Study on strength properties and soil behaviour type classification of Yellow River Delta silts based on variable rate piezocone penetration test

Fine-grained silt is widely distributed in the Yellow River Delta (YRD) in China, and the sedimentary structure is complex, meaning that the clay content in the silt is variable. The piezocone penetration test (CPTu) is the most widely approved in situ test method. It can be used to invert soil properties and interpret soil behavior. To analyse the strength properties of surface sediments in the Yellow River Delta, this paper evaluated the friction angle and its inversion formula through the CPTu penetration test and monotonic simple shear test and other soil unit experiments. The evaluation showed that the empirical formula proposed by Kulhawy and Mayne had better prediction and inversion effect. The Yellow River Delta silts (YRD silts) with clay contents of 9.2 %, 21.4 % and 30.3% were selected as samples for the CPTu variable rate penetration test. The results show that: (1) The effects of the clay content on the tip resistance and the pore pressure of silt under different penetration rates were summarized. The tip resistance $ {Q}_{t} $ is strongly dependent on the clay content of the silt, the $ {B}_{q} $ value of the silt tends to 0 and is not significantly affected by the change of the CPTu penetration rate. (2) Five soil behavior type classification charts and three soil behavior type indexes based on CPTu data were evaluated. The results show that the soil behavior type classification chart based on soil behavior type index $ {I}_{SBT} $, the Robertson 2010 behavior type classification chart are more suitable for the silty soil in the Yellow River Delta.