Enhancing the compressive strength of soil-cement piles via drill string kinematics optimization in deep mixing

Abstract

This study proposes an improved method for manufacturing soil-cement piles using deep soil mixing (DSM) technology to increase the bearing capacity and durability of foundations in soft soils. The relevance of the work is due to the need to increase the efficiency of the arrangement of bases and foundations in complex engineering and geological conditions, where traditional methods of soil reinforcement do not always provide the proper strength and homogeneity of the massif. The study presents a conceptual model of local compaction, which considers the borehole as a combined mechanical-hydraulic system, which allows for a more accurate description of the process of forming a soil-cement element and controlling its physical and mechanical properties. This approach integrates continuous injection of cement mortar with discrete reverse movements of the drill string every 350-400 mm, which ensures intensification of the mixing and compaction process of the soil-cement mixture throughout the depth of the borehole. This technological scheme contributes to the formation of a denser and more homogeneous structure of the material, reducing porosity and increasing the adhesive properties between soil particles and cement stone. Laboratory tests on clay, loam and sandy loam (cement content 10-20%) confirmed that stepped compaction increases the compressive strength by up to 47% (nearly 1.5 times), reaching 12.9 MPa for clay and 15.2 MPa for sandy loam, which indicates the high efficiency of the proposed method. 
The results of the studies show that a compaction step exceeding 400 mm leads to structural heterogeneity and a decrease in the operational characteristics of piles, while the optimal interval provides maximum density and uniform distribution of stresses in the array. In addition, it was found that control of process parameters (tool lifting speed, mortar consumption, multiplicity of reverse movements) is of crucial importance for achieving stable results in field conditions. The technology reduces resource consumption by 25-35% due to the effective use of local soils, reduced cement and energy costs, and reduced work duration.
The proposed approach provides a resource-saving and environmentally sound solution for the construction of foundations and retaining walls in difficult geotechnical conditions, and also has the potential for widespread implementation in civil and industrial construction practice. The results obtained can be used in the development of regulatory recommendations and improvement of technological regulations for the performance of deep soil mixing works.