The construction of embankments on soft saturated soils can be a challenge due to the low shear strength and high compressibility of these soils. The same may be true for constructions on porous collapsible soils, because the collapse of the soil structure can lead to large foundation soil deformations leading to damage to the embankment, particularly in the case of bridge abutments. Conventional piles and granular columns have been used to stabilize such embankments when there are limits for embankment settlements. More recently, geosynthetic-encased granular columns have been increasingly used as an alternative solution. This study examined the performance of geosynthetic-encased columns for the stabilization of embankments on porous collapsible structured unsaturated soil. Field load tests were performed on conventional sand and gravel columns and on geotextile-encased sand columns and on geogrid-encased gravel columns. During testing, the collapse of the surrounding soil was induced by water injection through the granular column top to investigate the influence of the casing on the column performance. The results obtained show that significant increases on pile load capacity can be obtained depending on the materials used and construction conditions. The effects of foundation collapse can also be reduced with the use of a geosynthetic casing in the granular column.

This paper extends the design philosophy for piled rafts by exploring the factors that control the design of a published case history where the piled raft was instrumented. The case history studied differs from most published case histories in that concentrated column loads, rather than average “spread” loads, were considered in the foundation design. An extensive series of backanalyses was initially carried out with this case history, in order to calibrate the numerical program adopted herein. These analyses were followed by a parametric analysis for the evaluation of different design alternatives. These alternatives adopted distinctive pile characteristics (number, location, and length), which were varied for different raft thicknesses, yielding 26 different cases for cross comparison and comparison with the “reference” case history. Each of the solutions was also assessed in terms of relative costs against the reference case, allowing the establishment of conclusions of practical interest for those involved in the design of piled raft structures.

In piled raft systems (PRSs), the piles are used to support load or to control settlements. These systems, when founded in soft soils that are then consolidated by loads or subsidence processes, can induce negative friction in the piles and other phenomena related to variations in the distribution of load or settlements. This paper presents the results of physical modeling in a geotechnical centrifuge capable of different distributions of piles under a raft. As a result, the influence of consolidation and extraction of water from a deep soil layer on the behavior of the PRS model was analyzed. It was determined that the processes associated with the extraction of water from the deep soil layer induce larger settlements. A separation between the raft and the soil is possible, as well as a change in the behavior of the PRS.

This paper deals with Plaxis 3D finite element simulations of the mechanical response of deep foundations founded in a collapsible tropical soil. Main attention is initially paid to differences between single continuous flight auger (CFA) pile behavior and the behavior of CFA piles in standard groups. The numerically computed load-settlement curves are compared to field load test data obtained at the experimental research site of the University of Brasília (UnB), leading to conclusions about the appropriateness of adopting laboratory, in situ or back calculated parameters as input of numerical programs that simulate 3D foundation systems. Further, the contribution of the contact surficial soil/top raft is numerically examined by simulating the behavior of identical “piled raft” systems founded in the same site. The numerical simulated results of “piled raft” and standard pile group systems are then compared in terms of load capacity, system stiffness, load share between pile tip, shaft and raft, and mean developed lateral pile shaft friction. Having the results at distinct loading stages, as at working and failure levels, the analyses show the differential behavior, and design obtained responses, one may expect from conventional pile groups and “piled rafts” of CFA floating piles when founded in tropical soils. It is a mixed theoretical/experimental paper with practical interest for foundation designers and constructors.

Compacted earth embankments are routinely used in dams and many others infrastructure projects in Brazil. It is common to use fine-grained soils for these embankments, which are placed and compacted in the field at specific values of unit weight and water content. Their design is usually performed using geotechnical parameters from laboratory tests on compacted samples, although in situ tests could emerge as an alternative for determining specific parameters, as such tests can be conducted reasonably rapidly and can somewhat account for local inherent conditions of the soil such as confining stress levels, water content and mineralogical variations. Therefore, this paper explores the application of Ménard-type pressuremeter tests to determine the Young’s modulus of compacted soil layers from the side flank of a large-scale earth embankment constructed in the city of Goiânia in the Midwest Region of Brazil. The embankment was compacted under controlled conditions, permitting the extraction of undisturbed soil blocks at distinct levels during its erection. Laboratory tests, such as consolidated isotropic triaxial and oedometer tests, were performed on samples at their natural water content. Young’s moduli were derived from these laboratory tests and compared with the elastic moduli measured using the pressuremeter, either directly under different (external) conditions or at normalized levels of the effective confining octahedral stress. This comparison of results enabled the establishment of preliminary statistical correlations between the average (in situ and laboratory) moduli, which will be useful when using the Ménard pressuremeter for a preliminary design or a post-construction check of compacted earth embankments.