Gravel impact compaction piers (GICPs) and Cement-gravel impact compaction piers (C-GICPs) have been established as a reliable method for soil improvement, particularly for silty and clayey soils with a soft to medium consistency and sandy soils with a low to medium relative density. The primary objectives of using C-GICPs are to enhance bearing capacity, reduce settlement, and prevent local shear failure. Given their technical and economic advantages, these piers are a promising option for the rehabilitation of weak coastal and liquefiable soils. This research presents a simplified method for predicting the primary parameters of the composite soil bed following soil improvement. To optimize soil improvement parameters, including pier spacing, diameter, and length, in both square and triangular patterns, a field study was conducted in a soft, silty clay soil located in Bandar Bushehr, southern Iran. The study aimed to prevent liquefaction and local shear failure at the top of the piers and to validate the proposed theoretical framework. In this study, a total of 32 piers were installed, including 8 cement-treated impact-compacted sand piers with a length of 5 meters, 8 cement-treated impact-compacted sand piers with a length of 3 meters, and 8 conventional impact-compacted sand piers with lengths of 5 and 3 meters. Standard penetration tests and plate loading tests were conducted on the soil between the piers to compare the effects of pier length and cementation on improved soil parameters, soil compaction around the pier, and the elimination of local shear failure at the top of the pier. Additionally, the compaction properties and drainage capacity of the piers were investigated. To determine the bearing capacity of cement-treated impact-compacted sand piers, a compressive load test was conducted according to ASTM D-1194. The field tests were carried out in the 350-hectare coastal area of Bandar Bushehr. Based on geotechnical investigations, the groundwater table w