The A82 Project. Alex Macleod A82 Project Officer. Forestry Commission Scotland Head Office

Transcription

1 The A82 Project Alex Macleod A82 Project Officer Forestry Commission Scotland Head Office Tel: Office: Mobile: Oct 2015

2 Presentation Contents Outline of the A82 Project Timber harvesting and slope stability operations at Glen Righ & Loch Lochy near Fort William Safety, landslide & rockfall incidents that affected the A82 during the past two years Management of steep slopes on the National Forest Estate (NFE) into the future by Forestry Commission Scotland (FCS) 2

3 A82 Project Strategic Context Above : Map of Scotland Right: The A82 corridor and Project Area through the Great Glens 3

4 The scope of the A82 Project Left: Tintern, Monmouthshire May 2007 DF tree blocking A466 alongside River Wye after it became detached during a steep ground harvesting operation Above: Mature 1920 s forest on steep slopes above the A82 Loch Ness A82 is main link through West Highlands Trees at increasing risk of being blown down during storm events Safe, sustainable & cost effective harvesting 4

5 Project Challenges Extreme harvesting Slope stability Adequate resources Infrastructure Traffic management Effective Communications Above: A82 trunk road at Glen Righ South of Fort William Right: Large trees on steep slopes above A82 at Glen Righ 5

6 A82 Skyline Harvesting Above: High spec skyline needed 7 year LTC offered Awarded to Duffy Skylining in Mar 2013 Built by A&B Services of Killin Base unit 35 tonne Volvo 7 tonne mainline pull Can extract up to 1000m Glen Righ experiences have led to skyline upgrade for Loch Ness Duffy skyline team working in Clunes Forest near Spean Bridge 6

7 Glen Righ - Background Geotechnical issues found pre-harvesting High risk to A82 Urgent need to remove a particular crag Extensive slope stability works and tree felling to date Left: Above: Unstable rock crag (RC4) above A82 trunk road at Glen Righ Chainsaw operator next to large Sitka Spruce above A82 trunk road at Glen Righ 7

8 Glen Righ RC4 Removal Left: View from directly below (RC4) down onto the A82 Right: View from directly above RC4 after it s safe removal 8

9 Glen Righ Geotechnical Clockwise from Left: Installation of mesh & bolt rock crag support, rock bolting ops below temporary catch fence and permanent 500KJ catch fence above A82 Principal contractor Georope Coffey & Mott MacDonald design Use of catch fences & drones Incidental tree felling & removal FCS developing knowledge & skills 9

10 Slip/Trip Incident Glen Righ Only reportable incident during over man hours of geotechnical work Essentially a slip/trip fall resulting in fracture to wrist Loose rock handhold a contributory factor Casualty evacuation procedure worked well Pre-constructed access path proved invaluable Keeping a Rescue Kit on site RAMS modified to highlight not using unstable rock as hand holds Above: Crag above location where geotechnical operator slipped May

11 Predominantly skyline harvesting High risk of debris being dislodged Red to Red traffic management Tree removal can trigger instability Forestry ops must take account of geotechnical concerns Innovation Glen Righ Harvesting Clockwise from above Right: Mechanised harvesting at Glen Righ, cross cutting large stem on steep slope and extraction of young Spruce 11

12 Use of bottle jacks in felling & taking down large trees on steep slopes Use of catch fences to support harvesting TM Red to Red times Explored use of helicopter extraction, fast felling & road shelters Harvesting Innovations Above: Left: Felling large trees at Glen Righ Take down of large Spruce tree using a tree jack 12

13 Trees contribute to instability Risk of damaging Geotechnical infrastructure & built assets Practical approach required Collaboration, flexibility & support needed Glen Righ Integrated Ops Above: Helicopter lifting catch fence posts into place at Glen Righ Left: Felled trees awaiting extraction above A82 at Glen Righ, 13

14 Glen Righ Key Success Factors FCS taking a proactive approach Collaborative working with Transport Scotland & others Effective communications Flexibility around road space Project management approach Lessons learned exercise Right: Traffic management deployed in support of forestry ops on A82 at Glen Righ 14

15 A82 closed by flooding and washout incidents Incidents across NW Scotland FCS led on the clear up Many issues through Glen Righ forest FCS received some criticism Glen Righ Landslides Left: Excavators clearing debris from a masonry bridge 50m upsteam from A82 at Glen Righ Above: Felled trees (awaiting extraction) and debris washed out onto the A82 at Glen Righ 15

16 Glen Righ Landslides Landslides on open hill above forest Very high levels of water and debris Culvert and bridge failures Forest slowed down the debris flows. Some learning points for FCS Above: Shallow landslide scar on open hill above Glen Righ Forest Left: Forest road bridge blocked by debris in Glen Righ Forest 16

17 Loch Lochy Extensively windblown Persistent problems with trees on A82 Unlike Glen Righ no crags & boulder fields Water management very important as area prone to landslide & washouts Clockwise from above Right: Windblown Cedar at Loch Lochy, windblown spruce at Loch Lochy and MEWP clearing windblown stems overhanging the A82 17

18 Skyline extraction High risk of debris reaching road & Red to Red TM required Minimal working area on forest road Secondary extraction of timber and all lop & top (including stumps) required Recent accident on the site Loch Lochy Harvesting Clockwise from above Right: Winch assisted tree takedown, skyline on forest road and forwarder secondary extraction of lop & top 18

19 Some root-plates fully detached Aim to reduce weight Removal of soil/debris Reduction of root buttresses Winch extraction to roadside Operation requires specific RAMS Loch Lochy Rootplate removal Clockwise from above Right: Rootplate breakdown & removal in stages 19

20 Loch Ness Rockfall Dislodged boulder led to 4 day road closure. FCS was aware of geotechnical issues in the wider area Decision taken to close road once vehicles cleared. Above: FCS and Police teams at the site of the rockfall north of Alt Sigh on the A82 Right: Uprooted Oak tree which dislodged the 4-5 tonne boulder 20

21 Loch Ness Rockfall TRACK (+290m Above Ordinance Datum) CRAG UPROOTED OAK TREE (+150m AOD) Large (3m) boulders requiring support / removal Rockfall CRAG Temp fence approx. 3m high and 30m long, approx. +60m AOD A82 (+30m AOD) Loch Ness 21

22 Loch Ness Rockfall Rocks broken up in situ Helicopter used in operation Mesh hammock constructed Hammock anchored to trees Temporary catch fence Left to Right: Geotechnical team fragmenting unstable rock, constructing mesh hammock and helicoptering materials to site 22

23 Loch Ness Rockfall Need for long term solution Anchored concrete beam preferred Constructed summer 2015 Helicopter used Future inspections required Left: Completed anchored concrete beam above Alt Sigh at Loch Ness Above: Scaffold platform & heli drop point above Alt Sigh at Loch Ness 23

24 Future Operations Loch Ness Harvesting moves to Loch Ness in Autumn 2016 Deployment of upgraded skyline Geotechnical concerns Forest road upgrade carried out Lengthy OHP outage required 3 year program of ops Left: Large DF trees below crags above Loch Ness Above: 500KJ catch fence being installed above Loch Ness 24

25 Principles of Long Term Management Below: A section of newly harvesting slope above the A82 Erosion and instability on steep sites is a natural process Low intensity management probably more conducive to slope stability Manipulation of natural processes likely to be more successful & cost effective than technological fixes Each site has its own characteristics and will require an individual solution with regard to its future management 25

26 The Problem Left: Typical conifer stand on a steep slope Right: Trees susceptible to windblow lead to a reduction in slope strength & stability 26

27 Tree Removal Left: Clearfell & complete canopy removal potential short term increase in instability Right: The post harvesting effects on net rooting strength 27

28 Stability - rooting Restocking Root systems of tree species: flat root heart root tap root Left: Tree root properties a mix of flat, heart and tap rooting systems will enhance slope stability several main horizontal roots plus smaller vertical tap roots SS, NS, ASP, AR, BI, PO 1-2 vertical main roots plus several main roots reaching laterally down JL, EL, BE, DF, HBM, AH, RC, EM, LI, SY, NOM 1 vertical main root plus several short lateral roots SF, SP, OK, CP, LP Right: Replanting at a high density & with high diversity of species 28

29 Passive Management Left: Mixed root development as tree cover returns Right: Protection Forest - Ecotechnological engineering solution as apposed to geotechnical engineering, but could require a combination of both 29

30 Conclusion The A82 project represents a practical approach to tackling timber harvesting & slope stability issues within the Great Glen FCS is gaining experience and developing systems and processes to proactively manage steep ground and potentially unstable slopes into the future 30

31 Moran Taing (Thank You) Website Twitter pages 31