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Duston Action Group has recently uncovered a vitally important planning document that had somehow been ‘lost’ by Northampton Borough Council. The report, entitled “Southern District Trial Hole Surveys - Northampton Land Unsuitable for Development”, Download a copy of the original report warns of the hazards of building on sloping land in most of Northamptonshire, slopes as gentle as 7 degrees may be subject to disastrous land slips if construction work is attempted.
This applies to the whole route of the planned Sandy Lane Relief Road (SLRR), parts of Sandy Lane Improvement North (SLIN) and the proposed housing estate of 2,600 houses at Upton Lodge.
In advance of the WNDC Planning Committee meeting, which was set to decide the fate of the SLRR planning application on Tuesday 4th September, NRA provided a copy of the damning report and a strongly worded complaint to WNDC. On the day, Stephen Kelly advised us that the seriousness of the revelation meant that WNDC were obliged to withdraw the planning hearing from the evening’s agenda.
The Duston Action Group submitted this complaint to WNDC in advance of the planning meeting:
Summary of: Tapsell, Wade and Partners Consulting Engineers Report to Chief Architect & Planning Officer, Northampton Development Corporation. Dated: 16th September 1983
Southern District Trial Hole Surveys -Northampton Land Unsuitable for Development
This report was commissioned by Northampton Development Corporation following an unfortunate event in nearby Daventry, when an 18-metre cutting for road construction caused a mass movement of earth on Fox Hill, which affected an area some 40 metres beyond the road works. See article entitled “Daventry Bypass Landslip (A lesson for Road Engineers)” after page 7 of the attached report.
The report discusses the land formation that is prevalent in the Northamptonshire area, although the accompanying letter from NDC to Northampton Borough Council specifically mentions East and West Hunsbury. It refers to ‘Solifluction’, which is a feature of land formed in the Periglacial period, and is a widespread hazard in this area. It points out that whereas the land is stable for farming purposes, construction work may cause the land to slip. The chances of a slip occurring are increased during wetter weather.
The report declares that any land with a slope greater than 7 degrees is suspect.
On page 3, the report asserts: “In addition [to geomorphic or accurate slope angle surveys] …..this survey should, ideally, be supplemented with a series of very deep exploratory holes which should be monitored over a lengthy period.” (Twelve months).
At the foot of page 3, the report states: “The construction of any civil engineering or building works in suspect areas should be considered with caution.” “Engineering works could easily give rise to reactivation of the relic land movements.” “This movement can occur by the formation of cuttings formed for road, foundation or services excavations which remove lateral support of ground upslope, or by the formation of embankments and construction of superstructures which increase the normal stresses on the existing slip planes.”
On page 4 it continues: “It is quite normal for solifluxed soils to extend to depths of from 2m up to 12m and therefore, normal trial hole excavations carried out by conventional digger can easily miss the critical sub-soil aspects.”
Later on page 4, the report goes on to recommend: “that slopes, in this area, of greater than 7 degrees be deleted from land suitable for building.” Also: “foundations for higher density housing on land approaching 7 degrees could be considered as raft foundations to minimise the loading upslope from the potentially hazardous land.”
The most telling point is on page 5 where the report declares: “As we understand it, the situation is now that all land slopes exceeding 7 degrees have been deleted from your [Northampton Development Corporation] land deals with developers.”
- · The following is an excerpt from a list of advice to be given to other landowners and developers:
“Unless an extremely rigorous geotechnical survey be provided to prove otherwise, all land of greater slope than 7 degrees be considered as potentially hazardous.”
- · “On land approaching 7 degrees above potentially hazardous areas, consideration be given to keeping the housing density low or utilising raft foundations, so as not to overload the crests of the hill slopes.”
The Duston Action Group Opinion
Many of our members live on the crest of the hill above the proposed route of SLRR and the proposed Upton Lodge Housing Development. Some of us have already witnessed some landslip at the bottom of our gardens. This news puts our properties directly at risk from any kind of building work proposed at Upton Lodge and also questions the safety of existing property.
We are shocked to discover the existence of this document so late in the planning stage of the proposed road. Mr Stephen Kelly advised us today (31st August 2007), that he had become aware of this report some six months ago, although he felt it was a matter for Building Control, not planning. However, Government guidelines PPG14 declares that a planning authority must make available to landowners and developers all information concerning unstable land. The legal liability for the result of any landslip following construction work does, however, remain with the landowner and the developer. Nevertheless, we think it very disingenuous of WNDC to fail to disclose this information, once it had come to light. As residents at risk from this potential hazard, DAG members consider that this information should have been made known to us as soon as WNDC became aware of it.
In 1983, the NDC obviously did the right thing by removing suspect land from sale – a brave, but honest decision. Much of this land now belongs to English partnerships and the entire route of the SLRR falls within the affected area. The majority of the proposed route is on a hillside and sloped at an angle greater than 7 degrees. When they received this report, Northampton Borough Council also stood up to the mark and, for a period between 1983 and around 1998, had a policy of providing every planning applicant with a copy of the report as guidance. Unfortunately, when DAG asked NBC (under the Freedom of Information Act 2000) to provide a copy of the document – none could be found! This is most worrying and we have asked our MP to investigate how many developments have been constructed on or close to slopes since 1998 – we are concerned that many properties may already be at risk because of this failure to enforce known safety measures.
In the light of this irrefutable evidence, the Duston Action Group expect the WNDC Planning Committee of 4th September 2007 to refuse planning permission for SLRR until such time as the land in question has been thoroughly surveyed by solifluction experts and identified as safe to build on. Additionally, we expect that the proposed planning application for 2,600 houses on the slopes at Upton Lodge should be discouraged for the same reason. Finally, WNDC must undertake to provide a copy of this report to all landowners, developers and prospective developers that have a current or future interest in land in Northamptonshire as part of its published advice to developers.
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