Assessment of Dynamic Soil Stiffness of Lump-Sand Mixtures: Insights from Bender Element Tests
摘要
The present study examines shear wave velocity (Vs) and the small-strain shear modulus (Gmax) through bender element (BE) testing on lump-sand mixture from the Middle Ganga Plain, considering different lump contents, confining pressures, and moisture states. BE tests were carried out on various proportions of cohesive lump-sand mixtures, as well as on pure sand and pure lump specimens, under completely dry and fully saturated states. Confining pressures ranging from 0 to 400 kPa (0, 100, 200, 300, and 400 kPa) were applied, and excitation frequencies between 1 and 30 kHz were used to evaluate their influence on Vs and Gmax. In fully dry conditions, the results show a clear increase in Gmax with increasing lump content. At zero confining pressure, Gmax rises from 65.90 MPa for pure sand to about 165.70 MPa for pure lump, representing an increase of about 151% and at 400 kPa confining pressure, Gmax value of 215.66 MPa increases to 269.58 MPa showing 20% increase. This indicates a diminished influence of lump content at higher confining pressures for fully dry sand. In contrast, under fully saturated conditions, Gmax decreases significantly with increasing lump content. At a confining pressure of 100 kPa, Gmax reduces from about 103 MPa for pure sand to 35.10 MPa for pure lump, corresponding to a reduction of 65%. Even at higher confinement (400 kPa), Gmax decreases substantially from 224.80 MPa to 67.40 MPa, indicating pronounced stiffness degradation of lump-rich mixtures in the presence of water. Several empirical relationships between Gmax and confining pressure were established to provide valuable insights for predicting several dynamic soil parameters in regions with similar lump-sand mixtures. Additionally, the study underscores the profound impact of saturation on Vs, with fully saturated samples exhibiting lower Gmax values compared to their dry samples. This research enhances the understanding of the behaviour of lump-sand mixtures under seismic loading, offering essential data for seismic hazard assessments and guiding earthquake-resistant infrastructure, particularly in regions such as the Middle Ganga Plain (MGP) in India.