The Chekka tunnels of Northern Lebanon highwaySamuel 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▫ In dispersed with limestone rocks, phosphate nodules and organic
material▫ Formation thickness ranges between 100-500m, with bed thicknesses
of about 20-50cm
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
Geological Setting
TunnelExit / Entrance Structures
Highly Eroded Zone 27o
Slumping / Failure
23o
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
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
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
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