The technique of vertical rigid inclusions has been widely used to improve the soft soil problem due to its low cost and resulting small differential and total settlements. Obviously, experimental studies on rigid inclusion improvement systems have been conducted by several researchers. This paper presents an experimental study focusing on the mechanisms taking place in a granular platform supported by piles in soft soil under monotonic loading. An original three-dimensional laboratory model was developed. The model contained 16 rigid piles, and the compressible soil was explicitly simulated by a soft material (a mixture of polypropylene balls with granular soil). Settlement accumulation and an increase in the load transmitted to the piles or pile caps were observed during the loading application. Based on the experimental results, an increase in pile diameter played an important role in load transfer mechanisms, including the total settlement. The importance of this campaign in terms of parametric study will constitute rich experimental data in the context of soft soil improvement reinforced by rigid inclusions to develop and validate the numerical part.