Jet grouting for mitigation of installation disturbance

Abstract

To reduce the impact of installation of horizontal jet grouting columns on surrounding ground, a new horizontal jet grouting technique termed controlled discharge horizontal jet grouting is developed. A field trial programme is conducted to verify the application of the technique technology. Field measurements of ground surface displacement and induced excess pore-water pressures are obtained during implementation of the technique. Five trial jet grout columns are installed at 2 m below the ground surface and subsequently exposed for measuring and testing. The observed vertical displacements of the ground surface range from 0·4 to 9·4 mm, with maximum excess pore-water pressures generated during the field trial varying between 3·5 and 25·6 kPa. The diameters of the exposed jet grout columns range from 1·1 to 1·4 m. Core samples extracted from the trial jet grout columns indicate that the quality of the jet-grouted soil formed is good, with total core recovery of 70–95% and rock quality designation of 79–92%. Unconfined compressive strength tests show that the 28-d strength ranges from 0·9 to 1·5 MPa, and Young's modulus at 50% failure load (E50) is between 61·5 and 145·3 MPa. The field trial results confirm the applicability of the technique for achieving low-impact installation of horizontal jet grouting.