# Predictive Modeling and Experimental Analysis of Cyclic Shear Behavior in Sand-Fly Ash Mixtures
###### Abstract
Fly ash may also be utilized in the building of embankments that may vary from little fills in road shoulders to huge fills in the case of state highway embankments [23]. For highway embankments, earth dams, roadway subgrades, and various other structures, soil, either in its clean form or when blended with fly ash, is compacted. This process aims to increase its strength and reduce the potential of settlement [24]. Two types of specifications (performance and method specifications) are used commonly for fly ash embankments construction [25]. In a limited number of studies, fly ash within a mixture of soil, was used as a backfill material for retaining walls. [PERSON] et al. [26] indicated fly ash and cohesive soils in a mixture that adhered to the requirement of filling material for geosynthetics reinforced earth retaining walls. [PERSON] and [PERSON] [27] developed numerical models of a retaining wall with a backfill of fly ash where the material parameters were defined with experimental studies and laboratory model experiments carried out on cellular reinforced fly ash retaining walls. It is indicated that the FEM model analysis demonstrates a reduction effect of horizontal deformation on panel walls with the use of fly ash as a backfill for retaining walls. [PERSON] and [PERSON] [28] performed laboratory model tests utilizing fly ash as backfill material for geotextile reinforced retaining walls. As a stabilization agent of sand, the improvement of liquefaction resistance with the inclusion of fly ash was investigated by [PERSON] et al. [29]. It was observed that the inclusion of 6% fly ash to sand led to an increase in the cyclic response of the soil to the liquefaction in comparison with the specimens of sand mixed with 4% flax ash under varying confining pressures. Similar enhancing results of fly ash inclusion on liquefaction resistance of sand-bentonite mixtures were observed [29]. The addition of fly ash to sand resulted in a decrease in liquefaction resistance initially and then an increase in liquefaction resistance for fly ash contents up to about 20-25%. The increase in fly ash content beyond 25% was seen to decrease the liquefaction resistance [30]. On the other hand, estimating the stress-strain response of soils is fundamental for designing the geotechnical components of engineering structures. This response, which varies under monotonic and cyclic loading conditions, is examined in the laboratory through various static and dynamic methods. Laboratory experiments show that deformations caused by loading can negatively impact engineering structures. In a cyclic direct shear testing device, load transfers from one soil particle to another across the interface, generating frictional resistance that depends on the characteristics of the particle pair [31]. In a limited number of studies, the cyclic behavior of fly ash soil mixtures was investigated. The inclusion of sand causes up to a 20% decrease in the cyclic resistance of pure fly ash [32]. At higher loading cycles with lower deviatoric stress levels and at a lower number of cycles having higher deviatoric stress levels, soil-fly ash mixtures indicate higher stability under cyclic loading [33]. Similarly, fly ash treated soils observed to be sensitive to stress intensity and loading frequency [34]. Recent studies have already confirmed that fly ash can be used for different applications in geotechnical engineering to improve the engineering characteristics of various soils. However, there remains a substantial gap in understanding the behavior of fly ash-soil mixtures subjected to cyclic loading. To address this research gap, the present study adds to the recent research by exploiting cyclic direct shear tests on a series of sand-fly ash mixtures with various mixing ratios to accurately quantify the effect of fly ash on the cyclic behavior of sand. The effect of fly ash content was examined by mixing sand with it at five different percentages (i.e., 0%, 2.5%, 5%, 10%, 15%, and 20%).