The failure mechanisms of reinforced soil segmental walls with extensible reinforcements were studied by performing a numerical analysis using the finite element method. The numerical approach was first verified against the results of three instrumented full-scale structures reported in the literature. Finite element models with different combinations of reinforcement spacing, reinforcement length and backfill soil were analysed. The ϕ–c reduction method, which is a special shear strength parameter reduction technique, was applied to simulate the failure conditions. The results of ϕ–c reduction analysis were used to evaluate assumptions used in current design procedures for geosynthetic-reinforced soil walls. In particular, shear strains were used to identify failure surfaces. Interpretation of the results indicated that, for both granular and cohesive backfills, the potential failure surface gradually shifts to a direct sliding mode as the system approaches failure. As a result, under working loads the potential failure surface used in current design analysis is correct, but the failure plane of a geosynthetic-reinforced soil-retaining wall at failure approaches a direct sliding type or a bilinear plane, which starts from the toe of the wall with a very shallow slope.

Passive site stabilization is a developing technology for the in situ mitigation of the risk of liquefaction without surface disruption. It involves the injection of stabilizing materials into liquefiable saturated sand. In this study, a pilot-scale facility (243 cm by 366 cm in plan  122 cm deep) was used to inject a dilute colloidal silica stabilizer into liquefiable sand specimens. The grout advancement was monitored in real time using electrical conductivity cells embedded in the specimens. Injection rates ranging from 65 to 9000 ml/min/well were used to investigate the optimal rate of grout delivery. In tests with low injection rates, the delivery performance was low due to sinking, while at higher injection rates, sinking was less noticeable. After the treatment, the degree of grout penetration was evaluated by excavating the model. The in situ unconfined compressive strength was measured using a pocket penetrometer, and soil blocks were excavated for additional unconfined compressive testing. Moreover, the 3-D flood simulator, UTCHEM, was utilized to simulate the experimental results and to predict the injection rates for adequate stabilizer delivery. The results of the strength testing demonstrated that as little as 1% by weight of the colloidal silica provides a significant improvement in strength after a month of curing. The study also revealed the feasibility of delivering colloidal silica to liquefiable sands by implementing a large-scale treatment.

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Novel approaches to the dynamic analysis of the reinforced soil walls have been reported in the literature. Use of marginal soils reduces the cost of geosynthetic reinforced soil walls if proper drainage measures are taken. Therefore the affect of using cohesive marginal soils as backfill in geosynthetic reinforced retaining structures were investigated in this research. The dynamic response of reinforced soil walls was investigated in a similar focus, using finite element analysis. The results obtained from walls with cohesive backfill were compared to the results obtained from walls with granular backfill. The height of the wall was chosen as 6 m in the two-dimensional plane strain finite element model and the base acceleration was chosen to be a harmonic motion. The effects of various parameters like the backfill type, facing type, reinforcement stiffness, and peak ground acceleration on the cyclic response of reinforced soil retaining walls were investigated. After analyzing the wall response for end of construction and dynamic excitation phases, it was determined that the deformations and reinforcement tensile loads increased during the cyclic load application and that the amount of additional deformation that occurred during cyclic load application was strongly related to backfill soil type, facing type, reinforcement type and peak ground acceleration. It was determined that a cohesive backfill and geotextile reinforcement was a good combination to reduce the deformations of geosynthetic reinforced walls during cyclic loading for medium height walls.

The UTCHEM lood simulator was used to develop a numerical model to simulate colloidal silica transport through sand columns. Most existing numerical models for colloidal silica modeling include the gelation process, in which the viscosity gradually becomes orders of magnitude greater than the initial grout viscosity. However, in ield grouting applications of shallow, loose, cohesionless deposits, injection at high viscosities may be limited due to allowable pressure limitations. In these cases, the injection is planned to be completed just before the gelling reaction begins. Thus, modeling the gelation process may not be necessary. The UTCHEM simulator accounts for luids with varying densities and viscosities, making it a useful tool for simulating colloidal silica injection in cases where gelation does not need to be modeled explicitly. The model was validated using laboratory data from ive column tests in which loose sand was treated with colloidal silica grout and one column test in which sand was treated with sodium silicate. The numerical model accurately represented the physical experiments. The numerical model provides a validated tool that can be used to design and optimize stabilizer delivery for laboratory and ield applications in which gelation does not need to be modeled explicitly.Abbreviations: CS, colloidal silica.We have developed a numerical model for simulating colloidal silica transport through sand columns using the existing reservoir simulator UTCHEM. Colloidal silica (CS) has recently been investigated for use as a grouting material to mitigate liquefaction risk at developed sites. It has been shown to reduce liquefaction risk in laboratory, centrifuge, and ield applications (e.g., Gallagher and Mitchell, 2002;Gallagher et al., 2007;Gallagher and Lin, 2009;Conlee et al., 2012). Although CS is more expensive than the more traditional sodium silicate grout, it has numerous advantages that may make it cost efective for use at developed sites. Colloidal silica nanoparticles are inert and nontoxic and can penetrate ine sands without iltration, dilute solutions (e.g., 10% w/w) have initial viscosities similar to water, and gel times can be controlled with NaCl. Barriers constructed from CS are expected to have lifetimes in excess of 25 yr (Whang, 1995); when kept saturated, they are expected to be permanent. he performance of CS in laboratory, centrifuge, and ield testing applications has been discussed extensively in the studies cited above; the purpose of this study was to design and validate a numerical model to design and optimize stabilizer delivery for laboratory and ield applications. In this research, a numerical model was developed using UTCHEM and validated using experimental results from Lin (2006), Lin (2009), andHonma (1984).Numerous researchers have developed new or modiied existing codes to simulate various aspects of the low and transport of variable-viscosity, variable-density gelling luids in the saturated (e.g.