Laboratory investigation of two basic configurations for inhomogeneous soils

Lumpy soils are inhomogeneous materials which can be encountered in land reclamation and open pit mining. The lumps are randomly distributed in the reconstituted soil but on a mesoscale their configuration can be expressed by two simplified configurations of both constituents. In order to investigate the behaviour of these two basic configurations, isotropically consolidated drained triaxial shear tests were performed on artificially prepared specimens with parallel and series structures. The laboratory tests show that the failure plane of the series specimens is located in the constituent with the lower strength; the specimens with the parallel structure have a failure plane which crosses both constituents. As a result, the shear strength of the series specimens is only slightly higher than that of the constituent with the lower strength and the strength of the parallel specimens lies between those of the constituents. Furthermore, the maximum volumetric strain of the series specimens is lower than that of its constitutes, which is significantly different from that of the parallel specimens. The stress concentration ratio of the parallel specimens μ_σ^*, B, defined as the ratio of stress in the stiffer constituent to that of the weak one, increases with the consolidation stress; while, the strain concentration ratio of the series specimens μ_ε^*, B, defined as the ratio of strain in the stiffer constituent to that of the weak one, is not sensitive to the consolidation stress.