Modeling unconfined compressive strength of fine-grained soils: Application of pocket penetrometer for predicting soil strength

Abstract

Abstract In recent years, the pocket penetrometer (PPT) test has been used to measure soil compaction and has gained attention due to its simplicity, high speed, and low cost. This study aimed to predict soil strength using a regression relationship between unconfined compressive strength (UCS) and PPT. We collected 45 large soil samples from a forest district in a part of the Hyrcanian Forest. In the laboratory, soil samples were classified according to unified soil classification system. Samples were classified as either silt or clay with a low or high liquid limit. These four soil groups were, brought to four different moisture contents (14%, 25%, 31%, and 36%; n\xa0=\xa0180 measurements). Samples were then brought to a constant dry unit weight (1.387\xa0kg/m3). Once the samples were prepared, we measured soil compression strength using a PPT and then determined UCS. We modeled our lab results to determine if PPT could be used as a surrogate for UCS. As soil moisture content increased UCS decreased non-linearly. The behavior of silt and clay with low liquid limit plasticity were similar; likewise, the silt and clay with high liquid limit plasticity produced similar results. According to the values of Eta-squared, soil moisture is more important factor than soil type class in explaining the variance of UCS. In addition, PPT data can accurately predict soil UCS (R2\xa0=\xa00.98). Therefore, PPT data can be used to predict UCS of fine-grained soils with good accuracy and very low cost.