Triaxial test pdf

Click here to sign up. Download Free PDF. Meaghan Gail. A short summary of this paper. Download Download PDF. Translate PDF. This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade TBT Committee.

A number in parentheses indicates the year of last reapproval. Scope test results in units other than SI shall not be regarded as 1. In this system, the pound soil. Specimens are isotropically consolidated and sheared in lbf represents a unit of force weight , while the unit for mass compression without drainage at a constant rate of axial is slugs.

This implicitly combines two axial load, axial deformation, and pore-water pressure. Generally, standard. However, the use of balances or scales recording 1. Density is mass per unit volume whereas unit weight is force per unit volume. In this standard density is 1. After the density has been determined, guidelines for significant digits and rounding established in the unit weight is calculated in SI or inch-pound units, or both.

Practice D It is the calculated, or recorded in this standard are regarded as the responsibility of the user of this standard to establish appro- industry standard. In addition, they are representative of the priate safety, health, and environmental practices and deter- significant digits that generally should be retained. The proce- mine the applicability of regulatory limitations prior to use. It is beyond the scope of this test method to ization established in the Decision on Principles for the consider significant digits used in analysis methods for engi- Development of International Standards, Guides and Recom- neering design.

The values given in parentheses are provided for information only and are not considered standard. Reporting of 2. Referenced Documents 2. Published April Last previous edition approved in as D— No further reproductions authorized. This shear strength may solidation Properties of Soils Using Incremental Loading be applied to field conditions where full drainage can occur D Test Method for Unconsolidated-Undrained Triaxial drained conditions or where pore pressures induced by Compression Test on Cohesive Soils loading can be estimated, and the field stress conditions are D Practice for Minimum Requirements for Agencies similar to those in the test method.

The precision of this test method is dependent on the competence of the personnel performing it and the suitability of the Construction Materials Testing equipment and facilities used.

Agencies which meet the criteria of Practice D Practice for Using Significant Digits in Geotechnical D are generally considered capable of competent testing. Users of Data this test method are cautioned that compliance with Practice D does not ensure reliable testing. Reliable testing depends on several factors; 3. Terminology Practice D provides a means of evaluating some of those factors.

Apparatus nical terms, refer to Terminology D See Fig. The rate of the specimen. Vibration due to the operation defined strain for a test specimen. Failure is often taken to of the loading device shall be sufficiently small to not cause correspond to the maximum principal stress difference maxi- dimensional changes in the specimen or to produce changes in mum deviator stress attained or the principal stress difference pore-water pressure when the drainage valves are closed.

Significance and Use accuracy prescribed in this paragraph and may be a part of the 4. The axial load-measuring device shall be pression depends on the stresses applied, time of consolidation, capable of measuring the axial load to an accuracy of within strain rate, and the stress history experienced by the soil. If the load-measuring device is located inside the triaxial compression chamber, it shall be 3 The last approved version of this historical standard is referenced on insensitive to horizontal forces and to the magnitude of the www.

The chamber shall provide a effective consolidation stress and the back pressure. It shall connection to the cap. It is desirable to use a in axial load due to friction does not exceed 0. The top piston during loading. The baseplate shall have an inlet NOTE 4—The use of two linear ball bushings to guide the piston is through which to fill the chamber, and inlets leading to the recommended to minimize friction and maintain alignment.

The device must be able to pressures greater than kPa. The vacuum-control device withstand the maximum back pressure. The piston travel shall be capable of applying and controlling pressures or partial vacu- measured with an accuracy of at least 0.

These tests can require a test specimen height. The deformation indicator shall have a range duration of several day. They shall be constructed of a rigid, noncorrosive, devices shall be capable of measuring pressures or partial impermeable material, and each shall, except for the drainage vacuums to the tolerances given in 5.

They may consist of provision, have a circular plane surface of contact with the electronic pressure transducers, or any other device capable of porous disks and a circular cross section. It is desirable for the measuring pressures, or partial vacuums to the stated toler- mass of the specimen cap and top porous disk to be as minimal ances.

If separate devices are used to measure the chamber as possible. If the mass is greater than 0. Since the applied axial load at failure and greater than 50 g, the axial load chamber and back pressure are the pressures taken at the must be corrected for the mass of the specimen cap and top mid-height of the specimen, it may be necessary to adjust the porous disk.

The diameter of the cap and base shall be equal to calibration of the devices to reflect the hydraulic head of fluids the initial diameter of the specimen. The specimen base shall in the chamber and back pressure control systems. During undrained shear, the pore-water relative to the vertical axis of the specimen does not exceed 1. The end of the piston and specimen cap contact as possible is allowed to go into or out of the specimen. To area shall be designed so that tilting of the specimen cap during achieve this requirement, a very stiff electronic pressure the test is minimal.

The cylindrical surface of the specimen transducer or null-indicating device must be used. With an base and cap that contacts the membrane to form a seal shall be electronic pressure transducer the pore-water pressure is read smooth and free of scratches.

With a null-indicating device a pressure control is 5. The disks shall be the pore-water pressure. Both measuring devices shall have a regularly cleaned by ultrasonic or boiling and brushing and compliance of all the assembled parts of the pore-water checked to determine whether they have become clogged.

If filter strips or system due to a pore pressure change, mm3 in. To avoid hoop tension, filter specimen and the measuring device should be short and thick-walled with small bores. To measure this compliance, assemble the triaxial cell periphery. Filter-strip cages have been successfully used by without a specimen. Then, open the appropriate valves, increase the many laboratories.

Membranes shall be carefully inspected prior to use is no direct contact with sunlight. The membrane tent cans, and data sheets shall be provided as required.

An equation for 6. The average height- the effect of the stiffness of the membrane is given in If, after completion of a test, it is found based on valves may result in inaccurate volume change and pore-water visual observation that oversize particles are present, indicate pressure measurements. For this reason, valves in the specimen this information in the report of test data A valve may be NOTE 10—If oversize particles are found in the specimen after testing, a particle-size analysis may be performed on the tested specimen in assumed to produce minimum volume change if opening or accordance with Test Method D to confirm the visual observation and closing the valve in a closed, saturated pore-water pressure the results provided with the test report All valves must be capable of withstanding 6.

Samples shall be preserved and transported change characteristics; however, any other type of valve having suitable in accordance with the practices for Group C samples in volume-change characteristics may be used. Specimens obtained by tube sam- 5.

Handle speci- the specimen. If compression or any type calipers for measuring the diameter. Prepare trimmed specimens, in an entered the tube and with minimum disturbance of the sample. Where removal of to avoid bending stresses on the core due to gravity. Conditions pebbles or crumbling resulting from trimming causes voids on at the time of sample removal may dictate the direction of the surface of the specimen, carefully fill the voids with removal, but the principal concern is to minimize the degree of remolded soil obtained from the trimmings.

If the sample can disturbance. Trim the surfaces with the steel 5. Perform one or more water content determina- quirements of Specification D readable to four significant tions on material trimmed from the specimen in accordance digits. Reconsituted specimens may be prepared by be subtracted from the measurements. Specimens may be reconstituted to pressure measurement device with deaired water. The top of each layer shall be scarified prior to the porous disks and specimen, saturate the paper with water prior addition of material for the next layer.

The tamper used to to placement. After a specimen is formed, with and wipe away all free water on the disk. The failure envelopes will usually be a horizontal line for saturated specimens and a curved line for partially saturated specimens.

The unconsolidated-UNDRAINED shear strength is applicable to situations where the loads are assumed to take place so rapidly that there is insufficient time for the induced pore-water pressure to dissipate and for consolidation to occur during the loading period that is, drainage does not occur.

The tangent to these circles is then drawn to provide a reasonable good observation. The soil has an UNDRAINED strength known as Su, this is taken as the interception of the shear stress which is on the y axis, after this the slope is obtained, which is done by on the failure envelope line. Compressive strengths determined using this procedure may not apply in cases where the loading conditions in the field differ significantly from those used in this test method.

In the consolidation stage, the cell pressure is increased to a chosen amount, which provides a uniform confining stress all around the specimen, which signifies the preliminary point of the next stage which is the shear stage. In the shear stage a load is applied vertical through the ram, this loads causes an increase in stress at the top of the specimen.

The vertical stress is increased until the specimen fails. Samples of saturated soil, about 38mm diameter were obtained from a larger sample, most likely from a trial pit or a borehole investigation.

Each of the samples obtained were pushed the end of its tube, with the aid of a screw jack extruder fixed to the bench. The end square is then cut using a palette knife when the first 10mm has been extruded. After this a further 76 mm was cautiously extruded and this 76mm of the specimen was then cut off from the clay remaining in the tube. In order to prevent any drying out the sample is then wrapped in cling film.

After which a base loading cap was then placed on top. A rubber membrane was then placed upon the loading cap, pedestal and sample. This was done initially, by placing the membrane inside the membrane stretcher tube and bending the ends over outside ends of the tube.

In order for the membrane to be slipped over the sample, suction was required. The ends of the membrane were released onto pedestal and loading cap when the membrane is in position. Then the Perspex cylinder and cell top was slowly raised over the sample, and on top of the three bolts which it is secured firmly with wing nuts. This is shown by small deflection, maybe 2 divisions, as observed from the dial gauge.

In this lab test, the machine was switched off when the proving ring gauge started going backwards. Then the Perspex cylinder top was removed and the soil sample extracted. Shear strength of fissured clays adopted from Barnes. When drainage becomes allowable, the volume of the sample will decrease. This was measured by the strain dial gauge which indicates the change in length of the specimen. Drainage conditions during shearing will heavily affect the strength parameters of the soils.

The specimen in the experiment was subject to compressive stresses set along three orthogonal axes, applied in two stages. The test was continued by increasing the axial load as the cell pressure is held constant. The compressive stress is increased with deviator stress. Graphs were used to analyse the data, as plots shows the stress condition at failure for each test. Failure occurs at the peak of the graph as shown above on the different specimens used.

Ultimate strength- From the graph it is observed that there is an increase cell pressure applied, in proportional to the peak strength. This is due to the resistance of the soil. The soil with the greatest cell pressure is having the greatest resistance as seen in figure 2. Residual strength- It is observed that there is an increase cell pressure applied, in proportional to the residual strength.

Critical state strength- Sometimes referred to as to the ultimate strength mostly in loose sand or soft clay. After a significant amount of shear strain, a soil will achieve a constant volume state and it will continue to shear at this constant volume without change in volume or void ratio. It is observed that specimen with the intermediate cell pressure specimen 2 has the greatest critical state strength, due to the specimen having the longest constant shear.

There is no shear stress developed on the sides, but only on the vertical and lateral axial planes, these were then referred to as the principal stresses. As the specimen shortens under the load, the diameter will increase in dense or over consolidated samples in which the specimen may shear clearly along the slip surface as the peak stress is reached. In lightly over-consolidated soil the shear will be less clear.

From the failure mode of the specimen it is observed that the soil is an over consolidated soil with physical evidence of fissures. Fissures exists in most over consolidation clays producing planes of weakness. The shear strength of a cohesive soil depends upon the degree of saturation, pressure and drainage conditions. During testing, the drainage valve was closed during the consolidation stage, this caused the soil not to gain any strength during this phase. This then proves that this was a failed lab test.

The expected theoretical value is equal to zero. Failure is due to the soils being compacted with few air void contents present and the test being a multistage UU test. In a multistage process, shear stress is applied under confining pressure at a slower rate to allow more readings to be taken.

The steps in stress-strain curve are as a result of the initial stiffness increase caused when the cell pressure was increased.