PRINCIPAL INSPECTION REPORT
ASHTED TUNNEL, BIRMINGHAM & FAZELEY CANAL (DIGBETH BRANCH)
FUNCTIONAL LOCATION:WZ-001-019
INSPECTION DATE: 16thNovember 2011
SAP EXECUTIVE SUMMARY
WZ-001-019 – Ashted Tunnel – Dimensions: Width 3.8m, Min. Headroom: 2.4m, Length: 102m. Type: Small, one-way working tunnel with single towpath. Brick lined with brick portals.
Condition: Reasonable. The lining is largely intact but affected by structurally insignificant open and displaced construction joints, perished brickwork and recessed mortar joints. There are repointing repairs below water level. Vegetation growth on both portals. Poor handrail to towpath with rotten and loose sections.
LI/AI: Check handrail for further damage.
Recommendations: Repair or replace handrail in short to medium term. Remove vegetation from portals in medium term.
ASSESSMENT
Name:Ashted Tunnel
Functional Location:WZ-001-019
Inventory number:WZ-00057
National Grid Reference:408014 287536 – Centre of tunnel
407986 287578 – North portal
408041 287495 – South portal
Location:Nechells Green, Birmingham
Length of tunnel:102m
Minimum width (inc. towpath):3.8m(min. channel width approx. 2.3m)
Minimum headroom:2.4m
(above normal water level)
Maximum cover:4m
(intrados crown to ground level)
Design of tunnel:S1 (Single one towpath)
Main construction material:BRK (Brick)
Condition Grade:C
Serviceability Grade:1
Consequence of Failure:2
Next PI due:5 years (2016/17)
SUMMARY OF RECOMMENDATIONS & ESTIMATED COSTS
Short Term (<1 yr):None.
Medium Term (1-5 yrs):Repair or replace the rotten wooden handrail.
Remove vegetation from Portals.
Long Term (5-10 yrs):General pointing repairs - maintenance.
INTRODUCTION
The original detailed survey of the tunnel was undertaken by the former Mining Section in March 1984 (above and below normal water level). This original survey is used as a benchmark for subsequent inspections and the detailed tunnel sheets are updated following each inspection.
This Principal Inspection was undertaken from a workboat by Chris Reynard and Jon Muir – Tunnels & Confined Spaces Team, Leeds on 16th November 2011.
The tunnel was classed as a low risk confined space for the inspection due to the nature of the tactile tunnel inspection.
A walk over the surface above the tunnel was undertaken to check for any changes.
The weather on the day of inspection was dry with cool temperature.
The previous Principal Inspection was undertaken on 18th October 2006.
The tunnel is inspected on a standard five year principal inspection interval as recommended by the Tunnels & Confined Spaces team.
A below water level inspection was undertaken on7th January 2009. The maximum water depth was recorded as 430mm (reduced water level achieved by drawing down the pound between the locks – water level reduced by approximately 1.55m) and there was no significant silt deposits on the invert. A good view of the invert was obtained through clear water, the lower side walls being largely exposed.
GENERAL DESCRIPTION
Ashted Tunnel is a small size tunnel with a single towpath and operates on a one way traffic system using line of sight procedure. There is a lock at the north end of the tunnel which restricts visibility of on-coming traffic.
The tunnel isarch shaped with bricklining founded onbrick footings to the side walls and dished brick invert. The tunnel portals are also constructed in brickwork.
There are no open air shafts in the tunnel.
The tunnel was constructed at some time between 1783 and 1790 with John Smeaton as the engineer for the canal. There has been no detailed historical search of information relating to the tunnel.
The tunnel is 102m in length and approx. 3.8m wide at normal water level including the towpath (towpath varies in width between 1.24m – 1.50m). There is between 1.1 – 1.5m water depth below normal water level and 2.48 – 2.77m headroom above normal water level.
There is one former shaft at ch.28m from the south end (probably an old loading shaft from former factories above tunnel). Probing has revealed that the shaft is almost certainly fully backfilled with no evidence of stagings or a cap (from ground investigation for surface development in 1988).
The tunnel was constructed by cut and cover techniques between the South Portal and at least ch.37m from the South Portal.
Fill material extends down to at least shoulder level of the tunnel.
The depth of cover over the tunnel is shallow with approx. 4m depth of maximum cover.
The tunnel is located in an urban area in Birmingham and the B4114 (Jennens Road) dual carriageway crosses over the tunnel.
The tunnel previously carried a road crossing (Ashted Row) and was also assessed as a road bridge up to 1973 when a relieving bridge was constructed. The new dual carriageway road crossing was constructed in 1991 and is not carried by the tunnel lining; it is independently supported on a concrete raft with bored piles.
There is good access to both ends of the tunnel.
The geology surrounding the tunnel briefly consists of Bromsgrove Sandstone overlain by superficial glacial deposits consisting mainly of sands and gravels.
There was a site investigation of the tunnel in 1973 and a ground investigation in 1988 for a proposed surface development.
In 1984/85 extensive repairs were undertaken with re-pointingof the mortar joints below water level and occasional brick patch repairs below water level. Also at this time the towpath was raised and surfacedin concrete.
The South Portal has been rebuilt but the date of construction is unknown.
The canal tunnel is orientated in a general north to south direction with the towpath on the east side.
There are new tunnel information and safety signs at both portals.
OBSERVATIONS
TUNNEL (above normal water level)
The tunnel remains in reasonable condition and thebrickwork lining is largely intact with no significant deterioration noted since the last P.I.
The tunnel was generally dry on the day of inspection however there are some minor areas of slight dry calcite deposits on the tunnel lining indicating previous water seepage.
There is a series of open and slightly steppedcircumferential construction joints at both ends of the tunnel (between ch.0m – 20m & ch.85m – 102m approx.). The bricks are occasionally perished along the construction joint edges. There are also some areas of open mortar joints surrounding the open construction joints but the brickwork remains tight.
The shape of the tunnel arch remains good with occasional as built slight misalignment and bulges. There are some occasional boat rubbing marks on the offside shoulder but generally the profile is adequate for narrow boat passage.
The internal dimensions were measured at three locations on the last P.I. as follows:-
Ch.12m – Tunnel 3.83m wide at water level including 1.24m wide towpath.
Tunnel 2.48m high from water level to crown.
Ch.50m - Tunnel 3.85m wide at water level including 1.50m wide towpath.
Tunnel 2.71m high from water level to crown.
Ch.97m – Tunnel 3.83m wide at water level including 1.30m wide towpath.
Tunnel 2.77m high from water level to crown.
The profile splays outwards slightly at the north end beyond ch.99m.
In addition the height from water level to crown of tunnel was measured at 2.61m at ch.45m.
The South Portal (ch.0m) has been re-built at some time and the rebuilding works extend to ch.4m inside the tunnel. The new blue engineering brick lining is all intact and well mortared.
The original brick lining in the remainder of the tunnel is also generally intact with occasional open pocket holes in the lower side walls (some holes filled with loose bricks) and occasional slightly perished bricks.
There are areas of recessed mortar joints throughout the tunnel.
There is a hairline circumferential crack around the arch ring brickwork at the north end (ch.101m in the crown). This is a long standing defect and there is no further deterioration or movement.
TUNNEL (below normal water level) – Inspected 7/01/09
The lining remains largely intact and in reasonable to good condition with only occasional slightly perished brickwork. The repointing repairs remain intact and there are occasional brick patch repairs on the offside and extensive brickwork repairs to the lower wall on the towpath side. The repairs on the towpath side appear to be placed to protect the original timber foundation which is exposed between ch.33 – 37.5m and is slightly rotten resulting in some slight undercutting of the towpath wall.
There is a short brickwork repair to the invert between ch.81.4 – 82.5m with some concrete chamfering to both sides of the repair.
The water level was reduced in the tunnel by approximately 1.55m leaving a reduced water depth of 430mm at ch.15m and 230mm at ch.42m, i.e. the invert is not level, some of the invert was exposed towards north end of tunnel (i.e. upstream).
Some missing front skin brickwork was noted to the approach walls ate both ends of the tunnel (offside wall at south end and immediately below rotten timber curbing on towpath side at north end).
SHAFT
The brick ring to the shaft (probable former loading shaft) at ch.28m sits slightly proud of the tunnel lining (as built) but the brickwork seal is all intact and tight. There are some dry calcite deposits covering the brick ring to the shaft indicating previous water seepage either through the shaft fill material or around the old shaft lining. The surface area above the shaft is derelict land with no public access.
TOWPATH
The towpath was repaired in 1984 at the same time as the below water level repointing repairs. The towpath is surfaced in concrete which level and in good condition.
The old wooden handrail to the towpath is in poor condition and is low; measured at 0.75m from towpath level to top of top rail.
The bottom rail to the handrail is missing at both ends of the tunnel and the top rail is rotten in parts and split at one point. The wooden stanchions are rotten around the bases and are loose at numerous points. The handrail is also generally bowed outwards (into the canal channel).
There are a series of strip lights down the centre of the crown throughout the tunnel which provide good illumination of the towpath and tunnel in general. These lights are maintained by Birmingham City Council but two lights were not working on the day of inspection.
PORTALS
The South Portal is a new brick portal but the date of construction is unknown.
The portal is intact, well mortared and in good condition and comprises English bond brickwork with a four skin arch ring to the tunnel (with a rounded inner skin), concrete coping course to the top of the wall, corbelled string course (three courses deep) above the arch ring and pilasters to both ends of the wall, the portal wall is also battered below string course level on either side of the tunnel.
There is some general vegetation/tree growth above the portal with a small tree growing above the centre of the wall.
The retaining wall to the side of the portal wall on the towpath side was previously noted as in poor condition and unstable on the last Principal Inspection this has now been supported with scaffolding and is fenced off. The supportworks were undertaken by Birmingham City Council who is responsible for this retaining wall.
The North Portal is constructed in brickwork and is situated immediately downstream of Ashted Lock. The portal is in reasonable condition with isolated perished bricks and areas of recessed mortar joints in the upper wall with vegetation growth through the wall. There is a one and a half brick thick arch ring to the tunnel (with rounded inner edge) and a parapet wall with rounded brick coping course to the top of the wall. There is some general perished brickwork to the rear of the parapet which also contains minor vertical cracks at both ends.
There is an existing displacement crack between the portal wall and the retaining wall constructed at a right angle to the portal on the towpath side. This crack is filled with an old rubber/bitumen type expansion filler and shows no signs of further movement.
The retaining wall continues round the edge of the towpath around the bottom gate of Ashted Lock. There are some vertical cracks in the retaining wall but these do not appear to have deteriorated significantly since the last P.I. and the wall is in reasonable condition.
TUNNEL SAFETY FEATURES & SIGNS
There are new Tunnel Information and Safety signs at both portals.The information sign states the tunnel is 94m in length and is actually 102m in length. The signs also have some slight graffiti damage.
There is good access to both ends of the tunnel.
SURFACE
The surface remains unchanged since the last Principal Inspection with no surface development.
It was noted that the rough ground above the south end of the tunnel had been used as a lorry park in the past but this activity has now ceased and the ground is fenced off and has become slightly overgrown with vegetation.
DISCUSSION
The tunnel remains in reasonable condition with no significant deterioration since the last P.I. but the old wooden handrail to the towpath is in poor condition.
It is recommended that the handrail is repaired or replaced in the medium to short term. If the handrail is replaced then the new rail should be made 1.1m high to comply with current tunnel safety standards.
The reason for the construction of a new portal wall at the south end is not known but there used to be a large retaining wall to an old industrial bakery building above the portal.
The North Portal remains largely unchanged from the last Principal Inspection and still requires vegetation clearance.
The retaining wall to the towpath side of the North Portal contains some vertical movement cracks but these do not appear to have deteriorated significantly since the last P.I.
The are some slightly stepped and open construction joints at both ends of the tunnel (between ch.0m – 20m & ch.85m – 102m approx.) with some areas of recessed mortar joints around the construction joints. These defects are the result of old movement and weathering and display no significant deterioration since the last P.I.
RECOMMENDATIONS
Recommend vegetation clearance from the North Portal in the medium term to prevent damage to the wall.
Recommend vegetation clearance/tree removal from above the South Portal in the medium term to prevent long term damage to the wall.
Review of existing notifications:-
10400924 – ‘P4 RM WZ 001 Repoint North Portal’
Recommend long term pointing repairs to the North Portal.
This remains a low priority long term maintenance issue and the vegetation growing through the wall should also be removed.
10400926 – ‘P4 RM WZ 001Repoint open joints’
Recommend long term pointing repairs to the tunnel lining, in particular to the open circumferential joints near both ends of the tunnel.
This is a long term maintenance issue but as there has been no significant deterioration to the joints it remains a low priority at present.
10400928 – ‘P1 ENG Ownership of wall north portal’
Recommend monitoring vertical movement cracks in retaining wall on towpath side of North Portal if wall is BW responsibility. Furthermovement can be quantified by installing demec points across the cracksand undertaking regular measurement as part of the tunnel inspection.
01.11.2006 Mike Crick (MCRICK) - Retaining wall is adjacent to recent development. (which was not presentat time of construction of the tunnel). It is unclear if the land hasbeen raised and the wall is now to the benefit of the land supported. BW
boundary is the wall. Ownership and liability for the wall needs to be checked
01.06.2011 Ryan Jones (RYJONES) - Waterway Engineer to check condition of wall and more than likely the ownership will be under BW since it was constructed when the tunnel was constructed. Notification will be updated once site visit has been undertaken.
There has been no further visible deterioration to the cracks and the condition of the retaining wall does not give cause for concern.
10401648 – ‘P2 RM WZ 001 Replace handrail’
Recommend replacement of the low wooden handrail in the short term with new post and rail handrail to 1.1m height above the towpath surfacelevel. This is a health and safety related recommendation to comply withBW Tunnel Safety Standards.
27.10.2009 - Remove loose brickwork and re-build area under handrail. Remove handrail and replace with H&S/Heritage approved handrail along the full length ofthe tunnel.
The wooden handrail is in poor condition with numerous rotten stanchions and occasional rotten and loose rails. Repairs are still recommended in the short to medium term. However the height of the current handrail is not of concern and repairs can be undertaken to the existing handrail. If the handrail is completely replaced then the newly constructed handrail should comply with the 1.1m standard.