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In 1999, The Republic of Lebanon embarked upon a comprehensive programme of rehabilitation of the country's road network - the Lebanon National Roads Project - with the funding assistance of the IBRD (World Bank).
One of the first packages of consultancy work was awarded to a joint venture of Lebanese and American consulting engineers, and Andrew Sadleir was commissioned as structures engineer by the U.S. JV partner, Wilbur Smith Associates, Inc.
Based in the Beirut offices of Spectrum Engineering Consultants s.a.r.l., Sadleir led and coordinated work with Spectrum's engineers to inspect and appraise existing structures, and to design for future requirements for a total of 78km of highway.
While the capital Beirut had seen, in the 7 years following the end of Lebanon's civil war, an almost unprecedented campaign of reconsruction, much less attention had hitherto been focussed on redevelopment in the Beka'a Valley, where the several sections of the project roads were located.
Existing structure configurations were found to be generally straightforward; but their extent and number - retaining walls in particular - required the development of a highly-systematic approach, employing standardised solutions wherever practical, in order to produce finished construction contract documentation within the very tight project deadlines and design cost constraints.
Sadleir's remit also included the preparation of a comprehensive structures report and detailed Contract Specification. The aims of the rehabilitation programme included conformity with modern, internationally recognised design and construction norms - the (US) AASHTO specifications being adopted for this project (Lebanon was then in the process of developing its own system of technical norms for highways engineering).
An under-capacity bridge on a main route (Pri062) - to be improved in situ.
This bridge was already carrying heavy truck traffic, which was forecast to increase substantially in volume. By reason of its severe (67°) skew, and consequent long effective span, it had neither strength nor stiffness adequate to the task.
A new sub-structure was designed, enabling the bridge to be strengthened in situ to sustain AASHTO standard design loads, with minimal disruption to traffic. The revised highway profile was to be accommodated by jacking the deck onto modified supports, while the full freeboard of the watercourse channel below was preserved.
Provision was also made for testing and verification of the existing structure's condition, and protective coating works for enhanced durability.
Progressive degradation of the retained fill material has destabilised this wall, necessitating urgent, and unattractive, remedial measures.
Many of the existing “retaining walls” were, in reality, little more than limestone facings to marginally stable slopes. This kind of gravity structure, while relativel inexpensive and aesthetically unobtrusive, is very limited in capacity.
In this (typical) instance, a crude concrete revetment has already been applied over a section of wall, in an attempt to stabilise it. Adjacent, exposed masonry is also now exhibiting signs of failure.
Rehabilitation, in such cases, requires the introduction of a permanent structural solution, i.e. a new wall.
This limestone masonry viaduct illustrates the limits of vernacular construction techniques. Note the isolated projecting blocks - early indicators of local instability.
A more ambitious use of the traditional ‘retaining wall’ construction technique is this viaduct in the northern Beka'a. As would be expected, the topmost masonry courses would be the least stable, and this difficulty has been circumvented by means of an unsightly concrete capping.
An additional complication is posed by the requirement to enlarge the section of the under-sized culvert (visible on the right of the picture).
At this location, highway re-alignment necessitated an asymmetrical widening of the viaduct; and the proposed solution makes use of in situ drilled and ducted tie cables, providing restraint balanced between a new wall to one side and the reinforced existing wall on the other. As with many other sites in this project, alternative routes are not readily available, and solutions must be so devised as to minimise road closures.
Although structurally sound, some cosmetic work is necessary here, to restore superficial war damage, evident here in the portal voussoirs.
Wherever possible, existing sound structures were retained, and such considerations informed adjustments of the highways alignments.
In all cases, rapid preliminary appraisals were required; these being supplemented by specification for more rigorous investigations prior to finalisation of construction plans.