**Abstract**



The rapid expansion of satellite cities surrounding metropolises such as Tehran, driven by the dominance of physical and engineering-oriented approaches over social dimensions, has led to profound crises in social sustainability. This study aims to assess the status of social sustainable development in Qarchak City and identify the root causes of unsustainability, with an emphasis on modeling causal relationships among indicators. The research employs an applied-developmental approach with a descriptive-analytical nature; data were collected via a structured five-point Likert-scale questionnaire from 47 experts, urban managers, and planners. Data analysis utilized one-sample t-tests, Wilcoxon tests, and structural equation modeling based on partial least squares (PLS-SEM). Statistical findings reveal that social sustainability in Qarchak is at a critical level, with an overall mean of 2.22, and the dimension of "spatial and physical justice" exhibiting the lowest status (mean = 2.04). Confirmatory factor analysis (CFA) results indicate that "access to education" (factor loading = 0.728) and "trust in urban management" (factor loading = 0.79) are the most critical drivers of social sustainability. The study's innovation lies in elucidating the "physical failure–social erosion" mechanism, which demonstrates that inequalities in urban service distribution are not merely technical issues but fundamental factors fostering perceptions of discrimination and diminishing place attachment. The findings underscore the urgent need for revising Qarchak's urban development plans and strengthening local governance, with a focus on regenerating spatial justice.