10th September 2008, 01:49 PM
My bad, I meant SURCHARGING (I was thinking of soap, super-fatted.... It must've been the thought of all that exciting new literature. Me thinks I should move into spying and correction, it can't be anymore traumatic and I'm sure the pay's better.)
I'm sure you know it under its correct name. As we all know, different types of soils vary in strength/cohesiveness etc which is why there is no hard and fast rule on shoring anymore.
In short adding weight on top (spoil heap and plant) stress the underlying soil and this can lead to collapse when it would otherwise not do. At its most basic, you stand on the trench edge and it collapses because the downward thrust of your weight is not evenly distributed. This is not relevent most of the time, but worth bearing in mind on deep excavations, VIBRATIONS can weaken the soil structure. And on all sites, heavy water saturation is a danger too. Fissures can open up a good meter from the edge on even just ordinary deep slots. It really is about thinking further than the archaeology in front of your nose, which is often easier said than done.
Back to the big urban site. Again, this is not just about the spoil heap. It's also about all heavy vehicles, particularly the dumpers. At the risk of turning into Troll, it's not nice when the section edges quiver every time plant drives by a good 1.5m above your head.
For those fresh out of uni, people die in collapses not because their faces get covered, but because their chest gets crushed.
This is an American guide, but the illustrations are very relevent:
http://159.238.91.226/osha/pamphlets/excavation.pdf
This one's from an British H&S consultancy, but is ultimately American as well:
http://www.healthandsafety.co.uk/otm_v_2.html#9
I'm sure you know it under its correct name. As we all know, different types of soils vary in strength/cohesiveness etc which is why there is no hard and fast rule on shoring anymore.
In short adding weight on top (spoil heap and plant) stress the underlying soil and this can lead to collapse when it would otherwise not do. At its most basic, you stand on the trench edge and it collapses because the downward thrust of your weight is not evenly distributed. This is not relevent most of the time, but worth bearing in mind on deep excavations, VIBRATIONS can weaken the soil structure. And on all sites, heavy water saturation is a danger too. Fissures can open up a good meter from the edge on even just ordinary deep slots. It really is about thinking further than the archaeology in front of your nose, which is often easier said than done.
Back to the big urban site. Again, this is not just about the spoil heap. It's also about all heavy vehicles, particularly the dumpers. At the risk of turning into Troll, it's not nice when the section edges quiver every time plant drives by a good 1.5m above your head.
For those fresh out of uni, people die in collapses not because their faces get covered, but because their chest gets crushed.
This is an American guide, but the illustrations are very relevent:
http://159.238.91.226/osha/pamphlets/excavation.pdf
This one's from an British H&S consultancy, but is ultimately American as well:
http://www.healthandsafety.co.uk/otm_v_2.html#9