Summary: | 碩士 === 國立交通大學 === 土木工程學系 === 100 === This paper presents experimental data on the settlement and relative density change of a cohesionless soil due to cyclic torsional shearing compaction. A new cyclic torsional shearing compactor was designed and constructed at National Chiao Tung University. Torque wrenches were attached to the compactor to apply the cyclic torque
and cyclic shearing to the soil surface. Air-dry Ottawa sand was used as fill material. The thickness of the soil to be compacted was 0.6 m. The initial relative density of the backfill was 34.5 %. The static vertical normal stress of 9.24 kPa was applied on the soil surface with a 0.3 m-diameter circular steel disc. Then cyclic shearing was applied with rotation angles of plus and minus 5 degrees, and the number of cycles of 1, 2, 5, 10, 20, 30 and 40. Surface settlement of the fill was measured with a laser distance
meter. Soil density cups were buried in the cohesionless specimen to monitor the relative density of soil. Test results showed that the density increase due to the static vertical load was obvious in the top 150 mm (radius of the circular loading disc) of the fill. Below the depth of 150 mm, the density increase due to the static surface loading was less obvious. In the first 2 cycles of cyclic torque application, surface settlement increased significantly. However, after 20 cycles, soil particles were rearranged and reached a densely-packed condition, little surface settlement was observed. After 20
cycles, the relative density of soil located 150 mm below the surface was successfally increased to a value greater than 70 %. The cyclic torsional shear soil improvement was effective for the top 150 mm (disc radius) of soil. The relative density of soil increased with increasing number of cycles of torsional shearing. After the first 20
cycles of shearing, the compaction effect became less significant. For the compaction on four 0.15 m-thick lifts, the relative density achieved in each lift was greater than the required value of 70 %.
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