The Influence of Preconsolidation Pressure on Undrained Shear Strength Characteristics of Peaty Clay in Sri Lanka

This research study investigated the effect of preconsolidation pressure on the shear strength parameters of very soft peaty clay based on a series of laboratory tests. The study included 15 Consolidated Undrained (CU) triaxial tests on peaty clay extracted from the Nilwala river basin, with preconsolidation pressures ranging from 0 to 100 kPa in 20 kPa intervals and cell pressures of 50, 100 and 150 kPa. The results indicated that the peak deviator stress of peaty clay decreased with increasing preconsolidation pressure, indicating decrease in its shear strength parameters with preconsolidation pressure. It was observed that peaty clay is highly sensitive to disturbance and requires sufficient time to regain its shear strength once its natural microstructure is altered. The study has significant implications for the construction of embankments on soft soils, particularly peaty clays. It highlights the need for accurate estimation of the undrained shear strength parameters of peaty clay, considering soil composition, structure and type of loading. It also emphasizes the importance of minimizing disturbance during construction activities to avoid compromising the stability of embankments.