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1-Adequacy of Seepage Analysis in Core Section of the Earthen Dam with Different Mix Proportions (2015)
Abstract
Earthen dams are built since early days of civilization. These dams constitute to be the most common type, because it is generally built of locally available materials which derive strength from their position, friction and cohesion. Many earth fill dams are vulnerable to failures due to seepage problems that take place in the core since all soils are pervious to a smaller or larger extent. One of the ways to control seepage problem in earthen dam is by using proper materials for core section since the core section of earthen dam provides impermeable barrier within the body of the dam. Thus, this paper analyses the usage of various materials with different combinations to zone type earthen dams with central impervious vertical core and to study the behavior of phreatic line at downstream phase by varying effective length of horizontal drainage filter. The results obtained from laboratory, proposed geometry of dam and corresponding stability analysis made for various materials showed that materials with impervious nature only provides safety to core part of the earthen dam.
2- On the role of topographic amplification in seismic slope instabilities (2015)
Abstract
Surface wave generation due to body wave propagation near ground surface has been discussed in the literature. This phenomenon, typically occurring in topographic changing areas, along with its interaction with body waves (SV), decreases precision of formulas for evaluation of slope displacement. This significant fact caused the researchers not only to investigate the combined surface and SV waves motion pattern, but also to consider its effect on structures built on the slopes. In order to reveal the phenomenon, several finite element numerical studies have been performed by ABAQUS programme. Besides, two physical model slopes simulating the landslide occurrence have been constructed and tested by shaking table device. The results of induced and calculated accelerations obtained by two approaches have been compared and Rayleigh wave generation has been proved. Furthermore, the slope displacements have been calculated by various empirical methods and the results were compared with numerical ones. The results proved that in order to increase the precision of empirical formulas for displacement prediction, surface wave effect should be taken into account. Finally, a concept of “effective depth of surficial amplification” is introduced and its effect on dynamic slope stability is analysed.
3- Seepage and Stability Analyses of Earth Dam Using Finite Element Method (2015)
Abstract
Dams are mainly constructed of earth and rock-fill materials and hence they are generally referred to as embankment dams or fill-type dams. Earth-fill dams are simple structures which are able to prevent the sliding and overturning because of their self weight. Due to lack of suitable clay materials, sometimes the dams are designed as zoned core that is composed of three vertical zones including central impermeable core and two permeable shells on either sides of the core. A failure of earth dam is attributed to the following: hydraulic failure, seepage failure, piping through dam body and structural failure due to earthquake. The design and construction of an earth-fill dam is one of the key challenges in the field of geotechnical engineering, because of the unavoidable variation in foundation condition and the properties of the available construction materials. A homogeneous earth-fill dam should be designed with relatively flat slopes to reduce the risk of failure. The practical seepage problems are not easily convertible into an equivalent numerical counterpart because of the heterogeneity of the natural soils and the varying boundary conditions. The role of drainage system is also vital as it shifts the phreatic surface ensuring the safety of downstream toe. This paper presents the results of seepage and stability analyses of the considered earth dam using finite element method. The seepage analysis is divided into two categories viz. Steady state and Transient analyses. Based on the parametric sensitivity analysis, both the seepage and stability studies have brought out the importance of considering the coupled effects on the overall stability of the earth dam. It is concluded that the coupled analysis is a prerequisite for the design and performance evaluation of the earth dam under all conditions of seepage and stability. The study shows that increase in the Young's modulus of core and shell resulted in the decrease of the maximum crest displacement and the variation in angle of internal friction plays a vital role in the fulfilment of the overall stability criteria. The slope of 1V:2.5H was adopted for both the downstream and the upstream sides. The factor of safety (FS) was greater than 1.6 for both the full (high) reservoir condition and low reservoir condition whereas, the FS values were found to be less than the stipulated values for the other stability considerations.
4- The Washout Mechanism of the Niedów Dam and its Impact on the Parameters of the Flood Wave (2014)
Abstract
On 07 August 2010 a disaster occurred at the barrage Niedów located on the river Witka as a result of unprecedented rainfall in the Nysa Luzycka catchment area. The flood wave swept through the dam crest destroying almost the whole structure within a few dozen minutes. The only element that did not vanish was the concrete structure of the spillway and water-power station. The process of dam breach is not so far completely resolved and reliable predictive models of dam breaching are still challenging problem. Modelling of the process requires an evaluation of parameters affecting this phenomenon, namely, the breach size and the timescales for the breach formation. The latter is particularly important for characterizing the outflow hydrograph and, consequently, for the assessment of the damage risk of areas below the dam. The paper presents a mechanism of breaching of the Niedów dam which consists of three stages: the downstream slope wash out, the breaking down of the dam crest and the damaging of upstream slope revetments. The comparison of breach parameters with that evaluated based on several empirical formulas and numerical modelling is also presented.
5- Selection of soils as clay core embankment materials for rock fill dams to resist hydraulic fracturing (2014)
Abstract
Soil is widely used as clay core materials in rock fill dam engineering. As a clay core material, soil should be impermeable, for it has sufficient shear strength and tensile strength to resist against hydraulic fracturing. Hydraulic fracturing may occur in the upstream face of clay core of a rock fill dam in the case of vertical effective stress in the core is reduced to levels that are small enough to allow tension fracture to occur. This situation may arise if the total stress in the core is reduced by arching effect, and by increasing pore water pressure in the core during impounding that will further reduce the effective stresses in the core. Wedging due to water pressure may crack the upstream face of clay core. This paper presents the research on hydraulic fracturing of clay core of rock fill dams on their variation of fine contents in the laboratory. Soil specimens were obtained from six major rock fill dams in Indonesia, and were modelled into six (6) different fine contents (
