Quasi-brittle fracture in geo-materials plays a crucial role in geotechnical engineering, and numerical methods represent a valuable approach for modeling this complex problem. This study introduces a mixed bilinear failure model considering bond effects in a modified Discontinuous Deformation Analysis (DDA) framework. Several benchmark crack-propagation problems for different materials and geometries, including three-point beam, Lshaped structure, semi-disc test and cemented granular packing, are presented to validate the novel DDA method proposed in this study. The simulation results show the accuracy of the model in predicting the mixed-mode failure of quasi-brittle materials with complex structures and assess its great potential for investigating the mechanical properties of geo-materials.

This study investigated the effect of compaction effort and soaking time on the shear strength properties of fine-grained gypsum-containing soils. The objective was to demonstrate that increasing compaction effort increases soil strength, specifically cohesion and the angle of shear strength, when subjected to soaking in freshwater. Unconsolidated undrained triaxial tests were carried out on CBR soil samples with different soaking times. The results showed a transition from brittle to ductile failure behaviour as the soaking time increased. Mohr-Coulomb failure envelopes showed reduced cohesion and angle of shear strength with increasing soak time. Regression models were developed to establish correlations between soaked and unsoaked strength parameters. Strong relationships were found between soil strength properties, compaction effort and soaking time. Empirical equations were proposed to estimate the cohesion and angle of shear strength from compaction effort and soaking time. This study highlighted the importance of considering gypsum-rich soils in civil engineering design. Gypsum dissolution during wetting significantly affected soil strength parameters. The regression models and empirical equations provide engineers with tools to assess the influence of compaction effort and soaking time on soil strength, thus aiding decision making when designing structures on gypsum-rich soils.