Today, the use of composites to achieve the ideal mechanical properties and optimization of the structures from an economic and engineering point of view in the various fields of technology has a growing horizon. The common literature in the composite engineering field is often concerned with the use of polymers as reinforcing phase and/or matrix (Gowthaman, Nakashima, & Kawasaki, 2018; Hejazi, Sheikhzadeh, Abtahi, & Zadhoush, 2013; Rajagopalaiah, 2018). The study of the effects of adding particles (Menbari, Ashori, Rahmani, & Bahrami, 2016; A. Moallemzadeh, Sabet, Abedini, & Saghafi, 2019; Rasana, Jayanarayanan, & Ramachandran, 2020), fiber and fabric (Gholizadeh, Najafabadi, Saghafi, & Mohammadi, 2018; Ali Reza Moallemzadeh, Sabet, & Abedini, 2017; A. R. Moallemzadeh, Sabet, & Abedini, 2018) reinforcing phase to the composite matrix with the aim of enhancing their mechanical properties over different loadings, are investigated by different researchers.

The use of polymer reinforcement in soil composite for enhancing mechanical properties and improving its tensile strength is recognized as one of the fastest and most economical ways to stabilize soil structures and build retaining walls that the dominant mechanism is reinforced phase and matrix continuity, friction and mechanical interlocking (Chegenizadeh & Nikraz, 2012; Jeon, 2018; Shi, Peng, & Kongkitkul, 2016). In addition, the flexibility of soil/polymer composite structures improves their seismic performance (Panah, Yazdi, & Ghalandarzadeh, 2015; Razzazan, Keshavarz, & Mosallanezhad, 2018). Lack of understanding of the behavior of geosynthetic reinforced soil slope surfaces makes it necessary to investigate the behavior of these soil structures for understanding the mechanisms of their failure. In general, the design of reinforced soil structures requires its analysis from two perspectives: stability and deformation. Conventional low-rise reinforced soil structures usually do not require calculating and controlling wall deformations, but with the development of reinforced soil applications in the construction of high-rise walls, load-bearing walls, and wall bridges in addition to stability, wall deformation during operation is also considered. Therefore, the study of the formability changes of reinforced soil structures with increasing application of geosynthetic layers in recent decades has received more attention. Hence the scientific and practical basis of reinforced soil composite structures was first put forward by Henri Vidal (Jones, 2013). In this regard, Qu et al. (Qu, Zhao, & Li, 2015) investigated the effect of random distribution of palm fibers as a reinforcing phase on soil composite. Also Gowthaman et al.(Gowthaman et al., 2018) studied the technology of reinforcing soil structures using the natural fiber reinforcing phase.

Physical modeling in the field of reinforced soil structures is classified into three general sections: 1. small- scale models, 2. large-scale models and monitoring of structures in operation, and 3. modeling under high acceleration using a geotechnical centrifuge.

In small-scale experiments, the number of reinforcement layers, the amount of subsidence, the impact of additives to the soil, and the distance of the first reinforced layer from the surface has been investigated to determine the mechanism of fracture (Sommers & Viswanadham, 2009). Accordingly, small-scale laboratory models in ambient conditions with a gravity acceleration of 1 g = 9.81 ms− 2 do not fully reflect the behavior of reinforced soil structures in reality, and due to the scaling effect and other simplifying assumptions have always differences with the real model (Sommers & Viswanadham, 2009) .

In the modeling of large-scale reinforced soil structures, the effects of parameters, such as type of reinforcement (Bathurst, Walters, Vlachopoulos, Burgess, & Allen, 2000; Haza, Gotteland, & Gourc, 2000), vertical loading (Thamm, Krieger, & Krieger, 1991; Yoo & Kim, 2008), covering coating (Bathurst et al., 2000) and the additives (Guler, Cicek, Demirkan, & Hamderi, 2012), are considered.

Up to now, modeling under high acceleration conditions is one of the best available methods to solve the above-mentioned problems caused by laboratory models of small-scale and full-scale reinforced soil structures. In centrifuge reinforced soil modeling, parameters such as type and number of reinforcements, loading levels, and additives have been investigated (Djeffal & Belkacemi, 2020; Zhang, Chen, & Yu, 2019). The first research was carried out by Bolton(Bolton & Pang, 1982) using geotechnical centrifuge instrument to investigate the behavior of reinforced soil structures with stainless steel strip, mild steel welding rod, and aluminum strip reinforcements. Other experiments also included the effects of constant loading (Matichard, Blivet, Garnier, & Delmas, 1988) soil compaction (Goodings & Santamarina, 1989; Mitchell, Jaber, Shen, & Hua, 1988), soil type and the addition of lime to the matrix (Güler & Goodings, 1992; Porbaha & Goodings, 1994), the number of geotextile layers in reinforced soil slope (Jorge Gabriel Zornberg, 1994; Jorge G Zornberg & Arriaga, 2003), and loading by rectangular plate and slope angle investigation (Aklil & Wu, 2013) on the behavior of reinforced soil structures under high acceleration.

The published results of reinforced soil structure experiments by centrifuge, have been performed largely at 90° with steel reinforcements (Moein, Bazargan, & Derakhshani, 2015). On the other hand, all the experiments have been done with gradual acceleration increase, and in only two cases, the effect of loading with strip (overhead) at constant acceleration directly on the behavior of the reinforced soil mass have been investigated. In this research, the investigated variables were the number of layers and the angle of the structure surface with the horizon, and the loading plate with a constant rectangular shape of 180 ×50 mm located at 60 mm away from the sloping edge (Aklil & Wu, 2013; Sommers & Viswanadham, 2009).

Therefore, in this study, modeling of reinforced soil wall of 35 cm height with six reinforcement layers using centrifuge method was performed under ambient conditions by applying an acceleration equal to 30 times of the gravitational acceleration (N × g = 30 × 9.81 ms− 2). This is equivalent to study a real structure with height of 30 times of the current modeled structure (under the conditions of gravity equivalent to Earth's gravity). Also, in order to study the response of soil/PP composite structure to the vertical loadings, the effect of three different geometries of the loading level (rectangular, strip, and square) with different distances from the structural slope edge was investigated.