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UBC Theses and Dissertations

Characterisation and modelling of a uniformly graded, well-rounded coarse sand Rouse, Pascale C.


Strength parameters and intrinsic properties of sand are very important for engineering design. It is well known that such properties depend on factors including grain size distribution, fines content, mineralogy and grain shape. Recently, several authors have sought to establish a relation between the constant volume friction angle, as well as the maximum and minimum void ratios, and the roundness of the sand grains. Little information exists on well-rounded sands. A series of triaxial tests were performed on a uniformly graded, well-rounded coarse sand (R=0.81). Interpretation of the results confirms the available relations, and provides a link between the data on commonly found sands (0.2<R<0.7) and glass beads (R≅1.0). Additionally a comparison of drained and undrained triaxial test data indicates ϕ[sub MC] ≅ ϕ[sub PT] ≠ cv, ϕ[sub CV] ≅ϕ[sub MO], ϕ[sub MO] ≅ϕ[sub PT] + 3° and ϕ[sub CV] is very similar to ϕ[sub rep]. The behaviour of the well-rounded sand is modelled using the critical state soil mechanics constitutive model, NorSand. The results show that the parameters needed for the model fall within the expected range of values, and that NorSand captures both the drained and undrained response of the sand in triaxial testing. However, the volumetric coupling coefficient N, shows an unusual value indicative of unusual dilation of this sand. To account for this, a modification of the flow rule is proposed. In addition, the NorSand constitutive model is implemented in the commercially available software FLAC. For this, the standard method used within FLAC, F=0, will not work. But by solving F = 0 it is possible to introduce any critical state soil mechanics (CSSM) constitutive model. This approach is described in detail for two selected CSSM models, Original Cam Clay and NorSand.

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