Mechanical response of grading loading and unloading of backfill sand under confinement constraint.

In subgrade and levee projects, local subsidence problems often occur due to insufficient compaction of backfill sand. In order to reduce the possibility of such damage, the three-dimensional stress-strain testing technology is used to study the mechanical response of backfill sand compaction under axisymmetric conditions. The collected raw data is calculated using mathematical analysis software, and the stress, strain, K0 value and stressstrain path are analyzed under cyclic loading. The studies show that more compaction is not better, but there exist an optimal number of compaction times for backfill sand. In the initial stage of the test, as the number of cycle increases, the coefficient of earth pressure at rest increase, that is, the density inside the sand increases; when cycle index is greater than 6, the coefficient of earth pressure at rest no longer increases. Under the action of onedimensional vertical load, the effective normal stress response in the normal direction of plane of the load lags behind the effective normal stress in the parallel plane of the load. Therefore, it is recommended to control the compaction rate during the compaction process to achieve effective vertical compaction and horizontal extrusion. In addition, different loading tonnages and compaction methods (different forms of load) will affect the stress path, and then affect the strain deformation. The research results can provide objective reference for the mechanical properties of sand as filling material, and also provide reference for in-situ three-dimensional stress-strain research in practical engineering. [ABSTRACT FROM AUTHOR]