A three-dimensional micromechanical damage model that enables the simulation of mechanical response of microcrack-weakened quasi-brittle solids is presented. The occurrence of residual strains is attributed to two reasons, namely, the release of preexisting residual stresses due to microcracking and the microscopic plastic deformation near crack tips. An approximate scheme is proposed to estimate effects of microcrack interaction on the overall effective moduli of a quasi-brittle material subjected to complex loading.