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The Chekka tunnels of Northern Lebanon highway

The Chekka tunnels of Northern Lebanon highway. Samuel King Greg Bullen. Geological Setting. Rock Type Senonian limestone (Chekka Marl) Chalky Marl Limestone formation Marl Beds with bands of Chert in the upper layers

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The Chekka tunnels of Northern Lebanon highway

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  1. The Chekka tunnels of Northern Lebanon highway Samuel King Greg Bullen

  2. Geological Setting • Rock Type • Senonian limestone (Chekka Marl) • Chalky Marl Limestone formation • Marl Beds with bands of Chert in the upper layers • In dispersed with limestone rocks, phosphate nodules and organic material • Formation thickness ranges between 100-500m, with bed thicknesses of about 20-50cm

  3. Geological Setting • Strength (weak) • Differential weathering between soft marl layers and hard chalky beds • Orientation • Marl Layers dip between 21o-28o towards the Northwest • Several joints identified and measured dipping at approx 80o • Surveys have indicated strata are susceptible to erosion with dips identified towards tunnel entrances • Condition • Area affected by tectonic activity in the Northern Lebanon region • Landslides and slumps are noticeable features in this area • Important aquiclude confining Miocene aquifer in the North of Lebanon • High degree of fracturing

  4. Geological Setting Highly Eroded Zone 27o Slumping / Failure 23o Tunnel Exit / Entrance Structures

  5. Issues • Critical section of the North Lebanon Highway • The tunnels were completed in the early 1970’s • No maintenance was carried out for 25 years after completion • Surface/storm water channels were blocked • Weaknesses developed within tunnel lining • Resulting erosion, slumping and slope instability

  6. Issues • Loading related damage • Lateral deformation • Major cracks appearing along tunnel lining • Incomplete backfilling caused differential loading • Poor drainage related damage • Additional loading • Steel corrosion • Carbonation of the concrete • Leading to durability problems

  7. Engineering Approaches • Rock Bolts/ Anchors with wire messing • Drainage control for stability • Stabilise with lime/concrete (shotcrete) • Trim overhanging blocks using prybars, jacks or explosives • Excavate - cutting benches • Support - buttresses, retaining walls, dowels • Catch - ditches, catchwalls

  8. Solutions Adopted • Remove slumped soil from structure • Installation of rock bolts /nails with a high strength steel wire mess • Repair of distressed structural elements by provision of passive rock bolts tying into the intact parent rock • Repair and sealing of cracks, spray 4mm thick waterproof membrane with fibre reinforced concrete • Control of surface water and drainage • Interceptor and drainage channels concrete lined feed sumps • New drainage channels designed to incorporate existing drainage structures • To stop water seeping into the rock around the tunnel perimeter drains were placed

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