Abstract—Expanded polystyrene (EPS) geofoam is often used in below ground applications in geotechnical engineering. A most recent configuration system implemented in roadways to protect lifelines such as buried pipes, electrical cables and culvert systems could be consisted of two EPS geofoam blocks, “posts” placed on each side of the structure, an EPS block capping, “beam” put atop two posts, and soil cover on the beam. In this configuration, a rectangular void space will be built atop the lifeline. EPS blocks will stand all the imposed vertical forces due to their strength and deformability, thus the lifeline will experience no vertical stress. The present paper describes the results of a numerical study on the post and beam configuration subjected to the static loading. Three- dimensional finite element analysis using ABAQUS software is carried out to investigate the effect of different parameters such as beam thickness, soil thickness over the beam, post height to width ratio, EPS density, and free span between two posts, on the stress distribution and the deflection of the beam. The results show favorable performance of EPS geofoam for protecting sensitive infrastructures. Keywords—Beam, EPS block, numerical analysis, post, stress distribution. I. INTRODUCTION IFELINES play vital role in human life. Damage of these infrastructures can result in loss of their performance, thus time and expanses for rebuilding of such structures are considerable. In order to protect these structures, the imposed load on them must be reduced to some consideration. EPS is a cellular geosynthetic material that can be used in geotechnical engineering applications. The geosynthetic functions of EPS geofoam can be thermal insulation, lightweight fill, compressible inclusion, and small-amplitude wave damping [1]. EPS geofoam was first introduced and used in 1970 in Norway by the Norwegian Public Road Administration (NPRA) to enhance the bearing capacity and to reduce the settlement of soft foundation soil to construct a road atop [2]. Because of its lightweight and compressible inclusion quality [3]-[5], many researchers have investigated the efficiency of EPS materials when used as a soft zone above the pipeline [6]-[8]. This method, known as imperfect trench, reduces the imposed stress on the pipeline due to M. Abdollahi is MSc student at Civil Engineering Department, K. N. Toosi University of Technology, Tehran, Iran (e-mail: masood.abdollahi91@gmail.com). S. N. Moghaddas Tafreshi is Professor of Geotechnical Eng., Civil Engineering Department, K. N. Toosi University of Technology, Tehran, Iran (e-mail: nas_moghaddas@kntu.ac.ir). reverse arching deformation [9]. More recently, another configuration of EPS geofoam block, so called post and beam (e.g. Fig. 1 (a)), was used in a Utah roadway to protect a pipeline from soil severe subsidence and the transferred stresses due to soil settlement [10]. In the post and beam configuration, EPS blocks were placed aside the pipe (posts) and a capping beam was put atop of the posts (beam), therefore the desirable free space above the pipe was achieved. Because of the existing space, the soil could settle without imposing any additional stress to the pipeline. Few researchers have studied this configuration through numerical simulations. Reference [10] simulated the post and beam configuration using a finite difference method and reported the system functionality under traffic load. They used a 2D model to simulate the mentioned configuration and assumed that EPS material would act as elastic material, under imposed strip loading. They found that system would experience stresses which are lower than stresses at 1% strain of blocks. So, they concluded that system would remain in elastic range. In this paper, a 3D numerical method is utilized through using ABAQUS software to evaluate the system efficiency in protecting lifelines subjected to static load. The effect of various parameters on the soil surface settlement, stress distribution, and deflection of post and beam system is investigated. II. NUMERICAL MODEL The 3D simulation of EPS block of post and beam system and soil cover is performed utilizing the finite element method offered by ABAQUS (6.14.1). It has been assumed that beam thickness, post height to width ratio, free span between two posts, thickness of soil cover, and EPS density play vital role in the system performance. Therefore, the impact of each parameter is investigated through sets of models, each set only one parameter considered variable. Model Geometry A. Table I summarizes the model parameters, model geometry, number of elements, and nodes used in the simulations. A mesh type for these models was considered C3D8. The model general display is shown in Fig. 1 (a). The boundary conditions used in the models are shown in Fig. 1 (b). The displacement of outer nodes in X-Z and Y-Z planes was restrained respectively in Y and X directions. The basal nodes were fixed in Z direction. M. Abdollahi, S. N. Moghaddas Tafreshi Numerical Investigation on Performance of Expanded Polystyrene Geofoam Block in Protecting Buried Lifeline Structures L World Academy of Science, Engineering and Technology International Journal of Geotechnical and Geological Engineering Vol:11, No:9, 2017 744 International Scholarly and Scientific Research & Innovation 11(9) 2017 scholar.waset.org/1307-6892/10007857 International Science Index, Geotechnical and Geological Engineering Vol:11, No:9, 2017 waset.org/Publication/10007857