11th September 2011, 04:46 PM
Marcus
I suspect all the 100% on this thread is all for the benefit of PP, so :face-topic:
To explain better the issues with the site I described above:
Evaluation (trial trenching and monitoring of window-sampling) had established that c.1m of post-medieval garden-related deposits overlay around 2m of in-situ medieval deeposits backing onto a castle wall (which was responsible for the substantial depth of stratigraphy). This deposit model can probably be applied in general to all of the gardens behind properties on that side of the street, except where a small number more recent developments can be seen to have taken great bites out of it.
As a response to the results of the evaluation, the building, which had originally been designed with poured-concrete founds down to bedrock (c.3m), was redesigned on the minimum number of 300mm piles (still around 40 though) with all the pile-caps, ground beams etc up within the post-med garden soil horizons. However, due to surviving remains of the castle wall below one end of the development, that end had to be redesigned with a cantilever over the wall. In order to accomodate the cantilever, the post-med material in that area was archaeologically hand-excavated down to 1.2m, which incidentally recorded part of a rather nice 18th century formal garden, in order to provide a lowered construction working area. The contentious part is that the subsequent founds to support the cantilever were then machine-excavated by mini-digger (the only access to the site is via two narrow doorways through a standing building) down to bedrock in a single exercise, the machine being too small and with too limited a reach to go back and do the thing in spits and hence only providing extremely limited opportunities for archaeological recording - I have a pretty good idea what was there but with only limited records to back it up. The resulting trenches were too deep and narrow for access, and in fact the ground proved too unstable to even stand on the sides safely to take measurements in some areas.
On the up-side (and this was the general view taken), the excavation of the founds in this area has merely removed narrow vertical slices through the archaeology leaving significant blocks of material in situ, and the general nature of the excavated deposits across the area appeared to be reasonably consistent. Hand-excavation of the founds would have required removal of c.5 times as much material, allowing for stepping the trenches which would have needed on safety grounds to have been far wider than the machine trenches, and would then have needed shuttering to cast the founds merely to put all the excavated soil back in to support the shuttering! Although painful to watch, as an archaeologist, the machine approach probably caused less damage to the overall archaeological resource than a partial hand-excavation of relatively disconnected bits of it. 100% excavation, given the prevailing 'retain-in-situ' culture, was never going to happen since most of the known archaeology lies below the invert level of the majority of the new structure. Gonna be a b***er to write up though....
Also on the upside, pursuaded them that frankly a compound with grass was generally better than a compound with mud - builders can be reasonable if archaeologists bother to explain things to them, and those ones are a good bunch
I suspect all the 100% on this thread is all for the benefit of PP, so :face-topic:
To explain better the issues with the site I described above:
Evaluation (trial trenching and monitoring of window-sampling) had established that c.1m of post-medieval garden-related deposits overlay around 2m of in-situ medieval deeposits backing onto a castle wall (which was responsible for the substantial depth of stratigraphy). This deposit model can probably be applied in general to all of the gardens behind properties on that side of the street, except where a small number more recent developments can be seen to have taken great bites out of it.
As a response to the results of the evaluation, the building, which had originally been designed with poured-concrete founds down to bedrock (c.3m), was redesigned on the minimum number of 300mm piles (still around 40 though) with all the pile-caps, ground beams etc up within the post-med garden soil horizons. However, due to surviving remains of the castle wall below one end of the development, that end had to be redesigned with a cantilever over the wall. In order to accomodate the cantilever, the post-med material in that area was archaeologically hand-excavated down to 1.2m, which incidentally recorded part of a rather nice 18th century formal garden, in order to provide a lowered construction working area. The contentious part is that the subsequent founds to support the cantilever were then machine-excavated by mini-digger (the only access to the site is via two narrow doorways through a standing building) down to bedrock in a single exercise, the machine being too small and with too limited a reach to go back and do the thing in spits and hence only providing extremely limited opportunities for archaeological recording - I have a pretty good idea what was there but with only limited records to back it up. The resulting trenches were too deep and narrow for access, and in fact the ground proved too unstable to even stand on the sides safely to take measurements in some areas.
On the up-side (and this was the general view taken), the excavation of the founds in this area has merely removed narrow vertical slices through the archaeology leaving significant blocks of material in situ, and the general nature of the excavated deposits across the area appeared to be reasonably consistent. Hand-excavation of the founds would have required removal of c.5 times as much material, allowing for stepping the trenches which would have needed on safety grounds to have been far wider than the machine trenches, and would then have needed shuttering to cast the founds merely to put all the excavated soil back in to support the shuttering! Although painful to watch, as an archaeologist, the machine approach probably caused less damage to the overall archaeological resource than a partial hand-excavation of relatively disconnected bits of it. 100% excavation, given the prevailing 'retain-in-situ' culture, was never going to happen since most of the known archaeology lies below the invert level of the majority of the new structure. Gonna be a b***er to write up though....
Also on the upside, pursuaded them that frankly a compound with grass was generally better than a compound with mud - builders can be reasonable if archaeologists bother to explain things to them, and those ones are a good bunch