Elucidation of improvement mechanism and evaluation of improvement effect on ground improved by compaction grouting

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In this study, the performance of compaction grouting has been investigated through laboratory and field experimental works. For the laboratory experimental work, large-scale calibration chamber was developed. In this chamber, sandy samples (1.40 m in diameter and 1.45 m high) are prepared, consolidated and injected (using grout mortar) under conditions highly simulating the actual field conditions As the results, it was confirmed its accurate basic performance. As for the field tests, analytical study was involved based on the results of three field tests conducted in Nagoya, in Osaka and under the old taxiway of Tokyo International Airport.The main findings of this study are as follows : (1) The performance in terms of ground surface upheave is dependent on the injection depth. (2) The critical depth that characterizes the shallow and deep injections is dependent on the compaction grout pile diameter. (3) The relatively shallow injections are governed by the condition of conical shea … More ring failure of the soils overlying the masses being injected. At conical shearing failure, the attained injection pressure and grout volume are dependent on the overburden pressure and shear strength characteristics. (4) The treatment effectiveness of relatively shallow injections may be improved by terminating the injection process at just before the onset of ground surface upheave. (5) In planning the grouting works for the applications for lifting of settled structures and foundations, the required lifts can be provided only by the injections shallower than the critical depth. (6) For the applications such as in liquefaction prevention works, smaller-diameter piles may be injected while going shallower. (7) For relatively deep injections, the vertical overburden pressure has no appreciable effect on the performance. However, the performance is highly influenced by the local soil compressibility. If deformation by relative displacement of the soil particles is the dominant mechanism, the attained injection pressure will be highly correlated to the local fines content. If deformation by particle crushing is the dominant mechanism, the resulting crushing depends on mainly injection pressure. (8) The maximum pressure from injecting a given grout volume correlates well with the tip resistance of CPT test. This correlation qualifies the maximum injection pressure as reliable criteria for evaluating the performance of compaction grouting operations. (9) In the loose sand, the improved area is limited around the grouted area. However, the wide area is uniformly improved in the dense sand. Less