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