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Progressive Design-Build (PDB) facilitates involvement of the design-build team during the earliest stages of the owner’s project development, ensuring they are part of the project team developing design solutions. This promotes the greatest amount of collaboration between the three key players in a construction contract – the owner, the designer and the contractor and achieves faster project completion compared to conventional design-bid-build delivery.
While a project design is usually 35 percent complete (or more) by the time a design-builder is procured in the traditional two-step design-build process, PDB adds the design-builder to the owner’s team earlier in the design phase and taps into the contractor’s experience to allow value and innovation in the design. When the design is somewhere between 50 and 75 percent complete, the design-builder prepares a firm price to complete the design and construction.
The other major feature of PDB is that the design-builder is selected on qualifications as well as cost (versus design-bid-build which is based on lowest cost only). The design-builder is brought in at an early stage, allowing the owner to be involved in design decisions that may affect cost and risk, as well as on the finished facility and its impact on future operational costs.
To learn more about how the TBM works, please view this short video.
Tunneling is a construction method involving Tunnel Boring Machines (TBMs) that range from 8-feet to over 20-feet in diameter to construct tunnels without intermediate access shafts. Tunnelling work can extend for several miles in rock or in softer ground. SVCW’s Gravity Pipeline tunnel extends for 3.5 miles in stiffer Bay Mud that underlies the Young Bay Mud characteristic of the San Francisco Bay Front soils. TBMs are occupied by a tunneling crew that advances the TBM through the soil while building the excavation support one ring at a time, with each ring connected to the most recently installed ring to create a continuous excavation support (tunnel) along the entire length of the tunnel alignment. Tunneling avoids disturbing or interfering with ground surface activities and traffic during construction. Various types of machines are chosen based on the underground soil geotechnical properties for tunneling construction.
Micro-tunneling is another underground tunneling method used in construction. Micro-tunneling machines (MTBMs) typically range in diameter from 2 feet to 5 feet and are operated with the crew at the ground surface and in the launching shaft. MTBMs are unoccupied and advance through the soil by means of hydraulic jacks at the launch shaft that push the entire casing or pipe string behind the MTBM through the soil. This method of construction limits the distance that microtunneling can advance in a single tunneling drive, ranging between 500 and 1000 feet, depending on soil conditions. Intermediate shafts for receiving and launching the MTBM must be planned carefully in advance to minimize surface disruption during and after construction. Microtunneling alignments are typically straight between launching and receiving shafts, but more projects are being completed with curvature (both horizontal and vertical) in the alignment. Benefits of microtunneling are similar to larger diameter tunneling: avoiding sensitive habitat and/or water, reducing planning time required to bring projects to construction, and minimizing surface disruption during construction.