Briars Lane Survey I
Pelorus Surveys have recently completed two months of fieldwork which formed part of a large Ground Investigation contract around the area of Briars Lane, Hatfield.
The development of the area has been carried out over some old chalk quarry workings which were infilled. Over the past few years, subsidence has been evident across the area affecting some of the residences. The Local Authority has contracted Soil Mechanics, Wokingham to carry out a detailed investigation of the area to identify areas of weak ground or any other features that may be causing this subsidence.
At 28,000 square metres, much of it within private property, targeted drilling of any anomalies is required to minimise the disruption to the public. Due to this, a phased investigation was necessary.
Phase 1 of the works involved a detailed geophysical survey of the area. Pelorus Surveys collected data using two specialist geophysical techniques. Over the whole site at a grid spacing of 3 metres, detailed measurements of the gravity field where taken using gravity meters. These very sensitive instruments can measure extremely small variations in the earths gravity, these variations being caused by small changes in the density of the ground beneath which the measurement is being taken. So sensitive are these instruments that corrections for height differences in stations have to be made, thus accurate survey information for instrument position and height had to be obtained.
After QC checks, the gravity data was forwarded on a daily basis from site via email to a specialist consultant who will remove the gravity effects of the site topography and even buildings. The final plans will show a gravity anomaly map of the area highlighting areas of infilled, less dense material which could be due to the former quarry areas. This will allow targeting of the works for the second phase which involves probing, trial pitting and rotary coring.
In addition to the microgravity survey, resistivity imaging techniques were used to provide a profile of the sub-surface along lines identified by the Client.
This integrated offering allowed the Client to come to a single source for the Site Investigation which only Soil Mechanics has the capability of. The GI is expected to be completed by the middle of 2005. |
