Simplified arching theories assume that shear strength is fully mobilized at the vertical boundaries of the soil prism on the pipe [50; 51], but the degree of positive soil arching depends on the magnitude of the relative settlement. The induced trench method can increase the degree of positive soil arching on a buried thermoplastic pipe regardless of pipe deflection. As a result, a significant reduction in pipe deflections can be achieved. A buried thermoplastic pipe installed in the conventional method deflects vertically downwards under soil load. Since the displacement of the pipe crown is more than the side backfill soil, differential settlements occur in the soil medium above the pipe crown level. Differential settlements lead to the development of a positive soil arching within the soil medium, and as a result, a smaller vertical stress than geostatic stress reaches the thermoplastic pipe. Being a low-stiffness material, EPS deforms more than the soil adjacent to the thermoplastic pipe and, therefore, causes larger differential settlements in the soil medium above the pipe. When the thermoplastic pipe is buried in the ITI and ETI methods using EPS Geofoam, as shown in Figure 1, there will be an additional vertical settlement in the pipe crown, and positive arching will be increased regardless of the pipe deflection. For this purpose, there are a limited number of laboratory tests and numerical analyses studies in the published literature on the ITI and ETI models using EPS Geofoam surrounding the thermoplastic pipes [10; 27; 36; 39; 49; 52; 53; 54; 55; 56; 57; 58; 59]. [PERSON] et al. [36] pioneered studies about PVC pipes protected by embedded trench installation using EPS Geofoam, investigating the optimum compressible zone geometry for a deeply buried thermoplastic pipe using finite element analyses. [PERSON]; [PERSON] and [PERSON] [52; 55] investigated the effects of using EPS Geofoam compressible inclusion by performing full-scale laboratory tests on the responses of a buried small-diameter, lined, corrugated wall HDPE pipe to deflections, soil stresses, and settlements around the pipe. EPS Geofoam with 10 and 15 kg/m\({}_{3}\) nominal densities were selected as the compressible material, and five different pipe compressible inclusion configurations were designed for the laboratory test program. It was reported that the induced trench installation (the single EPS panel above the pipe crown) offered the best solution regarding pipe performance and cost efficiency. Embedded trench installations (one EPS saddle above the pipe crown and one below the pipe invert) significantly reduced the soil stresses around the pipe and improved the pipe behavior [59]. [PERSON] et al. and [PERSON] et al. [60; 61; 62] investigated through full-scale laboratory tests the efficacy of using EPS alone or in combination with other geosynthets (i.e., geogrid or geocell) in protecting the high-density polychene (HDPE) pipe buried in a shallow trench against repeated surface loads. [PERSON] et al. [61] showed that using EPS with a density of at least 30 kg/m\({}_{3}\), combined with geocell over the HDPE pipe, provided the best solution in terms of both pipe performance and trench surface settlements. However, since design concerns (i.e., burial depths and load types) are different, the optimal configuration proposed by [61] is not deemed suitable for the induced trench installation of the thermoplastic pipe under high embankment fills. In this current study, induced trench installation (ITI) and embedded trench installation (ETI) models in large diameter (0.762 m to 1.524 m inner diameter) thermoplastic pipes subjected to high fill stresses were investigated by numerical analysis. The study evaluated the effects of crushed stone, sand, and clay backfill material on the pipe deflections and stresses by considering the pipe diameter, rigidity, and thermoplastic material type (HDPE and PVC). Using EPS Geofoam as compressible material, the ETI and ITI models proposed by [10] were used for the soft zone geometry.