<p>This study aims to investigate the installation effects of stone columns in weak soils involving loose sand and sabkha. Analytical and numerical methodologies were utilized. A closed-form solution for the induced horizontal stress was derived. The cylindrical-cavity-expansion method was employed to simulate the lateral displacement induced during the installation and its effects on soil properties. The parameters studied included percentage of cavity expansion, column length, initial soil stiffness, and column configurations. The properties included the lateral earth pressure coefficient (K), soil stiffness (E), and load-bearing capacity. Results showed that cavity expansion increases K up to 4.1. The improvement in E of sand is 72% and only a small improvement in the case of sabkha, 18%. Shorter columns gave higher values for K (for sand K = 3.3 for 4 m vs. 1.35 for 12 m), while those for sabkha were 2.7 and 0.9, respectively. The effects on the load-bearing capacity are significant. At a settlement of 50 mm and high cavity expansion, the capacity increased to 443% for sand and to 152% for sabkha. For sand, the group effect on K/K_i is found to be 120 and 128% for spacings of 10 and 15 m, respectively. The corresponding effect on E/E_i is only 26 and 19%. For sabkha, the group effect on K/K_i is 205, 130 and 90% for spacings of 5, 10 and 15 m, respectively. The corresponding effect on E/E_i is only 10, 7 and 7%. Passive failure was observed at high percentages of cavity expansion for the single column, and at low cavity expansion for the group with close spacing. The results were compared with each other and with those reported in the literature from field observations.</p>