Assessing the influence of displacement rates on the failure behavior and undrained shear strength characteristics of reconstituted varve laminae prepared at different moisture contents

The geotechnical behavior of varved clays in cold regions remains inadequately understood despite their widespread occurrence. This study addresses this gap by investigating the behavior of homogeneous and reconstituted varved clay samples through Unconfined Compressive Strength (UCS) testing. Homogeneous samples consist of Red Soil (RS) and Black Soil (BS), while reconstituted varved clays are prepared by layering RS and BS in configurations of 2, 4, 8, and 16 layers. UCS tests are conducted at displacement rates of 1.25, 0.24, and 0.024 mm/min, hypothesized to simulate the velocity of glacial override on soils. Samples are prepared at five moisture contents ranging from 0.8 to 1.2 OMC. Results indicate that as moisture content decreases below OMC, undrained shear strength increases for all samples, accompanied by a reduction in strain, while the opposite trend is observed for samples on the wet side of OMC. For reconstituted varved clays, undrained shear strength increases as number of laminae rises from 2 to 8, but decreases in the 16-laminae sample, which suggests a threshold exists for the number of laminae beyond which strength reduces. Displacement rate significantly influences failure modes and patterns, with samples exhibiting more ductile behavior at lower displacement rates and higher moisture contents.