Abstract:
Jet grouting was performed to form a grout slab and grout wall to mitigate deep seated lateral wall deflections for an excavation 67 ft x 80 ft in plan with subgrades at 50 and 70 ft depths. The excavation was retained by secant pile walls up to 110 ft deep. 7 ft diameter jet grout columns were installed at a triangular grid spacing at 5.25 ft centers within the varved silts and clays between 50 to 75ft depths using double fluid jetting. This case study reviews the grouting performance in the varved silts and clays. In situ soil properties were derived from laboratory and field CPT tests. Unconfined compressive strength and modulus of grouted soils were obtained from laboratory tests on cored samples. The total core recovery records from core logs were used to interpret groutability of the soils. Specific gravity measurements of discharged spoils were reviewed to evaluate mixing performance. Records of drilling deviation were examined to determine potential overlap issues between jet grout columns. The impact of secant pile wall deflections on jet grouting sequence is discussed, and productivity records were reviewed for downtimes and causes of delay. The aim of the paper is to provide an improved appreciation of the grouting issues relating to deep jet grouting in the varved silts and clays of Manhattan.