| 1. |
- Ansal, A., et al.
(författare)
-
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
-
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)
-
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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| 11. |
- Bowman, Elisabeth T., et al.
(författare)
-
Debris flows in a geotechnical centrifuge
- 2006
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Ingår i: Physical Modelling in Geotechnics, 6th ICPMG'06. - 041541587X - 9780415415873 ; , s. 311-316
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Konferensbidrag (refereegranskat)abstract
- A new apparatus to allow the examination of laboratory debris flows at prototype stress levels within a geotechnical drum centrifuge is described. The apparatus consists of a curved aluminium flume that lies within the circumference of the drum, the inclination of which can be altered from 0 to 40 degrees. PPTs may be placed in the base and along one aluminium side wall, while the other wall is made from Perspex, to enable viewing of the flow during a test. A tube at the head of the flume enables flow materials to be introduced after preparation external to the centrifuge, while tests may be carried out with both fixed and erodible beds. A high speed camera is used to capture images of the flow during centrifuge flight. Initial tests suggest a maximum particle size of 4mmmay be introduced to the flow.The influence ofwater content and fluid viscosity is discussed. © 2006 Taylor & Francis Group, London.
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| 12. |
- Bowman, Elisabeth T., et al.
(författare)
-
Experimental modelling of debris flow behaviour using a geotechnical centrifuge
- 2010
-
Ingår i: Canadian geotechnical journal (Print). - 0008-3674 .- 1208-6010. ; 47:7, s. 742-762
-
Tidskriftsartikel (refereegranskat)abstract
- Physical modelling of debris flows has been carried out in the geotechnical drum centrifuge at ETH Zürich. A new apparatus to model debris flows in the centrifuge is described. The apparatus permits the final reach of a typical debris flow to be modelled within the centrifuge, with unconsolidated material flowing down a slope to deposit as a fan around the drum. Experiments are described for both fixed base conditions and erodible bases. Tests to examine the verification (modelling) of models show that debris flow behaviour is governed mainly by friction and consolidation processes, although some resolution is required between flow behaviour downslope and flow arrest during runout. The results are compared with bulk parameters determined for field-scale debris flows. It is found that some important flow mechanisms, such as contact-dominated behaviour and high pore pressures, are developed that are closer to those developed at fieldscale than tests conducted at 1g. Velocity profiles for erodible beds are compared with a semi-empirical expression derived for experimental debris flows at 1g. Normalized velocity profiles are found to be in agreement; however, absolute velocities differ from those predicted. Scaling, the limitations of the apparatus, and potential for future work are discussed
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| 13. |
- Bowman, Elisabeth T., et al.
(författare)
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Geotechnical centrifuge modelling of debris flows
- 2007
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Ingår i: International Conference on Debris-Flow Hazards Mitigation. - 9789059660595 ; , s. 229-239
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Konferensbidrag (refereegranskat)abstract
- A granular debris flow may grow in size through erosion of its substrate, resulting in an increased hazard through greater mass, speed and runout. Exactly what governs the erosion potential of a particular flow is a matter of some debate, however, with apparently similar conditions producing very different entrainment behaviour. Some theories use an extension of sediment transport models that involve the removal of soil through a shear stress applied by the flow. However, comparison of field and laboratory-scale data suggests that other processes, such as undrained loading of the bed, are also likely to have influence at large scales. Hence properties of the bed need to be considered as well as the characteristics of the flow material. The modelling of erosion processes at laboratory scale is generally limited by the low stresses applied by the soil-water mixture at small scale. Modelling flows in a geotechnical centrifuge overcomes this problem by increasing the g-level, therefore allowing for correct prototype stress levels to be accounted for at small scale. This paper describes the development and use of a model debris flow apparatus on a geotechnical drum centrifuge at ETH in Zurich, Switzerland. Preliminary tests have been undertaken to compare fixed and erodible bed conditions - enabling erosion processes to be examined at prototype stress levels. © 2007 Millpress.
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| 14. |
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| 15. |
- Chikatamarla, R., et al.
(författare)
-
Modelling of rockfall on protection galleries
- 2006
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Ingår i: Physical Modelling in Geotechnics, 6th ICPMG'06. - 041541587X - 9780415415873 ; , s. 331-336
-
Konferensbidrag (refereegranskat)abstract
- Rockfall impact energies can reach magnitudes of the order of millions of Joules, requiring understanding of the energy absorption mechanisms at high energy levels for improved design of the protection gallery. These high-energy ranges can be achieved at the laboratory scale with the help of a geotechnical centrifuge. In centrifuge, rockfall protection galleries are studied with an aim to optimise the design procedure by using a cushion material. Different cushion materials have been modelled against vertical and inclined impacts of steel block with input energy levels up to 20 MJ.A simple FE model (LS-DYNA) is used in addition to model the boulder impact on different cushion materials. The results from the centrifuge tests in terms of acceleration values of the boulder and deflection of the slab are discussed and a new design procedure for the protection galleries based on the centrifuge and numerical investigations has been proposed. © 2006 Taylor & Francis Group, London.
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| 16. |
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| 17. |
- Chikatamarla, R., et al.
(författare)
-
Rockfall impact on protection galleries
- 2004
-
Konferensbidrag (refereegranskat)abstract
- Rockfalls are one of the most prevailing natural hazards in the mountainous regions in Switzer- land. Concrete protection galleries are used to protect the local infrastructure and lifelines against these poten- tial rock impacts. Cushion materials are laid on these galleries to absorb the rockfall impact energy, which is one of the main input parameters in the design of the protection gallery. An attempt has been made to reduce the impact energies by placing a better damping material on the gallery. The high rock impact energy ranges are difficult to model at the laboratory scale. Field tests are generally avoided due to the high costs involved and also due to the singularity of the potential tests. The prototype energy levels can be achieved at the labo- ratory scale with the help of a geotechnical centrifuge. An instrumented model of the protection gallery is ro- tated under high g levels, thereby increasing the unit weight of the material. With the help of appropriate scal- ing laws, the prototype energy levels can be achieved. This paper focuses on the determination of the impact force of a rockfall of a specific energy and the forces induced in the gallery. The maximum acceleration val- ues of the rock and deflection of the galleries are compared for different energy ranges and cushion materials. The test results are later compared with numerical modelling using the finite element program LS-DYNA. Rockfall impact on protection galleries | Request PDF. Available from: https://www.researchgate.net/publication/242415233_Rockfall_impact_on_protection_galleries [accessed Aug 20 2018].
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| 18. |
- Chikatamarla, R., et al.
(författare)
-
Stress distribution of rockfall events on galleries
- 2005
-
Ingår i: Proceedings of the 16th International Conference on Soil Mechanics and Geotechnical Engineering. - 9059660285 - 9789059660281 ; , s. 2789-2792
-
Konferensbidrag (refereegranskat)abstract
- Rockfall galleries are built to protect local infrastructure and lifelines against rockfall events. They are covered usually with a soil layer, sometimes for aesthetical reasons but also for protection against impact from rockfalls and snow avalanches. The effect of the impact has been quantified in a research project by investigating the properties of the cover (cushion) material. The stress distribution caused by a rockfall event is measured in centrifuge model tests by means of a tactile multipoint pressure transducer on the gallery below the cushion material as well as point load measurements at supports and strain gauges to determine bending of the gallery slab. The technique of measuring stress distribution under a soil layer is adapted from bio-medicine and the car industry to soil mechanics. Features of these pressure sensors will be discussed in relation to the response to a rockfall event and for different types and thicknesses of cushion material. Numerical modelling has also been carried out using LS DYNA. Knowledge gained can be used for formulation of guidelines for the gallery design.
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| 19. |
- Chikatamata, R., et al.
(författare)
-
Centrifuge scaling laws for guided free fall events including rockfalls
- 2006
-
Ingår i: International Journal of Physical Modelling in Geotechnics. - : Thomas Telford Ltd.. - 1346-213X .- 2042-6550. ; 6:2, s. 15-26
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Tidskriftsartikel (refereegranskat)abstract
- Concrete protection galleries are generally used in mountainous regions to protect the local infrastructure and lifelines against potential impacts from rock boulders. These can be protected further by carefully designed cushion systems, most of which rely on granular geomaterials. Rockfall impact energies can reach magnitudes of the order of millions of Joules, requiring understanding of the combined energy absorption mechanisms at high energy levels for improved design of the gallery and cushion. These prototype high-energy ranges can be achieved at the laboratory scale with the help of a geotechnical centrifuge. The model is rotated under high g levels, thereby increasing the unit weight of the material. Prototype energy levels can be represented in a small scale model with consideration of appropriate scaling laws, and although free fall events in a centrifuge experience components of the Coriolis acceleration, projectiles (boulders) will move out of the centripetal gravity field when losing contact with the rotational field. A guiding tube is used in this case to keep the boulder in the acceleration field (ng) in order to achieve sufficient input energy levels to represent existing design criteria. The change in the g-level during the fall of the boulder in the centrifuge, due to the change in the radius, has to be taken into account for determination of the impact energy. In this case, direct application of traditional scaling laws for centrifuge modelling is invalid. This paper focuses on the determination of the change in the g field with time during the fall of the boulder to estimate the g level at the time of impact and this value is used in the calculation of the prototype energy levels. A summary of the performance of various cushion materials is given
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| 20. |
- Gautray, J., et al.
(författare)
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Investigation of the spatial distribution of installation effects around stone columns with an electrical needle
- 2014
-
Ingår i: Physical Modelling in Geotechnics - Proceedings of the 8th International Conference on Physical Modelling in Geotechnics 2014, ICPMG 2014. - 9781138022218 ; , s. 289-294
-
Konferensbidrag (refereegranskat)abstract
- Stone columns provide valuable ground improvement in soft soils in numerous projects around the world. They increase the stiffness of the subsoil and reduce time needed for consolidation. This last aspect is due to the fact that the main drainage direction switches from being vertical to being radial, significantly reducing the length of the drainage path. However, driving the installation mandrel into the ground causes changes in the structure of the subsoil, usually referred to as smear zones, which decrease the drainage performance of granular inclusions. The implementation of a needle to measure the impedance (electrical resistivity) in-flight in the geotechnical centrifuge at ETH Zürich enables an insight to be made into the pore size distribution with depth close to a stone column constructed in-flight. © 2010 Taylor & Francis Group, London.
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| 21. |
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| 22. |
- Imre, Bernd, et al.
(författare)
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A centrifuge experiment to derive insight on rock fragmentation within sturzstroms
- 2010
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Ingår i: Physical Modelling in Geotechnics. - 9780415592901 ; , s. 1253-1258
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Konferensbidrag (refereegranskat)abstract
- This study presents boundary conditions and instrumentation for a centrifuge experiment to simulate fragmentation within a fast moving rock mass as part of a research effort to investigate the thermodynamics of sturzstroms. Sturzstroms are rock slides of very large volume and extreme run out, which display intensive fragmentation of blocks of rock due to inter-particle impacts within a collisional flow regime. The mechanical set up of this physical model delivers a guided experimental rock slide imposed by a dynamic acceleration field. Analogue rock material is stored in a hopper and released in-flight by a pneumatic trap door into an acceleration chute, and progressing to a run out chute. This reflects the prototype situation of a sturzstrom which includes a source, transit, and deposition zone. The instrumentation includes light barriers, a triaxial force sensor, frictional heat sensors, and high and low speed cameras with illumination provided by light emitting diodes. © 2010 Taylor & Francis Group, London.
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| 23. |
- Imre, Bernd, et al.
(författare)
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Fractal fragmentation of rocks within sturzstroms: Insight derived from physical experiments within the eth geotechnical drum centrifuge
- 2010
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Ingår i: Granular Matter. - : Springer Science and Business Media LLC. - 1434-5021 .- 1434-7636. ; 12:3, s. 267-285
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Tidskriftsartikel (refereegranskat)abstract
- An investigation of the behaviour and energy budget of sturzstroms has been carried out using physical, analytical and numerical modelling techniques. Sturzstroms are rock slides of very large volume and extreme run out, which display intensive fragmentation of blocks of rock due to inter-particle collisions within a collisional flow. Results from centrifugal model experiments provide strong arguments to allow the micro-mechanics and energy budget of sturzstroms to be described quantitatively by a fractal comminution model. A numerical experiment using a distinct element method (DEM) indicates rock mass and boundary conditions,which allowan alternating fragmenting and dilating dispersive regime to evolve and to sustain for long enough to replicate the spreading and run out of sturzstroms without needing to resort to peculiar mechanism. The fragmenting spreading model supported here is able to explain the run out of a fluid-absent granular flow beyond the travel distance predicted by a Coulomb frictional sliding model. This, and its strong relation to internal fragmentation, suggests that a sturzstrom constitutes a landslide category of its own. This study provides a novel framework for the understanding the physics of such sturzstroms.
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| 24. |
- Kailey, P., et al.
(författare)
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Modeling Debris flow behavior in a geotechnical centrifuge
- 2011
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Ingår i: Italian Journal of Engineering Geology & Environment. - 1825-6635 .- 2035-5688. ; , s. 339-349
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we examine the effect of flow massand moisture content on debris flow velocity, discharge,and runout using a series of smallscale flumetests in a geotechnical centrifuge. We found that anincrease in mass and an increase in moisture contentincreased peak velocity during down-slope movement.However, the effect of increased moisture contentis much more pronounced than that of increasedmass. The maximum cross-sectional area observeddid not depend on mass or moisture content, althoughmay have been affected by the flow rate entering thecentrifuge. Consequently, flow velocity largely determinedthe peak discharge of each flow. An increasein moisture content increased the mobility of the flowin terms of depositional area and runout. Further, therunout of the centre of mass of the flows appears tobe linearly related to the momentum of flow materialentering the flume.
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| 25. |
- Kailey, P., et al.
(författare)
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Modelling debris flow processes with a geotechnical centrifuge
- 2011
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Ingår i: International Conference on Debris-Flow Hazards Mitigation. - 9788895814469 ; , s. 339-349
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Konferensbidrag (refereegranskat)abstract
- In this paper, we examine the effect of flow mass and moisture content on debris flow velocity, discharge, and runout using a series of smallscale flume tests in a geotechnical centrifuge. We found that an increase in mass and an increase in moisture content increased peak velocity during down-slope movement. However, the effect of increased moisture content is much more pronounced than that of increased mass. The maximum cross-sectional area observed did not depend on mass or moisture content, although may have been affected by the flow rate entering the centrifuge. Consequently, flow velocity largely determined the peak discharge of each flow. An increase in moisture content increased the mobility of the flow in terms of depositional area and runout. Further, the runout of the centre of mass of the flows appears to be linearly related to the momentum of flow material entering the flume. © 2011 Casa Editrice Università La Sapienza.
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| 26. |
- Kapogianni, Elena, et al.
(författare)
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Investigation of the Mechanical Behaviour of the Interface between Soil and Reinforcement, via Experimental and Numerical Modelling
- 2016
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Ingår i: Procedia Engineering. - : Elsevier BV. - 1877-7058. ; 143, s. 419-426
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study is to investigate the interface properties between soil and reinforcement, via experimental and numerical modelling of reinforced slopes. In particular, several scale models were built and tested under enhanced gravity in the geotechnical drum centrifuge at ETH Zurich and corresponding prototype numerical models were analyzed via a finite element stress analysis code. Optical fibre sensors were attached on the reinforcement layers of the experimental scaled models in order to measure linear strain during the increase of the g-level, and the results were compared to linear strain that was derived by the numerical analysis of the correspondent prototype reinforced slopes. The interface between soil and reinforcement was expressed in terms of normal and shear stiffness on the soil-reinforcement boundary and different values were tested in order to achieve validation of the experimental and numerical results.
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| 27. |
- Kapogianni, Elena, et al.
(författare)
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The use of optical fibre sensors in a geotechnical centrifuge for reinforced slopes
- 2010
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Ingår i: Physical Modelling in Geotechnics. - 9780415592895 ; , s. 343-348
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Konferensbidrag (refereegranskat)abstract
- The purpose of this paper is to investigate making strain measurements via optical fibre sensors in a geotechnical centrifuge. This study is part of a test series, which has been carried out in the ETH Zurich geotechnical centrifuge, with the main goal being to investigate the behaviour of reinforced slopes that are subjected, initially, to self weight loading and, subsequently, to impact from a rockfall event. Several reinforced slope models were built with a height of 18 cm and a slope inclination of 2V:1H. The maximum g-level applied was 100 g and the optical fibre sensors were placed on the reinforcement layers at various positions in the model in order to measure the deformations of the reinforcement during the different loading events. © 2010 Taylor & Francis Group, London.
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| 28. |
- Laue, J., et al.
(författare)
-
15 years of experience using a physical model exercise in a Masters' course
- 2014
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Ingår i: Physical modelling in geotechnics. - Leiden : CRC Press/Balkema. - 9781138022218 ; , s. 445-450
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Konferensbidrag (refereegranskat)abstract
- Modelling in Geotechnics' has been taught for two hours over 14 weeks in the 2nd, and later 3rd, semester of the Masters' studies at ETH Zurich. In addition to a series of frontal lectures on modelling techniques, as well as for their application to various boundary value problems, this course contains an exercise that compares 3 ways of modelling a practical case. Students are invited to investigate a common boundary value problem through complementary analytical, physical and numerical (finite element) modelling. A suitable boundary value problem, such as for shallow foundations or slopes, is selected to ensure that the exercise can be conducted in the limited time available for the students, and that the physical model takes only a finite amount of time so that all students can witness a test from start to finish. A comparison allows the assumptions made for the various models or calculations to be discussed and trains the students to put the different results into perspective. Practical aspects such as feasibility and timing, as well as applicability to reaching the learning goal of the class, will be reviewed. © 2010 Taylor & Francis Group, London.
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| 29. |
- Laue, Jan, et al.
(författare)
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A soil exploration exercise in Bachelor's level education in soil mechanics
- 2009
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Ingår i: Proceedings of the 17th International Conference on Soil Mechanics and Geotechnical Engineering. - 9781607500315 ; , s. 2752-2755
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Konferensbidrag (refereegranskat)abstract
- Geotechnical education at Bachelor level usually commences with a simplified theoretical introduction into soil mechanics, which may be supported later during the course by hands-on laboratory experiments to cover classification of soils and provide the evidence for the elementary mechanical behaviour of soils. The application of such a curriculum to practice is challenging because the students are not confronted with practical reality where limited information is available to develop a model of the ground. An exercise on site investigation has been developed and incorporated into the ETH Zurich soil mechanics course to help to bridge this gap based on an initial development for undergraduate education in soil mechanics at the University of Sheffield. This exercise, focusing on the three aspects of practical site investigation, creation of a soil model and decision making for best soil condition for a foundation will be introduced and described here. It has been compulsory for the Bachelor students in their first geotechnical course during the first three years after its development. After gaining more experience with the exercise, and under the pressure of growing numbers of students, it has been changed from being compulsory for all students to one of the challenges, from which the students have to select and pass 4 out of 6. Regular evaluation by the students shows that the students appreciate this practical experience and are surprised how little information is often available for practical design tasks. © 2009 IOS Press.
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| 30. |
- Laue, Jan, et al.
(författare)
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Creating seafloor conditions in geotechnical centrifuges
- 2005
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Ingår i: Proceedings of the 16th International Conference on Soil Mechanics and Geotechnical Engineering. - 9059660285 - 9789059660281 ; , s. 1741-1744
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Konferensbidrag (refereegranskat)abstract
- Soil models can be built in geotechnical centrifuges under specified procedures with good reproducibility between 40 and 100 % relative density. Nevertheless, many problems require model making with loose samples, especially when seafloor conditions are to be represented. Samples for arm centrifuges are disturbed during transport of a model container from the laboratory to the centrifuge and they require complex procedures to create a model in-flight. Nevertheless, loose granular soil samples can be produced in flight in a geotechnical drum centrifuge, which even offers a large area for potential offshore tests. The procedure adopted to create the sample, as well as first site investigation tests using a piezocone, and shallow foundation tests will be presented, together with a critical discussion on the quality of the sample.
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| 31. |
- Laue, Jan, et al.
(författare)
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Einsatz moderner Modell- und Messtechniken für geotechnische Untersuchungen in der Trommelzentrifuge der ETH – Zürich
- 2003
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Ingår i: Bauingenieur. - 0005-6650 .- 1436-4867. ; 78, s. 66-72
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Tidskriftsartikel (refereegranskat)abstract
- The use of modern modelling and measuring techniques is discussed for physical geotechnical modelling in the drum centrifuge of ETH Zürich, which was inaugurated officially in June 2001. Developments in these techniques in recent years allow increasingly complex geotechnical problems to be modelled physically, for example for research on soil-structure interaction as well as natural hazards. Results may be used for comparison with full scale data or theory and for calibration of numerical models. These advances are related to all areas of physical modelling including testing facilities, preparation of models, control of the physical model as well as observation methods and data acquisition. In addition to the introduction of this new testing facility, multifunctional actuators will be shown using the latest developments in mechatronics. Preparation of models will be discussed as well as new data acquisition and other test control options. Finally some examples of the use of modern transducers, for instance flexible tactile pressure pads, will be given allowing the measurement of normal stress distribution at the soil-foundation interface.
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| 32. |
- Laue, Jan, et al.
(författare)
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Preparation of soil samples in drum centrifuges
- 2002
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Ingår i: Physical modelling in geotechnics, ICPMG '02. - Lisse : Balkema. - 9058093891 ; , s. 143-148
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Konferensbidrag (refereegranskat)abstract
- The controlled preparation of a soil sample in a drum centrifuge is rather more difficult than in a beam centrifuge. Nevertheless, the challenges of model-making also offer another dimension to this process. The techniques developed for the sample preparation in the ETH Zurich Drum Centrifuge will be described in this paper. This includes a short description of the machine and the associated equipment, together with some preliminary results and findings of a study on model-making in sand. Preparation of clay samples is also mentioned, although some of these findings are not restricted to drum centrifuges.
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| 33. |
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| 34. |
- Morales, W. F., et al.
(författare)
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Controlled water-level system for breach analysis of levees within an enhanced acceleration field
- 2012
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Konferensbidrag (refereegranskat)abstract
- Correct scaling of breach analysis of river levees is a challenging task that is not easilyaccomplished by physical modelling. Several small-scale physical model tests have been conducted at 1-glevel, which cannot truly represent the stress-dependency of soils, whereas the scaling issues arising fromcentrifuge modelling have not been fully explored.Two key features have to be considered whenmodelling the prototype behaviour. On the one hand, the whole embankment should be included in themodel to ensure that flow nets are valid. This is not always easy to achieve due to space limitations withinthe strongboxes used. On the other hand, full control of water levels, prior and during breaching, is ofprincipal interest.This contribution shows how both of these features can be modelled for levee breachingby taking advantage of the availability of space within a drum centrifuge and its versatile toolplate.
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| 35. |
- Morales, W. F., et al.
(författare)
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Design and analysis procedure for centrifuge devices with a Product Lifecycle Management (PLM) system
- 2012
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Konferensbidrag (refereegranskat)abstract
- Structural analysis of new devices to be used in centrifuge facilities can be a challenging task. Initial calculations, based on simple basic static principles, are usually used. However, as devices placed in a geotechnical centrifuge are often complex structures, advanced analysis methods to assess their performance under enhanced acceleration fields are desirable. This paper presents the analysis of the performance of a new strongbox designed for a centrifuge facility at ETH Zurich by using a commercial Product Lifecycle Management (PLM) software.
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| 36. |
- Morales, W. F., et al.
(författare)
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On the use of unsaturated properties of a sandy material for centrifuge model preparation
- 2013
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Ingår i: Advances in Unsaturated Soils. - 9780415620956 ; , s. 159-164
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Konferensbidrag (refereegranskat)abstract
- This contribution shows how the unsaturated properties of a uniform sandy material are used to create stable vertical surfaces when building dyke models for testing in a geotechnical drum centrifuge. The model is constructed inside a 1.0 m (length) × 0.54 m (depth) × 0.36 m (width) box with a semi-circular base, which must then be tilted through 90° to place the model into the channel of the centrifuge drum. A construction procedure has been developed to create unsaturated conditions in the sand so that the suctions are large enough to ensure that the 0.5 m high vertical walls remain stable for a short period of time until the centrifuge test can begin. This has been backed up by 3D numerical finite element calculations of the performance of the model in an unsaturated state. © 2013 Taylor & Francis Group, London.
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| 37. |
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| 38. |
- Najser, Jan, et al.
(författare)
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Mechanisms controlling the behaviour of double-porosity clay fills : in situ and centrifuge study
- 2010
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Ingår i: Quarterly journal of engineering geology and hydrogeology. - : Geological Society of London. - 1470-9236 .- 2041-4803. ; 43:2, s. 207-220
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Tidskriftsartikel (refereegranskat)abstract
- Two instrumented embankments built on a double-porosity landfill of clayey lumps were monitored in situ and modelled in a geotechnical drum centrifuge. Field measurements of hydrostatic levelling, depth reference points and pore pressure gauges showed high and variable compressibility of the landfills. Introductory modelling in a mini-centrifuge, combined with oedometer testing, demonstrated the key mechanisms in the double-porosity fills: irreversible deformation at low stress ranges as a result of rearrangement of the lumps, and reversible deformation (swelling) at higher stresses, similar to the behaviour of reconstituted material. Placing fill under water resulted in high initial void ratios followed by large deformations while loading. Dry filling followed by saturation may be recommended for further development of the landfills in future. Data from the geotechnical centrifuge models confirmed that permeability was controlled by the complex structure of the clay fills. Similarly to the field measurements, there were significant initial settlements on loading as a result of compression of open macro-voids. The double-porosity structure in the fresh fill allowed excess pore pressures to dissipate quickly, which accelerated the consolidation process initially. Thereafter, dissipation was controlled by the permeability of the intragranular pores in the clay, once the intergranular pores had closed
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| 39. |
- Nater, P., et al.
(författare)
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Modelling of shallow foundations on homogeneous and layered soils
- 2001
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Ingår i: Proceedings of the Fifteenth International Conference on Soil Mechanics and Geotechnical Engineering, Istanbul, 27-31 August 2001. - Lisse : Balkema. - 9026518536 ; , s. 755-760
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Konferensbidrag (refereegranskat)abstract
- Major Swiss development zones lie mostly upon infilled sedimentary deposits where layering becomes an important feature. Swiss foundation design methods are revisited to focus on these typical soil conditions. Other tools are also introduced, compared and applied to calculation examples to clarify the range of results and interpretation for similar soil properties; e.g. numerical and physical modelling. The physical modelling has been carried out in the geotechnical centrifuge facilities in Bochum and Zurich.
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| 40. |
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| 41. |
- Pooley, Emma J., et al.
(författare)
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Assessment of the use of dynamic compaction on double porosity clay landfill
- 2009
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Ingår i: Proceedings of the 17th International Conference on Soil Mechanics and Geotechnical Engineering. - 9781607500315 ; , s. 2252-2255
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Konferensbidrag (refereegranskat)abstract
- Open cast coal mining in Northern Bohemia produces overburden waste of overconsolidated clay lumps that are placed in spoil heaps or used as backfill in exploited mines. This forms landfills with a double porosity structure consisting of voids between lumps (inter-granular) and voids within lumps (intra-granular). The total porosity can be up to 70 %, making the soil highly compressible even after self-weight consolidation. Soil behaviour is characterised by large absolute and differential settlements. Dynamic compaction is one of the ground improvement methods used before construction on these clay landfills. Model tests on scaled double porosity clay landfills were carried out in the ETH Zurich drum centrifuge. A period of self-weight consolidationwas followed by in-flight dynamic compaction. To assess and compare the strength of the clay fill, in-flight displacement-controlled rigid foundation tests were carried out on the centrifuge models. The total load on the foundation, and pressure distribution under it, were measured. © 2009 IOS Press.
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| 42. |
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| 43. |
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| 44. |
- Pooley, Emma J., et al.
(författare)
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Centrifuge modelling to compare ground improvement techniques on double porosity clay landfills
- 2009
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Ingår i: Geotechnics of Soft Soils - Focus on Ground Improvement. - 9780415475914 ; , s. 281-285
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Konferensbidrag (refereegranskat)abstract
- The ETH geotechnical drum centrifuge was used to model ground improvement on soft double porosity clay. Ground improvement was carried out in-flight and the techniques tested were dynamic compaction and an array of stone columns. Foundation tests on improved soil models showed that stone columns were more effective at increasing subsoil resistance at higher load. This may be because stone columns improve drainage of the clay layer and thus allow the clay itself to become stiffer. © 2009 Taylor & Francis Group.
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| 45. |
- Pooley, Emma J., et al.
(författare)
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Comparison of ground improvement on double porosity soil : A centrifuge study of pore pressure response
- 2014
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Ingår i: Physical Modelling in Geotechnics. - Leiden : CRC Press/Balkema. - 9781138022225 ; , s. 1137-1143
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Konferensbidrag (refereegranskat)abstract
- The ETH geotechnical drum centrifuge was used to model various ground improvement techniques on double porosity clay. Embankments, sand compaction piles, and dynamic compaction were applied to similar soil models in a series of tests. Ground improvement was carried out in-flight. The pore pressure response to different ground improvement regimes was used to compare effectiveness and suggest likely mechanisms. An optimal ground improvement technique for double porosity soil is concluded to be the use of Sand Compaction Piles (SCPs) since they decrease the intergranular porosity locally, but maintain a relatively high permeability to facilitate the further consolidation of areas of the clay where the double porosity structure is still problematic. Questions about the validity of centrifuge modelling these ground improvement methods are also discussed. © 2014 Taylor & Francis Group.
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| 46. |
- Springman, Sarah M, et al.
(författare)
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Ground improvement for embankments on soft ground
- 2014
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Ingår i: Institution of Civil Engineers. Proceedings. Ground Improvement. - : Thomas Telford Ltd.. - 1755-0750. ; 167:3, s. 149-161
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Tidskriftsartikel (refereegranskat)abstract
- Constructing embankments on soft ground to adhere to the requirements of modern codes of practice is challenging without ground improvement. An overview is presented on the types of columnar inclusions and embankment base reinforcement in terms of load–settlement behaviour, together with calculation procedures using partial safety factors. These are based on the Swiss Code 267, Switzerland's national annex to Eurocode 7; they are relevant in the project phase and in understanding the general behaviour of the whole system. Three-dimensional inclusions have been incorporated in a two-dimensional slip circle analysis. Simple assumptions are validated against a physical model for the serviceability limit state, with good agreement. First design approximations may therefore be calculated in this way.
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| 47. |
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| 48. |
- Springman, Sarah M, et al.
(författare)
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The ETH Zurich geotechnical drum centrifuge
- 2001
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Ingår i: International Journal of Physical Modelling in Geotechnics. - : Thomas Telford Ltd.. - 1346-213X .- 2042-6550. ; 1:1, s. 59-70
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Tidskriftsartikel (refereegranskat)abstract
- A new 2.2 m diameter drum centrifuge with a maximum acceleration level of 440 g has been installed at the Institute of Geotechnical Engineering of the Swiss Federal Institute of Technology in Zurich (Eidgenossiche Technische Hochschule: ETHZ). Twin concentric shafts allow separate control of a central tool table and a drum channel. Together with multipurpose actuator units, which can be fitted to the tool table, radial, circumferential and vertical control of construction processes or test activities may be achieved. Control and data acquisition systems are provided in modular form, allowing a flexible choice of sampling and recording modes. The development of the facility, the additional accessories required and the first geotechnical centrifuge test are described.
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| 49. |
- Springman, Sarah M., et al.
(författare)
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The evolution of a physical modelling course over two decades
- 2014
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Ingår i: Physical Modelling in Geotechnics. - 9781138022218 ; , s. 433-439
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Konferensbidrag (refereegranskat)abstract
- The "Modelling in Geotechnics" course was created in 1996 and was delivered in the final year of diploma studies in civil engineering at ETH Zürich. The principles of modelling were presented and discussed with reference to aspects of physical, constitutive and numerical modeling. This was followed by a series of applications to demonstrate that models can deliver a fast track to developing engineering judgement for promoting optimal geotechnical design, without the concomitant damage that occurs due to real failures, as long as the model is suitable and adheres to the requisite scaling laws. This course is now entitled 'Physical Modelling in Geotechnics' and has seen a significant rise in enrolment. A wide-ranging set of notes was developed at the beginning. These have since been extended, together with an in-house Geotechnical Information Platform GEOTip, which provides the virtual environment for documentation and exchange of ideas. © 2010 Taylor & Francis Group, London.
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