Reactivated settlements in peat
Reactivated settlements in peat
(OP)
We have been asked to look at a 150 year old, 4m high, railway embankment constructed over approximately 5m of peat over chalk. Over the past 3 years the embankment has begun to settle (approimately 500mm of downward movemnt). The embankment was never a problem previously and I would assume that after 20 years or so most of the settlemet would hace occuredd and the peat would be pretty well consolidated. The renewed movemnets correspond with the recent creation of an area of wetland next to the site. Is there likely to be a connection? Also how can a rise in groundwater level in an already consolidated material cause renewed settlements? Any advise on how to analyse the problem would also be appreciated. There is no indication of any slope instability (other than some minor surface slips in the over steepened ballast shoulder)and there is no deflection of track side masts so I don't think that it is a slope failure.
Thanks
Thanks





RE: Reactivated settlements in peat
RE: Reactivated settlements in peat
RE: Reactivated settlements in peat
RE: Reactivated settlements in peat
RE: Reactivated settlements in peat
RE: Reactivated settlements in peat
RE: Reactivated settlements in peat
although there have been already answers that cover beyond my knowledge possible causes I would just like to point out that there are perhaps one main cause that triggers some others. Since you asked about the decrease in effective stresses due to water level rise, you are right that since they get smaller there will be also smaller deformation. Never-the-less increase of pore pressure would lower the shear strength and in that case have deformations due to local failure. I don't know if the small slip indications can be integrated in any failure mode.
If I may I would like to agree with tomsklucki's question also for the possible change of the type of trains (heavy loads instead of/or increased frequency).
Please consider the above as sharing thoughts (probably already known) that are neither an expert's opinion nor necessarily correct.
Regards