"Commencement of Tunneling" Event

August 9, 2010

The cheers and applause could barely be heard above the grinding of concrete and the whirling of the 1000-volt engine as the long arm of the tunnel excavator reached the portal wall, its drilling head grinding out small divots, symbolic of the great drilling and earth moving tasks that lay ahead.

After seven busy months of preparatory work, the digging has officially begun. Before that could happen, the portals walls and several retaining walls needed to be built, essentially to keep the hillsides in place when the digging occurs.

Spectators could see the outline of the east portal on lower portion of the ninety-foot wall. Within the next two weeks, hoe-rams will break up the concrete and blow torches will cut through the reinforcing steel. The outline of the tunnel will be more pronounced, clearly visible from the freeway. Next, the work with the giant roadheader will begin in earnest, as it breaks through a thin concrete wall that once sat behind the heavy wall into the mountainside.

The Chief Administrator of the Federal Highway Administration, Victor Mendez, spoke at the event, praising the stimulus program for delivering funds when it looked like the project might be stalled.

Other speakers included Caltrans Director Cindy McKim, State Senator Mark DeSaulnier, Assemblymember Nancy Skinner, Metropolitan Transportation Commissioner Amy Worth, Contra Costa Transportation Authority Chair John Taylor and Oakland City Councilman Larry Reid. Caltrans District 4 Director Bijan Sartipi was the master of ceremonies.

Work Progresses at East Portal

July 23, 2010

The wall shown in the photos below is in its ragged, rudimentary shape, but eventually it will become the east portal wall.

Most walls are built from the base upwards. Think of a house, a tower or a highrise. But in this case, workers begin at the top of the wall, and build the wall beneath them.

First, an auger drills large holes, ninety feet deep and several feet apart. Concrete is poured into the circular holes and allowed to harden. Next, a series of holes are drilled between the original holes, overlapping the edges. Steel cages are dropped into the holes for extra support and then concrete is poured into the hole. When the concrete hardens, it forms a series of underground interlinking piles.

Starting at the top of the wall, the dirt in slowly excavated revealing the front of the wall. You can see the circular shape of the piles that were once underground. Supports are added to the wall as the excavation goes deeper. Note the large concrete ediface built horizonatally across the piles. The machine in the lower photo is drilling holes to insert tie-back cables, which as the name indicates, will tie back the wall against the hillside.

Look at the semi-circular pattern on the wall in the top photo. That is the outline of the tunnel. The tunnel will be excavated straight through the portal wall. This could begin in as little as three weeks.

Tunneling Machine Assembled at East PortalJuly 7, 2010

A giant roadheader, a machine built in northeastern Germany, shipped in pieces to the Port of Oakland, and assembled at the east portal of the tunnel, is almost ready to begin excavation at the east portal. However, several weeks of work of preparatory work remain before the digging can begin. The $5.2 million machine weighs 130 tons and has been attended to by several German workers who arrived with the machine to oversee its assembly and testing.

Kay Street Project Finished July 1, 2010

The Kay Street Project was completed in mid-June 2010, the first of four construction contracts for the Caldecott Fourth Bore Project to be completed. The contractor installed a traffic signal at the intersection of Kay Street and Broadway and built a right-turn pocket at the southwest corner of Caldecott Lane and Kay Street. For more information, see Kay Street Project

Portal and Retaining Walls being Built May 31, 2010

Portal Walls

Construction crews are busy at the east and west sides of the tunnel, building the portal walls and retaining walls to hold back the hillsides. Most of this work must be completed before excavation of the tunnel can begin.

Each portal wall is being built as a secant wall, a method where the retaining wall is built underground and later excavated. First, a series of holes are drilled into the earth several feet apart. A steel cage in inserted into each hole, then filled with concrete, forming a "cast in drilled hole" pile. Once the piles have hardened, new holes are drilled between the existing piles, so they overlap the existing piles by about six inches on both sides. When the new pile is hardens, it will interlock with the existing piles, forming a sturdy underground wall.

Eventually, the subterranean wall will be excavated, revealing the load-bearing wall of the portals. The wall is strong enough that it will drilled through to form the entrance to the tunnel. The secant wall is strong, but it's rough appearance isn't much to look at. Finally, another concrete wall will be cast over the face of the secant wall, providing additional strength and a surface over which architectural details can be rendered.

Retaining Walls

The portal walls are being set back into the hillside, so far that retaining walls need to be built perpendicular to each portal wall to hold back the hillside. These walls on either side of the portal wall will be soil nail walls. Unlike the secant walls, the soil nail walls will be built on the exterior of the hillside. Holes are drilled into the hillside, a steel bolt (soil nail), is inserted, then grout is injected into the hole and allowed to harden. The bolts will protrude through the face of the wall, and will be tightened, pulling the wall tightly against the hillside.

Near the east portal, parallel to the freeway, a long, steep section of the hillside will be shored-up with another soldier pile wall. Along Fish Ranch Road, deep holes are drilled, nearly thirty feet deep, until they reach the level of the freeway. Steel beams are driven into the bottom of the holes, then concrete slurry is poured, forming large cast in drilled holes piles. Little by little, the area between the soldier piles is excavated. The concrete slurry is also chipped away from the steel beams. Large timber planks are inserted between the flanges of the I-beams to form a wall. The excavation and adding of the steel beams will continue in this manner until they nearly reach the freeway level. Then concrete will be cast over the timber, forming a completed retaining wall.