Experimental Study on Mechanical Properties of the Yellow River Alluvial Silt under Plane Strain Unloading Condition

The experiments of lateral unloading were conducted on the Yellow River alluvial silt under different consolidation confining pressures and water contents using a true triaxial instrument. Its mechanical properties under plane strain state of lateral unloading were studied. The applicability of the classical strength criterion to the silt was compared and analyzed based on the test results. The results show that: The stress-strain curves of silt show a weak hardening type under plane strain state of lateral unloading. The curves show brittle failure at a low water content, and plastic failure at a high water content, with a failure strain between 1% and 6%. The unloading strength is affected by confining pressure significantly, whereas the water content has a relatively small impact on it. The initial change of small principal strain during unloading is small, and the small principal strain begins to grow almost linearly when the axial strain reaches about 1%. The medium principal stress is greatly affected by the confining pressure, and it decreases rapidly in the early stage of unloading. The value tends to stabilize and does not decrease when the axial strain reaches 0.5% to 1%. The medium principal stress coefficient decreases rapidly and then increases slowly with the increase of axial strain. It is between 0.27 and 0.37 when the sample is damaged. The Lade-Duncan strength criterion could predict the unloading strength of silt well under plane strain state of lateral unloading.