A model for rockfill compressibility

Abstract

The paper presents a macroscopic constitutive model for rockfill that includes the effect of water on compressibility and collapse phenomena. Breakage of rock particles and fracture propagation are basic underlying mechanisms controlled by the relative humidity of the air filling the rockfill voids. A conceptual deformation model based on these mechanisms is first proposed and discussed. The results of oedometer tests on a quartzitic slate rockfill, in which the air relative humidity was controlled, are then presented. A significant finding is that bringing the relative humidity within the specimen to its maximum (100% RH) leads to a collapse strain equal to that observed in flooded specimens. An elastoplastic constitutive model, consistent with the basic deformation framework, is developed. Its parameters have a clear physical meaning. Guidelines for parameter determination are given. Model performance is finally compared with the results of the experimental programme.

Discussion: Theoretical investigation of the time-dependent behaviour of rockfill

“…a preconsolidation stress) was not observed during compression of the specimens from zero up to 2 . 8 MPa (Oldecop & Alonso, 2001). In fact, the material experienced permanent strains from the very beginning of the loading path.…”

“…The slope and position of those lines seem to be completely determined by the stress and total suction applied to the material (Oldecop & Alonso, 2002). The authors' research work related to rockfill materials, presented in the reference paper and in some previous works (Chávez & Alonso, 2003;Oldecop & Alonso, 2001;2002; is oriented towards the formulation of phenomenological constitutive equations capable of predicting the behaviour of rockfill under complex mechanical and environmental actions. Such conditions typically occur in engineering structures, such as embankments and dams, and moreover they may vary with time and combine in arbitrary loading sequences and cycles.…”

Study on collapse behaviors of coarse grained soils

“…For low plasticity unsaturated clay, it is accepted that with the increase of the water content results in decrease in matric suction (u a − u w ), thus, wet-induced deformation occurred. But the mechanism of coarse soil's collapse behavior was somewhat different from clay's, It was likely to be caused by breakage and rearrangement of soil particles which were affected by water content (Oldecop & Alonso 2001) [3].…”

“…Nobari & Duncan (1972) [4] conducted triaxial tests with soils in both dry and wet state separately, the strain difference between dry specimen and wet specimen was thought as the collapse strain when they at the same stress state. However, many scholars (Zuo & Zhang et al 1989, Shen & Yin 2009 [5,6] thought that stress paths were not consistent with the soils actually experienced in this method, they suggest a so-called "single triaxial test method", i.e. in the collapse test, kept the stress state of dry specimen constant, then flooded the specimen, additional deformation during this period was thought to be the collapse deformation.…”

An Elastoplastic Model for Unsaturated Rockfills and its Simulations of Laboratory Tests

“…As the saturation collapse is the phenomenon that arises from the breakage of rock particles, most of the deformations should be regarded as plastic deformations. Oldecop and Alonso (2001) proposed an elastoplastic model that was only valid to express compression properties of unsaturated rockˆlls. Thus elastoplastic models, which can describe the saturated and unsaturated mechanical behavior (both compression and shear) of rockˆlls, have not been proposed.…”