Soils consolidation testing

A site consists of 66 feet of organic, clayey silt having high plasticity (OH soil) which is to be consolidated for eventual placement of large oil storage tanks. The soil is underlain by mixed strata of sand and silt. Consolidation tests have given, at loads equivalent to 3000 pounds per square... 

Important applications for coupled finite element strategies can be found in the theory of consolidation of partially saturated soils. Some test cases were performed, (see Kohlmeier et al. (2002)) using the Richards formulation. 

Towhata, 1., Kuntiwattanakul, P., Seko, I. Ohishi, K. 1993. Volume change of clays induced by heating as observed in consolidation tests. Soils and Foundations 33(4) pp. 170-183. 

The parameters used in defining the consolidation characteristics of a soil are best illustrated with reference to a laboratory consolidation test. The test can be conducted either with or without back pressure. Use of back pressures insures that the sample is completely saturated. A schematic illustration of a back pressure consolidation test cell is... 

The existing state of consolidation in marine soils can also be predicted by use of a non-desfructive measurement technique (Richards and Chaney, 1997). Using this technique void ratio (e) versus log o relationships can be determined directly. A flowchart of the process is presented in Figure 6.17. Results of the sedimentation consolidation curve from both the nondestructive method and the conventional consolidation test is presented in Figure 6.18 for a site in the Bauer Deep, east of fhe East Pacific Rise and west of Callao. 

Comparison of permeability values measured in the laboratory, and computed from consolidation tests have been reported by Nickerson (1978) and Olsen and Daniel (1979). In addition, Nickerson and Olsen and Daniel both show that the direct determination of permeability gives higher values than back-calculating values from consolidation tests. Nickerson suggests that the discrepancy between the direct determination of permeability in the laboratory and back calculated from the consolidation test are due to the variation of hydraulic gradients and/or the formation of a filter cake at the sediment-porous stone interface during consolidation. Olsen and Daniel (1979) attribute at least part of the discrepancy to the fact that Terzaghi s consolidation theory makes no adjustment for the structural viscosity (creep) of the soil. However permeability derived from one-dimensional consolidation tests may provide sufficiently accurate information for preliminary analyses. 

Soil deformation One-dimensional and compression BS 1377 tests and consolidation tests ... 

Consolidation tests are commonly performed to (1) evaluate the compressibOity of soil samples for the calculation of foundation settlement (2) investigate the stress history of the soils at the boring locations to calculate settlement as weU as to select stress paths to perform most advanced strength tests (3) evaluate elastic properties from measured bulk modulus values and (4) evaluate the time rate of settlement. Consohdation test procedures also can be modified to evaluate if foundation soils are susceptible to coUapse or expansion, and to measure expansion pressures under various levels of confinement. Consohdation tests include incremental consohdation tests (which are performed at a number of discrete loads) and constant rate of strain (CRS) tests where load levels are constantly increased or decreased. CRS tests can generally be performed relatively quickly and provide a continuous stress-strain curve, but require more sophisticated equipment. 

Direct shear test of soils under consolidated drained conditions Consolidated-undrained triaxial compression test on cohesive soils One-dimensional consolidation properties of soils One-dimensional consolidation properties of soils using controlled-strain loading... 

Soil samples are generally taken vertically consolidation samples are taken from a horizontal slice. The coefficient of consolidation from such a test is based on vertical flow, which is applicable for much field work. (For projects using, for example, vertical sand drains, much of the flow is in the... 

The method described above forms the basis of the standard determination of the one-dimensional consolidation properties of soils for civil engineering purposes16. The diameter of the cell is not specified other than it should be at least 6 mm smaller than the soil samples available for testing, and the depth of the ring is... 

One-dimensional consolidation or confined compression, has a wide range of applicability in soil mechanics for testing insensitive and uncemented sediments. This arises because the sedimentation and subsequent consolidation of level ocean sediments is essentially... 

One of the more popular of the recent procedures based on this technique is SHANSEP (stress history and normalized soil engineering properties), which was proposed by Ladd and Foott (1974). This laboratory strength-testing procedure normalizes the undrained strength (Sy) and stress-strain characteristics with respect to the consolidation stress, Results from laboratory tests have shown that for a given OCR, the normalized stress can be used to represent the behavior of other samples with different consolidation stresses when sheared in the same type of test, at the same temperature, and at the same rate of loading. 

For soils exhibiting a normalized behavior, tests can be performed on specimens consolidated in the laboratory to the virgin compression line and then subjected to a stress condition equivalent to the in-situ OCR. By using the in-situ effective consolidation pressure, the in-situ stress-strain-strength characteristics of the soils can be evaluated from the normalized test results. To obtain the relationship between S /Cy and OCR, good quality to slightly undisturbed soil samples are consolidated to pressures as much as four times the in-situ preconsolidation pressure (o and then rebounded. Samples in which the structure... 

Results of identical types of strength tests on an NC soil expressed as shear strength versus volumetric strain were fmmd to plot as a straight line parallel to the normal consolidation line. The raho of strength to consolidation pressure was constant for each particular t5qje of test, S /o = C2, where C2 is a constant dependent on the value of the OCR and the type of test. 

A further difficulty with this method is that for many soils, the behavior in a laboratory test does not lead to a well-defined failure condition. Rather, the sample simply strains progressively with increasing number of cycles. This difficulty is overcome by defining failure of a laboratory test specimen in terms of developed strain amplitude. Five percent single amplitude is a common criterion, but other strain amplitudes have also been used. The strain amplitude refers to the cyclic strain developed in a laboratory test specimen imder-going the simulated cyclic field stresses superimposed on static-field consolidation stresses. The F.S. at each element is therefore a comparison between the dynamic-induced stress in the field and the cyclic stress required to cause 5% strain in a laboratory test specimen. 

ASTM. D2487. Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System). American Society for Testing and Materials, Philadelphia, PA, p. 12. ASTM. D4767. Standard Test Method for Consolidated Undrained Triaxial Compression Test for Cohesive Soil. American Society for Testing and Materials, Philadelphia, PA, p. 14. 

ASTM. D2435. Standard Test Method for One Dimensional Consolidation Properties of Soils Using Incremental Loading. American Society for Testing and Materials, Philadelphia, PA, p. 15. 

---