Flaws in Salwa road pavement construction

Web posted at: 2/6/2007 3:46:28
Source ::: The Peninsula

Doha •

The Qatar General OrganiSation for Standards and Metrology (QGOSM) has said that there was clear evidence of a structural failure in the construction of the pavements of Salwa International Highway.

Attending a joint meeting of concerned officials, convened by the Public Works Authority (Ashghal) to look into the massive cracks developed on Salwa International High way, the QGOSM nominees said that there was very clear evidence of extensive fatigue cracking. At the meeting they expressed their serious concern about the use of the Type 5 pavements utilising a specific crack-arrest- layer (GSB).

Top Ashghal officials, who attended the meeting, wanted the Parson International Ltd (PIL), the company responsible for the design work for phase 1 of Salwa International Highway, to clarify the details of the joint interface between Type 5 pavement and the full depth construction type 1 pavement. They also asked the company why a full-depth construction had not been adopted in accordance with Qatar Highway Design Manual (QHDM).

The PIL clarified that the pavement design was done according to the findings of a report prepared on behalf of Roads Department of Government of Qatar.

Henry Saville, currently Parsons Sector manager for Roads and Highways in Europe, said that though the PIL did not agree with the contents of the report, they had been required to base their design on the contents of the ERI report which stated that the structure of the existing road pavement was adequate for the traffic loading foreseen.

Saville, who said that he was responsible for the design works of the highway, added that the design thickness of the required granular sub base layer was increased by 20 per cent in order to accommodate any increase in traffic as well as to allow for then likelihood of overloaded trucks and tyre pressures in excess as anticipated by ERI report.

Responding to a query from Ashghal authorities, the PIL confirmed that a `crack arresting layer' was not included in the pavement type in the Qatar Highway Design Manual (QHDM). It said that a granular subbase crack arresting layer, which was used in Salwa Road project, had been used in road pavement rehabilitation in at least three other nations including Vietnam, Greece and Romania and it was performing satisfactorily in these countries.

The PIL pointed out that sections of the new road, where the Type 5 pavement had been constructed on Salwa Road, had been under traffic pressure for many months. But no pavement distress was recorded. The pavement developed cracks only after the heavy and incessant rains in the beginning of December 2006. “A series of tests had been carried out on materials taken from the failed areas, as well as on samples taken from other areas of type 5 pavements. The test results indicated that the materials used had fully complied with the specific standards", the PIL said.

PIL pointed out that in one or two of the areas where failures had occurred, some of the asphalt surfacing had not been laid in accordance with the specification and Non-Conformance Reports (NCR's) had been issued to the contractor.

The volume of traffic had increased over twenty per cent allowed for in the original design. It also suggested Ashghal to carry out a Benkelman Beam test (BBT).

However, Ashghal nominees in the committee pointed out that although the first failures were experienced on sections where only the 60mm asphalt base-course had been laid, there were now almost as many failures on sections of road where wearing course had also been laid. There were a number of pavement failures on sections where the road was constructed on high fill, they said.

Responding to a point that there is a clear evidence of structural failure on the crack arresting layer of the pavement, PIL replied:" The trial pit investigations carried out and the associated test results on the GSB layer had produced no evidence of structural failure to the crack arresting layer.