Mechanical Properties and Seismic Isolation Mechanism of Foamed Concrete Longitudinal Joints of Tunnel in Rock

Abstract

Foamed concrete has excellent shock absorption properties, so it can be used as one type of seismic isolation material for tunnels. The objective of this study is to investigate the mechanical properties and seismic isolation mechanism of foamed concrete longitudinal joints. In this paper, under the moderate strain rates (10⁻⁵ s⁻¹–10⁻² s⁻¹), a series of uniaxial and triaxial compression tests were conducted to study the effects of density, confining pressure and strain rate on the mechanical properties of foamed concrete. The test results showed that the strength of foamed concrete grows with the increase of the density. Besides, the foamed concrete has the high volumetric compressibility and rate dependence properties: (1) as the confining pressure increases, its strength increases; (2) as the strain rate increases, its strength increases logarithmically. Then, based on the test results, a rate-dependent constitutive model of foamed concrete was chosen and the fitting parameters involved the model were obtained. Finally various parametric studies were performed to study the influence of density, thickness and spacing on the seismic isolation effect of tunnel joints. It found that the seismic isolation effect would be better when the density is lower, the thickness is thicker and the spacing is smaller.