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Muskeg soil is widespread in Canada. It covers around 15% of the Canadian landscape. Its problematic nature is attributed to its high compressibility and low shear strength when subjected to loads because of its high initial void ratio and water content. Therefore, in this study, microbially induced calcite precipitation (MICP), an emerging and potentially environmentally friendly technique for soil stabilization, is used for enhancing the compressibility and shear strength properties of muskeg soil. The urease active bioslurry approach is adopted in this study, which comprises the mechanical mixing of bioslurry with soil and the injection of cementation solutions in subsequent phases. Muskeg soil was collected from Bolivar Park, Surrey, British Columbia, Canada. Different bioslurry concentrations were tested for the compressibility properties to determine the optimum concentration. Afterward, the optimum concentration was used to check the effect of the bioslurry percentage by weight and the number of cementation solutions injected on the soil stiffness and strength. Microstructure analysis by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were conducted for untreated and treated samples to check the change in the soil microstructure due to stabilization. The results showed that the 0.4 mol/L bioslurry concentration demonstrated the best compressibility properties. [ABSTRACT FROM AUTHOR]

The postcyclic reconsolidation response of low-plastic Fraser River silt was examined using laboratory direct simple shear testing. Specimens of undisturbed and reconstituted natural low-plastic Fraser River silt and reconstituted quartz powder, initially subjected to constant-volume cyclic loading under different cyclic stress ratios (CSRs) and then reconsolidated to their initial effective stresses ([[sigma]'.sub.vo]), were specifically investigated. The volumetric strains during postcyclic reconsolidation ([[epsilon].sub.v.ps]) were noted to generally increase with the maximum cyclic excess pore-water pressure ([DELTA][u.sub.max]) and maximum cyclic shear strain experienced by the specimens during cyclic loading. The values of [[epsilon].sub.v-ps] and maximum cyclic excess pore-water pressure ratio ([r.sub.u-max]) were observed to form a coherent relationship regardless of overconsolidation effects, particle fabric, and initial (precyclic) void ratio of the soil. The specimens with high [r.sub.u-max] suffered significantly higher postcyclic reconsolidation strains; [[epsilon].sub.v-ps] ranging between 1.5 and 5% were noted when [r.sub.u-max] > 0.8. The observed [[epsilon].sub.v-ps] versus [r.sub.u-max] relationship, when used in combination with the observed dependence of cyclic excess pore-water pressure on CSR and number of load cycles, seems to provide a reasonable approach to estimate postcyclic reconsolidation strains of low-plastic silt. DOI: 10.1061/(ASCE)GT.1943-5606.0000349 CE Database subject headings: Shear tests; Soil liquefaction; Earthquakes; Silts; Cyclic loads; Soil consolidation; Pore water; Water pressure; Canada. Author keywords: Direct simple shear testing; Liquefaction; Earthquake response of silts; Cyclic loading; Postcyclic reconsolidation strains.

The performance evaluation of buried extensible plastic pipelines, such as polyethylene pipes in the gas distribution industry, in areas prone to ground movement is a key consideration for many utility owners. Considering the relatively smaller deformation stiffness and nonlinear stress-strain response of these pipes compared with those of steel pipes, a good understanding of the basic soil–pipe interaction mechanisms forms a critical part in these evaluations. The increase in soil normal stress on the pipe attributable to soil dilation and gradual degradation of interface friction with axial pipe displacement was investigated. An analytical method was developed to estimate the pipe response when subject to axial frictional loads arising from soil movements, which accounts for these factors and the nonlinear stress-strain response of the pipe material. For a known relative axial soil displacement, the approach provides a convenient way to determine the axial force, strain, and length along which the friction is mobilized. The proposed analytical solution was used to model the response of five large-scale field pipe pullout tests. It is shown that the analytical solution is capable of effectively forming a framework to relate pipe displacement, pullout resistance, strain, and mobilized length. The findings also highlight the significance and need to account for soil dilation effects in describing the soil–pipe interaction in extensible plastic pipes. [ABSTRACT FROM AUTHOR]

It is commonly assumed that within inundated sand the Skempton B value and P-wave velocity decrease with decrease in saturation. In centrifuge tests a common saturation procedure is to inundate the specimen with carbon dioxide while under a vacuum and then slowly introduce the viscous pore fluid. The B value and related saturation is difficult to measure in centrifuge models and P-wave velocity—saturation correlations have been used for this purpose. A laboratory emulation of centrifuge saturation procedures was made using a triaxial cell with top and bottom bender elements and a viscous methyl cellulose–water pore fluid. Contrary to expectations, the laboratory tests showed high P-wave velocities indicative of full saturation when B values were low. Numerical modeling of the laboratory tests indicated that if air bubbles within the pore fluid are numerous and closely spaced then there is a good correlation between saturation, B value, and P-wave velocity. However if the air bubbles are larger and only present in some of the pores then the P-wave velocity is not a good indicator of B value and average saturation. The laboratory tests also showed that placing the specimen under backpressure for several days increased saturation and related B values. It is suggested that this common laboratory procedure should be considered for saturating centrifuge test specimens. [ABSTRACT FROM AUTHOR]