# Experimental and Numerical Study in Dynamic Compaction of Weakly-Cohesive Soils
## 1 Introduction  
From a technical and economic point of view, the mechanical compaction process represents one of the most common and effective methods for improving the characteristics of the terrain. This process works by changing the structure of the soil by increasing its density as the volume of air-filled pores decreases and the particles rearrange. These structural changes lead to improvements in characteristics such as strength, deformability, and permeability, achieved by applying mechanical energy transferred by specialized technological equipment [1; 2; 3]. The fundamental principles of soil compaction were demonstrated by [PERSON] in 1933 during studies carried out for dam construction in Los Angeles to establish solutions regarding the behavior of soils with unstable structures. [PERSON] demonstrated that the dry density of soil is influenced by moisture content, compaction effort, and soil characteristics such as granularity, mineralogy, and uniformity [4]. The vibrating compaction process is considered a modern method of improving difficult foundation grounds, having a wide range of applicability. The compaction effect will be greater the smaller the bonding forces between the particles and the more different the particle masses. Thus, this technology is recommended to be used especially in non-cohesive soils where the bonding forces between the particles are very small but also in the case of inhomogeneous fillings, not being applicable to claye soils. At the international level, the specialized literature highlights significant interest in the qualitative and quantitative parametric analysis of the compaction process, particularly in contexts controlled by technological factors. In the case of compaction soils with vibrations, research was conducted towards a better understanding of the influence of key technological factors, such as the following [5; 6; 7]:  
* Characteristics of the compaction equipment (mass per drum, drum width, frequency and amplitude of drum vibrations);
* Soil characteristics (initial density, granularity, grain shape, moisture);* Working procedures (number of passes, thickness of the layer to be compacted, working frequency, speed of displacement of the compactor). Depending on the type of terrain, the working technology can be either static (without vibrations) or dynamic (with vibrations). The roller can work with a single vibratory drum or in tandem, depending on its constructive model (as shown in Figure 1). Also, soil type plays a critical role in determining its compaction characteristics. In general, cohesive soils show high resistance to compaction, and non-cohesive soils (such as sand or gravel) can undergo easier compaction because their particles are larger and lack strong cohesive forces. The effort or energy of compaction is closely related to the type of technological equipment and the parameters of the working regime used in the compaction process [8; 9]. It was found that as the compaction effort increases, the compaction quality is better. Moisture is a key factor that significantly affects the outcome of the compaction process. Optimal compaction moisture refers to the water content at which the highest soil density is achieved for a given compaction effort. A major focus is on compaction energy and its correlation with key compaction characteristics. Thus, the optimal compaction moisture values, considered to be approximately 85% of the saturation value, decrease with the increase of the compaction effort [10]. To analyze the influence of soil dry density on the soil-water characteristic curve (SWCC), a linear and nonlinear fitting analysis was conducted on various dry density levels. The analysis aimed to determine how changes in dry density affect the soil's ability to retain water at different matric suction levels. By applying both linear and nonlinear models, the relationship between soil density and moisture retention characteristics could be better understood.