This standard outlines the procedure for evaluating the unconfined compressive strength of clayey soil samples, including undisturbed, remoulded, or compacted types. The test applies axial loading until failure in an undrained condition, offering essential parameters for geotechnical stability and design assessments.
Overview
This standard outlines the procedure for evaluating the unconfined compressive strength of clayey soil samples, including undisturbed, remoulded, or compacted types. The test applies axial loading until failure in an undrained condition, offering essential parameters for geotechnical stability and design assessments.
Audience
Contents
Structure
This section defines the extent and application of the test for determining the unconfined compressive strength of soil samples. Essential initial measurements include specimen diameter, length, cross-sectional area, volume, mass, density, water content, saturation degree, and soil specific gravity. Key formulas for axial strain, cross-sectional area under load, compressive stress, unconfined compressive strength, and undrained shear strength are presented. Observations cover deformation readings, failure mode sketches, and moisture content determination from failed specimens.
This part highlights related standards referenced for sampling and water content determination, including IS 2132 and IS 2720 Part 2. It lays out the necessary data tables for specimen dimensions and test parameters. A procedural flowchart illustrates measurement and calculation steps from initial specimen preparation to strength determination, emphasizing the need to consult the latest BIS revisions.
Defines terms such as soil specimen types (undisturbed, remoulded, compacted), initial dimensions, physical properties, and test parameters. Includes detailed formulas for axial strain, cross-sectional area changes during loading, compressive stress, and strength parameters. Clarifies the significance of each measurement and observation for test accuracy.
Describes the requirements for compression devices capable of controlled axial loading, including screw jacks with proving rings and hydraulic systems. Details the need for precision measuring tools such as vernier calipers and timing devices to ensure accurate specimen dimensioning and strain rate control. Lists additional equipment like specimen trimming tools and water content containers.
Specifies minimum specimen diameter, allowable maximum particle size relative to specimen diameter, and recommended height-to-diameter ratios. Emphasizes precise measurement techniques and specimen shaping for consistent test results. Provides tables summarizing specimen size requirements and preparation steps to ensure compliance with standard.
Outlines the stepwise method for conducting the unconfined compression test, including specimen details, loading application, deformation measurement, and calculation of stress and strain. Specifies observation protocols such as failure mode documentation and water content measurement post-test. Advises on apparatus calibration and data recording for test reliability.
Presents formulas and procedures for calculating axial strain, instantaneous cross-sectional area, and compressive stress. Describes plotting stress versus strain curves to identify peak compressive strength. Provides guidance for interpreting failure patterns and recording moisture content variations before and after testing.
Details the format for recording soil sample data, apparatus calibration, specimen characteristics, and test observations. Includes tables for deformation, strain, force, and stress values, along with remarks on failure type and particle size. Covers post-test requirements such as sketching failure modes and documenting moisture content.
Provides a pro forma template for systematically documenting all relevant details during the unconfined compression test, including soil sample description, apparatus particulars, specimen dimensions, and compression test results. Includes key formulas and instructions for accurate computation of test parameters and comprehensive reporting.
Frequently Asked
The unconfined compressive strength test outlined in this standard is intended primarily for clayey soils. Suitable specimens include undisturbed samples preserving natural structure, remoulded soils that have been disturbed and reworked, and compacted samples prepared in the laboratory to specified densities. The test is not recommended for soils containing significant amounts of sand or silt due to their lack of cohesion and potential for unreliable results.
Specimens must have a minimum diameter of 38 mm, with the largest particle size not exceeding one-eighth of the specimen diameter (approximately 4.75 mm for a 38 mm diameter specimen). The height-to-diameter ratio should range between 2 and 2.5 to ensure valid test results. Specimens should have a uniform circular cross-section with ends cut perpendicular to the axis. Measurements must be made with an accuracy of ±0.1 mm using vernier calipers or equivalent tools.
Recommended equipment includes a compression device capable of applying controlled axial load, such as a platform scale with screw-jack or a hydraulic loading system equipped with a calibrated proving ring. Vernier calipers with 0.1 mm precision are used for specimen dimension measurements, while timing devices with 1-second accuracy are necessary for controlling strain rates during testing. Additional tools include specimen trimming instruments and containers for water content determination.
The unconfined compressive strength is obtained by plotting the axial compressive stress against axial strain during the test and identifying the maximum stress value. If no peak stress is observed before 20% axial strain, the stress at 20% strain is taken as the strength. Calculations involve determining axial strain from deformation, adjusting the cross-sectional area assuming volume constancy, computing compressive stress from applied load and area, and analyzing the stress-strain curve accordingly.
No, the unconfined compressive strength test is not appropriate for soils containing significant amounts of sand or silt. Such soils lack sufficient cohesion to maintain specimen integrity without lateral confinement, which leads to unreliable test results. For sandy or silty soils, alternative tests like triaxial shear or direct shear tests that apply lateral confinement should be employed.
Ask AI about any clause, requirement, or provision in IS 2720 PART 10. Get instant, clause-cited responses powered by our indexed library.
Free tier includes 150 queries (50 AI + 100 Reference) · No credit card required