I am new to this feature and would like help with the inputs on the Basic Soil Modeler page. Is the thermal Expansion Coefficient intended to be for the soil backfill? Same for the temperature change? What does the program do with this info in computing pipe movements or restraint forces?

The expansion coefficient and temperature are for the pipe. We use it to estimate the length of pipe that would crate a virtual anchor. That is the length of pipe which provides enough axial restraint (through accumulated friction) to resist the thermal growth (and pressure extention). The soil data will develop a bilinear stiffness (K1 & K2 with a break at Fy)per unit length of pipe in the axial, lateral and vertical directions. That Fy will be the load at which the soil goes from elastic to plastic response and pretty much matches what we might call the friction load per unit length of pipe. So the Virtual Anchor Length (VAL) equals the axial load in the pipe (A E alpha) divided by this axial load per unit length.

Why are a material property and a pipe load repeated in the soil modeler? Seems like an opportunity for a mistake. Does this overwrite information from the other screens or do you enforce compatibility?

That material data (T & alpha) is used only to calculate the Virtual Anchor Length (VAL) in the soil modeler. It is a fucntion of your soil model (number) and not tied directly to the pipe.

This data is not used elsewhere other than calculating VAL.

You would use that VAL to determine how much buried straight pipe you should include in your buried analysis. The idea is that any thrust coming from beyond this point will have no effect on the part that you are modeling.

Is there ever an instance where one would wish to have T & alpha different in the soil modeler than in the main model?

Does the program consider any ring bending type effects for buried pipe? Applies more to larger diameters.

Thanks.

I cannot think of a situation where a user would want to specify one T & alpha set in the input and a different T & alpha set in the soil modeler.

I will assume your next question will be "Then why do we have to specify it a second time?". Our buried pipe modeler is a batch operation - you layout the pipe as if it was not buried and then bury it with our modeler. Once buried, you shouldn't be playing around with the layout or loads because that layout and those loads uniquely set the soil supports. (Only constructed underground restraints need be added to the buried model.)

If you do change the T and/or alpha, you will still get the same buried restaint layout. Changing these terms will only display a different VAL.

Ring bending? No, we're working with a simple centerline (simple beam bending) model. We have no circle to crush.

What about the bury depth? I was looking at another person's model with a dozen soil models varying only the depth. How do you handle a sloped pipe underground - or I suppose a vertical one?

It is up to the user to decide when a change in cover depth is sufficient to warrant creating a new soil model.

If there is an up or down run, I would probably set one model for each run of pipe and change from one to the other somewhere along the riser.

Don't confuse the burial depth with the pipe's elevation.

Thanks for quick responses