Six drilled shafts were installed at NGES-Amherst by using a Soilmec R-515 hydraulic rotary drill rig and a Champion 36 rock auger. The shafts were located at a distance of 5D from one another to avoid group effects. To facilitate construction, a hole 900 mm (36 in.) in diameter was augured to a depth of approximately 6 m (20 ft). A temporary casing with an outer diameter of 1 m (40 in.) was inserted into the augured hole. Next, a 900-mm-diameter hole was augured through the casing to a final depth of 14.3 m (47 ft) below grade. Below the casing, shafts were drilled open-hole without the use of slurry. The hole remained open for several hours without the accumulation of more than 50 mm (2 in.) of water before the concrete was poured. The shaft bottoms were sounded before concrete placement.
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Concrete having a 28-day compressive strength of 35 MN/m2 (4000 lb/in.2 ) was placed by using both free-fall and tremie methods, as indicated in Table 1. The mix design consisted of 10 mm ( 3 ⁄ 8-in.) aggregates (maximum), sand, Type II cement, and water (6.7:6:2.6:1 by weight). Plasticizers (REO1000), retardant (100XR), and an airentrapment agent were added to improve the mix properties. The resulting mix was plastic and flowable and had a slump of 180 to 230 mm (7 to 9 in.). Twelve test cylinders were collected from every shaft, and all tested cylinders exceeded the design strength.
Reinforcement, placed before concrete placement, consisted of 10 No. 9 bars [28.5 mm (1.125 in.)] and No. 4 [12.5 mm (0.5 in.)] stirrups, located 45 cm (18 in.) on center. Select reinforcement was replaced by similar-size Dywidag threadbar to facilitate load testing. All reinforcement was full length.
Four black iron pipes 50-mm (2-in.) inside diameter were installed for cross-hole sonic logging in all test shafts except one, where only three pipes were installed, to study the effect of tube placement on NDT results. Sister bars and inclinometer casing also were installed in all shafts for use in axial and lateral load testing; this is not presented here.
Summary
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