Liquefaction resistance of bio-cemented calcareous sand

Calcareous sands are known as problematic soils in nature and challenge geotechnical engineers in many practical projects. Microbially induced calcite precipitation (MICP) is an innovative soil imp...

Strength, stiffness, and microstructure characteristics of biocemented calcareous sand

Strength and deformation behaviors of rockfill materials, key factors for determining the stability of dams, pertain strongly to the grain crushing characteristics. In this study, single-particle crushing tests were carried out on rockfill materials with nominal particle diameters of 2.5 mm, 5 mm and 10 mm to investigate the particle size effect on the single-particle strength and the relationship between the characteristic stress and probability of non-failure. Test data were found to be described by the Weibull distribution with the Weibull modulus of 3.24. Assemblies with uniform nominal grains were then subjected to one-dimensional compression tests at eight levels of vertical stress with a maximum of 100 MPa. The yield stress in one-dimensional compression tests increased with decreasing the particle size, which could be estimated from the single-particle crushing tests. The void ratio-vertical stress curve could be predicted by an exponential function. The particle size distribution curve increased obviously with applied stresses less than 16 MPa and gradually reached the ultimate fractal grading. The relative breakage index became constant with stress up to 64 MPa and was obtained from the ultimate grading at the fractal dimension ( α = 2.7 ). A hyperbolical function was also found useful for describing the relationship between the relative breakage index and input work during one-dimensional compression tests.

Effects of particle size on crushing and deformation behaviors of rockfill materials

Microbial-induced calcium carbonate precipitation (MICP) represents a promising approach to improve the geotechnical engineering properties of soils through the precipitation of calcium carbonate (...

https://tspace.library.utoronto.ca/bitstream/1807/96867/1/cgj-2018-0573.pdf

Effect of relative density and biocementation on cyclic response of calcareous sand

This paper presents the results of laboratory investigations into the deformation of coal fouled ballast stabilized with geogrid at various degrees of fouling. A novel track process simulation apparatus was used to simulate realistic rail track conditions subjected to cyclic loading, and the void contamination index (VCI) was used to evaluate the level of ballast fouling. The experimental results show that coal fines act as a lubricant, causing grains of ballast to displace and rotate, and as a result, accelerate its deformation. However, coal fines also reduce ballast breakage because of a cushioning effect, that is, by reducing interparticle attrition. The inclusion of geogrid at the interface between the layer of ballast and subballast provides additional internal confinement and particle interlocking via geogrid apertures, which reduces deformation. A threshold value of VCI=40% is proposed to assist practitioners for conducting track maintenance. If the level of fouling exceeds this threshold,...

Deformation of coal fouled ballast stabilized with geogrid under cyclic load

Polyurethane foam adhesive (PFA), a product resulting from exothermic chemical polymerization reactions between the diisocyanate functional group and polyol monomers, can form a closed cell...

Stress-Strain-Strength Response and Ductility of Gravels Improved by Polyurethane Foam Adhesive

The invention discloses a device for testing the mechanical properties of a pile-soil contact surface. The device is composed of a sealed pressure chamber, a hollow cylindrical soil sample, a solid cylindrical concrete pile sample and the like. The pile sample is prefabricated, and its diameter is equal to the internal diameter of the hollow cylindrical soil sample, and the two samples joint together closely. The lower end of the concrete pile sample is disposed on a pedestal through a spring assembly, and the upper end is connected to a stress loading system through a dowel bar, which is provided with a stress sensor and a displacement sensor I. The outside of the concrete pile sample is the hollow cylindrical soil sample. Filter paper and permeable stones are disposed at the lower end of the soil sample, and the lower end is positioned on the pedestal, while the upper end of the soil sample is provided with filter paper, permeable stones and connected with a displacement sensor II. During test, a confining pressure is exerted first for consolidating, and then a static, dynamic load is exerted on the pile sample for measuring the axial deformation and pore water stress of the pile and the soil. The device provided in the invention has a simple structure, is easy to realize, and can be used to measure the mechanical properties of a pile-soil contact surface under the action of a static, dynamic load.

Device and method for testing mechanical properties of pile-soil contact surface

Polyurethane foam adhesive (PFA) has been introduced as an alternative stabilizer in geotechnical applications because PFA can improve the engineering characteristics of soil by filling the pore space and generating adhesive bonding among the particles. However, the dynamic properties of PFA-reinforced soils are not well understood. To analyze the dynamic characteristics of PFA-reinforced gravels, a series of cyclic triaxial tests were carried out to investigate the shear modulus and damping ratio of PFA-reinforced gravels, and to determine the corresponding effects of the PFA content, confining pressure, consolidation stress ratio and loading frequency. The results showed that the shear modulus increased, and the damping ratio decreased as the PFA content, confining pressure and consolidation stress ratio increased. In contrast, the effect of the loading frequency, which ranged from 0.05 to 1 Hz, was negligible. A modified hyperbolic empirical model can consider the effect of the PFA content on the maximum shear modulus and predict the relationship between the normalized shear modulus and the normalized shear strain was proposed. Moreover, the upper and lower bounds of the damping ratio were also proposed.

Ping Liu

Papers

Stress-Strain-Strength Response and Ductility of Gravels Improved by Polyurethane Foam Adhesive

Device and method for testing mechanical properties of pile-soil contact surface

Dynamic properties of polyurethane foam adhesive-reinforced gravels

Large-sized hollow cylindrical sampler for coarse grained soil and use method thereof