# how much force is required to drive a fence post 2ft into soil or sand using a hydraulic press?

I'm building a post driver for the farm and it got me thinking:

what force is required to drive a 6ft(1.8 m) 4 inch (100 mm) post 2 ft into the ground? I'm wondering how different soils affect driving ability and where I could find information on soil resistive force.

I have a spare 20 ton hydraulic cylinder that I'm going to use to press the posts into the soil. imagine the tractor has infinite mass and the output force of the cylinder will be fully transferred into the post.

thanks for any help!!!

What you are proposing is similar to the cone penetration test (CPT) used by geotechnical engineers to characterize the soil layers of a site before construction.

The measured resistance to a continuously pushed tapered probe varies by soil type.

By researching on the web the resistance by soil type values, (see Olsen Chart) you may get a feel for the feasibility of your idea.

This is a highly technical topic, that is very difficult to explain in this space. In general, we can't get accurate/meaningful soil resistances (bearing, friction) until actually driving the pile/post. The linked paper contains a few popular pile driving formulas, that can help you to get start. But it is imperative to consult a geotechnical engineer, or experienced pile installer, to get it right.

https://bestengineeringprojects.com/pile-driving-formula-engineering-news-formula/

• @Sharaf From engineering point of view, I think you shall just dig a hole (deeper than local frost depth), and embed the post in concrete. Note that you will need lateral stability, that the 2' embedment onto soil may not provide (image the wind may tip it over).
– r13
Mar 14, 2021 at 0:22

You could always size the cylinder so it's powerful enough to lift the tractor. You could then measure the actual force required using a pressure gauge.