This was another interesting aspect of the crane job we finished up yesterday I wanted to mention.
As I wrote in yesterday’s post we had been on site two months prior with exactly the same model of crane with nary a sign of this very heavy vehicle passing through. Margarethen Park is situated on the southern edge of Basle on a north-facing slope which is full of natural springs, so there is an abundant flow of water down the hillside allowing trees to grow very tall, with many very beautiful, mature specimens of a range of species forming a spectacular display in the tradition of English landscape parks. One of the largest hornbeams I know of is on this site with a height of probably close on 30m.
Anyway, I digress. There has been prolonged, heavy rainfall the past week or so, leaving soils well saturated with water.
We arrived in the park just after the crane had arrived and I was surprised by the amount of damage to the tarmac it had caused on its way in. The spot we had to manoveuver it into is pretty tight, it was a hassle the first time and proved to be no better this time round: the lads from the city and the crane crew were fiddling around trying to get it in the right position… when I was struck by how the crane was sinking into the tarmac as though it were jelly. You could actually watch is sinking in! Ack! Not something you see every day and not very reassuring…
As you can see in the pics above, the struts were on non-reinforced ground and despite the plates to distribute the load over a larger area were being depressed into the ground considerably. I was really struck by how differently the ground responded to being loaded between the first time we had been on site, in dry conditions, and this second time when it was wet. Obviously the foundation under the tarmac had been washed out over the years and the layer of tarmac itself was not very thick. These factors combined led to terra firma being, well… somewhat less than firm, more like trying to position a very heavy machine on a sponge.
I was feeling increasingly uneasy about all this until I decided that enough was enough and got everybody together to discuss how to resolve this issue – and if this were not possible to call off and postpone the whole operation. After a chat with the crane crew and their dispatcher we decided to give it another crack with larger load-distributing plates to spread the load over an even larger area, but these had to be brought in first, which meant another 45 minutes of waiting. When these finally arrived and were positioned, things started to feel somewhat more coordinated and together.
What this situation illustrated very clearly to me is that ultimately as I was going to be positioning the chains off the hook and was going to be positioned downhill from the crane during the lift it was my right to question a situation that I felt uncomfortable with. More than that: as the crane company was a subcontractor to us it was my duty to ensure that all possible measures were being taken make procedures as safe as possible.
Obviously, getting the crane stable is a prerequisite.
This is another example for a situation where if it cannot be sorted out satisfactorily – and despite the fact that machinery and personell are on site – saying no is always a viable and permissible option.