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... After Isbash (1936), dozens of studies have been conducted to investigate riprap stability on different slopes in order to derive stone-sizing equations under overtopping flow conditions (see Olivier, 1967;Stephenson, 1979;Abt and Johnson, 1991;Wittler and Abt, 1997;Mishra, 1998;Robinson et al., 1998;Siebel, 2007;Eli and Gray, 2008;Peirson et al., 2008;Khan and Ahmad, 2011). The mathematical structure and accuracy of each predictive equation may vary significantly and are sumptuously contingent on the range and extent of the database used by each investigator and the purposed application . ...
... D 50 denotes the median diameter of stones. Olivier (1967) considered flow running through and over rock-fill dams to propose a stone stability formula. His equation depicts unit threshold flow rate as a function of slope, and median rock size for crushed or rough stones: ...
... Recently, Abt et al. (2013) and Abt and Thornton (2014) evaluated the empirical equations aiming to define the particular use of each equation. They reported that among the presented equations in this section, four formulas, i.e. Olivier (1967), Siebel (2007), Khan and Ahmad (2011), and Thornton et al. (2014) may offer the least erroneous predictions for the full-spectrum stone-size. Hence, in this investigation, predictions of these four relationships were compared with the results of the selected AI techniques. ...
Rock riprap is commonly used to protect levees, embankment dam, steep channels, and other structures being vulnerable to deteriorative erosion caused by overtopping flow. A review of the literature in this context indicates that over 24 riprap design expressions exist to predict the stone size in the riprap layer. However, each equation was originally derived on the basis of limited data sets under certain experimental conditions. In this investigation, Gene-Expression Programming (GEP), Model Tree (MT), and Evolutionary Polynomial Regression (EPR) were evaluated to estimate riprap stone sizing by virtue of 102 experimental data sets. Efficiency and performance of GEP, MT and EPR approaches for training and testing stages were analysed and discussed. Results analysis revealed that the EPR technique provided an accurate prediction of riprap sizing in testing stage compared with other selected data-driven models as well as the empirical equations. The robustness of the developed data-driven predictive techniques was verified through the external validation: the selected data-driven models are definitely valid, have the strong capability to predict the riprap stone size which were not achieved by a chance. The prediction uncertainties of the data-driven models were quantified and compared with the selected empirical equations.
... If a slope revetment is subjected to overflow, seepage and infiltration vary along the slope face. However, despite the variation in seepage, stability formulas often do not explicitly take the seepage into account (Olivier 1967; Stephenson 1979; Martin 1991). In contrast, findings of Howard and McLane (1988) indicate that seepage may have a significant effect on slope mobilization in relation to surface flow. ...
... Fine sediments move for practically all shear stresses larger than zero (Lavelle and Mofjeld 1987), hence incipient motion is usually defined as a small reference transport rate (Taylor and Vanoni 1971; Wilcock i988). For coarser grains, such as stones and blocks, the distinction between a stable and a mobile state of the soil can be defined as zero transport rate (Olivier 1967; Stephenson 1979; Martin 1991). The present study concerns the stability of coarse soil slopes subjected to throughflow, a case for which the latter incipient motion criterion is appli- cable. ...
... Hence, variation of the buoyancy factor with changes in slope angle and seepage exit angle is not represented. The fact that the buoyancy force is directed normally to the face led Ulrich (1987) to modify the original stability equation for rock slopes based on submerged weight by Olivier (1967). At the point where the phreatic surface intersects the downstream face, seepage is parallel to the slope and the surface flow shear stress is zero. ...
An expression is derived for the critical shear stress of surface flow on a noncohesive soil slope subjected to seepage-induced mass wasting, i.e., erosion caused by a successive mobilization of flake aggregates of surficial grains. The expression is supported with data from experiments with stone fill subjected to throughflow. In current theories for hill-slope erosion or riprap protection on slopes, buoyancy is assumed to be a constant vector directed vertically, or the seepage force is omitted as a variable. However, the present analysis shows that, for many conditions, buoyancy should be described in accordance with the dynamic pressure distribution and the seepage force should be included as a variable in the theory. Furthermore, a parameter denoted “minimum stable volume” per unit width of stone fill is introduced as a measure of global stability of the stone fill, along with seepage height on the downstream face and grain size. Experimental results indicate that the minimum stable volume decreases with increase in grain size and, for the materials investigated, is about 20% lower for crushed rock than for gravel.
... As an example, in order to create a reservoir of some 100 000 m 3 for irrigation purposes a promoter will consider the construction of a 10-30 m high earthfill dam with available local material, including an intake, a simple culvert bottom outlet and a conventional spillway for a few cubic meters. Surprisingly or not, the cost of the flood control structures, including excavation and concrete dumping, can amount to 45-50 % of the overall budget (ICOLD, 1997; Olivier, 1967) 3 . Such an investment is sometimes difficult to justify, especially if the consequences of dam failure by overtopping are low. ...
... The highly aerated turbulent flow conditions do not allow an accurate measurement of the flow depth (Olivier 1967). In fact, the identification of the flow depth or the flow velocity is not straightforward in two-phase flows. ...
... The initial stone that came to hand wasn't discarded for a better fit, replicating real-world scenarios where placement adjustments are limited during construction (Figure 3). The packing factor has been defined as the number of stones of a given size contained in a unit squared area (Olivier 1967 Single Stone Layer pump was then operated to supply water to the constant head regulation tank. The water level at the sharp crested weir was measured to determine the discharge in the experiment. ...
Permanent link: https://doi.org/10.3929/ethz-b-000675981
... Over the past several decades, a considerable number of studies have focused on better understanding the stability aspects of ripraps under overtopping conditions. Contributions in this regard have been made by studies such as Ravindra et al. (2020), Hiller et al. (2018, Peirson et al. (2008), Dornack (2001), Chang (1998), Frizeii et al. (1998), Sommer (1997, Abt and Johnson (1991), Larsen et al. (1986), Knauss (1979), andOlivier (1967). However, few past experimental studies have investigated the behaviour of rockfill dams with toe structures under extreme scenarios. ...
Rockfill dams must be equipped with defence mechanisms to counteract the destabilizing effects of throughflow forces under accidental leakage scenarios. A key component of the rockfill dam overtopping system is the rockfill dam toe, constructed in tandem with the downstream rockfill shoulder. Quantitative descriptions of effects of different toe configurations on throughflow hydraulic properties of rockfill dams are currently unavailable in international literature. To address this, experimental investigations were conducted on 1 m high model rockfill dams with disparate toe configurations. Investigation outcomes describe the effects of internal, external and combined toe configurations on pore-pressure distributions within rockfill dam models subjected to throughflow conditions. Research outcomes provide vital information which can facilitate effective decision-making with regards to rockfill dam design. The accumulated data sets could also enable development, calibration and validation of numerical design tools and dam breach models.
... The term packing factor was defined as Eq. (1) by Olivier (1967). ...
A novel approach quantitatively describing two-dimensional displacements of placed riprap stones exposed to overtopping flows is developed and validated, coupling experimental data with Euler’s buckling theory for columns. Past studies investigating the failure mechanisms of placed ripraps with toe support have analysed unidirectional displacements of riprap stones parallel to the slope. 2D description of this process is currently not available in the literature. To address this issue, datasets obtained from a physical modelling investigation conducted on model ripraps constructed with angular stones on a slope of 1:1.5 (vertical : horizontal) were further analysed along with additional experimental data. Investigation results demonstrated that placed ripraps supported at the toe underwent progressive deformations in 2D when exposed to overtopping flows. The deformation behaviour closely resembled buckling of a slender-long column pinned at one end and free at the other and this ultimately led to total riprap failure at the upstream section of the riprap.
... It is important to note that these new guidelines [Keller 2003], and existing design guidelines [Standing Committee on Rivers and Catchments 1993; Robinson et al. 1998;Olivier 1967] are mainly directed at designing rock chutes so they do not fail because of rock movement on the crest and face of the chute (damage mode 1 and 2 above). There has been less discussion of best practice design and construction to protect against the other failure modes. ...
Rock chutes (also known as rock ramps and rock riffles) are an important technique for controlling erosion, and have been widely used in Victorian streams. Occasionally, for a number of reasons, they are damaged or fail. Based on a survey of 170 rock chutes in north east Victoria and Gippsland, eight damage or failure modes have been identifi ed. These failure mechanisms include loss of rock from the face and crest, downstream erosion, undermining of the chute apron, stream bed instability, abutment damage, total loss of the chute and willow infestation. The greatest risk to rock chutes arises from three mechanisms, loss of rock from the face of the chute, willow infestation and abutment damage. It is important to consider the complete range of possible failure mechanisms when designing rock chutes. Improved design procedures are discussed which especially target the greatest risk to chutes, loss of rock from the chute face.
... To the best of the writers' knowledge, no systematic research is presently available on the closure of breaches and thus trial-and-error procedures are used, as was the case in New Orleans. In contrast, several procedures have been developed for the closure of cofferdams for river diversion Blanchet 1947;Das 1972;Izbash and Khaldre 1970;Izbash 1936;Oliver 1967;Sandover 1971;San- dover and Tallis 1966a,b;Zhu et al. 2004 and actual data on real-life projects are available, such as Itaipu Dam in Brazil Cortim et al. 1977, Cabora Bassa Dam in Lisbon Manzanares et al. 1973, Mangla Dam in Pakistan Thomas and Gwyther 1967, and Mica Dam in British Columbia Parmley 1978. Cofferdams are structures that divert the river temporarily to dry out the areas for the construction of dams, powerhouses, water intakes, or navigation locks. ...
On August 29, 2005 Hurricane Katrina resulted in several breaches in the levees and flood walls protecting New Orleans. Of the 20 breaches, the 17th Street Canal breach caused much of the city flooding. In this paper, the results of studies on a 1:50 scale hydraulic model of this breach based on the Froude similitude relationships are presented. It is assumed in the model that the bed is fixed and the levee below the flood wall remains intact during breach closure. This was the case in the 17th Street Canal breach. Because of the many uncertainties in the values of various variables, a range of conditions were run on the model in an attempt to bracket the results for the flooding depths and the initial failed attempts to close the breach. Then, various possible methods for breach closure were investigated utilizing the procedures developed for cofferdam closure for river diversion, e.g., toe dumping, transverse dumping, single- and multibarrier embankments, etc. Closures of the breach and the closure of the canal at the Old Hammond Highway Bridge were investigated. Results from the case study show that some of these methods could have been utilized for closing the Katrina breaches. However, special care should be exercised when extending them for breach closure at other sites.
... Furthermore, this category of dams will see the largest construction rate around the world in the forthcoming years (ICOLD 1997), being used mainly for irrigation, water supply, and flood management. Izbach and Khaldre (1959), Olivier (1967), Powledge and Sveum (1988), and Powledge et al. (1989) extensively studied the overflow of embankments. Such overflow will go through different stages as shown in Fig. 1. ...
A macro-roughness lining system for the protection of earth embankment dams during overflow is presented. It consists of precast concrete elements placed on a drainage-separation layer. The main difference between this system and other existing concrete element systems is the stability concept, based on the self-weight of the blocks. Several types of elements were developed and tested in a physical model for a typical dam slope of 1V:3H. Failure conditions were identified after submitting the elements to increasing flow discharges. Furthermore, different foundation drainage and shear conditions between the elements and their foundation and different joint alignments were studied. Flow characteristics were observed and measured for quasi-uniform flow conditions. Based on the experimental results, a stability model was developed to compute the design safety factor. The model is based on the governing overturning equation (predominant failure mechanism) and on assumptions concerning the acting hydrodynamic forces, the hydrostatic uplift, and the concentration of air in the flow. Synoptic design charts were derived for 1V:3H dam slopes, allowing the rapid estimate of the lining characteristics as dimensions and weight for a certain withstood design unit discharge, for various margins of safety. The developed macro-roughness lining system is envisaged for the spillway rehabilitation of existing dams, but also for the design and construction of spillways of low dams (up to 30 m in height) and for the protection of overflow cofferdams.Key words: overflow dams, erosion protection, linings, macro-roughness, stability, drainage and spillways.
Improving the knowledge of the failure mechanism of riprap exposed to overtopping is valuable to enhance the construction and reinforcement techniques of rockfill dam defense systems. In this research, four experimental overtopping tests were carried out on 1∶10 rockfill dam models with placed riprap protection layers supported at the toe. Axial reaction loads were measured and 3D models were built using the structure from motion technique to study the displacement of riprap stones exposed to overtopping. The importance of throughflow in the rockfill shoulder is brought to light by comparing these results with previous data from a placed riprap model built on a ramp without throughflow. The structure from motion technique demonstrates to be very effective and highlights the existence of a buckling phenomenon, along with the compaction of the riprap. The displacement data show that the compaction mechanism is more important (both horizontally and vertically) and appears at lower overtopping discharges for less packed placed riprap layer. Finally, similar trends for vertical and horizontal riprap displacements are demonstrated between the initial position and the last position before failure. Such information suggests that the critical discharge value is not as critical as the riprap displacement to predict dam failure under overtopping conditions.
This article is aimed at investigating the influence of toe support conditions on stability aspects of placed ripraps on steep slopes exposed to overtopping flows. All past experimental model studies investigating placed riprap stability under overtopping conditions have been conducted with ripraps constrained at the toe section. However, ripraps constructed on the downstream slopes of rockfill dams are generally not provided with any form of toe support. Hence, it is of importance from stability and economical standpoints to understand the failure mechanism in placed ripraps with realistic toe support conditions. This article presents findings from experimental overtopping tests conducted on model placed ripraps unsupported at the toe section. Employing Smartstone probes, a new technology in stone movement monitoring, laser measurement techniques and Particle Image Velocimetry (PIV) techniques, detailed description of failure mechanism in placed ripraps under overtopping conditions is presented within this study. Study findings demonstrate sliding as the underlying failure mechanism in placed ripraps with unsupported toes. Further, comparison of experimental results with past findings revealed that placed ripraps with unrestrained toes experience a fivefold reduction in stability, characterized by the critical overtopping magnitude as compared with placed ripraps provided with fixed toe supports. Furthermore, toe support conditions were found to have no effects on either the failure mechanism nor the overall stability of dumped ripraps. Further research is recommended to arrive at well-defined methodologies for design and construction of toe supports for placed ripraps.
Raue Rampen sind ein wichtiger Bestandteil im Repertoire des naturnahen Gewässerausbaus. Das Stichwort heißt hier Durchgängigkeit. Rampen ermöglichen die Überwindung von Sohlenstufen im Fließgewässer, ohne die Durchgängigkeit flussabwärts zu behindern oder flussaufwärts sogar ganz zu unterbinden. Eine besonders naturnahe Alternative stellt die Rampe in aufgelöster Bauweise dar, die eine natürliche Gewässerdynamik unterstützt und durch vielfältige Sohl- und Strömungsstrukturen auf dem Rampenkörper die Artenvielfalt der Gewässerfauna unterstützt. Sowohl in Modellversuchen als auch in der Praxis hat diese Rampenform bewiesen, dass es sich um ein stabiles und hydraulisch wirksames Bauwerk handelt.
Riprap is widely used as erosion protection consisting of either dumped or, in an interlocking pattern, placed stones. Data about the stability and failure mechanism of riprap on steep slopes is scarce and hence subject to research. Dumped and placed ripraps constructed on a slope of 1:1.5 (vertical: horizontal) were exposed to overtopping scenarios in small scale model tests and in the field with large-scale riprap stones. Detected stone displacements in the riprap depict a two-dimensional deformation of the placed riprap structure. The displacements along the flow direction led to gap formation at the upstream section of the riprap where the adjacent stones lost their interlocking and became prone to erosion. In combination with a lift in the middle of the riprap, buckling is described as the failure mechanism for placed riprap with a fixed toe with analogy to Euler’s Buckling theory. Dumped riprap failed by sliding down the filter layer as soon as the top of the stones were overtopped by the flow.
Ageing dams located across the west coast of North America, both in the USA and Canada, are threatened by potential for large earthquakes. Assessing the seismic performance of these dams has been a challenge. This paper presents a synthesized approach for assessing the seismic and post-earthquake performance of a dumped rockfill dam built in the 1960s with a gunite (shotcrete) face as the water barrier. The dam may lose its freeboard due to seismic settlements. If loss of freeboard does not occur, the gunite face can still crack and allow leakage. Excessive discharge at the downstream toe due to the through-flow may cause the rockfill at the toe to unravel. Such unraveling and consequent sloughing of the slope may cause a dam breach. The synthesized approach consists of a dynamic analysis and methods for assessing the cracks in the gunite face, leakage through the upstream face, and potential for unraveling and instability of the downstream slope.
The comparability of large-scale field tests of dumped and placed riprap with a stone diameter of 0.37 m and corresponding model tests in a scale of 1:6.5 was investigated in terms of stability, packing density and visually observed flow pattern. The tested riprap protections were exposed to overtopping on a slope of 1:1.5 (vertical: horizontal). The results for dumped riprap revealed similarity between the field and model tests based on the critical stone-related Froude number as a measure of the stability, packing density, flow pattern and overtopping depth. The field and model tests with placed riprap showed good agreement in regard to flow pattern and overtopping depth. However, the placed riprap in the model tests was denser packed and more stable than in the field indicating laboratory effects. Placed riprap withstood up to 10 times higher unit discharges than dumped riprap, 6–8 m²s⁻¹ in the field tests.
Australian Bulk Mineral’s Savage River iron ore mine is located in rugged topography in the NW of Tasmania, a region with rainfall in excess of2000mm per annum. Over its 30 years of operation to date, around 260 million m³ of waste rock has been generated and current mining plans allow potential for a further 160 million m³ over the next 20 years. Disposal of this material poses significant difficulties, not least of which is the practical placement of such large volumes of material.
Erosion of early dumps placed in Broderick Creek was recognised as an environmental issue and led to a review of spillway options for the dump, which was effectively damming the valley. Lying parallel to and to the west of the northern deposits of the mine, Broderick Creek was a logical waste rock disposal site if stormwater flow could be properly managed. The review led to adoption of an innovative flow-through spillway, which utilised hard coarse waste rock as a drainage zone. Construction was successful and has led to extension of this concept for further major development of waste dumps at the site.
Design of flow-through spillways in Tasmania was first looked at by the eminent Hydro Electric Commission engineer, the late John Wilkins. Wilkins used the concept successfully at Laughing Jack Dam and later at the North Slot Dam at Savage River.
The paper describes the work of Wilkins and how this was used to design the Broderick Creek structure. Results of site flow monitoring are used to demonstrate the effectiveness of the design and actual permeability values achieved.
Rockfill dam, a kind of embankment or so-called earth–rock dams, is a water retaining barrier composed of three major parts: fill of loose rock by dumping or roller compaction; impervious membrane made of masonry, concrete, asphaltic concrete, steel sheet piles, timber, or other materials; and transition layer. The impervious membrane is employed as the waterproof and can be placed either within the embankment or on the upstream slope. Although the history is short compared to that of other ancient dam types, the development of rockfill dams during the last several decades was booming around the world.
The origins of through and overflow rockfill dams can be traced, in Australia at least, to the Cascade Dam (Fig. 1), built to supply sluicing water to the Briseis alluvial tin mine at Derby in north-east Tasmania (Anon, 1989). It was to enter the annals of history as the only large dam in Australia to fail causing loss of life. However, despite this disastrous beginning, theensuing sixty years have seen the techniques of mesh protection develop to the stage whereflood flows can now be passed over rockfills with confidence, and where such provision isalmost a normal feature in the construction of rockfill dams. These techniques now permit substantial economies to be made in the scale of river diversion works, and even the total elimination of such works in some cases.
provided funding for this work. Wayne Graham, with Reclamation’s Sedimentation and River Hydraulics Group, and Rod Wittler, with the Water Resources Research Laboratory, made initial contributions to the literature survey and case study database. They, as well as Bob Dewey, Jeff Farrar, Jim Melena, Dan Mares, Brent Mefford, and Phil Burgi, have provided many helpful comments in review of the document. Robert Rood and Larissa Casey assisted with the editing and final preparation of the manuscript and made many significant improvements to the final product. Darrel Temple, of the Agricultural Research Service, Stillwater, Oklahoma, assisted with the organization and hosting of the February 1998 technical workshop on dam breach processes and also provided many helpful source documents for the literature review. i
Crossbar block ramps are a common solution for a naturelike channel. Current investigations deal with energy dissipation processes on block ramps, where large stones are arranged on the complete slope. Contrary, crossbar block ramps build several basins by arranging stones in a row transversal to the flow direction. Lower stones guarantee a minimum water level in each basin and allow for an overfall for small discharges and fish climb capabilities. With increasing discharges, the water also overflows the large stones and the basin flow regime changes over a waved flow regime into a channel flow regime. This paper deals with physical and numerical crossbar block ramp models. The physical model allows for the variation of discharges from 1 to 50 l/s; numerical simulations are run up to 200 l/s with varying slopes, crossbar heights, and distances. Water levels, velocities, and drag forces on single stones are measured. New approaches to relative energy dissipation and the friction factor to evaluate water depths for channel flow regimes are developed. Additionally, drag forces on single stones in various crossbars are measured and analyzed. DOI: 10.1061/(ASCE)HY.1943-7900.0000522. (C) 2012 American Society of Civil Engineers.
Rock riprap is one of the most widely used erosion control techniques for protecting embankments, levees, spillways, and in-stream structures subjected to overtopping flow conditions. The literature indicates that over 21 riprap design expressions exist to appropriately size the stone. However, each of these relationships was developed from limited databases with narrow bands of boundary conditions. A power regression analysis was performed using 102 overtopping observations from 10 separate investigations; the analysis related median stone size to slope, unit discharge, coefficient of uniformity, rock layer thickness, and stone specific gravity. A unique, riprap-sizing expression was developed with a coefficient of determination (R2) of 0.97 and a variance of 11%. The resulting design relationship expands the boundary conditions of the independent variables beyond earlier efforts, thereby reducing the need for extrapolating previous relationships.
Rock riprap is one of the most widely used erosion control methods for protecting embankments, levees, spillways, and instream structures subjected to overtopping flow conditions. At least 21 stone-sizing relationships exist to determine the median stone size of a protective riprap layer based on the results of 96 overtopping, laboratory experiments. Test parameters include median stone size, slope, unit discharge, coefficient of uniformity, and riprap layer thickness. A regression analysis was performed relating the observed median stone size to the predicted median stone size to each of the 21 relationships, yielding a coefficient of determination (R2) and percent error for the full spectrum of data. Zonal (partial spectrum of rock sizes) and complexity analyses were also conducted for each relationship. It was resolved that the Khan and Ahmad, and Chang relationships best aligned with the composite dataset. The predictive expressions by Olivier, Hartung and Scheuerlein, Knauss, Maynord, Abt and Johnson, and Siebel yield a noteworthy second tier of stone-sizing relationships for overtopping conditions.
The outflow hydrograph from a dam failure is a boundary condition of a dam break flood model used on the downstream valleys risk management. Limited research has been made on the rockfill dams breaching process and there are no specific models to this type of structures yet. This paper describes a lumped model for the computation of the outflow hydrograph due to a Rockfill Dam Breaking named RoDaB. The methodology is based on the governing equations of reservoir routing and depletion, and breach erosion. Results obtained from experimental tests performed in a laboratory flume were considered to fulfil the phenomenological aspects to which does not exist any analytical approach so far. The erosion process from the dam breach is modelled as a function of two erosion parameters and of the breach final geometry dimensions obtained from the experiments. Finally, the model RoDaB is applied to a rockfill dam, with characteristics typical of this type of structure, and the results are compared with the ones from the BREACH model. © 2004 Internationl Association of Hydraulic Engineering and Research.
A series of 26 tests was performed on a riprap layer in which median round-shaped stones ranging from 32.3 to 99.1 mm (from 1.27 to 3.90 in.) were subjected to overtopping flow conditions. Embankment slopes range from 10 to 45% with median stone sizes ranging from 23.9 to 104.2 mm (from 0.94 to 4.1 in.). The database was analyzed, yielding a unique expression in which the median size of a round-shaped stone can be predicted as a function of the unit discharge, embankment slope, and coefficient of uniformity. It was determined that the requisite round-shaped stones range from 5 to 42% larger than angular stones to stabilize the riprap layer for similar flow conditions with unit flows of 0.2 cm/s and slopes of 40%. The maximum deviation between rounded and angular-shaped stone may approach 70% as flow and bed conditions are extrapolated.
Conventional stability analysis methods for determining rock armor size to protect steep (tan θ>0.1) embankments from erosion due to downslope flow do not predict the correct dependency of armor size on the slope. Consequently, such methods become very conservative (discharge factor of safety ∼8) at high slopes. We review published large-scale measurements recorded in the literature and show that adequate representation of flow aeration is important as proposed by Hartung and Scheuerlein in 1970. However, the assembled measurements show that the Hartung and Scheuerlein design method is not conservative. The aerated flow equations of Hartung and Scheuerlein, when combined with a correctly formulated stability equation, yield good collapse of the available large-scale data and a conservative design method.
A pilot study was conducted to evaluate existing rock-sizing techniques for stabilizing transition toes of embankments. The U.S. Bureau of Reclamation and the U.S. Army Corps of Engineers (Campbell) procedures were applied and determined to be conservative in sizing riprap. Embankment-overtopping tests were conducted placing 8.9, 13.0, and 19.8-cm-diameter stones at the slope transition. An alternative method was developed for sizing toe rock based upon the unit discharge, embankment slope, and flow concentration. The results indicate that an embankment toe can be stabilized with a smaller median stone size than previously anticipated. These results were verified for unit discharges of 0.54 m(3)/s/m or less.
Near-prototype flume studies were conducted in which riprap-protected embankments were subjected to overtopping flows. Embankment slopes of 1, 2, 8, 10, and 20% were covered with riprap layers with median stone sizes of 1, 2, 4, 5, and/or 6 in. Each riprap layer was tested by slowly increasing the discharge to failure. Riprap design criteria for overtopping flows were developed for estimating incipient stone movement and riprap layer failure as a function of the unit discharge, stone shape, median stone size, and embankment slope. Incipient stone movement occurred at approximately 74% of the riprap layer failure unit discharge. It was determined that rounded shape stone should be oversized approximately 40% to provide comparable protection of an angular shape stone. Flow channelization was observed to occur at approximately 88% of the unit discharge at failure. A flow concentration factor of approximately 1 to 3 was introduced for sizing stone.
The stability of rock protection on slopes attacked by a flow requires two conditions. The first is the resistance to sliding that is provided if the ratio of tangential forces to normal forces on one or several rock layers is less than the tangent of the angle of friction of the layers on their support. The second is the resistance to wrenching of the surface layer blocks and is covered by equations derived from the Shields criteria. This paper proposes a new approach to two factors in the analysis, namely: (1) For downslope flow the hydrostatic pressure gradient is not vertical but normal to the slope, and thus existing equations expressing the effect of slope on the threshold shear stress are modified; and (2) a condition of stability that involves the bearing angle of a surface-layer block thrusting on neighboring stable blocks that is wider than the commonly used angle of repose.
Flume studies were conducted in which riprap-protected embankments were subjected to overtopping flows to determine the average interstitial velocity of the through-flow. Velocity measurements were made in riprap having median stone sizes D50 ranging from 1.02 in. (2.6 cm) to 6.2 in. (15.8 cm) on embankment slopes of 1–20%. A tracer solution injection and recording system was developed to estimate the through-flow velocities. The average interstitial velocities for 19 flume tests were measured and reported. A predictive relationship was developed in which the average interstitial velocity was a function of the embankment slope and rock size D10. Flow measurements varied ±40% about the average velocity.
Stability of the downstream slope of rockfill dams Experiments in the closure of rivers with sand/gravel Wiener Akad., IIA, 136, 271. LELIAVSKY S. Irrigation and hydraulic design A laboratory investigation of self-spilling rockfill dams
- Forchheimer P Hydraulik
FORCHHEIMER P. Hydraulik. Tebner Verlag, Leipzig, 1930. GALLOWAY J. D. The design of rockfill dams. Proc. Am. Soc. cio. Engrs, 1939, 65, HAUSER R. et al. Stability of the downstream slope of rockfill dams. Proc. 8th Int. ISBASH S. V. Construction of dams by depositing rock in running water. 2nd Znf. JACOBSON A. G. Damming of the Volga at the site of the Stalingrad Hydroelectric KALIZNUK C. K. et al. Experiments in the closure of rivers with sand/gravel KOZENY J. S. Ber. Wiener Akad., IIA, 136, 271. LELIAVSKY S. Irrigation and hydraulic design. Chapman and Hall, London, 1955, MISSBACH A. Listy cukrova. 1937, 55, 293 ff. NOSOFF R. P. et al. Damming of the Volga at the Gorky Hydroelectric power PARISET E. et al. Rockfill dams built by toe dumping. Proc. 8th Inf. Congr. Ass. ROSE H. E. Further research in fluid flow through granular material. Proc. Znstn ROUSE H. (ed.) Engineering hydraulics. John Wiley, New York, 1950. SANDIE R. B. A laboratory investigation of self-spilling rockfill dams. M.Eng.Sc. SCHEIDEGCER A. E. Thephysics offlow throughporous media. University of Toronto SLICHTER C. S. U.S. Geol. Surv. 19th Ann. Rep. 1899, 2, 295 ff. SOGREAH. Kariba scheme. Report on tests conducted