DIRECT RAILWAY LINE DAMMAM - RIYADH

The need for an efficient transportation system in the Kingdom of Saudi Arabia was recognized at the beginning of the 1970's at which time the country's great economic growth gave way to a very large increase in transportation demand which constantly surpassed the supply, especially in the more important areas like the strip which extends approximately 450 km. between the Capital, Riyadh and Dammam, the main Saudi Arabian port on the Persian Gulf.  This led the Saudi Arabian Government to concentrate the nation's financial resources on the development of transportation systems which required short-term realization times, like the highway and airline systems, penalizing in this manner the development of the railway network.

It was only toward the mid 1970's that following a change in interest for the railway sector, the S.R.O. began to understand the need to give new energy to the sector through the process of reorganizing the existing infrastructural assets and through the construction of new railway lines.

Therefore, following the contract to carry out the executive project and supervise the works to overhaul the existing Dammam-Hofuf-Harad-Al Kharj-Riyadh railway, the S.R.O. also entrusted Technital with the task of conducting the feasibility study, the preliminary and final designs and supervision of the works for the new direct railway line between Dammam and Riyadh which would shorten travel time considerably with respect to the existing line through Harad and Al Kharj.

An in-depth and complete analysis of the transportation within the Dammam-Riyadh corridor was done, also by evaluating the convenience of starting a direct high speed (250 km/h) connection for passenger service. The study began with the preparation of a 1:250.000 scale map and identification of five possible alternatives.

Successively, based on the traffic data collected, and on-site inspections done along  the different alternative routes, two possible hypotheses for intervention were chosen for comparison in the economic analysis :

-  connection between Dammam and Riyadh through Hofuf (alternative no. 1)

-  a direct connection between Dammam and Riyadh  (alternative no. 2)

Based on the data collected, a graph of the transportation system associated with each alternative was developed. Through the same mathematical model, the demand for transportation within the system was then assigned, also by simulating the volume of freight and passenger traffic in the year 2000 based on various hypotheses of growth in transport demand.  Each alternative was subbsequently developed on the preliminary design level by defining the technical and operating standards of the new railway line and the related investment, operating, and maintenance costs.  Cost breakdowns were then elaborated and, through comparison with the opportune system of general reference, the benefits associated with each alternative and the relative economic indexes were defined.

Upon termination of the economic analysis and in agreement with the S.R.O., alternative no. 1 was chosen, envisaging a single-track line Dammam-Hofuf-Riyadh which, flanking the existing railway in the stretch between Dammam and Hofuf, in fact doubles it.

The final design which followed the feasibility study was divided into the following work phases :

-        aerophotogrametric survey of the terrain followed by a topographic survey for the identification,  staking and benchmarking of the photograms and subsequent mapping;

-        geophysical and geotechnical surveys on the nature and bearing capacity of the terrain and the availability of borrow pits for construction materials.  Particular attention was paid to defining  the  influence that the presence of quicksand and vast deposits of sulphate sand (sabkhah) could have on the infrastructure;

-        hydrological and hydraulic study;

-        preparation of the final design which included the definition of the horizontal and vertical lay-out of the structure, the permanent way and all of the other elements comprisaing the railway infrastructure;

-        preparation of the tender documents for the construction of the railway line.

The final alignment of the railway line originated from the necessity to guarantee the most direct connection possible between Dammam and Riyadh while taking into consideration the various constraints which could effect it.  Therefore, for the section between Dammam and Hofuf, the lay-out followed the existing railway line, whereas in the section between Hofuf and Riyadh the lay-out was conditioned by :

-     constraints  of a geomorphological nature related to crossing  the Dhana desert;

-     constraints deriving from the crossing of the areas where petroleum is extracted;

-     constraints deriving from the presence of military zones;

-     constraints linked to the necessity to run the route through the city limits of Riyadh.

The railroad was designed for a diesel-electric traction system with standard 1,435 mm. rail gauge, a project velocity of 150 km/h, and a maximum axial weight of 22 tons (locomotive) and 25 tons (wagons).  The horizontal curve radius was set at a standard measure (2500 and 5000 m.), when possible.The minimum radius in straight stretches is 2000 m. and 1750 m. in the sections between Hofuf and Riyadh and Dammam and Hofuf respectively.  The maximum gradient is 10 per 1,000 (non-conpensated).  The total length of the line is 449 km.

The location and number of stations along the line were defined to serve the major inhabited areas, as well as the areas of special interest, and to guarantee an adequate level of railway capacity in relationship to the amount of traffic expected.  Four intermediate stations were planned between Dammam and Hofuf and seven between Hofuf and Riyadh.

The permanent way was built with U/C 60 rails which were continuously welded between  stations.  The sleepers are of the monobloc p.r.c. type which were produced locally in two new plants built in Riyadh and Hofuf,  for which the installation and production tests were followed by Technital on behalf of the S.R.O.  The coupling devices are the indirect elastic type (Pandrol and Vossloh).  The switches are U/C 60 type with a 1/12 tangent  (on the railway line), 1/9 (at stations), and 1/7.5 (in freight yards).

The track formation has an overall width of 7.69 m. on embankments and 17.6 m. in trenches, in that two 5 m. lateral paths were planned to enable transit of maintenance vehicles and to protect the track from slopes.  A layer of a granular mixture of subballast was also foreseen in the composition of the superstructure.

Lastly, a special effort was required for the protection of the railway in crossing the areas of quicksand and sabkhah.

In the first case, sand slopes with a slight gradient (1:4) were utilized and were stabilized with a series of superimposed layers of compact granular mix (protective windrows).  In cuttings, ample, adequately shaped sections were planned in order to halt the advance of the dunes.  In the second case, protection of the sabkhah was obtained through the use of non-woven fabric and preloading of the embankments.  The aggression of the sulphate of the sabkhah on the concrete elements cements was controlled through the use of sulphate-resistant cements, of waterproof cements produced with a low water/cement ratio, and of superfluidizers to keep the mix in good working order, even in a hot climate.

The hydological survey led to dividing the territory crossed by the railway into three areas, each one characterized by its own rainfall pattern.  Therefore, the three distinct equations of climatic probability were elaborated first, even if the equation relative to the zone of the highest precipitation was later considered opportune for all three zones.  Based on the rainfall data collected from the Saudi Arabian Ministry for Agriculture, as well as specific site surveys, the maximum flow rates were calculated, on the basis of which  the hydraulic works were then dimensioned.

The structures foreseen in the project were located in the Hofuf-Riyadh section and include a total of  six bridges and two viaducts for an overall length of 2,150 m.  Considering the rather difficult environmental conditions and the difficulty in transporting heavy loads along the route, utilization of structures in prestressed, precast concrete were used at the base of the works and then launched.  All of the construction works were planned in view of the possibility of doubling the Hofuf-Riyadh line with the purpose of reducing future interruptions to railway operations to a minimum.