Celso Romanel

Design of Buried Pipes Considering the Reciprocal Soil-Structure Interaction

Finite element models have been surveyed for the numerical evaluation of the behavior of buried pipes with emphasis on soil-structure interaction. The following characteristics are recognized as defining finite element models: the material model for the soil and for the pipe; two or three dimensional geometry description; finite element type; contact conditions; and type of analysis which, according to the engineering problem and analysis purpose can be selected.

A correction in the CDM methodological tool for estimating methane emissions from solid waste disposal sites.

Solid waste disposal sites (SWDS) - especially landfills - are a significant source of methane, a greenhouse gas. Although having the potential to be captured and used as a fuel, most of the methane formed in SWDS is emitted to the atmosphere, mainly in developing countries. Methane emissions have to be estimated in national inventories. To help this task the Intergovernmental Panel on Climate Change (IPCC) has published three sets of guidelines. In addition, the Kyoto Protocol established the Clean Development Mechanism (CDM) to assist the developed countries to offset their own greenhouse gas emissions by assisting other countries to achieve sustainable development while reducing emissions. Based on methodologies provided by the IPCC regarding SWDS, the CDM Executive Board has issued a tool to be used by project developers for estimating baseline methane emissions in their project activities - on burning biogas from landfills or on preventing biomass to be landfilled and so avoiding methane emissions. Some inconsistencies in the first two IPCC guidelines have already been pointed out in an Annex of IPCC latest edition, although with hidden details. The CDM tool uses a model for methane estimation that takes on board parameters, factors and assumptions provided in the latest IPCC guidelines, while using in its core equation the one of the second IPCC edition with its shortcoming as well as allowing a misunderstanding of the time variable. Consequences of wrong ex-ante estimation of baseline emissions regarding CDM project activities can be of economical or environmental type. Example of the first type is the overestimation of 18% in an actual project on biogas from landfill in Brazil that harms its developers; of the second type, the overestimation of 35% in a project preventing municipal solid waste from being landfilled in China, which harms the environment, not for the project per se but for the undue generated carbon credits. In a simulated landfill - the same amount of waste for 20 years -, the error would be an overestimation of 25% if the CDM project activity starts from the very first year or an underestimation of 15% if it starts just after the landfill closure. Therefore, a correction in the tool to calculate emissions from landfills as adopted by the CDM Executive Board is needed. Moreover, in countries not using the latest IPCC guidelines, which provides clear formulas to prevent misunderstandings, inventory compilers can also benefit from this paper by having more accurate results in national GHG inventories related to solid waste disposal, especially when increasing amounts of waste are landfilled, which is the case of the developing countries.

Numerical Analysis of the Seismic Behavior of Alpamarca Tailings Dam in Peru

This paper presents an investigation of the seismic behavior of the Alpamarca tailings dam which is being raised from elevation 4603 m to 4670 m above the sea level in a region of high seismic activity in Peru. A seismic hazard assessment was carried out taking into account the attenuation law recommended for Peru’s geology and the design earthquake was generated through a spectra matching method. The seismic responses of the dam were computed using FLAC 2D software and the results are presented in terms of accelerations and permanent displacements. In order to observe the influence of the duration of the earthquake, the results computed with the total record of accelerations (218 s) were compared with those determined using a significant duration D5−95 = 99.36 s.

Evaluation of the Load Bearing Capacity of Piles by Numerical, Analytical and Empirical Approaches

The evaluation of axial bearing capacity of piles plays an essential role in foundation design. It can be estimated by theoretical methods, through an analytical or numerical solution, or by semi-empirical methods, whose application is generally based on field test results. Semi-empirical formulations are often preferred by geotechnical engineers since theoretical approaches are generally limited to particular applications. This paper compares the axial bearing capacity of bored piles estimated by different methodologies, based on instrumented load tests carried out in the Campinas and the Brasilia university campi, in Brazil. The semi-empirical approach involved settlement control and extrapolation of load-settlement curve while the theoretical approach was based on both analytical and numerical solutions, the latter computed through finite element analyses. When compared to the bearing capacity measured in the instrumented load tests, both numerical and the settlement control results showed close agreement, while the extrapolation of the load-settlement curve estimated higher than expected results and the theoretical method presented conservative values when introducing the negative skin friction effects.

Probabilistic Seismic Hazard and Dynamic Stability Assessment of a Tailings Dam Located in Jamaica

This research presents a probabilistic seismic hazard analysis (PSHA) and evaluation of the dynamic response of a tailings storage facility (TSF) located in Jamaica, country of high seismic activity situated along the North American and Caribbean tectonic plates. PSHA was performed in order to study the regional seismicity and to obtain the appropriate ground motion parameters. The stability of the dam and the permanent displacements caused by the design earthquake were estimated by pseudo-static method and a more complex solution using 2D finite element method (FEM). The signal treatment for the design earthquake and the definition of the Rayleigh damping based on the 1D equivalent linear method (ELM) are also discussed.

Static Liquefaction Analysis of the Limonar Tailings Dam in Peru

Tailings disposal has been a major concern for mining companies around the world with the overall goal to protect the environment and population from hazards associated with tailings storage. Large amounts of waste are produced daily in ore processing plants and depending on the industrial production waste the storage structure (tailings dam) needs to be redeveloped. A typical method for expanding the reservoir capacity is by raising the height of the dam body. The upstream method begins with the construction of a starting dike; after this step, tailings are deposited upstream, forming a beach that thickens over time, gradually increasing the waste strength and serving as a foundation for future dikes. This procedure goes on until the planned design size is reached. It is a simple and low cost method but its main drawback is that an excessive construction speed can induce static liquefaction, the main cause of the collapse of several tailings dams. This paper investigates the liquefaction potential of a copper tailings dam situated in Peru. Results from an empirical method, based on Standard Penetration Test data, are compared with those obtained with a more complex analysis carried out with a finite element program using an elastoplastic constitutive model. It has been concluded that both methodologies were suitable in order to predict the possible occurrence of static liquefaction.