Static and Dynamic Properties of Leighton Buzzard Sand from Laboratory Tests

The Leighton Buzzard sand is an English sand commonly used at the University of Bristol to study soil-shallow foundation interaction (Maugeri et al., 1999a; 199b) and soil-retaining wall interaction (Carafa et al., 1998) by means of the shaking table. These experiments require an accurate definition of geotechnical characterisation of soil. To define the mechanical behaviour of uncemented Leighton Buzzard sand a large number of static and dynamic laboratory tests were performed on dry reconstituted specimens. The static tests includes direct shear tests performed on specimens reconstituted by pluvial deposition method with different relative density Dr. To evaluate the equivalent shear modulus Geq and damping ratio D, resonant column tests and torsional shear tests were performed by mean of Resonant Column/Torsional Shear apparatus. The secant shear modulus Gs had evaluated during monotonic torsion tests by means of the same apparatus. Particular attention was devoted to the shear modulus at very small strain (g < 10-3 %) where the soil behaviour is supposed to be elastic and at intermediate strain level (from 10-3 % to 0.5 %) for simulating the prefailure deformation during the shaking table tests. The behaviour of soil at intermediate strain level is relevant for the serviceability limit state according the European Codes (EC7 and EC8). The dry reconstituted samples were subject to an initial anisotropic confining pressure able to simulate in situ effective stress status. Finally, two expressions to allow the complete shear modulus degradation with strain level and the inverse variation of damping ratio with normalised shear modulus respectively were proposed.