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# Cofferdams (suspended solids question)

## Cofferdams (suspended solids question)

(OP)
Does anyone know how to calculate the relative density (specific gravity) of water with 40,000 ppm of suspended solids (fine silts).

This is not structural question, but I would assume structural engineers that design cofferdams in rivers may have encountered this before.

VOD
Replies continue below

### RE: Cofferdams (suspended solids question)

Try (40,000/1,000,000(150 pcf)+ 960,000/1,000,000(62.5 pcf))/62.5 pcf.

### RE: Cofferdams (suspended solids question)

JedClampett got you pretty close.  He used a specific gravity of 2.4 for the silts (150/62.4).  The specific gravity is closer to 2.7.

The corrected equation is:

40000/1000000*(62.4*2.7)+960000/1000000*(62.4)

which yields a value of almost 67 pcf.  That's pretty thick stuff.

(The equation above can be copied straight into Excel.)

(OP)
Outdone again :)

Regards

VOD

### RE: Cofferdams (suspended solids question)

You could use a cheap hydrometer with a sample of the material.

### RE: Cofferdams (suspended solids question)

Yeah, but calculating it is so much fun!

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