| 1. |
- Ansal, A., et al.
(författare)
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Seismic microzonation for earthquake risk mitigation in turkey
- 2004
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Konferensbidrag (refereegranskat)abstract
- As a tool to improve the state of land use management in Turkey and to better mitigate earthquake risk inthe future, a microzonation project was initiated after the 1999 Kocaeli earthquake. The project had twocomponents (a) drafting a microzonation manual [1], (b) conducting pilot case studies in the selected tworegions affected by the 1999 Marmara earthquakes [2]. The main purpose of the study was to test anddemonstrate the applicability of the methodology proposed in the Seismic Microzonation Manual preparedfor the project. The major contributions of the study are the probabilistic assessment of the regionalearthquake hazard, interpretation of the microtremor records, and interpretation of the available geologicaland geotechnical data based on a grid approach. All the available data was transformed to GIS format andthe results are evaluated to obtain a microzonation with respect to site amplification, liquefactionsusceptibility and landslide hazard. An attempt will be made to summarize the results of the pilot studyconducted for the Gölcük region to give an overview of the proposed methodology.
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| 2. |
- Ansal, A., et al.
(författare)
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Site Characterization and Site Amplification for a Seismic Microzonation Study in Turkey
- 2004
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Konferensbidrag (refereegranskat)abstract
- The pilot areas were divided into cells by a grid system of 500 m x 500 m for estimating the effects of site conditions at a scale of 1:5000 by assigning representative soil profiles at the centre of each grid. These soil profiles were classified according to the Turkish Earthquake Code, NEHRP site classification, equivalent shear wave velocity and used for site response analyses. The zonation maps involve the division of the area into three zones as (A, B, and C). In all cases, the variations of the calculated parameters are considered separately and their frequency distributions were determined. Thus the zone A shows the most unsuitable 33 percentile, zone B the medium 34 percentile and zone C shows the most favorable 33 percentile. A suitable pa-rameter is considered to be the average spectral acceleration between 0.5-1.5 sec periods obtained from site response analysis. Even though more empirical, the spectral amplifi-cations calculated using equivalent shear wave velocities gave consistent values that appear to be realistic when compared with the selected soil profiles. Thus microzonation maps with respect to ground shaking were based on the average of spectral accelerations and spectral amplifications obtained from equivalent shear wave velocities.
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| 3. |
- Askarinejad, Amin, et al.
(författare)
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Physical modelling of rainfall induced landslides undercontrolled climatic conditions
- 2012
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Konferensbidrag (refereegranskat)abstract
- A series of small scale physical modelling tests are performed in a geotechnical drumcentrifuge in order to investigate the triggering mechanisms of landslides due to rainfall. They areconducted under controlled conditions of rainfall intensity and duration, ambient relative humidity, wind,and temperature. These tests have been designed to study the possible failure mechanisms proposed for afull scale landslide experiment. Accordingly, different shapes and hydraulic properties of the bedrock, interms of drainage and exfiltration, are provided for the model. A three dimensional close rangephotogrammetric technique is used to track the movements and monitor the volumetric changes of theground during the cycles of wetting and drying. The slope elevation is filmed during and following therainfall events using a high speed camera and the deformation vectors and strains are elaborated using thePIV method. Details of the design of the climate chamber are discussed in this paper.
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| 4. |
- Caprez, M., et al.
(författare)
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Testing of TBM excavation material in sandstone and marl for reuse in embankments or as fill
- 2001
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Konferensbidrag (refereegranskat)abstract
- Several tunnels in geological formations of molasse, marl or sandstone are planned or are presently under construction in Switzerland. The excavation of these tunnels is very often carried out by tunnel boring machines (TBM). This kind of excavation tends to produce lamellar excavation materials (chips). For the reuse of these materials in road embankments etc., there are certain disadvantages concerning the compression properties. Limiting deformation will be the main restriction on design in the reuse of this material and this is manifested also in terms of the possible changes of volume as a function of time. On the one hand, volume may increase due to instability in relation to water and possibly frost, whereby swelling occurs. On the other hand, volume may decrease due to repeated dynamic loading. Inevitably these volume changes will not occur to the same degree and within the same timeframe. The material can be stabilised by using a variety of cementing agents to improve the key properties. A range of laboratory experiments were performed to find the optimal mixture to be used as a base to the reinforced concrete slabs, which formed the railbed to the major railway line passing through this tunnel. An experimental field test was carried out using this specific mixture to confirm the suitability in relation to the construction method proposed and the properties measured at full scale.
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| 5. |
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| 6. |
- Weber, Toni M., et al.
(författare)
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Centrifuge modelling of sand compaction piles in soft clay under embankment load
- 2006
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Ingår i: Physical Modelling in Geotechnics, 6th ICPMG'06. - 041541587X - 9780415415873 ; , s. 603-608
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Konferensbidrag (refereegranskat)abstract
- Sand compaction piles are used in practice for ground improvement of soft subsoil in order to accelerate consolidation, reduce compressibility, and increase strength. The current design procedure of sand compaction piles is based on simple empirical calculations, which does not take full account of the sand pile behaviour. This research project investigates the behaviour of a base reinforced embankment constructed on a soft clay layer, which is improved with sand compaction piles. In order to gain a better understanding of interactions within the structure, physical investigations are being conducted by means of centrifuge modelling. Tests were performed under plane strain conditions in a strong box, using a newly developed sand compaction pile installation tool for in-flight pile construction. Initial analysis of test data shows the change in stress state due to sand compaction pile installation and the influence on clay behaviour. © 2006 Taylor & Francis Group, London.
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| 7. |
- Weber, Toni M., et al.
(författare)
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Modelling the inflight construction of sand compaction piles in the centrifuge
- 2005
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Ingår i: Proceedings of the 16th International Conference on Soil Mechanics and Geotechnical Engineering. - 9059660285 - 9789059660281 ; , s. 1291-1294
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Konferensbidrag (refereegranskat)abstract
- Sand compaction piles are used in practice for ground improvement of weak subsoil. These columnar inclusions improve the consolidation behaviour as well as reduce the compressibility of the soft ground. The current design procedure of these sand piles is based on simple empirical calculations, which does not fully take account of the sand pile behaviour. In order to gain a deeper understanding of the behaviour of sand compaction piles, physical and numerical investigations are being conducted. The basic system behaviour of soft soil and column is simulated physically by centrifuge modelling. Because the stress situation in the soil changes significantly due to installation, a sand compaction pile installation tool was developed and applied successfully in the first tests. This allowed the stress paths encountered by the soil during the construction process of a displacement sand pile to be modelled realistically. The results will be compared to real geometries and the behaviour is also studied numerically by means of finite element modelling. These findings provide the basis for further analysis of this geotechnical interaction problem extending the model by including geotextiles below embankments to be able to formulate some recommendations for the design procedure of sand compaction piles under embankments.
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| 8. |
- Weber, Toni M., et al.
(författare)
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Smear zone identification and soil properties around stone columns constructed in-flight in centrifuge model tests
- 2010
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Ingår i: Geotechnique. - 0016-8505 .- 1751-7656. ; 60:3, s. 197-206
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Tidskriftsartikel (refereegranskat)abstract
- Stone columns are primarily used for the purpose of ground improvement in fine grained soils in order to reduce settlements and the risk of bearing failure. They are also designed to improve the drainage conditions in the ground and to accelerate the consolidation processes within the clay. However, smear and disturbing effects caused during the construction of stone columns result in degradation of consolidation performance in comparison with the theoretically ideal conditions. Model stone columns are constructed in-flight under 50 times gravity in centrifuge tests and the soil micro-structure in the vicinity of these columns is investigated by applying different methods, including environmental scanning electron microscopy and mercury intrusion porosimetry. The results these tests confirm that smear and disturbance occur owing to stone column installation and the region influenced can be divided into three sections: a penetration zone (1) where the sand particles are squeezed through the clay; a smear zone (2) where the soil particles have experienced a significant reorientation; and a densification zone (3) where the structure of the clay does not appear to change, but compaction of the clay is measurable. The extremes of the disturbed zone around model stone columns are determined to extend to about 2.5 times the column radius.
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| 9. |
- Arnold, André, et al.
(författare)
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Centrifuge modelling of the behaviour of flexible raft foundations on clay and sand
- 2010
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Ingår i: Physical Modelling in Geotechnics. - 9780415592895 ; , s. 679-684
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Konferensbidrag (refereegranskat)abstract
- In recent decades, foundations used for housing constructions changed from strip foundations to flexible rafts including the whole ground floor. Strip foundations were usually calculated with the assumption of an even stress distribution, and this is often applied to modern flexible raft foundations. The result of these calculations does not represent reality and may often lead to inappropriate design and unexpected structural damage. Physical model tests have been carried out to study the stress distribution on different foundation types on a variety of soils, and under various loading scenarios. A better understanding of the stress distribution between foundation and soil is possible due to normal stress measurements at the interface. For working loads, a clear difference in stress transfer between foundation and clay and sand soils could be observed while a change in depth of soil or shallow inclined bedrock has less effect on the stress distribution at the interface. © 2010 Taylor & Francis Group, London.
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| 10. |
- Askarinejad, Amin, et al.
(författare)
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Effect of bedrock shape and drainage properties on the stability of slopes
- 2014
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Ingår i: Physical Modelling in Geotechnics - Proceedings of the 8th International Conference on Physical Modelling in Geotechnics 2014, ICPMG 2014. - 9781138022225 ; , s. 1211-1217
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Konferensbidrag (refereegranskat)abstract
- Rainfall induced slope failures were investigated in a series of centrifuge tests on slopes underlain by different bedrock profiles. These tests were designed to interpret observations made during two full scale landslide triggering experiments, focusing on the effect of hydro-mechanical interactions between a soil layer and bedrock during rainfall events. A climate chamber was designed and constructed for the ETH Zurich geotechnical drum centrifuge (Springman et al. 2001). Two different bedrock profiles were tested. The bedrock was parallel to the slope surface as the benchmark, whereas a convex form was placed at the toe of the slope in the alternative, which has potential to act as a supporting buttress. The changes in the pore pressures at the interface of the soil and bedrock were measured. Moreover, the surface movements were monitored by means of cameras installed in the climate chamber. The hydraulic and mechanical responses of the slopes suggested that a convex form of bedrock at the toe might have a "buttressing" effect to the upper parts of the slope due to arching. Moreover, this stabilising effect would be more pronounced if an efficient drainage system was in place behind the buttress to drain locally high pore pressures. © 2014 Taylor & Francis Group.
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