The contractor consortium working on the largest of two lots on Phase 1 of Cairo metro’s Line 4 recently reported the successful factory acceptance test (FAT) of a 6.73m diameter Herrenknecht Mixshield TBM that will be employed for a section of the twin tunnel boring works.

The contractor, AHPC Consortium – comprising Arab Contractors (lead), Hassan Allam, Petrojet and Concord – will use four TBMs in total to construct the twin bored tunnels on Lot CP401 on Phase 1 of west-to-east running Line 4. The project client is National Authority for Tunnels (NAT). Consultants are EHAF, ACE, OC Global, NOCE, and Nippon Kowi.

The TBM that recently had the successful FAT is the third of the machine on Lot CP401 and is responsibility of consortium partner Petrojet, explains Khaled Bassuni, the company’s senior TBM project engineer who was in attendance at the ceremony at Herrenknecht’s manufacturing facility, in Germany. The TBM (S-1238a) will bore on part of the East Bound Down Line.

LINE 4 – PHASE 1 – LOT CP401

Located in the western part of Greater Cairo, Phase 1 of Line 4 metro line extends from the Hadaek El Al Ashgar open cut station, in the west, and runs underground eastwards via twin tube, single track rail tunnels to just beyond El Malek El Saleh underground station, near the east boundary of the section.

Both of the end stations are also interchange/ intermodal hubs on the capital’s transport network and between them the Phase 1 project will include construction of 14 intermediate, underground stations, including two further hubs.

The 18.8km length of Phase 1 is divided into two lots – CP401 and CP402, respectively, with the former being the longer by far – almost 2.5 times the length of the shorter package. The CP401 lot is 13.6km long and CP402 is 5.2km long, respectively. Consequently, CP401 includes more underground works and stations than CP402.

AHPC Consortium is contractor on Lot CP401 and was awarded the lot in late 2020.

The larger, CP401 package is located in the western and central portion of Phase 1, in the Giza region.

It will have 12 stations in total connected by twin tube tunnels – the Hadaek El Al Ashgar station (hub), in a shallow groundwork setting, and 11 underground stations, as follows (west to east):

Hadaek Al Ahram station; El Nasr station; Grand Egyptian Museum station; El Remaya station (hub); Al Ahramat station (closest to the pyramids); Maryoutia station; El Arish station; El Matba’a station; El Talbeya station; Madkour station; El Mesaha Square station.

In total, the stations account of 2.9km, or slightly more than a fifth, of the length of the lot.

Joining the stations calls for a total of 9.8km of TBM bored tunnel to be constructed for each of the two parallel tubes, bringing the total length of mechanised tunnelling for the twin tunnels to 19.6km.

The tunnels on lot CP401 are to be constructed by AHPC Consortium to have 5.8m i.d. concrete segmental lining located at least 7.5m and up to 40m below ground level along the alignment.

The lot also includes 1km of cut and cover construction, at the far western end, from where the line initially descends underground from the Hadaek El Al Ashgar station hub. Soon after is located a vertical shaft for TBM launch and supply. TBM boring will also take place farther to the east, from Al Ahramat station.

Geography and Geology

TBM tunnelling on Lot CP401 of Line 4, Phase 1, will be in sand, primarily.

Topographical conditions along the route of the lot fall into three different zones (Zones 1-3).

? Zone 1 – a slightly higher plateau setting with a gentle slope, from where the tunnel descends in the west to just beyond the first intermediate station, El Nasr. Geology is fill over a sand/gravel layer, which overlays a deep clay/sandstone interlayer.

? Zone 2 – slightly steeper ground slope from near El Nasr station to the next station, at the Grand Egyptian Museum. The slope results in reducing cover to the tunnel going eastward, reducing to 8.2m. Geology is sand.

? Zone 3 – generally flat ground of the Nile Valley lays on the route east of the Grand Egyptian Museum station. Geology is fill over silty clay of high plasticity, then sand over hard silty clay of high plasticity.

Tunnelling

Tunnel boring is to be undertaken in two sections which are (west to east) as follows: Section 1: the alignment proceeds in a circuitous route from the west-side vertical shaft to Al Ahramat station, including going around the Grand Egyptian Museum and Giza pyramid area; and, Section 2: from Al Ahramat station on a straight route to just beyond El Mesaha Square, the last station on Phase 1.

With its circuitous route, Section 1 of the TBM tunnelling includes topographical Zones 1-2 and part of Zone 3.

Section 2 only includes Zone 3. A total of four TBMs are to be employed on Lot CP401 to bore the parallel tunnels between the metro stations, said Bassuni.

His machine – which had the recent FAT in Germany, in late 2022 – is the Mixshield coded S-1238a, which on the project is referred to as TBM03. This is the third of the TBMs for the works, he explains.

Bassuni further explains that the TBMs are identical types of machines but the technical responsibility for each machine rests with each contractor, separately, in AHPC Consortium. He works with Petrojet and is only in charge of TBM03.

The TBMs have 10.14m long shields and capable of working to a minimum horizontal curve radius of 250m and maximum gradient of +/- 4.5%. Maximum face pressure on the tunnel axis is 5 bar. The weight of the TBM and backup is approximately 690 tonne and the installed power of the machine is 2970kW.

The tunnel lining is to be constructed of 1.2/1.5m-long rings (5+1) with 300mm thick segments. The inner diameter of the lining is 5.8m, including construction tolerance, 5.7m without. Including allowance for maintenance and repair, the tunnel lining inner repair width is 5.5m.

Single component grout is to be employed, says Bassuni.

He adds that the lot has three segment factories – one owned by Petrojet, another by Arab Contractors, and the third owned by a subcontractor serving both Concord and Hassan Allam.

In addition to the sections of bored tunnels, each consortium member will also construct three stations.