Alignment of Vertical and Inclined Jet Grout Columns for Waterproofing

Good overlapping among jet grout columns is crucial for the success of waterproofing in the ground. Drilling alignment, column spacing, and diameter of jet grout columns are the controlling factors of good column overlapping. This study evaluated the drilling alignment of vertical and inclined jet grout columns using field-measured alignment data and statistical analysis. A three-dimensional (3-D) image of a jet-grouted mass was established by combining the measurement results of drilling alignment and jet grout column diameter from the trial test. The 3-D image was used to examine the overlapping of the jet grout columns and identify possible locations of windows (non-grouted zones) in the jet-grouted mass. Vertically drilled jet grout holes maintained excellent alignment, with an average estimated inclination angle of 0.43 degrees and standard deviations of 0.11 degrees. However, to avoid underground obstacles, inclined drilling is often required. An inclined drill jet grout hole can easily deviate from its designed drilling alignment because of gravity and result in poor overlapping and potential windows. The average estimated inclination angle and standard deviation of inclined drilling were approximately three times those of vertical drilling.