Concrete slabs are frequently used for concrete batter protection, in which case the concrete is normally reinforces with mesh to control cracking. Typical slabs thicknesses may range from 100 to 150 mm.
When a floodway is inundated the slabs may be subjected to water pressure, which tends to lift them. Consequently, for stability, batters are normally made 1:1.5 or flatter. Pressure relief holes may be provided in the concrete slabs in order to reduce the uplift pressures.
In order to minimize scour adjacent to the protection work, protection on the downstream batter may be shaped so as to defect the tail-water jet upwards away from the stream bed.
In practice it has been found that despite the upward deflection of the tailwater jet by the curved apron some scour does occur beyond the protection. However, generally it does not reach serious proportions.
Alternate treatments of downstream batters are:-
(a) Provide a cut off wall in lieu of an apron, accepting some scour downstream of the batter but isolating it from the embankment;
(b) Provide a flexible stone filled wire mattress apron to protect the end of the concrete slab.
The principal requirement of concrete for floodway batter protection is durability. Mixes with an aggregate/cement ratio of between 8:1 and 10:1 (28 day compressive strength of 10 to 20 MPa) have been found to be sufficiently durable.
The concrete is normally cast in alternate bays, the first bays cast being screeded from forms set to the profile of the batter. The intermediate bays are screeded from the previously cast bays. A stiff mix is used because of the sloping surface. A kerbing machine has been found to be effective for casting the concrete margins adjoining the pavement.
The principal advantage of concrete slope paving is that concrete aggregate is generally readily available, whereas stone for rip rap (or stone filled wire mattress protection) is not always available on economic leads.
The principal disadvantage of concrete slope paving is its rigidity. Also it cannot adapt to scoured conditions and is subject to greater uplift forces than free draining rip rap or stone filled wire mattress protection. Please leave a comment about concrete batter protection