How heavy must foundations be to support a garden arch?

Question

I am building an arch for my garden. It will stand 2.4 m above ground and weigh 160 kg. There are two vertical posts, each of which will extend 60 cm into the ground. How heavy must the foundation be to support the arch's weight? That is, how much cement must I pour to create a firm foundation?

Answer 1

As a good rule of thumb, at least 1/3 of the length of the post above the ground should be extended into the ground. In other words, 0.8 m should be buried. Use treated rot-resistant wood, of course. Normally, again, a hole is dug maybe twice as wide as the size of the post, and after the posts are inserted, concrete is filled to within maybe 10-20 cm of the surface. That alone should be sufficient to hold up your posts and arch and keep it from falling over. This is consistent with standard practices of fence work, you aren't erecting a building. Figure about 1 to 2 bags of cement for each hole. Make sure the bottom of the holes are wide and well packed, otherwise your poles could sink into them over time.

Answer 2

shouldnt take a whoe lot, just as much as you would use for a fence post, if your building the arch out of wood, just use enough to keep it grounded, you dont need a whole lot