http://repositorio.lnec.pt:8080/jspui/handle/123456789/1007778 2026-04-04T21:10:30Z 2026-04-04T21:10:30Z Aljundi, K. Pereira, C. Vieira, A. Maranha, J. R. Lapa, J. Cardoso, R. http://repositorio.lnec.pt:8080/jspui/handle/123456789/1017579 2024-10-07T15:28:21Z 2024-01-01T00:00:00Z

Test conditions influence on thermal conductivity and contact conductance of sand at transient state Aljundi, K.; Pereira, C.; Vieira, A.; Maranha, J. R.; Lapa, J.; Cardoso, R. The proper assessment of soil thermal properties, such as thermal conductivity, assumes a particular relevance for the design of Ground Source Heat Pump systems, as it determines the heat transfer and the energy efficiency design. Multiple methods can be used for thermal conductivity estimation, however significant scatters in measurements are often reported when using different (or even the same) methods. This work presents a detailed study of the thermal conductivity and the thermal contact conductance of a reference sand tested in transient conditions, analyzing the effect of several factors, such as the heating time, degree of saturation, soil density, temperature and heat flux intensity, on thermal conductivity measurements for dry state or fully saturated conditions. To avoid measurement errors and heterogeneity effects, only three samples were prepared with different compaction ratios, and systematically tested in dry and fully saturated conditions, under different control variables (temperature, testing time, and injected heat flux). Two analytical methods based on the line source solution were used to estimate soil thermal conductivity and to assess the probe-to-soil thermal contact conductance. Significant relationships were obtained between thermal conductivity and soil state conditions and testing variables, highlighting that a heating time longer than the one usually recommended in the standards is clearly needed. Finally, this study uses measured temperature values to determine the probe-to-soil thermal contact conductance, indicating its relevance in soil thermal conductivity estimation.

2024-01-01T00:00:00Z Carvalho, M. R. http://repositorio.lnec.pt:8080/jspui/handle/123456789/1017578 2024-10-07T15:27:01Z 2024-08-27T00:00:00Z

The practice of testing ground nails Carvalho, M. R. Balkema The soil nailing construction technique is often used to stabilise a ground mass by installing reinforcing elements (nails). The European Standard EN 14490:2010 defines general principles for execution, supervision, testing and monitoring of soil nailing. This paper presents tests results obtained in several ground nails executed in recent geotechnical works. These tests were carried out in sacrificial nails, before and during the works. As shown in this paper, the execution of the nails, the test system and test procedures affect their results quality. Thus, a critical analysis of the tests results is performed to assess the behaviour of the ground nails, framed by EN 14490:2010, in accordance with the design and contract specifications.

2024-08-27T00:00:00Z Carvalho, M. R. Juvêncio, E. http://repositorio.lnec.pt:8080/jspui/handle/123456789/1017505 2024-10-07T15:27:05Z 2023-05-14T00:00:00Z

Métodos de ensaio para verificação da carga instalada em ancoragens de serviço Carvalho, M. R.; Juvêncio, E. 18º Cong Nacional de Geotecnia-Universidade de Évora As ancoragens no terreno em estruturas de contenção, apresentam-se como “obras vivas”, carecendo de inspeção e de manutenção periódicas. A carga nas ancoragens pode variar com o tempo, nomeadamente para valores inferiores aos da blocagem, geralmente na presença de problemas associados com fenómenos de corrosão da armadura ou por redução dos impulsos do terreno, ou para valores superiores por aumento das solicitações do terreno, por exemplo. O ensaio de verificação da carga instalada realiza-se em ancoragens de obra, em serviço, com o objetivo de esclarecer o respetivo comportamento mecânico e de fluência, entre outros aspetos. Neste contexto, avaliar a magnitude da carga instalada nas ancoragens é fundamental para garantir a longevidade e segurança das obras. Entre os ensaios que permitem avaliar a carga instalada nas ancoragens, destacam-se: o ensaio de verificação da tração (EVT), cuja metodologia se desenvolveu no LNEC, e o ensaio do tipo Lift-Off. Neste artigo apresenta-se uma descrição dos fatores responsáveis pela variação da carga em ancoragens no terreno, do ensaio EVT e de Lift-Off, bem como resultados de ensaios de obra, sua análise e considerações.

2023-05-14T00:00:00Z Miranda, L. Caldeira, L. Bilé Serra, J. Gomes, R.C. http://repositorio.lnec.pt:8080/jspui/handle/123456789/1016791 2023-11-21T11:04:04Z 2023-06-21T00:00:00Z

Geotechnical characterization of a novel material obtained by injecting a closed cell expansive polyurethane resin into a sand mass Miranda, L.; Caldeira, L.; Bilé Serra, J.; Gomes, R.C. This paper reports the findings of experimental studies on a novel application of a closed cell expansive polyurethane resin injection into a sand mass, regarding some common engineering properties. Previous papers on injecting expansive polyurethane resins into sand masses as mitigation measures of different hazards, e.g., liquefaction, settlements and seismic displacements, deal with the open cell sub-class of polyurethane resins. Seeking to make up for the shortcomings of open cell methods, the paper addresses a prototype application of a closed cell polyurethane resin for ground improvement/control on sands. A new system for the preparation of the sand-resin mixture (SRM), which mimics the field application conditions, is introduced. It allows to inject the polyurethane resin into saturated sand with a prescribed mass density. The results of an extensive laboratory testing program are presented and discussed regarding some relevant engineering properties, e.g., Young’s modulus, Poisson’s ratio, uniaxial compressive strength and peak and residual friction angles. Namely, it was concluded that the SRM may be studied as a soft rock and that it shows an essentially plastic behaviour for large deformations, as well as a high shear strength and low permeability. It is envisaged that these fundamental results may encourage and assist the execution of in situ tests under controlled conditions, concerning the resin injection and its performance assessment, further promoting the application of closed cell polyurethane resins in geotechnical practice in a near future.

2023-06-21T00:00:00Z