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Gloucestershire County Council is asking residents to have their say on proposals to focus on
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Prison Copse Wall, Northleach (also known as 'The Old A40')

The temporary road closure at this site in Northleach began in December 2015 following a geotechnical inspection into increased cracking in the carriageway.

Ongoing Movement: The defect in the wall continues to grow.Following this inspection the road was closed due to the severity of the defect in the wall retaining the highway, the resultant risk of its failure and the safety of the travelling public.

Currently the council is looking to extend the road closure due to the significant defect in the retaining wall supporting the carriageway which is getting worse. However, the council is not applying for an indefinite road closure to ‘stop up’ the highway in this location.

The site is routinely monitored and has been entered into our forward programme of geotechnical works. At present this site is scheduled for construction work during the financial year 2019/2020; however, this is a priority assessed programme and is subject to change.  

Schemes of this nature are complex, our engineers need to understand the detailed geology of the site and where the movement is occurring to advise on the most suitable solution.

The council are taking all the necessary steps to resolve the situation but defects such as this do take considerable time to fix. Although it is not anticipated that the road will be re-opened in the immediate future it is our intention that a solution will be implemented that will fully restore the road and resolve the issues that have led to the failure in this location.

Frequently Asked Questions

The temporary closure started in December 2015 after an inspection into increased cracking noted in the carriageway. The road was closed due to the severity of the defect in the wall retaining the highway, the resultant risk of its failure and the safety of the travelling public.

We understands that the closure is causing local concern, but it is not intended to be  the permanent solution.

Fixing these types of road faults is complicated - the engineers need to understand the detailed geology of the site and where the movement is taking place to advise on the most suitable way to fix the problem.

A ground investigation was completed in February 2017, this gave us the information to help us understand where and how the failure is happening. This is a specialist survey which unfortunately took time to arrange and complete.

A ground investigation was carried out in February 2017.

The ground investigation indicated that the foundations of the retaining wall are on  soft land. Ground water has been found at about 1metre below the base of the retaining wall. These observations indicate that the failure is likely to be close to the surface, but beneath the foundations of the wall as opposed to a failure behind the retaining wall itself.

The ground investigation included the drilling of boreholes to find out the condition of the ground and to install monitoring equipment to measure ground movements. The monitoring will continue to so we can work out exactly what is going on and get on with the detailed design of the repair work needed.

The road closure being arranged at present is an extension of the temporary closure currently in place due to the significant defect in the retaining wall supporting the carriageway. The council is not applying for an indefinite road closure to ‘stop up’ the highway in this location. The temporary closure is likely to be longer than the standard 18 month period so our legal team have followed a slightly different procedure which means we have presented documents without an end date.

The county council are taking all the necessary steps to fix the problem but faults like this do take considerable time to repair. Although we do not think the road will be re-opened in the near future it is our intention that the solution we come up with will fully re-open the road and solve the issues that have lead to the failure in this location.

At present we are planning to carry out the construction work to repair the site sometime between April 2019 and March 2020, however, work of this type is prioritised and so is subject to change.  

The county currently has a number of landslips on major roads and it is necessary to prioritise available funding to fix these. The forward programme of projects of this type (‘geotechnical schemes’) is prioritised based on the risk of failures, measured land movement, the class of road and the inconvenience of the diversion.

Significant work has been programmed ahead of Prison Copse Wall (‘The Old A40’) - on the B4058 near Horsley, the A46 at Coopers Hill, the B4632 at Cleeve Hill (Lye Lane) and the A435 at Charlton Hill.

These landslip sites are all on very much busier sections of the road network considered economic lifelines for the county and of strategic importance - any alternative diversions for these sites are extremely disruptive.

We understand that the road closure has caused inconvenience to local residents, however the diversion in place is relatively minor and minimal properties are affected.

The road currently closed was previously recorded as carrying less than 400 vehicles per day which is a very low volume of traffic compared with the higher priority schemes:-

  • A435 Charlton Hill 7300 vehicles per day (both directions)
  • A46 Ermin Street 7300 vehicles per day (both directions)
  • B4632 Cleeve Hill 7000 vehicles per day (both directions)
  • B4058 Horsley Road 3350 vehicles per day (both directions)
  • Prison Copse ‘Old A40’ 400 vehicles per day (both directions)

The budget available annually for ‘geotechnical’ work is £1million and this means that on average only two large projects of this type a year are completed.

At present there are two options being considered. The costs quoted here are budget estimates and more work will be done to refine these in the design process.

Option A - ‘Sheet Pile’ solution - estimated cost  £600,000

Whilst this would be the most expensive solution to construct it is the option with the least design, construction and financial risk.

Option B - ‘King Post’ solution – estimated cost £300,000

This solution, whilst considerably cheaper than option A, depends on how the ground is moving below and in front of the wall - this will be found out through analysis of the monitoring data while we work on the design.

The site workers would also need to spend more time at the bottom of the damaged wall presenting health and safety risks. More work needs to be done and advice taken from specialist engineers to find out if this option would work.

Both of these repair options are suitable to fix the fault if it is not far below the surface of the ground under the wall. However, if continuing monitoring suggests that the problem is deeper underground, further design options will need to be considered.

The site is routinely monitored as there are concerns that the retaining wall could collapse and a report about the inspection made on 26 November 2015 says ‘The defective carriageway could potentially be at risk from a catastrophic failure if the wall collapses’.

Further inspections have found more movement in the wall. As a responsible Highway Authority we can not let the public use this section of the road when there are such significant safety concerns.

Option A - ‘Sheet Pile’ solution - estimated cost £600,000

Whilst this would be the most expensive solution to build it is the option with the least design, construction and financial risk.

Option B - ‘King Post’ solution – estimated cost £300,000

This solution, whilst considerably cheaper than option A, depends on how the ground is moving below and in front of the wall - this will be found out through analysis of the monitoring data while we work on the design.

The site workers would also need to spend more time at the bottom of the damaged wall presenting health and safety risks. More work needs to be done and advice taken from specialist engineers to find out if this option would work.

Both of these repair options are suitable to fix the fault if it is not far below the surface of the ground under the wall. However, if continuing monitoring suggests that the problem is deeper underground, further design options will need to be considered.

Unfortunately the area of failure of the road includes both lanes and if a catastrophic failure occurred it would affect the whole road.

We need to make sure that all roads are inspected and safety standards are met so it is essential that the maintenance of local roads continues.

 

 

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