Integrity Testing of Three Drilled and Grouted Piles

THE PROJECT The work described in this article was done to evaluate the ability of oil field grout logging technology to determ1ne the integrity of drilled and grouted piles. Three drilled and grouted piles were constructed at one of the two Texas A&M University sites for geotechnical experimentation. At the site the soil is a stiff to very stiff clay. One boring with Shelby tube sampling and pressure meter testing was drilled. Three cone electrometer soundings were also performed. Unconsolidated Untrained Tests and some Drained Direct Shear Tests were performed. Figure 1 gives a summary of the soil data. The drilled and grouted pile designed for logging purposes was 110 ft (33.5 m) long, and had an average diameter equal to 30 in. (0.76 m). The steel casing was 20 in. O.D. (0.51 m) and had a wall thickness equal to 0.75 in. (19 mm). The hole was drilled dry, the grout was placed at the bottom of the hole and the closed end steel casing was lowered to the bottom squeezing the grout up in the annulus. From 0 to 20 ft (0 to 6.1 m) the annulus was made of loose cuttings of clay, from 20 to 40 ft (6.1 to 12.2 m) the annulus was left unfilled by creating a 360° chamber void, from 40 to 60 ft (12.2 to 183 m) a 45° vertical channel void was created in the grout curtain, from 60 ft to 85 ft (18.3 to 26 m) the pile was fully grouted with a 5 in. (127 mm) thick grout curtain and from 85 to 110 ft (26 to 33.5 m) the pile was fully grouted with a 2 in. (5 mm) thick grout curtain. Figure 2 shows the pile. The two drilled and grouted piles designed for capacity determination were 40 ft (12.2 m) long and 8 in. (203 mm) in diameter. The steel casings were 5 in. (127 mm) in diameter. The holes were drilled with betonies drilling mud, the grout was tremied to the bottom of the hole and the closed end casings were slowly lowered in place. The grout filled the annulus from 40 ft (12.2 m) depth to 5 ft (1.52 m) depth. The no defect pile had no purposely designed defects, while the defective pile had a 45° defect from 5 ft (1.52 m) to 25 ft (7.6 m) depth and a 45° defect from 15 ft (4.57 m) to 35 ft (10.7 m) depth at 180° from the other defect. Figure 3 shows the defective pile. The logging pile and to a lesser extent the two load test piles were logged by Schlumberger with a series of sonic, ultrasonic, gamma-gamma, and neutron logging tools. A well head was placed on the three piles so that the logging could be done at various pressure levels. The two load test piles were subjected to various tension load tests after the logging. This article gives the details of the logging part of the work.