Search

Naturally formed soils (e.g., residual soils and deposit clays) usually show an absent range of particle size. Frequently used by geotechnical communities worldwide, such gap-graded soils can be simplified as binary mixtures composed of fine soil matrix and coarse rock aggregates. In this study, an elastoplastic model is proposed for gap-graded soils based on a volume average scheme and homogenization theory. The proposed model incorporates a structural variable to account for the evolution of the inter-granular skeleton of rock aggregates. The model is then implemented in a numerical code by the linearized integration technique proposed by Bardet and Choucair (1991). It is shown that the model can predict a wide range of variations of the overall shear responses with the increase in volume fraction of rock aggregates. An isotropic loading induces a nonuniform stress distribution in gap-graded soils, where the stress in the soil matrix is lower than that of the rock aggregates. The stress path of the matrix is approximately parallel with that of the rock aggregates during triaxial shear loading. The proposed model contains only one additional structure parameter compared with the generalized modified Cam clay model, which can be easily calibrated from the data of a conventional triaxial compression tests. Comparison between our model predictions and the experimental data from literature indicates that the propose model can well reproduce the mechanical responses of gap-graded soils within a wide range fraction of rock aggregates.

In this paper, the compression behavior of sand-marine clay mixtures was investigated, both experimentally and theoretically. The test data reveal that the Normal Compression Line of a sand-clay mixture depends on both the sand fraction and the initial water content of the clay matrix. The local stress in the clay matrix σ ′ c is approximately close to the overall stress of the sand-clay mixture σ′ for a sand mass fraction of 20%. The stress ratio, σ′ c / σ′ , falls significantly with increasing overall stress for a sand fraction of 60%, which may be attributed to the formation of clay bridges between adjacent sand particles. A compression model was formulated within the homogenization framework. First, a homogenization equation was proposed, which gives a relationship between the overall stiffness E and that of the clay matrix Ec . Then, a model parameter ξ was incorporated considering the sensitivity of the structure parameter on the volume fraction of the clay matrix. Finally, a simple compression model with three model parameters was formulated using the tangent stiffness. Comparisons between the experimental data and simulations reveal that the proposed model can well represent the compression curves of the sand-marine clay mixtures observed in the laboratory.

Fresh lumpy soils from open-pit mining have a relatively open structure, which transforms gradually into a lumpy composite structure due to weathering factors. The resulting lumpy composite soils consist of natural stiff lumps and a reconstituted soil within the inter-lumps space. The stress and strain distributions are not uniform, since there is a significant difference of the stiffnesses for these two constitutes. The lumpy soils with a composite structure are investigated in this paper, both experimentally and theoretically. First, the volume of the lumpy composite soil is divided into separate parts and the evolution of the volume fraction of the lumps is considered. A nonlinear Hvorslev surface considering soil structure is proposed for the lumps on the dry side of the critical state and evaluated based on laboratory data. Finally, a simple model for the lumpy soils is proposed within a homogenization framework. Comparisons between the experimental data and simulations reveal that the proposed model can well represent the stress–strain and volume deformation behavior observed in the laboratory.

Clay mixture is a waste material in open pit mining from the excavation of various soil layers. In the present study, a general constitutive framework is proposed for the prediction of compressibility of remolded clay mixtures. First, the resulting structure of a clay mixture is simplified as a composite structure, in which the elements of the constituents are randomly distributed in a representative elementary volume. Afterwards, the initial water contents of the constituents are estimated based on a simplified model for the undrained shear strength of the clay mixture. Then, the representative elementary volume of the mixed soil is divided into separate individual parts and the volume fractions of the constituents are formulated as functions of the overall porosity and those of the constituents. Finally, a homogenization law is proposed based on the analysis of the randomly arranged structure together with a simple compression model for clay mixtures. Parameters required by the model correspond only to the constituents, which are simple to calibrate based on standard laboratory tests. By making comparisons of the predictions with test data, it is shown that the proposed model can well represent the compression behavior of the clay mixtures.

Sandstone usually disintegrates into gap-graded granular materials with a matrix-sustained structure due to weathering factors. This paper presents an investigation on the small strain stiffness of this type of granular materials based on Discrete Element Method (DEM) simulations. Our numerical results indicate the percentage of sliding contact is negligibly small within the small strain range, and the small strain stiffness of fines is well consistent with the widely recognized Hardin’s equation. Both findings confirm the validity of DEM simulations on the study of small strain response of granular materials. The simulation results are further analyzed based on mixture theory. A structure variable is introduced to correlate with the evolution of inter-aggregates structure. This variable is found to increase with the volume fraction of coarse aggregates but is rather independent of the confining stress and the initial void ratio of the fine matrix. Based on the insights drawn from DEM simulations, a homogenization equation is proposed for the small strain stiffness of gap-graded granular soils to reproduce the small strain stiffness of gap-gaped materials observed in our numerical simulations and is further validated by laboratory test data from the literature. The equation can be conveniently incorporated into classical elastoplastic models to model gap-graded granular materials.

For the excavated clayey cover of a coal seam in open-pit mining, the shear strength is the most important issue after its deposition in landfills. For this purpose, an artificial lumpy material was investigated in this paper. A transition form between a reconstituted soil and natural lumpy soil governs the mechanics of the soils artificially deposited after the excavation. This paper presents triaxial and oedometer tests (including K0 and isotropic consolidation tests conducted in triaxial cell) both on an artificial lumpy soil and its corresponding reconstituted form. Compression, permeability and strength of lumpy materials have been evaluated. When normalized by Hvorslev pressure, the shear strength of both lumpy materials and reconstituted soil lies on unique lines, with strength parameters of the lumpy materials lower than that of the reconstituted soil. Both the consolidation and triaxial test results indicate that the reconstituted soil, which exists in the inter-lump voids, plays a crucial role in the behaviour of lumpy materials.

Heat production (HP; indirect calorimetry) of six Large White castrated sows (mean BW 208 kg) kept individually in metabolism cages at 24°C and fed once a day (d) at about maintenance energy level (415 kJ ME/kg BW 0.75 ) and their physical activity (standing versus lying) were recorded continuously over 24 h after a meal. Each measurement lasted 5 consecutive days and was repeated 8–10 times for each sow over 9 months. HP related to activity (AHP) was calculated according to a statistical model in which HP was a function of time after the meal and standing activity. Resting heat production (RHP) corresponded to the difference between HP and AHP. HP and AHP averaged 402 kJ kg BW −0.75 d −1 and 14.9 kJ/min (or 0.26 kJ kg BW −0.75 min −1 ), respectively. Mean duration of daily activity was 241 min. AHP was then equivalent to 62 kJ kg BW −0.75 d −1 or 15% of HP. Consequently, RHP averaged 340 kJ kg BW −0.75 d −1 . Minimum RHP (23 h after the meal) was 290 kg BW −0.75 d −1 . These values were significantly different between sows. Meal duration averaged 14 min. Variations in activity, total HP and RHP over the day are presented. The mean increment of HP related to food intake represented about 15% of ME supply. Compared to other species, the energy requirement for standing activity in pigs is distinctly higher.