Standard Test Methods for One-Dimensional Consolidation Properties of Soils Using Incremental Loading

Importancia y uso:

5.1 The data from the consolidation test are used to estimate the magnitude and rate of both differential and total settlement of soils or earthfill, or both, induced by loading of a structure or additional earthfill. Estimates of this type are of key importance in the design of engineered structures and the evaluation of their performance.

5.2 The test results can be greatly affected by sample disturbance. Careful selection of field sampling techniques and preparation methods of test specimens is required to reduce the potential of disturbance effects.

5.3 Consolidation test results are affected by the magnitude of the load increments. Traditionally, the axial stress applied to the specimen is doubled for each increment resulting in a load increment ratio of one. For intact samples, this loading procedure has provided data from which estimates of the preconsolidation stress, using established interpretation techniques, compare favorably with field observations. Other loading schedules may be used to model particular field conditions or meet special requirements. For example, it may be desirable to inundate and load the specimen in accordance with the wetting or loading pattern expected in the field in order to best evaluate the response. Load increment ratios of less than one may be desirable for soils that are highly sensitive or whose response is highly dependent on strain rate.

5.4 The interpretation procedure specified by these test methods to estimate the preconsolidation stress provides a technique to verify that one set of time readings are taken after the preconsolidation stress is exceeded and that the specimen is loaded to a sufficiently high stress level. Several other evaluation techniques exist and may yield different estimates of the preconsolidation stress. Alternative techniques to estimate the preconsolidation stress may be used when agreed to by the requesting agency and still be in conformance with these test methods.

5.5 Consolidation test results are dependent upon the duration of each load increment. Traditionally, the load duration is the same for each increment and equal to 24 h. For some soils, the rate of consolidation is such that complete consolidation (dissipation of excess pore pressure) will require more or less than 24 h. The apparatus in general use does not have provisions for verification of pore pressure dissipation. It is necessary to use an interpretation technique which indirectly determines that consolidation is essentially complete. These test methods specify procedures for two techniques (Interpretation Procedure 1 and Interpretation Procedure 2), however alternative techniques may be used when agreed to by the requesting agency and still be in conformance with these test methods.

5.6 The apparatus in general use for these test methods do not have provisions for verification of the degree of saturation. Most intact samples taken from below the water table will be saturated to a degree sufficient to assume fully saturated conditions. However, the time rate of deformation is very sensitive to degree of saturation and caution must be exercised regarding estimates for duration of settlements when partially saturated conditions prevail. For intact specimens obtained below the water table, inundation of the test specimen may not significantly change the degree of saturation of the test specimen but rather provides boundary water to eliminate negative pore pressure associated with sampling and prevents evaporation during the test. The extent to which partial saturation influences the test results may be a part of the test evaluation and may include application of theoretical models other than conventional consolidation theory. Alternatively, the test may be performed using an apparatus equipped to saturate the specimen.

5.7 These test methods use conventional consolidation theory based on Terzaghi's consolidation equation to compute the coefficient of consolidation, c_v. The analysis is based upon the following assumptions:

5.7.1 The soil is saturated and has homogeneous properties;

5.7.2 The flow of pore water is in the vertical direction;

5.7.3 The compressibility of soil particles and pore water is negligible compared to the compressibility of the soil skeleton;

5.7.4 The stress-strain relationship is linear over the load increment;

5.7.5 The ratio of soil permeability to soil compressibility is constant over the load increment;

5.7.6 Darcy’s law for flow through porous media applies; and

5.7.7 The deformation (strain) of the soil is one-dimensional in the axial direction.

Note 3: The quality of the result produced by this standard is dependent on the competence of the personnel performing it and the suitability of the equipment and facility used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/inspection. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some, but not all, of those factors.

Subcomité:

D18.05

Referida por:

D6026-21, D4767-11R20, E1266-20, D4829-21, D3213-19, F1962-25, D5321_D5321M-21, D6243_D6243M-20, D5311_D5311M-25, D0653-24A, D4767-11R20, D4546-21, D8296-19, D3080_D3080M-23, D3080_D3080M-23, D4829-21, D5084-24, D5084-24, D6528-24, D4546-21, D5321_D5321M-21

Volúmen:

04.08

Número ICS:

93.020 (Earth works. Excavations. Foundation construction. Underground works)

Palabras clave:

coefficient of consolidation; compressibility; compression curves; consolidation; consolidation test; consolidometer; preconsolidation pressure; preconsolidation stress; primary consolidation; rebound; secondary compression; settlement; swelling;