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Experiments were carried out to characterise the influence of soil water retention properties on the corrosion of a cast iron specimen buried in Fraser River silt. The corrosion rates were measured at different degrees of saturation using standard corrosion tests, along with separate water retention tests for the Fraser River silt. Building on previous work on this topic, a numerical model solving moisture flow, oxygen diffusion, electrical conductivity and their coupled influence on metallic corrosion in unsaturated soil was developed. The experimental data and preliminary numerical modelling results were then used as inputs to a field-scale numerical model to examine climate-induced moisture migration around a pipeline and the resulting levels of corrosion. The time-dependent corrosion mass loss and the resulting loss in pipe wall thickness of a buried pipeline were modelled, and it was demonstrated that the cyclic climatic variations predominantly perturb the corrosion rates during the initial cycles, and subsequently a gradual corrosion rate arises depending on general climatic conditions. Further analysis of the influence of electrical resistivity on the levels of corrosion revealed that a decrease in resistivity due to effects such as seawater intrusion or naturally saline soils may result in a significant increase in the levels of localised corrosion. [ABSTRACT FROM AUTHOR]

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The effect of vibro-replacement ground improvement on the mechanical response of a low-plastic silt was examined using constant-volume monotonic and cyclic direct simple shear (DSS) testing. The silt samples representing "pre-improvement", "post-improvement", "post-improvement-aged" phases were retrieved from the field for testing. The pre- and post-improvement silt specimens consolidated to in-situ stress state, under constant-volume monotonic DSS shearing, displayed no strain-softening. Cyclic-mobility type strain accumulation with a stress-history-normalizable response was noted when pre- and post-improvement silt specimens were tested under constant-volume cyclic DSS loading, in spite of the ground improvement imparted in the latter case. In contrast, the post-improvement-aged silt specimens at in-situ stress state displayed a dilative strain hardening response. Under similar cyclic stress ratios, the rate of build-up of excess pore water pressure with increasing number of loading cycles was found to be least for the post-improvement-aged silt specimens when compared with pre- and post-improvement cases. As such, the cyclic resistance ratio of the post-improvement-aged silt specimens were significantly higher when compared with those from pre- and post-improvement silt specimens. These findings also highlight the importance of understanding the effects of vibro-replacement on the soil fabric/microstructure especially considering the time elapsed since the application of ground improvement. • No systematic laboratory studies to understand the effect of ground improvement on the mechanical response of silt. • Laboratory study was undertaken to assess liquefaction resistance of silt due to ground improvement using vibro-replacement. • The study findings show the importance of elapsed time after treatment in improving the silts subjected to vibro-replacement. [ABSTRACT FROM AUTHOR]

The cyclic shear response of soils is commonly examined using undrained (or constant-volume) laboratory element tests conducted using triaxial and direct simple shear (DSS) devices. The cyclic resistance ratio (CRR) from these tests is expressed in terms of the number of cycles of loading to reach unacceptable performance that is defined in terms of the attainment of a certain excess pore-water pressure and (or) strain level. While strain accumulation is generally commensurate with excess pore-water pressure, the definition of unacceptable performance in laboratory tests based purely on cyclic strain criteria is not robust. The shear stiffness is a more fundamental parameter in describing engineering performance than the excess pore-water pressure alone or shear strain alone; so far, no criterion has considered shear stiffness to determine CRR. Data from cyclic DSS tests indicate consistent differences inherent in the patterns between the stress-strain loops at initial and later stages of cyclic loading; instead of relatively "smooth" stress-strain loops in the initial parts of loading, nonsmooth changes in incremental stiffness showing "kinks" are notable in the stress-strain loops at large strains. The point of pattern change in a stress-strain loop provides a meaningful basis to determine the CRR (based on unacceptable performance) in cyclic shear tests. [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 (σvo′), were specifically investigated. The volumetric strains during postcyclic reconsolidation ([variant_greek_epsilon]v-ps) were noted to generally increase with the maximum cyclic excess pore-water pressure (Δumax) and maximum cyclic shear strain experienced by the specimens during cyclic loading. The values of [variant_greek_epsilon]v-ps and maximum cyclic excess pore-water pressure ratio (ru-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 ru-max suffered significantly higher postcyclic reconsolidation strains; [variant_greek_epsilon]v-ps ranging between 1.5 and 5% were noted when ru-max>0.8. The observed [variant_greek_epsilon]v-ps versus ru-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. [ABSTRACT FROM AUTHOR]