Granular materials are a useful analogue for the Earth's crust in laboratory models of deformation. Constraining their mechanical properties is critical for such model's scaling and interpretation. Much information exists about monomineralic granular materials, such as quartz sand, but the mechanical characteristics of bimineralic mixtures, such as commonly-used quartz sand mixed with gypsum powder (i.e. plaster), are largely unconstrained. We used several mechanical tests (density, tensile, extension, shear) to constrain the failure envelope of various sand-plaster mixtures. We then fitted linear Coulomb and parabolic Griffith failure criteria to obtain cohesions and friction coefficients. Tests of the effects of emplacement technique, compaction and humidity demonstrated that the most reproducible rheology is given by oven-drying, pouring and mechanically compacting sand-plaster mixtures into their experimentation container. As plaster content increases, the tensile strength of dry sand-plaster mixtures increases from near zero (pure quartz sand) to 166 ± 24 Pa (pure plaster). The cohesion increases from near zero to 250 ± 21 Pa. The friction coefficient varies from 0.54 ± 0.08 (sand) to 0.96 ± 0.08 (20 wt% plaster). The mechanical behaviour of the resulting mixtures shifts at 20–35 wt% plaster from brittle Coulomb failure along a linear failure criterion, to more complex brittle-plastic Coulomb-Griffith failure along a non-linear failure criterion. With increasing plaster content, the brittle-plastic transition occurs at decreasing depth within a pile of sand-plaster mixture. We infer that the identified transitions in mechanical behaviour with increasing plaster content relate to (1) increasing porosities, (2) increasing grain size distributions, and (3) a decrease in sand-sand grain contacts and corresponding increase in contacts of anisotropic gypsum-gypsum grains. The presented characterisation enables a more quantitative scaling of the mechanical behaviour of sand-plaster mixtures, including their tensile strength. Sand-plaster mixtures can thereby realistically simulate brittle-plastic properties of the Earth's crust in scaled laboratory models.

在实验室变形模型中，颗粒材料是地壳的有用类似物。约束它们的机械性能对于此类模型的缩放和解释至关重要。关于单矿物颗粒材料（如石英砂）的信息很多，但双矿物混合物（如常用石英砂与石膏粉（即石膏）混合）的机械特性在很大程度上不受限制。我们使用了几种机械测试（密度、拉伸、延伸、剪切）来约束各种砂灰泥混合物的破坏范围。然后我们拟合线性库仑和抛物线格里菲斯破坏准则以获得内聚力和摩擦系数。对放置技术、压实和湿度影响的测试表明，最可重现的流变学是通过烘箱干燥，将砂膏混合物倒入并机械压实到他们的实验容器中。随着石膏含量的增加，干砂-石膏混合物的拉伸强度从接近零（纯石英砂）增加到 166 ± 24 Pa（纯石膏）。内聚力从接近零增加到 250 ± 21 Pa。摩擦系数从 0.54 ± 0.08（砂）到 0.96 ± 0.08（20 wt% 石膏）。所得混合物的机械性能在 20-35% 的灰泥中从沿线性破坏准则的脆性库仑破坏转变为沿非线性破坏准则的更复杂的脆性-塑性库仑-格里菲斯破坏。随着灰泥含量的增加，脆塑性转变发生在砂灰混合物堆内的深度减小处。我们推断，随着石膏含量的增加，机械行为的确定转变与（1）孔隙率的增加，（2）粒度分布的增加，以及（3）砂砂颗粒接触的减少和各向异性石膏接触的相应增加有关。石膏粒。所呈现的表征能够对砂灰泥混合物的机械行为进行更定量的缩放，包括它们的拉伸强度。因此，砂膏混合物可以在按比例缩放的实验室模型中真实地模拟地壳的脆塑性特性。所呈现的表征能够对砂灰泥混合物的机械行为进行更定量的缩放，包括它们的拉伸强度。因此，砂膏混合物可以在按比例缩放的实验室模型中真实地模拟地壳的脆塑性特性。所呈现的表征能够对砂灰泥混合物的机械行为进行更定量的缩放，包括它们的拉伸强度。因此，砂膏混合物可以在按比例缩放的实验室模型中真实地模拟地壳的脆塑性特性。