São Paulo is the largest city in Latin-America. Within its metropolis live more than 17 million people, many of them coming from other regions of the country or immigrants from overseas. The cultural and ethnic diversity of the city is remarkable, as is the city’s economic power. São Paulo represents 18% of the Brazilian GDP and is undoubtedly the most important financial centre of the country. T

Currently the São Paulo Metro carries approximately 486 million passengers/year through its 49.2km network of lines with 46 stations. Through the auspices of PITU – Integrated Program of Urban Transportation, this subway system is under expansion to connect it with other transportation systems, such as urban trains and buses.

The Project

The new line will connect the city district Luz with Villa Sônia and have 11 stations along its 12.8km length, allowing connection with the railway lines of CPTM-Companhia Paulista de Trens Metropolitanos (São Paulo Metropolitan Train Company) as well as with other subway lines (Figure 1).

Development of the project has been split into two phases by the client, Companhia do Metropolitano de São Paulo Metrô. Phase 1, scheduled for completion in 48 months, consists of the construction of a 12.8km underground extension from its tail track northeast of Luz Station to the maintenance facility portal at Vila Sônia, the complete construction of 5 stations, partial construction of 4 stations and of the Vila Sônia Maintenance Yard, permanent way and supply and assembly of the systems necessary for partial operation of the line. Phase 2 consists of the completion of the 4 stations on Phase 1, the construction of two new stations and the supply of systems and rolling stock in order to allow the line’s full operation. The line sections will consist of:

  • 10.35km of TBM constructed double track tunnel;

  • 286m long double track and twin single-track NATM tunnel;

  • 68m of double track tunnel to be constructed by cover and cut (top-down process);

  • 507m of three-track NATM tunnel;

  • 354m of double, three and four-track cover and cut tunnel;

  • six stations to be constructed by NATM and five stations by cover and cut.

The two phase project has an estimated cost of US$1.26bn and will be totally funded by foreign and local sources to the Government of São Paulo. In addition to a World Bank loan, the Government will be also applying for a matching loan amount from other financial institutions. The Government of São Paulo will fund the balance from its own resources.

The bid

The project will have two bids; the first one, divided into three lots, will be a turnkey contract for design, civil works, supplies and installation for Phase 1. The pre-qualification of this contract has been running since December 2001.

The invitation of the pre-qualified applicants to submit bids is expected this month with works scheduled to start in September 2002. The second bid for implementation of Phase 2 has yet to be scheduled.

A truly international field of 17 consortia including top contractors from France, Germany, Italy, Spain, Portugal, Japan, the United States of America and Brazil have submitted applications for pre-qualification of the first contract.

The geology

The geology of the São Paulo sedimentary basin is split into three main geological units: Precambrian bedrock (gneiss-migmatite), tertiary sediments, and current sedimentary deposits (Figure 2).

The gneiss-migmatite is further divided into three different groups, based on its mineralogical, textural and structural characteristics as: granite-gneiss, banded-gneiss and biotite-gneiss.

Geomechanical characteristics of the three domains were submitted to statistical treatment. Results showed that the granite-gneiss rock mass shows average Q values (Barton) between 1 and 15; the banded-gneiss is between 0.2 and 10 and the biotite-gneiss rock mass shows Q values between 0.1 and 1 (Figure 3).

The São Paulo Basin is a depression with colluvial/alluvial, alluvial and lacustrine sediments. The stratigraphic column of the tertiary sediments of the Line 4 area were grouped into the following formations:

  • Resende Formation – made of alternate of fine sandy gray clay, and gray and yellow silty sand, generally argillaceous. The gray clays correspond to clays known as “Taguá” and the roughest silty sands correspond, at least partially, to the so-called “basal sands” and the rest to “argillaceous average gray and yellow sands.”

  • São Paulo Formation – occurs predominantly above an elevation of 760m in the central region of the city and is composed of two main lithofacies. The first is of rough sandstone, sometimes conglomeratic and graded, that reaches the silt and clay fractions at the top of the layers. The second is of sandstone with average to rough grains, also graded, up to claystone and siltstone, with plain-parallel horizontal stratifications.

Due to their origin, these sediments have both vertical and horizontal sharp grain size variations. This aspect is of key importance to underground works, since it is rather difficult to interpret a geological and geotechnical section based on spot drilling due to the great variation of sediments.

  • The major modern sediments are mostly alluvial deposits and are seen along the valleys of Tietê River and its tributaries. They are composed of sands, clays and gravels deposited by the present fluvial system.

625 boreholes with a 36m average length were made along the alignment approximately every 24m. In-situ and laboratorial tests in soft soil and rock samples included tridimensional permeability (SHM), self boring pressuremeter (CamKometer) and petrographic analysis.

The tunnels

The choices of excavation methods were based on three main factors: safety, predictability of schedule and costs and work quality. Because of this, for some 10.40km, representing 80% of the total extension, two TBMs will be used to bore the 9.3m diameter single tube, double track tunnel. A soft ground EPB shield machine will bore approximately 6km from Luz to Faria Lima mostly through clays and silty sands, whilst a mixed face EPB will construct some 4.5km of tunnel between Faria Lima and Villa Sônia through rock. They will work at depths of 15m-45m erecting a 9.03m o.d. precast concrete segment ring with a thickness of 300mm leaving the required 8.43m i.d.

Recently, a new study of the TBM tunnel diameter has been developed to include emergency exit catwalks on both sides of the tunnel. In this case, a 9.55m i.d. tunnel would be necessary. The design incorporates waterproofing elements around the segments of the rings (Figure 4). The soft ground EPB shield machine was chosen due the particle size zone and water pressure that will occur through its alignment. The mixed face EPB TBM was chosen for its capacity to bore saprolites with boulders and hard rock with a maximum compressive strength of 180 MPa. Between Faria Lima and Butantã stations it is thought the machine will need a cutter change and move to EPB mode to bore the weathered granite gneiss. The Barton theoretical curve shows a better performance from a hard rock TBM than NATM tunnelling by drill and blast (Figure 3).

NATM was chosen to excavate 12% of the track tunnels due to the variable cross-section being incompatible with TBM construction; one three-track parking tunnel with a width varying from 13.3m-15.6m and height varying from 10.9m-12m and another two single-track tunnels, each 6.50m wide and 6.50m high. The three-track parking tunnel will be excavated in soft ground with a side-drift, primary support will be made up of jet grouted piles and steel lattice girder reinforced shotcrete. The section will be finished with a cast in-situ reinforced concrete lining with two layers of welded mesh. The twin single-track tunnels will be constructed in soft ground by NATM using a top heading method with supporting core, bench and invert. The roof will be reinforced by vertical jet grouted columns drilled from the surface.

When the NATM tunnelling was considered incompatible with the low depth of the tunnels or with the high risk to the buildings, cut and cover was chosen. Because of intense traffic, a top-down method, with diaphragm walls incorporated in the permanent box structure, has been specified for 8% of the track tunnels. To avoid damage to nearby structures, a dewatering system has been designed into the box excavation and diaphragm walls to support the hydrostatic pressure of the ground water level. All the track tunnels constructed by cover and cut will use diaphragm walls at depths of 12m-30m and at thickness of 0.80m-1.20m.

Steel piles will be used, when necessary, to support the walls in addition to the box structure slabs. To obtain a watertightness anchors were excluded to avoid holing the diaphragm walls, and polyurethane injections in the wall joints and internal cast in-situ concrete walls were designed.

The stations

Six stations will be constructed by NATM. These additions to the original design were conceived using NATM and architecture together to resolve the complex problems posed by their location. The stations will compose three principle elements: a large circular shaft with a diameter varying from 20m-40m; a platform tunnel 132m long, 20.3m wide and 14.8m high and; a 16.4m wide and 15.3m high connecting tunnel linking the shaft to the platform tunnel. For some stations, when the platform tunnel is located away from streets, the circular shaft is designed on the platform tunnel, eliminating the connection tunnel. The function of the shaft is to allow access for underground construction and to contain escalators linking the mezzanine to the platform tunnel. It will contain the ventilation system too, composed of an exhaust shaft and natural air insulation.

Paulista station is a good example of this new station design. It will be constructed in soft ground in the São Paulo Formation geology. The access shaft will compose two 16.6m i.d. shafts at 40m depth. The platform tunnels will be excavated at these depths of 40m, underwater with a provisory drainage system and by twin side drifts (Figure 5). The primary and permanent supports designed are similar to the three-track tunnel described above.

Two of the six stations to be constructed by NATM will be in rock. They will not have connection tunnels. The platform tunnelling will be by drill and blast with an advance heading of 6.7m in height with excavation of the bench coming in at a later phase. The support is made up of sprayed concrete with welded mesh reinforcement and bolts.

Five stations will be constructed by cover and cut. The República Station because of a pre-existing construction. The Três Poderes and Morumbi stations will be constructed in Phase 2 of the project after operation of the trains has commenced. The Fradique Coutinho Station will also be constructed by cover and cut because of its low depth, the soft ground condition with alluvium and tertiary deposits and water ground level next to the ground surface and the buildings.

All stations to be constructed by cover and cut will use diaphragm walls with 20m to 28m depths and thickness ranging from 0.8m to 1.0m. The walls have all been designed to support the hydrostatic water pressure.

Related Files
Figure 3: Average Q values
Figure 2: Geological profile of the Sao Paulo basin
Figure 4: Cross-section of double track
Figure 5: Cross section of the Paulista Station platform tunnel
Figure 1: The new Line 4