<p>This study investigates the mechanical behaviour of face mask chips-sand mixture (MSM) from experiments to constitutive modelling. The length-to-width ratio of mask chips is focused as a main factor in this study when preparing MSM samples mixed with Fujian sand. A series of drained triaxial tests are conducted to examine the influence of mask chips on the mechanical behaviour and properties of MSM. Next, the critical state theory and a non-associated flow rule are adopted to model the behaviour of MSM within the framework of elastoplasticity. A new parameter (<i>p</i>_<i>R</i>) is introduced into the yield function, plastic potential, critical state line, and elastic modulus of the SIMSAND model to characterize the tensile strength induced by mask chips. As a result, the strength and deformation characteristics of MSM with different relative densities under various loading conditions are properly modelled. All results demonstrate that the proposed model is applicable to construction projects relating to MSM.</p>