DEVELOPMENT OF METHOD AND CRITERIA FOR EVALUATION OF DRY-WASHING EFFICIENCY WITH RE-CON ZERO EVO

acceptedVersio

Influence of large-scale asperities on the stability of concrete dams

For concrete dams founded on rock, there are only a few options in the common analysis methods to account for large‐scale asperities. However, previous research alludes that they have a significant impact on the behaviour of interfaces under shear. This study investigates the behaviour of concrete dam scale models with varying interface geometries, under a realistic set of eccentric loads. The outcome of the scale model tests shows that not only the capacity of the scale models was significantly impacted by the asperities, but also the type of failure in the scale models.Influence of large-scale asperities on the stability of concrete damspublishedVersio

Concrete Dams Constructed on Soil Materials

Rock may not always be encountered at economical depth to have foundation dam on it. It is a typical situation in Nepal where several meters deep alluvium is expected before reaching competent rock. Several dams have been constructed on soil materials and several other are in planning or construction. Uncertainties in foundation behavior of soil due to heterogeneous properties makes soil foundation unique. This study attempts to find the methods of estimating foundation response and applying it to Upper Tamakoshi hydroelectric project in Nepal. A 2D model of dam was prepared in PLAXIS 2D. The model was built in a sequence similar to construction of dam at site to get reasonable response in FEM. Due to insufficient field studies all parameters required as input parameters in PLAXIS cannot be obtained. Hence, average values of soil parameters from literature were taken for soil of similar grain size distribution. Model was run for different loading (water level) scenarios at different sections of dam. In addition, liquefaction susceptibility study was carried out and possible consequences of liquefaction was studied. Safety of dam against sliding and overturning were studied. In addition, settlement and differential settlement were studied and stress induced in dam body and on foundation soil due to differential settlement were evaluated at different stages of construction and operation. Furthermore, seepage analysis was carried out for different water level scenarios. Seepage analysis with different design of grout curtain was done and the results were evaluated and compared with current design. Bearing capacity in the soil was checked and stresses development in the dam body and foundation were checked with allowable stresses. As no penetration test were done, liquefaction susceptibility and their effects were presented in curves for different penetration resistance. In conclusion, this study has been successful in identifying key issues related to concrete dams constructed on soil materials and estimating their magnitudes and effects. Foundation studies and input parameters play key role in estimation of response close to insitu situation. Improvements on this study can be made by applying this case to a monitored dam, and comparing the results of these analysis with monitored data

Influence of location of large-scale asperity on shear strength of concrete-rock interface under eccentric load

The location and geometry of large-scale asperity present at the foundation of concrete gravity dams and buttress dams affect the shear resistance of the concrete-rock interface. However, the parameters describing the frictional resistance of the interface usually do not account for these asperities. This could result in an underestimate of the peak shear strength, which leads to significantly conservative design for new dams or unnecessary stability enhancing measures for existing ones. The aim of this work was to investigate the effect of the location of first-order asperity on the peak shear strength of a concrete-rock interface under eccentric load and the model discrepancy associated with the commonly used rigid body methods for calculating the factor of safety (FS) against sliding. For this, a series of direct and eccentric shear tests under constant normal load (CNL) was carried out on concrete-rock samples. The peak shear strengths measured in the tests were compared in terms of asperity location and with the predicted values from analytical rigid body methods. The results showed that the large-scale asperity under eccentric load significantly affected the peak shear strength. Furthermore, unlike the conventional assumption of sliding or shear failure of an asperity in direct shear, under the effect of eccentric shear load, a tensile failure in the rock or in the concrete could occur, resulting in a lower shear strength compared with that of direct shear tests. These results could have important implications for assessment of the FS against sliding failure in the concrete-rock interface.publishedVersio

Influence of location of large-scale asperity on shear strength of concrete-rock interface under eccentric load

The location and geometry of large-scale asperity present at the foundation of concrete gravity dams and buttress dams affect the shear resistance of the concrete-rock interface. However, the parameters describing the frictional resistance of the interface usually do not account for these asperities. This could result in an underestimate of the peak shear strength, which leads to significantly conservative design for new dams or unnecessary stability enhancing measures for existing ones. The aim of this work was to investigate the effect of the location of first-order asperity on the peak shear strength of a concrete-rock interface under eccentric load and the model discrepancy associated with the commonly used rigid body methods for calculating the factor of safety (FS) against sliding. For this, a series of direct and eccentric shear tests under constant normal load (CNL) was carried out on concrete-rock samples. The peak shear strengths measured in the tests were compared in terms of asperity location and with the predicted values from analytical rigid body methods. The results showed that the large-scale asperity under eccentric load significantly affected the peak shear strength. Furthermore, unlike the conventional assumption of sliding or shear failure of an asperity in direct shear, under the effect of eccentric shear load, a tensile failure in the rock or in the concrete could occur, resulting in a lower shear strength compared with that of direct shear tests. These results could have important implications for assessment of the FS against sliding failure in the concrete-rock interface.publishedVersio

Influence of location of large-scale asperity on shear strength of concrete-rock interface under eccentric load

The location and geometry of large-scale asperity present at the foundation of concrete gravity dams and buttress dams affect the shear resistance of the concrete-rock interface. However, the parameters describing the frictional resistance of the interface usually do not account for these asperities. This could result in an underestimate of the peak shear strength, which leads to significantly conservative design for new dams or unnecessary stability enhancing measures for existing ones. The aim of this work was to investigate the effect of the location of first-order asperity on the peak shear strength of a concrete-rock interface under eccentric load and the model discrepancy associated with the commonly used rigid body methods for calculating the factor of safety (FS) against sliding. For this, a series of direct and eccentric shear tests under constant normal load (CNL) was carried out on concrete-rock samples. The peak shear strengths measured in the tests were compared in terms of asperity location and with the predicted values from analytical rigid body methods. The results showed that the large-scale asperity under eccentric load significantly affected the peak shear strength. Furthermore, unlike the conventional assumption of sliding or shear failure of an asperity in direct shear, under the effect of eccentric shear load, a tensile failure in the rock or in the concrete could occur, resulting in a lower shear strength compared with that of direct shear tests. These results could have important implications for assessment of the FS against sliding failure in the concrete-rock interface

Influence of location of large-scale asperity on shear strength of concrete-rock interface under eccentric load

The location and geometry of large-scale asperity present at the foundation of concrete gravity dams and buttress dams affect the shear resistance of the concrete-rock interface. However, the parameters describing the frictional resistance of the interface usually do not account for these asperities. This could result in an underestimate of the peak shear strength, which leads to significantly conservative design for new dams or unnecessary stability enhancing measures for existing ones. The aim of this work was to investigate the effect of the location of first-order asperity on the peak shear strength of a concrete-rock interface under eccentric load and the model discrepancy associated with the commonly used rigid body methods for calculating the factor of safety (FS) against sliding. For this, a series of direct and eccentric shear tests under constant normal load (CNL) was carried out on concrete-rock samples. The peak shear strengths measured in the tests were compared in terms of asperity location and with the predicted values from analytical rigid body methods. The results showed that the large-scale asperity under eccentric load significantly affected the peak shear strength. Furthermore, unlike the conventional assumption of sliding or shear failure of an asperity in direct shear, under the effect of eccentric shear load, a tensile failure in the rock or in the concrete could occur, resulting in a lower shear strength compared with that of direct shear tests. These results could have important implications for assessment of the FS against sliding failure in the concrete-rock interface

Influence of location of large-scale asperity on shear strength of concrete-rock interface under eccentric load

The location and geometry of large-scale asperity present at the foundation of concrete gravity dams and buttress dams affect the shear resistance of the concrete-rock interface. However, the parameters describing the frictional resistance of the interface usually do not account for these asperities. This could result in an underestimate of the peak shear strength, which leads to significantly conservative design for new dams or unnecessary stability enhancing measures for existing ones. The aim of this work was to investigate the effect of the location of first-order asperity on the peak shear strength of a concrete-rock interface under eccentric load and the model discrepancy associated with the commonly used rigid body methods for calculating the factor of safety (FS) against sliding. For this, a series of direct and eccentric shear tests under constant normal load (CNL) was carried out on concrete-rock samples. The peak shear strengths measured in the tests were compared in terms of asperity location and with the predicted values from analytical rigid body methods. The results showed that the large-scale asperity under eccentric load significantly affected the peak shear strength. Furthermore, unlike the conventional assumption of sliding or shear failure of an asperity in direct shear, under the effect of eccentric shear load, a tensile failure in the rock or in the concrete could occur, resulting in a lower shear strength compared with that of direct shear tests. These results could have important implications for assessment of the FS against sliding failure in the concrete-rock interface

Influence of concrete’s mechanical properties on the cracking of concrete dams

Analytical methods of structural stability assessment of concrete dams are often too simple and thus conservative in their predictions.Without the actual foundation geometry, capacity for some rigid body failure modes are underestimated. This is problematic when deciding upon remediation activities of a dam that is considered unstable and may divert the restoration activities from where they are most impactful. In a previous study by Sas et al. 2019 where a section of an existing dam was scaled down and tested experimentally, the model indicated that several areas were experiencing large stresses, potentially leading to failure. This raised the research question whether another type of failure would occur for different material properties. Therefore, this paper delves into a probabilistic numerical approach, through finite element analysis, to evaluate dam stability based on randomization of a number of material properties such as modulus of elasticity, tensile strength, compressive strength, and fracture energy. The variation of the aforementioned material properties did not impact the failure mode, which was consistent among a broad range of material strengths.publishedVersio

Influence of large-scale asperities on the shear strength of concrete-rock interface of small buttress dams

This paper presents an investigation of the influence of large-scale asperities on the shear strength of four physical models of a pillar (also known as buttress web)from Kalhovd dam in Norway. The objective was to observe the structural behaviour of the pillar under design and ultimate loading scenarios and to compare results of the tests with those of nonlinear finite element analysis (FEA) and standard guideline methods. Four models at 1:5 scale were prepared with different interface profiles and tested. The results from model test and the results of a benchmarking process carried out with nonlinear FEA are presented. Furthermore, the FEA was expanded to other hypothetical scenarios to extend understanding of effects of the locations and inclinations of large-scale asperities on the sliding stability of concrete dams. The results are compared with those obtained using standard design methods and estimated safety factors are presented