Utilizing Multivariate Adaptive Regression Splines (MARS) for Precise Estimation of Soil Compaction Parameters  
[PERSON]  
1 Department of Civil Engineering, Faculty of Engineering, University of Misan, Amarah 62001, Iraq; [EMAIL_ADDRESS] (M.S.A. ); [EMAIL_ADDRESS] (F.J.K. ); [EMAIL_ADDRESS] (J.K.A.) [PERSON]  
1 Department of Civil Engineering, Faculty of Engineering, University of Misan, Amarah 62001, Iraq; [EMAIL_ADDRESS] (M.S.A. ); [EMAIL_ADDRESS] (F.J.K. ); [EMAIL_ADDRESS] (J.K.A.) [PERSON]  
1 Department of Civil Engineering, Faculty of Engineering, University of Misan, Amarah 62001, Iraq; [EMAIL_ADDRESS] (M.S.A. ); [EMAIL_ADDRESS] (F.J.K. ); [EMAIL_ADDRESS] (J.K.A.) [PERSON]  
2 Department of Environmental Science, College of Energy and Environmental Science, Alkarkh University of Science, Baghdad 10081, Iraq; [EMAIL_ADDRESS] (J.K.A.) [PERSON]  
3 Department of Civil Engineering and Architecture, GeoBioTec-UBI, University of Beira Interior, 6201-001 Covil  
its significance in the field of civil engineering. Initially suggested by [PERSON] in 1933 [2], soil compaction involves applying specified compactive effort in a controlled laboratory setting, allowing for various water contents. This process enables engineers to pinpoint the optimal moisture content and maximum dry density--two essential parameters obtained from the compaction curve [3; 4; 5]. In field compaction, the key parameters are the optimum water content (\(w_{opt}\)) and maximum dry density (\(\rho_{\text{dmax}}\)). These are crucial in determining the maximum dry density of soil, which indicates an enhanced soil bearing capacity. The optimum water content is the specific moisture level at which soil can attain its highest dry density following a certain compaction effort. It is the minimum water necessary to form a thin film on soil particles, aiding their sliding movement for compaction. Compressing soil to its greatest theoretical density involves eliminating gases within the soil via expelling them through voids in the soil matrix. This process of gas expulsion is fundamental to soil densification, allowing soil to reach its maximum potential density. Hence, \(w_{opt}\) and \(\rho_{\text{dmax}}\) are vital in achieving the desired soil densification and stability [6]. These parameters form the backbone of long-term performance for a myriad of geotechnical structures, such as landfill liners, highway embankments, railway track-beds, earth dams, nuclear waste disposal facilities, and airfield pavements [7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17]. For example, study [7] found that \(w_{opt}\) and \(\rho_{\text{dmax}}\) are crucial factors affecting the compression of compacted Oklahoma soils, influencing collapse potential in embankments. Another study [8] used \(w_{opt}\) and \(\rho_{\text{dmax}}\) as critical parameters to understand the behavior and performance of MX80, which is a versatile clay for nuclear waste barriers. Furthermore, study [14] investigated the microstructure and hydraulic properties of high-speed railway subgrade soil using different values of \(w_{opt}\) and \(\rho_{\text{dmax}}\) to understand its behavior. Thus, accurately predicting and understanding the compaction parameters of diverse soil types is paramount for the successful construction and maintenance of these geotechnical structures. To find compaction parameters, two main compaction approaches emerged: the standard Proctor compaction and the modified Proctor compaction [1]. The standard method is typically adopted for regular traffic loading situations, while the modified approach is used when dealing with heavy unit weights like those considered for airfield pavements. Outcomes derived from laboratory tests conducted using either the standard Proctor compaction method (ASTM D698) [18] or the modified Proctor compaction method (ASTM D1557) [19] are visually represented via an inverted 'V' curve. This graphical representation illustrates the peak, known as \(\rho_{\text{dmax}}\), and the corresponding moisture content, termed as the \(w_{opt}\) of the soil.