Destroying LOFAR — Load #4

Could we actually get an entire tonne of snow into the digger bucket? Well, with the HBA tile still sitting there unfazed, we decided that now was the time to try.

Whumpp!

Over a tonne of snow lands on the tile... which doesn't even flinch. The score now, showing the mass of each individual load, and the new cumulative total that it would amount to is as follows:

Load   Mass    Total
#1   400kg    400kg
#2   550kg    950kg
#3   950kg   1900kg
#4  1050kg   2950kg

Wot? More snow needed?

Destroying LOFAR — Load #3

With no discernible damage to the tile, it was time to start getting tough. Rather than easing on a few hundred kilogrammes at a time, we decided to place a larger load.



This time the digger scooped up 950kg of snow. This would double the total quantity that was already on the tile. We expectantly waited for the crash...



... nothing happened. The snow fell from the digger bucket, now piling even higher on the tile. We now have a serious weight being applied to this HBA tile.

Load   Mass    Total
#1   400kg    400kg
#2   550kg    950kg
#3   950kg   1900kg

Still more snow needed!

Destroying LOFAR — Load #2

During the tests there were numerous members of the team taking photographs. In addition we also had a video camera running ready to catch the moment of collapse.


So, having successfully placed the first load, we then proceeded to put on a second. This time the digger bucket weighed in with a total of 550 kilogrammes of new snow.


Again, the tile withstood the load. So, the score now stands at:

Load   Mass    Total
#1   400kg    400kg
#2   550kg    950kg

More snow needed!

Destroying LOFAR — Load #1

With the initial preparation work completed, it is time to actually go for it. So, with the area cleared, the digger ready, staff on stand-by, and cameras rolling, the first load of snow was gingerly dropped onto the raised test tile.

The digger had picked up four hundred kilogrammes of snow and was going to attempt to drop half of it onto the tile.

We held our breath.

As the sequence shows, the first drop went on just fine. The tile showed no sign of stress or strain and so the remainder of the digger bucket was also put onto the tile. Thus, a 400 kg load was in place and the tile (or at least part of it) was hold it out without any problems. We also didn't have any problems with the snow not leaving the digger bucket or issues to do with the reach of the digger to a suitable drop area. Additionally, all the snow that was in the bucket actually then stayed in a solid pile on the tile, without any sliding or blowing off.

So, the result that we have so far is as follows:

Load   Mass    Total#1   400kg    400kg

With smiles all around, we sent the digger over to get a second load of about the same size. But the outcome of the next dump of snow will be in the next post, which will be posted up in the next hour or so.

Destroying LOFAR — Preparation

Before starting, we experimented with the digger by scooping up loads of snow and dumping them on the ground. Using the same technique that we used for the ice/snow core samples we checked the density and condition of the material we had to use.


As it turned out, the snow in the area was very dense. It was also icy, bordering on slushy in places. This means that it would pack well and, when piled up compress into an even denser mix. This was not quite what we'd hoped for, as we had anticipated more powdery snow. However, the area had been subjected to some (relatively) warm weather and prolonged sunshine.

In addition to the snow tests, we also used the digger to clear the surrounding area.


This would give us a good view of the frames and underside of the tile and permit easy access.

Coming next... the first load of snow is placed on the tile!

Destroying LOFAR — Introduction

One of the purposes of the winter testing, was to check whether a conventional LOFAR High-Band Array (HBA) tile would withstand the Arctic conditions. Apart from the sustained cold temperatures and the high-winds, the main concern was the loading of snow on the tile.

As we have seen during the last few days, the full site inspection has revealed that both test tiles (the raised tile and the one on the ground) have survived the winter intact.

This is a major relief.

What this means is that the conditions that we incurred over winter were insufficient to damage the tile. But what about the extreme case. And just because it didn't break, doesn't mean that it didn't come even close. Therefore we'd like to do an experiment (umm, what did you expect... we're scientists!)

This is the HBA tile:



It is the raised tile as seen after the surrounding snow had been cleared away, measurements have been done and initial testing completed. So, the idea is to deliberately put some snow on it.

This is the digger:



Over the course of the next few hours, we were going to use this 15-tonne machine to gently put snow onto the tile. The digger has a built-in load measuring system, so we can weight the snow as we pile it on to the HBA tile.

What we are looking for is:

a) What is the breaking point? That is, how many tens, or even hundreds, of kilogrammes of snow can we place on the tile before it collapses?

b) What is the mode of failure? In other words, which part gives way first? Do the lids fail, or the walls, or the timber supporting frame underneath?

If you want to have a guess, do it now... and then stay tuned over the next few hours as we post up the results.

Ice cores — Part 2

In the last post, we explained how we had started taking a small set of snow/ice cores around the site to assess how the snow had built up and the solidified. Although some areas were quite deep with snow, as the recent site images show, there is plenty of exposed rock and some of the samples were actually quite shallow.

Toivo Iinatti extracts a small core from between the two test tiles.

However, we've now got back the initial data from the measurements. These data have been kindly provided by Markku Postila and show some of the sample points and what we found.

(Click on the image to see it at full-size)

Further assessment and analysis will be needed, but it does give a first indication as to what could be expected in the case of partially melted-and-re-frozen conditions at the end of the season where packing densities can be quite high.

And, despite the large outcrops of exposed rock on the site, there are still considerable areas where the snow remains moderately thick. Obviously the drift areas exceed 50cm, but 30 cm is about the expected depth in uniformly distributed areas.