The Koschny Observatory - building the pier

Introduction

Today - 01 Nov 2003 - I wanted to pour the concrete pier. It was not freezing at night, not raining, and Saturday. My wife woke me up with the words "somebody is hammering in our garden!". Indeed there was the guy who would build the foundation for my hut - exactly on the same day. Well, so be it.

Preparing the form and the pier head

I started to prepare the wooden plates that would give the pier its shape, while he drilled holes in my garden . Also, I took the aluminium plate that I had machined by a professional shop and put in the threaded rods that would anchor it in the pier.

Holding the wood together.

Two sheets of the wood

The pier head with threaded rods

The foundation for the hut

The Dutch way to drill a hole in the ground is to take a powerful pump, put it next to the canal behind our lot, and use a long tube where the water comes out to make the hole. While everything is still wet, take a long wooden pole, push it in, then hang on it to get it deep into the ground. In the end, the 280 cm poles only stuck 10 cm out of the ground.

Drilling the hole.

The complete foundation.

Pouring the pier

I started to mix the concrete. All I needed to do is to add 2.5 l water for each 25 kg of "ready-mix" concrete. All in all I carried around 700 kg of concrete.

Overview - in the yellow bags are 700 kg concrete

Testing - inside the form. You can see the re-bars and the threaded rods of the pier head.

The first 100 kg concrete were poured!

Until 10 cm below the end everything went well. But then I heard a strange "popp" - the screws came out of the wood! Oh no! I run to my shop and get my two large clamps to hold everything together.

So here is a lesson to learn:

A 1.2 m high pier excerts a pressure on the wooden form which is larger than ten 4 x 40 screws can hold together!

Shortly before darkness fell the pier was done. Now I wanted to mount the pier head. It is supposed to be anchored to the pier with three M16 threaded rods and one central M20 threaded rod. These were cut to 60 cm length in order to not interfer with the re-bars. When I wanted to put it in, however, I was shocked - it only went in 20 cm and then was stuck! Fortunately, I have a 5-kg-hammer with which I could hammer it all the way in. With a water level I ensured that it the pier head was level. It is done!

The savior - the big hammer.

It is done! - the pier head on top of the concrete pier.

Prepared by dvk, 01 Nov 2003
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