Advanced laboratory testing of a sand-resin mixture liquefaction mitigation measure

Abstract

In the framework of a third Tagus River crossing, through an immersed tunnel, a novel liquefaction mitigation measure, namely injection of a duromeric expansive polyurethane resin, was tested on its highly liquefiable foundation sand. Three laboratory injection tests were executed: the first consisted in injecting a central column, inside a specifically designed box filled with Tagus River sand, to characterize the properties of the sand-resin mixture (SRM); the second and third comprised injecting five separate columns each, with different replacement ratios, to measure the effect of the injection on the sand densification between columns. An injection rod withdrawal rate (IRWR) of 0.01 m/90 s, 0.01 m/10 s and 0.01 m/15 s was used for the first, second and third tests, respectively. Specimens were core drilled from the injection test’s columns, SRM behaving like a single-phase material. To characterize the SRM cyclic behaviour and to provide high quality data, essential to calibrate advanced constitutive models used in the design of the tunnel, laboratory tests were performed on the specimens, of which four cyclic torsional tests are presented in this paper, using two specimens from the columns of the second and third tests, respectively (base and top). In these tests, imposed strain increased progressively up to the maximum strain that could be applied in LNEC’s torsional shear device, without slipping at the top of the specimen. Therefore, it was possible to analyse the amplitude, damping ratio and shear modulus of the cycles and characterize some elastic properties of the SRM.