Science Buddies: "Ask an Expert"

I have a science fair project due March 22 and I am going to perform the experiment suggested on your site called " Factors that Affect the Transfer of Force through Saturated Soil" but some of the details are vague. I don't know if you have access to the experiment or not, but I'll assume that you do. My questions are how long do the wooden dowels need to be? How exact do the holes that we drill for the dowels need to be? If we are measuring the force that it takes to remove the dowels after we simulate the liquefaction, how can I prove that it wasn't from friction between the PVC pipe and the dowel?

Please help.

Hi,

Welcome to Science Buddies!

think you are doing this excellent project from this website:

https://www.sciencebuddies.org/science- ... p002.shtml

Here is an explanation that should help you. The diameter of the PVC pipe and the dowel rods that are inserted at an equal distance down the pipe are controlled variables. You choose the diameter and length or the pipe and cut dowel rod that are long enough to be inserted across the pipe. You would keep the the pipe and dowel rods the same for each experiment and the only variable is the experimental filler.

I haven't done this experiment, but I would recommend using 2 inch diameter PVC pipe at a minimum, and it would probably be good to use wider diameter tubing since some of the filler materials are relatively.

Another parameter that is not defined in the procedure is the percentage of filler material in the sandy soil. You would need to define this for your experiment. For example, you would state that the filler material is 10% of the total volume of sandy soil (or whatever percentage you decide to use).

Does this help?

Donna Hardy

O.K. that makes sense why it wasn't stated specifically. Thank you for responding so quickly.

Hi newinschool3,

I like your project! Donna has given you good suggestions about how to get started.

There's one thing I would like to add. The Materials list includes a spring scale that is used to measure the force needed to pull the dowels out of the soil. This is a critical piece of equipment since you will be using it to obtain the force data.

I don't know if you have a spring scale, but they are made for different weights. Small ones weigh ounces or fractions while bigger ones can weigh in pounds. You need to get one that can weigh accurately in the range you need. How do you do that? One way would be to do a practice run and pull the dowels out by hand. Then you would have an approximate idea how much 'pull' it will take.

Your question about friction of the dowel on the pipe is a good one and shows that you are thinking. If the holes in the pipe are all the same size and the dowels are all the same size, then the frictional drag should be the same for each so that the force differences will be due to the soil.

I think this is a really interesting project, so if you have any more questions I will be happy to help.

SciB

Hi newinschool3,

SciB has posted some excellent advice. Let us know if you need more help.

Donna