Structural Design After the geometry of the culvert was determined from the hydraulic requirements, structural analysis was accomplished by a combination of static plane frame analysis using STAAD-PRO, and output from the finite element soil-structure interaction PLAXIS analysis. Reinforced concrete design was completed using a strength design method with a single load factor of 1.7 for all loads except seismic loads. A plane frame model was created to assess member forces and deflections based on the design loads. The model was constructed considering a 5 ft (1.5 m) effective width with stiffness of the secant piles neglecting the “cut” pile portion of the pile and reinforcing within the cut piles. Construction The drainage culvert was completed in four stages: First, we installed approximately 1,600 34.6 in (880 mm) CFA secant piles through a cast-in-place guide wall. Pile installation was performed using two Bauer BG 36 rigs and one BG 22 drill rig with service cranes that set the full length reinforcing in the piles. It was necessary to install under suitable crowd and rotation rates to avoid disturbing the soils because there were soft organic soils and silts present. A high slump plastic 5,000 psi concrete with 0.75 in (19 mm) aggregate was used for both the male and female piles. After the piles were installed, we dipped the concrete to cut-off elevation and back-filled the secant wall template back allowing the port traffic to track over the secant piles within days. Next, we poured the top slab of the culvert, which was approximately 3 ft (0.91 m) thick, on existing grade, eliminating the need for props and formwork that would have been required for a typical poured-in-place culvert roof in a bottom-up approach. Again, once the concrete attained adequate strength, the port traffic was free to track over the top slab, essentially eliminating traffic restrictions from that point forward. After construc- Installation of a full length reinforcing in secant pile ting the top slab, we built an access ramp to facilitate excava- tion of the soils below the top slab. Next, a series of well points along the length of the culvert were placed, to remove groundwater from the upper sandy fill soils prior to exca- vation. However the lower si l ts were essentially impervi- ous and groundwater seepage within this stratum was not an issue. During exca- Excavated culvert showing the parallel secant walls prior to pouring of the base slab and culvert walls vation, we used low-track pressure Komatsu dump trucks, capable of rotating 360 degrees on their frame, to remove spoils in the relatively tight work area within the culvert. Four access points along the length of the 2,000 ft (600 m) long culvert were constructed to facilitate follow-up work as excavation proceeded. Next, after excavation, we performed fine grading of the bottom of the cut, and pressure washed the secant pile wall to remove all soil from the concrete surface. At some locations, where concrete bulges exceeded the allowable limit, we chipped concrete to allow casting of the sidewalls with adequate thickness. After the grading and pressure washing, we drilled dowels into the secant wall to tie in the base slab and placed a water seal prior to pouring the bottom slab. This essentially sealed the culvert and acted as a permanent strut for the secant pile walls. We finished the culvert by drilling dowels into the sidewalls and pouring the cast-in-place sidewalls using vertical Peri forms. MSB’s VE alternate resulted in the following benefits: • Reduced construction time from 30 months to 12 months. • Optimized the culvert width using a more efficient single cell structure. • Reduced the construction right of way from 300 ft (90 m) to 100 ft (30 m). • Provided a contiguous construction process from one end of the project to the other, with minimal impact to port users. • Cost savings over the base bid option. Conclusion MSB developed “outside-the-box” concepts that, together with in- house design capabilities and state-of-the-art construction practices, led to a solution to the drainage requirement and offered significant benefits to the project. The solution met the needs of the engineering requirements of the U.S.ACE, benefited both the Port Authority and surrounding businesses by minimizing construction impacts. Through the dedication of all parties to the project, we maintained high construction standards and safe working con- ditions. The work significantly improved the level of flood pro- tection for the industrial and port users in the Puerto Nuevo area. DEEP FOUNDATIONS • MAR/APR 2012 • 11
