Settlement Calculation by Schmertmann method(1978) 2

[Chunil]

I want to know Schmertmann approximation's(1978) limitation.

Does that Eqns can be applicable to weathered rock ?

Weathered rock has N value of 50/10~ more!!!

Can i use Schmertmann approxiamtion for settlement calculation on that weathered rock ????

Thank u!

 

[BigH]

Well, I suppose that you could - as the method is nothing more than modeling the strain with depth. If you know the elastic modulus value for your rock. With weathered rock though, depending on the type of rock, you may have clayey inclusions in joints/fractures that might have more impact on the actual settlement than of the weathered rock mass itself. And, you must take into account the degree of weathering. Why not just use a normal elastic solution for determining the settlement as per those given in Poulos and Davis?

 

[dmoler]

No way. Use the load transferred to the rock for an equivalent mat area with the appropiate lateral distribution per Poulous or other reference (should be same load but larger area due to lateral spread down to the rock top).

Then, model the weak rock layer as a beam on an elastic foundation. You will have to come up with the EI of the rock and the EI of the underlying strata.

 

[Chunil]

Weathered rock means RIPPING ROCK in here!!

 

[fndn]

There is also a great settlement of sands and gravels by Bazaraa. It is near page 390 of Soil Mechanics in Engineering Practice-1996 edition. It is fast, reliable and uses all the data from the borings and footing widths. Also a study that came out around 15 yrs ago performed comparison of settlement predictions by various researchers and compared with actual observed settlements. I recall that D'Apolonia's method predicted best followed by Peck and Bazaraa method.