More than 27,000 secant piles, 900mm in diameter, are being bored into the city clays of Los Angeles. Carved in between even bigger, 1,200mm diameter ‘female’ mix-ground piles, they will create two vertical walls for a twin track railway cutting running for 16km through the southern city, the Alameda trench.
The trench, 10m deep, will take twin track loads of containers from the twin ports of Los Angeles and Long Beach to the start of the big transcontinental rail routes across the USA. State-of-the-art signalling will let the huge 2km long freight trains run at a maximum 65kmh, instead of crawling on three at-grade lines through LA’s huge urban sprawl.
Currently trains amble at sometimes just 10kmh and it can take a whole day to make the 30km city crossing from the ports, says Duane Kenagy, the deputy programme manager for the Alameda Corridor Engineering Team (ACET). “The trench will remove 200 different crossing points on the three lines which will be replaced,” he says.
The complete Corridor will also have two sections at ground level north and south, where new major bridges and viaducts will achieve separation from the roads. Total length of the whole corridor formed will be 32km and the cost will be $2.4bn.
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 a $717m design/build contract for the work in August 1998. Parsons Transport Group and HNTB are in the joint venture on the design side, as equity participants.
The extended worksite runs up the central section of the broad Alameda Street along an existing train route. Trains from those tracks now use a new 10km long diversion alongside.
Utilities must also be diverted. All will be bunched up and concentrated at bridges, some 3,000 interfaces.
On the corridor, the major activity is with big piling rigs, both for the corridor walls and for the foundations of half a dozen of the major bridge crossings currently underway. Some two dozen crossings are eventually required. There are two headings for the piling, one on each side and the hope is to reach 40 installed a day.
Numerous rigs based frequently around Manitowoc 777s are busy in the city’s seemingly permanent sunshine. A 4600 is used for bored piles, and lifting rebar cages, and other cranes on site include 120t-capacity Liebherr 883 and 90t Link Belt LS-218H units. Miscellaneous lifting is done also with a Link-Belt/Sumitomo LS-248RH, and a 90t Manitowoc 222 is used for stone column construction.
Before excavation, concrete beams must be formed between the opposite walls, these will be at 8m intervals. The trench design works with a combination of pile cantilever action – they are 18m deep – and strutting between the capping beams. Towards the narrower northern end, struts will be placed every 4m to carry street lanes over the trench.
At several junctions along the route concreting activity is underway for bridges and approaches. It makes sense for TST to build these top down; most will be lifted-in precast concrete double T-beams.
Further bridge work is underway in the north sector where the twin lines cross the Los Angeles river and then diverge on the respective tracks of the three different rail users. The rail crosses or is crossed by streets and commuter rail lines, all of which ruled out continuing the trench. Several smaller bridges are underway, and biggest of all, the $45m Redondo junction by Japanese joint venture Shimmick Obayashi. A huge steel truss must soon be lifted in across the LA river. Design was by Frederick R Harris for the 750m long bridge and viaduct which will carry commuter trains.
On the southern end of the project the track is forced to run above ground level because of a number of water courses which need new bridges and will involve further heavy lifts. Longest is the Henry Ford viaduct, a 1km long grade separation with two 90m steel truss bridges across a freeway and a water channel. Equipment in use down here includes a Manitowoc mounted pile rig for pre-drilling and placement of 24-inch (600mm) octagonal concrete piles. It is fitted with an HPSI Vari-Torque power head and H-6 drill head for pre-drilling.
“This is the most complex part of the southern sector,” says Dick Chan, an associate vice president of Moffat & Nichol Engineers and chief engineer for ACET. “There are stone columns needed there because of liquefaction problems.” The work on the $80m contract, also with Shimmick Obayashi has only just got underway.
