Abstract

Soil supporting foundations for infrastructural assets such as bridges are repeatedly subjected to dynamic loading from passing traffic. The load-displacement characteristics are nonlinear at even small to medium strains, however this effect is mostly modelled using secant stiffness models with effective linear stiffness. This simplification enables a pseudo linear model to encapsulate the effects of a nonlinear system with some accuracy. Linear models have a frequency related to the amplitude of the load used to specify the secant stiffness. Nonlinear models, however, have a range of frequencies due to the changing stiffness of the system resulting from the amplitude of the input load. There is growing uncertainty surrounding the response of foundation systems to damage effects. In particular scour erosion, which is the term used to describe removal of soil from around foundation elements by hydraulic action, presents a significant hazard to infrastructure and is becoming more prevalent with increased flooding risk due to climate change effects. This paper describes a numerical framework to incorporate a basis for nonlinearities in the load-displacement response modelling of pile foundations. The Newmark-Beta nonlinear integration solver is implemented in the study. A case study is presented of a pile foundation subjected to a range of load types and progressive scour damage, and the calculated response from the various conditions is evaluated. Periodic loads of varying amplitude are implemented. Effective linear models are developed based on the secant stiffness approach and compared to the nonlinear systems. The paper presents the numerical basis for the analysis, results of the case study and advice on modelling issues relevant to analyses of this nature.

Abstract

A real case of consolidation works is presented in which only field testing methods can reveal the causes of instability. This paper is an update of the one presented at the SAHC 2018 conference, concerning the study of the partial collapse of the Church of Itria in Piazza Armerina (Sicily, Italy). The previous paper beared hypotheses and design solutions based only on indirect investigations, theoretical formulations and checks with software. The consolidation works, started in November 2018 and still in progress, have made it possible to formulate new and documented hypotheses on the collapse and to integrate and partly modify the solutions hypothesized previously. In particular, the reconstruction techniques of the wall and chains have been confirmed. The new interventions have, instead, concerned the consolidation of the foundation soil which was found to be insubstantial,following electrical tomographic investigations, due to the presence of voids. At the same time, inspections were carried out on an old masonry sewage pipe which revealed several points of discontinuity through which large quantities of water entered under the walls of the church causing the removal of inconsistent elements from the ground. At first, the reconstruction of the collapsed wall was done and the restoration of the existing wall structures, to eliminate the causes of the collapse through the intervention on the sewage pipe and filling the voids under the foundations. The most important intervention, which required the use of innovative materials, forefront equipment and skilled labor, involved the filling the voids under the foundations through perforations every 50 cm, both on the inner and outer wire of the collapsed wall. Clamped canes were set in order to intercept the voids highlighted by the tomography. A 100% expansive mortar was injected at low pressure through the canes, filling one cane at a time and progressively raising the point of exit of the mortar until the higher far end. After this consolidation, the foundation and the wall were rebuilt with local limestone ashlars to have fair faced aspect as the original masonry. At the end of the work, further tomographic tests are planned to verify the validity of the interventions carried out.

Abstract

Historically, the analyses of tailings storage facilities (TSFs) have primarily focused on understanding the characteristics of tailings, while often overlooking a comprehensive evaluation of the foundation, as seen at Mount Polley in 2014. The Global Industry Standard on Tailings Management (GISTM) Requirement 5.4 stresses the importance of comprehensively addressing all potential failure modes. Numerous platinum TSFs in Southern Africa are underlain by residual clay, specifically a residual mafic rock from the Bushveld Complex. Similar soils, known as "tropical black clay soils", are found in other regions of the world. Surprisingly, there's limited public information on testing and modelling the behaviour of this clay foundation. This paper presents a case study that employs a novel approach to assess the impact of loading from tailings deposition on the underlying clay foundation of an upstream TSF. The analysis investigates how shear behaviour and consolidation characteristics of the clay foundation change with varying TSF heights and construction rates. The approach includes quantifying excess pore water pressures and their influence on the clay foundation's effective stress. The analyses primarily employ traditional limit equilibrium methods to assess TSF stability and foundation behaviour, with the potential to expand to numerical modelling. The study concludes that excess pore water pressures will significantly affect the Factor of Safety (FoS) of a TSF, particularly with adverse consolidation characteristics and increasing TSF height. This is primarily due to the low permeability and changing consolidation coefficient (cv) of the clay layer as the surcharge load increases. Furthermore, the research reveals that, depending on the rate of rise, tailings deposition may induce excess pore water pressures, potentially reducing the FoS. The ability to quantify excess pore water pressures using this novel approach enables a more accurate estimation of the FoS for facilities underlain by low-permeability materials, either residual or transported.

Abstract

The Cañaveral shopping center is located on a low slope formed by recent alluvial deposits of low consistency, supported on sedimentary rock of the Girón formation, which is found at depths that change abruptly between one and twelve meters in short distances, influenced by the presence of a geological fault line and processes of erosion and weathering by subway water currents. Considering that the loads on the foundation are of great magnitude, it is necessary to build about 100 deep caisson foundations to reach the rock. However, performing a borehole on each one of them represented a very high cost and long execution times that would generate discomfort in the operation of the warehouse. Therefore, an alternative was proposed to determine the depth levels of the rock through different geophysical tests of seismic lines and electrical tomography and try to calibrate the results through the correlation of some boreholes. During the execution and data processing phase of the geophysical tests, difficulties were encountered due to the level of environmental noise and the obtaining of the wave records, given the variability of the rock levels and even the effect that in some sectors of the study area the rock is very sub-surface. In conclusion, it was possible to identify the strengths and weaknesses of each of the exploration methods and generate a 3D map of the depths of the rock levels that served as input for the design and budget of the foundations, which were verified by constant supervision during construction and thus be able to determine the error percentages, as well as to present recommendations for future works where it is intended to use this type of techniques

Abstract

The Metropolitan Area of Bucaramanga is located within one of the three seismic nests in the world and therefore presents a high seismic and geotechnical threat (INGEOMINAS, 2001), therefore certain zones, especially those with alluvial and colluvial deposits, have limitations for the development of infrastructure projects, unless a threat assessment is carried out that indicates otherwise or, in its absence, it is reduced to low levels with stabilization works. The thicknesses of these deposits vary from a few meters to two hundred meters and their definition and dynamic behavior (damping coefficient and terrain degradation curves), would allow analysis with special non-linear constitutive models to better understand their response to a possible earthquake and to ensure the stability of the structures and even an optimization based on a possible lower spectrum. A new two-tower housing project of up to 36 stories high is a perfect scenario to carry out a local seismic response study and perhaps transform the way future projects are designed. It should be noted that, given the acceptable stiffness and granular composition of the soils, it is difficult to take unaltered samples and the Colombian NSR-10 standard does not require local behavior studies and therefore its study has not been properly established. It is sought through geophysical tests and laboratory tests such as triaxial, resonant column and bender element to perform such characterization and to perform soil modeling that allows the calculation engineer to have the appropriate inputs for their analysis.