An elastic-viscous-plastic structured UH model

On the basis of the structured unified hardening model (structured UH model) considering soil structured collapse, the time effect is take into account, and an elastic-viscous-plastic structured UH model is extended. In the presented model, the moving normal compression line (MNCL) is extended to a moving instant normal compression line (MINCL) for simulating both soil structure effect and time effect. Then the instance plastic strains irrespective of time effect are calculated by referring the MINCL, and the plastic strains due to time effect are calculated by referring the traditional instant normal compression line. Comparisons between test data and model simulation indicate that the presented elastic-viscous-plastic structured UH model is qualified to simulate the combined actions of soil structure and time effects both in compression and in shearing.

A single-stress model for the prediction of yielding of unsaturated cemented soils under isotropic loads

This paper presents a bounding surface model predicting the combined effects of cementation and partial saturation on the mechanical behaviour of soils subjected to isotropic loading. The loss of cementation caused by loading, wetting or drying of a normally consolidated soil is described by a “cementation bonding function”. This states that, under virgin conditions, the ratio between cemented and uncemented void ratios monotonically decreases with increasing levels of scaled stress. The scaled stress is the variable governing the intrinsic behaviour of the soil under both saturated and unsaturated conditions. Combination of the cementation bounding function with a previously proposed model for unsaturated soil behaviour leads to the formulation of a “cemented unified normal compression line” (CUNCL). This describes the virgin behaviour of both cemented and uncemented soils under saturated and unsaturated conditions. Progressive yielding is modelled by assuming that the slope of the generic loading curve tends towards the slope of the CUNCL as the soil state moves from overconsolidated to virgin conditions. The model has been calibrated and validated against existing experimental data demonstrating a good ability to predict the void ratio of cemented soils during isotropic loading, unloading and wetting under both saturated and unsaturated conditions.

An Earthquake Nest in Cascadia

We investigate an isolated cluster of temporally persistent, intraslab earthquakes (ML<3.2) at >60 km depth below the Georgia Strait in southern British Columbia that is unique in Cascadia and meets the criteria for identification as an earthquake nest. A total of 129 relocated hypocenters define two northwest‐dipping structures in the subducting Juan de Fuca mantle within an ∼30×10×10 km3 volume. Focal mechanisms for 15 events represent a mix of strike‐slip and reverse faulting, and a stress regime of down‐dip tension and plate‐normal compression, consistent with a previous regional study. Converted seismic phases inferred to originate at the boundaries of subducted oceanic crust are observed at several receivers and are consistent with a local slab depth of ∼45 km, shallower than some JdF plate models. The geographical isolation of the nest within the confines of an extrapolated propagator wake suggests that its location is controlled by this pre‐existing and presumably hydrated structure.

Mechanical behaviour of Panzhihua iron tailings

Safety problems have concerned many researchers studying tailings dams in recent years, as they have a high risk of failure due to liquefaction. Existing analysis of liquefaction in tailings within a critical state framework has relied on the critical state line (CSL) being unique in the volumetric plane. However, recent advances have highlighted a so-called “transitional” behaviour in which the location of the normal compression line (NCL) and CSL is a function of the density of the soils at deposition. This paper presents a detailed investigation of the mechanics of tailings taken from three locations of an iron tailings impoundment. Reconstituted samples were prepared by different methods and at different densities. No transitional behaviour was found, although the results show that the rate of convergence of the compression curves changes, with the finest pond material reaching a unique NCL earliest. The preparation method was found not to have a large effect on the behaviour for these tailings. Unique CSLs could be clearly identified for all the three tailings, but with different shapes, giving rise to a changing susceptibility to liquefaction. This susceptibility tends to increase from the pond to the upper beach.