Buried Arch/Soil Modulus

[dilukshi]

Hi,

I need to estimate the Soil Modulus to design a buried semi-circular arch (underpass) with radius around 6.5m. In calculating the soil modulus, in accordance with M.J.Tomlinson's 'Pile Design and Construction' book (page 224-5), it is not clear whether to consider a constant thickness as B (total or element) or whether to consider the distribution of wheel load as B. This assumption influence the soil modulus considerably. What could be the best estimate for as stiffness for a medium dense dry soil?

Is there any other better way of calculating the soil stiffness (modulus) or any recommended refernce?

I will post this in structural forum as well.

Thanks in advance
Dilukshi

 

[Focht3]

I don't have a clear picture of your question. I don't have Tomlinson's book, so the page reference doesn't help me to help you.

In general, calculating stresses due to wheel loads is done per tire, and the results superimposed on one another. This can be tedious when done by hand, but pretty easy when done by computer.

Keep in mind that 'soil modulus' is a rather ambiguous term; are you referring to elastic modulus?

 

[dilukshi]

Yes, I have been referring to the Elastic Modulus of soil.

The arch is made up of pre-cast concrete beams tied at the crown. These members are 1.5m in width. I calculate the soil modulus with the equation K=nh x/B where nh is the coefficient of modulus variation and taken as 7.5MN/m3, x is the depth of soil and B is the width of the member.

First assumption was B as 1.5m and it gave me very stiff soil (41500kN/m/m2 - 8100kN/m/m2) and I have my doubts about using this value. Then I did another analysis with the Wheel load distribution as B, which gave me stiffness between 5500kN/m/m2 and 2600kN/m/m2 from foundation level to the crown of the arch. Is this a reasonable estimate?

The road surface is 1.6m above the crown level.

 

[Focht3]

I posted to this about three weeks ago - must have had a problem. Sorry.

8100kN/m[super]3[/super] = 30 pounds per cubic inch
(if I got the conversion right...)

A stiffness of 30 pci isn't really all that stiff. That's equivalent to a CBR of 0.3 ...

Your estimate of 2600 to 5500 kN/m[super]3[/super] appears reasonable -