Experimental Evaluation of Geocell and EPS Geofoam as Means of Protecting Pipes at the Bottom of Repeatedly Loaded Trenches

Abstract

With growing populations and continuing urban development, embedding pipes in the ground that are then over-run by traffic is inevitable. This paper describes full-scale prototype tests on high-density polyethylene (HDPE) flexible pipes (of 250 mm diameter), buried at shallow depth, under simulated traffic loading. The paper studies the effect of surface load diameter (0.6×, 0.8× and 1× pipe diameter) and the amplitude of repeated load (400 or 800 kPa) on pipe behavior. The effects of EPS (expanded polystyrene) geofoam block of various densities and also of geocell as a 3D reinforcement, in reducing the pressure transferred to the pipe, the deformation of the pipe and the surface settlement of the backfill were investigated.The results show that, with increase in loading surface diameter, the pipe's vertical diametral strain, the pressure transferred to the pipe and the surface settlement grow significantly, irrespective of applied pressure. Using an EPS block over the pipe, increases the soil settlement but reduces transferred pressure onto the pipe and, consequentially, results in lower pipe deformations. The increase in density of an EPS block helps improve response, but was still found to be insufficient to prevent increase in surface deflections. The use of geocell reinforcement beneath the loading surface not only reduces the pressure transferred to the pipe and decreases its deformation, but also significantly negates the tendency of the EPS block to increase the soil surface settlement.Thus, a geocell reinforcement layer placed over two EPS geofoam blocks (with a total thickness 0.3×, and width 1.5×, the pipe diameter) all above a pipe buried at a depth of twice pipe diameter, was found to deliver acceptable, stable response. By these means, the vertical pipe strain, transferred pressure over the pipe and soil surface settlement were reduced, respectively, by 0.45, 0.37 and 0.53× those obtained for the comparable unmodified buried pipe installation, and are within allowable limits.

The Role of Expanded Polystyrene and Geocell in Enhancing the Behavior of Buried HDPE Pipes under Trench Loading Using Numerical Analyses

“…The geocell and pipe parameters are as given by the manufacturer. Meanwhile, the soil parameters used were in close alignment with other research [14].…”

“…The performance and durability of these vital substructures depend on their safe and proper design to preserve their safety and operation. One of the approved practical advantages of geosynthetics is their performance in stress attenuation on buried conduits and pipes; thus, this area has been investigated by many researchers [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Anil et al [2] studied the performance, strength, and energy absorption competency of EPS blocks over buried pipes against impact forces.…”

“…Their results indicate that the dimensions of geofoam blocks in the embedded soil trench have an influential role in the behavior of the embedded pipes. Moghaddas Tafreshi et al [14] analyzed the behavior of pipes buried under a protective layer of geocell and EPS geofoam blocks with flexible arrangements. Their results indicate that the combination of a geocell layer with EPS geofoam blocks has significant effects on ameliorating the behavior of the embedded pipe.…”

Effects of Pipe Deflection and Arching on Stress Distribution and Lateral Earth Pressure Coefficient in Buried Flexible Pipes

“…The r vs and r vd values were computed for various r s with reference to the Es value of 28 MPa (Figure 21). Increasing the stiffness of the backfill enhances Fv [14,58], amplifying the horizontal stress component acting on the central soil prism. In other words, the lateral earth pressure coefficient, which represents the horizontal effect of the vertical stresses, also increases with Fv.…”

“…While these materials significantly reduce stresses and pipe deflection, the resulting surface displacements are larger than of the original case [13]. Tafreshi et al [14] explored the use of geocell to minimise surface displacements resulting from the use of EPS in shallow buried pipes with successful outcomes. However, they also pointed out that the combined use of EPS and geocell was not economical.…”