Search

This technical note assesses the widely accepted Thompson's equation used to approximate design resilient modulus () for lime-stabilized soils from the results of unconfined compressive strength () testing. There is limited evidence in the literature to support Thompson's equation relating and for lime-stabilized soils, and other studies have suggested that the relationship provides an excessively conservative approximation for design , specifically above . Laboratory and testing was performed on multiple specimens of three lime-stabilized soils. These data reveal that Thompson's equation provides a lower-bound estimate of from and that Little's recommended relationship provides a more reasonable match to the data. This study also illustrated a lack of a clear correlation between and . [ABSTRACT FROM AUTHOR]

The design of deep tunnels underneath the water-table in clayey soils should carefully take into account the influence of pore pressures and seepage forces on the stability of the excavation and on the loading conditions of the support systems. This paper focuses on the application of analytical solutions and numerical models to the analysis of stress and deformation around deep tunnels, in the short and long term, considering the idealized situation of axisymmetric conditions. General remarks on the influence of hydro-mechanical coupling, artificial boundary conditions and lining permeability are presented. Theoretical predictions are compared with measurements made in tunnels excavated in the Boom clay formation at Mol (Belgium). [ABSTRACT FROM AUTHOR]

Civil engineers are at times required to stabilize sulfate-bearing clay soils with calcium-based stabilizers. Deleterious heaving in these stabilized soils may result over time. This paper addresses critical questions regarding the consequences of treating sulfate laden soils with calcium-based stabilizers. The authors describe the nature (chemistry and structure) of the minerals (ettringite/thaumasite) blamed for deleterious reactions and explain why these structures may lead to damage. The writers also describe the mechanisms of the mineral growth, and the extent of mineral growth based on the amount of sulfate minerals present in the soil. The writers explain why the rate of ettringite growth in treated soils should not be expected to follow a controlled rate of ettringite development such as that which normally occurs in portland cement concrete. The writers compare the rate and degree of ettringite development in soils to the classical model of nucleation and growth typical of most crystal structures. Finally, the writers evaluate the role of soil mineralogy in controlling soil behavior at varying sulfate contents and verify the existence of a threshold level of soluble sulfates in soils that can trigger substantial ettringite growth. [ABSTRACT FROM AUTHOR]

A modified method is proposed for predicting the lateral displacements of the ground caused by installation of soil-cement columns. The method is a combination of the original method derived on the basis of the theory of cylindrical cavity expansion in an infinite medium and a correction function introduced to consider the effect of the limited length of the columns. The correction function has been developed by comparing the solutions obtained using the spherical and the cylindrical cavity expansion theories for a single column installation. Both the original and the modified methods have been applied to a case history reported in the literature, which involves clay soils, and the predictions are compared with field measurements. The advantage of the modified method over the original method is demonstrated. Finally, the modified method has also been applied to a case history involving loose sandy ground, and the calculations show that the method can also be used for this type of soil provided that appropriate consideration is given to the volumetric strain occurring in the plastic zone of soil surrounding the soil-cement columns. [ABSTRACT FROM AUTHOR]

This paper presents the findings of a digital image analysis based study of clay fills, compacted with dynamic compaction for a building foundation in northeast Beijing, People’s Republic of China. Three levels of compaction energy were used at three compaction pits, respectively. Ground settlements and soil density increased with the number of dynamic impact blows. Microstructures of dry clay fill samples from the pits were examined with a scanning electronic microscope (SEM). Their microstructural parameters were further measured and analyzed quantitatively using digital image analysis. The clay SEM images are automatically converted into ternary images representing particles, pores, and contact zones for effective and efficient calculation of the clay microstructural parameters. The effect of dynamic compaction on the clay microstructural properties at different blow numbers and compaction energy levels is examined. Analysis revealed that the changes of the soil microstructural properties have a good correlation with the observed ground settlements at the three pits. The ground settlements are due to the size and shape changes and reorientation of the grain particles and pores of the clay fills. [ABSTRACT FROM AUTHOR]

Tests were conducted to determine the variation of water content and pore water suction for compacted clayey soils. The soils had varying amounts of clay fraction with plasticities ranging from low to high plasticity. The unsaturated soil behavior was investigated for six conditions, covering a range of compactive efforts and water contents. The experimental data were fit to four commonly used models for the water content-pore water suction relationship. Each model provided a satisfactory fit to the experimental data. However, the individual parameters obtained from the curve fits varied significantly between models. The soil water characteristic curves (SWCCs) were more sensitive to changes in compaction effort than changes in compaction water content. At similar water contents, the pore water suction increased with increasing compaction effort for each compaction condition and soil type. For all compaction conditions, the lowest plasticity soils retained the smallest water content and the highest plasticity soils retained the highest water content at a specified suction. In addition, SWCCs for soils compacted in the laboratory and in the field were similar. [ABSTRACT FROM AUTHOR]