Experimental study on the influence of clay content on the shear strength of silty soil and mechanism analysis

Shear strengths of silty soil were determined for shallow destruction of the soil sites frequently occurring in the Central Plains area. Specimens were prepared with five different clay contents (5, 10, 15, 20, and 25%) prior to compaction at dry densities of 1.60, 1.70, and 1.80 g/cm3. Soil specimens were saturated and then the consolidated undrained shear test was conducted with eight confined pressures ranging from 1 to 400 kPa. Results indicate that the shear strength increases significantly as the clay content increases from 5 to 25%, and the cohesion c shows bilinear function with the inflection point at the clay content of 10%. The difference of cohesion in the high and low stress sections decreases gradually to almost the same value until 25% of the clay content, while the internal friction angle φ decreases with the increase in clay content. Within the range of dry density and clay content tested, the shear strength of silty soil in the low stress range obtained is higher than the measured value. Therefore, for the shallow damage of soil site, the shear strength parameters should consider the low stress test conditions. The bilinear growth of cohesion c with clay content can be attributed to the changes from “sand-like soil” to “clay-like soil” with the skeleton of soil specimen transitioning from sand particles to “clay grid” when the clay content exceeds approximately 10% combined with the results of scanning electron microscopy.