Experimental study on bed pressure around geotextile mattress with sloping plate.

Liquan Xie,Yanhong Li,Yehui Zhu,Tsung-Chow Su,Jianguo Wang

doi:10.1371/journal.pone.0211312

Liquan Xie, Yanhong Li + Show 3 more

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https://doi.org/10.1371/journal.pone.0211312

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Abstract

A geotextile mattress with sloping curtain is a newly proposed countermeasure against river and estuarine scour. In previous laboratory experiments, a geotextile mattress with sloping curtain was capable of protecting the bed downstream from scour and stimulating sediment deposition on both sides. However, the seepage scour under its geotextile mattress is inadequately researched at present. In this study, the Geotextile Mattress with Sloping Plate (GMSP) is proposed based on the simplification of the geotextile mattress with sloping curtain with the construction feasibility considered. A series of experiments was conducted to investigate the pressure distribution around the GMSP and the averaged seepage hydraulic gradient beneath its mattress. The results indicate remarkable pressure difference on two sides of the GMSP. The minimum bed pressure appears about 1.3 times the plate height downstream to the GMSP. The averaged seepage hydraulic gradient beneath the mattress increases with the sloping angle increasing from 35° to 60° in general. The averaged hydraulic gradient also ascends as the relative plate height increases, but reduces as the opening ratio increases at opening ratios greater than 0.143. The safety boundary for the averaged hydraulic gradient under the geotextile mattress of the GMSP could get much smaller than the critical hydraulic gradient of piping and can easily be overwhelmed. This phenomenon can mainly be attributed to the discontinuous contact between the mattress and the seabed. A suggestion for the parametric design of the GMSP is to extend the width of the mattress to reduce the risk of seepage failure.

Highlights

Scours in river channels and coastal areas are long-lasting threats to the underwater structures and dikes
Where im is the averaged seepage hydraulic gradient beneath the mattress, Δp is the difference of bed pressure readings on two sides of the Geotextile Mattress with Sloping Plate (GMSP), ρ is the density of water (ρ = 1 × 103 kg/m3) and g is the gravity acceleration (g = 9.8 m/s2)
(1) The bed pressure drops remarkably on the downstream side of the GMSP compared with the upstream side

Summary

Introduction

Scours in river channels and coastal areas are long-lasting threats to the underwater structures and dikes. The failure of these structures and dikes could lead to considerable economic losses and heavy casualties. The scour on the river banks could shape the bank slope much steeper, which would cause bank collapses [1, 2]. Underwater scours may endanger the structures installed on the seabed like bridge piers [3, 4], pipelines [5,6,7] and wind turbine foundations [8,9,10]. Degradation of river channel and scour around bridge piers may cause.

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