Riprap Stability: Transverse and Longitudinal versus Continuous Protections

Almeida, Gustavo A. M. de; Vide, Juan Pedro Martín

doi:10.1061/(asce)hy.1943-7900.0000031

Cited by 7 publications

(2 citation statements)

References 16 publications

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“…Most of these design methods are limited to dumped and medium size blocks. The incipient motion of particles is used as a failure criterion (De Almeida & Martin-Vide, 2009) and block movement is assumed to begin only when the upper part of the riprap becomes partly exposed (Townson, 1988). However, if large and heavy blocks are required for stability reasons, they have to be placed individually by machines because of their weight.…”

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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“…Existing design methods are generally limited to dumped blocks and first movement of particles is used as failure criterion (De Almeida and Martín-Vide, 2009). However, if large and dense blocks are needed for stability reasons, they must be positioned individually due to their heaviness.…”

Section: Introductionmentioning

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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