used for the drilled shaft axial load test, while lateral testing on the drilled shaft was performed using a rapid load test setup. All of the data from the load test program, including field inspection and observation reports, were provided to all teams. In addition, each concessionaire team could have a representative on site during the installation and testing of the foundations. This gave all teams an equal opportunity to make observations of the pile driving operations since the contractor was on one of the concessionaire teams. Drilled Shafts The drilled shaft portion of the load test program was located near the proposed west pylon for the cable-stayed bridge main span. This location is on the bank of the Mobile River with ground surface elevation of about El. +5 ft (El. +1.5 m). Performing the test at the east pylon would have required installation of the drilled shaft in the river, increasing complexity and cost. The shaft was constructed with a 78 in (1981 mm) diameter, permanent casing with 0.5 in (13 mm) wall thickness and a length of approximately 57 ft (17.4 m), with the top of casing around El. +10 ft (El. +3.05 m). Below the permanent casing, a drilled shaft with a diameter of 72 in (1,829 mm) was drilled to a tip elevation of about El. - 170 ft (El. -51.8 m) for a total length of about 180 ft (54.9 m). The shaft was excavated under polymer slurry to stabilize the excavation using 72 in (1,829 mm) diameter tooling consisting of a combination of soil auger, digging bucket and clean out bucket. The polymer slurry properties (e.g., viscosity, density, pH and sand content) were tested at various times throughout the construction process. Once the final tip elevation was encountered, the shaft bottom was cleaned, and the full column of the polymer slurry exchanged using a sub- mersible pump. Integrity testing of the completed shaft was performed using crosshole sonic logging (CSL) using eight tubes installed in the shaft. Approximately 227 cu yd (173.6 cu m) of concrete, under a continuous pour, was used in the con- struction of the shaft. Applied Foundation Testing (AFT) installed two bidirectional load cells, each cell assembly capable of a force of 4,000 kips (17.8 MN), in the shaft at two different elevations to create a multistage test arrangement. The lower cell was placed at the bottom of the rebar cage at an elevation of about El. -161.6 ft (El. -49.3 m), which was about 8 ft (2.4 m) from the bottom of the shaft. The upper cell was installed at El. -118.2 ft (El. -36.0 m), which was about 50 ft (15.2 m) above the bottom of the shaft. In addition, four levels of four strain gages were embedded in the concrete using “sister bars” attached to the reinforcement cage. The drilled shaft was loaded in three stages in general accordance with ASTM D8169 Standard Methods for Deep Founda- tions Under Static Axial Compressive Load, Procedure A - Quick Test. The first stage activated the bottom cell to mobilize the base resistance using the side resistance of the shaft above the cell for resistance. Following successful mobilization of base resistance, the pressure was released, and the upper load cell was activated to measure the side resistance in the drilled shaft segment between the upper and lower cells. The final stage involved hydraulically locking the bottom load cell to provide additional resistance and prevent move- ment between the cells. The upper cell was engaged and the side resistance on the top portion of the shaft above the upper load cell was measured. Based on this informa- tion, an equivalent shaft top load vs. displacement graph was constructed. The resultant equivalent shaft resistance, con- sidering buoyant shaft weights, measured about 11,600 kips (51.6 MN) with a maximum shaft head displacement of about 3 in (76 mm). The estimated unit base resistance was about 180 ksf (8.62 MPa) and the unit side resistance varied from 0.5 to 3 ksf (0.02 to 0.14 kPa). Lateral load testing on the drilled shaft was performed using a rapid load test mechanism in four incremental load cycles. Measurements of displacement at each load increment were made with accelerometers installed in an inclinometer casing and externally attached to the permanent casing, while strain gauges were embedded in the drilled shaft. The maximum load applied was 1,450 kips (6450 kN) with a top of shaft displacement of 6.2 in (158 mm). Installation of the rebar cage for the test drilled shaft 16 • DEEP FOUNDATIONS • JULY/AUG 2019 Locations of the instrumentation
