This paper presents a fairly comprehensive experimental study on the failure stresses of LECA grains, with diameters ranging from 12 to 20 mm. With that purpose, more than 700 LECA grains were driven to failure under uniaxial and biaxial load conditions by applying forces using a standard PLT apparatus and an additional tool able to exert horizontal forces, specially designed and manufactured for this investigation. The whole equipment allows controlling and measuring the value of the forces applied on two perpendicular axes while the test is running. The results were analyzed by a probabilistic approach using Weibull distributions with the octahedral shear stress as failure criterion. Additionally, the average diameter, sphericity and weight density of all the grains failed were determined to correlate them with their octahedral shear stress at failure. Based on the results, a new model is proposed that allows estimating the failure stress according to a Weibull distribution that depends on grain diameter and weight density. (c) 2021 Elsevier B.V. All rights reserved.