When making a design against quicksand (boulance) at the downstream toe of a dam, the critical gradient is calculated from the ratio of effective weight to water weight. But even if the exit gradient is higher than the critical gradient, there may not be any piping because the velocity is too small for the water to lift the soil particule. Considering this, what are the design criteria for soil particule transport in suspension due to high gradient in water flow? Attached is the only criteria available to me and I am looking for other sources of information.
You may like to search in the sand production literature where velocity gradients are used as a criterion for deposition of the sand grains.
Thanks very much for your answer. Could you enlighthen me on what is the "sand production litterature". I am not quite sure to understand the meaning. Any link in particular?
Dear Oliver
The answer to your question can be given as follows: It is known that clays and gravels are not susceptible to piping failures. Clays will not fail by piping because clay is cohesive and posses some strength at zero effective stress. On the other hand gravel will not suffer piping failure because a large seepage rate, unattainable in practice, is required to cause piping. Now returning to the question you asked: piping may not occur even though the critical hydraulic gradient is exceeded because the velocity is too small. Darcy's law states that v = ki = - k∂h/∂s, where v = velocity, k = coeff of permeability and h = head. It is obvious that v will be small if and only if k is small and this is true of fine silts and clays. In conclusion, soils that are liable to piping failure are soils in the range coarse silts to medium sands. The criteria developed by Terzeghi and Casagrande work very well for such soils. Don't expect to find any piping criteria for clay soil in the literature. Clays do not suffer from hydraulic piping. instead susceptible clays may suffer from dispersion piping.
Dear Anyaegbunam,
Thank you for you answer. It is very well explained. You are right the criterias work very well to determine if piping will occur between 2 granular materials.
I suppose now that in the case of a toe dam, the velocity of the flow for quicksand will be equal to the permeability X critical exit gradient.
Regards,
Hello Olivier,
I was referring to sand production in oil and gas wells due to reservoir depletion. It is a well known problem for the oil and gas industry particularly in brown fields(old fields) I would also look at erosion sand production models. Vardoulakis and Papamichos have published a lot in this area. For a review of various models see
http://www.hindawi.com/journals/jpe/2013/864981/
Regards
Reem
For those following this question, I have found some very good information on the calculation of flow velocity which can transport soils particules. You can find this information summarized in ICOLD Bulletin : internal erosion of existing dams, levees and dikes and their foundations, draft 2013.
In section 5.3 : Methods to estimate loads and resistance to contact erosion, a few formulas are presented on the calculation of flow velocity creating transportation of particules based on Brauns (1985) and Guidoux (2010).
REFERENCES :
Brauns, J. (1985), Erosionsverhalten geschichteten Bodens bei horizontaler Durchstromung, Wasserwirtschaft, vol 75, p. 448-453.
Guidoux, C., Faure, Y.H., Beguin, R. and Ho, C.C. (2010). Contact erosion at the interface between granular filter and various base-soils with tangential flow, Journal of Geotechnical and Geoenvironmental Engineering, Vol. 136(5), 655-775.
- Badges
- Science topic
- Similar topics
- Linguistics
- Composition Studies
- Publication