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Abstract: Recent regulations introduced a limit state approach to geotechnical design by using representative values of the actions and of the strength parameters, partial safety factors that affect them, and by including safety margins in the calculation models. Moreover, Eurocode 7 stresses the importance of making use of test results for establishing ground parameters, and so rock joint shear tests are set to play a relevant role in the assessment of the shear strength required in the design of important projects, such as concrete dams, large bridge foundations, slopes, or underground excavations. In this keynote, joint shear tests are described, along with a presentation of their equipments and different procedures. Test results and calculations for the assessment of relevant shear strength parameters are illustrated, and several topics regarding sampling and variability are discussed. Opportunity is taken to present a practical apparatus allowing to perform simple shear tests (push tests) under very low normal stresses with advantages over tilt or pull tests. 1 INTRODUCTION Certain projects, such as concrete dams, rock slopes, or relatively shallow under-ground works, require the design of geotechnical works in rock masses where stresses are low when compared with the intact rock strength. In these cases, stability is structurally controlled by the shear strength of kinematically unfavourable rock discontinuities (joints, bedding planes, shear zones, faults, and cleavage or foliation planes). The analysis of this type of limit state requires the estimation of the shear strength of the rock joints, which is usually done by means of shear tests (Goodman 1976; Hoek & Brown 1977, Muralha 2007). Though Eurocode 7 is intended to be applied mainly to common civil engineering works, it establishes a comprehensive framework for the design of any kind of structure, such as underground caverns, tunnels, slopes, and dam or large bridge foundations.
- Europe (1.00)
- South America > Brazil (0.28)
Effect of Topography On the Distribution of In Situ Stresses Due to Gravity And Tectonic Loadings At Paradela Site (Portugal)
Figueiredo, B. (National Laboratory for Civil Engineering – LNEC) | Lamas, L. (National Laboratory for Civil Engineering – LNEC) | Muralha, J. (National Laboratory for Civil Engineering – LNEC) | Cornet, F. H. (Institute de Physique du Globe de Strasbourg – IPGS)
Abstract: A methodology is proposed for dealing with the unbalanced stresses that arise from numerical models due to topography effects when horizontal stresses are applied at the vertical boundaries. The proposed methodology is used for understand-ing the role of topography on the distribution of in situ stresses due to both gravity and tectonic loadings. In particular, the influence of Poisson's ratio on the orientation of principal stresses is illustrated for the case where only gravity loading is introduced. This approach is applied to the Paradela site, in Portugal, where a large underground repowering scheme is underway. INTRODUCTION The design of Paradela re-powering scheme requires a sound understanding of the regional stress field, since the state of stress is frequently the main load to be considered in the design of underground works in rock masses. The determination of rock stresses is a great challenge, due to its spatial variability and the many factors that influence it. Overcoring tests (OC), hydraulic fracture tests (HF), and hydraulic tests in pre-existing fractures (HTPF) were carried out in order to characterize in situ stresses at the locations of the new hydraulic circuit and powerhouse. Overcoring tests were performed in two parallel 60 m deep vertical boreholes (PD1 and PD2), 150 m apart. They were drilled 160 m bellow ground surface inside an existing adit located approximately 4550 m downstream from the water intake and 1850 m upstream from the future powerhouse cavern (Fig. 2). The adit is located 620 m above sea level and 170 m above the future hydraulic circuit. HF and HTPF were carried out in two 500 m deep vertical boreholes (PD19 and PD23), 100 m apart, located 1600 m downstream from the PD1 and PD2 boreholes (Fig. 2). The boreholes were drilled at an elevation of 730 m above sea level.