Experimental study of strain accumulation of silica sand in a cyclic triaxial test

The experimental and phenomenological investigation of the elasto-plastic long-term behaviour of soils under dynamic loading is important for the development of risk analysis tools and numerical accumulation models for settlement prediction. Soil parameters, test equipment and loading conditions have a significant influence on strain accumulation, therefore a parameterization of the silica sand and a description of the re-engineered cyclic triaxial test device are performed in this paper. Long term cyclic triaxial tests are performed on a silica sand to investigate the influence of the number of cycles, the initial void ratio, the mean pressure and packages of cycles on the accumulation of residual strains. Empirical formulations of existing strain accumulation models are validated with test results on dry test samples

One-dimensional compression of a crushable sand in dry and wet conditions

This paper presents the results of a series of dry and wet one-dimenional compression tests on a calcareous sand from the Persian Gulf. Calcareous grains crush more easily compared to silica grains, a fact that is mainly attributed to their angular shape and weaker mineralogical and complicates their geotechnical behaviour. With regard to the use of crushable sands in construction projects, the question arises whether the presence of water further influences their crushability, and thus performance. The oedometer tests discussed in this paper, are part of a larger study on the influence of water on the stress-strain behaviour of calcareous sands. Dry samples are prepared in oedometers at a relevant density and either kept dry or flushed with water. Loading occurs in ten increments up until a vertical stress of 8.6 MPa and afterwards the sand is sieved to evaluate crushing. The behaviour of the crushable sand is shown to be significantly affected by the water as soon as crushing is initiated. The total settlements and the crushability are higher for the wet sand. When a distinction is made between primary and secondary compression, it is found that wet sand compresses more than dry sand during consolidation phase, but less during secondary compression phase. As a result, the observed net differences decrease with longer loading time whereas a higher rate of loading furthers the increased compression of wet calcareous sand. The tests are repeated on Molsand, a non-crushable silica sand. For this sand, within the stress range tested, the net deformation is identical for wet and dry conditions. The elevated stresses were not high enough to crush the grains and yield the material. The water dependency of crushable sands already exists at moderate stress levels, so it is of great importance to incorporate the accelerated crushing of wet particles in the geotechnical engineering practice

Triaxial compression tests on a crushable sand in dry and wet conditions

A calcareous sand from the Persian Gulf is subjected to a series of dry and fully drained saturated triaxial shear tests. The samples are prepared at relative densities of 65% and either left dry or saturated. They are consolidated to confining pressures ranging from 50 to 750 kPa, and sheared until shear strains of 20%. It is shown that the stress-strain and strength characteristics of crushable sand are significantly affected by the presence of water. During shearing of wet samples, there is less dilation, the peak is postponed and a lower shear strength is reached compared to dry samples. Crushability is assessed by comparing the granulometry before and after the triaxial tests. While both dry and wet samples show breakage, the wet sand is consistently more crushable. It is stated that the higher crushability of the wet sand suppresses its dilation during shearing