DFI DEEP FOUNDATIONS. Aerial View of a Flood Control Project in San Juan, Puerto Rico: An OPA Finalist F E

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1 U N DAIONS IN O F P D DFI S I U DP FOUNDAIONS Mar/Apr 2012 he Magazine of the Deep Foundations Institute Aerial View of a Flood Control Project in San Juan, Puerto Rico: An OPA Finalist

2 op slab construction Secant Pile op-down Construction for a Drainage Channel in Puerto Rico: An OPA Finalist For a drainage channel built in San Juan, Puerto Rico, a value engineering (V) proposal incorporating a secant pile top-down approach saved time and facilitated construction work on the larger flood control project. he channel, at the Bechara Industrial Area, Puerto Nuevo Port Facility and the Puerto Rico Maritime Shipping Authority Dock, was needed to allow drainage of the Rio Puerto Nuevo into San Juan Bay. he port area, one of the busiest in the Caribbean, has over 6,000 ft (1,800 m) of berthing wharves for ocean-going container ships along with over 500,000 sq ft (46,000 m²) of container loading and unloading areas, and is critical to the local economy. Planners wanted to minimize the impact of construction to the port and dock users, and developed a construction methodology and work sequencing that would prevent a complete barrier to port traffic. his plan involved non-contiguous and limited work areas AUHORS: Bill Shea, Morris-Shea Bridge Company Gordon King, Morris-Shea Bridge Company that leapfrogged along the alignment so as to prevent long barriers to lateral traffic movement across the culvert alignment. After reviewing the project plans and schedule, Morris-Shea Bridge Company (MSB) proposed an alternate design and construction approach that provided significant cost and schedule benefits, and also provided better access for the port and dock users. he alternate V proposal involved top-down construction methodology and redesigned drainage culvert geometry with two parallel 2,000 linear ft (lf) (600 m) secant walls installed on each side of the culvert. hese walls facilitated excavation and formed part of the culvert permanent walls. he result was a significantly reduced required construction right of way that allowed construction work in contiguous areas largely without impact on ongoing port activity. MSB conceived the design concept, and engineered design and construction of the V alternate secant pile culvert. he project initially consisted of an open channel in the industrial area picking up water from the existing Rio Puerto Nuevo, transitioning to an enclosed culvert through the port and dock areas, and outfall through the existing dock. he base bid construction included three main areas of work: 8 DP FOUNDAIONS MAR/APR 2012

3 Rio Puerto Nuevo River Channel: his work included furnishing and driving of king pile walls with a concrete capping beam and partial facing on each side of the open channel. Box culvert through the port and dock: he construction of a pile-supported 2,000 ft (600 m) long, 14 ft (4.25 m) high by 40 ft (12.2 m) wide double barrel cast-in-place box culvert had to be completed with minimized impact to the working dock. he double barrel box culvert was to be constructed using tiedback sheet piles to facilitate excavation and the construction of a conventional cast-in-place double barrel box culvert using conventional bottom-up construction. his design would have required a six month lead time for Belgian manufactured sheet piling, 300 ft (90 m) of construction right of way, and would limit work to only 200 ft (60 m) long non-contiguous sections. he work approach would have significantly impacted container traffic running perpendicular to the channel center line. he non-contiguous operation would also have significant impacts to the construction approach and schedule. New dock/outfall structure: Demolition of the existing active dock and construction on new pile supported dock and a multi-barrel culvert outfall discharging the drainage water into San Juan Bay. Ultimately the open river channel and outfall structures were built in accordance with the project plans. However, the box culvert was redesigned for the top-down construction. op-down construction stages Value ngineering Alternative In an effort to produce cost savings, cut construction time and minimize construction impacts to the industrial facilities and port users, MSB proposed the V option to the U.S. Army Corps of ngineers (USAC) for consideration by the design team. he design concept was to substitute the double barrel box culvert and the temporary sheeting with a drilled overlapping pile wall (secant wall), a cast-in-place base slab, and a cast-in-place top slab to be built using top-down method. his option formed a more efficient single channel culvert, thus reducing the required width that provided hydraulic equivalency to the base bid option. he alternate top-down approach also facilitated a continuous construction methodology, drastically minimizing the impact to the port users. he structural concept of the V was to design a secant pile wall to provide earth retention, support the drainage structure and form part of the structure permanent walls. We redesigned the connection between the wall and the top slab to transfer moment in accordance with the relative stiffness of the wall and slab. he secant piles were 34.6 in (880 mm) diameter piles spaced 30 in (762 mm) center to center so that alternate piles were full section and cut. he full-section fully reinforced piles extended to competent bearing in the lower very stiff clays to support the full dead and live loads. he cut piles had relatively light reinforcing and were extended below the culvert to form lagging between the full piles. he base slab was designed as a simple span doweled into the secant pile walls, and a cast-in-place culvert wall liner served both to simulate the hydraulic roughness of the base design and to transfer uplift forces to the secant pile wall. he top-down secant pile wall option design eliminated the need for an open excavation, and allowed port container traffic to flow above the secant pile supported roof structure while channel excavation and floor slab construction was progressing below. We built access points every 500 ft (150 m) to allow port traffic lanes in between each point; the construction approach only required 100 ft (30 m) of right-of-way clearance. his saved the port operations from dealing with significant delays to its operations that would have resulted from large sections of the container area being closed for excavation. he V option was approved based upon a technical review of geotechnical, structural and hydraulic design considerations, in addition to cost and schedule issues. All hydraulic, geotechnical, seismic and structural design was performed by MSB and our design consultants erratech, Inc., and Christy/Cobb, Inc, with constructability review by MSB. he Corps design team reviewed the construction approaches and work schedules. Hydraulic Design. he base bid double barrel cast-in-place box culvert was replaced by a narrower, and more efficient, single chamber culvert with an equivalent hydraulic efficiency to the base bid option. he single chamber transitioned into a four-chamber structure at the outlet into San Juan Bay where the dock has very high surcharge loads from cranes and container transporters required shorter top slab spans. he geometry and hydraulic calculations were submitted and reviewed by the design team for approval prior to further geotechnical and structural design. o ensure similar flow characteristics to the base-bid option all surfaces of the V culvert option comprised finished concrete surfaces. Geotechnical Conditions and Design. he existing grade along the culvert alignment was typically at elevation +7 to +10 ft (+2 to +3 m), with a step up to approximately +15 ft (4.5 m) at the upper container storage yard. Soil borings and laboratory test data indicated that the subsurface conditions comprised surficial sand, silty sand and sand with gravel and shell fragment fill to typically elevation -6 to -10 ft (-2 to -3 m). he fill soils overlie highly organic deposits representing the original mangrove environment located along the coastal area prior to construction of the port. Underlying the fills and organic soils were soft to very soft silty clays and clayey silts to elevation -38 to -45 ft (-11 to -14 m), which were in turn underlain by very stiff to hard clays with occasional limestone fragments. DP FOUNDAIONS MAR/APR

4 Soil profile determined from supplemental CPs o better define the geologic variations along the culvert alignment and determine pertinent engineering parameters for design, an extensive program of supplemental geotechnical investigation and testing was performed. hese included Cone Penetrometer esting (CP), Seismic Cone esting, Vane Shear testing and Standard Penetration est soil borings. he use of insitu CP and Vane Shear tests resulted in more accurate strength parameters for design than the relatively limited laboratory test data determined from extracted soil samples. Calibrating CP determined shear strength measurements with the in-situ vane shear data, allowed for detailed modeling of the shear strength profile along the alignment of the culvert, greatly aiding design. After completing the supplemental field and laboratory testing, the engineers completed a site-specific seismic response analysis using the computer program UFSHAK. Using shear wave velocity profiles derived from the seismic cone data, we performed the one dimensional wave propagation analysis and developed the site vertical and horizontal acceleration responses. he site specific accelerations were applied to a PLAXIS two-dimensional finite element model along with the pertinent soil and structural parameters and surcharges to determine the structure displacements and forces. his information was used for the secant wall structural design at various critical construction stages. hese included the excavated culvert prior to placement of the base slab under temporary construction surcharges, and final construction conditions with the base slab and side walls in place under permanent working surcharges of 600 to 1,000 lbs per sq ft (30 to 50 kpa). ngineers conducted four fully-instrumented static pile load tests along the culvert alignment to develop unit friction and endbearing capacities for design of the full secant pile lengths. he results of the test piles were used along with the CP data to set required pile tip elevations along the length of the alignment. Vane shear strength profile sounding output 10 DP FOUNDAIONS MAR/APR 2012

5 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 SAAD-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. he 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 he drainage culvert was completed in four stages: First, we installed approximately 1, 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 constructing the top slab, we built an access ramp to facilitate excavation 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 excavation. However the lower silts were essentially impervious and groundwater seepage within this stratum was not an issue. During exca- Installation of a full length reinforcing in secant pile xcavated 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. his 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 V 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 inhouse design capabilities and state-of-the-art construction practices, led to a solution to the drainage requirement and offered significant benefits to the project. he solution met the needs of the engineering requirements of the U.S.AC, benefited both the Port Authority and surrounding businesses by minimizing construction impacts. hrough the dedication of all parties to the project, we maintained high construction standards and safe working conditions. he work significantly improved the level of flood protection for the industrial and port users in the Puerto Nuevo area. DP FOUNDAIONS MAR/APR

6 U O F P D N DAIONS IN DFI S I U Deep Foundations Institute 326 Lafayette Avenue Hawthorne, NJ USA Fax PRSORD SANDARD U.S. POSAG PAID PHILADLPHIA, PA PRMI NO. 102 Secant Pile op-down Construction Drainage Channel During Construction at a Busy Working Port An OPA Finalist