I'm looking for some experiences on using riprap or other types of mechanical protection methods on soft soil and specially saturated marly slope. Is there any special consideration for using this type of protection on marl?
Channelisation, Controlling surface runoff, Benching, Biotechnical Measures, Local Cut Slopes with stabilisation measures at toe portions. Nevertheless, considering the softer nature of rock mass, affects of weathering and erosion must be kept in mind. Better to keep the cut slope angles of the order of 25-30 depending upon the condition and then cover it or seal it with layer of excavated material itself. Scope of biotechnical stabilisation is also to be worked out. The idea is that effect of weathering to surface of cut slopes/benches and even to some depth below the slope surface should be avoided to the best possible extent. Channelisation to divert slope run off are also required to be designed appropriately for such slopes, where effect of weathering, drying/wetting and related processes are of concern and should be dealt carefully.
In practice, you may use rock bolts and shotcrete for relatively higher strength marl. For very weak marl, you may use stone pitching, and in even worse cases, slope stabilizing piles with stone pitching.
In the case of protecting with Riprap, you must take care to place layers of sand and gravel filter in the contact between the marl and the bedrock, to avoid washing and dissolution, reduce the hydraulic gradient of the possible filtration flow and separate the surface runoff.