IMPACT OF SOIL AND GEOCHEMICAL PARAMETERS ON GROUND IMPROVEMENT USING MICROBIAL INDUCED CALCITE PRECIPITATION

Microbial induced calcite precipitation (MICP) is a biomediated ground improvement method that represents a relatively new innovation in the field of ground improvement. Due to its adaptability in urban environments and because microbes are ubiquitous in soils, MICP has emerged as a promising method to treat the soil in challenging urban environments. However, many challenges exist before the technique can be widely applied in practice. Because MICP is a complex process affected by a wide variety of factors, including the soil grain size, the concentration of bacteria, the concentration of reagents, nutrient injection rate, and flow direction, work remains to be done before widespread field implementation. The work performed in this study focused on quantifying the impact of multiple geochemical and soil variables on the performance of MICP as a biocementation method. Experimental investigations were performed at the bench scale to quantify the relationship between soil conditions (grain size ratio, fines content, nucleation sites, iron content, and surface roughness) and the mass of precipitated calcite produced during the treatment process, while the changes in the engineering properties of the treated soil were monitored using geophysical methods. The study compared changes in shear wave velocity of untreated control soils, chemically treated soils, and biologically treated sandy soils using column and batch tests with simulated groundwater conditions. Finally, a field scale demonstration of the MICP treatment method was performed at the Integrated Field-Scale Subsurface Research Challenge (IFRC) uranium mine tailings site in Rifle, Colorado, USA. Field scale treatment and monitoring were performed to demonstrate scale-up of laboratory results, to prove field adaptability, as well as to identify potential problems during field implementation. The study demonstrated that MICP could effectively be implemented at the field scale, with soil shear wave velocity increasing by approximately 50% during in situ treatment. Field tests also demonstrated that changes in the geochemical parameters and the microbial community could be tracked to monitor progression of the treatment scheme. The bench scale laboratory investigations demonstrated that precipitated calcite mass and shear wave velocity increased with silt and colloidal particle content (with controlled distribution), and with particle surface roughness.Ph.D

Numerical investigation of the at-rest earth pressure coefficient of granular materials

© 2015, Springer-Verlag Berlin Heidelberg. The at-rest earth pressure coefficient, $$\hbox {K}_{0}$$K0, is one of the most fundamental values for evaluating in-situ soil stresses and designing foundation. Research has been expanded to investigate the correlation between $$\hbox {K}_{0}$$K0 and micro-scale characteristic of granular soils, beyond the macroscopic approach empirically correlated with internal friction angle. This study presents the evolution of $$\hbox {K}_{0}$$K0 values of irregularly shaped natural sand, spherical shaped smooth and rough surfaced glass beads along with the stress history, estimated by the discrete element method. The surface roughness and non-spherical particles were emulated by inter-particle friction coefficient and the clumped particles. Results exhibit that the $$\hbox {K}_{0}$$K0 during loading stage nonlinearly decreases with increasing values of friction coefficient and the assemblies with clumped particles present the lower values of $$\hbox {K}_{0}$$K0 than spherical particle assemblies of the same friction coefficient. The varying friction coefficient seems enough to capture the evolution of $$\hbox {K}_{0}$$K0 during loading, unloading and reloading cycles, while the natural sand inevitably requires the assembly with clumped particles to capture the experimentally observed $$\hbox {K}_{0}$$K0 evolutions.Link_to_subscribed_fulltex

The Effect of Particle Size on Thermal Conduction in Granular Mixtures

Shredded rubber tire is a geomaterial that is potentially useful in environmental and engineering projects. Here, we study the effect of particle size ratio on the thermal conductivity of granular mixtures containing rubber tire particles. Glass beads were mixed at various volume fractions with rubber particles of varying size. The 3D network model analysis using synthetic packed assemblies was used to determine the dominant factors influencing the thermal conduction of the mixtures. Results present that mixtures with varying size ratios exhibit different nonlinear evolutions of thermal conductivity values with mixture fractions. In particular, mixtures with large insulating materials (e.g., rubber particles) have higher thermal conduction that those with small ones. This is because the larger insulating particles allow better interconnectivity among the conductive particles, thereby avoiding the interruption of the thermal conduction of the conductive particles. Similar tests conducted with natural sand corroborate the significant effect of the relative size of the insulating particles. The 3D network model identifies the heterogeneity of local and effective thermal conductivity and the influence of connectivity among conductive particles. A supplementary examination of electrical conductivity highlights the significance of local and long-range connectivity on conduction paths in granular mixtures