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Vertical paper drains were installed at very soft soil layers to accelerate settlement rate. Several types of monitoring devices were instrumented to measure the changes in settlement and ground pore water pressure. The measured results are consistent with consolidation theory. Also, the standard penetration test N values become higher after soil improvement. For these measurements, the effects of construction sequences on the performance of vertical drains and monitoring devices were described. Six cast-in-place piles were constructed subsequently in the improved soil. The effects of vertical drains on the efficiency of construction and the accuracy of pile diameter were observed.