing Machines