Stability Of Riprap Research Articles

Investigation of riprap stability at downstream of spillway flip bucket without and with energy dissipators

ABSTRACT Spillway is one of the most cost-effective energy dissipating structures used in dams which leads to dissipation of flow energy at the end of the structure. Scouring is a phenomenon occurring next to the hydraulic structures, and which can lead to deterioration and even collapse of such structures. One of the methods to control the scouring downstream of a dam is using riprap. In this study it was investigated the stability of riprap based on relative particle diameter downstream of spillways of four different categories of energy dissipators, namely simple flip bucket, dentated flip bucket, simple triangular sill, and dentated triangular sill. The experiments were performed in a rectangular test flume. Ripraps of the same density and of four different diameters were investigated at five discharges at the movement threshold. Results of the study suggested that the relative particle diameter was an important factor in stability of the riprap. Besides, in all of the four aforementioned spillways, the stability number at the movement threshold was found to decrease with increase in the relative particle diameter. For all of the relative particle diameters, use of dentates led to an increase in the stability number 11% and 7% in spillways with simple flip bucket and triangular sill respectively. Also, a formula for estimating relative particle diameter was proposed. The correlation coefficient of the results yielded by this formula and the laboratory results was found to be 0.9 and 0.6 for the spillway with simple flip bucket and the other three types of the spillways respectively.

Investigation of riprap stability of a dam: risk assessment by InSAR method and rock mechanical test

Riprap resistance is a widely used solution for protecting earth dams from erosion but riprap can be displaced on the dam surface. This study examines the stability of riprap in the Taleqan Dam, Iran using rock mechanical tests and InSAR technology. Uplift of dam stairs and erosion of the riprap material have been observed during field work at the study site, and samples have been gathered from three rock categories. The purpose of this study is to explore the factors influencing the deformation of the Taleqan Dam. The InSAR method has been employed for monitoring surface deformation and the Los Angeles ASTM C test was used to establish the cause of dam deformation. InSAR analysis was carried out using Sentinel-1A images from 2014 to 2019. The results revealed subsidence at an average rate of 4 mm/yr over that period. The results of Los Angeles ASTM C indicated that the Andesite riprap was more easily eroded, has a relatively low durability and specific weight, and low resistance erosion. Therefore it is unsuitable for use as a protection layer for the crest and lower sectors of the riprap. It can also be concluded that the inadequate durability of certain rock materials may potentially cause weathering, depression, reduced thickness and displacement of the riprap.

Effect of a second layer on the time to failure of compressed riprap as mountain riverbank protection

ABSTRACTRecently, Jafarnejad, Franca, Pfister, and Schleiss [2017. Time-based failure analysis of compressed riverbank riprap. Journal of Hydraulic Research, 55(2), 224–235. doi: 10.1080/00221686.2016.1212940] presented an experimental study on the stability of compressed riprap, which means that it is composed of individually placed blocks with a single layer as riverbank protection. The relationship between the time to failure and dimensionless bed shear stress was presented. Here, the authors complement the previous investigation with results regarding the effect of a second riprap layer. In total, 49 tests (28 tests with one and 21 tests with two riprap layers) were performed using a single block size, three longitudinal channel slopes and three different riprap bank inclinations. Under similar conditions, the second layer can significantly delay the time to failure, whereas the block erosion rate was found to increase. The second layer has a more stabilizing role when the bank angle of the riprap is approaching the angle of repose of the blocks.

연결호안 주변 흐름의 수리적 특성을 고려한 사석호안의 안정성 분석

연결호안 주변 흐름의 수리적 특성을 고려한 사석호안의 안정성 분석

Time-based failure analysis of compressed riverbank riprap

ABSTRACTMethods to design riprap-lined channels usually refer to dumped material. Large blocks placed individually by machinery are used when more stability is required. They offer additional resistance against flow erosion since space between blocks is minimized and interlocking increased. The behaviour of this protection has rarely been studied. An experimental investigation was carried out on the stability of compressed riprap as riverbank protection. Riprap was reproduced by uniform crushed limestones with three block sizes. Tests were conducted for three channel slopes under supercritical flow conditions and for constant bank slope. A time-based analysis allowed establishing relations among time to failure, friction velocity, and dimensionless bed shear stress. The results of 45 tests confirm that the rate of block erosion is significantly reduced with increase in the riprap diameter. The time to failure of the riprap protection depends strongly on the longitudinal slope and on the block sizes. An empirical prediction to estimate the riprap time to failure is shown.

Effect of Bridge Abutment Geometrical Shape on Riprap Stability in River Bend

Riprap is used to control scouring around the bridge abutment. In order to study the stability of riprap around two bridge abutments with two different shapes, experiments were conducted in a laboratory flume made of Plexiglass in 180 degree bend. In this research, several experiments were done by placing the two bridge abutments made of Plexiglas in a series of riprap. Experiments included two different types of riprap with different densities, four different diameters and constant rate of discharge under pure water condition. In each experiment, flow depth was measured in terms of moving threshold, then stability was calculated by using the data obtained. The results showed that in the same conditions chamfered wing-wall is greater than vertical-wall. So, chamfered wing-wall is, on average, 9 percent more stable than the vertical wall.

Evaluation of Stream Grade Control Structures in Loess Soil Region

Grade control structures are used extensively to control river channel degradation. Although their use is widespread, the durability and performance of these structures, namely, sheet pile, H-pile, rock sill, and concrete block weirs have not been systematically evaluated. In this study, stream grade control structures in a loess area (western Iowa) were quantitatively evaluated with a performance number system to determine their field conditions and durability. For these evaluations, two dimensionless parameters (erosion control ratios and discharge ratios) were developed to correlate field observations and measurements. Structures that experienced small flows performed relatively well, whereas those that carried large discharges had poor performance. The stability of riprap decreases as the discharge ratio increases. Better riprap performance was obtained at structures with greater erosion control ratios. Based on these evaluations, problems associated with the structures were identified. In-channel movement of rock riprap was found to be a prevalent problem. Considerations for future designs and construction are recommended. The evaluation method and procedure can be applied to loess soil regions in the central United States and other regions worldwide. The information gathered can be used to guide field surveying and modeling studies.

Stability of riprap and concrete blocks in highly turbulent flows: M. Escarameia & R. W. P. May, Proceedings - ICE: Water, Maritime & Energy, 112(3), 1995, pp 227–237

Stability of riprap and concrete blocks in highly turbulent flows: M. Escarameia & R. W. P. May, Proceedings - ICE: Water, Maritime & Energy, 112(3), 1995, pp 227–237

Damage Mechanisms and Influence of Gradation for Steep Riprap

Model tests in a laboratory flume were performed to verify certain hypotheses put forward to explain steep riprap behavior observed in the field at several embankment dam sites. The laboratory study has focused on riprap degradation under wave attack, and on the influence of fine blocks incorporated into riprap. Unlike flatter riprap, steep riprap is characterized by a low rate of damage until a point of acceleration, after which damage progresses rapidly. At that stage, damage is characterized by sliding and crumbling, which results in an upward propagation of damage toward the crest. The inclusion of a portion of small blocks, into the riprap significantly reduces the stability of steep riprap. This detrimental effect is gradually reduced as the riprap slope becomes flatter.

Stability of Riprap at Bridge Piers

An experimental investigation was performed to determine the critical conditions for displacement of riprap placed on streambeds surrounding bridge piers. A functional relation between stability number, a dimensionless grouping of rock size and density to fluid velocity and density, and relative approach flow roughness, approach flow depth, riprap size, and placement depth was presented. Pier model tests conducted in a laboratory flume were used to determine the influence of each dimensionless parameter on the stability number. Analysis of the experimental results showed that the relative depth of placement and the relative rock size significantly affected the stability number for rectangular piers. A comparison of this data with similar data for round‐nosed piers and other data for unobstructed flow conditions showed that rock sizes required for stability at piers must be substantially larger than those required for unobstructed flow. In addition, rock sizes for rectangular piers must be substantially la...

Stability of Armor Units on Composite Slopes

Riprap and sandbag model tests are conducted in a wave flume to investigate the effects of berm‐type slopes on the stability of armor units and wave runup as compared to uniform slopes. Measurements of wave runup, rundown, wave height, breaker type and the response of armor units under regular wave action are made for each test run. The uniform and composite slope test results are analyzed using a modified Saville's method which accounts for the overall effects of the slope configuration on the stability of armor units and wave runup. A simple analysis procedure based on the proposed method is developed for a preliminary design of a berm configuration. An example computation is made for a composite slope protected with riprap. The berm width, the berm slope and the water depth at the shallowest point of the berm are varied so as to determine the optimal berm configuration for increasing the stability of riprap under the assumed wave conditions.