An experimental testing program was undertaken to investigate failure mechanisms induced by the active movement of a deep rectangular trapdoor underlying a granular soil. Reduced-scale models were tested under normal gravity as well as under an increased gravitational field using a centrifuge facility. Some models were used to evaluate the performance of both flexible and rigid pipes undergoing a localized loss of support. Failure mechanisms in the longitudinal direction of the models were characterized by a single, well-defined failure surface that developed within the limits of the trapdoor. However, failure mechanisms in the transverse direction of the models were characterized by multiple failure surfaces extending outside the limits of the trapdoor. Significant dilation of the soil located immediately above the trapdoor was identified in the failure of the models. The pattern of the failure mechanisms was found to be affected by the stress level and backfill density. Higher stress levels were found t...

The use of geotextiles as reinforcement in soil-retaining walls may offer benefits over the use of other types of reinforcement, such as metallic strips or geogrids. These include ease of construction, expediency, and significant cost reduction. However, the lack of field monitoring results documenting the behavior of geotextile-reinforced structures, mainly regarding deformations, has precluded widespread utilization of these systems. A better understanding of the behavior of geotextile-reinforced soil structures could be gained by systematic monitoring of full-scale structures, combined with a thorough material characterization program. Accordingly, eight prototype geotextile-reinforced soil structures were built as part of a comprehensive study aimed at analyzing their behavior. This paper presents the characteristics of the prototype wall used as baseline for this series of structures, including construction details, instrumentation layout, and the results of laboratory tests conducted to characterize the soils and geosynthetics involved in this structure. The lateral displacements at the face of the wall were small, with increasing lateral displacements observed over time, particularly in association with precipitation events during the summer season in Brazil. The largest horizontal strains occurred towards the face, at mid-height of the prototype wall. The use of sigmoid curves to fit displacement results within the geotextiles was found to be very useful to define the value and the location of the peak strain in each reinforcement layer. The location of maximum reinforcement strains within each layer was found to be consistent with the development of a potential failure surface starting at the toe of the wall and propagating into the soil mass. The maximum reinforcement tension predicted using the K-stiffness method was found to compare well with reinforcement tension values obtained from monitoring results.

This paper provides theoretical background, laboratory data and full-scale measurements useful in understanding the interaction between soils and geosynthetics under unsaturated conditions. It also includes an evaluation of the current state of knowledge regarding the hydraulic properties of porous geosynthetics under unsaturated conditions relevant for geosynthetic capillary barrier design. These properties include the water retention curve and the hydraulic conductivity function. In addition, the mechanisms involved in the development of capillary barriers are evaluated to explain the storage of water at the interface between materials with contrasting hydraulic conductivity (e.g. a fine-grained soil and a nonwoven geotextile). Finally, specific applications are presented to illustrate new opportunities and applications that may result from a better understanding of the unsaturated hydraulic properties of geosynthetics. Experimental data are provided illustrating that geosynthetic capillary barriers are superior to soil-only capillary barriers. Based on this observation, it is emphasized that no capillary barrier should be designed without consideration of the enhanced performance offered by the inclusion of nonwoven geotextiles under the fine-grained soil component of the cover.

Fiber reinforcement represents a promising alternative in projects involving localized repair of slopes and reinforcement of thin soil veneers, where planar reinforcement (e.g., with geotextiles and geogrids) is difficult to implement. Current design methodologies allow quantification of the shear strength of fiber-soil composites in terms of the parameters that independently characterize the soil matrix and fibers. The shear strength of fiber-reinforced soil is considered to have two components, including the shear strength of the soil matrix and the tension mobilized within the fibers. Triaxial compression tests and fiber pullout tests were conducted to evaluate how the fiber tension is mobilized for varying shear strain levels. The results of this evaluation provide insights into whether the shear strength of fiber-reinforced soil is governed by the peak or residual shear strength of unreinforced soil. A revision to existing design methodology is proposed in which the individual contribution of...

This paper presents an evaluation of the performance of two instrumented sections of a geosynthetic-reinforced soil wall, 5.6 m high, constructed using a lateritic fine-grained soil. Two sections with identical layout of a nonwoven and a woven geotextile were monitored for comparison purposes. The unconfined tensile stiffness of the nonwoven geotextile was three times smaller than that of the woven geotextile. This allowed direct evaluation of the effect of soil confinement on geotextile stiffness. Instrumentation was used to measure face displacements, reinforcement displacement and strains, and soil matric suction. Rainfall occurred both during and after construction, which facilitated evaluation of the effect of soil wetting on the walls performance. Ultimate and serviceability limit state analyses were conducted to gain further insight into the performance of the two walls. The results show that the performance of the section reinforced with nonwoven geotextile was equivalent to the one reinforced with woven geotextile, even after the observed reduction in matric suction after rainfall. For both sections, the overall deformations occurred during construction. Negligible deformations were observed during service. Maximum face displacements were measured in the lowest instrumented layer for the nonwoven geotextile section whereas it was in the highest layer for the woven geotextile section. These behaviours of face displacement distributions can be the result of the significant differences in global stiffness of the sections. Design analyses and field performance show that soil confinement has a beneficial effect on the nonwoven geotextile stiffness. The significant contribution of the soil cohesion of the lateritic soil played an important role in the behaviour of the nonwoven geotextile-reinforced wall.