Ducts for cables under ancient Turkish tomb

KAYSERI, known as Caesarea in Roman times, one of the oldest cities in Anatolia, has a 6000-year history and because of its geographical position, it always has kept its importance. It is located on the so-called Silk Way, and situated at the foot of an extinct vulcano, Mt Ercyes (3.916m), which these days has become a popular ski resort. The inner city, dominated by the Byzantine fortress, is full of historic buildings, minarets and mosques, Turkish baths, fountains, tombs, and inns. The presence of all these historical monuments, throughout the city, makes the planning of traffic throughways and infra-structural works difficult.

The Municipality of Kayseri has planned a junction-free throughway through the city centre, passing very close to the walls of the fortress. This by-pass will run below the level of the local streets with bridges connecting the side streets at the opposite sides of the new road. In the middle of the planned route was an ancient Tomb, the Alaca Kumbet, dated from the year 1208. According to the plans, the lanes of the new road had to pass left and right of the foundation of this monument. In order to reinforce the foundation, before the excavation works started, a series of 11-m deep boreholes was made surrounding the tomb, and concrete was poured in, to create concrete piles.

Anchoring, to connect the concrete piles at opposite sides, was to be made at two levels, by means of steel cables, first at 3.5m and later at 5.5m deep, as the excavation progressed. Instead of using a special drill rig for anchoring bolts, the main contractor contracted TT-Insaat to install 60-mm PE pipes as ducts for the tension cables. TT-Insaat is the first contractor in Turkey specializing in trenchless installation of pipes and cables, and the project was performed in co-operation with Hidrotek, the Tracto-Technik distributor in Turkey.

22 bores had to be made with lengths ranging between 12 and 15m, and it was decided to use a Grundomat 75 for this job. The difficulty was to find a method of aiming the machine on the target, which was to be the space between two concrete piles at the opposite side. The concrete had been poured directly in the soil, without casing, and therefore the piles were very rough.Because of the depth of the excavation and the location of the building itself, a special method of aiming the mole in the proper direction had to be found: by means of accurate measurement and sighting, the direction of the target point was transferred to the rear side of the machine, after which a Grundoscope was used for steering, directed at the rear of the machine instead of at the front.

After the aiming method was established, the job was performed successfully, although the machine was sometimes slowed down considerably because of stone enclosures under the tomb. From the pattern of these obstacles, it was concluded that there was probably the circular wall of an old well or other foundation under the tomb. However, the power of the Grundomat was able to overcome all these obstacles; 18 out of 22 bores were on target, while in the other four cases the machine had to be assisted by widening the opening between the concrete piles by means of a jackhammer.

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