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All to the goods

After a decade of planning and discussion Los Angeles is pushing ahead with the construction of the Alameda Corridor, a huge sunken railway which will carry freight trains under the city streets. Words and pictures by Adrian Greeman

Building the Alameda trench is rather like doing press-ups, says Duane Kenagy, the deputy programme manager for the engineering team on the $2.4bn Alameda Corridor project.

'One is easy; 27,000 is difficult.'

This is the total count for piles being installed on the mid-project trench, which is key to speeding up crucial freight train movements through the city. The 900mm diameter secant piles, 18m deep, will form two walls of a 10m deep trench running 16km through the southern towns and communities that make up the urban sprawl of Los Angeles.

The trench is essentially an open tunnel, into which will go two heavy duty rail lines. Equipped with state of the art signalling and newly centralised train control, these will allow huge, up to 2km long, freight trains to run at speeds of up to 65km/h hour. Each locomotive will pull hundreds of containers from the twin ports of Los Angeles and Long Beach to the start of the transcontinental routes. Growth of trade through the two ports is phenomenal and is expected to treble to 23M units annually by 2030.

'The important point is not the maximum possible speed, ' says Timothy Buresh, director of engineering for the client, the Alameda Corridor Transportation Authority, 'but the minimum; the fact that the trains will run without interruption.' Currently trains amble along at speeds as slow as 10km/h and it can take a whole day to make the 30km journey from the ports through to the north of LA.

The trench will remove 30 different at grade crossing points on this route alone.

Altogether 200 level crossing points will be eliminated from three lines that currently take 25 trains each day through the city for the Union Pacific, including the former Southern Pacific, and the Burlington North Santa Fe rail companies. They will share the new rail corridor which can accommodate up to 100 trains each day.

Trains will run below ground in the trench and at grade in two complementary sections north and south at either end of the project. Major new bridges and viaducts will separate the rail corridor from the roads. Total length of the whole corridor will be 32km.

The biggest chunk of work however is the trench, currently the focus of major activity by a joint venture contractor Tutor Saliba Team (TST) which won $717M design and build contract in August 1998, setting a precedent for both size of contract and method. Previously, client the State of California has used conventional design and construction bid methods (see box). Parsons Transport Group and HNTB are equity participants in the joint venture, supplying design expertise.

The extended work site runs up the central section of the broad Alameda Street previously occupied by the Union Pacific line. Those trains now run on a 10km long bypass line built alongside as an early part of the contract. This line will later serve as a local feeder for a multitude of small industries.

'A lot of businesses are affected, ' says Alameda Corridor Engineering Team (ACET) programme manager Gene Courtney. Co-ordinating traffic diversions, land requisitions and community disruption issues with the six different community authorities along the route is a major part of the contractor's work. 'It is extremely complex, ' he adds.

So too is dealing with the utilities. Currently water lines, sewers, gas lines, electrical cables and telecommunications link run higgledy piggledy across the route. 'All will be bunched and concentrated at the point of the bridge crossings, ' says Courtney.

'Altogether there are 3,000 utility interfaces relocating, protecting, diverting, ' Kenagy adds. 'They all want to take advantage to reroute, clean up old problems and deal with capacity questions.'

On the route itself work crews are busy ripping up the old sleepers and rails from the existing line. But the major activity lies with the big piling rigs, working on the corridor walls and on the foundations of half a dozen of the major bridge crossings currently under way.

Some two dozen crossings will eventually be required.

'The contractor is working on two headings for the piling, one on each side, ' says Kenagy 'and we hope installation will reach 40 a day.' A slow learning curve initially bothered the ACET but the contractor seems to be over it and a large number of rigs are busy in the almost permanent sunshine. The trench wall is made up of mix in place earth columns alternating with 900mm diameter concrete piles at 1,200mm centres. Ground conditions are fairly consistent, either clayey silt or silty-clay.

'A 1m square concrete cap is formed along the length of the wall by a follow on crew. Later it will get an interior concrete facing, ' Buresh explains. This will be constructed once the wall has been exposed. Excavation has just begun at one point and a second face will be opened up later.

Prior to excavation, concrete beams are placed between the trench walls at 8m intervals. The trench works by a combination of cantilever action of the 16m deep piles and strutting between the capping beams, explains Buresh.

Towards the northern end the struts will be every 4m, he adds. There the urban fabric is denser and to provide the street capacity above will mean extending lanes out over the trench. At one point the rail line supplying local links will also be supported on a slab over the trench, virtually closing it in.

Excavation involves the disposal of a certain amount of contaminated ground because the top 500m of the line has suffered years of hydrocarbon and lead deposition from passing trains. 'It is not hugely significant, ' says Kenagy.

Taking charge

The Alameda Corridor project is funded by a $400M input from the two container ports, federal monies, plus state and county transportation funds. A $1.2M bond issue provides the balance. Income to repay the bond will come from trains tolls at$30 for each full container.

The project is managed by Alameda Corridor Transportation Authority (ACTA), a joint powers agency set up by the two ports in 1989. Currently a seven-strong board unites port and city representatives, replacing the previous 15-person composition which included representatives from local communities. The communities receive a contribution to fund local improvements and landscaping, as well as having an input into the architectural aspects of the design.

The Alameda Corridor Engineering Team is engineer and project manager for ACTA. Members include consultants Moffat & Nichol, and Daniel, Mann Johnson & Mendenhall

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