NAVFAC Consolidation Nomograph

[RockDoktor]

I'm trying to use the NAVFAC "Nomograph for Consolidation with Vertical Drainage" (p 7.1-229) and it is looking for a Cv ratio or value between 0-1. I've got a Cv value, but it is not a ratio value and I can't seem to find out what I should be dividing my value (12.7sf/day) by to complete the nomograph.

Thanks for any help!

 

[BigH]

RockDoctor - the axis on the nomograph (far left) is actually in ft2/day. The question is, in my mind, what kind of soil do you have? A "typical clay" might have a

cv of 0.08 ft2/d to 0.4 ft2/d

(see Bowles, 5th ed. Fig 2.16a/2.16b (5x10-6 m2/min); see typical values in Lambe and Whitman, SI Edition, Table 27.1 (2 to 5 x 10-3 cm2/sec for LL < 60).

If you are having a value of 12.7 ft2/day I would suggest that you are dealing with sandy gravel and using the nomograph is really academic and unnecessary as settlement is generally assumed to be instantaneous (except, perhaps under seismic conditions where the permeability might still permit some short term porewater pressures to develop).

 

[RockDoktor]

Thanks BigH. We're dealing with a fly ash paste material in an industrial decanting pond. The material is a classified as a non-plastic "silt", although it is not really a sediment to speak of.

I was hoping to use the nomograph as a secondary check on the hand calcs (and nomographs are fun!) but it doesn't look like the material fits within the limits.

As an FYI, we estimated that the 10 feet of paste will be at 60% consolidation in about 2 days.

Thanks again!