Determination of maximum shear modulus of dry sands using piezoelectric Bender elements

Stress-strain behavior of soils under loading is elasto ? plastic and it varies within a wide range of strains. Typically, the range of shear strains is between 10-6%-10% which also has a non-linear distribution. Instead of this range, it is sufficient to consider shear strains larger than 10-4% practically for steady-state problems. However, it is necessary to evaluate this wide range of strains for steady state analyses, such as dynamic stress-strain analyses and soil movements around an excavation. The most important material property for such analyses is initial modulus of elasticity or shear modulus. In-situ and laboratory testing methods are devised to determine these modules. In this study, it is aimed to determine the initial (maximum) shear modulus of dry sand samples under varying relative densities and cell pressures using piezoceramic bender elements applied to the laboratory triaxial testing equipment. Within the context of this thesis, the small strain shear wave velocity of a dry sandy soil is measured for which large shear strain values ( ?? =%10--4) were previously determined through dynamic simple shear testing. Şile Sand is used in these tests. A special triaxial compression cell, in which piezoceramic bender elements are placed, is utilized for testing loose (Dr=%30), medium dense (Dr=%50) and dense (Dr=%70) samples subjected to cell pressures of 0, 50, 100, 150 ve 200 kPa. Tests are conducted on dry sand samples. In these tests, an excitation voltage (20 Vp-p) and different input signal frequencies (1-1.5-2-4-6-8-10-12-15 and 20 kHz) produced by the function generator are applied to the transmitter bender element and measured with an oscilloscope. The measured travel times are identified with the first arrival time (ta) and first peak-to-peak time (tp) methods.The shear wave velocities obtained with these two methods varied between 1.4 to 1.6 %. Based on the test results, it is observed that the shear moduli and shear wave velocities increased with increasing cell pressures and applied signal frequency.