This standard outlines the procedure for performing plate load tests on soil to evaluate its ultimate bearing capacity and subgrade reaction modulus. It is intended for professionals involved in evaluating soil properties for foundation design of various structures. The document covers equipment requirements, loading techniques, data collection, and analysis of load-settlement relationships across different soil conditions.
Overview
This standard outlines the procedure for performing plate load tests on soil to evaluate its ultimate bearing capacity and subgrade reaction modulus. It is intended for professionals involved in evaluating soil properties for foundation design of various structures. The document covers equipment requirements, loading techniques, data collection, and analysis of load-settlement relationships across different soil conditions.
Audience
Contents
Structure
The standard describes the methodology for executing plate load tests aimed at determining soil bearing capacity beneath shallow foundations. It mandates rounding off numerical results in accordance with IS 2-1960, retaining the same significant digits as the reference values. Definitions are adopted from IS 2809-1972 for soil engineering terminology and IS 6403-1981 for allowable bearing pressure criteria. Bearing plates must be fabricated from mild steel, with a thickness of at least 25 mm and sizes ranging from 300 mm to 750 mm, either circular or square. Test setups typically include wooden joists spaced at 300 mm centers for the loading platform, dial gauges combined with plumb bobs for settlement measurements, ball and socket joints for load transfer, and reaction platforms equipped with crossbar channels and loading trusses. Test plates are chequered or grooved and possess handles for placement, with a minimum depth of two-thirds of their width. Recommended plate sizes vary by soil type: 300 to 450 mm for cohesive soils and 450 to 750 mm for cohesionless soils. Rounding off follows IS 2-1960 rules to maintain consistency and accuracy.
This section consolidates essential references and specifications related to the execution of plate load tests. Bearing plates must be mild steel with a minimum thickness of 25 mm and size between 300 mm and 750 mm, shaped circular or square. Rounding off numerical values is governed by IS 2-1960, ensuring the same number of significant figures as prescribed. The glossary and terminologies refer to IS 2809-1972 and IS 6403-1981. Typical test apparatus includes wooden joists spaced at 300 mm centers, ball-and-socket joints for load application, and test plates with a depth of at least two-thirds the width, featuring chequered or grooved bases for enhanced grip. Illustrations cover gravity loading platforms, reaction loading platforms, loading trusses, and detailed test plate features.
Key equipment for plate load testing includes ball and socket arrangements that facilitate flexible load transmission. Loading columns, steel shims, wooden blocks, and collars enable precise alignment and load transfer. Reaction girders fitted with adjustable cradles accommodate the reaction platform setup. Hydraulic jacks must be equipped with calibrated load measurement devices such as pressure gauges, electronic load cells, or proving rings. Plate dimensions are specified according to soil types (cohesive, cohesionless, partially cohesive). All final test values require rounding per IS 2-1960, matching the significant figures of the original specified values.
The testing procedure mandates adherence to specified arrangements for plate bearing tests, including documentation of test elevation, the natural water table, and the profile of the test pit. Appropriate bearing plate sizes must be selected based on the soil classification — smaller plates for cohesive soils, larger for cohesionless. Continuous recording of time, load, and settlement is required, with notation of any anomalies in setup. Rounding of final results follows IS 2-1960 guidelines. Plate diameters typically range from 300 mm for cohesive soils to between 450 mm and 600 mm for cohesionless. Zero correction must be applied to settlement data, and load-settlement curves for cohesionless and partially cohesive soils should be plotted on log-log scales for proper interpretation.
Final results must be rounded according to IS 2-1960, preserving the same significant figures as specified. Bearing plates are mild steel, circular or square, with a minimum thickness of 25 mm and size between 300 mm and 750 mm. The formula to estimate footing settlement (St) from plate settlement (Sp) is: St = Sp × [B × (Bp + 0.3)] / [Bp × (B + 0.3)], where B represents footing width, Bp is plate width, and Sp is measured settlement. Continuous data recording includes time, load, settlement, test elevation, water table level, test pit profile, and bearing plate details. Load-settlement curves assist in determining safe bearing pressures for various soil types, including loose to medium cohesionless, dense cohesionless, cohesive, and partially cohesive soils.
During testing, continuous recording of time, applied load, and settlement measurements is essential. Additional details such as test elevation, natural water table level, test pit profile, bearing plate size, and any irregularities must be documented. Numerical values must be rounded as per IS 2-1960, maintaining the significant digits of specified values. Bearing plates should be mild steel, at least 25 mm thick, and sized between 300 mm and 750 mm, featuring chequered or grooved undersides for better grip. Settlement is measured using dial gauges with 25 mm travel and 0.01 mm accuracy. Typical apparatus includes wooden joists spaced at 300 mm centers on the loading platform and ball & socket fixtures to ensure accurate load transfer.
The test evaluates soil behavior only to a depth less than two times the plate width, while actual foundations may engage deeper soil strata influencing settlement and shear strength. Variability in shallow soil properties can lead to misleading results. The test does not reliably predict ultimate settlements, particularly in cohesive soils. For clayey soils, shear-based bearing capacity values are nearly independent of plate size, but settlement responses may differ. Loading platforms must be positioned at least 1 m above the pit bottom, supported beyond 2.5 m from the test area, and free of any supports within 3.5 times the plate radius to avoid interference. It is advised to complement plate load tests with comprehensive soil investigations as per IS 1892 for a more accurate foundation design.
Final test and analysis values require rounding as per IS 2-1960, maintaining the number of significant digits. Test setups utilize calibrated hydraulic jacks fitted with load measuring instruments such as pressure gauges, load cells, or proving rings. Loading platforms typically consist of wooden joists spaced 300 mm apart, supporting mild steel bearing plates with thickness at least 25 mm and sizes between 300 mm and 750 mm. Precision displacement measurements employ dial gauges with plumb bob assemblies, securely clamped to avoid movement errors. Ball and socket joints ensure uniform load application. These measures collectively enhance safety and accuracy during plate load testing.
Annexures specify bearing plates as mild steel, minimum 25 mm thick, ranging from 300 mm to 750 mm in circular or square shapes. Excavation depth beneath the test plate must extend to twice the plate dimension. Rounding of numerical results follows IS 2-1960, preserving significant figures. Illustrations include gravity loading platforms with wooden joists spaced at 300 mm centers, reaction loading platforms with ball and socket arrangements, loading trusses, chequered/grooved test plates with handles and center markings, and load-settlement curves plotted on log-log scales. Plates may be cast-in-situ or precast concrete blocks meeting minimum depth requirements. Settlement measurements employ dial gauges with plumb bob devices for accuracy.
Frequently Asked
The standard requires bearing plates made of mild steel with a minimum thickness of 25 mm. Plates can be either circular or square, with sizes ranging from 300 mm up to 750 mm depending on soil conditions. For clayey or silty soils and loose to medium dense sandy soils (N-value less than 15), a 450 mm square plate is typically used. For dense sandy or gravelly soils (N-value between 15 and 30), plates can range from 300 mm to 750 mm, ensuring the plate size is at least four times the largest soil particle size. Plates must have a chequered or grooved underside to enhance grip, be centered and leveled on a fine sand layer not exceeding 5 mm thickness, and the loading apparatus aligned vertically using a ball and socket joint.
Load increments must be applied in equal cumulative steps, with each increment not exceeding 1 kg/cm² or one-fifth of the estimated ultimate bearing capacity, whichever is less. Loads should be applied gradually, avoiding impact, fluctuations, or eccentricity. When using hydraulic jacks, load measurements are taken remotely via pressure gauges connected through pipes to prevent interference near the test plate. Before commencing load increments, a seating pressure of at least 70 g/cm² must be applied and removed. Load must be applied centrally and vertically, utilizing ball and socket joints to ensure no eccentric loading. The dead weight of the equipment should be recorded prior to loading increments.
IS 1888 identifies four typical load-settlement curve types: Curve A corresponds to loose to medium cohesionless soils with an initial linear portion followed by a flattening without a distinct failure point. Curve B represents cohesive soils with a slightly curved initial segment and a clear failure point indicated by a steep settlement increase. Curve C is characteristic of partially cohesive soils, exhibiting combined features of Curves A and B. Curve D depicts dense cohesionless soils, showing a well-defined failure point. Settlement readings must be zero-corrected. For soils without distinct failure points (Curves A and C), plotting load versus settlement on logarithmic scales aids in determining yield points, whereas Curves B and D allow direct observation of ultimate bearing capacity.
In dense sandy soils, bearing capacity tends to increase with larger plate sizes; smaller plates generally produce conservative, lower values. To accurately estimate foundation capacity, tests should be conducted using a minimum of three different plate sizes ranging from 300 mm to 750 mm, with results extrapolated to the actual foundation size. For clayey soils, the bearing capacity based on shear strength is nearly independent of plate size, though settlement behavior may vary. Plates must be at least four times the size of the largest soil particles. Since plate load tests only reflect soil response to a depth about twice the plate width, larger foundations may engage deeper soil layers not captured by small plate tests.
To achieve precise and reliable data, the loading platform must be supported at a minimum distance of 2.5 meters away from the test area and elevated at least 1 meter above the bottom of the test pit. No supports should exist within a radius of 3.5 times the plate size center to prevent interference. The test plate should rest on a fine sand layer no thicker than 5 mm, be centered using a plumb bob, and leveled with a spirit level to avoid eccentric loading. The hydraulic jack should be positioned centrally over the plate with a ball and socket joint to maintain vertical load application. A seating pressure of at least 70 g/cm² should be applied and removed before testing. Continuous recording of time, load, settlement, test elevation, water table level, pit profile, and plate characteristics is essential for data accuracy.
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