Sizing Dumped Rock Riprap

Froehlich, David C.; Benson, Craig A.

doi:10.1061/(asce)0733-9429(1996)122:7(389)

Cited by 19 publications

(6 citation statements)

References 5 publications

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“…Wittler and Abt (1988) completed the study of Stevens et al (1976), adding frictional and contact forces from adjacent blocks. Froehlich and Benson (1996) worked on different angles of repose in order to show the role of the bank slope effect on riprap stability. They used the "particle angle of initial yield" concept which was introduced earlier by Straub (1953) and Grace, Calhoun, and Brown (1973).…”

Section: Introductionmentioning

confidence: 99%

Time-based failure analysis of compressed riverbank riprap

Jafarnejad

Franca

Pfister

et al. 2016

Journal of Hydraulic Research

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Methods 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.

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Section: Introductionmentioning

confidence: 99%

Time-based failure analysis of compressed riverbank riprap

Jafarnejad

Franca

Pfister

et al. 2016

Journal of Hydraulic Research

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“…Although φ r is related to slope stability, it does not necessarily provide the appropriate angle needed to evaluate resistance of a single particle. The value of φ for the median diameter particle of a riprap mixture is greater than the angle of repose of the mixture, but for the largest particles of the mixture, φ is approximately the mass angle of repose (Froehlich and Benson, ). Therefore, letting φ = φ r will yield a safety factor that applies to the most easily moved particles in a mixture, which will then define the stability of the entire riprap lining.…”

Section: Particle Stability Analysismentioning

confidence: 99%

Sizing Loose Rock Riprap to Protect Stream Banks

Froehlich

2011

River Research & Apps

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Stability of loose rock riprap used to protect stream banks from erosive forces because of flowing water is evaluated based on the ratio of static moments resisting overturning and those promoting overturning of a single rock particle. The ratio of moments defines a safety factor that describes the potential for riprap failure. The buoyant force acting on a particle is treated separately from the gravitational force and is further split into components that resist and promote overturning. This approach provides consistency in reasoning throughout the formulation, which results in a particle safety factor that tends to unity as rock-specific gravity approaches one. The safety factor formulation is tested using 38 onsite measurements of riprap-lined stream channels that have experienced floods approaching or exceeding the flow rates used to design the protective covers. Comparison to two other commonly used riprap-sizing methods by means of the Hanssen-Kuipers skill score and the equitable threat score shows that the particle stability procedure provides significantly better damage predictions and, for this reason, is shown to be more accurate. Based on the onsite measurements, safety factors that provide increasing levels of security against failure are suggested for use in calculating the size of loose rock riprap needed to protect stream banks against erosion by currents. Figure 6. Graphical relations between K r , the bank side-slope ratio m and the safety factor f s for standard values of coefficients and rock properties SIZING LOOSE ROCK RIPRAP TO PROTECT STREAM BANKS

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“…Side-slope failure of the riprap begins mostly due as well introduced earlier by Straub (1953), Grace et al (1973), and Reese (1984). Probabilistic procedures for design of riverbank riprap were developed by Li et al (1976), PIANC (1987), and later by Froehlich and Benson (1996). Froehlich (2011) studied the stability of loose rock riprap regarding the protection of stream banks from erosive forces and proposed an evaluation based on the ratio of static moments resisting overturning.…”

Section: Introductionmentioning

confidence: 99%

“…Froehlich (2011), Ulrich (1987) and Stevens et al (1984) also considered the weight of the submerged rock as the only resisting force. Froehlich and Benson (1996) worked on wide angles of repose to refer the slope of embankment effect on riprap stability. They proposed a "particle angle of initial yield" which was…”

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confidence: 99%

Effect of compressed riprap thickness on the stability of river banks

Jafarnejad¹,

Pfister²

2014

River Flow 2014

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One of the common measures for river bank protection is the installation of riprap. There are several methods to design riprap appropriately, which are however generally limited to dumped medium size blocks. Nevertheless, an additional resistance against erosion can be achieved by individually placing blocks in one or several layers instead of dumping them arbitrarily. An experimental investigation has thus been performed to study the stability of large blocks which are compressed as a river bank protection. Tests were carried out including one layer of stones as well as two layers, to evaluate the influence of the riprap layering (e.g. riprap thickness) on the bank stability. The effect of the thickness on the stability of ripraps is investigated in a 10 m long and 1.2 m wide tilting flume, with a rough fixed bed. Riprap median particle size was D 50 37 mm. Testing was conducted for channel longitudinal slopes 0.015 and 0.030 and riprap bank inclinations of 27, 31 and 35 degrees. The riprap was installed on the top of a wide grain size distribution filter. Supercritical flow conditions were considered, given the steep channel slope. The complete removal of the riprap in a section under a constant discharge was defined as the failure criterion. The riprap failure threshold discharge was determined based on the series of tests with duration of maximum 180 minutes. In each test, riprap transport rate was measured every minute while the stones were tracked by a video camera and collected in a sediment trap at the channel end. The time of total failure was defined by standard video-image processing techniques. A time based analysis of failure was performed and first results revealed that, for similar conditions, the second layer stabilizes the riprap significantly and delays the time for total failure. Nonetheless, transport rate was found to be increased in this latter situation.

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Sizing Dumped Rock Riprap

Cited by 19 publications

References 5 publications

Time-based failure analysis of compressed riverbank riprap

Time-based failure analysis of compressed riverbank riprap

Sizing Loose Rock Riprap to Protect Stream Banks

Effect of compressed riprap thickness on the stability of river banks

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