EXTENDED ABSTRACT. Technical Control of geotechnical risk in buildings: Geotechnical investigation

Transcription

1 EXTENDED ABSTRACT Technical Control of geotechnical risk in buildings: Geotechnical investigation Sónia Filipa Manjua Henrique Pires Pereira Supervisor: Doutor Nuno Gonçalo Cordeiro Marques de Almeida Supervisor: Doutor Rui Pedro Carrilho Gomes Outubro de

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3 1. Introduction The conformity assessment of buildings is a subject widely discussed at national and international level. In this sense, the technical control has gained importance on construction. This concept is based basically on a sequence of identification, analysis evaluation and treatment of risk situations of engineering construction activities, and the reporting of findings to the various interested parts of the risk of construction engineering and the state of managing that risk. Apart from the obvious advantages on improving the construction quality and optimization of the construction process, the technical control is also closely related to the issuing of insurance coverage for construction defects. The insurance is intended to grant quality guarantee of the construction to the owner. The main objective of the dissertation is to apply the concept of technical control on construction to geotechnical aspects of the buildings during the design phase, focusing on the geotechnical investigation, taking into account the different levels of complexity of the job. Therefore, we intend to reveal the methodology of technical control to contribute in improving the construction quality of buildings and the harmonization of the motivations and requirements of different parties in the projects, including final users, job owners, designers, construction companies and insurance companies. The control model of the geotechnical risk results from the analysis and identification of the aggravation of this risk, which can be detected during the revision phase of the geotechnical prospection (design phase), in the Geotechnical investigation. The aim is to synthesize in the model the necessary information to allow the assessment and monitoring of geotechnical risk associated with the geotechnical investigation, which is usually dispersed in various documents. 2. Construction Quality and Technical Control The quality in all its amplitude is notoriously recognized as a dynamic factor essential to promote productivity, competitiveness and sustainable development in economies and societies (Peixoto, 2008). Due to the enormous disclosure of the quality concept, the construction sector eventually adopted the methodologies associated with this concept to satisfy the needs and expectations of the various parties and the long-term success, being these methods simultaneously a marketing tool in order to gain competitive advantage in the industry. 3

4 In the construction industry, quality is demonstrated by correct performance and appropriate durability of the buildings and therefore the quality of associated services is of high importance in obtaining the quality of construction projects (Peixoto, 2008). In Portugal, the construction quality and technical control have been debated for some time. In this area, we highlight a number of studies (Jafar, 2013; Decker, 2013; Deman, 2013; Fagundes, 2013; Jafar et al, 2013; Almeida, 2011). The growing concern over the construction quality due to the pathologies found in buildings demonstrates the need to develop a national program to develop technical documentation that promotes increased quality of constructions. In addition, the implementation of a responsible system, safe guarantees, safe and effective insurances, associated to a technical control during the construction process, can make a significant contribution to ensure increased quality of buildings (Borges 1991; Bento 2009). Although there is a large number of ISO 9001 certificates in the construction sector, it is important to recognise that these do not reflect a quality guarantee of the final product, although indicating the determination of organizations to implement quality management systems, resulting in a higher probability that products or services may acquire high quality. The implementation of the technical control in Portugal in addition to quality management systems is aimed at improving the quality of construction of buildings. It may be considered relevant to establish an effective insurance system and guarantees to cover construction defects. This system can support responsibility of possible damage to the building with the various parties of a job, being the Insurance Company responsible for the costs of repair when necessary. In most cases, the activity of technical control arises from the need of an insurer and other entities involved having guarantees in engineering fields to ensure the construction has quality insured, requiring the presence of a quality control organization in both the design and the execution of the job (Jafar, 2013). Although there may be some link between the responsible parties for monitoring and the insurance companies, these entities must act independently to ensure the integrity of the technical control process. The technical control entities are responsible for quality and with their technical elements allow insurance companies to create the definition of inherent risk. In turn insurance companies guarantee the risks, committing to any financial consequences of non-compliance (Doumeyrou, 1986; Fagundes 2013 ). The objectives of the technical control may, in general, be translated into only one fundamental goal: to bring the reality of the buildings constructed to the requirements (technical performance and 4

5 technical risk) formulated by final users and technical regulations (Almeida, 2011). Therefore, with the technical control it is intended to ensure that the requirements established in applicable regulations are met and that risks can be covered by the insurance policy ( Jafar et al., 2013 ). In relation to the characteristics of the responsible organizations to develop the activities of technical control, they must be independent of all entities involved in the project and construction and must meet a set of technical skills appropriate and necessary to their duties, and have professional experience, which should be previously defined. Hiring outside companies for risk assessment led to a new element in the construction process: the Office of Technical Control (OTC). The OTC, hired by the project owner and subject to acceptance by the insurance company, has its main function to predict and audit risks at the project level and during the execution of the job, in order to follow the different construction processes. When an anomaly or defect is detected that could lead to situations of technical risk, a Technical Reserve should be issued by the OTC. This Technical Reserve, which may be partial or total, should allow the Insurance Company to consider whether to accept the risk or the exclusion of insurance coverage for that risk, when the conditions of global stability of the building are not affected and are this are then cancelled when the detected anomalies are resolved. 3. Geotechnical risk control of buildings The activities of technical control include, among others the different geotechnical aspects relating to the building since its design phase, to the end of its execution. These activities allow identifying and assessing risks to the building, informing the various parties of such risk. The experience shows that the cost of repairs due to problems of geotechnical nature is extremely high in countries that sell decennial damage guarantee insurance for buildings. Therefore, it is essential to identify the aggravating factors of the technical risk associated with the building site (Almeida, 2011). The main reason for this high accident rate is the absence inadequacy and incorrectness of a geotechnical study (Bartholomé, 2008). Although there are currently geotechnical studies for major jobs, for small and medium sized jobs quality and information covering is generally poor, if not totally non-existent. The very high levels of claims prove the need to review and control the geotechnical studies, proving later on in building site through geotechnical inspections, the assumptions previously made in the design phase. Thus, one should not consider a geotechnical study as right and exact just because it 5

6 was issued by a company specialized and / or certified, and must always ascertain the veracity of its findings throughout the execution of the building (Bartolomé, 2008). With the technical control we intended to control the level of technical risk of a structure. The effectiveness of this control level depends on a correct management of the technical risk structures (engineering risk) and the completion of the identification, analysis, evaluation and treatment of aggravating risk factors. Specifically for geotechnical aspects, i.e., for factors related to aggravating ground, the necessary activities to materialize are focused mainly in three phases: verification of the geotechnical study (during the design), geotechnical inspection (during the construction phase) and the conclusions resulting of the geotechnical study and geotechnical inspection (adapted from Almeida, 2011). The verification procedure culminates in assigning a risk level to the building, object of this process. According to the methodology presented by Almeida (2011), the assessment of the technical control results in three levels: "not aggravated, " aggravated " and " very aggravated. In general, it is considered that the level " not aggravated " covers the building systems where the phases of design and execution do not contain engineering solutions that aggravate the inherent risk (initial technical risk that is not fully eliminated). Levels aggravated" and "very aggravated ", correspond to occurrences at the stages of design and / or execution, where somehow there is an increase of the initial technical risk (Fagundes, 2013). 4. Geotechnical Risk Control Model of Buildings: Geotechnical investigation The control model of the geotechnical risk is developed based on the Spanish model - type, where the factors of aggravation of geotechnical risk of buildings related to the geotechnical investigation are analysed. Changes and adaptations were made, considering the specificities of the national context, including the Eurocodes applicable, so as to identify the main points that should be examined and evaluated, to the assessment and risk control in the geotechnical investigation. These adaptations and improvements have taken into account the crucial issues that most influence the constructions quality, allowing the identification of the main aggravation factors of the geotechnical risk and the development of the control model. Table 1 presents the main points covered by style. 6

7 Table 1 - Aspects analysed in the control model of geotechnical risk Factors of increasing risk of geotechnical buildings analysed Number of profiles of tests Depth of recognition Investigation techniques Ground sampling Laboratory tests Analysed aspects - Presentation of criteria for estimating the minimum number of profiles of tests and their correct distribution ; - Indication of the influence of the type of construction and the type of ground to determine the minimum number of profiles of tests; - Influence of insufficient number of profiles of tests in geotechnical risk; - Presentation of the most frequent errors related to the number of profiles tests ; - Analysis of technical risk associated with the number of profiles tests ; - Presentation of criteria to estimate the minimum depth of recognition; - Presentation of the main points relating to ascertain the depth of recognition; - Influence of insufficient depth of recognition in geotechnical risk ; - Presentation of the most frequent errors related to the depth of recognition; - Analysis of technical risk associated with the depth of recognition; - Description of the main investigation techniques and its applicability ; - Presentation of the sources of errors for the SPT test ; - Comparison between penetration tests : SPT and CPT ; - Influence of inadequacy or failure of investigation techniques in geotechnical risk; - Presentation of the most frequent errors related to the investigation techniques ; - Analysis of technical risk associated with investigation techniques ; - Influence of inadequate quality class samples in geotechnical risk ; - Presentation of the main causes of disturbance of soils and phase identification of the sampling process in which this can occur ; - Description of the classes of quality of the samples according to the EN (2007); - Correspondence between classes of sample quality and ground types and building types ; - Presentation of the minimum quality grade of the sample used in accordance with the type of test ; - Analysis of technical risk that may be caused by inaccuracies of the sampling process ; - Description of the main laboratory tests and their applicability ; - Presentation of the main required for geotechnical characterization parameters according to the type of soil ; - Presentation of the reference number of laboratory tests necessary for each geotechnical unit according to the type of ground and construction ; - Influence of inadequacy or insufficiency of laboratory tests in geotechnical risk ; - Presentation of the most frequent errors related to the testing laboratory ; - Analysis of technical risk associated with laboratory testing ; Accreditations laboratories of - Influence of the use of results from tests performed by entities not accredited in geotechnical risk ; - Advantages of implementing quality management systems in companies responsible for laboratory testing; - Indication of the number of tests performed in a testing laboratory accredited by IPAC; - Analysis of technical risk associated with the accreditations of testing laboratories ; 7

8 5. Case Study The geotechnical study used as a first case study was developed to support the design of an industrial building, including a cogeneration plant. Through the geotechnical study available, it was possible to analyse the information required for completing the monitoring report of the geotechnical risk. The inspection report of the geotechnical risk (Appendix 1), results of compilation and analysis of geotechnical risk aggravation that can be detected in the verification of geotechnical study factors, specifically in geotechnical investigation. This report is represented in six points: introduction to the report; parties in the preparation of the geotechnical study; initial data; reviewed documentation; conclusions and attachments. In the appendixes the main factors of aggravation of geotechnical risk are individually analysed: number of profiles of tests; in-depth recognition; investigation techniques; ground sampling; laboratory testing and accreditation of laboratories. 6. Conclusions With the goal of applying the concept of technical control of construction to the geotechnical aspects of buildings in the Geotechnical investigation (design phase), a review of knowledge on the topics of quality of construction of buildings and technical building control was elaborated. Thus, we determined the need to implement the control activity to improve the outcome of construction procedures and promote the quality of the final product under study, the buildings. With the activity of technical control defined, and the framework made, the technical aspect of control that focuses on geotechnical risk buildings was analysed. It was possible to prove the importance and the need to act in geotechnical component of projects in order to reduce accidents associated with them, which have immediate and long-term consequences. The terrain is a subsystem, including soil or rock or existing landfill at the site before the execution of construction work of the building and it involves many factors as an object of technical control, highlighting the importance of controlling due to the economic costs associated with geotechnical deficiencies. The monitoring of the geotechnical risk activity should begin by checking the geotechnical study, which should analyse in detail the factors that enhance the aggravation of the geotechnical risk. The phase of the geotechnical inspection visit follows, the assumptions made in preparing the project should be checked and ensure that the building process runs smoothly and safely, allowing to obtain a final product, in this case, buildings with the desired quality. The information resulting from verification of geotechnical study and the geotechnical inspection should be summarized and reported to the parties, including the project owner and the insurance companies. 8

9 The main objective of the analysis and monitoring of the geotechnical risk is determined to ensure the interested entity (an insurance company or only the project owner) that the final product has the quality required in relation to geotechnical aspects, so it is necessary to design quality, controlling all factors that may increase the geotechnical risk and hence the respective errors and future repercussions on the quality of the structures. The check must be performed with the help of the constituent statements of the model presented in this thesis and concurrently with the applicable standards. With the completion of this work we performed the analysis of the aggravation of geotechnical risk that can be detected in the verification of geotechnical study factors, specifically in the Geotechnical investigation. These factors include the verification of the following aspects: adequate amount of recognition and respective spatial distribution, depth of necessary recognition, suitability of the exploration, suitability of field trials, matching the quality of the samples to the laboratory tests, matching laboratory testing to the geotechnical characteristics of the site and laboratory tests carried out in accredited entities. As a final result of the control model of geotechnical risk presented, a simple report was elaborated, which allows synthesizing conclusions and the steps to perform the technical inspection. The entity responsible for the technical control and, consequently, for completing the report should have the right skills to be able to assess the risk associated with different factors within the model. The proposed future studies in order to continue with the subject studied in this thesis are related to the further development of the control model of geotechnical risk, points not specifically covered by it, and strategies for improving risk assessment of points already covered. To complement the study of geotechnical risk started, we highlight two groups of technical control activities: verification of the geotechnical study (design phase) and geotechnical inspection (construction phase). Regarding the verification of geotechnical study (design phase), it is suggested the development of studies on the following factors of the geotechnical risk aggravation (Almeida, 2011): - Related to the geotechnical characteristics of the ground : Aggressiveness of soil and water ; possibility of expansion or collapse; possibility of deferred settlement; heterogeneous ground; steep slopes; proximity to natural or artificial embankments; proximity of the water; fluctuations in groundwater level; erosion; seismicity; and complex geotechnical or special events; - Related to the determination of the calculation parameters: inaccuracy of the basic assumptions and from empirically estimates or correlations; inaccuracies in geotechnical modelling; inadequacy of calculation methods for determining the parameters; and errors in the calculations for determining the parameters; 9

10 - Recommendations related: inadequacy of recommendations to address the design parameters or characteristics of the ground; and uncertainties and weaknesses in determining the conditions for projects of foundations, substructures or excavations; - Related to the specific geotechnical risks: identification of the existence and definition of it. Regarding the geotechnical inspection (construction phase), it is suggested the development of studies on the following factors of the aggravation of the geotechnical risk (Almeida, 2011): - Related geotechnical study deviations: deviations in the geotechnical characteristics of the ground; deviations from the recommendations of the geotechnical study and other specific deviations. Also it is suggested a more consistent approach to the definition of global reports for geotechnical risk, which brings together the findings of the verification of the geotechnical study and the geotechnical inspection visit. Would be desirable that models were developed to control the technical risk for the remaining structural subsystems: foundations, substructures and superstructures. References Almeida, N. C. M. d. (2011) Modelo de Gestão Técnica de Edifícios Baseada no Desempenho e no Risco - Concepção, Desenvolvimento e Exemplo de Aplicação a Estruturas, Instituto Superior Técnico (IST), Lisboa. (in portuguese) Bartolomé, D. C. & de la Osa, G. G. L. (2008) Actividades de control técnico relacionadas com la geotecnia en el âmbito de la edificación: chequeo geotécnico. La visita de inspección geotécnica, Elementos de apoio do Curso Técnico Superior en Evaluación de Riesgos Técnicos en Edificación (O.C.T.), Universidad Politécnica de Madrid. (in spanish) Bento, N. R. O. S. (2009) Responsabilidades, Garantias e Seguros para a Cobertura de Danos na Construção, IST, Lisboa. (in portuguese) Borges, J. (1991) Some basic concepts in building: their multidisciplinary character, Laboratório Nacional de Engenharia Civil (LNEC), Lisboa; cited by Bento, (in portuguese) Bureau Veritas (2012) Controlo Técnico da Qualidade, Bureau Veritas, consultado em (in portuguese) Decker, Thomas de (2013) Building control systems and technical control activities in Belgium, Germany and the United Kingdom, IST Lisboa; 10

11 Deman, Jonas (2013) Building control systems and technical control activities in Belgium, The Netherlands, Sweden and France, IST, Lisboa; Doumeyrou, J. (1986) As relações entre as companhias de seguros e o grupo de contro técnico, Encontro Nacional sobre Qualidade na Cosntrução, LNEC; cited by Fagundes, (in portuguese) Fagundes, Fábio L. A. (2013) Atividades de Controlo Técnico de Impermeabilizações em Coberturas Planas, IST, Lisboa. (in portuguese) Jafar, K. F. A. (2013) Controlo Técnico da Construção: Enquadramento e definição da actividade, IST, Lisboa. (in portuguese) Jafar, Khairunissa; Almeida, Nuno; Dias, Alves & Sousa, Vitor (2013) A contribution for the technical control of construction projects in Portugal: state-of-the art review and analysis of national and international experiences, International Conference on Engineering UBI2013, Universidade da Beira Interior, Covilhã. Peixoto, Maria Pereira (2008) Metodologia da fiscalização de obras-planos de Controlo de conformidade de fachadas, FEUP, Porto. (in portuguese) 11