Behaviour Of Loose Sand Research Articles

Behaviour of loose sand treated using bio-gelation method

Bio-gelation is a new method for improving the hydraulic and mechanical properties of sandy soil through the production of polymeric gel to fill in the pores of the soil. In this paper, a study on the engineering behaviour of loose sand treated using this method is presented. A series of permeability and undrained monotonic and cyclic triaxial tests was carried out on both clean sand and bio-gelled sand. The test results showed that the coefficient of permeability was reduced by three to four orders of magnitude in the bio-gelled sand samples, and the higher the alginate concentration, the lower the permeability. In the monotonic triaxial tests, sand samples that would have liquefied under static conditions manifested strain-hardening behaviour after treatment. The shear strength of the bio-gelled sand also increased, as was indicated by an increase in the slope of the failure line from 1·08 to 1·27. In the cyclic triaxial tests, the number of cycles at failure increased from 183 for clean sand to 485 for bio-gelled sand, and the excess pore water pressure response was also much reduced. The hydrogel produced by the bio-gelation process was stable under both hydrostatic and seepage conditions. The other advantages of the bio-gelation method include: (a) the massive formation of hydrogel can be controlled to be 28 h later after injection; (b) the pH value of the soil fluid can be maintained at neutral; and (c) it is cost-effective for liquefaction or seepage control for sand compared with other conventional methods.

Static liquefaction mechanisms in loose sand fill slopes

To investigate potential triggering and failure mechanisms of loose fill slopes, two centrifuge model tests were conducted on loose sand with a contractive tendency andhigh liquefaction potential. The behaviour ofloose sand fill slopes subjected to rising groundwater or rainfall was simulated using a geotechnical centrifuge. Moreover, a three-dimensional back-analysis and parametric study were conducted to investigate the role of soil nails in preventing the triggering of static liquefaction in loose fill slopes. Contrary to the rainfall test where only excessive settlements are observed, arapid, and brittle fluidised flowslide in the slope can be identified whensubjected to rising groundwater. The fluidised flowslide is triggered by a localised drained surface failure in the form of a gully at the crest of the slope. The initial failure at the crest induces the generation of significant excess pore pressures within the slope, causing a significant reduction in effective stress andloss of shear strength due to static liquefaction. For an identical slope, numerical simulations indicate that a fluidised flowslide can be prevented by soil nailing. Soil nailing can prevent the peak shear strength of the soil from being mobilised and limits the excessive strains required to trigger static liquefaction.

Specimen size effects on behavior of loose sand in triaxial compression tests

Triaxial tests are often used to determine the behavior and strength characteristics of soils without due attention to the differences in specimen size. Several drained and undrained monotonic triaxial compression shear tests are performed in this study on three different specimen sizes of the same sand to investigate the influence of specimen size and scale effect on sand compression and shear behavior. The behavior of a sand specimen is strongly influenced by shear banding and specimen boundary conditions, which are manifested as specimen size effects in the test results of this study. The measured sand compressibility and shear strength parameters are employed to describe scale effects, and investigate specimen size effects in liquefaction triggering analysis. The results show that while larger specimens exhibit a less compressible behavior during isotropic compression, larger shear strengths and effective friction angles are mobilized in the smaller specimens during shearing. A number of geotechnical analyses can be significantly affected by variations in strength parameters of the same soil determined from different specimen sizes. While using small size specimens for determining shear strength parameters might result in an unconservative design, a large specimen size provides a more accurate representation of different soil strength conditions and field deformations.

Modeling of the Cyclic Behavior of Loose Sand by an Elasto-Plastic Fuzzy Set Model

The paper focuses on the development of a cyclic plasticity model based on the fuzzy set theory, which is implemented as a computational tool in order to simplify the computer programming of the constitutive driver. The constitutive model is a rate independent elasto-plastic model which is capable of describing repeated load cycles, dilatancy, material memory, and critical state soil mechanics features. Also, with the aid of membership function, the validity of the constitutive model is enhanced by comparing the theoretical output with a set of experimental data obtained from a variety of cyclic triaxial tests of loose sand.

Numerical study of spudcan penetration in loose sand overlying clay

Spudcan installation in sand overlying clay carries a risk of potential punch-through failure. This paper investigates the penetration resistance of spudcans on loose sand overlying clay soils using large deformation finite element analysis. Comparison with existing experimental results shows that the Mohr–Coulomb yield criterion with unchanging shear strength parameters simulates well the behaviour of loose sand, for which strain softening is not significant. The paper quantifies the effects on the punch-through behaviour of the spudcan of the main input parameters, including the undrained shear strength of the underlying clay, and the thickness, friction angle and stiffness of the upper sand. The current design guideline, SNAME [2], significantly underestimates the peak bearing capacity of the spudcan in comparison with the numerical results.

Reply to the discussion by A. Eliadorani and Y.P. Vaid on "Effect of undrained creep on instability behaviour of loose sand"

The discussers stated that the definition used in the note is “misleading.” According to the Oxford Advanced Learner’s Dictionary, the word “misleading” means “giving the wrong idea or impression and make them believe something that is not true.” The definition of instability is clearly defined and used consistently in the note. Therefore, we fail to see in which way it is “misleading.” If the discussers’ disagreement is on the term “undrained creep” or whether the instability should be called creep induced instability, we have explained in the note that the same term has been used and similar behaviour has been studied by Arulanandan et al. (1971) and Sheahan (1995) before for other types of soil. The discussers also stated “drained perturbation will not cause instability” and “there is only one instability line.” This may not be generally true, as it has been observed by a number of researchers (Eckersley 1990; Sasitharan et al. 1993; Chu et al. 2000, 2003b) that instability can occur under drained conditions and the instability line is not unique, but affected by many factors (Imam et al. 2002; Yang 2002). Creep is one of the factors and is studied in this note. The influence of void ratio on the instability line is also illustrated in Fig. 3 of the discussed note.

Behaviour of loose sand under simultaneous increase in stress ratio and principal stress rotation : D. Wijewickreme & Y. P. Vaid, Canadian Geotechnical Journal, 30(6), 1993, pp 953–964

Behaviour of loose sand under simultaneous increase in stress ratio and principal stress rotation : D. Wijewickreme & Y. P. Vaid, Canadian Geotechnical Journal, 30(6), 1993, pp 953–964