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Gestão do risco na construção de estacas moldadas e dúcteis cravadas e suas implicações económicas
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O crescimento demográfico e a migração populacional para as zonas urbanas, nomeadamente as grandes cidades, têm induzido a necessidade de construir em locais geotecnicamente menos adequados o que, aliado a estudos geotécnicos de fraca qualidade técnica, leva muitas vezes a alterações ao projeto e ao planeamento e à reorçamentação de fundações profundas, por vezes já durante a fase construtiva, levando a que a execução destas fundações seja uma das etapas do processo construtivo onde os desvios orçamentais são mais frequentes. Estas situações são potencialmente geradoras de litígios durante a construção, aumentando os custos associados para os diferentes stackeholders.
A geologia constitui uma fonte de incerteza significativa nos projetos de fundações, em particular quando estes são realizados em gabinetes expatriados relativamente ao local de construção, encarecendo assim as soluções adotadas. O que se referiu pode ser quantificado em termos financeiros, económicos ou monetários, e gerido com base num risco aceitável com vista a uma adequada perceção e gestão do problema em análise.
Neste contexto, desenvolve-se uma metodologia de gestão do risco a implementar na fase de construção de estacas moldadas com vara Kelly e dúcteis cravadas, visando contribuir para a sustentabilidade da construção e evitar litígios. A dissertação inicia-se com uma introdução ao tema em estudo, seguindo-se a descrição dos principais métodos de execução de fundações profundas, dando-se uma enfase maior às estacas moldadas e dúcteis cravadas. Em seguida discutem-se alguns conceitos de temática da gestão do risco e da gestão económica.
A metodologia proposta para a gestão do risco em fase construtiva tem por base as ocorrências registadas em empreitadas de construção de estacas moldadas ou dúcteis cravadas coordenadas pelo autor, em Angola, em zonas não sísmicas, num total de cerca de 70.000 m de estacas. Para aplicar a metodologia, identificam-se os perigos potenciais e obtém-se os valores das verosimilhanças para os eventos perigosos detetados naquelas empreitadas que possibilitam estimar os danos associados, os valores financeiros envolvidos e o risco na fase de construção. Com base nas obras analisadas, concebeu-se ainda um conjunto de árvores de eventos. A metodologia desenvolvida identifica os perigos potenciais, geológico-geotécnicos, técnicos, humanos e económico-financeiros, através de listas de verificação, avalia os riscos associados e classifica a sua magnitude, propondo depois um conjunto de medidas para os controlar, eliminando ou mitigando os referidos riscos sempre que os valores económicos envolvidos sejam considerados inaceitáveis.
Para validação da metodologia, a gestão do risco é aplicada a 12 empreitadas, também coordenadas pelo autor, em Angola, que envolveram a construção de cerca de 50.000 m de estacas moldadas e dúcteis cravadas em solos grosseiros, com intercalações pouco espessas de solos finos. Além disso, mostra-se como a componente económica do contrato é alterada e pode influenciar e/ou ser afetada em função da decisão para o tratamento do risco. A implementação simples, aliada ao efetivo controlo de custos, em tempo real, dos resultados de produção no contexto da gestão dos riscos obtidos naqueles casos de obra, validam a metodologia proposta.
Conclui-se assim que a metodologia desenvolvida revela aplicabilidade e eficiência na fase construtiva de empreitadas de estacas moldadas ou dúcteis cravadas, em solos grosseiros, com ou sem intercalações de solos mais finos, verificando-se uma melhoria nas margens produção por comparação às margens comerciais. Regista-se ainda que, caso a metodologia da gestão do risco não tivesse sido aplicada, os resultados das margens económicas das empreitadas seriam em média 21% mais gravosos relativamente às margens reais obtidas.
Population growth and its migration to urban areas, particularly large cities have induced the need to build in geotechnically less suitable sites which, combined with geotechnical studies of poor quality, often lead to changes in the design, planning, and re-budgeting of deep foundations, sometimes already during the construction stage, making its construction process one of the stages where budget deviations are more frequent. These situations potentially generate litigation during construction, increasing the associated costs for the different stakeholders. Geology is a source of significant uncertainty in foundation projects, particularly when these are carried out in expatriate offices in relation to the construction site, thus making the adopted solutions more expensive. The aforementioned can be quantified in financial, economic or monetary terms, and managed based on an acceptable risk aiming to an adequate perception and management of the problem under analysis. In this context, a risk management methodology is developed to be implemented at the construction stage of bored piles (Kelly technique) and ductile driven piles, aiming to contribute to the sustainability of the construction and avoid litigation. The dissertation begins with an introduction to the subject under study, followed by a description of the main methods of execution of deep foundations, giving greater emphasis to cast-in-place and ductile driven piles. Then, some concepts related to risk management and economic management are discussed. The methodology proposed for risk management in the construction phase is based on the occurrences recorded at construction contracts for bored and ductile piles coordinated by the author, in Angola, in non-seismic areas, in a total of approximately 70,000 m of piles. To apply the methodology, the potential hazards are identified, and their likelihood values are obtained for the hazardous events detected in those contracts making it possible to estimate the associated damages, the financial amounts of losses involved, and the risk in the construction stage. Based on the analyzed works, a set of event trees is also conceived. The developed methodology identifies potential geological-geotechnical, technical, human, and economic-financial hazards, through checklists, assess the associated risks and classifies their magnitude, then proposes a set of measures to control them, eliminating or mitigating such risks, whenever the economic values involved, are considered unacceptable. To validate the methodology, risk management is applied to 12 contracts, also coordinated by the author, in Angola, which involves the construction of around 50,000 m of bored and ductile driven piles into coarse soils, with thin intercalations of clays. In addition, it shows how the economic component of the contract is changed and can influence and/or be affected, depending on the decision to deal with the risk. The simple implementation, allied to the effective cost control, in real-time, of the production results in the context of risk management obtained in those cases of study, validate the proposed methodology. It is thus concluded that the developed methodology reveals applicability and efficiency in the construction stage bored piles (Kelly technique) or ductile driven piles, in coarse soils, with or without intercalations of clays, verifying an improvement in production margins compared to the predicted commercial ones. It should also be noted that, if the risk management methodology had not been applied, the results of the economic margins of the works would have been, on average, 21% more burdensome in relation to the real margins obtained.
Population growth and its migration to urban areas, particularly large cities have induced the need to build in geotechnically less suitable sites which, combined with geotechnical studies of poor quality, often lead to changes in the design, planning, and re-budgeting of deep foundations, sometimes already during the construction stage, making its construction process one of the stages where budget deviations are more frequent. These situations potentially generate litigation during construction, increasing the associated costs for the different stakeholders. Geology is a source of significant uncertainty in foundation projects, particularly when these are carried out in expatriate offices in relation to the construction site, thus making the adopted solutions more expensive. The aforementioned can be quantified in financial, economic or monetary terms, and managed based on an acceptable risk aiming to an adequate perception and management of the problem under analysis. In this context, a risk management methodology is developed to be implemented at the construction stage of bored piles (Kelly technique) and ductile driven piles, aiming to contribute to the sustainability of the construction and avoid litigation. The dissertation begins with an introduction to the subject under study, followed by a description of the main methods of execution of deep foundations, giving greater emphasis to cast-in-place and ductile driven piles. Then, some concepts related to risk management and economic management are discussed. The methodology proposed for risk management in the construction phase is based on the occurrences recorded at construction contracts for bored and ductile piles coordinated by the author, in Angola, in non-seismic areas, in a total of approximately 70,000 m of piles. To apply the methodology, the potential hazards are identified, and their likelihood values are obtained for the hazardous events detected in those contracts making it possible to estimate the associated damages, the financial amounts of losses involved, and the risk in the construction stage. Based on the analyzed works, a set of event trees is also conceived. The developed methodology identifies potential geological-geotechnical, technical, human, and economic-financial hazards, through checklists, assess the associated risks and classifies their magnitude, then proposes a set of measures to control them, eliminating or mitigating such risks, whenever the economic values involved, are considered unacceptable. To validate the methodology, risk management is applied to 12 contracts, also coordinated by the author, in Angola, which involves the construction of around 50,000 m of bored and ductile driven piles into coarse soils, with thin intercalations of clays. In addition, it shows how the economic component of the contract is changed and can influence and/or be affected, depending on the decision to deal with the risk. The simple implementation, allied to the effective cost control, in real-time, of the production results in the context of risk management obtained in those cases of study, validate the proposed methodology. It is thus concluded that the developed methodology reveals applicability and efficiency in the construction stage bored piles (Kelly technique) or ductile driven piles, in coarse soils, with or without intercalations of clays, verifying an improvement in production margins compared to the predicted commercial ones. It should also be noted that, if the risk management methodology had not been applied, the results of the economic margins of the works would have been, on average, 21% more burdensome in relation to the real margins obtained.
Descrição
Palavras-chave
Gestão do risco fase de construção fundações profundas estacas moldadas estacas dúcteis controlo de custo