The “CONTRACT AREA 108” project
(Terra Rossa problem)
This document is dedicated to the foreign workers
in construction sites all over the world because they are
the essential stream which transfers and distributes
knowledge through countries.
A Google-earth snapshot showing the in brief the contract sites that Company XEKTE
SA , was constructing in 1980’s in Benghazi, Libya .
The Contractor Company XECTE SA (Benghazi branch) was considered to be a middle
sized contractor in Benghazi during the decade 1980-1990. At that time, the 2nd
Ring Road of
Benghazi, the “Shari Al Andalus” highway, some drainage networks around the city, and the
development of Urban Area 108A, were some of the projects that this company was constructing.
As a Contractor this Company had about one hundred workers, all foreigners, most of them
from Philippines, some from Pakistan and India, a few from Palestine, Syria, Egypt and other
countries as well. The leading personnel, Engineer Manager, Supervising Engineers, Surveyors,
Foremen, Operators of construction machines etc were all from Greece.
The Company operated a concrete pre-casting unit manufacturing cement tiles for
sidewalks, kerbs and concrete drainage pipes, one asphalt drum mix plant and a warehouse
providing maintenance for the fleet of heavy construction machines (excavators, trucks, graders etc)
that was in full operation. A mine for aggregates was occasionally operated in “El Abiar” providing
materials for the road construction.
The above mentioned projects, that were running that time, were also the main operational
concern of the Engineer Manager but as a Contractor the company was a provider of general
technical services to the Municipality of Benghazi such as repairs of public roads and substructures.
The general outline of the main projects was:
1. The 2nd
Ring Road of Benghazi project was a 5.5km road connecting Algeria street which
is close to harbor with “Assudan” Street in the area of “Northen Fwayhat”. The 2nd
Road was a two-way traffic, 12,0m / 15,0m wide with two lanes on each side. Six major
junctions, planting, drainage, traffic signs and street lighting were the complete design and
construction scheme of the contract.
2. The “Shari Al Andalus” project was the 3.4km city's section of a 9.9km highway leading
from the center of the city to the south suburbs.
3. The development of Urban Area 108A (contract 108A) concerned a complete and ready to
use network of local roads and consisted of the construction of Public Utilities such as water
supply network and house connections, sanitary sewerage (foul and gray waters) networks,
storm (surface) water drainage networks (manholes, inlets/gullies and drainage pipes), kerbs
and sidewalks, street lighting, base and sub base aggregate courses and two layers of asphalt
pavements. This contract imposed very strict specifications for road construction. Due to the
flat landscape, the design of the roads required a small gradient of no more than 0,1%
longitudinal slopes in favor of a sufficient drainage network. The accepted difference in
elevations between design and construction should have been less than 1,5 millimeters / km.
The outflows from sewers and storm water pipes were conveyed to the pumping stations.
Specifications that were applied to the works were for example AASHO T99-700, AASHO
T193-63, AASHO T 27-70 and BS 1377, BS 1881, BS 812 etc.
All the above projects were constructed under the same main articles of works as they
approved by the Municipality. However the applied specifications were causing technical or
compatibility problems having impact to the cost of works. For example the use of sulfur resisting
cement for the concrete sewers appurtenant structures and the gutters-kerbs as well, as the
specifications predicted instead of Pozzolanic cement, was a failure since this concrete was cracking
at the following the construction stages. Another example is the design of box culverts in some
locations were the circular shape was more appropriate. Further more the handling of dust on the
road’s surface during desert winds was a seasonal problem related to maintenance procedures.
During the time that I was assigned as a Deputy Engineer to the project of Urban Area 108A
(contract 108A), a problem appeared and was initially considered relative to the false compaction of
the backfills of the sanitary sewer trenches. The deformation (settlement) of sub grade surface in
roads, where sanitary sewers existed, was a sign that the upcoming works of base and sub base
aggregate courses would be affected as well.
The Office of Resident Engineers (Ove Arup & Partners) stated that «this was a construction
of sewers error since the specification defined that backfills should be compacted to (at least) 95%
of standard Proctor Test». If the compaction rate of 95% of Proctors Test was achieved then
settlement of backfill would be zero.
On this statement, the Contractors argument was that it was a problem of the approved
backfill material. In this case «approved material» was the originally excavated material for which
initially the Contractor had claims rejecting it as unsuitable.
The following investigation lead to these conclusions: The existing material was a type of
clay known as «Terra Rossa» in the Mediterranean area, which is a stiff when dry and very reddish
soil, its color due to iron oxides originating from weathering of initial rock formations. This Terra
Rossa has a part of Montmorillonite (mineral) crystals, a rather long and flat molecule forming
cornflake-like particles, which expands when it absorbs water. So when the laboratory executed the
Standard Proctor Test under different moisture contents it was unavoidable that the volume of
compacted material would be inflated. On site this meant to be the problem. When the compacted
material dried under the extreme heat of Africa, the volume shrunk and the backfill settled.
A new statement coming from the RE's led to additional and extensive investigation. They
stated that «if the California Bearing Ratio (CBR) value of material for fill was according to
specifications (ie over 10%) then the problem would be avoided». Since this test measures the load-
bearing capacity of soils used for building roads, the Contractor (XEKTE SA) suggested that the
evaluation of the results should be contacted on site. A program of site tests was agreed with RE's so
that from the results to decide if CBR value was the necessary and efficient parameter to approve
the material. This program included
· Excavating the trenches again to a suitable depth,
· Backfilling with the excavated material in layers of 10cm,
· Compacting to 95% of Proctor Value,
· Measuring the levels on a predefined grid and
· Flooding the trenches with water and wait to dry
· When the trenches dried the surveyor should again measure the levels and
· Finally the laboratory should test the CBR value on site.
Depending on the results the RE would decide if the settlement of the backfills was a matter
of compaction or suitability of used material.
This was the procedure which finally led to the total rejection of the excavated material as
unsuitable for backfilling. After all these years of Engineering experience, today I can state that a
necessary test to determine the acceptable clay-like materials is based on the amount of Methylene
blue dye absorbed by the sample. If a soil fails this test then it should be rejected from use in
(1) Excavating the trenches
again to a suitable depth,
(2) Backfilling with the
excavated material in layers of
(3a) Compacting to 95% of
Proctor Value (around
(3b) Compacting to 95% of Proctor Value (over
I recall with admiration an employee from
Syria, hard working under the summer sun and
heat, hours and hours compacting, the backfill
material. The result was always a well
compacted layer stiff as a stone.
(3c) Compacting to 95% of Proctor Value (Field
(3d) Compacting to 95% of Proctor Value (Field laboratory tests)
(5a) Flooding the trenches with water and
wait to dry
(5b) Flooding the trenches with water and
wait to dry (monitoring the drying procedure)
(5c) Flooding the trenches with water and wait to dry
(monitoring the drying procedure)
Paving asphalt wearing course on the “Shari Al Andalus” highway